A new oscillation controller design and induction machine stability analysis of volts/Hz based industrial adjustable speed drives

Open-loop Volts/Hz controlled industrial adjustable speed drives (ASD) can often experience undesirable sustained 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 discussed the instabilities in light load or low frequency operating conditions. Quite a few methods have been proposed for stabilizing such a system. However, the instability problems at different power levels, have not been completely described. This paper analyzes the causes of this instability for Volts/Hz based industrial ASDs as power levels change. A 2.2kW and 15kW IMs are evaluated to illustrate how the motor parameters affect the system stability. Additionally, a new oscillation mitigation method is introduced to demonstrate its effectiveness in solving the instability problems. It is based on the dynamic current feedback through its magnetic flux current component band pass filtering and proportional control. Theoretical stability analysis before and after the current feedback compensation, simulation studies are presented and verified through a 20hp (15kW), 380V, 50Hz IM ASD experimental system.