Study On Sensorless Control System Of Brushless DC Motor

Along with the rapid reform of the economic system and the development ofmarket economy, people pay more attention to environment, energy issues. Highefficiency, energysaving,environmental protection become an important developmenttrend in the market, brushless DC motor which has high efficiency, good speedperformance, simple structure and a series of advantages is gradually extended tothe industrial automation, military equipment, and civilian life in every field. In thispaper, take brushless DC motor as the research object, the position sensorless controlmethod has been carried on in-depth study.The composition and working principle of this paper brushless DC motor aredetailed analyzed, and the mathematical model of brushless DC motor is also build.The topology of three-phase six switch driven selection and the modulation ofH_PWM-L_ON are chosen in this paper. Based On the basis of traditional counterpotential detection, this paper puts forward an improved direct counter potentialdetection principle. And through the PWM-ON and PWM-OFF two differentsampling methods for mathematical analysis, the back EMF sampling during thePWM–OFF is determined. Based on ST7MC2S4of St microelectronics Company,the control system of BLDC motors is designed according to the operation principleof brushless DC motor. The control method of sensorless brushless DC motor ispresented, and the system’s simulation model is established based onMatlab/simulink software platform in order to verify the design. The system ofhardware was designed according to the experimental data obtained form thesimulation. The control strategy of speed, current double loop, and combined withthe back EMF three-resistance detection method was adopted which makes thesystem have good control performance. The results show that the control system ofBLDCM can make the motor start smoothly and have automatic commutation withreliable operation and speed regulation.