Optimization of the loadability of an induction servomotor with a coupled electromagnetic-thermal model

In motion control, high servomotor over loadings are required to maximize the acceleration and deceleration rates and thereby the process throughput. Typically the pull-out torques of the induction servomotors vary in between 3...5 times the rated value, while with standard industrial motors, the ratio is typically between 1.6...3. As the stator copper losses are proportional to the stator current squared, the only method to enable occasionally such high over loadings, is to utilize the motor thermal capacitances to slow down the heating of the machine. In this paper, a coupled electromagnetic-thermal model is presented, that takes into account both electromagnetic and thermal transients, and the model is then utilized to find the optimal control strategy, that minimizes and compensates the drawbacks due to the heating. The model is implemented in the Matlab-Simulinktrade environment, and the simulation results are verified with a 4 kW prototype machine in the laboratory