A Simple Zero-Sequence Voltage Injection Method for Carrier-Based Pulsewidth Modulation of the Three-Level NPC Inverter

This article proposes a simple zero-sequence voltagei injection method for the carrier-based pulsewidth modulation (CBPWM) of the three-level neutral-point-clamped (NPC) inverter. The injected zero-sequence voltage signal is simply determined by comparing the three reference voltage signals and the dc-link capacitor voltages, respectively. Theoretical analyses show that the CBPWM with the proposed method can balance the dc-link capacitor voltages and eliminate/reduce the ripples of the dc-link capacitor voltages of the NPC inverter. Compared with other CBPWM schemes, the CBPWM with the proposed method has lower computation cost, does not need the information of the three-phase currents, and can reduce the switching loss of the NPC inverter. The CBPWM with the proposed zero-sequence voltage injection method and its superiority is validated experimentally in comparison with existing CBPWM schemes. The proposed method works in both inverter and rectifier modes, which is validated by simulation results.