Synchronous Optimal Pulsewidth Modulation for Low-Switching-Frequency Control of Medium-Voltage Multilevel Inverters

This paper presents the mechanism and details of synchronous optimal pulsewidth modulation (PWM) generation for control of medium-voltage induction motor drives using multilevel inverters at low switching frequency. Multilevel inverters allow operation at multiple of dc-link voltage and reduce the total harmonic distortion (THD). Synchronous optimal PWM control permits setting the maximum switching frequency to a low value without compromising THD. Low switching frequency reduces the switching losses of the power semiconductor devices. An optimal control procedure is explained in detail. The performances of three- and five-level inverter topologies are compared. The experimental results of a five-level inverter drive using optimal PWM control are presented.