This paper look into synthetic inertia control of doubly fed induction generator (DFIG) based wind turbines to provide dynamic frequency support. In conventional synthetic inertia control if a large disturbance occurs in a power grid, two additional loops are implemented in each DFIG controller: droop
loop and rate of change of frequency (ROCOF) loop. Because of their fixed control gains, difficulties arise in determining them suitably, depending on the architecture of power system to which the wind turbines are connected and wind conditions. This paper proposes an optimal synthetic inertial control by means of using the particle swarm optimization algorithm (PSO) to calculate the optimum values of the control gains. The proposed approach aims to enhance the frequency nadir and ensure stable operation of the wind turbine.
The development of Variable Renewable Energy (VRE such as wind and solar power) at high share introduces a new source of uncertainty in electrical power systems. The resulting power imbalances should be integrated into the balancing studies, and in particular when sizing the automatic Frequency Restoration Reserve (aFRR). Traditionally, Transmission System Operators (TSO) use deterministic approach for aFRR sizing, even though some TSOs have already opted for probabilistic methods. Indeed, probabilistic method enables to tackle explicitly the uncertainty driven by VRE. Moreover, probabilistic method is undoubtedly going to be broadly adopted with the entry in force of European Network Codes (cf. article 157 of System Operation code).
“OPIUM” is a tool developed at EDF R&D since 2013. This tools is based on a probabilistic approach and aims to evaluate the needs in power margin for a given time horizon (e.g. 15 minutes for aFRR) while taking into account a predefined risk level, at the scale of a country and for each hour of the year considered.
More specifically OPIUM consists in a 3-steps process (realized for each of the 8760 hours of a year):
In the full paper, the methodology will be presented in detail. After being validated in the French case with 2015 data, OPIUM is then used considering prospective scenarios with higher VRE penetration levels (> 50%) developed in the European project EU-Sysflex. The results give an insight in the potential evolution in the aFRR sizing across Europe. Moreover, several conclusions can be drawn from the results:
A requirement for power systems connected to larger systems through high-voltage, direct-current (HVDC) interconnectors is that frequency must be managed internally. In particular, connected generation needs to have sufficient inertia and emergency reserve to cope with loss of a major infeed or interconnector. Sufficient inertia is needed to limit rate of change of frequency (ROCOF) to a value that does not compromise loss-of-mains (LOM) protection on distributed generation, including wind farms. A ROCOF of 1.0 Hz/s has been adopted in Ireland. A ROCOF greater than 1.0 Hz/s is deemed to indicate loss of mains, triggering disconnection of the affected generation only.
The challenge for a system with significant wind and/or solar generation is that such generation does not generally provide inertia. Hence such non-synchronous generation, including HVDC import, is limited to a proportion of demand, including export. The proportion, known as system non-synchronous penetration (SNSP), is currently set at 65% in Ireland, with an ambition to increase it to 75%. When the SNSP limit is active, wind generation is curtailed. Such action is taken in preference to reducing HVDC import. SNSP-induced curtailment in Ireland for 2017 was 2.75% of potential wind generation.
Clearly, as wind penetration increases beyond the current level of 29%, so also will curtailment, even with SNSP increasing to 75%. Eventually the cost to wind farm developers and consumers will stifle investment in the sector. Hence it is important to study the factors affecting curtailment, and to assess possible remedies.
The paper will consider the effects of import reduction and export on potential wind penetration in the Iriosh power system for various curtailment toleration levels up to 10%. The scenarios are based on extrapolation of historic demand and wind power data. SMP data have also been used to explore the scope for extra penetration levels when curtailment is based on value rather than magnitude. It will be shown that import reduction can extend the practical wind penetration level, especially when based on curtailment value rather than magnitude. More significant improvement is possible if export capacity is fully exploited.
It will be argued that import reduction to avoid curtailment is justified by basic economics as well as by decreased emissions. However, the major benefit is that the system can accept a significantly greater wind penetration for a given curtailment tolerance.
This paper presents the system analysis 2019 of German TSOs on demand for reserve generation capacity to maintain system security.
