| Brushless DC Motor(BLDCM)is widely used in many areas due to its simple structure,high efficiency and low cost.The exsistence of rotor position sensor increases the cost of BLDCM and restricts its use in extreme environment.Research on sensorless control of BLDCM has been a hot topic in recent years.Considering the structure difference between salient pole motor and non salient pole motor,this paper carries a further research on sensorless control of different type of motors..The history of Brushless DC control system is introduced and the characteristics of different sensorless control methods are discussed in chapter one.Chapter two introudces the basic knowledge of BLDCM and its control system.Siumlation model of Brushless DC Motor is built based on MATLAB/SIMULINK.Meanwhile,hardware experiment platform and software code are designed for the following work.As for salient pole motor,its inductance varies according to rotor position,which provides possibility for rotor position detection.The article analyzes the difference between terminal voltage sample values during on and off time when motor is injected in a PWM pulse.An initial position detection method based on the theory above is realized with 30° resolution.A new coummutation threshold based rotor positon method is proposed when the motor is running.Considering the method will lose its effectiveness when PWM dutycyle reahces 100%,a detection method suitable for the extreme circumstance is proposed.Full speed range running is realized by combining the methods aforementiond.As for non-salient motor,a new PWN_ON_PWM based rotor position detection method is proposed considering the disadvantages of traditional back_EMF based method.Back_EMF can be directly acquired using this mehod.Combining the existing method of detecting the difference of line voltage,rotor position dection can be realized in wider speed range.Besides,low pass filter circuit is not needed in the new method,so the phase delay problem can be avoided. |
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