A Novel PWM Strategy Capable to Operate in Overmodulation Range With Low Switching-to-Fundamental Frequency Ratio

In this paper, a novel pulse-width-modulation (PWM) strategy to operate in overmodulation range with low switching-to-fundamental frequency ratio is developed for permanent magnet synchronous machine drives based on a two-level voltage source inverter (VSI). The proposed strategy is able to operate at low switching-to-fundamental frequency ratio and presents an inherent overmodulation capability. The strategy applies a fixed switching sequence in a fundamental period, similar to six-step modulation, but including zero-vectors to regulate the voltage magnitude, and then, conventional control techniques can be employed. The duty cycles of the output voltage pulses and the switching angles are computed as linear functions of the modulation index. Two switching angles are used to reduce the number of commutations and avoid the problems associated to low switching-to-fundamental frequency ratios. A harmonic analysis of the generated voltage is also presented. The performance of the proposed strategy is tested and validated with simulations and experiments on a laboratory prototype.