Adaptive variable structure control law for a variable speed wind turbine

Presentado en el 13th WSEAS International Conference on Automatic Control, Modelling and Simulation, ACMOS'11The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, an adaptive robust control for a doubly feed induction generator drive for variable speed wind power generation is described. In the presented design it is applied the so called vector control theory. The control scheme uses stator flux-oriented control for the rotor side converter bridge control and grid voltage vector control for the grid side converter bridge control. The proposed robust control law is based on a sliding mode control theory, that presents a good performance under system uncertainties. The stability analysis of the proposed controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally simulated results show, on the one hand that the proposed controller provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to plant parameter variations and external disturbances

A Real-Time Sliding Mode Control for a Wind Energy System Based on a Doubly Fed Induction Generator

In this paper, a real time sliding mode control scheme for a variable speed wind turbine that incorporates a doubly feed induction generator is described. In this design, the so-called vector control theory is applied, in order to simplify the system electrical equations. The proposed control scheme involves a low computational cost and therefore can be implemented in real-time applications using a low cost Digital Signal Processor (DSP). The stability analysis of the proposed sliding mode controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. A new experimental platform has been designed and constructed in order to analyze the real-time performance of the proposed controller in a real system. Finally, the experimental validation carried out in the experimental platform shows; on the one hand that the proposed controller provides high-performance dynamic characteristics, and on the other hand that this scheme is robust with respect to the uncertainties that usually appear in the real systems.The authors are very grateful to the Basque Government by the support of this work through the project S-PE12UN015 and S-PE13UN039 and to the UPV/EHU by its support through the projects GIU13/41 and UFI11/07

Sliding mode control law for a variable speedwind turbine

Modern wind turbines are designed in order to work in variable speed operations. To perform this task, wind turbines are provided with adjustable speed generators, like the double feed induction generator. One of the main advantage of adjustable speed generators is improving the system efficiency compared to fixed speed generators, because turbine speed can be adjusted as a function of wind speed in order to maximize the output power. However this system requires a suitable speed controller in order to track the optimal reference speed of the wind turbine. In this work, a sliding mode control for variable speed wind turbines is proposed. An integral sliding surface is used, because the integral term avoids the use of the acceleration signal, which reduces the high frequency components in the sliding variable. The proposed design also uses the vector oriented control theory in order to simplify the generator dynamical equations. The stability analysis of the proposed controller has been carried out under wind variations and parameter uncertainties by using the Lyapunov stability theory. Finally simulated results show, on the one hand that the proposed controller provides a high-performance dynamic behavior, and on the other hand that this scheme is robust with respect to parameter uncertainties and wind speed variations, that usually appear in real systems

Model Predictive Control for Enhancing Wind Farms Participation in Ancillary Services

The increasing penetration of Renewable Energy (RE) systems into the electric grid is creating new challenges into the power system. The unpredictable and variable nature of renewable power generation is increasing the imbalances between generation and demand. For this reason, wind farms, which are the main source of RE in Europe, are required nowadays to support the grid, providing services of voltage and frequency regulation. To be able to increase their power production during a frequency event, Wind Power Plants (WPPs) need to work below their maximum generation capacity, keeping an additional amount of power, called power reserve, that can be injected into the grid when required. The power reserve of a wind farm strongly depends on the interaction among the wind turbines. The wake effect produced by the upstreams turbines affects the wind condition that each turbine faces and reduces their maximum available power. This study aims to present the effects of different distribution of the Wind turbines (WTs) individual power contribution on the power reserve. Three control strategies, based on Model Predictive Control (MPC), are tested on a fifteen turbines wind farm under different wind conditions. Simulation results show that, in almost all cases, prioritizing the power contribution of the most downstream turbines and deloading the upstream ones, leads to a maximization of the wind farm power reserve. Furthermore, an additional MPC strategy aiming to combine active and reactive power control, for providing both frequency and voltage regulation at the Point of Common Coupling (PCC), is presented. The advantage of a combined active and reactive power control is the possibility of improve the voltage support capability of the WPPs, by controlling the active power set-points. The MPC is also tested on a fifteen turbines wind farm, in order to validate the performances of the controller while solving the multi-objective problem. The ability of the controller to handle simultaneously the different requirements is proven

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

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

Real time observer and control scheme for a wind turbine system based on a high order sliding modes