System Security, Market Simulation, Load Flow Analysis, Load Flow Optimization, RES Integration, Congestion Management, Redispatch, Reserve Generation Capacity
In 2011 the German government decided to shut down existing nuclear generation units successively until 2022 and to accelerate electricity generation based on renewable energy sources (RES). Since then the RES target figures were repeatedly increased in accordance with the European energy policy objectives. As nuclear generation units were erected close to load centres in Southern Germany and wind power generation is mainly located in Northern Germany, a significant increase in North-South load flows during strong wind situations has been observed. This is amplified by changes in the power generation portfolio together with the political commitment to increase cross-border trading capacities beyond physical transmission capacities. Especially in high wind generation scenarios with additional transit flows through Germany, the maximum transmission grid capacities may be exceeded. The congestions in the transmission grid need to be mitigated by TSO instructed generation redispatch.
The so-called “Reserve Generation Capacity Ordinance”, revised 2016, was introduced 2013 and obliges the German TSOs to jointly assess/determine the measures necessary to maintain adequate system security. The annual TSO report is based on coordinated detailed analyses and is submitted to the national regulatory authority for confirmation.
The paper covers the periods 2019/20 and 2022/23 and considers annual trends, as well as severe scenarios. It takes the progressive reinforcement and reported delays to the transmission system into consideration, and the results show that the most challenging situations occur near peak load, combined with high wind energy generation or in case of high transit power flows through the German transmission network. The need for market-related measures to maintain system security increases continuously, as well as the corresponding demand for reserve generation capacity. The analysis determines for 2019/20 a total need of more than 15 GW redispatch capacity, of which 5 GW is derived from reserve generation capacity located in Southern Germany.
This paper provides insight into the legal, regulatory and analytical background of this system analysis. Beside refining the process for determining the robust reserve generation portfolio, in 2019 the flow-based market coupling methodology was implemented to adequately consider the future market framework as defined by the EU clean energy package. The methodologies are outlined and the results of the market and grid analyses are presented. Concluding, the paper illustrates the increasing challenges to maintain system security and the need for adequate transmission system reinforcement.
This presentation provides an overview on key objectives of the new European energy policy legislative framework and on the essential role of Network Codes in implementing it. The revised competences of ENTSO-E, ACER, the EC and the new European DSO entity in drafting and amending network codes will be illustrated. Additionally, ENTSO-E’s view on the challenges for the power system implied by the updated energy policy targets and their impact on new and refined connection requirements is outlined.
Energy Policy Objectives, European Legislation, Connection Network Codes, RES Integration, System Challenges
The European energy policy legislative framework is currently changing. The existing framework will be replaced by a set of directives and regulations, known as the “Clean Energy for all Europeans Package (CEP)” with the main motivations of even more ambitious objectives to facilitate the European internal energy markets and to decarbonize the energy sector.
Network Codes and Guidelines are an essential vehicle for implementing the CEP. For new network codes, drafting committees will be established, which shall be chaired either by ENTSO-E, or jointly by ENTSO-E and a new EU DSO entity, as the case may be. Relevant stakeholders shall be actively involved already at an early stage as members of these committees. Topics for new network codes are still under discussion. Possibly more important than new network codes, existing codes and guidelines will be amended. The amendment process foresees a central role for ACER in collecting and assessing amendment proposals and proposing them to the EC.
Reconciling electricity system needs with energy policy objectives will remain a major challenge for Connection Network Codes. The massive RES integration entails an accelerated displacement of conventional, synchronously connected generators by mainly converter‐connected, non‐synchronous RES generation, which has a significant impact on system needs and characteristics, like the reduction of system inertia with its impact on frequency stability. Connection requirements need to anticipate such developments based on long-term scenarios and system analysis to conclude on the relevant capabilities of system users.
This presentation shall provide an overview of the key objectives and figures of the CEP. It will describe the process, roles and responsibilities for drafting and amending network codes and guidelines. An emphasis will be given on connection network codes, outlining how electricity system needs can be reconciled with the energy policy objectives.
As agreed with Thomas Ackermann, the presentation will not be accompanied by a paper, because the CEP key objectives and the processes for drafting and amending network codes are defined by the legislative package itself. It is however foreseen to provide the presentation in due time to publish it in the conference proceedings.
Abstract--Northeast China is part of a very cold and wind-rich area. The coal-fired heating consumption is very large and air pollution is quite serious during the whole winter heating period. The energy vector coupling between wind power and heating has remarkable economic benefits and environmental value.
