Provision of Frequency Response from Wind Farms: A Review

Renewable sources of energy play a key role in the process of decarbonizing modern electric power systems. However, some renewable sources of energy operate in an intermittent, non-dispatchable way, which may affect the balance of the electrical grid. In this scenario, wind turbine generators must participate in the system frequency control to avoid jeopardizing the transmission and distribution systems. For that reason, additional control strategies are needed to ensure the frequency response of variable-speed wind turbines. This review article analyzes diverse control strategies at different levels which are aimed at contributing to power balancing and system frequency control, including energy storage systems.This research was funded by the Basque Government, through the project EKOHEGAZ (ELKARTEK KK-2021/00092), Diputación Foral de Álava (DFA) through the project CONAVANTER, and UPV/EHU through the project GIU20/063

New contributions to frequency control based on virtual synchronous generators: application to power systems with high renewable energy sources integration

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. Tradicionalmente, servicios como la regulación y mantenimiento de la frecuencia de los sistemas eléctricos, cobertura de la demanda eléctrica o la existencia de las reservas rodantes (spinning reserves) han sido suministrados y asegurados por las fuentes de generación de energía eléctrica tradicionales. Sin embargo, los sistemas eléctricos han sufrido una serie de cambios en los últimos años que están afectando de manera directa al propio funcionamiento de los mismos. Por un lado, el aumento constante del consumo de energía y de la intensidad del propio uso energético, unido al aumento de las restricciones legislativas medioambientales, y por otro el concepto de la energía eléctrica como un producto comercial junto con la liberalización de los mercados energéticos, hacen que se tambaleen algunas de las premisas hasta ahora asumidas. En este sentido, y en un entorno de promoción de recursos renovables, hace que los servicios hasta ahora proporcionados sólo por la generación clásica deben también ser compartidos por todos los puntos de generación. No obstante, la alta penetración de este tipo de fuentes renovables en el sector eléctrico acarrea una seria de cuestiones derivadas de sus características y peculiaridades que es necesario abordar antes de proceder de manera masiva a su integración y, por tanto, a la independencia de la generación convencional. Adicionalmente, y debido a la naturaleza variable de la generación renovable (principalmente el viento y el sol) recobra mayor importancia el asegurar por parte de los organismos reguladores una reserva energética que permita actuar de manera eficiente y fiel en casos de desequilibrio de potencias. En este nuevo escenario, en el que el director de tesis ha trabajado a lo largo de la última década, se hace necesario contar con el desarrollo y adaptación de nuevas herramientas y soluciones que faciliten la integración de fuentes renovables sin que ello suponga una merma en las capacidades del sistema eléctrico en términos de estabilidad y de respuesta ante contingencias. Así pues, el objetivo principal de esta tesis consiste en el estudio, implementación y evaluación de sistemas eléctricos con alta penetración de recurso eólico y fotovoltaico con el fin de evaluar posibles soluciones para emular inercias virtuales y respuestas similares a las que se obtendrían con generación clásica, integrando así de manera efectiva el recurso renovable al control de la frecuencia del sistema eléctrico. En este escenario, resultaría crucial poder aliviar en parte las necesidades de almacenamiento de energía a los puntos de generación mediante la implementación de estrategias alternativas de control de respuesta ante excursiones de frecuencia en las unidades renovables, aportando éstas el apoyo necesario para mantener la frecuencia de red dentro de los límites establecidos. Por tanto, la solución aquí estudiada favorecería la integración masiva de recursos renovables, dentro de un escenario de estabilidad del sistema eléctrico apoyado por estas instalaciones, y donde la eliminación paulatina de elementos rotativos directamente conectados a la red debe sustituirse y/o emularse de manera que el sistema eléctrico ofrezca la misma fiabilidad que se percibe ante la presencia de generación convencional. Sólo así se conseguirá fomentar de manera argumentada las posibilidades tangibles de integración a gran escala de recursos renovables, adelantándonos a las necesidades que surgirán de manera inevitable como consecuencia de la disminución inicial de inercia del sistema (entendida de una manera clásica como elementos rotativos directamente conectados a red) y como consecuencia de la entrada de fuentes que poseen una variabilidad en sus niveles de generación. Destacar igualmente la importancia cada vez mayor del control de la frecuencia del sistema eléctrico, debido a la sensibilidad y dependencia que poseen de este parámetro la mayoría de las cargas y equipos con algún tipo de etapa de electrónica de potencia.