高压大容量电压源换流器LCL滤波特性及控制稳定性分析

Characteristic Analysis and Design of LCL Filter for High-Voltage Large-Capacity VSC

电压源换流器(VSC)一般采用常规的LCL低通滤波器滤除换流阀产生的高频谐波分量,但会造成一次系统的谐振以及谐振频率处控制器的响应特性的变化。高压大容量换流器的开关频率低,其滤波器参数设计更为复杂。针对滤除谐波及抑制谐振,分析了基于LCL滤波器的VSC系统的一次系统阻频特性以及系统电压传递函数,得出滤波器参数设计方法。基于阀侧电流反馈的dq电流直接控制,建立了包含LCL滤波器在内的电流内环控制系统模型,分析其开环及闭环的控制响应特性,研究得到在抑制系统不稳定及抑制谐振处谐波增益时反馈采样环节的截止频率选取原则。基于LCL的三相VSC建立了高压大容量换流器的仿真模型及等比例缩小的试验系统,仿真及试验结果验证了针对高压大容量换流器的LCL滤波器参数设计方法的合理性及谐振抑制方法的可行性。

LCL filter are commonly used for VSC(Voltage source converter) to filter highfrequency harmonic components which are generated by VSC valves. But resonance of the primary system might occur and response characteristics of converter's controller at resonant frequency might change. The switching frequency of high-voltage large-capacity converter is low and parameter design method of filter is complicated. Aiming at harmonic filtering and resonance suppression, impedancefrequency characteristics of the primary system and system voltage transfer function for VSC based on LCL are researched. Parameter design method of LCL-filter is obtained. Based on feedback of current at valve side, control system model of current regulation loop is established and the open loop and close loop control response characteristics are analyzed. For suppressing system instability and harmonic gain at resonance frequency, design method of cutoff frequency for the sampling feedback link is researched. Simulation model of VSC based on LCL and its scaling down experimental system are established, and simulation and experimental results prove rationality of parameter design method for LCL filter and resonance suppression method.