混联式直流电网的协调控制策略

Coordinated control strategy for hybrid HVDC grid

为解决传统电网换相高压直流输电与电压源换流器高压直流输电在直流电网中的混联问题,针对一种新型的混联直流输电系统进行了研究。该系统是整流侧采用模块化多电平换流器、逆变侧采用晶闸管换流器的四端双极混联直流电网。推导了该系统稳态时的数学模型,针对其逆变侧易发生换相失败的问题,设计了新的抑制换相失败的协调控制策略。在整流侧换流站中通过低压限压和低压限功率控制的配合,抑制逆变侧故障电流的增大,从而减小换相失败发生的概率。在PSCAD/EMTDC中对该混联直流电网的稳态和暂态特性进行了仿真分析,仿真结果证明了所提控制策略的有效性。

A hybrid HVDC system is studied for the interconnection of conventional LCC-HVDC （Line Commutated Converter based HVDC） system and VSC-HVDC（Voltage Source Converter based HVDC） system, which is a four-terminal bipolar hybrid HVDC grid with modular multilevel converter at its rectifier side and LCC at its inverter side. Its steady-state math model is deduced and a coordinated control strategy is designed to avoid the commutation failure at the inverter side,which coordinates the low-voltage voltage-order limiter and low-voltage power-order limiter at the rectifier side to suppress the augment of fault current and reduce the probability of commutation failure at the inverter side. The steady-state and transient performances of the studied hybrid HVDC system are simulated with PSCAD/EMTDC and the simulative results prove the effectiveness of the proposed control strategy.