Abstract
Dynamic stability studies are vital for wind plants as they ensure the reliable and secure integration of wind power into the electrical grid. By assessing grid stability, fault ride-through capability, power quality and the compliance with grid codes, stability studies help to optimize system planning and wind plant performance while contributing to the overall stability and efficiency of the power system. Following a short introduction of the technical guidelines for grid integration of power generating units and their simulation models, this paper explains the control structure and functionality of a simulation model for a central controller that was developed as a Grid Control System. The considered wind plant system consists of five individual sub wind farms and is feeding into the transmission grid. Results of several test scenarios are presented to demonstrate the integration between the central controller model and the farm models. In Conclusion, the adjustment of specific control parameters was investigated to exemplify possible controller optimizations.

Introduction
One of the most important problems in the distribution grid for grid operators is a rising number of distributed generators with individual control systems from several producers and hence different behaviour. The increasing amount of these decentralised generators influences large-disturbance voltage stability which denotes the ability of the distribution grid to maintain steady voltages during or directly after system faults or loss of generation‎. Due to this reason, grid codes demand standardised simulation models for generators like wind plants and wind turbines.

This work is aimed to show how synchronous condensers (SCs) can improve the voltage stability in power systems with a large penetration of variable renewable energy (VRE). In this report, a modified version of the IEEE 39 Busbar System has been modelled in DIgSILENT Powerfactory and various Winter and Summer scenarios were created to test voltage stability under different conditions. With the help of PV curves, the weakest buses in the grid were identified to see whether voltage stability would improve if SCs were placed in these locations instead of at the point of common coupling (PCC) with the VRE sources. Implementing SCs saw an overall increase in voltage stability in all scenarios in terms of busbar voltage magnitudes, and it proved to be more effective to place the SCs at the weakest busbars. Fault ride through (FRT) tests were formulated to confirm that the SCs have the capability to support a single line to ground fault and placement of SCs at the weakest buses compared to the PCC with VRE reduced the severity of this fault.

The growing need of inertial support and evolving grid codes are pushing the manufacturers of wind turbines to introduce novel configurations based on the grid-forming concept in their product portfolio. In parallel, system operators should ensure that the interconnection of additional regulating resources improves the grid robustness and transient stability properties of the netwrok. Following these objectives, the paper includes a comparison between the HVAC and HVDC solutions for offshore wind plants connection to the main high-voltage transmission, under different possible control architectures for the wind turbines (grid-following and grid-forming) and for the HVDC system.
A set of transient stability tests for the Nordic32 network has been executed in DigSilent PowerFactory, assuming different control alternatives for the wind turbines and for the HVDC. The obtained results are critically assessed both in terms of performance (capability of providing inertial support to the network) and robustness (transient stability). Insights in the underlying theoretical principles and in the inherent dynamical properties of the systems are also provided.
The results confirm the capabilities of the HVDC to effectively transfer the grid-forming functionalities of the turbines from the offshore distribution toward the onshore network, additionally improving the network transient stability properties and robustness.

As several GW-scale AC wind power plants (WPP) are being designed in the USA, grid compliance and economic factors have driven higher utilization of wind turbine reactive power capability. However, using the full reactive power capability of the wind turbines has the potential to violate voltage or current limits of elements along the export path, impacting cable life and equipment maintenance. Improper use of this capability can also create voltage stability concerns. The goal of this paper is to illustrate a flexible process for considering these constraints and visualizing their impact on WPP reactive power capability by developing an onshore reactive power profile for an example 500 MW wind power plant 40 km offshore. This reactive power profile can then be used in further design aspects, such as sizing static and dynamic reactive compensation for grid compliance, as well as capital cost reduction. The profile can also be used in control design, enabling the engineer to choose a control strategy (e.g., voltage or reactive power control). As various elements or constraints of the WPP are adjusted during the design process, the reactive power profile can be quickly re-evaluated to visualize impact on sizing and control strategy. This can be seen particularly in the application of dynamic current limits for offshore export cables, as demonstrated in this paper.

This presentation will cover the progress of two projects of Energy System Integration Group’s High Share of Inverter Based Resources Task Force. The first project is focusing on new services needed in the absence (scarcity of) of synchronous machines, how to define and quantify the services as well as ability of IBRs with advanced controls to provide these services. The second project focuses on testing and verification of grid forming IBR capabilities. A more detailed description of these services is provided below.

Services
This work aims to combine learnings from two previous reports; the first is the G-PST Pilar 1 System Needs and Services for Systems with High IBR Penetration report; the second is ESIG’s Grid Forming Technology in Energy Systems Integration. The former work identified how system needs are changing with increasing penetration of IBRs and declining amounts of synchronous generation; ESIG’s report developed a framework for solving a “chicken and egg” problem involving deployment of new inverters with advance controls termed grid forming.


Figure 1: Process for deploying grid-forming capabilities as proposed in ESIG’s report Grid Forming Technology in Energy Systems Integration

The framework will identify a target system (in terms of target IBR penetration) with target reliability, and operating parameters; determining needs of such systems, and formulating these needs as services that are either procured through markets or required through interconnection codes. Definitions of services and methodologies to identify amounts of each service that are needed will be developed. A test system(s) will be used to conduct a number of case studies to understand when existing services become insufficient and new services are needed, and how to specify these new services.

GFM Testing
A number of requirements for GFM capabilities have been defined with some requirements at a very high level e.g., HECO and UNIFI, while others are providing more detailed technical specifications e.g., NGESO in Great Britain in their grid code change GC0137. This project team will examine the question of how to test for such requirements and demonstrate expected performance. This project aims to demonstrate how to verify the expected performance from inverters with advanced controls for various high-level requirements that are being defined by the industry (using both frequency scans and time-domain characterization). The purpose of this project team is to provide more clarity to the industry on meaning of these requirements and behavior sought as well as provide some guidance on possible testing and verification procedures. It may also inform development of the future interconnection requirements for advanced inverter controls.

Green transition of electric energy systems deploys more inverter-based generation and consumption. In Denmark, large inverter-based generation units are primarily wind and solar power, while large consumption will include Power-to-Hydrogen and data centers. The inverter-based generation and consumption units may have common coupling substations in the transmission grid, such as a prosumer center including a Power-to-Hydrogen facility and a large wind power plant to be connected to the same existing or new 150 kV, 220 kV or 400 kV substation. Deployment of such prosumer centers will not increase the net power exchange with the grid as almost entire power generation will be used within the center. However, the short-circuit current contribution of the inverter-based prosumer centers in the common coupling substations may drastically increase with a risk of exceeding the short-circuit current rating of the existing equipment. For economically efficient integration of the prosumer centers into the existing infrastructure, one of the ideas is to separate the 150 kV meshed grid into the so-called grid islands to be interconnected through the 400 kV grid. At the same time, the politically motivated grid development target in Denmark has been replacement of the 150 kV overhead lines (OHL) with underground cables (UGC). The challenge is that increasing share of the inverter-based units in combination with more UGC may lead to increasing the background harmonic distortion in the transmission grid. This paper presents the harmonic assessment results of a large grid-reconstruction project using a measurement-validated model of the Western Danish transmission grid. The assessed grid-reconstruction project includes removal of 135 km OHL, establishment of new 162 km UGC, and separation of a part of the 150 kV meshed transmission grid into islands. This paper will describe the predicted evolution of the 5th harmonic voltage distortion during the process with establishment of cables and separation into the 150 kV islands. The time frame and volume of the entire grid-reconstruction project and the period of the harmonic distortion evolution correspond to a long-term prediction. The assessment shows that the 5th harmonic voltage distortion within a 150 kV area with initially high magnitudes will noticeably reduce during the initial grid reconstruction in a remote part of the meshed grid until the separation shall result in a drastic increase of the 5th harmonic voltage magnitudes within the islanded grid area. The assessment will link the predicted 5th harmonic distortion within the 150 kV island to the power quality measurements in the present, interconnected, meshed transmission grid strengthening confidence of the simulation results. The paper will also present assessment results of the best location of a new harmonic filter within the 150 kV island with the excessive 5th harmonic distortion.

In this paper, a small-signal model of a grid-forming (GFM) permanent magnet synchronous generator (PMSG) wind turbine is developed and presented, which can be utilized to study the electromechanical dynamics. The study demonstrates that there is a significant negative impact of GFM control on the torsional mode of the two-mass drive train, and explores the sensitivity of damping ratios to control and system parameters, such as short circuit ratio, dc capacitance, and control parameters of GFM. Finally, simulations are carried out to corroborate the theoretical findings.

Energy decarbonation is a critical issue for humanity, for which both the expansion of the Renewable Energy Sources (RES), and the development of the use of carbon-free hydrogen, are part of the solution to reach the EU climate-neutrality target in 2050.
To obtain fully carbon-free hydrogen, the Power to Gas (P2G) conversion of carbon-free power into hydrogen should gradually replace the Steam Methane Reforming process, which is the predominant process today. For this, major investments in electrolysers are planned in Europe for the next 20 years.
However, to correctly assess the profitability of such electrolysers, different methodologies to benefit from carbon-free power for P2G generation have been studied using various adequacy models, in cooperation with ENTSOG[1] and ENTSO-E[2], within the framework of the Ten-Year Network Development Plan (TYNDP).
This work was carried out for a year and a half with a group of experts from different electricity and gas TSO companies in Europe and aims to increase coordination between the electricity and gas TYNDPs.

More precisely, two main methodologies have been studied:

• Methodology 1: it consists in freely optimizing the sharing of RES between the Power Grid and the P2G on a European scale. Due to efficiency considerations, we can show that with such a methodology, decarbonation of power takes priority over P2G, which means that electrolyser facilities will only run if the marginal price where they are located corresponds to fully carbon-free power generation at that time.
  
• Methodology 2: it consists of favouring the RES to supply the P2G, which significantly increases the load-factor of electrolysers and makes them profitable more quickly. Everyone agrees that with such a methodology the production of hydrogen only from carbon-free electricity sources is guaranteed. However, a premature expansion of electrolysers, as a significant part of the electricity generation is not yet carbon-free, can have negative effects on the global amount of carbon emission. This effect is reinforced by the optimization of the Steam Methane Reforming process that can include a high rate of 90% in Carbon Capture and Storage, which makes this process low in carbon emissions.

Depending on these 2 methodologies, various Cost-Benefit Analysis have been computed to evaluate electrolyser projects and fix the optimal scenario for their development.

