不平衡电网下变流器多机系统的稳定性分析

Stability analysis of multi-VSC system under unbalanced power grid

基于不平衡电网条件下的并网交互系统,研究了电压源型变流器(VSC)的稳定性问题。首先提出了不平衡电网下带双二阶广义积分器锁相环(DSOGI-PLL)的变流器导纳模型。分析总结了带不同类型锁相环的VSC系统导纳特性。基于导纳模型研究了配置不同类型锁相环的多VSC系统稳定性问题,指出了多VSC系统稳定性的改善方向。进一步提出,带DSOGI-PLL变流器的并入可以在增加并网系统输出功率的同时有效改善变流器的稳定裕度。同时,研究了公共耦合点处负序电压改变时VSC与电网阻抗的交互机理。最后,对理论分析进行了实验验证。

The stability problem of voltage source converter(VSC)is studied based on the grid-connected interactive system under unbalanced grid conditions.A converter admittance model with double second-order generalized integrator phase locked loop(DSOGI-PLL)is proposed under three-phase unbalanced power grid conditions.The admittance characteristics of VSC systems with different types of phase locked loop(PLL)are analyzed and summarized.Based on the admittance model,the stability of multi-VSC systems with dif⁃ferent types of PLL is studied,and the improvement direction for the stability of multi-VSC system is pointed out.Further,it is proposed that the integration of DSOGI-PLL converters can effectively improve the stability margin of converters while increasing the output power of the grid-connected system.At the same time,the interaction mechanism between VSC and grid impedance is studied when the negative sequence voltage changes at point of common coupling.The theoretical analysis is verified by experimental results.