Voltage Lifting Control + Third Harmonic Circulating Current Injection for Capacitance Reduction in Delta-CHB STATCOM

The Delta-CHB emerges as an interesting topology for STATCOM applications. An important drawback of this topology is the low-frequency ripple in the submodule voltage, which leads to high energy storage requirements. One way to reduce this ripple is to control the converter circulating current, which results in the asymmetric capacitor voltagewaveform. This work investigates the capacitor voltage lifting to extend the capacitance reduction provided by the traditional third-harmonic circulating current injection (THCCI) scheme in Delta-CHB STATCOM. This scheme is investigated in simulation and its viability is proved through experiments. The proposed strategy reduces the required capacitance by 35% compared to the conventional Delta-CHB design.