This paper proposed three measures aimed at solving the economic and technological problems for the coupling, considering the major forms of urban heat-sources, i.e. thermal power plants and coal-fired boiler centers. For coupling on the generation side, co-generation units combined with heat storage electric boilers (e-boiler) have been adopted, and a Northeast Power Peak Regulation Ancillary Service Market was established, which solved the problem of economic compensation of wind electric heating. For load side coupling, coal-fired boilers combined with e-boilers have been employed, and a direct trading model between wind power and thermal storage electric boilers (e-boilers) has been built. A third measure is establishing a coupling between the potential e-boilers and wind power curtailment by planned capacity of curtailment-based e-boiler and advanced on-line optimizing dispatch. The results show that wind power is achieving a significant level in Northeast China.
Index Terms-Energy vector coupling, cold and wind-rich area, wind power, coal-fired heating, thermal storage electric boiler(e-boiler), power peak regulation ancillary service, direct trading model, planning capacity of wind curtailment-based heating e-boiler.
Developing an integrated pan-European energy system based on renewable energy sources (RES) has technical and economic benefits. In this way, harmonized rules for grid connection of RES are required at the international level. Wind energy is one of the most promising renewable energy worldwide. The integration of wind energy into the power system is overgrowing through onshore and offshore installations. The European network of transmission system operators for electricity (ENTSO-E) has published international requirements for HVDC- and AC-connected power plants in two separate international network codes. This paper presents the main aspects of these codes and compares them. It is recommended to define the national network codes based on RES connection type (AC and HVDC) rather than the onshore and offshore categorization. Also, the main requirements for HVDC connected generations are being regulated by ENTSO-E all around Europe. Therefore, the integration of RES into European power systems via HVDC transmission would be easier. However, there are particular stability and control challenges in HVDC connection which need to be considered.
To document compliance with grid code requirements an extensive test program is needed in many countries. Irish Transmission System Operator, EirGrid have a very thorough test procedure for Grid Code testing on every Wind Farm Power Station, where everything in the Grid Code is tested on every WFPS. This is a long and time-consuming process that is highly dependent on wind and grid conditions.
But can we do this in a more efficient way by using type testing combined with field testing to demonstrate compliance to the Grid Code?
This paper will be based on EirGrid‘s test procedures and present a split between performance testing and functional testing according to the working draft of the IEC 61400-21-2. The idea in the upcoming standard is to conduct performance testing at every WFPS, however functionality testing is instead to be done in a “hardware in the loop” simulation set-up, that is valid for all WFPS using the same power plant controller and software.
The paper will present results from Grid Code testing on a WFPS in Ireland and compare this to functionality tests completed on the power plant controller in at simulation set-up in the laboratory.
This will show a consistency between the results from the WFPS and the simulation and indicate that large part of the testing can done covered by a type test.
The following sub-set of the full suite of Grid code tests will be proposed as the (on-site) performance tests:
• Active power control, DMOL test from frequency control and start up APC on and APC Off
These tests are proposed as the function (or type) tests:
• Active power control setpoint handling
• Frequency control
This split between simulator and site tests will reduce the number of tests on site and the dependency of wind and grid conditions, without compromising the quality of grid code compliance achieved.
In 2017, Denmark had a share of 62% RES of electricity demand, with 45% provided by variable RES. Aiming for 100% electricity share in 2030, the country enters the next phase towards a future, when not only electricity, but energy has to be fossil free in 2050.
The Danish TSO being responsible for the electricity and gas infrastructure investigated possible pathways towards that future. So far, a strong coupling between the electricity and heat sector has harvested synergies for several decades already, strong transmission lines have benefited exchange possibilities with neighbours, power plants are maximal flexible and controllable and proper means of electricity market design as well as up-to-date forecasting means have provided best conditions for variable RES integration.
For the countries’ further decarbonizing it is important to determine economic viable pathways with all sectors coupled, i.e. the electricity, heat, gas and transport sectors.
To investigate this sector coupling, the Danish TSO has modeled the countries’ energy systems and has spread so called “energy plants” of several sizes across the country. These energy plants link various sectors and act dependent on power prices. Determination of their size is part of the results showing sector coupling potential depending on their location and related individual conditions.
To capture the development of the whole region, the ENTSO-E’s future scenarios for 2030 and 2040 have been applied. They reflect a consistent regional development, as not only Denmark, but all Europe is expected to go green. Big electrification activities are foreseen in all countries with an impact on hourly energy prices, import- and export potential of electricity - as variable RES often is correlated across country borders. New applications are expected to enter the markets on the generation and consumption side as well. To name a few, there are electric vehicles (EV), big data centers, power to gas (P2G) units, power to X (P2X) units linking especially gas and transport sector closer to the classical electricity system.
