Research On Commutation Torque Ripple Of Permanent Magnet BLDCM For Electric Vehicle

Permanent magnet brushless DC motor (BLDCM) has advantage of great powerdensity, torque output, simple control and stable run, so it is widely applied in the fieldsof aerospace and industry. With the development of the power electronics andpermanent magnet materials, the BLDCM starts to be used in electric vehicles andhybrid electric vehicles. However, it has a problem of torque ripple due to structuralcharacteristics and conventional commutation method. Especially, the commutationtorque ripple is inherent in the BLDCM. It influences the stability and reliability ofBLDCM and its control system, also limits the fields of BLDCM’s applications. Thispaper starts from the point of reducing and minimizing the commutation torque ripple ofBLDCM, researches on some methods to control it.This paper analyses the basic structure and principle of BLDCM, deduces themathematical model, and establishes a simulation model of BLDCM control system inMatlab/Simulink. The results of simulation show that the model is correct. The modelprovides theories for research on the reason of commutation torque ripple and methodsto reduce and minimize it.The reason of commutation torque ripple is stated in detail in this paper, analysesthe performances of commutation torque ripple under several different pulse widthmodulations. Based on pwm_on method, this paper proposes a new method to reduceand minimize commutation torque ripple: in non-commutation interval, use the pwm_onmodulation; in commutation interval, use the three-phase corporative modulation. Inthis paper, the phase current changes and flows circuit are analyzed in commutationinterval，in addition the duty cycle of each phase is calculated and the mathematicalexpression is proposed.In order to verify the validity of this new method, this paper designs and makes aBLDCM controller for electric vehicle, states the structures and principles of everymodule in detail. In addition designs and tests the hardware and software, also builds atest bed to test the controller with the conventional method and new method. Comparethe results of conventional method and the new method, the results show that theBLDCM controller can operate normally and acquires good performance. Thecommutation torque ripple is reduced obviously with the new method this paperproposed, so the new method is valid.