Software Pulsewidth Modulation for μP Control of AC Drives

Abstract
The on-line pulsewidth modulation (PWM) of a voltage source inverter for converter-fed ac drives is presented. The modulation is realized by software, thus allowing a direct interface between the microprocessor-based speed control and the on-off commands for the inverter. An efficient modulation technique is achieved by asynchronous switching of the inverter phases; a current control loop provides fast feedback, so that a fast step response of the stator currents can be obtained. All control functions, including field-oriented speed control of an induction motor, are performed by a 16-bit microprocessor. Experimental results obtained with a 22-kW induction motor prove that the proposed scheme provides a very good performance of the drive from standstill up to the field weakening range.

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