不同控制策略对VSC-HVDC系统向无源电网供电的影响特性研究

Study on characteristics of VSC-HVDC system for passive power grid with different control

利用电压源型高压直流输电系统向弱交流系统、无源电网供电的优点,分析双端三电平VSC-HVDC系统结构和工作原理,结合无源电网固有特性,基于无源性理论设计一种电压电流双闭环无源控制器。整流侧采用定无功功率控制和定直流电压控制;逆变侧采用交流电压下垂控制,取代传统的恒压恒频控制,并在PSCAD/EMTDC环境下搭建基于不同控制策略向无源网络供电的双端VSC-HVDC仿真系统,对电网交流电压下降、无源电网负荷功率变化和逆变侧电网故障3种工况进行仿真分析。结果表明:设计的电压电流双闭环无源控制与交流电压下垂控制策略相较于传统VSC-HVDC系统控制策略,系统动稳态性能得到改善,可有效抑制负载突变和电网发生故障时的电压跌落,缩短系统恢复时间。

The VSC-HVDC system has the capability of supplying power to a weak AC system and a passive power grid and it can control the real and reactive power control individually and achieve a 4-quadrant operation. Under this background, this paper analyzes the structure and operational principle of the double ended three-levels VSC-HVDC system and the inherent characteristics of passive power grid. Then a controller is designed on the basis of the voltage and current double closed-loop passive theory. The rectifier side of the controller is consisting of a constant DC voltage controller and a constant reactive power controller. While the inverter side uses an AC voltage-drooped control method, instead of the traditional constant-voltage and constant-frequency control system. By using the PSCAD/EMTDC, a VSC-HVDC simulation system is established. Different control strategies are studied for supplying power to a passive network. In addition, three cases are stimulated including the AC voltage drop, the passive network load power mutation and the inverter grid fault.The results show that the voltage and current double closed-loop passive control system and the AC voltage drooped control strategy can improve the dynamic stability of system.The loads variations as well as the fault probabilities are suppressed effectively during the voltage drop moment and the power system recovery time is reduced consequently.