Study On Commutation Of Brushless DC Motor

Brushless DC motor (BLDC) not only has small size, simple structure, high reliability, but also perform a good DC motor speed control. Thus it has been widely used in household appliances, aerospace, office automation and other aspects. The traditional BLDCM need rotor information, but the signal will be affected by the temperature of the Hall magnetic field or the like, which not only increases the size and cost of the motor and reduces the reliability of the system. Therefore, in recent years control of brushless DC motor without position sensors has been a research focus. In this paper, we will study the control of sensorless brushless DC motor systematic and more in-depth.Firstly the development, the detection of the rotor position and start-up of the BLDC is described in detail. The advantage and disadvantage of position detection of BLDC including back_EMF method、flow-wheeling dinodes method、inductance method and state of observation method are anylisised in detection of rotor position. And then discussed the three-step start-up method、rotor presetting、raising voltage and frequency method and short voltage pulse method. Then the basic structure, conmmutation circuit, detection of rotor position, working principle, the corresponding mathematical model and basic equations of the BLDC is analysis in detail. Secondly the start-up method and back_EMF control of the BLDC are discussed and propose the method the paper use. And we choose dsPIC33FJMC204as the control unit to design the corresponding hardware and software. In the hardware design, the inverter circuit, the detection of back-EMF circuit and the protect circuit are expounded. And for the modular software part, the fuzzy PID control, initialization of the system, start-up of the motor and the check of zero-crossing are expounded in detail. In the initialization of the system, start-up, the check of zero-crossing part parts, the detail settings are expounded and corresponding flow charts are provided.At last, the system of BLDC controlthe is tested and experimental results including start-up、control of BEMF and fuzzy PID control of BLDC control system are analyzed. The correctness and validity of the control system is verified through the analysis of the experimental results.