Minimum Voltage Operation of Cascaded H-Bridge StatComs Using Discontinuous Modulation

Operating cascaded H-bridge (CHB) static compensators (StatCom) at low dc capacitor voltages reduces voltage stress on submodule capacitors and switching semiconductors, resulting in enhanced system reliability and reduced power loss. Understanding the minimum allowable value for peak capacitor voltage is crucial for the optimal capacitor voltage operation of CHB StatComs. This letter proposes an offset-free discontinuous pulsewidth modulation (DPWM) strategy for CHB StatComs. Unlike conventional DPWM strategies, the proposed offset-free DPWM allows the CHB StatCom to operate with minimum peak capacitor voltage. This results in reduced switching loss and lower voltage stress across submodule components. In contrast to existing third-harmonic zero-sequence voltage strategies, the proposed offset-free DPWM does not require accurate capacitance knowledge and is effective in unbalanced grid conditions and low-capacitance applications. The feasibility and effectiveness of the proposed offset-free DPWM are experimentally validated under both balanced and unbalanced grid conditions.