A Novel Modulation Strategy of Reduced Device-Count Hybrid Multilevel Inverter for Wide-Speed Range Motor Drive

Start-up and low-speed motor drives are difficult for traditional multilevel inverters without transformer since capacitor voltage fluctuations are huge. This paper proposed a novel modulation strategy of reduced device-count hybrid multilevel inverter (RDHMI) for wide frequency range motor drive. The proposed modulation strategy can realize capacitor charging-discharging balance in one basic switching cycle. Thus the RDHMI can work at low frequency or even zero hertz. The zero-sequence voltage injection method is proposed to improve the performance with the small modulation index and DC voltage utilization. And the control strategy of this topology is proposed to drive a permanent magnet synchronous motor at variable speed. The simulation shows the motor drive by start-up, low-speed and high-speed operation with rated torque. The topology and control methods were validated by the simulation results.