[1] ENTSOG : European Network of Transmission System Operators for Gas
[2] ENTSO-E : European Network of Transmission System Operators for Electricity

In future power systems, non-synchronous, distributed energy resources (DER) will be increasingly demanded to provide dynamic ancillary services. This induces significant challenges in handling the weather-volatile renewable energy sources and device-specific limitations of individual DERs. The concept of dynamic virtual power plants (DVPP) has been proposed to tackle dynamic ancillary services provision by DERs. DVPPs are ensembles of heterogeneous DERs (all with individual constraints) aggregated to collectively provide desired dynamic ancillary services such as fast frequency and voltage control. In particular, while none of the DERs can provide these services consistently across all power and energy levels or all-time scales, a sufficiently heterogeneous group of DERs can do so.

Among the control design methods for DVPPs available in the literature, a highly versatile and fundamental approach is experimentally validated in this work that has been theoretically presented in previous works. Here, various DER units in a DVPP will be controlled so that their overall behavior corresponds to a desired dynamic I/O behavior specified as a desired transfer function. More specifically, the approach is based on an adaptive divide-and-conquer strategy, which is composed of two main steps: First, the disaggregation of the desired dynamic behavior among the DVPP units using so-called adaptive dynamic participation factors (ADPFs) to obtain local desired behaviors while taking device-specific, possibly time-varying DER constraints (e.g., power/energy limitations) into account. In the second step, a local feedback control is designed for each DVPP unit to achieve the desired local behavior.

The effectiveness of the grid-following frequency control in the presence of load variations and fluctuating generation capacities of DER units is shown in simulations and by means of a multi-converter hardware-in-the-loop (HIL) test bed system. We also show the superiority of the used ADPFs over more basic DVPP control methods based on static (SPF) and dynamic participation factors (DPF), where SPFs can be considered as a standard droop control with first-order filters. The test bed system contains three 11 kW back-to-back converter systems and a 22 kW synchronous generator operated on a scaled AC grid with a load unit. The DVPP controller is running on an industrial PLC from Bachmann and generates the power setpoints for the three inverter systems from the measured grid frequency provided by a grid acquisition module. The synchronous generator provides a frequency-variable grid so that reactions of the DVPP to long-term changes in the grid frequency can be performed. Short-term grid frequency changes are generated via load increase or reduction via the load unit. For the validation of the DVPP, the converter systems are operated in the grid-following mode. All test scenarios are performed with and without DVPP, where all three DVPP concepts (SPF, DPF, ADPF) are evaluated.

In recent years, high-voltage direct current (HVDC) connected offshore wind farms (OWF) have gained attention as a potential solution for onshore grid restoration. To enable participation in restoration, a) the onshore HVDC converter needs to operate in grid-forming (GFM) mode, and b) the HVDC link must be energized from the offshore side. This, in turn, requires the wind turbine generators (WTG) of the OWF to be black-start capable and grid-forming. Publications on grid-forming WTGs have already shown their general ability to black start an OWF and HVDC-link– while generally assuming simplified electrical component models and a global access to all control variables. However, a black-start of an HVDC-connected OWF is a complex task distributed among different manufacturers and operators, such that influencing factors translating into technical requirements and interfaces need to be further researched.
In this paper, a detailed analysis is conducted on the black start of an HVDC link through GFM-WTGs, and insights into major factors influencing the black start process are provided – both in terms of actual components and in terms of modelling detail. The model used contains the OWF, the HVDC-link including type-4 MMC models, and the AC switchyards. It was developed in co-operation with the “HVDC-BLADE” project partners consisting of Amprion GmbH, Siemens Energy AG, and the Offshore Wind Accelerator working with the Carbon Trust. To achieve a realistic level of detail in the PSCAD simulation, the OWF consists of detailed and partially aggregated strings, and a sensitivity analysis is performed on the accuracy of the aggregation. The WTGs are modelled with a modelled DC-link and machine side, where the grid-side converter controlled via a virtual synchronous machine.
A two-stage “hard start” approach is chosen, as it potentially leads to clear boundaries and interfaces within the system: In a first step, the different strings of the OWF are energized either sequentially or in parallel, such that the OWF is operated in an islanded state. In a second step, the HVDC link is energized from the OWF. For the HVDC system, different startup methods are investigated in order to determine which part of the process – OWF start up or HVDC energization is more challenging for the overall system. Results show that during the OWF startup the reactive power demand, while during the HVDC energization the active power demand is the challenging factor for the WTGs. For the entire process, a supervisory controller is used to initiate the different phases of the black start process, while no direct communication between OWF and HVDC system is required. Finally, it is derived which components and model aspects have an influence or effect on the black start. From this, system-level functional requirements are derived, which can be translated into separate specifications on WTGs, HVDC system, and communication architecture.

The paper presents a comparison between grid-forming controls with enhanced damping characteristics and the wide-area control
with participation of grid-forming converters, the so called wide-synchronization control. First, an analytical comparison of
the considered solutions is provided, deriving the closed-loop transfer functions for all the schemes under specific assumptions.
Then, a simulation-based comparison is discussed, referring to the large scale dynamic model of the European power system and
considering two possible scenarios of grid-forming integration. The results of both analytical and simulation-based comparisons
consistently indicate the better performances of the wide-synchronization control, for a significant reduction of frequency oscillations
and instantaneous frequency deviations occurring after a disturbance in the system. The wide-synchronization control
proves to be effective already with a limited number of grid-forming sources participating in the control.

This paper examines the influence of grid forming control on power system oscillations in in systems incorporating renewable energy sources. One of the grid forming control approaches is considered in detail: virtual synchronous generator (VSG) control, which have proven its effectiveness in large power systems. VSG with detailed control blocks is employed for analyzing their influence on the power system oscillations. The 4-machine 2-area system is utilized as a platform for implementing the VSG. Modal analysis is performed for evaluating the contribution of different states on the power system oscillations. Additionally, time domain simulation results are presented for validating the findings of the modal analysis.

An emerging approach for effective grid integration of renewable energy sources (RES) involves hybridizing one or two types of RES with a battery energy storage system (BESS). The BESS in such a hybrid power plant (HPP) allows for maximizing generation and profitability while offering ancillary services to the grid, for example, real-time balancing and maintaining power quality. Various grid operators around the world are also exploring stand-alone BESS with the intention of avoiding grid reinforcements and boosting the capacity of existing network assets such as transmission lines. It is unclear however if an HPP with BESS has leverage over a stand-alone BESS, or vice versa, from the perspective of the network operator with the objective to maintain steady state operating conditions in the grid and boost the hosting capacity.This research aims to analyze and compare the active and reactive power benefits offered by BESS as a part of co-located HPP and a stand-alone system. A 48-bus medium voltage Danish distribution grid model is used as a test system. The distribution grid boasts high penetration of renewable energy sources, especially WPPs. A stand-alone BESS consisting of a 5 MW Li-ion battery, and a back-to-back converter is connected to a point of congestion in the distribution grid in scenario one. Improving grid operating conditions is considered as the principal focus of the stand-alone BESS by reducing line congestion, active power loss, and maintaining voltage profiles. In scenario two, the BESS is connected to a 15 MW WPP and simulated as a co-located HPP. The HPP configuration aims to maximize power generation considering the economic profit of the generator by balancing generation revenue against the cost of fatigue damage for the HPP operator/owner. However, the HPP is required to follow the control set points deployed by a centralized grid optimizer.The BESS is modeled with constraints on input and output power, state-of-charge, and the internal resistance of the battery as a function of battery state-of-charge and state-of-health to capture battery degradation. An equivalent impedance model is used to represent the power electronics in both the WPP and BESS. Second-order conic programming is deployed for solving the optimal power flow using the CVXPY library in Python. The objective for the centralized grid optimization is chosen as minimizing the active power loss in the distribution grid. The two cases are compared concerning the optimization objective, node voltages in the distribution grid, active and reactive power exchange at the TSO-DSO interface, as well as battery degradation during the simulated time from the perspective of the distribution grid. A comparison of the two scenarios presented highlights the benefits of a BESS as a part of co-located HPP and a stand-alone system to provide active as well as reactive power flexibility to the distribution grid

Grid-forming (GFM) controlled wind power plants (WPPs) has emerged as a promising solution to facilitate the stable integration of renewable energy into power grids. GFM-WPPs operate as voltage sources, capable of responding promptly to voltage disturbances. However, it remains uncertain whether their reactive current profiles (RCPs) conform to the present grid codes. This paper analyses the RCP of an aggregated GFM-WPP system. It offers transmission system operators a reference for grid codes compliance. It is found that the reactive current is naturally provided in proportion to voltage sag depth when inverter current is not limited, adhering to grid codes. However, when the current is limited during faults, the RCP is mainly affected by the active power rather than reactive power setpoints. By using the conventional fault ride-through setpoints of active power, the GFM-RCP can cover the grid code requirements. The profiles are validated by the electromagnetic transient simulations.

The 2008 UK Climate Change Act sets a legally binding commitment to ensure the UK reduces its greenhouse gas emission by 100% from 1990 levels by 2050. This commitment has become known as the ‘net zero target’. To meet this target the act also specified that legally-binding five-year ‘carbon budgets’ must be set, at least 12 years in advance, to act as stepping stones towards the 2050 target. To date, six carbon budgets have been set which limit emissions across all sectors to 78% of 1990 levels by 2037.

For the electricity industry to meet this challenge will require significant investment in generation and the transmission network over the course of the next thirty years. Policies will need to put in place to ensure the market delivers the necessary signals to incentivise investment when and where required. However, much of this new capacity will be restricted into where it can be located on the network, for example wind and solar will be concentrated in specific areas with both suitable resources and geographies while new thermal generation potentially will be located near CCUS and Hydrogen hubs. This means that the available transmission network capacity will play a driving role in shaping the least cost pathway to UK meeting the net zero targets.

In this study, we evaluate different investment pathways to meet this net zero target, including different scenarios on the build out of renewable, nuclear, batteries and low carbon thermal generation across Great Britain to quantify the cost and impact to the system on a ‘zonal’ basis. This zonal modelling captures the current limitation of the transmission network to deliver net zero, either by deterring new investment or through curtailment of generation. The challenge to the system will be how to incentivise these transmission upgrades – Based on our projections on the variation of prices across the zones under the different scenarios, we conclude on how the market design through locational pricing, in this case zonal, could provide the signals for required transmission reinforcements/upgrades necessary to deliver net zero.

