Pulse removal in sinusoidal PWM with constant switching frequency to reduce switching frequency or current harmonics

This paper proposes a method for voltage source inverter supplied three-phase induction machines to reduce the switching frequency or the current harmonics for sinusoidal PWM with constant switching frequency. Due to the continuous removal of individual impulses in the control signals, either a reduction of the switching frequency of 33.3% with unaltered current harmonics or about 1/3 less current harmonics with unaltered switching frequency are obtained. Pulse removal affects only the inverter output voltages without any changes in the signal forms of the motor voltages. For two-level and three-level voltage source inverters, a comparison between the standard PWM with symmetrical carrier signals and the pulse removal with sawtooth shaped carrier signals will show the advantage of the proposed method especially for 3-level inverters. The proposal was extensively verified and analysed by a 400 kVA laboratory setup at ETH Zurich