Advanced wind farm control strategies for enhancing grid support

Nowadays, there is rising concern among Transmission System Operators about the declining of system inertia due to the increasing penetration of wind energy, and other renewable energy systems, and the retirements of conventional power plants. On the other hand, by properly operating wind farms, wind generation may be capable of enhancing grid stability and ensuring continued security of power supply. In this doctoral thesis, new control approaches for designing wind farm optimization-based control strategies are proposed to improve the participation of wind farms in grid support, specially in primary frequency support.Hoy en día, existe una significativa preocupación entre los Operadores de Sistemas de Transmisión sobre la cresciente penetración de le energía eólica y la tendiente eliminación de las centrales eléctricas convencionales que implica la disminución de la inercia del sistema eléctrico. Operando adecuadamente los parques eólicos, la generación eólica puede mejorar la estabilidad de la red eléctrica y garantizar la seguridad y un continuo suministro de energía. Esta tesis doctoral propone nuevas estrategias para diseñar controladores basados en optimización dinámica para parques eólicos y mejorar la participación de los parques eólicos en el soporte de la red eléctrica. En primer lugar, esta tesis doctoral presenta los enfoques clásicos para el control de parques y turbinas eólicas y cómo los conceptos de control existentes pueden ser explotados para hacer frente a los nuevos desafíos que se esperan de los parques eólicos. Esta tesis doctoral asigna un interés especial a cómo formular la función objetivo de que la reserva de potencia sea maximizada, para ayudar por el suporte de frequencia, y al mismo tiempo seguir la potencia demandada por la red. Sin embargo, el impacto de la estela de viento generada por una turbina sobre otras turbinas necesita ser minimizado para mejorar la reserva de potencia. Por lo tanto, a lo largo de esta tesis se proponen estrategias de control centralizado para parques eólicos enfocadas en distribuir óptimamente la energía entre las turbinas para que el impacto negativo de la estela en la reserva de potencia total se reduzca. Se discuten dos técnicas de control para proporcionar los objetivos de control mencionados anteriormente. Un algoritmo de control óptimo para encontrar la mejor distribución de potencia entre las turbinas en el parque mientras se resuelve un problema iterativo de programación lineal. En segundo lugar, se utiliza la técnica de control predictivo basada en modelo para resolver un problema de control multi-objetivo que también podría incluir, junto con la maximización de reserva de potencia, otros objetivos de control, tales como la minimización de las perdidas eléctricas en los cables de la red de interconexión entre turbinas y un controlador/supervisor. Además, la investigación realizada resalta la capacidad de las estrategias de control propuestas en esta tesis para proporcionar mayor reserva de potencia respecto a los conceptos comúnmente usados para distribuir la potencia total del parque eólico. La idea principal detrás del diseño de una estrategia de control de parques eólico es de encontrar una solución óptima dentro de un cálculo computacional relativamente bajo. Aunque los controladores centralizados propuestos en esta tesis reaccionan rápidamente a los cambios en la potencia de referencia enviada desde el controlador, algunos problemas pueden ocurrir cuando se consideran parques eólicos de gran escala debido a los retrasos existentes por el viento entre turbinas. Bajo estas circunstancias, la producción de energía de cada turbina está altamente acoplada con la propagación de la estela y, por ende, con las condiciones de funcionamiento de las otras turbinas. Esta tesis doctoral propone un esquema de control de parques eólicos no centralizados basado en una estrategia de partición para dividir el parque eólico en sub-conjuntos independientes de turbinas. Con la estrategia de control propuesta, el tiempo de cálculo se reduce adecuadamente en comparación con la estrategia de control centralizado mientras que el rendimiento en la distribución óptima de potencia es ligeramente afectado. El rendimiento de todas las estrategias de control propuestas en esta tesis se prueba con un simulador de parque eólico que modela el comportamiento dinámico del efecto de estela mediante el uso de un conocido y consolidado modelo dinámico de estela y, para un análisis más realista, algunas simulaciones se realizan con software avanzado basado en la técnica de Large Eddy Simulation

Multiple adaptive model predictive controllers for frequency regulation in wind farms

