基于阻抗特性的级联H桥型PET并网稳定性分析

Stability Analysis of Grid-connected Cascaded H-bridge PET Based on Impedance Characteristic

电力电子变压器(powerelectronictransformer,PET)是一种由电力电子变换器与高频变压器构成的电能变换设备,在交直流混合配电网中有着良好的应用前景。以三相级联H桥型PET拓扑为研究对象,分别将高压与低压侧直流母线电压作为控制器的反馈调节信号,分析PET在不同电压闭环控制策略下系统的动态响应及稳定性差异问题。首先利用状态空间平均值法建立级联H桥型PET小信号统一数学模型,基于节点电压稳定性建立的Nyquist判据,评估PET接入电网系统稳定性。在此基础上,分析不同控制器参数及有功功率静态工作点对系统稳定性的影响,并判定稳定性边界条件,进而对系统参数设计及闭环控制策略的选取提供理论研究基础。最后通过仿真与实验结果验证了所分析的阻抗模型与系统稳定性边界条件的正确性。

Power electronic transformer(PET)is a new electric power conversion equipment including power electronic converter and high-frequency transformer broadly applied in AC/DC hybrid distribution network.This paper takes cascaded H-bridge PET as research object and analyzes the difference of dynamic response and stability under diverse closed-loop control strategy,taking high or low DC voltage as controller feedback signal respectively.Besides,a PET small signal unified mathematical model is built with state-space average method to assess stability of the system based on Nyquist criterion.On this basis,the influence of different controller parameters and active power on stability is analyzed.Meanwhile,the boundary condition of stability is judged to provide a research foundation for system parameter design and control strategy selection.Finally,simulation and experimental results show validity of the small signal impedance model and the stability boundary condition.