Phase leg voltage balancing of a cascaded H-Bridge converter based STATCOM using zero sequence injection

In cascaded H-bridge wye and delta connected STATCOMs the phase leg capacitor voltages can diverge, even under ideal balanced voltage conditions, due to different leg losses and capacitor values. This paper presents a novel strategy for achieving phase leg voltage balance for wye and delta connected STATCOMs by making use of zero sequence injection into the STATCOM. The proposed strategy also makes the STATCOM leg voltages tolerant to terminal voltage imbalance.