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A four-level five-phase open-end winding drive topology is introduced in the paper. The system comprises a five-phase induction machine with an open-end stator winding, supplied using two twolevel voltage source inverters with isolated and unequal dc-link voltages, in the ratio 2:1. The topology offers the advantages of a modular structure with fewer semiconductor components and has a greater potential for fault tolerance, compared to an equivalent single-sided four-level drive. Due to the large number of switching states, development of a suitable modulation method can be challenging. In this paper two carrier-based PWM strategies are developed and the performance is investigated using simulations.

Abstract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.