Electromagnetic Transient (EMT) models are essential to wind power plant developers and transmission system operators alike. Therefore, during the development of any new Wind Turbines (WTs), EMT models are also developed. These models are quality-assured by validating against measurements from a prototype turbine, specifically for fault ride-through (FRT) cases. One way of performing model validation is through the voltage play-back method described in IEC 61400-21-2, where a voltage-dependent source reproduces the voltage measurements from the site (at the MV terminals of the WT transformer) and the current/power injections from the WT are compared against the measurements (at the LV terminals of the WT transformer). WPPs are designed and developed with the help of these models. However, a WPP electrical system can be complex with wind turbines, passive components, cables, and active components such as filters, Static VAr Compensators, and/or HVDCs. So it is interesting and sometimes essential to ensure that the assessment studies performed during the development of WPP are accurate. Furthermore, passive equipment in the WPP may change important characteristics either due to internal failures or aging, wind turbine control software version, and parameters may be updated, etc. It is often valuable to ensure that models are still capable of representing the actual behaviors seen on the field so that grid compliance and stability can be studied throughout the operation. In this context, this paper presents the EMT model validation of an offshore WPP with Siemens Gamesa Renewable Energy's (SGRE) direct-drive (DD) Type IV Wind Turbines using the voltage play-back method under real power system events. The faults were unbalanced and happened at the nearby grid, leading all the turbines of the plant into FRT mode. The model used was developed during the design of the WPP and the evaluation is done at both the plant and turbine levels. It is shown that the EMT models of operational WPPs were able to reproduce the real measurements with high accuracy. The paper also discusses the different challenges concerning measurement location placement, data acquisition, aggregation methods, preprocessing, turbine connection status, and production at the time of the fault.

Manufacturers of power generation units as well as plant and grid operators face new challenges arising from the aspects of integrating modern renewable technologies into the grid. To ensure grid stability, new technical requirements and guidelines are continuously being developed, where test benches support electrical certification and validation of models. Nevertheless, field measurement campaigns are still likely to be needed to carry out worst-case tests or to validate the overall properties of electrical and mechanical components for future requirements. Thus, Fraunhofer IWES, together with ABB Switzerland, and ABB Poland have developed a new approach for field tests of generation units up to 20 MW using a mobile grid simulator in the Mobil-Grid-CoP project. The aim of this paper is to give an overview of the hardware structure, functional principle, and potential applications of the advanced power-hardware-in-the-loop concept. The most relevant aspects of hardware and software design are addressed and the main features and innovations to improve output voltage quality and perform realistic tests beyond electrical certification are discussed. Simulations of transient events with a simplified grid-feeding source are used to verify the grid simulator’s capabilities and an outlook for future grid compliance and integration tests is given.

Power oscillations are causing greater concerns in modern power systems, and today’s grid codes require to a greater extent that wind, solar and hybrid power plants (WSHPPs) participate in power oscillation damping (POD). Prior research [1] has shown feasible values for the phase angle between voltage oscillation and modulated reactive power at the Point of Common Coupling (PCC) that will lead to damping of the electromechanical oscillations occurring at the generators of conventional power plants. However, there are also infeasible values for the phase angle that will lead to amplified oscillations. The majority of grid codes regarding voltage control at PCC have dynamic requirements like rise time of 1 second that, for the industry’s best practices of control design, would lead to a bandwidth of approximately 0.5 Hz where the phase angle of the SISO voltage control system is not compatible with the required phase angle for POD-Q in the frequency areas of interest, e.g. 0.1-2.0 Hz. The paper describes the problem in detail and discusses potential control solutions so that conflicting objectives in the grid codes to handle voltage control and POD-Q can be avoided. The paper also shows results of a recent field test campaign on a Vestas test site to demonstrate the fulfilment of prevailing grid code requirements for POD and the required coordination of a classic voltage controller and POD-Q.

As more and more conventional synchronous generation capacity is replaced by converter-based generation on a global scale, the first grid connection codes with specified grid-forming capability are emerging. However, since grid-forming has not been implemented widely for grid connected operation of large-scale converter-based power plants, the currently known and discussed grid code requirements are considered as still very immature. Equipment manufacturers, do not have full clarity on the possible use-cases of the grid-forming power plants, leaving them to rely on the immature grid code requirements as design targets.
The formulation of grid codes, however, misses several interactions that can occur in real applications of large-scale grid-forming power plants. Not understanding these interactions can lead to immature design choices by the equipment manufacturers.
This paper highlights some of the issues when manufacturers only focus on fulfilling the grid connection code. For example, over- / under-frequency against time profiles that grid-forming plants shall be capable to withstand. Additional test should be performed that show the required active power production during these frequency changes.
This paper proposes a simple grid model, that can be parameterized by grid operators, maybe not directly as grid codes, but as attachments, that allow manufacturers to tune the power plants according to most-likely scenarios when in operation.

Voltage vector jump in FRT-Tests can be partly used for the capability estimation of grid forming capability of generation units. However, a generic model of a passive FRT-Tester based on an autotransformer for vector jumps is still pending. In this paper, a mathematical model is presented, derived from measurable real individual inductances. This is essential for the transition from measurements to the simulation level. The generic approach can be flexibly transferred to different platforms and is therefore manufacturer independent.

In the last decade, the international wind energy industry has experienced a far-reaching paradigm shift in wind turbine testing,
revolutionizing the diverse test processes through efficient test execution on test benches. In contrast to system-level testing and
tests on so-called electrical generation test benches, a larger number of simulated systems is required to holistically test the
wind turbine’s converter and control system on a component test bench. We propose a component-level test procedure for wind
turbines where the wind turbine converter is the device-under-test. We present the current test bench concept from the early
stages of development, which uses two power-level hardware-in-the-loop (PHiL) systems for emulating the wind turbine and
grid behavior. Secondly, we define software and hardware components, interfaces, and control systems associated with this test
concept and, finally, propose a new approach to geographically-distributed simulations using PHiL emulators (GDS-PHiL).

In order to operate power grids with high penetration of renewable energies but low coverage of real time measurements of wind and solar power plants, extrapolation methods to derive the total wind power or PV generation for large regions are indispensable. Primary requirements for extrapolation techniques are robustness in operation against missing or wrong data and flexibilityregarding aggregation to different grid areas like control zones or grid nodes. The method used at Fraunhofer IEE, here called standard method, is in particular suitable for extrapolation with a low coverage of power plants with available real time measurements. The gradually increasing number of available measurements in Germany allows new approaches of the extrapolation method. We present a two-layer extrapolation method, called residual extrapolation, which aggregates the measurements or forecasts of available power plants directly within a grid area of known capacity and only extrapolates the residual capacity. In this paper we are investigating the performance of the residual extrapolation method compared to the standard method according aggregation zone, effective radii for extrapolation weights and artificial/simulated changes of available measurement coverage within the aggregation levels.

This paper presents the stability challenges of integrating large-scale renewable generations into the weak grid based on a review of literature and other public information. Moving from synchronous generator-based grids to converter-dominant power grids, various new types of power system stability problems are arising around the world. In this regard, first, definitions including classification of power system stability are reviewed considering the transition towards modern converter-dominated power systems. Then cases of stability challenges with converter-based generation in Australia, China, Hawaii, Texas, Chili, and Nigeria are reviewed, using publicly available information to describe the experienced stability challenges and solutions. Finally, the paper summarises viable solutions and the current challenges that still need to be addressed in these power systems.

This paper provides an overview on the historic development of wind power and grid codes in Sweden. It further describes a typical connection method for large-scale grid integration of wind farms and associated time frames. Selected exemplary challenges with the current grid code requirements are discussed. To mitigate these challenges, a structured process for development of grid connection requirements per voltage level is proposed. Finally, it is predicted that based on the expected future development of the electricity consumption and production such structured process will be beneficial for all involved parties.

Dealing with corrupted or missing data points is a common challenge in time-dependent data, such as wind speed and temperature
measurements. Our study introduces a two-stage Gaussian Process Regression (2sGPR) approach that addresses this problem by
first filling gaps in the corrupted time series with an initial value and then applying GPR to the distribution of multivariate inputs.
Different initial fill methods were evaluated by a hyper parameter optimisation to find the best model. The results indicate that
the 2sGPR approach effectively deals with both numerical and categorical input features. Compared to using persistence (i.e.,
carrying forward the last available value) for missing data, the 2sGPR approach reduces the error to the original data by up to
19%. The study also observed that the root mean square error of the model increases linearly with the size of the data gap.
The proposed 2sGPR approach offers a valuable tool for substituting missing time-dependent data in real-time applications. By
generating substitute values for incomplete data, the approach has the potential to improve the accuracy of machine learning
algorithms in various fields, including finance, healthcare, and transportation, where complete time-series data is crucial.

Grid-forming control (GFC) has seen numerous technological advances in their control types, applications, and the multitude of services they provide. Some examples of the services they provide include black start, inertial frequency response, and islanded operation capabilities with the possibility of re-synchronization without the need of additional support from other devices such as storage. State of the art literature proposes a variety of GFCs which can provide single or multiple of these services. However, study of these different GFCs for weakly-connected offshore wind power plants (WPPs) based on time-domain simulation and focusing on the large signal disturbance is not well covered. This paper reviews some of the most researched grid-forming control methods applicable to offshore WPPs and provides a comparative investigation and discussion of their stability properties and applicability, especially when connected to a weak-grid. The paper also provides a discussion on the prerequisites and challenges surrounding the comparative study of different GFCs.

Abstract - In the coming years, a strong increase in new controllable demand units connected to the German high-voltage and extra-high-voltage grid is expected. This increase will mainly be driven by power-to-gas facilities and data centers. Currently there are no sufficient connection requirements with respect to controllable demand units. This lack of requirements can lead to uncertainties in the grid behaviour of those units during disturbances. Anticipating their current capabilities for grid support, this expected upcoming increase of these demand units will negatively affect the future stability of the power system. Therefore special requirements will be needed for the connection of new and large demand facilities. For this reason the four German Transmission System Operators (4-TSO) have developed and published a first position paper on fault-ride-through requirements of power-to-gas units. Furthermore the 4-TSO will consolidate a position on additional fundamental requirements, which will be needed to ensure system stability in the future.

As more and more renewables, storage systems and, more recently, electrolysers are integrated into the power grid, the focus of testing and validating grid-connected frequency converters shifts from common grid code compliance measurements to more complex interaction assessments between systems and power equipment. The electrical properties of interest cannot be tested in the usual manor using field tests on prototype systems as they include, e.g., control interactions, impedance measurements, resonance phenomena, detailed model validation or grid-forming capabilities. Additionally, using the conventional approach does not allow effects originating from the system under test to be distinguished from those of the power grid and conclusive statements about its electrical behaviour can only be made at the end of the system’s development.

