Research on master-slave control strategy of capacitor voltage for cascade STATCOM

The loss difference of each inverter cell is one of the important reasons for capacitor voltage unbalance in a cascade STATCOM. A new master-slave control strategy of capacitor voltage is proposed in this paper. A voltage and current double closed-loop used in the master cell not only maintains the capacitor voltage balance of the master cell, but also realizes the fast tracking of reactive current reference; the voltage control reference from the master cell is slightly adjusted in each slave controller making use of DC voltage closed-loop in order to overcome voltage unbalance caused by loss difference. The feasibility and stability of this scheme is verified through simulation. The control scheme presented in this paper has practical values to a certain extent.