Torque Ripple Suppression In A Position Sensorless Brushless DC Motor

Keeping good mechanical properties, Brushless DC motor(BLDCM) eliminate drawbacks of DC motor, such as park in brush. So BLDCM is widely used in household appliances, robots, instruments and medical devices. But as torque ripple occurred in commutation section periodically, BLDCM is limited in high-end servo products. Meanwhile position sensor in BLDCM boost costs and reduce system reliability in complex environment. Therefore researching in commutation torque ripple restrain with sensorless control system is of great theoretical and practical significance.Development and research hotspots of BLDCM control system are introduced in this paper. Operating principle and mathematical model is deeply analyzed. Simulation model is built in MATLAB/Simulink with speed and DC bus current double closed-loop, laying the foundation of control system test.Principle of torque ripple in commutation section and the suppression method are analyzed. Meanwhile advantages and disadvantages are described. Back-EMF zero-crossing method is using to position detection. Commutation torque ripple suppression method based on three phase pulse width modulation(PWM) is designed. Hardware detection circuit of commutation section and back-EMF zero-crossing point are designed and integrated to lower the cost.Over-all structure of sensorless BLDCM control system with commutation torque ripple restrain strategy proposed in this paper is introduced. Control system based on TMS320F2812is designed. Design approach of key circuit is introduced; such as three-phase full bridge inverter circuit, auxiliary power supply, power-driven circuit, back-EMF and commutation section detection circuit, voltage and current detection circuit and so on.78.5W BLDCM control system experimental platform is build, magnetic powder brake is using as adjustable load. Experiment result show: commutation torque is eliminated significantly, back-EMF detection is accurate.