Publication: Control directo de potencia de convertidores electrónicos conectados a la red
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2007-07
Defense date
2007-07-17
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Abstract
Los convertidores electrónicos de potencia se han consolidado como un elemento fundamental
en los sistemas eléctricos, ya que hacen posible una transmisión más flexible de la
potencia por el sistema eléctrico y pueden actuar como compensadores. El constante incremento
del número de plantas de generación a partir de fuentes renovables de energía, principalmente
eólica y solar fotovoltaica, que requieren convertidores electrónicos para evacuar
a la red la potencia generada, ha propiciado un creciente interés en sus técnicas de control.
Para que su funcionamiento sea óptimo, es necesario diseñar sistemas de control robustos
y con una respuesta dinámica muy rápida. El Control Directo de Potencia se presenta como
una técnica de control muy adecuada para cumplir estos requisitos, ya que las variables
de control son directamente las potencias intercambiadas. Además, el continuo incremento
de la potencia unitaria de los sistemas de generación ha dado lugar a la aparición de los
convertidores multinivel como la solución idónea para su conexión a redes de tensiones
mayores, como la red de distribución o la red de transmisión.
El objetivo principal de esta tesis es desarrollar una nueva estrategia de Control Directo
de Potencia para convertidores multinivel. Esta nueva estrategia supone un cambio respecto
a métodos anteriores de control directo, ya que no se basa en tablas de diseño para la
obtención de los vectores de tensión del convertidor, sino en criterios de decisión a partir
de consideraciones geométricas. Además, el nuevo método integra el control de la tensión
en los puntos intermedios del enlace de continua, evitándose así la inclusión de reguladores
adicionales. La implementación en tiempo real de este control en un banco de ensayos en el
laboratorio confirma la validez del método.
Por otro lado, el incremento de la potencia generada a partir de fuentes renovables ha
provocado la aparición de nuevas normativas más estrictas para la conexión a la red, ya que
una pérdida repentina de esas cantidades de potencia podría inestabilizar el sistema. En
relación a esto, en esta tesis se propone una modificación del Control Directo de Potencia
para poder inyectar intensidades sinusoidales ante desequilibrios en la red. Nuevamente, el
método se valida experimentalmente en tiempo real en el banco de ensayos del laboratorio.
Con los resultados obtenidos se ha conseguido dar mayor versatilidad al Control Directo
de Potencia, que se puede aplicar a convertidores multinivel sin necesidad de diseñar
nuevas tablas y que puede inyectar intensidades sinusoidales durante un desequilibrio en las
tensiones de la red.
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Power electronic converters have become a fundamental component in modern utilities. The increasing number of renewable energy generation plants, mainly wind farms and solar photovoltaic power plants, which must be connected to the grid through converters, has caused great interest in their control methods. Besides, power converters make a more flexible power transmission possible and can act as compensators. In order to get an optimal performance, very fast and robust control methods must be designed. Direct Power Control appears to be very adequate to fulfil these requirements, as active and reactive powers are their control variables. Moreover, the increasing amount of power from renewable sources has yielded multilevel converters as a solution for connecting to higher voltage grids, such as distribution or transmission. The main objective of this thesis is to develop a new strategy of Direct Power Control for multilevel converters. This new strategy is no longer based on tables and sector division, but on decision criteria based on geometrical considerations. Besides, this new method includes middle point voltage control, avoiding the use of more controllers. Real-time implementation in a laboratory set-up has validated the proposed control. Likewise, due to the increasing amount of power from renewable sources, new grid codes have appeared, so that a sudden loss of power caused by a transient fault would not make the system unstable. Regarding this, a new Direct Power Control strategy under unbalanced grid voltages has been proposed. The aim is to inject sinusoidal currents in an unbalanced grid. Again, real-time implementation has validated the proposed control method. With theses results, a more versatile Direct Power Control method has been achieved, being applicable to multilevel converters, as well as under voltage imbalance.
Power electronic converters have become a fundamental component in modern utilities. The increasing number of renewable energy generation plants, mainly wind farms and solar photovoltaic power plants, which must be connected to the grid through converters, has caused great interest in their control methods. Besides, power converters make a more flexible power transmission possible and can act as compensators. In order to get an optimal performance, very fast and robust control methods must be designed. Direct Power Control appears to be very adequate to fulfil these requirements, as active and reactive powers are their control variables. Moreover, the increasing amount of power from renewable sources has yielded multilevel converters as a solution for connecting to higher voltage grids, such as distribution or transmission. The main objective of this thesis is to develop a new strategy of Direct Power Control for multilevel converters. This new strategy is no longer based on tables and sector division, but on decision criteria based on geometrical considerations. Besides, this new method includes middle point voltage control, avoiding the use of more controllers. Real-time implementation in a laboratory set-up has validated the proposed control. Likewise, due to the increasing amount of power from renewable sources, new grid codes have appeared, so that a sudden loss of power caused by a transient fault would not make the system unstable. Regarding this, a new Direct Power Control strategy under unbalanced grid voltages has been proposed. The aim is to inject sinusoidal currents in an unbalanced grid. Again, real-time implementation has validated the proposed control method. With theses results, a more versatile Direct Power Control method has been achieved, being applicable to multilevel converters, as well as under voltage imbalance.
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Keywords
Electrónica de potencia, Convertidores electrónicos, Sistemas eléctricos