Study On BLDCM Sensorless Control System Based On DsPIC

Brushless DC Motor (BLDCM) is a kind of electromechanical integration machinery,and it has been rapidly developing in recent years with the development of power electronictechnique and the appearance of new type of permanent magnet material. It takes electricalcommutator instead of mechanical commutator. Traditional BLDCM have a sensor whichdetects the position of the rotor and the controller receives the rotor position information bysensor. The sensorless technique in this paper gets the rotor position information by detectingthe phase-current and phase-voltage. Using attachment of sensorless control not onlyovercomes some problem generated by the sensor, but also expands the application range ofbrushless DC motor further. With widely used in many fields, sensorless control is more andmore useful than sensor control in many applications.This paper introduces traditional Back Electromotive Force (BEMF) method, and theprinciple of BEMF method is dissertated in detail. In addition, the zero-crossing of BEMFsensing method is concretely studied in the paper, and the circuit about simple zero-crossingof BEMF sensing is designed. The reason of rotor position error in the zero-crossing ofBEMF sensing method is analyzed, and the compensation methods are also proposed in thesoftware design. Considering BEMF is not easy to detect when voltage is low, this paperintroduces the three-step start technique which including the rotor pre-setting, acceleratingand state-changing step is discussed carefully.In this system, the BLDCM used on electric bicycle is taken as a sample and thedsPIC30F3011 type Digital Signal Control (DSC) is chosen as the controller core. At thesame time, the hardware of the BLDCM control system with BEMF method is designed, eachpart of this system is introduced deeply. In addition, the methods of reducing electromagneticinterference are also analyzed. Considering the advantages of the dsPIC30F3011, taking fulladvantage of resource in chip, the control software is designed. The experimental results showthat the control system can make the motor start successfully. What's more, the control systemrealizes the motor's correct commutation and smooth running. Finally, the feasibility of thesystem design is proved in the results.