AN IMPROVED METHOD FOR ANALYSIS OF PERMANENT MAGNETIC BRUSHLESS DC MOTORS CONSIDERING THE WINDING INDUCTANCE

摘要

There are obvious errors to predict the performances of the square wave permanent-magnet brushless DC motor using the general circuit model omitting the winding inductances, when the motor is operating at high speed. The winding inductances are key components of the design and analysis of the high-speed permanent-magnet brushless DC motors. In this paper, the equivalent circuit equation of the permanent-magnet brushless DC motor was constructed on the basis of the basic voltage flux linkage equations. As far as the three-phase full-bridge square wave motors with wye-connected phase windings and with two transistors conducting at any time was concerned, its fundamental operational patterns were revealed by means of equivalent circuits. For the first time, the analytical expression of the phase current was presented, and the average static current model considering the windings inductance was also developed. The reasons why the windings resistance on the operational condition is larger than its direct current value and why the torque constant K_T is larger than the back-EMF constant K_E and why its operational characteristic is non linear, were theoretically explained by this model.