考虑暂态功角稳定和故障限流的并网逆变器下垂暂态控制策略

Droop transient control strategy considering transient power angle stability and fault current limitation of a grid-connected inverter

为解决下垂控制型逆变器在故障工况时发生暂态功角失稳和故障过电流问题,提出了一种兼顾暂态功角稳定和故障限流的暂态控制策略。首先分析了下垂控制型逆变器的暂态功角失稳机理和故障电流暂态特性,定量分析了无功控制回路对暂态稳定性的影响以及暂态功角、短路电流与逆变器输出电压三者之间的关系。其次,以暂态功角稳定和故障限流为控制目标,通过在有功控制回路中引入暂态功角动态补偿项、在无功控制回路自适应调整电压参考指令值进行综合控制。最后,通过仿真实验验证了所提出控制策略不仅可以抑制故障过程中不平衡功率造成的功角持续增大和故障过电流,并一定程度上增加了故障期间无功功率,有利于故障电压恢复,从而实现下垂控制型逆变器在电网故障时的安全稳定运行。

There are issues of transient power angle instability and fault overcurrent in droop-controlled inverters in fault conditions.Thus a transient control strategy that considers both transient power angle stability and fault current limiting is proposed.First,the mechanism of transient power angle instability in droop-controlled inverters and the transient characteristics of fault currents are analyzed.The impact of the reactive power control loop on transient stability and the relationship among transient power angle,short-circuit current,and inverter output voltage are quantitatively analyzed.Second,to achieve transient power-angle stability and fault current limiting,a comprehensive control approach is proposed,one which introduces a dynamic compensation term for transient power-angle in the active power control loop and adapts the voltage reference command value in the reactive power control loop.Finally,simulation experiments are conducted to validate the proposed control strategy.It not only suppresses the continuous increase of power angle caused by unbalanced power during fault processes and mitigates fault overcurrent but also increases reactive power during fault periods to facilitate fault voltage recovery.Consequently,the proposed strategy enables the safe and stable operation of droop-controlled inverters during grid faults.