A simplified control strategy to balance dc-link capacitor voltage for multi-level diode clamped VSI based on discontinuous SVPWM

This paper proposes a simplified control strategy to balance dc-link capacitor voltage for multi-level diode clamped voltage source inverter (DCVSI) based on discontinuous space vector pulse width modulation (DSVPWM). Currents flowing into the neutral point of dc-link capacitors cause fluctuations of dc-link capacitor voltages in the diode-clamped inverter. Performance of the multi-level inverter system is affected by imbalances of the dc-link capacitor voltages. On the basis of a simplified SVPWM algorithm for multi-level inverter and discontinuous modulation, simplified DSVPWM methods are proposed here to balance the dc-link capacitor voltages. The proposed control method changes the path and duration time of the neutral point currents, making the voltages of series connected dc-link capacitors equal. While maintaining low switching losses and achieving effective voltage balancing, this method does not adopt any additional hardware or complicated calculations. Its feasibility and effectiveness are both confirmed by simulation results.