DC Capacitor Voltage Balance Control of Delta- Connected Cascaded H-Bridge STATCOM

In this paper, the DC capacitor voltage balance of delta connected cascaded H-bridge is deeply studied. From the point of view of currents and average active power, a three-layer controller of capacitor voltage at the DC side of delta-connected H-bridge is established. The first layer of control is the total DC side voltage control by generating active current. The second layer of control is the voltage control among three phases. Due to the delta configuration, there is a circulating current flowing through it. The cluster voltage balancing is realized by circulating current control even under unbalanced load. The third layer is the capacitor voltage control in each cluster, and the capacitor voltage balance in each cluster is completed by adjusting convert’s output voltage of each bridge-cell. For the capacitor-voltage balance control, the three-layer control strategy is analyzed theoretically in detail. Finally, the effectiveness of the control method is verified by simulation.