As part of the research project »PQ4Wind«, the Fraunhofer Institute for Wind Energy Systems IWES is developing and constructing a new power hardware-in-the-loop test facility to examine the higher frequency electrical properties of power electronic converter systems of wind turbines in the multi-megawatt range. The test bench is meant to help researchers, manufacturers, and suppliers develop, optimise and validate the electrical behaviour and generate measurements for model validation of frequency converters with up to 8 MW rated power in a wide frequency range up to the 200th harmonic. The new test bench is designed to provide a laboratory environment which – from an electrical point of view – replicates a wind turbine system while omitting all physical components present in real wind turbines. It does so by replacing the relevant electrical components of the turbine with its two fully programmable high-performance power electronic emulators in a 1:1 scale using the power hardware-in-the-loop approach.

Following the presentation at WIW 2022 showcasing the grid emulator, this paper now discusses the machine emulator of the new test bench in greater detail. Within the scope of the tests carried out, higher-frequency effects of the generator, converter and grid are focused on. Typically, fundamental frequency models are used for generator emulation. These models do not adequately represent higher-frequency effects, for example due to the assumption of infinitely small slot widths. In addition, frequency couplings between the individual components can occur. The paper therefore describes the requirements and the structure of the generator emulation with the use of a real-time simulator in the context of the test bench. In addition, an overview is given of the progress made in the construction of the test bench in relation to the last WIW.

The vast majority of inverter-based resources (IBRs) currently in service utilize grid-following (GFL) controls which were conceived to operate under strong grid conditions. GFL IBRs have a relatively low short-circuit power contribution compared to the synchronous generation that traditionally guaranteed the grid operability, and need an external source that establishes their terminal voltage waveform.

Weak network conditions produced by the increasing penetration of GFL IBRs can be identified by low values of equivalent short-circuit ratio (ESCR), which is an efficient heuristic index for the systematic screening of the grid strength in online applications and planning.

Technologies that allow to maximize the deployment of IBRs under weak network conditions include the installation of synchronous condensers (SCs) and IBRs with grid-forming (GFM) controllers. While SCs are a mature technology that has been used for several decades to stabilize the power system, GFM IBRs have recently started the path towards commercial deployment in large-scale applications.

Whereas in the long-term most new IBRs might have GFM controllers, there is a need to guarantee the operability of power systems during the transition from the current synchronous-generation-dominated power systems to the future IBR-dominated ones. This must be done as part of a more general problem, that of energy and economic development planning.

This paper addresses a generic power system planning framework in which the decision makers specify the IBR penetration scenario together with a target for the total GFM share (either new or retrofitted units) in a future scenario. We aim at answering the following two questions that are critical for the long-term development of a power system: 1) What is the minimum share and optimum location of GFM IBRs required to achieve a certain IBR penetration while meeting a minimum grid strength constraint? and 2) What is the maximum IBR penetration that can be unlocked from a grid strength perspective considering that a certain (predefined) share can have GFM controllers?

Previous works have primarily focused on the optimization of SCs' design, i.e., ensuring minimum grid strength by increasing the short-circuit power at predefined candidate buses. This paper proposes a model to address the counterpart of this planning sub-problem, related to the automatic definition of the minimum share and optimum allocation of GFM controllers to the IBRs in the network, subject to the target share of GFM IBR.

An alternative objective function is also defined to maximize the GFL IBR installed power that can be added to a given planning scenario subject to the maximum expansion capacity of each site. The proposed models are formulated as linear programming (LP) problems, and an alternative MILP formulation is also provided to consider that IBR can be either fully GFL or fully GFM.

The effectiveness of the proposed optimization model is shown using a modified IEEE 39-bus benchmark power system model in which synchronous generators were replaced by IBRs, thus leading to weak network conditions. Parametric analyses were run varying the minimum required ESCR and maximum share of conversion into GFM IBR for the LP and MILP formulations.

France has ambitious objectives for offshore wind development with a target of 40 GW by 2050. The Centre Manche (CM) 1 & 2 projects will have a combined capacity of approximately 2,500 MW and it will be tow first projects in France to use high-voltage direct current (HVDC) connections to the grid with two 320 kV converters, each with a maximum power of 1,250 MW. The offshore grid will consist of a 66 kV or 132 kV inter array cable. The connection is scheduled to be delivered in 2031.

As the transmission system operator in charge of the connection, RTE is responsible for onshore AC grid development and the AC offshore substation (OSS), as well as the HVDC substations onshore and offshore. RTE generally subcontracts the HVDC and OSS using EPCI) contracts. However, to reduce risk and better specify the different components of the connection to project’s specificities, RTE is conducting EMT studies in the early stages. These studies allow RTE to optimize the technical specifications and to anticipate potential issues on such innovative installation.

The present paper focuses on the generic study of offshore AC short circuit for the Centre Manche projects. The objective is to study the short circuit currents (SCC) at different locations of the OSS following different types of faults, including DC faults.
In the first step, the paper presents the hypotheses and EMT generic modeling used. For the simulations, mainly generic models for all the equipment, ie: IAC cables, transformers, wind turbine generator (WTG), HVDC, and neutral transformers are used. However, all these models correspond to realistic equipment. Different variations are considered to observe their impact on the SCC, including for example material parameters such as the length of the cables, the voltage level, or the Z0/Z1 ratio, the OSS configurations and some control parameter. Notably for the WTG, the study uses four different models (three manufacturer’s black-boxed WTG models [1]). The second step focused on parameter sensitivity on the SCC at OSS. The Elementary Effect analysis methodology [2] is applied to observe the sensitivity of the parameters to faults [3]. From this analysis, the most important parameters are selected to reduce the number of simulations bellow one thousand. This step aimed to ensure that the results are conservative in terms of high SCC and keep the most critical parameters. The last step of the study involved a qualitative analysis to discuss the key parameters. The qualitative analysis also aimed to identify potential risks, such as possible non-zero crossing of the current during a fault that need further analysis.

References :
[1] H. Saad, M. Vor Dem Berge, B. Marshall, O. D. Adeuyi, and R. Pabat-Stroe. "Dynamic studies on HVDC-OWF systems - Impact of WTG on HVDC performances." 17th International Conference on AC and DC Power Transmission (ACDC 2021), 2021 p. 102 – 107
[2] M.D. Morris, “Factorial sampling plans for preliminary computational experiments,” Technometrics, 1991, Vol. 33, No. 2, pp.161-174.
[3] H. Saad, P. Rault, M. Goertz, and S. Wenig. "Parameter sensitivity analysis on DC transients between MMC station and cable" Electric Power Systems Research (EPSR), 2021, Vol: 196: 107277.

When bidding with variable energy assets like wind and PV, forecast errors will ensure imbalances between the contractual market agreements and the actual physical deliveries. The cost of settling these imbalances is determined after the given settlement period has passed, and the outcome of the imbalance settlement can thus result in uncertainty and revenue losses for producers. At the last market gate closure for a given settlement period and throughout this period, a producer with dispatchable units in its portfolio can limit this uncertainty by internal balancing (i.e. ramp the dispatchable assets up/down compensating for the forecast error), or by mFRR market participation. We show that the latter is the most profit maximizing strategy.

Due to the increasing share of converter-interfaced generation in power systems, system inertia decreases and system stability is endangered. It has been shown in recent years that the use of grid-forming control methods for converter-interfaced generation systems can contribute to system inertia and could thus ensure system stability at very high share of converter-interfaced generation. Due to the limited overcurrent capability of converters in the event of grid faults, the implementation of safe and reliable overcurrent limitation is mandatory in real converter applications. This paper presents an enhanced Synchronverter-based grid-forming control method with current limiting capability for three-phase grid-side converters of type 4 wind power plants. In order to investigate the feasibility of the proposed control method on hardware as used in state-of-the-art wind power plants, the control method is implemented on a test converter, which realistically represents the converter of a 60 kVA laboratory scale wind power plant. Measurement results of the operation of the Synchronverter and its current limitation under grid disturbances are presented in the paper, demonstrating the applicability of the control method to wind power plants.

While every forecasting solution contains customized processes and practices, there are a number of attributes and components that are common to all forecasting solutions. For any industry, it is important to establish standards and recommended best practices in order to streamline processes, but also to ensure security of supply with a healthy competition structure.
The IEA Wind Task 36 "Wind Energy Forecasting" has started to develop, and it's successor, Task 51 "Forecasting for the weather-driven Energy System" has taken up the challenge of finalising a pre-standard recommended practice guideline for the forecasting of renewable energy solutions in 2022 in order to hamonise a globally growing industry in the second energy crisis since the 1070ies.
The IEA Wind Recommended Practice for the Implementation of Renewable Energy Forecasting Solutions (IEA-RP) is the first attempt to provide recommendations to the industry developed by a team of internationally active experts for implementation of wind and solar forecasting on a global basis.
The IEA-RP comprises four parts. The first part, Forecast Solution Selection Process, addresses the design of a customised process to select an optimal forecast solution for a user’s specific situation and application. In the second part, Design and Execution of Benchmarks and Trials, the design, execution and analysis of customised forecasting benchmarks and trials is addressed. In the third part, Forecast Solution Evaluation methods and guidelines for the meaningful evaluation of alternative forecasts, operational and non-operational forecasts and entire forecast solutions are presented. In the fourth part, Meteorological and Power Data Requirements for real-time forecasting Applications guidance for the selection, deployment and maintenance of meteorological sensors, power measurements and associated data quality control relevant to real-time forecasting is provided.
The purpose of the IEA-RP is to encourage both end-users and forecast service providers to standardize practices and components that are common to all forecasting solutions in order to achieve optimal forecast benefit for a user’s applications at lowest possible cost. The key element of this effort is to provide basic elements of decision support and thereby encourage end-users to analyse their own situation and use this analysis to design and request forecasting solutions and incentive schemes that fit their own purpose, rather than applying a ``doing what everybody else is doing'' strategy.
The guideline is designed to help streamline business processes for decision makers, system operators, traders, balance responsible parties and wind farm operators on a global basis, once the industry begins to adopt these recommendations. To assist in the practical application of the guideline, we provide three hands-on examples on how to use the guideline to design or improve forecast evaluation (Part 3) and measurement data quality (Part 4) in an efficient and impactful way. In the three use cases we demonstrate (1) evaluation of meteorological parameter forecasts (that could be used as input to a power prediction procedure) at a Danish coastal location, (2) verification of wind power predictions for a substation in the Northwest of Ireland and (3) quality control of meteorological measurements at an offshore location in the North Sea.

