A Study on The Electromagnetic Multi-Step Transmission Characteristics of Interior Permanent Magnet Synchronous Motors

Abstract

In this paper, electromagnetic multi-step transmissions are introduced as a method for increasing the torque and efficiency of electric vehicle driving motors. Motors using permanent magnets have a limited ability in increasing the speed as the back electromotive force increases as the speed increases. The electric vehicle driving motor performs field-weakening controls to increase the speed after the rated point. Field-weakening control increases the rotor’s speed by weakening the magnetic flux of the field. At this time, the output is constant as the speed increases. Motors have voltage limits, which also affect the maximum speed of the motor. In order to improve these constraints, there is a case study of electromagnetic shifting phenomena. Examples of the research include the wye-delta method and the method of changing the number of equivalent serial turns. As in the case of previous studies, the problem of increasing back electromotive forces as the speed increases is solved. In this paper, we propose a method to increase the maximum speed by changing the number of parallel paths. In order to lower the back electromotive force at high speeds, the number of parallel paths of the stator windings changed via the thyristor. As the number of stator parallel paths increases, the back electromotive force decreases. When the back electromotive force is lowered, the torque that can be output is reduced, but the maximum speed can increase as the voltage is also lowered. Before shifting, the number of parallel paths is set to two to satisfy high torque at low speeds. After shifting, the maximum speed can be increased to 4 with the number of parallel paths, which can broaden the operating range of the motor. In addition, the resistance of the stator windings is reduced by increasing the number of parallel paths in the high-speed region. The loss that accounts for the largest proportion of the electromagnetic loss of the motor is copper loss, and by reducing it, the efficiency increased. As a result, it increases the operating area and simultaneously increases the high-efficiency area. In order to analyze the electromagnetic characteristic, a finite-element-method-based simulation was used.