Current Based Restarting Method for Rotating Sensorless Induction Motor Drive

Variable frequency industrial drives are tuned to start from a standstill. However, in most of industrial applications, IM may spin due to external force offered by wind, load, etc. Apart from this, due to short power interrupts, the drive may trip, and bringing the motor to a standstill may require several hours due to its high inertia. In these scenarios, restarting the IM may draw a huge inrush current (which causes electric/mechanical shock to the system) if the speed is not known. A simple current based restarting (i.e., flying start) algorithm has been proposed in this letter for induction motor drives used for high inertia loads. In this algorithm, speed of the motor is estimated, by searching the minimum stator current during the input frequency sweep (from rated frequency to zero frequency) of the IM. The proposed algorithm is simple, and easy to implement since there were no controllers involved. Moreover, this algorithm is independent of the parameters of the motor. The performance of the proposed algorithm is verified using rapid control prototyping in the form of real-time results using Typhoon HIL platform and performance is found to be satisfactory.