In Japan, the National Strategic Energy Plan was published in 2021. The plan envisioned possibilities of an aggressive carbon
emission reduction in 2030 and a carbon neutral in 2050 in 2050 through mass integration of emission-free generation
including renewable energy such as PV and wind.
The study, after the introduction, firstly reviews the current and future generation curtailment under the penetration of
renewable energy in Japan based on the latest discussions in Japan’s government committees, including estimation of
renewable energy generation curtailment in the current and the future year. The study secondly discuss about congestion
management to maximize the transfer capability of a transmission system and give an example of congestion analysis of the
Tohoku Area in 2030s using a production cost simulation model “MR”. The study lastly discusses about various enabling
technology and place the importance of information disclosure to involve various stakeholders such as renewable energy
investors or generators, transmission and distribution system operator, suppliers and regulators. The lastly presents, using a
production cost simulation with transmission capacity constraints, an example of transmission congestion management which
will contribute the maximum use of transmission system to accommodate renewable energy at a sustainable infrastructure cost
and discuss about the difficulty of information disclosure.
Under uncertainties of technology, economy and society, it is important to development and dissemination the future enabling
technologies should proceed with the transition of society and the improvement of institutions.

The European Network of Transmission System Operators (ENTSO-E) uses the Pan European Climate Database (PECD) in European Resource Adequacy Assessment (ERAA) and Ten-Year Network Development Plan (TYNDP), and ENTSO-E and its member transmission system operators (TSOs) can use it also in other studies. In the framework of the C3S Enhanced Energy operational Service Lot 2, the PECD is being updated for the historical period (based on reanalysis data), and importantly upgraded to include climate change signal to make PECD as representative as possible of the next decades. Started in late 2022, the Service has delivered climate data, including temperature, wind speed, precipitation, river discharge and irradiance covering the PECD domain at a gridded level and aggregated to the PECD regions. Based on the climate data, solar photovoltaic (solar PV), concentrated solar power and onshore/offshore wind generation time series were delivered to ENTSO-E together with documentation and information about the dataset.
This paper provides an overview of the creation of the new version of PECD. The methods and results (climate data and generation time series) and the expected impacts and lesson learnt in the first year of the development of the Service are presented. The whole process of updating PECD is described, but presentation of the results focuses on wind power and solar PV . Key methods include 1) how to ensure coherence between the historical period (based on ERA5 reanalysis) and the multiple climate projections, 2) need of bias-correction (both ERA5 and the climate projections), and 3) modelling of future wind technologies. Key results include how climate change is expected to impact future wind and solar generation and how similar the signal is between the different climate models. The planned next steps in the Service, to improve the modelling and to include more climate projections, are also discussed.
The C3S Enhanced Energy Lot 2 Service results are relevant not only for ENTSO-E and its member TSOs, but the database and related tools and application are expected to meet the needs of many users in the energy sector in Europe, including producers, aggregators, project developers, energy agencies and governments. The development of the new PECD, done in close collaboration with ENTSO-E, strengthens the links between the users and the research, development, and innovation community. The work aims also at encouraging discussion and co-design of solutions to meet the future challenges in the energy sector among scientists, policymakers, and other stakeholders.

General scope and relevance
Offshore wind energy is of growing importance to the transition towards climate neutrality. The development of offshore wind farms takes place within the exclusive economic zones of states, where the activities of developers are managed through the allocation seabed lease licenses. Seabed licenses for offshore wind farms are linked to different fees that can range to simple cash payments to payments that are linked to specific design elements of offshore wind farms such as, for example, the nameplate capacity (measured in MW) or the area (measured in km2). These fees have impacts on the economics of offshore wind farms which, crucially, vary depending on the different designs of wind farms, thereby creating incentives to choose some designs over others. As the fees can be very large, they may significantly alter how the offshore wind sector develops, making it an important scientific gap to cover.
Methods
In this study we first, provide an overview and categorize these fees in four relevant jurisdictions. Second, we analyse the potential of these fees to change the optimal design of offshore wind farms using both economic theory and conclusions drawn from wind farm optimization literature. This is done through the perspective of modes of response, which represent the potential adjustments developers may make to the wind farms as a response to the fees. The information presented in this study is based on original analysis of publicly available documents on seabed lease agreements as well as scientific literature from different fields of offshore wind farm optimization. This abstract is linked to a scientific paper that was written as part of a PhD thesis on market design for offshore wind.
Main results
First, we categorize fees into lump sum fees, and fees measured per km2, per MW, per MWh and per unit of revenue. Based on these categories, we can say that per km2 are likely to lead to increased density of wind farms and per MW fees and even per MWh fees would make it more economical to install lower specific power turbines. It is also possible for per MWh fees to lead to changes in layout, per revenue fees to lead to more turbine downtime, and for any of the non-lump sum fees to lead to smaller wind farms. However, the effects of these incentives may be nullified through the use of constraints on the wind farm design.
Major conclusions
The conclusion of this study is that the fees present in seabed licenses should be rationalized to match the overarching goals for the development in this sector considering the limited resources. With seabed scarcity in some regions, fees measured per km2 could incentivize offshore wind farm developers to make the most of a limited resource. If grid stability is a major concern, per MW and MWh fees could help incentivize grid friendly offshore wind farms. The use of both incentives created by the fees and constraints in the seabed lease agreements should be better coordinated.

Global power is undergoing an extensive transition. The share of renewable energies and batteries increases constantly, posing new challenges for power system stability. With the integration of renewable energies the share of inverters in the grid increases and thus the system's inertia is weakened. A stable power system cannot be achieved with traditional current-controlled inverters. Therefore, grid-forming controls were developed. Grid-forming inverters can replace synchronous generators and make fully inverter-driven grids possible.
Grid-forming controls offer a high degree of freedom in their design process and offer new possibilities regarding the utilization of generators and loads. A high inertia constant of the grid is desired and operators want or have to achieve this cost efficiently. For this reason, concepts like asymmetrical inertia provision were developed. In this concept, renewables offer inertia in case of a rising frequency and loads contribute to inertia in case of a falling frequency. The simplest load you can think of is a charging battery interfaced with the grid with a grid-forming inverter. Grid-forming batteries are used to ensure power system stability. This poses the challenge, that the battery has to stay connected in case of a short-circuit even when it charges. Under these circumstances, a grid-forming inverter will decrease its frequency and all synchronous generators (or grid-forming inverters injecting power) will accelerate. The angle differences will rise fast and loss of synchronism will be the result. Due to this, the critical clearing time of the system is decreased compared to a system without grid-forming loads.
In the paper, we will confirm the aforementioned scenario with simulation results. Furthermore, we will show how the fault behavior of a grid-forming inverter feeding a load can be changed in order to achieve better transient stability. Different methods for the manipulation of the frequency behavior during faults will be described and assessed in simulations. Due to these methods, transient stability can be improved and offer the possibility for the integration of large grid-forming loads, without a negative impact on the critical clearing time of the power system.

This paper presents a comprehensive analysis of the effectiveness of legacy power swing blocking (PSB) and out-of-step tripping (OST) functions in grid-forming voltage-source-converter (GFM-VSC) systems, considering the first-order power synchronizing control (PSC). By characterizing the power swing dynamics of PSC-VSC, it is observed that re-synchronization may occur even if the fault-clearing time exceeds the critical-clearing time (CCT). Specifically, when the current limitation is not reached, the PSB and OST functions may not misoperate, except at the maximum power transmission situation. Further, if the electrical center (i.e., the electrical midpoint of the total impedance of the line and two sources in a two-machine equivalent system) of the system is on the transmission line, even though the current limitation is not reached, the impedance trajectory may move into the distance protection relay zone during the re-synchronization process, leading to the misoperation of the distance relay. Time-domain simulations conducted in the PSCAD/EMTDC platform validate the accuracy of the theoretical analysis.

The large-scale integration of Inverter-Based Resources (IBRs) significantly alters the fault characteristics of synchronous generator-dominated power systems, posing a challenge to the conventional sequence component-based directional elements in the grid protection system. To reveal the impacts of IBRs on sequence component-based directional elements during asymmetrical faults, this paper first investigates the impacts of various priority modes of current reference generation. Subsequently, the impacts of control dynamics in the cases where the control scheme has not yet reached a steady state are investigated. It is found that the current reference generation and Phase-Locked Loop (PLL) dynamic can adversely affect the performance of directional elements. Electromagnetic transient (EMT) simulations are given to verify the theoretical analysis.

The objective of this paper is to present the research activities performed within the ongoing TRINITY project, focusing on how the balancing reserve sharing and exchange through establishment of cross-border cooperation can support large scale renewables integration in South East Europe. TRINITY project addresses the EU’s Research Horizon Framework 2020 Programme. The aim of TRINITY is to develop a set of solutions that will support the integration of the electricity markets in South East Europe and enhance cooperation and coordination among the transmission system operators, whilst promoting higher penetration of clean renewable energies.
In this paper, overview of the current European electricity regulation (EBGL, SOGL) is given related to the requirements for FRR balancing reserve dimensioning, as well as the opportunities and prerequisites under which cross-border cooperation for balancing reserve sharing and exchange can be implemented. The special focus is then given on assessing the potential impact of variable renewables (VRE) integration on balancing reserve requirements of three power systems in South East Europe (Serbia, Montenegro and North Macedonia), and how the cross-border balancing cooperation can support the system to facilitate large scale VRE integration in the best technical and economic efficient manner.

The share of Variable Renewable Energy (VRE) sources, especially wind and solar, is increasing in the European energy systems. Despite their environmental benefits, variability and forecast uncertainty caused by VRE technologies pose challenges in maintaining the supply-demand balance. Yet, due to the current electricity market construct, a major volume of VRE generation is cleared in day-ahead markets. The considerable temporal separation between the gate closures and actual delivery often results in forecast deviations. Thus, aggravating the imbalances and leading to frequency fluctuations and electricity price spikes. European system operators are integrating balancing markets to uphold adequate reserves to meet imbalances. Initiatives such as MARI and PICASSO are being developed as integrated market-clearing platforms for manual and automatic Frequency Restoration Reserves (mFRR and aFRR, respectively). While it is evident that the integrated market clearing mechanisms help to ensure reserve sufficiency at optimal costs, it is equally important to comprehend the evolution of imbalance volumes and available generation capacity of future balancing markets. This can help in assessing the balancing reserve requirements, both in terms of volume and ramping, and underlying bottlenecks of capacity investment decisions of future European power systems. This paper focuses on such underlying aspects. The developed balancing tool chain relies on the generator-level operational profiles, tie-line power flows, and hour-ahead/real-time renewable power forecasts.

