Variable Structure Approaches for Current Control in Vector Controlled Inverter-Induction Motor System

Abstract

Up to now, the performance of current control for field-oriented control of the induction machine using pulsewidth-modulated (PWM) voltage source inverter have the problem that it can not provide high-accuracy and quick-tracking response simultaneously. For improvement, two variable structure approaches are proposed in this paper. One is the so called Discontinuous Damping System method implemented by software alone, which is suitable when switching frequency of inverter is higher. The other is a combination of software PI controller and hardware hysteresis comparator, which is necessary in the case of lower switching frequency. Experimental results show that both approaches have the dynamic response as fast as that of a hysteresis controller as well as an accurate static response with the least harmonic currents. An optimum PWM pattern of the inverter based on the space vector concept was also implemented so that not only the harmonic currents are limited but also, with the proposed methods, it becomes easy to compensate the dead-time of the inverter and to sample motor current eliminating the distortions.