Thesis: Soporte de frecuencia para redes de baja inercia
conectadas a estaciones HVDC-MMC
Date
2018
Authors
Carreño Henriquez, Alvaro Andres
Journal Title
Journal ISSN
Volume Title
Publisher
Universidad Técnica Federico Santa María
Abstract
En los sistemas de potencia existe una relación directa entre la potencia activa y la frecuencia de la red. Cuando ocurre un desbalance entre la potencia generada y consumida, se produce una fluctuación de frecuencia, cuya tasa de cambio depende principalmente de la inercia mecánica de las unidades generadoras. Considerando lo anterior, en una red de baja inercia se pueden generar con mayor facilidad desviaciones de frecuencia que pueden activar los mecanismos de seguridad antes de que los sistemas de control de frecuencia actúen, comprometiendo la operación y la calidad del servicio eléctrico prestado a los usuarios. Si estos sistemas son alimentados por estaciones DC de alto voltaje (HVDC), como puede ser el caso de una isla, y la potencia nominal es mayor que la de las unidades generadoras, los sistemas HVDC pueden cumplir un rol fundamental en la regulación de frecuencia.
En este trabajo se desarrolla un sistema HVDC basado en un convertidor modular multinivel (MMC) que permita atenuar las variaciones de frecuencia en una red de baja inercia cuando varíe la potencia consumida. El sistema de control se basa en modificar la referencia de potencia activa que genera o consume la estación HVDC para reducir las perturbaciones de carga en el generador. Adicionalmente, se obtiene un modelo de la red en estado estacionario, calculando la relación entre la potencia activa y reactiva en los terminales de los convertidores para distintos niveles de carga. Esta relación se utiliza para generar un lazo de control que permita a la estación HVDC actuar rápidamente sobre la potencia activa en lugar del generador.
Se obtiene un modelo del MMC adecuado para simulaciones de sistemas de potencia que permita largos tiempos de simulación. Utilizando este modelo se simuló una red con un cambio en la potencia activa consumida y el voltaje de referencia de los capacitores de los submódulos, y se comprobó el adecuado funcionamiento del control propuesto.
Las condiciones de operación de una red compuesta por una unidad generadora y la estación HVDC son analizadas utilizando un modelo simplificado del sistema de potencia. Se extiende el sistema de control considerando la magnitud y el ángulo de la impedancia de una sección adicional de la línea de transmisión que conecta el convertidor al punto de acoplamiento común.
Los resultados obtenidos muestran que el control propuesto permite disminuir las fluctuaciones de frecuencia en aproximadamente un 80% respecto a un controlador genérico cuando se opera bajo condiciones nominales. Cuando el convertidor debe invertir el flujo de potencia debido a un cambio de carga, la calidad de la regulación se ve afectada, disminuyendo las fluctuaciones a un 52%. Una de las desventajas de este método de control es la dependencia de los parámetros actuales de la red en la etapa de diseño. Sin embargo, al realizar un análisis de desempeño, el comportamiento del controlador es superior al de un controlador estándar, incluso cuando los parámetros se conocen con cierta incertidumbre.
In power systems there is a direct relationship between the active power and the grid frequency.When there is an unbalance between the generated and consumed power, a frequencydeviation is produced, whose rate of change mainly depends on the mechanical inertia of thegenerating units. In a low inertia system it is possible to produce frequency deviations that couldactivate the security systems before the frequency controllers act, compromising the operationand the users electrical service. When these systems are supplied by high voltage DC (HVDC)stations, like in an island, and their nominal power is greater than those of the generating units,the HVDC systems can have an important role in the frequency regulation.In this work a control system for a HVDC system is developed based on a modular multilevelconverter (MMC) that allows the attenuation of frequency deviations in a low inertia gridwhen the consumed power varies. The system control is based on modifying the HVDC stationconsumed or generated active power reference to reduce the low disturbances on the generator.To implement this controller, the grid steady state model is obtained, calculating the relationshipbetween the active and reactive power at the converter terminals for several load levels.This relationship is used to design a control loop that allows the HVDC station to rapidly modifythe active power reference in order to compensate the load changes.A MMC model is obtained for power systems simulations that allows long periods simulations.Using this model, a grid was simulated with a change in the consumed active power and thesubmodule capacitor reference voltage. The proposed control method was checked using thismodel.The operating conditions of a grid composed by a generating unit and the HVDC stationare analyzed using a simplified power system model. The control system is extended consideringthe magnitude and angle of the transmission line impedance that connects the converter to thecommon coupling point.The obtained results show that the proposed control diminishes the frequency deviation by80% with respect to a standard controller when it is operating under nominal conditions. Whenthe operating conditions change, especially when the converter must reverse the power flow,the regulation quality is affected, diminishing the deviations to 52%. A disadvantage of thiscontrol method is the dependence on the grid parameters in the design stage. Nonetheless, theperformance analysis shows that the controller behavior is superior with respect to a standardcontroller even when there is parameters uncertainty.
In power systems there is a direct relationship between the active power and the grid frequency.When there is an unbalance between the generated and consumed power, a frequencydeviation is produced, whose rate of change mainly depends on the mechanical inertia of thegenerating units. In a low inertia system it is possible to produce frequency deviations that couldactivate the security systems before the frequency controllers act, compromising the operationand the users electrical service. When these systems are supplied by high voltage DC (HVDC)stations, like in an island, and their nominal power is greater than those of the generating units,the HVDC systems can have an important role in the frequency regulation.In this work a control system for a HVDC system is developed based on a modular multilevelconverter (MMC) that allows the attenuation of frequency deviations in a low inertia gridwhen the consumed power varies. The system control is based on modifying the HVDC stationconsumed or generated active power reference to reduce the low disturbances on the generator.To implement this controller, the grid steady state model is obtained, calculating the relationshipbetween the active and reactive power at the converter terminals for several load levels.This relationship is used to design a control loop that allows the HVDC station to rapidly modifythe active power reference in order to compensate the load changes.A MMC model is obtained for power systems simulations that allows long periods simulations.Using this model, a grid was simulated with a change in the consumed active power and thesubmodule capacitor reference voltage. The proposed control method was checked using thismodel.The operating conditions of a grid composed by a generating unit and the HVDC stationare analyzed using a simplified power system model. The control system is extended consideringthe magnitude and angle of the transmission line impedance that connects the converter to thecommon coupling point.The obtained results show that the proposed control diminishes the frequency deviation by80% with respect to a standard controller when it is operating under nominal conditions. Whenthe operating conditions change, especially when the converter must reverse the power flow,the regulation quality is affected, diminishing the deviations to 52%. A disadvantage of thiscontrol method is the dependence on the grid parameters in the design stage. Nonetheless, theperformance analysis shows that the controller behavior is superior with respect to a standardcontroller even when there is parameters uncertainty.
Description
Keywords
HVDC , MMC , REDES DE BAJA INERCIA , SOPORTE DE FRECUENCIA
