Voltage spectra of two-phase PWM techniques in inverter fed AC drives

The voltage spectra of different types of two-phase PWM techniques for three-phase voltage inverters are investigated and compared. Different PWM control methods are suggested and adequate analytical equations of the motor voltage harmonics are given. The two-phase PWMs, however, for the low fundamental voltage region and the same commutation frequency of the inverter results in considerably higher voltage harmonics and, therefore, higher motor harmonic losses and torque pulsations than the three-phase modulation. The two-phase PWMs can only produce better results than the three-phase ones in the high voltage region. The theoretical results are verified by computer calculations as well as by means of simulation and experimental investigations.