Harmonic currents and torque pulsations with pulse width modulation methods in AC motor drives

The pulse width modulation (PWM) method used in AC motor drives influences the harmonic current content and the torque pulsations. To investigate this, two PWM methods are compared by means of computer calculations and measurements on an 11 kW squirrel-caged induction motor fed by a transistor inverter. The investigated drive, with a deep-bar squirrel-caged standard induction machine which has frequency dependent rotor parameters, introduces some discrepancies between the measurements and the simulations. The PWM methods investigated are the natural sinusoidal modulation and the staircase modulation, which is a new uncomplicated and efficient modulation method. The same pulse number is used in both methods. To present a reference case, results with a quasi-square wave voltage are also being given