Grid forming converter (GFC) controls can be designed with or without inner control loops. If inner control loops are used, they can be realised in various ways. The paper shows, investigates and explains the effect that such inner control loops can have on power quality aspects of power systems. The main focus is on voltage unbalances (negative sequence components) and low-order harmonics. The analysis is done in the time-domain by means of EMT simulations, and in the frequency domain via impedance characteristics. The results indicate that the design and the parametrisation of inner control loops define the beneficial effect that a GFC can have on the power quality of power systems. In this aspect, a virtual synchronous machine (VSM) implementation without inner control loops can achieve a behaviour similar to a real synchronous machine without additional effort, i.e. it can reduce existing voltage unbalance and low-order harmonics by a similar amount. As a conclusion, if inner control loops are used, they should be designed with care, and GFCs tested thoroughly with respect to the mentioned power quality aspects, in order to ensure a continuing high power quality in future power systems.

Quantifying grid-forming (GFM) capabilities of upcoming technologies is of great interest to grid operators, and to fulfill that objective various metrics and tests have been proposed. These proposed metrics, for the most part, rely on matching the performance of GFM devices to the well understood performance of synchronous generators. One parameter that is of special interest is the inertial capability of a GFM device. In the matching process, important technology differences and constraints might be ignored which would give the impression that the GFM device being evaluated has more or less inertial capability than expected. This work aims to qualitatively describe the inertial contribution of a doubly fed induction generator (DFIG) wind turbine for different operating conditions. By carefully analysing the limits of inertial capacity at different operating points we have shown that a single number or even a range of numbers does not accurately capture the real inertial contribution available to the DFIG turbine. This work also shows the performance of a prototype DFIG wind turbine using pre-existing available hardware and novel GFM controls that is connected to the grid and is demonstrating real inertia contribution when exposed to frequency events.

To ensure stable operation of the power system, there are currently two main control strategies, namely grid-following (GFL) and grid-forming (GFM). As the share of power converters in wind power plants (WPPs) continues to increase, there is a growing need to reassess grid-connection requirements and shift converter control strategies towards grid-forming control. To achieve this, it's essential to compare existing standards and compliance tests for grid-connected converters, highlighting both their commonalities and differences. This is particularly important for ensuring that the requirements for fault ride-through (FRT) and stable operation of WPPs are met.
Generally, modern weak power grids with reduced inertia and a lowered short circuit ratio (SCR) can present challenges to WPPs, particularly when it comes to FRT capability. In addition to the type of wind turbine used (III or IV), there are several factors that can influence the FRT capability of WPP grid-forming modules (GFMs).

• The GFM structure is a key factor, with three main categories: direct voltage-control based grid-forming (DVC-GFM), cascaded vector-control based grid-forming (CVC-GFM), and virtual-admittance based grid-forming (VA-GFM). DVC-GFM may not demonstrate safe FRT, the inertia contribution of CVC-GFM is significantly limited during fault conditions, and VA-GFM can face passivity problems.
• The GFM mechanisms such as the power synchronization control (PSC), synchronous power controller (SPC), virtual synchronous generator (VSG), synchronverter, dispatchable voltage oscillator for active and reactive power control loops can affect the transient behaviour under large-signal disturbances, and more research is needed in this area.
• Appropriate parameter tuning of the control loops is crucial to directly influence the FRT capability and performance of GFMs due to undesired control interactions.
• Stabilizing control methods such as feed-forward, gain-scheduling, or mode-switching strategies can ensure transient stability and improve the FRT capability of GFMs for both the power swing and virtual admittance loops.
• Current limiters are often implemented in the outer loops to prevent control errors, but effective current limiting control is crucial for influencing the FRT capability and performance of GFMs. It is important to find out how the GFMs behave during faults, when they are saturated, and how this issue can be addressed.

By considering these factors, the FRT capability of WPPs in modern weak power grids can be improved, ultimately leading to a more reliable and stable power system.
Based on these challenges, an analysis of grid forming requirements in the German and UK grid codes is presented in this study. In addition, a GFM WPP model is created in PSCAD and then connected to a HVDC converter with grid forming capability. This complete model is then utilised for a FRT study on GFM capabilities while WPP and HVDC both have a GFM functionality.

Energy system modelling has become a critical analysis tool for decision-makers in the energy transition. These models increase tremendously in complexity as many technologies and large sectoral, temporal, and spatial scopes are often considered. Efforts are therefore made to couple models with different scopes to perform holistic analyses, but coupling methodologies are rarely analysed, validated or even documented. This paper describes three overall categories of previous attempts to create holistic energy system analyses using bi-directional, soft-linked frameworks. Furthermore, a prototype modelling framework is developed for a small Danish-German electricity and hydrogen system with the state-of-the-art open-source energy system models Balmorel and Antares. A validation framework, where Balmorel is coupled with a high temporal resolution version of itself, is also constructed and compared with a comparable Balmorel-Antares run. This framework is utilised to test methods based on market value and loss of load expectation (LOLE). Results from the method comparison indicate that the LOLE approach is more adequate for assessing security of supply. The framework is considered adequate for security of supply assessments, but further work can increase both sectoral and spatial scope to utilise the European potential of both models and include the heating sector as modelled in Balmorel.

Distribution networks worldwide are on the verge of a significant transformation owing to the increasing share of distributed generation connected, especially wind and solar, at medium and low voltage levels. The traditional distribution network infrastructure, designed for uni-directional power flow, is non-optimal to accommodate generation sources, leading to a bi-directional power flow. Hydrogen systems, along with a PV power plant, wind power plant, or battery storage, have been investigated for optimal day-ahead operation, voltage regulation, and active and reactive power flexibility to mitigate the risk due to uncertain and variable renewable generation. A multi-energy framework offers greater flexibility for distribution networks to position themselves as an active participant in future distribution networks. However, as pointed out by many works, the path towards utilizing the full potential of hydrogen cost-effectively will require further research and development effort. This paper thus presents a brief survey of the existing electrolyzer technologies for hydrogen production in terms of their efficiency, operational characteristics and investment costs. The application and utility of hydrogen in future distribution networks are evaluated by studying existing research works and demonstration projects worldwide.

Like many nations, the Isle of Man is committed to net zero emissions by 2050. 75% of the island’s greenhouse gas footprint - 500,000 tonnes of CO2 per year - is related to energy use. The island is almost entirely reliant on gas & oil for electricity, heating & transport and there are currently no wind farms, solar parks or energy storage facilities.

The island lies in the Irish Sea, situated midway between the UK and Ireland, with 85,000 residents, a land area of 571 km2 and a shallow territorial sea of 4000 km2. In total, the island uses around 1300 GWh of energy per year, of which 360 GWh is electricity, most of which is generated from a gas-fueled (CCGT) power plant with diesel engines in reserve.

There has been some hesitation on utilising the island’s enviable natural resources of wind, water & mountainous terrain. There are worries around maintaining a stable & resilient electricity grid and the cost of upgrading & reinforcing the grid to accommodate intermittent renewables. The solution promoted by the state grid operator is to buy a majority of its future power from green sources in the UK via an existing and a planned interconnector. However, the steep rise and unpredictability in prices, has changed the question to Can the Isle of Man become self-sufficient in renewable energy and, if so, how?, the reason for the research reported here.

We have used a dual approach of energy system simulation and power-flow modelling to build two viable pathways to transition from gas & oil to self-sufficiency in wind & solar power, supported by varying amounts of energy storage. Other options such as biomass, nuclear, tidal, wave & geothermal energies were found to be either too expensive or not feasible based on the island’s geography & geology.

The first pathway is essentially a British Isles-style transition involving full electrification. The second pathway, based on Denmark-style plans involving district heating & a certain amount of green hydrogen. Both pathways lead to net zero emissions from power generation through broadly overlapping steps:

1) Phase in onshore renewables.
2) Develop energy storage schemes.
3) Phase out gas power from the CCGT plant.
4) Build a second interconnector & strengthen key parts of the grid.
5) Phase in electric vehicles with carbon pricing.
6) Phase in sustainable heating through incentives.

The CCGT plant could be converted to a synchronous condenser to stabilise electricity or, alternatively, a new hydrogen turbine would allow it to continue as a thermal power plant.

Both pathways are economic, the main difference being up-front cost versus operating cost. The models also show that, up to a reasonable size of over-capacity in wind energy, the larger the interconnector, the greater the value from exports, particularly if stored energy can be used in arbitrage. Ultimately, the island could serve as an energy hub for offshore wind farms, linked to markets in the UK & Ireland.

Traditionally, primary frequency control is performed by synchronous generators. The inertia provided by the rotating mass of the generators and the turbine-governor controllers are responsible for stabilizing the frequency for first few seconds after an imbalance between the generation and the load. With the rapid growth of power electronic converter-based technologies and increased integration of non-synchronous generation, the stability of the modern power system is challenged due to the loss of this inertia. This work aims at investigating the impact of embedded HVDC grids and different levels of grid-forming converter generation on the frequency dynamics of a hybrid AC-DC transmission grid. A dynamic model of an embedded point-to-point VSC-HVDC in the IEEE 4-machine, 2-area power system is implemented and time-domain simulations of different scenarios with varying renewable energy penetration for a load step event are simulated. The presented results suggest that for higher levels of grid-forming converter penetration, it is possible to guarantee frequency stability with proper controller tuning. However, with higher degree of penetration of grid-forming converters the rate of change of frequency also increases.

The increasing amount of power electronics, due to the fast dynamics, results in a change in the overall power system dynamics. Thus, stability analysis is required to analyze the converter induced interaction phenomena that can be attributed to converter-driven stability. A prerequisite for stability and interaction studies is the selection of an appropriate model that can represent electromechanical phenomena and electromagnetic transients (EMT) effects. A compromise between accuracy and computation time is required. Therefore, this paper compares the results of small signal stability analyses using converter EMT, detailed and a high level phasor models. The performed eigenvalue, participation factor, and indices analyses show, that interactions between the converters themselves, and between converters and the grid can be represented using EMT models. We outline a risk of instability for the interactions induced by the phase-locked loop, and the voltage delay. The delay induced interactions can be represented using the detailed phasor model of the converter, while those between the converters can only be represented partially. Even though faster computing time is possible with the high level phasor model, interactions between the converters and the grid cannot be represented.