[ENG] This doctoral dissertation has been presented in the form of thesis by publication. Over the last decades, most countries have been suffering an electrical energy transition, changing from a model based on non-renewable sources (mainly based on fossil fuels), to a new framework characterised by the integration of renewable energy resources (RES). These important changes have been mainly supported by the development of power electronics, environmental protection policies, and the need to reduce energy dependence on third countries. Moreover, the electrical sector stands out because of the diversity and heterogeneity of sources that can generate electricity. As a result, the current electrical scenario includes a high interest in the integration of variable renewable energy sources (vRES) shifting towards a new generation mix. In fact, these vRES (mainly photovoltaic and wind power installations) already play a relevant role, as some European countries have experienced generation levels over 50% during some time-periods of last years. As aforementioned, the two most mature renewable resources integrated into power systems are solar photovoltaic (PV) and wind power (especially variable speed wind turbines, VSWTs). Together with the integration of these two sources, and in contrast to traditional grids based on conventional power plants (i.e., hydro-power, thermal, and nuclear power plants), several important issues have emerged, needing to be analysed, assessed, and resolved.Los artículos que constituyen la tesis son los siguientes: 1. Fernández-Guillamón, Ana & Gómez-Lázaro, Emilio & Muljadi, Eduard & Molina-García, Ángel, 2019. "Power systems with high renewable energy sources: A review of inertia and frequency control strategies over time," Renewable and Sustainable Energy Reviews, Elsevier, vol. 115(C). 2. Ana Fernández-Guillamón & Jorge Villena-Lapaz & Antonio Vigueras-Rodríguez & Tania García-Sánchez & Ángel Molina-García, 2018. "An Adaptive Frequency Strategy for Variable Speed Wind Turbines: Application to High Wind Integration Into Power Systems,"Energies, MDPI, Open Access Journal, vol. 11(6), pages 1-21, June. 3. Fernández-Guillamón, A.; Vigueras-Rodríguez, A.; Gómez-Lázaro, E.; Molina-García, Á. Fast Power Reserve Emulation Strategy for VSWT Supporting Frequency Control in Multi-Area Power Systems. Energies 2018, 11, 2775. https://doi.org/10.3390/en11102775. 4. Fernández-Guillamón, Ana & Sarasúa, José & Chazarra, Manuel & Vigueras-Rodríguez, Antonio & Fernández-Muñoz, Daniel & Molina-Garcia, Ángel. (2020). Frequency control analysis based on unit commitment schemes with high wind power integration: A Spanish isolated power system case study. International Journal of Electrical Power & Energy Systems. 121. 106044. 10.1016/j.ijepes.2020.106044. 5. Fernández‐Guillamón, A., Vigueras‐Rodríguez, A. and Molina‐García, Á. (2019), Analysis of power system inertia estimation in high wind power plant integration scenarios. IET Renewable Power Generation, 13: 2807-2816. https://doi.org/10.1049/iet-rpg.2019.0220. 6. Fernández Guillamón, Ana; Martínez de Lucas, Guillermo; Molina García, Ángel y Sarasúa Moreno, José Ignacio (2020). An Adaptive Control Scheme for Variable Speed Wind Turbines Providing Frequency Regulation in Isolated Power Systems with Thermal Generation."Energies", v. 13 (n. 13); p. 3369. ISSN 1996-1073. https://doi.org/10.3390/en13133369. 7. Fernández-Guillamón, A.; Martínez-Lucas, G.; Molina-García, Á.; Sarasua, J.-I. Hybrid Wind–PV Frequency Control Strategy under Variable Weather Conditions in Isolated Power Systems. Sustainability 2020, 12, 7750. https://doi.org/10.3390/su12187750. 8. Fernández-Guillamón, Ana & Gomez-Lazaro, Emilio & Molina-Garcia, Ángel. (2020). Extensive frequency response and inertia analysis under high renewable energy source integration scenarios: application to the European interconnected power system.Escuela Internacional de Doctorado de la Universidad Politécnica de CartagenaUniversidad Politécnica de CartagenaPrograma de Doctorado en Energías Renovables y Eficiencia Energétic