Frequent and inadequate power regulation could significantly impact the main shaft mechanical load and the fatigue of wind turbines, which imposes a stringent requirement to perform frequency regulation. However, the existing work on frequency regulation mainly uses torque compensation to improve the frequency response, while few of them consider the mechanical fatigue of the main shaft caused by torque compensation of the frequency controller. In this paper, the mechanical fatigue of the main shaft can be mitigated in all of the speed sections thanks to the proposed frequency regulation controllers. Precisely, a multiple adaptive model predictive controller (MAMPC), which seamlessly integrates the multiple model predictive control (MMPC) and the real-time AutoRegressive with eXogenous inputs (ARX) model, is proposed. It nicely handles the rate of change in compensation torque to mitigate the mechanical load on the shaft in all of the speed sections. The effectiveness of our method is verified through extensive simulations. With the proposed method, the minimum frequency deviation can be reduced, and the number of fatigue cycles of the main shaft can be extended

Advanced wind farm control strategies for enhancing grid support

Aplicat embargament des de la data de defensa fins al maig 2020Nowadays, there is rising concern among Transmission System Operators about the declining of system inertia due to the increasing penetration of wind energy, and other renewable energy systems, and the retirements of conventional power plants. On the other hand, by properly operating wind farms, wind generation may be capable of enhancing grid stability and ensuring continued security of power supply. In this doctoral thesis, new control approaches for designing wind farm optimization-based control strategies are proposed to improve the participation of wind farms in grid support, specially in primary frequency support.Hoy en día, existe una significativa preocupación entre los Operadores de Sistemas de Transmisión sobre la cresciente penetración de le energía eólica y la tendiente eliminación de las centrales eléctricas convencionales que implica la disminución de la inercia del sistema eléctrico. Operando adecuadamente los parques eólicos, la generación eólica puede mejorar la estabilidad de la red eléctrica y garantizar la seguridad y un continuo suministro de energía. Esta tesis doctoral propone nuevas estrategias para diseñar controladores basados en optimización dinámica para parques eólicos y mejorar la participación de los parques eólicos en el soporte de la red eléctrica. En primer lugar, esta tesis doctoral presenta los enfoques clásicos para el control de parques y turbinas eólicas y cómo los conceptos de control existentes pueden ser explotados para hacer frente a los nuevos desafíos que se esperan de los parques eólicos. Esta tesis doctoral asigna un interés especial a cómo formular la función objetivo de que la reserva de potencia sea maximizada, para ayudar por el suporte de frequencia, y al mismo tiempo seguir la potencia demandada por la red. Sin embargo, el impacto de la estela de viento generada por una turbina sobre otras turbinas necesita ser minimizado para mejorar la reserva de potencia. Por lo tanto, a lo largo de esta tesis se proponen estrategias de control centralizado para parques eólicos enfocadas en distribuir óptimamente la energía entre las turbinas para que el impacto negativo de la estela en la reserva de potencia total se reduzca. Se discuten dos técnicas de control para proporcionar los objetivos de control mencionados anteriormente. Un algoritmo de control óptimo para encontrar la mejor distribución de potencia entre las turbinas en el parque mientras se resuelve un problema iterativo de programación lineal. En segundo lugar, se utiliza la técnica de control predictivo basada en modelo para resolver un problema de control multi-objetivo que también podría incluir, junto con la maximización de reserva de potencia, otros objetivos de control, tales como la minimización de las perdidas eléctricas en los cables de la red de interconexión entre turbinas y un controlador/supervisor. Además, la investigación realizada resalta la capacidad de las estrategias de control propuestas en esta tesis para proporcionar mayor reserva de potencia respecto a los conceptos comúnmente usados para distribuir la potencia total del parque eólico. La idea principal detrás del diseño de una estrategia de control de parques eólico es de encontrar una solución óptima dentro de un cálculo computacional relativamente bajo. Aunque los controladores centralizados propuestos en esta tesis reaccionan rápidamente a los cambios en la potencia de referencia enviada desde el controlador, algunos problemas pueden ocurrir cuando se consideran parques eólicos de gran escala debido a los retrasos existentes por el viento entre turbinas. Bajo estas circunstancias, la producción de energía de cada turbina está altamente acoplada con la propagación de la estela y, por ende, con las condiciones de funcionamiento de las otras turbinas. Esta tesis doctoral propone un esquema de control de parques eólicos no centralizados basado en una estrategia de partición para dividir el parque eólico en sub-conjuntos independientes de turbinas. Con la estrategia de control propuesta, el tiempo de cálculo se reduce adecuadamente en comparación con la estrategia de control centralizado mientras que el rendimiento en la distribución óptima de potencia es ligeramente afectado. El rendimiento de todas las estrategias de control propuestas en esta tesis se prueba con un simulador de parque eólico que modela el comportamiento dinámico del efecto de estela mediante el uso de un conocido y consolidado modelo dinámico de estela y, para un análisis más realista, algunas simulaciones se realizan con software avanzado basado en la técnica de Large Eddy Simulation.Postprint (published version

