Research In Torque Ripple Reduction Of Brushless DC Motor

Brushless dc motors with trapezoidal back-EMF have been widely used due to their high power density and easy control method. When the commutation occurs, the torque ripple may be generated in this period because the commutation requires a finite time due to the inductance and back-EMF. Also, if the machine has a nonideal trapezoidal back EMF, the torque ripple appears even though rectangle currents are fed. These torque ripples have made BLDCM less suitable for high performance position applications. In this paper, torque ripple suppression techniques have been studied in details and some novel effective measures have been proposed.At first, the dissertation analyses the principles, the operation theory and the control techniques of BLDCM. 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; At last, a method of the torque control attenuating the undesired torque pulsation for brushless dc motor with nonideal trapezoidal back EMF is presented-direct torque control. In . which the applied output voltage is calculated from the reference torque and the torque of the previous step in the two-phase conducting period and the in the commutation period.The brushless DC motor is modeled by using Matlab/Simulink in this thesis. A DSP(Digital Signal Processor) based control system is designed for experimental use. The validities of the proposed methods are strongly supported by the Simulink and experimental results.