A New Fault-Tolerant Strategy for a Cascaded H-Bridge Based STATCOM

This paper introduces a new fault-tolerant strategy for a cascaded H-bridge (CHB)-based static synchronous compensator (STATCOM) with a single failure in power switches. A modified selective harmonic elimination pulse width modulation technique is proposed for postfault operation which generates the maximum possible balanced line-to-line voltages at the ac side of the converter. The dc-link voltages of H-bridge cells are used as another degree of freedom; and by an efficient amount of increase at the dc-link voltages, the rated capacity of STATCOM is restored without any extra component. Furthermore, by applying an effective voltage balancing scheme, voltages of dc-side capacitors are kept balanced in postfault operation. A three-phase seven-level CHB-based STATCOM is simulated in PSCAD/EMTDC environment to verify the feasibility and performance of the proposed method and also experimental results are provided based on a three-phase five-level scaled down laboratory prototype which validates the effectiveness of the proposed strategy.