On the stability of a static slip energy recovery drive

It has been reported elsewhere that there are certain instability regions in the operation of the subsynchronous static slip energy recovery scheme for the speed control of a slip-ring induction motor. Eigen value analysis of the linearised model of an induction motor is used to study the stability behaviour of this scheme and the results show that the drive system does not become unstable. The effect of variation in system parameters has also been studied and it has been found that in spite of large variations in the parameters, the drive remains stable. These results are further verified by the transient response of the system to step changes in load torque at certain steady-state operating points which had been described as unstable by other authors. The transient response has been obtained by numerical integration of system equations. At all these points the steady state is reached within a reasonable time.