Research Of Sensorless Brushless DC Motor Control System

Permanent magnet brushless DC motor has the the advantages of small volume andlight weight. It not only has a series of advantages of the AC motor of simple structure,reliable operation, convenient maintenance, but also has the DC motor of highefficiency, good speed performance and other advantages. It has been widely used in themedical equipment, instrumentation, office automation equipment, textile chemicals andhousehold appliances and other fields. Permanent magnet brushless DC motor rotorposition is generally detected by an external type position sensor, due to externalposition type position sensor motor increased size and cost, excessive connection makesthe reliability variation, output signals are easily jammed, canceling position sensor andusing no position sensor detection becomes very necessary. At present, research ofsensorless control of brushless mainly concentrates in three aspects: one is a brushlessDC motor rotor magnetic pole position detection method. Due to the sensorless controlcancel position sensor, need to identify rotor magnetic pole position through thedetection of other motor parameters; the other is the sensorless brushless DC motorrotor position and starting. Because the motor in static or low speed condition, windingback-EMF zero or evey small, it is difficult to judge the rotor magnetic pole position,thus must use other methods of motor rotor positioning and starting; another is thebrushless DC motor torque ripple problems. Due to the uneven distribution of stator slotgap, current fluctuations and other reasons to form the torque ripple, so the torque ripplesuppression is also one of the main problems of the brushless DC motor with sensorlesscontrol.This paper was focused on the study of rotor magnetic pole position detectionmethod of sensorless brushless DC motor. Based on detailed analysis of the systemstructure and working principle of brushless DC motor, the mathematic model ofbrushless DC motor was established, the brushless DC motor basic equation was writing.Then the brushless DC motor mechanical characterisitic and regulating characteristicwas analyzed and the brushless DC motor and DC motor has good regulationperformance was validated. One kind method of rotor position for brushless DC motorbased on the line voltage difference was proposed, the back-EMF zero-crossing was gotback by calculating the line voltage difference. It is concluded the premise condition of applicability of this method is nonconduction phase without the freewheeling current. Non conduction phase currentgeneration time, amplitude, change situation, freewheeling diode conduction andcommutation impact in various PWM modulation mode was analyzed. The PWMmodulation mode which is appled this method was obtained.Control system simulation model under Matlab/Simulink environment based onthis method was established, simulation studies were performed. Each function modulein the system was introduced in detail. Finally the simulation results basically coincidewith the theoretical analysis was verified through the simulation waveforms, system ofsmooth starting, commutation accurately. Sensorless control simulation system of theBLDC Motor based on line voltage difference can accurately run.