Maximizing Linear Modulation Region of a Three-Phase Inverter for Single-Phase and Three-Phase Motor Drive

In a dual-motor drive system with a three-phase inverter for driving a three-phase motor connected in series with a single-phase motor, the magnitude of the single-phase motor voltage has a trade-off relationship with the maximum linear modulation region for the three-phase motor drive. This paper introduces a third-order harmonic voltage injection method in the dual-motor drive system to enhance the dc-link voltage utilization of a three-phase inverter. By determining the voltage reference for the single-phase motor drive to the third-order harmonic voltage, which is in phase with the three-phase voltage, the maximum linear modulation region can be expanded since the peak value of the pole voltage decreases compared to value of the three-phase voltage. If the magnitude of the single-phase voltage is determined to one-sixth of magnitude of the three-phase voltage, the dual-motor drive system has the same dc-link voltage utilization as in the single-motor drive system with a three-phase inverter. Simulation and experimental results are presented to validate the proposed method and demonstrate improvement in dc-link voltage utilization.