Study On Torque Ripple Suppression Technique Of Permanent Magnet Brushless DC Motor

Permanent magnet brushless DC (BLDC) motors are increasingly being used in industrial and household products because of their high torque density, high efficiency, and low noise. In order to reduce its torque ripple and improve its performance, the design optimization, sensorless control method and commutation strategy for torque ripple suppression of the BLDC motor are respectively studied in this dissertation.Firstly, the influence of the BLDC motor's structure parameters on commutation torque ripple is studied. Using the flat width of the back-EMF as criterion, the gap field and winding structure's influence on commutation torque ripple is analyzed quantitatively. The niching genetic algorithm is adopted, which can optimize multiple objects simultaneously. And the fuzzy logic controller is introduced to realize the self-adaptive regulation of the algorithm's parameters to enhance its convergent speed and stability. This technique is finally used into the optimization design of a BLDC motor. The motor's effectiveness is improved, and the torque ripple is reduced at the same time.Secondly, based on the mathematical definition of commutation torque ripple, the function of commutation torque ripple and commutation instant is deduced, and the proper commutation instants are proved to be the zero crossings of line back-EMFs. Then a novel sensorless control scheme based on the Kalman filter algorithm is presented. With this method, a wide range of speed regulation can be obtained, no neutral voltage, time shifted or silent phase required. Considering the time occupied by sampling, computing and operating in the control process, the corresponding compensation is also implicated.Finally, this dissertation analyzes the influence of the back-EMF, current commutation and PWM control on the torque ripple, and draws the conclusion that by turning on the active phase in advance, the torque ripple can be reduced effectively. The relationship among the optimal turn-on instant, maximums of steady current and back-EMF is concluded. A fussy logic controller is also used to obtain the optimal turn-on instant on line, based of which, a commutation strategy of a sensorless BLDC...