A Circuit Topology of Cascaded H-Bridge STATCOM to Operate With Multiple Faulty Bypassed Cells

In the present work, a circuit topology of cascaded H-bridge (CHB) converter for static synchronous compensator (STATCOM) application is proposed, which can operate with multiple faulty bypassed cells. The topology uses one redundant three-phase cell connected in series with the CHB converter. After the faulty cells are bypassed in CHB, the redundant cell is inserted into the power circuit of the CHB. The aim of the proposed topology is to tolerate multiple faulty bypassed cells in a single leg or multiple legs of the CHB converter and maintain prefault rated line voltage and reactive power capability of the converter during postfault conditions. A novel geometrical approach is proposed for output voltage generation for the healthy cells and the redundant cell during postfault operation, which ensures that the capacitor voltages are balanced for all the remaining healthy cells in CHB and the redundant cell. Additionally, the voltage stress on the remaining healthy cells does not increase during postfault condition. The proposed fault tolerant topology of CHB STATCOM is verified for single and multiple faulty bypassed cells using simulation and a downscaled experimental prototype.