Switching transient analysis of the cascade STATCOM by the equivalent model with redundant H-bridge submodules

Abstract

Cascade Static Synchronous Compensator (STATCOM) is a multilevel power electronic device, and its safety, reliability, and operation life are directly affected by switching transient processes. The work presented a switching transient analysis of the redundancy fault-tolerant control for the Cascaded STATCOM by the proposed contactor equivalent model. It was more accurate, ignoring fast dynamic changes and replacing the instantaneous speed with the average speed. Redundancy fault-tolerant control of submodules was crucial to the reliability of Cascade STATCOM. The closing and opening process of the AC contactor generally lasted for several milliseconds. When failure occurred in H-bridge, many factors such as the change of excitation circuit, the resistance, and the capacitance affected the electromagnetic transient process during the closing of the AC contactor. Arc discharge occurred when the H-bridge submodule was re-entered, and the AC contactor was turned off. Based on this, an equivalent model of ac contactor suitable for h-bridge was proposed, considering the influences of excitation circuit, arc discharge, and distribution parameters on switching transient. Simulation and experiments were used to analyze the electromagnetic transient waveform of a single H-bridge sub-module in the contactor closure and disconnection process, and the electromagnetic transient waveform of cascade STATCOM in the redundant sub-module contactor closure and disconnection process. The results showed that the transient change of the proposed model during sub module’s bypass and re-entry process was closer to the physical process. The equivalent model obtained in the work provides the theoretical and numerical basis for the design and operation of high-power power electronic equipment.