Maximum Output Torque Control in Improved Flux Path Homopolar Brushless DC Motor With Axillary Field by Using Optimal Control of Turn-ON and Turn-OFF Angles in Variable Speed Applications

This paper presents the principles of operation, electromagnetic behavior analysis, and a search technique based on the finite-element analysis in order to determine the optimum control parameters of an improved flux path Homopolar brushless dc motor (IFP-HBLDC). In the proposed IFP-HBLDC structure, a permanent magnet is replaced by a dc excited assisted field coil to control and regulate the flux. In this paper, for different values of speed, maximum torque is determined by calculating the optimal turn-on and turn-off angles and the optimal field current which provides more flexible control over wide ranges of speed. To such aim, the behavior of the commutation angles is analyzed first by a numerical technique using the 3-D electromagnetic field analysis, in which the analysis of the collected data has shown that the commutation angles providing the maximum electromagnetic torque. The technique was successfully used offline to determine the optimum firing angles for achieving the highest drive efficiency to maximize the electromagnetic torque in a prototype 1.5-kW three-phase IFP-HBLDC motor drive intended for variable speed application. The performance prediction and test results are found in good correlation.