It is well known that the efficiency of induction motor drives under partial load can be improved via manipulation of its field excitation. Among the numerous loss- minimization schemes previously proposed, the scheme that uses motor power factor as the main control variable has the advantages of high sensitivity and ease of implementation. But how the optimal power factor commands can be generated is not well documented. In this paper, a loss-minimization scheme that uses power factor control with automatic measurement of the minimum-loss power factor commands for vector-controlled induction motor drives is proposed. A fuzzy logic compensator is used in the controller to improve the accuracy of the command generator. The scheme is practical for implementation and does not require a priori knowledge of motor parameters. For verification, the loss-minimization controller was tuned according to the data from a set of commercially available induction servo motors ranging from 1 to 50 hp. The computed results shown that the errors between the calculated and the theoretical optimal power factor commands are all within 0.03. In addition, the experimental results have validated the effectiveness of this scheme in minimizing the motor operating losses at light loads.
Journal of the Chinese Institute of Engineers=中國工程學刊 26(1), pp.37-45