The introduction of advanced control algorithms may improve considerably the efficiency of wind turbine systems. This work proposes a high order sliding mode (HOSM) control scheme based on the super twisting algorithm for regulating the wind turbine speed in order to obtain the maximum power from the wind. A robust aerodynamic torque observer, also based on the super twisting algorithm, is included in the control scheme in order to avoid the use of wind speed sensors. The presented robust control scheme ensures good performance under system uncertainties avoiding the chattering problem, which may appear in traditional sliding mode control schemes. The stability analysis of the proposed HOSM observer is provided by means of the Lyapunov stability theory. Experimental results show that the proposed control scheme, based on HOSM controller and observer, provides good performance and that this scheme is robust with respect to system uncertainties and external disturbances.The authors are very grateful to the Basque Government by its support through the project EKOHEGAZ (ELKARTEK KK-2021/00092), to the Diputacion Foral de Alava (DFA) by its support through the project CONAVANTER, to Gipuzkoako Foru Aldundia by its support through the project Etorkizuna Eraikiz 2019, and to the UPV/EHU by its support through the project GIU20/063

Improved Wind Turbine Control Strategies for Maximizing Power Output and Minimizing Power Flicker

For reducing the cost of energy (COE) for wind power, controls techniques are important for enhancing energy yield, reducing structural load and improving power quality. This thesis presents the control strategies studies for wind turbine both from the perspectives of both maximizing power output and reducing power flicker and structural load, First, a self-optimizing robust control scheme is developed with the objective of maximizing the power output of a variable speed wind turbine with doubly-fed induction generator (DFIG) operated in Region 2. Wind power generation can be divided into two stages: conversion from aerodynamic power to rotor (mechanical) power and conversion from rotor power to the electrical (grid) power. In this work, the maximization of power generation is achieved by a two-loop control structure in which the power control for each stage has intrinsic synergy. The outer loop is an Extremum Seeking Control (ESC) based generator torque regulation via the rotor power feedback. The ESC can search for the optimal torque constant to maximize the rotor power without wind measurement or accurate knowledge of power map. The inner loop is a vector-control based scheme that can both regulate the generator torque requested by the ESC and also maximize the conversion from the rotor power to grid power. In particular, an ∞ controller is synthesized for maximizing, with performance specifications defined based upon the spectrum of the rotor power obtained by the ESC. Also, the controller is designed to be robust against the variations of some generator parameters. The proposed control strategy is validated via simulation study based on the synergy of several software packages including the TurbSim and FAST developed by NREL, Simulink and SimPowerSystems. Then, a bumpless transfer scheme is proposed for inter-region controller switching scheme in order to reduce the power fluctuation and structural load under fluctuating wind conditions. This study considers the division of Region 2, Region 2.5 and Region 3 in the neighborhood of the rated wind speed. When wind, varies around the rated wind speed, the switching of control can lead to significant fluctuation in power and voltage supply, as well as structural loading. To smooth the switch and improve the tracking, two different bumpless transfer methods, Conditioning and Linear Quadratic techniques, are employed for different inter-region switching situations. The conditioning bumpless transfer approach adopted for switching between Region 2 maximum power capture controls to Region 2.5 rotor speed regulation via generator torque. For the switch between Region 2.5 and Region 3, the generator torque windup at rated value and pitch controller become online to limit the load of wind turbine. LQ technique is posed to reduce the discontinuity at the switch between torque controller and pitch controller by using an extra compensator. The flicker emission of the turbine during the switching is calculated to evaluate power fluctuation. The simulation results demonstrated the effectiveness of the proposed scheme of inter-region switching, with significant reduction of power flicker as well as the damage equivalent load

Variable structure control for maximum wind power extraction

EuroPES 2009The actual wind turbines are provided with adjustable speed generators.Iike the double feed induction generator, that are capable to work in variable speed operations. One of the main advantage of adjustable speed generators is that they improve the system efficiency compared to fixed speed generators because twbine speed is adjusted as a function of wind speed to maximize output power. However this systems requires a suitable speed controller in order to track the optimal wind turbine speed reference. In this work, it is proposed a sliding mode control for variable speed wind turbines. The robustness analysis of the proposed controller under disturbances and pararneter uncertainties is provided using the Lyapunov stability theory and simulated results show that the proposed controller provides a good performance