Mitigation of Starting Transients in Slip-Energy Recovery Drives

Starting voltage and current transients in slip energy recovery drives (SERD) may damage the stator and rotor windings. The resulting torque oscillations damage the induction machine mechanical parts. In this paper three schemes for damping starting transients and torque oscillations are proposed. In the first scheme a parallel RL impedance is connected between the supply and the stator coils, in the second scheme a parallel RL impedance is added in the rotor circuit, and in the third scheme the two impedances are connected simultaneously. Transient performance is simulated and the results of the three schemes are compared. Also, the effect of each proposed scheme on the steady state values of the SERD currents, voltages, and electric torque is studied and demonstrated. Lower current and voltage transients, and lower torque oscillations resulted in all schemes, with optimum transient performance observed when adding the two impedances simultaneously.