Oscillations in voltage controlled induction motor drives

Oscillations in the range of 5 to 10 Hz are noticed in some underdamped Voltage Controlled induction motor drives fed from constant frequency constant voltage source. These oscillations produce noise and may damage the system. The results from simulation have shown that the oscillations are due to the asymmetry in triggering, resulting in a large rate of change of motor current. These oscillations are more pronounced with a 6-pulse 120° width triggering scheme than according to 12-pulse, concept. The experimental data are verified with the simulation results giving quantitative data for effective understanding of this phenomena. Two control strategies are suggested for damping of oscillations in such digital drive systems.