A Capacitor Voltage Balance Method for N-Level Neutral-Point-Clamped Converters

This paper proposes a generalized modulation method with capacitor voltage balance capability for the n-level neutral-point-clamped (NPC) converter. Firstly, the capacitor voltage model is analyzed and established. To improve the utilization of DC-link voltage, a suitable zero-sequence voltage is selected and injected into the original modulation signals. Secondly, the duty cycles are constructed by introducing the common-mode component (CMC) and the differential-mode component (DMC), where CMC is used to synthesize AC output voltage and DMC is used to achieve capacitor voltage balance. Then, a DMC design method is introduced based on sliding-mode control theory, and it was demonstrated that the designed DMC can balance the capacitor voltage in finite time. Finally, the range of CMC is given based on the duty cycle constraint. The proposed method achieves decoupling control of output voltage synthesis and capacitor voltage balance and has the advantages of simplicity and flexibility. Experiments verify the effectiveness of the proposed modulation method.