Torque Ripple Suppression Technique In Permanent Magnetic Brushless DC Motors

The brushless DC motor(BLDCM) is a DC motor using electronic commutation instead of the mechanical commutation, so it has excellent characteristics of DC motor, such as good start and timing performance, and on the other hand it overcomes the friction disadvantages of ordinary DC motor radically with its simple brushless structure. It has been extensively used in many industrial domains, such as aviations, robots, digital machine tools, and in medical, or home appliances. But the BLDCM has the disadvantages of torque pulsation, which is in the way of achieving accurate position and speed of higher performance. The objective of this dissertation is to study the control technology to minimize the torque pulsation of BLDCM.Firstly, introduce the working principle and conducting mode of Brushless DC Motor(BLDCM), establish the MATLAB simulation through on the basis of mathematical model, which was validated by emulation. Then, the effects on the torque ripples induced by the PWM methods are studied, and the conclusions are reached: the commutation torque ripple varies with the rotor speed; The commutation torque ripples in those PWM methods, in which the upcoming phase is modulated, are lower than that in those PWM methods, in which the non-commutation phase modulated; A method of restraining the torque ripples varying the speed are put forward; As for the non-commutation torque ripples, a novel torque ripple suppression scheme, PWM_ON_PWM, was analysed and researched. In the proposed PWM method, the diode freewheeling currents in the inactive phase are eliminated completely , so that the torque ripples caused by the conventional PWM methods in the non-commutation interval were eliminated.