Research On Torque Ripple Minimization Techniques For PM Brushless DC Motor

The objective of this dissertation is to minimize the torque ripple of BLDC motor. At first, the dissertation analyses the principles, the operation theory and the control techniques of BLDCM (Brushless DC motor). Then according to the different BEMF of different BLDC motor, the dissertation analyses the torque ripple in the BLDCM with ideal 120掳 trapezoidal waveform BEMF and non-ideal BEMF waveform respectively. Further more the dissertation presents different novel control techniques of the torque ripple minimization in BLDCM.The ideal BEMF waveform of BLDCM is trapezoid with 120! platform width. In the 120° conduction mode, the stator current is not ideal due to the stator inductance, and the torque ripple occurs. Firstly, the dissertation presents principles of commutation torque in the condition of ideal BEMF waveform. In addition, the effects on the torque ripple caused by the PWM modes, overlapping commutation and so on are analyzed, and the conclusion is reached: the commutation torque ripple varies with the rotor speed. Secondly, the applicable speed ranges of the motors using the overlapping commutation techniques are derived. Finally, the MATLAB simulation results verified that the proposed control technique is able to minimize the commutation torque ripple.The non-ideal BEMF waveform of BLDCM is often caused by two facts. One is that the platform width of BEMF waveform is less than 120°; the other is the cogging harmonics existed in the BEMF waveform. Aiming to minimize the torque ripple in condition of non-perfect BEMF waveform, the dissertation present a optimum current tracking control technique. In the proposed technique the BEMF waveform of BLDCM need to be measured in advance at first, through computer simulation and frame transformation, the optimum q-axis current command is achieved. In order to minimize the torque ripple, the d and 0-axis current command should be zero. Furthermore, through reference frame transformation from dqO-axis to abc-axis, we can get the optimum current command in static abc reference frame. Inaddition, the current hysteresis control is adopted. The MATLAB simulation results verified that the motor in the control technique produces hardly any commutation torque ripple.The hardware and software system are presented in the dissertation. Many problems are encountered in the research, and the accordingly solutions are also given in the dissertation.