An international research collaboration under IEA (the International Energy Agency) Wind TCP (Technical Collaboration Programme) Task 25 (Design and Operation of Energy Systems with large amount of Variable Generation) has previously performed an international comparison analysis on the curtailment of wind and solar power in various countries/areas in the world in 2022. This paper gives a comparison overview of the curtailment rates, presented as C-E maps (curtailment as a share of VRE and power system demand). As previous statistical data was as until 2020, some data has been updated. The latest information and the future estimations of curtailment in several countries/areas are summarised, including Ireland, California and Texas in U.S., and Japan. We also discuss the possible impacts of battery storage and demand response, which may contribute to reduced wind & solar curtailment, despite very high VRE (variable renewable energy) shares.

The dramatic increase in wind and solar PV has prompted a recent review on the status of these two key technologies to determine their long-term research challenges (Veers et al., 2019, Veers et al., 2022). They identified a common research challenge, grid integration, the all-important task of ensuring that with increased share of VRE the electricity system continue to meet the primary objective of maintaining supply demand balance reliably and at least cost.

VREs are replacing synchronous machines (SMs) in a planning time frame and operationally and are starting to become the dominant generating technology in some regions. The system needs and services need to be revisited to avoid providing services that are no longer needed which can be costly and not providing the services to meet existing or new needs and hence impacting on reliability. The end destination in this process is far from clear but will be heavily influenced by research and innovation in electricity grids and power systems and the technologies that make up the electricity system including wind.

We structure the future research needs along what are needed from the wind technology to provide future system needs. We list the needs as basic, fundamental services for power systems, including energy and capacity and six technical needs:
1. Energy
2. Capacity
3. Frequency control
4. Voltage control
5. Synchronisation
6. Damping
7. Protection and
8. Restoration
For each, the existing state of the art wind technology competitive services to meet these needs are given and their potential for improvement through research are detailed. Potential for improvement for wind technology enhanced with additional technologies which combined give them more capability with respect to meeting the future needs of the grids are also given.

This presentation, and paper, is based on the latest Grand challenges in the science of wind energy (Veers et al., 2022) and more specifically, a manuscript Grand challenges of Wind Energy Science – Meeting the needs of the Grid, https://www.wind-energy-science.net/articles_and_preprints/grand-challenges.html

References
Veers P., Dykes K., Lantz E., Barth S., Bottasso C.L., Carlson O., Clifton A., Green J., Green P., Holttinen H. et al. (2019). Grand challenges in the science of wind energy. Science Vol. 366, Issue 6464, https://doi.org/10.1126/science.aau2027
P. Veers, K. Dykes, S. Basu, A. Bianchini, A. Clifton, P. Green, H. Holttinen, et al. (2022) Grand Challenges: Wind energy research needs for a global energy transition. Wind Energy Science Discussions, 8p. https://doi.org/10.5194/wes-2022-66

Power oscillations pose a non-negligible threat to the stability of the grid. Static synchronous compensators (STATCOMs) allow damping of power oscillations to prevent the loss of synchronism and maximize power systems' transmission capacity.
However, the power oscillation damping control via reactive power (POD-Q) with STATCOMs shows undesirable fluctuations in its reactive power output whenever a generator's mechanical power is ramped.
The common control scheme includes high-pass filtering of its input signal to distinguish power oscillations from changes in the system's operating point.
In literature, washout filters are widely applied to perform high-pass filtering.
We improve the high-pass filtering in POD-Q control to reduce the STATCOM's reaction to changes in generator's mechanical power.
Therefore, we adapt filters used in Power System Stabilizers to POD-Q control. Furthermore, we propose a \textit{step filter} and a cascaded washout filter.
The different filters are compared and evaluated with respect to defined design criteria regarding their phase and magnitude responses. The filter's response to a ramp input, as well as its ability to contribute to power oscillation damping, are of main interest.
Both, the \textit{step filter} and the cascaded washout filter can significantly reduce the reactive power fluctuations compared to a washout filter while mechanical power changes occur.

Power-to-X (PtX) and electrolysers appear as versatile concepts to set significant changes for power systems and the whole energy sector because of their transversal application and flexibility enhancement. However, despite all the policy efforts to impulse PtX, few dedicated technical guidelines or test compliances for electrolysers connected to electrical grids have been set up until the moment. To this end, this paper presents a comprehensive analysis of the technical requirements governing the integration of inverter-based facilities, with a specific focus on Photovoltaic Power Plants (PVPPs), Wind Power Plants (WPPs), and Energy Storage Facilities (ESFs) in modern power systems, which can serve as references for PtX projects. The research explores the applicability of grid codes in Denmark and the United Kingdom, chosen due to their prominent utilization of renewable generators and frequent updates. Notably, the investigation emphasizes regulation requirements for active power and frequency control as the main scope of the study. Finally, some specific steps for defining technical guidelines and standardized parameters, ensuring a seamless and resilient integration of PtX technologies into modern power systems are presented as the main findings.

Integrating a high share of electricity from intermittent and non-dispatchable Inverter Based Resources (IBRs) predominantly from renewable energy sources such wind and solar are essential for meeting the future energy needs while decarbonising the power sector. However, short circuit responses and dynamic characteristics of IBRs connected to transmission grid are decided by the converter control strategy under different operating conditions which are fundamentally different from traditional synchronous generators (SGs). Consequently, the performances of commercially available protection relays used for transmission lines protection are challenged. Therefore, there is an extreme need for in-depth and groundbreaking studies to develop new or modified techniques on design and testing of protection relays to ensure effectiveness, reliability, and security of operation of the protection system used for transmission network. In this paper, the results of the literature review on the impact of IBRs on the performances of transmission line protections are presented and the emerging technologies that target these challenges to provide the required flexibility, adaptability, and dynamic capability of future protection relays under different operating conditions and regulatory requirements are introduced. In addition, the importance of setting regulatory frameworks and standardization of relay testing strategies using modern validation tools such as Hardware-in-the-loop (HiL), Software-in-the-loop (SiL) real time testing and digital twin environment is highlighted.

Developing innovative electricity market designs to facilitate a sustainable transition to (near) 100% renewable power systems while meeting societal needs is a crucial and actual topic of research. This article presents preliminary key findings from the H2020 European project TradeRES, addressing this critical topic. The project uses agent-based and optimization models to effectively capture the behaviour of different market players, and to analyse the current and future power system energy mixes of selected European case studies with different physical and spatial scales from: i) local energy communities and local energy markets (LEMs); ii) national/regional - the Netherlands, Germany, and Iberia (Portugal and Spain); and iii) pan-European energy markets. The first results on LEMs indicate a substantial economic benefit for participants and enhanced revenue streams for distributed energy resources, able to i) incentivise further decentralised investments; ii) promote the growth of variable renewable energy systems (vRES) and iii) increase flexibility at the local level. The outcomes are sensitive to the tariffs’ structure, while the retail sector competitiveness was identified as a critical parameter affecting its efficiency. For the pan-European and national/regional case studies, the first set of simulations had consistent outcomes, namely, by pointing out current design of energy-only markets to be insufficient to incentivize the high levels of vRES foreseen in Europe. Different support schemes (e.g., fixed market premia, contract for differences) were tested and results suggest they may play a relevant role in effectively covering the cost of vRES in a market environment.

Funding
This work has received funding from the EU Horizon 2020 research and innovation program under project TradeRES (grant agreement No 864276).

In early days of the energy transition, most inverter-based resources (IBR) had relatively simple requirements for grid connection and their overall impact to system reliability was low. As IBRs have been more widely adopted and technology has progressed, the industry has begun to develop and adopt new performance requirements/standards for IBR to promote grid stability. The established framework for dynamic grid performance requirements is largely based on “input-output” relationships – based on a certain input (e.g. change in voltage) generate a certain output (e.g. change in reactive current). As shown in this paper, prescriptive input-output requirements can be a barrier for advanced control designs and in certain grid conditions be counterproductive to grid stability.

As performance requirements are revised or established for newer technologies, such as grid-forming IBR, an opportunity arises to establish an improved framework for performance evaluation. Key aspects of this improved framework include: (a) standardized set of simulation scenarios reflecting typical range of grid connections and (b) system-level performance requirements based on impacts of the IBR resource to system stability. Simulation examples are provided in this paper demonstrating the risks of prescriptive input-output requirements and benefits of system-level performance evaluation.

With the expansion of renewable energy introduction, daytime power surpluses, especially from solar power, have become an issue in Japan. To address the issue of daytime power surpluses, power system operations are being conducted mainly by utilizing the flexibility of thermal generators. Since the installed capacity of storage batteries is still small compared to demand, operations are conducted to ensure the flexibility of conventional thermal power generators even during daytime power surpluses. Storage batteries have the advantage of being able to provide power transport services with the absorption of surplus power. In the future, the installed capacity of storage batteries is expected to expand to a scale that will have an impact on the power grid.
One of the major problems is that the charge and discharge plans that storage battery owners make are subject to the price forecasts of the electricity market. As the capacity of installed storage batteries expands, they will plan to charge and discharge at the same time because the time variability of the electricity market price forecast curve is small. The operation of the storage batteries with expanded installed capacity will affect electricity market prices. Discharging storage batteries lowers the peak electricity market price, while recharging raises the bottom price, thereby reducing arbitrage opportunities in the electricity market. Furthermore, if a generator has storage batteries, there is an incentive to underutilize them because their operation lowers the revenues of other generators.
This paper describes the formulation of the storage battery as a transmission asset in order to internalize storage losses into the electricity market.
The proposed formulation is designed as an optimal transmission switching problem based on the concept of treating storage batteries as transmission assets. First, losses during charging operation and discharging of the storage batteries are considered as well as transmission losses. Furthermore, the output upper and lower limit constraints of the storage batteries and the upper and lower limit constraints of the amount of energy that can be stored are also taken into account. Finally, the developed formulation will be compared to the existing battery storage formulation in a numerical simulation using Japanese power system data. The effectiveness of the proposed formulation will be evaluated based on the utilization of storage batteries and revenues.
The evaluation of the proposed formulation shows that the charge and discharge losses of the storage batteries are internalized into the electricity market, and the benefits of the storage batteries absorbing surplus power are linked to the power transmission service of the power system operation.
This result indicates that treating storage batteries as transmission assets is effective in expanding the installed capacity of renewable energy through the utilization of their ability to absorb surplus power.

Black start and system recovery contribution will be one of the first widespread use of grid forming converters.

