考虑严重故障下暂态切换控制的永磁直驱风电并网系统暂态同步稳定性分析

Transient switching control (TSC) of renewable equipment under severe faults makes transient characteristics of new-type power systems much more complicated. Although most of recent studies focused on the during-fault stage under low voltage ride through of grid-connected converters or detailed electromagnetic transient simulations, a unified understanding of entire transient process of permanent magnet synchronous generator (PMSG) grid-connected system is still lacking. Therefore, based on the TSC schemes of PMSG, this article considers the switching dynamical effects in detail, divides the transient process into four distinctive stages: prefault, during-fault, early postfault, and late postfault, and establishes the corresponding mechanism models with the associated machine–network interface relations for each stage. Furthermore, the influence of major parameters on the transient stability is studied, including the infinite-bus voltage dip depth and grid-side converter active current on the during-fault stage, and the active current climbing rate on the early postfault stage. It is also found that the large-disturbance stability on the sole during-fault stage is only a sufficient condition, but not a necessary condition, and actually the system after all four sequential stages can be stable under wider parameter regions. These findings are supported by wide numerical and experimental verification, and could provide a theoretical basis for transient synchronous stability analysis of PMSG grid-connected system.