Design and Control Features of Switched-Reluctance Motor with Minimization Torque Pulsation

Abstract

Permanent magnet motors are often used as electric drives in middle and low power vehicles due to their high density of power and torque. Neodymium magnets increase its cost, therefore, alternative motors made from cheaper materials are actively sought. One of the most perspective candidates are switched reluctance motors (SRM) which may be designed with ferrite or steel materials. Despite their simple design, low production cost, excellent speed and torque characteristics, simple power distribution between motor sections, high operational reliability, they are not widely used because of insufficient torque and power density and complex electric drive. These problems may be reduced with choosing proper structure of SRM and its drive that provides a constant predefined torque. In the paper an efficient structure of the SRM is proposed and the relationship between the stator and rotor poles for high efficiency is suggested. For determining current shape in stator poles of SRM that provide constant torque electromagnetic processes in SRM are analyzed. As result of analysis a criterion of SRM efficiency base of relationship between acceleration and braking forces is proposed. High efficiency of SRM operation is possible when the brake force Fbr tends to zero i.e. near rotor pole in direction of movement. Such condition has to be achievable permanently during the rotor rotation. For SRM structure with n rotor poles andn+1 stator poles one stator. Such feature allows to achieve high efficiency if simultaneously operates only one predefined pole. Based on such considerations, the total magnetic flow may be split to accelerated flow, brake flow and leakage flow in proportion reversed to magnetic resistance of accelerate, brake and leakage contours. As close the rotor pole to the stator pole as less the relation of braking force to accelerating force. With increasing the rotor poles number, the minimum value of distance is decreased and subsequently the SRM efficiency too. So, SRM efficiency is increased with number of poles. The high-frequency principle of magnetic flux formation is used to minimize torque ripples. A general algorithm for the development of a SRM with the proposed structure are presented. The algorithm consists of following steps: determining the number of poles according to the requirements of SRM efficiency; calculation the stator pole dimensions according to the criterion of providing the necessary force (the rotor pole is the same); check the placement of the stator winding in the core window; correction of the number of poles, if necessary; determining the number of turns of the winding according to the desired current of the converter. The proposed algorithm allows to calculate SRM structure and poles parameters for predefined torque and motor dimensions.