The paper studies pulse width modulation (PWM) techniques for a five-phase multilevel open-end winding drive with two inverters supplied with unequal dc-link voltages, which are in the ratio 2:1. It is shown in the paper that application of in-phase disposition modulation (PD-PWM), often used in multiphase multilevel converters, results in overcharging of the capacitor in the dc-link of the converter intended to operate at the lower dc voltage. The voltage space vector combinations which lead to the overcharging are identified and two decoupled modulation techniques which do not activate the troublesome vector combinations are proposed. The performance of the developed modulation techniques is investigated using simulations and an experimental prototype, and the results are presented in the paper.
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