Studies on the clustered voltage balancing mechanism for cascaded H-bridge STATCOM

To study the clustered voltage balancing mechanism for cascaded H-bridge STATCOM, the active power from the grid is decomposed of by using positive and negative sequences in dq frame. Based on the detailed analysis, portion of clustered active power generated by negative-sequence voltages and currents, referred as negative-sequence clustered active power (NCAP), can redistribute the active power among three clusters, which implies it can be utilized to balance the three clustered voltages. Then, the relationship between NCAP and control variables-duty cycle is built. The relationship reveals that three clustered voltages are capable of converging to stable voltages without any clustered balancing control, indicating the cascaded H-bridge STATCOM having the clustered voltage self-balancing feature. Finally a balancing control method is proposed to regulate NCAP. The effectiveness of the proposed control method is verified by the experiments.