柔性低频输电系统两相运行特性分析

Analysis of two-phase operation characteristics of a flexible low-frequency transmission system

针对基于M3C(模块化多电平矩阵式变换器)的柔性低频输电系统的两相运行方式,建立了低频系统复合序网,对常规控制策略下低频输电线路和M3C的稳态运行特性进行分析。分析表明,线路中将出现与正序电流等幅反相的零序电流,同时也会出现零序电压和负序电压;采用低频侧定功率控制和负序电流抑制策略的M3C子换流器间电容电压不均衡,M3C电容电压平均值存在2倍频振荡分量。在PSCAD/EMTDC中搭建双端型柔性低频输电系统仿真模型,验证了所得结论的正确性。

The two-phase operation mode of a flexible low-frequency transmission system is based on the M3C(modular multilevel matrix converter).This paper establishes a complex sequence network for the low-frequency system to analyze the steady-state operation characteristics of low-frequency transmission lines and M3C under the conventional control strategy.The analysis shows that:(1)There appears zero-sequence current that shares equal am⁃plitude and opposite phase of the positive-sequence current in transmission lines;(2)The zero-sequence voltage and negative-sequence voltage can also appear in the transmission lines;(3)There is an unbalanced capacitor voltage be⁃tween M3C sub-converters with fixed power control on the low-frequency side and negative sequence current sup⁃pression strategy;(4)There is a double frequency oscillation component in the M3C average capacitor voltage.A simulation model of the dual-terminal flexible low-frequency transmission system is built in PSCAD/EMTDC,and the correctness of the obtained conclusions is verified.