Fully digital-controlled PWM inverter with software based modulation for AC machine control

Abstract

A fully digitally controlled PWM (pulsewidth-modulation) inverter is presented with software modulation suitable for three-phase open and closed-loop power control, particularly AC machine control. The inverter is a three-phase 30 kVA voltage source PWM inverter using triple Darlington modules, operating at a 1 kHz switching frequency. The power circuit, base drive circuit, control circuit, and interface for the computer are described and related to the protection and monitoring strategy. The software-based stator flux oriented asynchronous vector modulation is also described. Some test results are presented. The system is suitable for both simple open-loop applications and demanding closed-loop servo drives with field oriented control.<>