Whereas system stability can be achieved with 10-20% grid forming generation (synchronous generator or converter based), it is simply not acceptable not to use the renewable energy installed capacity (more than 50% in many European Countries) during black start operation and in all phases of system recovery after a black-out.

However, during black-start and system recovery, system loads can change widely, faults are more likely to occur and, in general, both the electric system and the wind power plant would be working outside its normal operating conditions.

In this context, it is particularly important to assess the effects on both geared and direct-drive wind turbine mechanics, in order to ascertain up to which extent the gearbox or the blade roots would need additional reinforcement. It is also important to ascertain quantitatively up to which extent very stringent requirements could lead to additional costs on the WTGs.

The study has been carried out considering a real-time simulation of a HVDC connected wind power plant, consisting on 32 wind turbine generators, including aeroelastic models and detailed models of converter, cables, transformers and MMC converters.

Introduction
Hybrid Power Plant (HPP) is a combination of several renewable energy sources such as wind and solar combined with energy storage systems (ESS) and/or P2X connected behind a single grid connection point. In HPP oversized sub-plants in respect to the grid connection capacity contributes with better utilization of electrical infrastructure and added flexibility. Today, a vast increase in the capacity of newly built renewable power plants and a surge in demand for green hydrogen is foreseen, introducing the notion of large generating clusters such as Energy Islands and HPPs with offshore wind farms (OWF) hybridized onshore. Such large offshore HPP systems need coordinated control of the technologies to meet the grid code requirements. So far in literature only HPPs based on onshore technologies (onshore wind, PV and ESS) in close proximity have been considered.

Challenges of HPPs with Offshore Wind
Control of individual RES is well established, yet the active and reactive power generation of large offshore wind farms with High Voltage Alternating Current (HVAC) cables is a complex task, often involving additional compensating equipment on the offshore substation platforms, at the midpoint of the transmission cable to land, and at the onshore substation. In HPP, where such OWFs are hybridized far away onshore with PV, ESS and electrolyzers, a few additional operating scenarios appear, with varying power flows in the internal grid (e.g., generation of hydrogen, charge or discharge of the ESS). Those scenarios must be realized while power flow at the PoC fulfils grid code requirements and may require different control strategies. The known control architectures must be revisited to address new layers of complexities such as: i) the distance between the technologies; ii) high number of inverter-based resources (IBR); iii) additional communication delays, - amongst others not seen in the smaller onshore HPPs. Coordination and distinct role allocations between the layers of hierarchical control architecture of HPPs with offshore wind farm will have a key role in securing flawless power generation. Additional complexity lies in the fact that different assets are procured from different vendors without harmonization of control and communication protocols, thus creating interoperability challenges and hampering the performance of the HPP.

Outcome

Energy systems that are dominated by wind and solar power need long-duration storage to balance weekly, seasonal and annual
variations. While hydrogen storage in underground salt caverns is often considered because of its low cost, suitable salt deposits
may be far from good renewable sites and thus require long-distance transport of electricity or hydrogen. We explore methanol
storage as a promising alternative. As a liquid under ambient conditions, methanol can be stored in tanks at significantly lower
cost than hydrogen; the tanks can be built anywhere; and methanol can be easily transported by vehicle or pipeline. Converting
methanol back to power and heat in an Allam cycle turbine allows almost all carbon dioxide to be captured, stored and fed back into
methanol synthesis, thus closing the carbon cycle. We compare methanol with hydrogen storage in simulations of power systems
based on wind and solar for several European countries over 71 years of weather data. We find that methanol storage leads to
systems that are 29-43% lower cost than those storing hydrogen in steel pressure vessels, and 16-20% more expensive than storing
hydrogen underground in salt caverns. Future reductions in Allam cycle costs would reduce the gap with cavern storage to just
6-7%. Methanol storage could thus be attractive for regions without access to geological salt deposits. Since economies of scale
are already achieved at 100 MW scale, methanol could also be attractive for smaller autarkic systems. Methanol storage is built to
cover up to 92 days of electricity demand in order to get through all 71 historical weather years. Such a strategic methanol reserve
could offer resilience not just against extreme events such as low-wind years, but also against volcano eruptions and disruptions to
grid infrastructure.

With an increasing share of renewable energy sources being connected to electrical power networks at either grid or local utilization voltage levels, transient energy from the rotating inertia of traditional power plant is reducing. Renewable energy resources are highly dynamic and somewhat intermittent compared to more traditional generation sources. Hence, they pose a challenge to the electrical network operator in terms of effectively managing their resources to maximize energy transfer while maintaining a stable interconnected network. Further, there is an increasing percentage of electrical energy generation that is connected at the utilization end of the electrical power network which poses challenges for energy flow, voltage stability and protection systems. This local generation may well increase to a higher level of net generation in the future due to the shortfall in the build of large capital power generating plants (in the UK).
For traditional electrical power networks, frequency is the stabilizing measure with voltage control and circuit selection used to manage energy transfer. Even with the inception of more distributed generation and interfacing power electronics, system frequency will still be of paramount importance, since many distributed generation and utilization systems continue to interconnect to higher voltage AC systems for bulk energy transfer. An important feature of any future distributed network will be the derivation of the exact frequency relationship with other networks.
A particular aspect of existing renewable energy resources is that they have low transient energy capability and, as such, reduce the total system stored energy – often referred to as system inertia. Further, this lack of transient energy capability increases the specification requirements of other interconnected components, or reduces the energy conversion capability of the renewable resource.
The paper will initially discuss the operational concept of a synchronous condenser with reference to the support of renewable and localized embedded generation. An example synchronous condenser design is presented to illustrate the provision of some limited energy input during energy transients, some reactive VAr capability, but importantly, supply of high transient fault currents. The paper discusses the synchronous condenser electro-magnetic design in terms of machine impedance to realize high fault levels.

Electrical distribution grids play a crucial role in achieving decarbonisation goals by effectively integrating and utilizing clean and sustainable energy resources. However, these grids face significant challenges due to the unpredictable nature of the power system, including the variability and uncertainty associated with consumer behaviour, renewable energy generation, and the growing electrification of heat and transportation. Distribution grid operators must address increased power fluctuations, which can lead to power quality issues and operation near or beyond line loading and voltage band limits. Various strategies, such as feed-in management, load shifting techniques, and adaptive power factor control, can be investigated and implemented to mitigate these uncertainties and optimize grid performance. In Germany, grid operators are actively pursuing a smartification strategy, promoting the implementation of smart distribution grids by enhancing observability in medium- and low-voltage grids. With the ongoing smart meter rollout, accurate quantification of uncertainties may be possible not only at the medium voltage level, where measurement equipment is already utilized, but also at the low voltage level.

Although extensive research has been conducted on optimization under uncertainty in higher-level grids, there is a noticeable gap in comprehensive studies specifically focused on distribution grids. This gap primarily arises from the absence of measurement technology, particularly at the low voltage level. To bridge this gap, this paper presents a structured literature review that offers a comprehensive overview of existing studies, methodologies, and applications related to uncertainty quantification in distribution grids. The primary objective of this review is to cluster the various objectives pursued in these studies, identify specific characteristics that distinguish applications at the low voltage level, highlight the approaches employed to address uncertainty in each case, and potentially identify gaps and challenges that require further investigation in future research. By identifying best practices, limitations, and research opportunities, this review can contribute to knowledge advancement and informed decision-making for grid operators and other stakeholders. For the analysis of the literature, we utilized the text mining software Orange, in addition to individual reviewing to assess methodologies, applications, and other relevant aspects of the studies.

With the help of simulation models, energy system components can be analysed individually and in combination with other models to investigate the system’s behaviour under uncertain conditions. Therefore, a general procedure is proposed for integrating uncertainty quantification as a component into a quasi-dynamic energy system simulation of a residential district. Specifically, this quantification should support a flexible control strategy that corrects operation limits violations with the help of flexibility provision. The simulations, including various scenarios, are being developed within the research project "Future Energy Laboratory," which involves studying the interactions between highly integrated ICT and energy systems for district energy supply. Future studies should focus on selecting suitable calculation methods for an aggregated uncertainty quantification in energy systems at the district level.

Decarbonizing the U.S. energy system entails a significant expansion of wind and solar power and electrification of end-use applications. Both endeavors require expansion of high-voltage transmission, which is challenging given the fractured nature of the U.S. grid. Here, we explore the role of interregional transmission under a variety of decarbonization scenarios, using a capacity-expansion model to generate co-optimized portfolios of generation, storage, and transmission that meet decarbonization targets and electrification-driven demand. We explore portfolio and cost differences across 92 scenarios, from scenarios with limited transmission expansion to those that include a national high-voltage direct current macrogrid. In the core decarbonization scenarios, solar expands by ~20× and wind by ~10× compared to 2020, hundreds of gigawatts of battery storage are deployed, and interregional transmission expands by 3–6×. Transmission expansion occurs nationwide but is concentrated between the central “wind belt” and eastern load centers. The macrogrid scenarios result in hundreds of billions of dollars of savings in total system cost, demonstrating the economic benefits of interregional transmission. Transmission expansion is robust across several futures, and delivers the largest savings when nascent technologies like hydrogen are restricted, suggesting that transmission can be a valuable hedge against technology risk as well as an enabler of reduced decarbonization costs.

This paper presents the development and validation of a simulation model of a Type IV wind turbine generator, designed to assess the impact of the integration of renewable energy sources (RES) in the transmission grids, namely regarding the behaviour of the protection functions. This model was assessed using the Portuguese transmission grid as a use case, so it considers and complies with the relevant dispositions from the Portuguese Grid Code. In fact, the Portuguese Grid Code states that the injection of the reactive power into the grid shall occur for all types of faults, not only for 3-phase faults, as it happens in other European countries. Furthermore, the Portuguese context is important in terms of expected inverter-based resources (IBR) presence growth, which makes it a suitable test case to analyse possible effects on protection functions. The assessment was done by simulating faults at the point of connection to the transmission grid and in an adjacent transmission line, obtaining the corresponding measurements of current and apparent impedance and comparing them with a conventional generator. It was used a real-time simulator, to ensure close-to-reality measurement of values of the dynamic injected reactive power and voltage at the point of connection during the faults. Results show that current contributions from RES are considerably lower during faults when compared to traditional synchronous generators. In addition, it was verified that the mentioned low current contributions affect the distance protection behaviour causing them not recognize fault conditions, confirming the need of the additional dynamic injection of reactive current for all type of faults, requested by the Portuguese grid code.