Trinary Hybrid 81-Level Multilevel Inverter for Motor Drive With Zero Common-Mode Voltage

This paper proposes a trinary hybrid 81-level multilevel inverter for motor drive. Benefiting from the trinary hybrid topology of the inverter, 81-level voltages per phase can be synthesized with the fewest components. Bidirectional DC-DC converters are used not only to inject power to the DC links of the inverter but also to absorb power from some DC links in cases with a lower modulation index. The higher bandwidth of DC-DC converters alleviates the ripples of DC-link voltages caused by the load current. The space vector modulation used here, which selects voltage vectors that generate a zero common-mode voltage in the load, works at a low switching frequency. With up to 81-level voltages per phase, the total harmonic distortion is small, and the relationship between the fundamental load voltage and the modulation index is precisely linear. A vector controller is used to control an induction motor, which results in a high dynamic response for speeds or torques. The performance of the proposed inverter for the motor drive is confirmed by simulation and experiment.