Critical states in generating mode of switched reluctance machines

When switched reluctance drives operate in generator mode, overcurrents can occur due to high back EMF voltages. These overcurrents produce large torque pulsations. Moreover, they can become excessive, creating a thermal overload for the power converter. These phenomena have not been discussed in detail before and are analyzed in this paper. Two overcurrent limits have to be distinguished. A so-called critical factor is defined to assess the risk of overcurrents leading to torque pulsations. In addition, an absolute maximum overcurrent is calculated to specify converter device ratings, preventing converter overload or failure. To protect the drive against uncontrollable overcurrents and the resulting torque pulsations, an adaptation of the drive control to avoid such failure states is suggested.