主动抵御换相失败的增强型电网换相换流器控制策略

Control Strategy of Enhanced Line Commutated Converter for Active Resistance to Commutation Failure

为了进一步提高增强型电网换相换流器对换相失败的防御能力,结合换相回路的阻抗分流特性和晶闸管的关断特性,提出了一种应用于基于增强型电网换相换流器的高压直流(ELCCHVDC)系统的新型协调控制策略。该策略分为辅助换相控制和主动可靠关断控制,前者加速了换相过程,提高了系统换相裕度;后者可靠关断退出导通的阀臂,保障了阀内晶闸管恢复阻断能力的物理条件。此外,分析了子模块全控器件在所提策略下的电气应力并为其设计了最佳初始电容电压。PSCAD/EMTDC仿真结果表明,子模块全控器件的电气应力与理论分析相符,新型协调控制策略提高了ELCC-HVDC系统的换相失败防御能力。

In order to further improve defense capability of enhanced line commutated converters against commutation failure,this paper proposes a new coordinated control strategy applied to the enhanced line commutated converter based high voltage direct current(ELCC-HVDC)system by combining the impedance shunt characteristics of the commutation circuit and the turn-off characteristics of the thyristor.This strategy is divided into the auxiliary commutation control and the active and reliable shutdown control.The former accelerates the commutation process and improves the commutation margin of the system;the latter reliably turns off the valve arm which exits the conduction,thus ensuring the physical conditions for the thyristor in the valve to recover the blocking ability.In addition,the electrical stress of the fully controlled devices of the submodule using the proposed strategy is analyzed,and the optimal initial capacitor voltage is designed for it.The PSCAD/EMTDC simulation results show that the electrical stress of the fully controlled devices of the submodule meets the theoretical analysis,and the new coordinated control strategy improves the commutation failure prevention ability of the ELCC-HVDC system.