Research On Sensorless Control Of Brushless DC Motors For Electric Vehicles

Recently due to the advantage of energy-saving and environmental protection many kinds of electric vehicles (such as electric bicycle, electric wheelchair, and electric car) have been widely used. Brushless DC (BLDC) motors dominate the field of drive motors for electric vehicles, because of their simple structure, high efficiency, and excellent performance of speed regulation. Conventional brushless DC motors use position sensor to provide commutation signals, which will increase motor size, system cost and maintenance difficulty. Utilizing sensorless control technology will not only save the considerable cost and space for position sensor, but also simplify the procedures of system assembly and maintenance. Once sensorless control technology becomes mature, it will lead to a significant revolution in the electric vehicle industry.Based on the principle and the mathematical model of the BLDC motor drives, the theory of Back-EMF method and the zero-crossing detecting circuit are introduced and analyzed in detail, then compensation method are proposed.A novel starting method of the brushless DC (BLDC) motors without position sensor for electric vehicles (EV) is proposed, including detecting of rotor position at standstill and a start-up method to accelerate the rotor up to a certain speed where the conventional position sensorless control methods based on the back EMF could work effectively. The whole starting procedure is accompanied with rotor position estimation, which can avoid the temporary reverse rotation and the starting failure of electric vehicles.Further more, specific strategies of starting torque optimization and regenerative braking are developed to improve electric vehicles system performance. This hardware system needs only one current sensor at the DC bus of the inverter and a low-cost general-purpose microcontroller HCS08, which becomes a simple, compact, low-cost, and effective solution for sensorless BLDC motors in the field of electric vehicles. It is demonstrated experimentally that a rapid and stable starting can be achieved by the proposed method.