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Advances in Modelling and Control of Wind and Hydrogenerators

Rapid deployment of wind and solar energy generation is going to result in a series of new problems with regards to the reliability of our electrical grid in terms of outages, cost, and life-time, forcing us to promptly deal with the challenging restructuring of our energy systems. Increased penetration of fluctuating renewable energy resources is a challenge for the electrical grid. Proposing solutions to deal with this problem also impacts the functionality of large generators. The power electronic generator interactions, multi-domain modelling, and reliable monitoring systems are examples of new challenges in this field. This book presents some new modelling methods and technologies for renewable energy generators including wind, ocean, and hydropower systems

Virtual Inertia: Current Trends and Future Directions

The modern power system is progressing from a synchronous machine-based system towards an inverter-dominated system, with large-scale penetration of renewable energy sources (RESs) like wind and photovoltaics. RES units today represent a major share of the generation, and the traditional approach of integrating them as grid following units can lead to frequency instability. Many researchers have pointed towards using inverters with virtual inertia control algorithms so that they appear as synchronous generators to the grid, maintaining and enhancing system stability. This paper presents a literature review of the current state-of-the-art of virtual inertia implementation techniques, and explores potential research directions and challenges. The major virtual inertia topologies are compared and classified. Through literature review and simulations of some selected topologies it has been shown that similar inertial response can be achieved by relating the parameters of these topologies through time constants and inertia constants, although the exact frequency dynamics may vary slightly. The suitability of a topology depends on system control architecture and desired level of detail in replication of the dynamics of synchronous generators. A discussion on the challenges and research directions points out several research needs, especially for systems level integration of virtual inertia systems

Virtual Synchronous Generator Operation of Full Converter Wind Turbine ‒ Control and Testing in a Hardware Based Emulation Platform

Wind is one of the most promising renewable energy forms that can be harvested to into the electrical power system. The installation has been rising worldwide in the past and will continue to steadily increase. The high penetration of wind energy has bought about a number of difficulties to the power system operation due to its stochastic nature, lack of exhibited inertia, and differing responses to the traditional energy sources in grid disturbances. Various grid support functions are then proposed to resolve the issues. One solution is to allow the renewable energy sources to behave like a traditional synchronous generator in the system, as a virtual synchronous generator (VSG). On the other hand, testing the control of the future power grid with high penetration renewable often relies on digital simulation or hardware-based experiments. But they either suffer from fidelity and numerical stability issues, or are bulky and inflexible. A power electronics based power system emulation platform is built in the University of Tennessee. This Hardware Testbed (HTB) allows testing of both system level and component level controls, with a good balance between the fidelity of the hardware-based testing platform, and the coverage of the digital simulation.This dissertation proposal investigates the VSG operation of the full converter wind turbine (FCWT), focusing on its control and testing in the HTB. Specifically, a FCWT emulator was developed using a single converter to include its physical model and control strategies. The existing grid support functions are also included to demonstrate their feasibility.The comprehensive VSG controls are then proposed for a FCWT with short term energy storage. The dynamic response of the FCWT can be comparable to the traditional generation during grid disturbance. The control can also allow the FCWT to be dispatched by the system operator, and even operate stand-alone without other grid sources.To study the system response under faults, a short circuit fault emulator was developed in the HTB platform. Four basic types of the short circuit faults with various fault impedance can be emulated using the emulator. The power system transient stability in terms of critical clearing time can be measured using the developed fault emulator