The modeling results of a sector-coupled Denmark including potentials for P2G and PtX will be presented, embedded in the regional development of Northern Europe between 2030 and 2040.
Standards and industry guidelines in general are necessary in order to judge work objecitvely against a reference and to ensure that different working processes or interactions can be interlinked.
Wind power forecasting or more general renewables forecasting has matured in recent years. In this process it becomes evident that efficiency and interaction between supplier and end-users need to become more streamlined and pre-defined processes. The most important processes to achieve more ease and efficiency in implementation of forecasting processes require a common understanding of terminology, data structures and formats and communication layers.
By establishing a "business layer" through communication with pre-defined terminology between forecast users and forecast providers the "technical or logical layer" of data transfer and product definitions are easier and reduce misunderstandings, mismatches and decision making.
Other benefits are the comparability of products for the end-user and clear guidelines for newcomers as to at which level, or "standard" one's quality of service needs to be.
There are many different ways of developing a standard or a industry guideline. Our suggestion follows a 2 tier pathway: Level (1) defines the logical layer terminology and grouping information into logical entities and relevant parameters. Level (2) defines the data transfer protocols with exact description of parameter names, detailed meta data description, supported formats etc.
In this part of the workshop we want to discuss organisation and development of these levels and see
k for input from the participants. Forecast providers as well as forecast users are invited to join the work and dicuss how and what to:
▪ Review in relation to existing and related standards
▪ Structure the process for developing, reviewing and releasing a guideline
▪ form a key working group
Since several years there has been a constant effort at international level for the standardization and the validation of different types of wind turbine (WT) dynamic models. The paper focuses on the IEC 61400-27-1 type 4 model, proposing and fully describing two benchmark systems for the assessment of dynamic performance. The first system is a simple setup and it is designed to specifically assess the transient response of the WT controls. The second system is based on the IEEE 9-bus test system, and it is a multi-machine configuration allowing for the inclusion of the typical power system dynamics of synchronous machines and corresponding primary regulators. System configurations, models and parameters are designated with the purpose of interoperability and replicability, aiming to models comparison and validation.
The increase of converter-interfaced generation (CIG) typically related to renewable energy sources is progressively causing a significant change of power systems operation. The curtailment of synchronous generation with the consequent reduction of the overall kinetic energy is one of the related issues, currently under investigation in academia and industry. The work considers the problem of overall inertia reduction from a large-scale point of view, analyzing the impact of different CIG integration levels to the frequency response of the power system of Continental Europe. The kinetic energy is evaluated for each country of the synchronous area, and the system is modified substituting conventional synchronous generation with converter-interfaced generation. The models of power converters and corresponding controls follow typical representation for stability studies: they are modeled as controlled current sources with active and reactive power control loops, implemented as user-written equations within the overall mathematical model of Continental Europe power system. Comprehensive time-domain simulations are performed for each scenario, assuming the system subjected to a power plant outage: the obtained frequencies for Western, Central and Eastern Europe are reported, and typical frequency metrics are used to evaluate the response of the system across the different scenarios. Results show how the penetration of CIG affects the frequency response of the system, in terms of instantaneous frequency deviation and maximum frequency rate. A significant change in the inter-area oscillations is also observed, with a progressive increase of the oscillation frequency of the East-West mode, as confirmed by the modal analysis of the system.
The existing power network of a Mediterranean island is used as test bed for the study of grid-forming converter dynamics in weak grid conditions. The control scheme adopted for the converter falls in the category of the so called virtual synchronous machines (VSM). Particular attention is committed to the interaction between the converter controls and the synchronous machines dynamics. Time delays typically associated to measurements and filters are considered in the study, and included in the system model with a specific mathematical approach. Time-domain simulations show the occurrence of oscillatory instability in the system, with VSM and synchronous machines swinging against each other and progressively diverging. Comprehensive modal analysis is performed for a deeper grasp of the system dynamics: the reasons of the instability are identified as the lack of damping in the system and the swinging interaction between grid-forming converter and synchronous machines. The opportunity of different corrective actions is analyzed and discussed, recognizing PSS-like control and active power phase compensation as the most suitable methods for the stabilization of the system.