Seamless Transition Between Continuous and Discontinuous Modes Suitable for Natural-Sampled PWM in Variable-Frequency Two-Level VSI Operations

Abstract

In high-speed drive applications, including drone propulsion systems and high-speed spindle drives, switching frequency is often limited by thermal constraints or cost considerations when the adoption of wide-bandgap power devices is not economically justified. Under these conditions, natural-sampled PWM offers significant advantages over regular-sampled PWM, particularly at low switching-to-fundamental frequency ratios, by improving output waveform quality and reducing control-loop delay. This paper proposes an adaptive modulation strategy for two-level three-phase voltage-source inverters, enabling a seamless transition from space-vector PWM (SVPWM) to generalized discontinuous PWM (GDPWM). The proposed approach preserves the number of switching events by synchronizing the discontinuities of the modulation signals with the corresponding carrier peaks, thereby ensuring a consistent switching pattern while exploiting the benefits of discontinuous modulation.