A Position Sensorless Control Strategy For BLDCM Based On Flux-Linkage Function

BLDCM has many advantages including simple control,stable operation and easy maintenance,so it has wide applications in various fields including aerospace,industrial applications and household products.Rotor position sensor is usually required in order to realize precise commutations.However,the installation of the position sensor may do harm to the reliability of motor operation.Therefore,the sensorless control is of great importance to the improvement of the overall performance of the motor system.In this paper,the relationship between the commutation points and the permanent magnet flux linkage is obtained by analyzing the permanent magnet flux linkage of the three-phase windings in the commutation point.And three flux linkage functions which are independent of the motor speed are constructed by using the line to line permanent magnet flux linkage.In an electric cycle,each flux linkage function has two extreme value changing points,which are located at the intermediate time of the two commutations.So the commutation point of the motor can be obtained by detecting the extreme value changing point of the flux linkage function and further delay 30 degrees.Since each flux linkage function can only provide two commutation points,the flux linkage function and sector relationship table are established in this paper.So by selecting the corresponding flux linkage function in different sectors,all the commutation points needed for the motor operation can be obtained.In order to simply the hardware circuit design,three-phase current control method is adopted and the terminal voltage of the three-phase windings can be calculated by the switching state of the three-phase switch tubes.Compared with the traditional back EMF method,the proposed method can extend the range of motor speed with position sensorless control,and reduce the commutation error of the motor.Finally,the experiment platform with DSP+FPGA as the core controller is set up.Experimental results under different operating conditions show that the proposed method is suitable for a wide range of speed and has high commutation accuracy.Under the same experimental conditions,by comparing the commutation error of the proposed method and the commutation error of the traditional method,it can be seen that the proposed method has smaller commutation error.