Thesis SOPORTE DE FRECUENCIA PARA REDES DE BAJA INERCIA CONECTADAS A ESTACIONES HVDC-MMC
Date
2018
Authors
CARREÑO HENRIQUEZ, ALVARO ANDRES
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Abstract
En los sistemas de potencia existe una relaci´on directa entre la potencia activa y la frecuenciade la red. Al momento de ocurrir un desbalance entre la potencia generada y consumida, seproduce una fluctuaci´on de frecuencia, cuya tasa de cambio depende principalmente de la inerciamec´anica de las unidades generadores. Considerando lo anterior, en una red de baja inercia sepueden generar con mayor facilidad desviaciones de frecuencia que puedan activar los mecanismosde seguridad antes que los sistemas de control de frecuencia act´uen, comprometiendo la operaci´ony la calidad del servicio el´ectrico prestado a los usuarios. Si estos sistemas son alimentados porestaciones DC de alto voltaje (HVDC), como puede ser el caso de una isla, y la potencia nominal esmayor que la de las unidades generadores, los sistemas HVDC pueden cumplir un rol fundamentalen la regulaci´on 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 var´iala potencia consumida. El sistema de control se basa en modificar la referencia de potencia activaque genera o consume la estaci´on HVDC para reducir las perturbaciones de carga en generador.Adicionalmente, se obtiene un modelo de la red en estado estacionario, calculando la relaci´onentre la potencia activa y reactiva en los terminales del convertidores para distintos niveles decarga. Esta relaci´on se utiliza para generar un lazo de control que permita a la estaci´on HVDCactuar r´apidamente sobre la potencia activa en lugar del generador.Se obtiene un modelo del MMC adecuado para simulaciones de sistemas de potencia quepermita largos tiempos de simulaci´on. Utilizando este modelo se simul´o una red con un cambioen la potencia activa consumida y voltaje de referencia de los capacitores de los subm´odulos, yse comprob´o el adecuado funcionamiento del control propuesto.Las condiciones de operaci´on de una red compuesta por una unidad generadora y la estaci´onHVDC son analizadas utilizando un modelo simplificado del sistema de potencia. Se extiende elsistema de control considerando la magnitud y ´angulo de la impedancia de una secci´on adicionalde l´inea de transmisi´on que conecta el convertidor al punto de acoplamiento com´un.Los resultados obtenidos muestran que el control propuesto permite disminuir las fluctuacionesde frecuencia en aproximadamente un 80% respecto a un controlador gen´erico cuando seopera bajo condiciones nominales. Cuando el convertidor debe invertir el flujo de potencia debidoa un cambio de carga, la calidad de la regulaci´on se ve afectada, disminuyendo las fluctuacionesa un 52%. Una de desventaja de este m´etodo de control es la dependencia de los par´ametrosactuales de la red para en la etapa de dise˜no. Sin embargo, al realizar un an´alisis de desempe˜no, el comportamiento del controlador es superior a un controlador est´andar a´un cuando lospar´ametros 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
Catalogado desde la version PDF de la tesis.
Keywords
HVDC , MMC , REDES DE BAJA INERCIA , SOPORTE DE FRECUENCIA