PWM method for reduction of torque pulsations of an induction motor driven by voltage source inverter

It is inevitable that the torque of an induction motor driven by a voltage source inverter contains many harmonic components. The instantaneous torque of the induction motor pulsates with six times the fundamental frequency in the sine-wave PWM system as compared to the fundamental sine-wave signals with a triangular carrier signal. This phenomenon is similar to an optimal PWM system using a sine-wave pattern. This pulsation is based upon a voltage vector pattern. A 6th harmonic signal of fundamental frequency is added to sine-wave signals of the sine-wave PWM system, in order to eliminate this pulsation. The instantaneous torque and current of the induction motor were computed by the state variable method. As a result of computation, the 6th harmonic pulsation of torque vanishes as compared with the sine-wave PWM system, or the optimal PWM system. In the same manner as the sine-wave PWM system, however, the inner small ripple remains in the waveform. It does not appear in the optimal PWM system. On the other hand, such a waveform as an instantaneous maximum torque constant is shown by the use of a modification of the optimal pattern. In this case, the bottom of the torque waveform varies by six times to the fundamental frequency. The motor current is a sinusoidal waveform as is the sine-wave PWM system in all the patterns