Research On Sensorless Control And Advance Commutation Control Of Brushless DC Motors With 180° Commutation

For the brushless DC motor(BLDCM),180 degree commutation method can increase the voltage utilization and the torque output capality,which is suitable for high speed operation while the bus voltage is limited.This paper had some research on the sensorless control and advance commutation control method of the BLDCM,which is important for extending the application range of the motor and improving the performance of the motor.In this paper,the mathematical model and working principle of the BLDCM with 180°commutation is introduced.The a new sensorless control method is proposed for the BLDCM with 180°commutation.A phase current based function and bus voltage are compared to get the zero-crossing point(ZCP)of the phase back electromotive force(back-EMF),which is important for the commutation point.Compared with the convention back-EMF ZCP detection method with 120°commutation,this method is able to operate in heavy load.The influence of shapes of phase back-EMF for detection precision is also discussed.As the effect of winding inductance can make the phase current retarded from the phase back electromotive force(back-EMF),especially when the motor speed is high,an advance commutation control method for BLDCM with 180°commutation is proposed,which means the switch turns on with an advanced angle compared to the ZCP of the back-EMF.A phase current based function and bus voltage are compared to get the ZCP of back-EMF,a proportional-integral(PI)controller is used to eliminate the phase difference between the two signals,which are the ZCP signal of the phase current and the ZCP signal of phase back-EMF.This method can make the phase current and back-EMF have the same phase,which can improve the work efficiency of the motor.For the proposed sensorless control algorithm and the advance commutation control method,experiments were implemented with a BLDCM control system.As the digital controller cannot calculate current function and detect rotor position as precise as requirement when BLDCMs operate at high speed.The hardware is implemented in comparison module for current function and bus voltage in this paper.By cooperating with software system,the two control method is realized.Finally,the experiments were implemented and verified the validity.