Direct method of overmodulation with integrated closed loop stator flux vector control

Abstract

Overmodulation achieves full utilization of applied voltage, by modifying the magnitude and the phase of reference voltage vector. Due to the nonlinear behavior in this region, closed loop vector control becomes difficult. A simple method of overmodulation with closed loop control of stator flux vector is proposed in this paper. Instead of modifying the voltage reference by nonlinear equations or look up table, we propose a direct method to generate the switching times. In so doing, the average angular velocity of the stator flux vector is controlled linearly throughout the modulation range. The proposed method shows lower harmonic distortion compared with existing methods. It greatly reduces the complexity and cost of achieving overmodulation over existing schemes.