Fault tolerance ability analysis and evaluation of three-phase voltage source converters

Abstract

三相电压源型并网换流器由于含有大量电力电子开关器件及相应控制环节,是一种强非线性系统。在交直流混合系统中受到电网侧故障或直流侧负载变化等扰动影响,大容量换流器将产生复杂的响应行为,给电网带来难以预计的影响。文中考虑电网中三相电压暂降的典型故障,基于平均模型分析了三相电压源型换流器电流环的非线性特性。在此基础上,根据李雅普诺夫稳定性判据分析了故障前后换流器的稳定性,并以故障深度和故障持续时间为指标对换流器故障耐受能力进行评估。最后,通过并网系统的逐周期仿真验证了理论分析和计算的有效性。 The three-phase voltage source converter (VSC) is a strongly nonlinear system for a large number of power electronic switching devices and corresponding control links contained. Disturbed by the grid side fault or DC side load change in the AC/DC hybrid system, the large-capacity converter will generate complex response, which brings about unpredictable influences on the power grid. This paper studies the transient response of a three-phase VSC under typical grid fault conditions. Firstly, based on the average mode, the nonlinear characteristic of the inner current loop in the three-phase VSC is analyzed. And the Lyapunov stability criterion is adopted to analyze the stability of VSC after a grid fault. Then the fault depth and duration are taken as indices to evaluate the fault tolerance ability of VSC. Finally, the effectiveness of theoretical analysis and calculation is verified by cycle-by-cycle simulations of the grid-connected system.