Research On Sensorless Control System For Brushless DC Motor Based On DsPIC

Brushless DC (BLDC) motor has found widespread applications in the industry fields,due to not only its good performances at speed regulation and high efficiency as traditionalDC motor, but also its simple structure, convenient maintenance and long service life as ACmotor. Furthermore, the applying of sensorless control strategy can reduce the size and costsof the motor, eliminate many potential safety problems caused by the sensors and make theBLDC motor be more adaptable for some specific applications such as high-temperature,high-pressure and strong-corrosion. Therefore, the research on the sensorless control ofbrushless DC motor has revealed a wide range of practical value.After introducing the development of BLDC motor and its control strategy, this thesisanalyzed the structural characteristics and operating principle on this type of motor, andestablished the corresponding mathematical model. Then, this thesis discussed serveral crucialtechnological problems that implementing sensorless control, and proposed a simple andreliable method for obtaining the zero-crossing points of Back EMF in the nonconductionphase. Digital filter based on the majority function has been designed to eliminate theinterference of false zero-crossing events, which avoided the phase shift produced by thetraditional RC low-pass filter.“Three-step” startup method is also analyzed in details, whichcontains twice rotor pre-locations, one acceleration section and finally the switchover to thesensorless operating mode when the motor speed reaches a certain level.Based on the high-performance16-bit digital signal controller dsPIC60F6010A, made byMicrochip Company as an appropriative chip for motor control and power transformation, acontrol system of BLDC without position sensors has been designed. The bus current issampled and tranfered to the microprocessor, constituting the current closed-loop control. Theactual speed calculated from the Back EMF signal is compared with the reference speed, andthe error is regulated by a PID controller, constituting the speed closed-loop control.Combining with the control strategy and the peripheral resources of the microprocessor, thehardware circuit of the entire system has been designed, and the software system has beenprovided in the form of flowchart as well.Finally, some experimental results have been presented and analyzed. The practicaloperating results have verified the validity and feasibility of the proposed control system.