Research On Control Strategy Of BLDCM Through Sensorless Technology

BLDCM is widely applied in computer, household appliances, vehicles, etc. Because itnot only has the good characteristics of start and speed control with conventional DC motor,but also has the good features of simple structure, low noise, large output torque and so on.Traditional BLDCM control systems use the position sensor in the motor to detect the rotorposition signal. However, the presence of sensor in the motor increases either the size andweight or cost of production and difficulty of maintenance. Therefore, research on thetransmission system of sensorless technology has become the hot spot in the control field.The basic working principles of BLDCM from electrical are introduced by analyzing itsstructure and composition. Combining with the selected work principle, the mathematicalmodel and speed of controlling model of BLDCM are established. Sensorless control methodhas poor low-speed performance, difficult of staring control, filtering phase shift and otherissues at present time. Combined with the characteristics of the direct back EMF method andthe flux three harmonic method in commutation logic, a kind of Low/High speed controlstrategy based on speed control areas is proposed, named L/H control method. The speeddomain of the BLDCM is divided into low speed and high speed. The corresponding controlmethod is adopted in different area, which greatly broadens the speed control area of BLDCM.A new back EMF logic level integration is adopted to improve the performance in low speedarea of the controller, while in the high speed area the third harmonic back EMF is adoptedwhich is easy to implement and the phase shift is small. In order to switch successfullybetween the different control method, the transition zone is set to use hysteretic switchingaction mode. Meanwhile, basing on the traditional "three-stage" start method secondarypre-position is proposed and startup curve is optimized, so that the motor can be startedquickly and smoothly. At the same time, regenerative braking principle is used to bring theenergy generated of breaking torque back to DC power supply by using the boost choppertechnology. The compensation method is given for the signal phase shift.The software and hardware system are designed by using the L/H control method, andthe simulation system is established in the Matlab/simulink environment to test the rationalityof the L/H strategy. According to the designed hardware platform, the L/H control method forBLDCM is verified of the driver status for different structures and speed areas. Experimentalso compares with the effect of position sensor and sensorless control, which proves thefeasibility of the control strategy.