Investigating the vulnerability of slip energy recovery converters to voltage dips

Slip energy recovery (SER) drives provide increased efficiency and a cost effective means of speed control for large induction motors. The biggest disadvantage of SER drives is the vulnerability of the rotor circuit converters to power system disturbances, in particular voltage dips. Failure of converter IGBTs as a result of voltage dips can be a problem associated with the use of these drives. The aim of this study is to better understand the vulnerability of rotor circuit converters as a result of voltage dips at the terminals of wound rotor induction motors. The rotor transients developed by a wound rotor induction motor are investigated for a series of three phase and single phase dips. Measurements conducted on a simplified SER circuit are presented showing the transient rotor currents and voltages the converters will experience during a voltage dip. Simulations performed using ATP-EMTP confirm the measured results. The analysis provided in the paper better explains the response of wound rotor induction motors to voltage dips