Design of a Three-phase Inverter for Variable
AC Drive Purposes using a Pulse Width Modulation Based on a New Strategy

By Abdulkareem Mokif Obais
Professor at Department of Elect. Eng. College of Engineering University of Babylon


In this paper, a pulse width modulation (PWM) technique based on a new strategy is presented first. A three-phase voltage-source inverter based on this technique is then designed for variable AC drive purposes. The new strategy concerns the phase conditioning of the modulating signals such that almost pure sinusoidal balanced three-phase currents are supplied to the induction motor during variable speed operation. The harmonic distortion associating the inverter output currents is negligible. The inverter frequency can be varied from its nominal value (50 Hz) to one-fourth its nominal value (12.5 Hz) keeping constant voltage to frequency ratio. A complete design for this inverter is presented
and the whole system is tested on Pspice.