Research On Start Methods Of Sensorless Brushless DC Motor

permanent magnet motor because of its simple structure, small size, light weight, low loss and high efficiency attract more and more people’s attention, it have been broadly used in the industrial drives. BLDCM because of its adventages of simple control, low cost, higher power density has been widely used in electrical cars and household appliances and other fields. Sensorless BLDCM control can reduce cost and improve reliability, thus it become a important research direction.From the analysis and research to the method of BLDCM Sensorless control, I focus on the analysis of several key issues for BLDCM sensorless control.In this paper a detailed description of the structure of the ontology of the brushless DC motor has been offered, analyzed how the motor operate in two two power mode and three three power mode, then given the mathematical model of the brushless DC motor.According to the established mathematical brushless DC motor, a simulation model of a sensorless brushless DC motor control system has been built and also the model of BLDCM control with a sensor. Those simulation models are created in the Simulink environment of MATLAB. The feasibility of back EMF zero crossing detection method and the feasibility of a three-stage start are verified by simulation.Sensorless BLDCM control system perform as well as the BLDCM control system with a sensor.In order to analyze the starting characteristics of the brushless DC motor without position sensor, Two starting methods have been researched,the three-step starting mothod and the test pulse injection method.The first mothod is easily influenced by the various parameters of motor particularly the load.the second is less affected by the motor external parameters, smooth start can be accomplished under complex loads.Deep analysis has been given to how the position error impact on motor commutation. When the peak current of the motor in the former indicates a advanced commutation, when the peak current of the motor at the back indicates a delayed commutation, then it has given a position compensation method. The experiment result proved the feasibility of this method, the compensation method for motor commutation get more close to the optimal commutation logic.