Two-phase PWM technique for inverter fed AC drive

Different types of PWM techniques (with single-, two- and three-phase modulation) for the two- and three-level inverters are compared from the viewpoint of the motor voltage spectra, torque pulsations and harmonic losses. The voltage spectra of the two-phase modulation are investigated and given in details. The motor harmonic losses are deter-mined from the generalized loss-factors, which are expressed by analytical equations and usually independent of the commutation frequency of the inverter. It is shown that two-phase modulation - for the same commutation frequency of the inverter- produces considerably higher motor harmonic losses and torque pulsations for the low fundamental voltage region than three-phase modulation and lower ones for the high value of fundamental voltage. Only the two-phase unipolar modulation of three-level inverters can obtain lower harmonic losses in the whole fundamental voltage region.