Simple Technique of Initial Speed Identification for Speed-Sensorless Predictive Controlled Induction Motor Drive

This article presents a simple technique of identifying the initial speed that allows for restarting a sensorless induction motor (IM) drive controlled by a model predictive flux control (MPFC). Initial speed identification is required because, according to the research, the applied current-model reference adaptive system (C-MRAS) can restart the IM after failure only if the error of the initial speed set in the estimator is < 25%. The proposed technique is based on short periods of flux generation for the certain initial speed and observation of the estimated torque respond. The direction of the estimated torque determines whether the real speed is higher or lower than the initial one set in the estimator. In two steps, the algorithm identifies the initial speed with an accuracy of 25%. This allows for a quick restart of the IM from any speed, eliminating the disadvantage of the sensorless drive control system with the C-MRAS speed estimator. The experimental results measured on a 50 kW drive which illustrates the operation and performances of the system are presented.