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Per-phase Analysis and Efficient Implementation of a 24-Sector Discontinuous PWM for Split Phase Induction Motor Drives

Space vector-based 24-sector pulse width modulation (PWM) techniques for split-phase induction motor (SPIM) drive offer better performance than the 12-sector PWM methods; however, these methods are complex to implement. This paper analyses a space vector based 24-sector discontinuous PWM from a per-phase perspective. Analysis of three-phase average pole voltages, pertaining to this method, shows that each phase is clamped for a 60° interval in each half cycle, which is divided into three sub-intervals of 15°, 30° and 15°, respectively. The common-mode voltage is shown to be related to the fundamental voltage of one of the phases in each sector and to that of different phases in different sectors. This analysis leads to an understanding of the offset voltages to be added to the two sets of three-phase sinusoidal modulating signals in order to generate the equivalent modulating signals for the two inverters driving the SPIM. Further analysis of the switching sequences suggest appropriate carrier waves the modulating signals should be compared against. The computationally efficient implementation of the 24-sector discontinuous PWM (DPWM), thus developed, is validated on a 6-kW laboratory prototype SPIM drive. The proposed method offers lower THD at high speeds and also lower switching loss at high power factors than the 24-sector continuous space vector PWM with significantly low computational effort.