Short-Switch Fault Ride-Through andPost-Fault Reconfiguration Strategy for a Static Synchronous Series Compensator Based on Cascaded H-Bridge Multilevel Converter

The cascaded H-bridge (CHB) converter is one of the viable options for large-scale power conversion. Owing to the increased number of components involved in this topology, converter reliability and fault-tolerant control are important issues. This paper proposes a new short-switch fault protection scheme and a post-fault modulation (PFM) strategy to keep the performance of a CHB converter in a static synchronous series compensator (SSSC) application. The SSSC is a series converter to the transmission line, which controls the power flow in the line. Acting as a series converter, any abnormal action of SSSC can affect the whole line reliability. So following the fast fault detections and protections, remedial actions have to be considered to extend normal operation of the SSSC and, in some cases, derate the system to prevent unexpected shutdowns. The new method of short switch fault protection can eliminate the fault in the proper time, while the novel proposed PFM strategy guarantee the continuation of converter operation. This method is based on the application of increasing dc bus utilization techniques in conjunction with the phase shifted pulse width modulation method, which generates the balanced grid currents. Take the advantages of this method; the converter is able to control the transmission line power flow with the remaining healthy H-bridges. Simulation results validate the effectiveness of the proposed method.