Collaborative Control of Four-Level Hybrid Clamped Converter With CMV Suppression and Capacitor Voltage Fluctuation Reduction

Hybrid clamped converter (HCC) is a novel high-performance four-level multilevel converter. However, it faces the problem of common-mode voltage (CMV) and dc bus capacitor voltage fluctuation, which are difficult to suppress synchronously due to the coupling between them. Accordingly, this article establishes a CMV prediction model for HCC considering the capacitor voltage fluctuation and dead-time and proposes a collaborative control method based on zero-sequence voltage (ZSV) injection. By injecting the optimal ZSV at different times and compensating for the dead-time, the suppression of CMV and capacitor voltage fluctuation is jointly achieved. Experimental and simulation results show that the capacitor voltage fluctuation of the proposed method is reduced by an average of 25% compared to the conventional method. The CMV is suppressed from ±Vdc/6 to ±Vdc/18 and ±5Vdc/18 to ±Vdc/6 at medium and high modulation index, respectively. In addition, the proposed method reduces the THD of the output current and does not lead to additional power losses.