Discontinuous Carrier-Based PWM With Low Switching Frequency

In ultra high speed ac drives the ratio of the carrier frequency to fundamental one can be lower than 20 - 30. For this low inverter switching frequency all the possible discontinuous PWM methods are investigated and it is observed that dc components and subharmonics of carrier-based natural and regular PWMs can have considerable negative effect on the quality of the drive. The investigation and the computation of different discontinuous PWM showed that the dc components and the subharmonic voltage have the lowest values for PWM with 60 degrees clamping to DC bar and the worst situation is related to 60 degrees clamping to DC bar with 30 degrees lagging clamp as well as to 30 degrees clamping. The computation results are confirmed by experiments.