Stability Analysis and Mitigation of Oscillation in an Induction Machine

Open-loop constant voltage/frequency (v/f) adjustable speed drives (ASDs) can often experience undesirablesustained oscillations. Factors affecting these oscillation states include induction machine (IM) parameters, dead time,dc-link capacitor size, IM saturation, output voltage, carrier frequency, and IM speed. Many literatures have discussedthe instabilities in light-load or low-frequency operating conditions. Quite a few methods have been proposed forstabilizing such a system. However, the instability problems, at different power levels, have not been completelydescribed. This paper analyzes the causes of this instability for constant v/f drives as power levels change. The 2.2-and 15-kW low-voltage IMs and the 746-kW medium-voltage IM are evaluated to illustrate how the motor parameters affectthe system stability. Additionally, a new oscillation mitigation method is introduced to demonstrate its effectivenessin solving the instability problems. It is based on the synchronous reference frame dynamic current feedback through itsmagnetic flux current component bandpass filtering and proportional control. In a theoretical stability analysis beforeand after the current feedback compensation, simulation studies are presented and verified through a 15-kW 380-V 50-HzIM ASD experimental system.