Research On Drive System Of Permanent Magnet BLDC Based On Improved Drive Strategy

Brushless DC machine(BLDCM) is characterized by high power density, high torque/current ratio, high working efficiency, simple and reliable structure, which is introduced in more and more industrial applications. However, the most fatal disadvantage of brushless DC machine is the large current/torque ripple, which limits its application in high precision occasion. Hence, It is necessary to investigate the improved drive system.The conventional BLDCM drive system is powered by the voltage-source inverter(VSI). In this paper, the operating characteristic of BLDCM drive system applied PWM strategy is analyzed. Because of the little equivalent inductance, the stator current exists high frequency current ripple with large Vpp, which may cause more extra rotor loss, decrease the working efficiency, increase the risk of demagnetization. During commutation, because of the different current rate of the turn-off phase and turn-on phase, it forms the commutation ripple. The commutation ripple is usually large and is the low frequency ripple, which may seriously deteriorate the control effect.After detailed analysis, it is pointed that the key to suppress the current/torque ripple is the control of current rate. The current rate is directly determined by the amplitude of voltage space vector. Based on this theory, the extension of the amplitude of voltage space vector is proposed in this paper. A new voltage-switching control(VSC) strategy is proposed in this paper, which contains a multipleoutput DC-DC converter(MOC) which can output high and low voltage is designed in this paper, and a new type of hysteresis current regulator with two ring width. The amplitude of voltage space vector can be changed by switching the bus voltage of VSI, which can improved the control effect overall. During conduction, the dc-link voltage of VSI is automatically switched to the one closed to line-to-line back electromotive force(EMF), which brings less conduction ripple and extra loss. To acquire the most optimal current, a new type of hysteresis regulator with two different width is proposed. With the proposed regulator, during commutation, the dc-link voltage of VSI is automatically switched to the high value to suppress the commutation torque ripple. In addition, the proposed strategy can bring two additional advantages. Firstly, the high voltage can also improve dynamic performance for step torque. Secondly, the output of the multiple-output DC-DC converter can be set as the power source of controller or other equipment, which can save the auxiliary power of the system.Based on the theoretical analysis, the simulation model is built in MATLAB/SIMULINK. The conventional strategy is compared with the proposed strategy. Then the validity of the proposed strategy is verified by the experience. The simulation and experience result both prove that the proposed strategy can not only suppress the conduction and commutation torque ripple, but also can improve the dynamic response of the system.