Reserch On The Sensorless Control Technique Of Automotive Brushless DC Motor In Starting And Running

With the advantages of enviroment-friendly, safety and high efficiency, governments attach great importance to the development of electric vehicles and motor control is one of the core technology. Having advantages of a simple structure, reliable operation, high efficiency and good speed regulating performance, brushless DC motors have been widely applied in electric vehicles. As position sensors will increase the volume and the cost of motors, it is particularly significant to study the strategy of sensorless control among the whole speed range and enhance the applicability of automotive brushless DC motors.Inductive method can obtain the rotor’s position at rest, so it gurantees no inversion happening at the startup of the motor. A new launch strategy combining inductive method with back EMF method is put forward in this paper. This method can make the motor start quickly without inversion or jitter.To improve the accuracy of sensorless control, torque and speed closed-loop control is requried. Replacing sensors with sliding mode observer to estimate rotor position has been successfully used in contolling brushless DC motors. Since the EMF of the motor is not a standard sine wave and the chattering error of sliding mode control itself will affect the estimation of the rotor position, this paper designed the sliding mode control system based on PLL phase lock loop. The system can eliminate the negative influnce of system’s chattering and the back EMF in speed estimation. The simulation results proves that the system is reliable.The field-oriented control has advantages in controlling brushless DC motor so it is applied after the startup of the motor. Combining it with the inductive method and back EMF integral method, a sensorless control system at full speed range is constructed. After analyzing the requirements of automotive brushless DC motors, the control objectives of the system are set: start with no vibration, fast response speed, small torque ripple and stable operation.The hardware platform is built based on the TI development suite and the program is written according to the system. Experiment has verified the feasibility of vector control and the rotor position estimation system for brushless DC motors. The results shows that the system has the characteristics of no vibration in startup, fast response speed, small torque ripple and stable operation, which meet the demands of brushless DC motors applied in electric vehicles.