VSC连接弱交流电网的小扰动特性

Small Disturbance Characteristics Analysis of VSC Connecting to Weak AC System

主要研究电压源型换流器(voltage source converter,VSC)在弱交流电网,即低短路比电网的小扰动特性。首先基于VSC的稳态模型,研究VSC在弱交流电网下的稳态运行特性;之后推导了包含外交流电网、VSC、由内外环控制器构成的VSC传统矢量控制器以及锁相环(phase locked loop,PLL)在内的VSC线性化模型;最后研究了VSC传统矢量控制器中的内环控制器、外环控制器以及锁相环对VSC在弱交流电网中的稳定性能影响。研究发现传统矢量控制器中的内环控制器不会对VSC在弱交流电网中的稳定性能有影响,VSC在弱交流系统中更适宜于逆变运行模式,交流系统短路比越低,保证VSC系统稳定运行的锁相环的增益系数最大取值将越小。结果表明在弱交流电网下,VSC控制系统的参数需要合理选取以保证基于VSC的高压直流输电系统的稳定运行。

This paper focused on the small disturbance characteristics analysis of voltage source converter （ VSC ）, which was connected to low short circuit ratio （SCR） AC （ weak AC） systems. First, based on the steady state model of VSC, the steady state operating characteristics of VSC in weak AC system were studied. Then the linear model of VSC was derived, including external AC system, VSC, traditional vector controller of VSC composed of inner/outer loop controller, and phase locked loop （PLL）. Finally, this paper studied the impacts of the inner/outer loop controller in VSC traditional vector controller and the PLL on the stable performance of VSC in weak AC system. The research results show that the inner loop controller in traditional vector controller will not impact the stable performance of VSC in weak AC system; inverter operation mode is more suitable for VSC in weak AC system; the lower the AC SCR is, the smaller the maximum PLL gain coefficient is, which can guarantee the system stability. The results also show that： in weak AC system, the parameters of VSC control system should be selected reasonably to ensure the stable operation of VSC-HVDC.