Reducing Torque Ripple Of Brushless DC Motors With Bi-Directional DC/DC Converter

The brushless DC motor(BLDCM) is a DC motor using the electronic commutation instead of the mechanical commutation. So it has a lot of DC motors'traits of high operating efficiency, like no excitation loss, excellent speed adjusting performance. It also has a series of AC motors'advantages as simple in structure, reliable operation, convenience to maintain because its body motor is permanent magnet synchronous motor. However, because of the existence of the inductance and the characters of the control method, there is ripple in torque output of BLDCM when BLDCM is working in non-commutation state and commutation state. These disadvantages of BLDCM prevent the application of BLDCM from some fields, especially in accurate motor drive. So the research of eliminating the torque ripple has useful performance in practice.First, this paper introduces the basic principle of three-phase BLDCM. The model of BLDCM using a double loop control system has been built based on the mathematical model and the simulation results have proved the reasonability of this model. Second, the traditional types of Pulse Width Modulation(PWM) of BLDCM drive are analyzed on non-commutation state and commutation state. A new method for reducing torque ripple in BLDCM has been used by adding a Bi-directional DC/DC converter(BDC) which is used for avoiding the complicated PWM in the 3-phase inverter to reduce the torque ripple. At last, based on studying the principle of Bi-directional DC/DC converter, the model of the speed control system of BLDCM with a BDC has been built in Matlab/Simulink. The reasonability and validity have been testified by the contrast of the simulation results between this model and the model drived in traditional PWM method. It has given a new way of reducing the torque ripple of BLDCM.