Three-phase Brushless DC Motor Control System For Electric Vehicle

New source of energy and environmental protection are the demands of the development of the times. Owing to the advantages of energy-saving, pollution-free and so on, there is no doubt that electric motorcycles will turn to be the backbone of new energy vehicles. Based on the excellent speed performance and load characteristics, Brushless DC Motor (BLDCM) has been broadly adapted to the driving system.In this paper, the history of the development of electric motorcycle and BLDCM is displayed firstly, followed by the statement of developmental status of three-phase BLDCM control system. Then the paper analyzes the structural features, operation principle and mathematical model of three-phase BLDCM. Furthermore, the design scheme of the control system's hardware and software is presented in detail. Considering the design requirements and cost-effective, LC87F0808A, an product of Sanyo Semiconductor Corporation, is chosen as the controller.To solve the compatibility issue between the controller and motors maked by different manufacturers, this paper puts forward a method of identifying three-phase BLDCM phase sequence automatically. This method also applies easily to the motors who's Hall is installed every 120°or 60°.The system puts forward a new method of detecting phase current through testing tube voltage drop of the power switching device, adopting the full-bridge modulation. The tube voltage reacts quickly, and is easy to predict and compensate for temperature drift without additional current detection devices. Although it is easy to control the phase current peak by means of measuring phase current, it still need to limit the power output current (bus bar current) through limiting phase current. This paper presents the conversion between phase current and bus bar current based on the hardware system and modulation mode.The motor will generate vibration and noise when in start-up and low speed state, owning to the resonance between motor and bodywork caused by torque ripple due to phase commutation. To solve this problem, a method of delay commutation is adopted, which asks for adjustment on the PWM duty cycle when three phases turn on simultaneously. This paper gives specific adjustment method.The paper presents the experimental result and conclusion in the end.