Research Of Sensorless Brushless DC Motor Start Method

Brushless DC motoers(BLDC) are improved in performance and ever-increasingly utilized in many fields,inciding household appliances and industrial controllers.With its wide application in many fields,the traditional sensor control method is not applied in some application.so sensorless control method emerges as the times require,especially Back-EMF method is more and more useful than the traditional sensor control method.Now,it's becoming one of the most popular trend in BLDC control system.Based on the principle and the mathematical model of the BLDC motor drivers,the theory of Back-EMF method and the zero-crossing detecting circuit are introduced and analyzed in detail.But when the motor is at standstill or at a low speed,it is impossible or very difficult to get the position information from back-EMF.Therefore a particular method to start up the motor from standstill is needed in sensorless control method system based on Back-EMF detection.In this paper,the advantage and disadvantage of the common start-up method are analyed,and a novel start-up method is proposed which called new three-step-initial staring,it consists of three-step-initial rotor position estimation, new three-step-initial,turning to back-EMF driving.the experimental results have demonstrated its well starting performance.Rotor position detection error and intrtuption is also investigated in this paper,then restraination method are proposed.In the end, with software design accomplished in AVR studio 4,the hardware system of Brushless DC motors sensorless control based on ATmega 64 is built as an experimental platform.Experimental results and practical utilizations substantiate that the hardware platform and associated software design can supply good sensorless control capability; indicating the sensorless control system can greatly meet the required performance, and the experimental results have shown the accuracy,rapid response and high reliability of the proposed method.