Enhanced active power control of photovotaic systems

The share of electrical power generation from renewable energy sources is increasing and is expected to keep on increasing as various countries intensify their efforts to reduce CO2 emissions. Differences in the nature and characteristics of some renewable generation affect the ability of power systems to maintain frequency stability. This is because some renewable generation sources do not have inertia or are converter connected and decoupled from grid frequency. Solar Photovoltaic system do not have any stored inertia and usually operate at maximum power. There is need for control method for solar PV systems to contribute to frequency stability. This thesis proposes operation methodologies for photovoltaic (PV) systems to carry out active power control functions - including frequency control and proposes a framework for comparing frequency support ability of different generation sources. First, a modification to the conventional Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm is proposed to avoid leftward and rightward from maximum power. Results presented show that PV systems employing P&O with the proposed modification avoid both leftward and rightward drift when subjected to rapidly increasing irradiance, sinusoidal irradiance, and real irradiance. This drift-free P&O enables the PV system to participate in active power control function at rapidly increasing irradiance. An offline MPPT that uses the characteristics of PV modules to determine the maximum power point offline and reduce online computation is proposed for frequency support. Two methods for achieving de-loaded operation of a PV system using the offline MPPT are presented and compared for accuracy. The ability of offline MPPT and the P&O with proposed modification to maintain a power reserve under different irradiance conditions are compared. Second, this thesis examines the ability of a PV system to contribute to frequency support. Different methods for frequency support from a PV power plant under different penetration levels are examined. Results show with the appropriate amount of reserve and support parameters, PV systems can contribute to frequency support. The results also show that PV power plants with the proper support parameters can adequately compensate for the loss of inertia with regards to its effect on the nadir of frequency response. A variable droop control method for frequency support is proposed to reduce the amount of reserve required for frequency support. The effect of MPPT choice on frequency support is evaluated by comparing responses from PV systems with the offline MPPT, P&O with proposed modification, and the constant voltage MPPT. Lastly, this thesis proposes a framework for comparing the frequency support ability of different generating units based on their response speed and support parameters. Different response speeds are emulated by changing one the time constant of a Second-order system. The effect of response speed, support method, and support parameters on the nadir of frequency response and maximum power increase are evaluated for different response speeds. A method for comparing support ability by considering the economic cost and benefit for support is also presented.The share of electrical power generation from renewable energy sources is increasing and is expected to keep on increasing as various countries intensify their efforts to reduce CO2 emissions. Differences in the nature and characteristics of some renewable generation affect the ability of power systems to maintain frequency stability. This is because some renewable generation sources do not have inertia or are converter connected and decoupled from grid frequency. Solar Photovoltaic system do not have any stored inertia and usually operate at maximum power. There is need for control method for solar PV systems to contribute to frequency stability. This thesis proposes operation methodologies for photovoltaic (PV) systems to carry out active power control functions - including frequency control and proposes a framework for comparing frequency support ability of different generation sources. First, a modification to the conventional Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm is proposed to avoid leftward and rightward from maximum power. Results presented show that PV systems employing P&O with the proposed modification avoid both leftward and rightward drift when subjected to rapidly increasing irradiance, sinusoidal irradiance, and real irradiance. This drift-free P&O enables the PV system to participate in active power control function at rapidly increasing irradiance. An offline MPPT that uses the characteristics of PV modules to determine the maximum power point offline and reduce online computation is proposed for frequency support. Two methods for achieving de-loaded operation of a PV system using the offline MPPT are presented and compared for accuracy. The ability of offline MPPT and the P&O with proposed modification to maintain a power reserve under different irradiance conditions are compared. Second, this thesis examines the ability of a PV system to contribute to frequency support. Different methods for frequency support from a PV power plant under different penetration levels are examined. Results show with the appropriate amount of reserve and support parameters, PV systems can contribute to frequency support. The results also show that PV power plants with the proper support parameters can adequately compensate for the loss of inertia with regards to its effect on the nadir of frequency response. A variable droop control method for frequency support is proposed to reduce the amount of reserve required for frequency support. The effect of MPPT choice on frequency support is evaluated by comparing responses from PV systems with the offline MPPT, P&O with proposed modification, and the constant voltage MPPT. Lastly, this thesis proposes a framework for comparing the frequency support ability of different generating units based on their response speed and support parameters. Different response speeds are emulated by changing one the time constant of a Second-order system. The effect of response speed, support method, and support parameters on the nadir of frequency response and maximum power increase are evaluated for different response speeds. A method for comparing support ability by considering the economic cost and benefit for support is also presented

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

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