Comparison of the Effects of Continuous and Discontinuous PWM Schemes on Power Losses of Voltage-Sourced Inverters for Induction Motor Drives

In this paper, losses in a 4-kVA three-phase voltage-sourced inverter designed to drive an induction machine, are investigated. A comparison of inverter losses with sinusoidal pulsewidth modulation (PWM), space vector PWM and discontinuous PWM (DPWM) is presented, concluding that DPWM is the method of choice. These PWM schemes are implemented using a field-programmable gate array and modeled in Pspice. PWM excitation models are combined with an inverter model that incorporates the Hefner model for the insulated gate bipolar transistors. After verification of the complete inverter model with calorimetric measurements, the model is used to predict inverter losses under various conditions of modulation index, switching frequency, and gate resistance for each of the PWM scheme. A breakdown of losses into conduction and switching losses is presented. Moreover, the effects of different DPWM variants on inverter losses are also being considered. Overall, the use of DPWM is found to give minimum losses as a consequence of the reduced number of switching transitions.