| Compared with the traditional DC motor,Brushless DC motor(BLDCM)is a mechatronic product which uses semiconductor devices instead of mechanical brush for commutation.With the development of power electronics,control theory and motor technology,the advantages of BLDC motor has been found in many ways.Brushless DC motor usually adopts three-phase bridge inverters with two-phase conduction mode,but due to the influence of motor structure and permanent magnet materials,the actual back EMF waveform is not the ideal trapezoidal waveform,which will inevitably produce torque ripple during two-phase conduction;at the same time,in two-phase conduction mode,because of motor inductance,the commutation can’t be completed instantaneously during commutation period and the current change rates between incoming phase and outgoing phase are not equal,which also causes great torque ripple.Considered the principle and structure,brushless DC motor is similar to permanent magnet synchronous motor.The difference between them is that the back EMF waveform of brushless DC motor is non-sinusoidal.Therefore,based on the idea of vector control of permanent magnet synchronous motor(PMSM)and the non-sinusoidal back-EMF of brushless DC motor,a new vector resultant method is proposed in this paper.By introducing a new back-EMF vector and using the d-q coordinate system oriented by the new back-EMF vector,the linear relationship between q-axis current and torque is obtained,and the construction of vector control system of motor is completed.The purpose of vector control of brushless DC motor is realized.At the beginning,this paper introduces the basic working principle and common circuit topology of BLDC motor,then the mathematical model of BLDC motor has been discussed based on the most commonly circuit topology and conduction mode.Then the vector control and its application in PMSM and brushless DC motor are described.After these studies,a new back-EMF vector is introduced for the non-sinusoidal back-EMF of brushless DC motor.Through the new back-EMF orientation and basic derivation,the relationship between torque and q-axis current is obtained,which avoids the complex calculation process of coordinate transformation in vector control of permanent magnet synchronous motor and simplifies the vector control strategy of brushless DC motor.Then,according to the vector control theory mentioned above,the vector control system of BLDC motor is established by speed-current double closed-loop control and is verified by simulation and experiment.The simulation is based on the M file of MATLAB.The stability and accuracy of proposed vector control system under different loads and speeds are tested to verify the effectiveness and feasibility of this method.After that,an experimental control platform with DSP28335 is built to verify the simulation results.The validation of simulation and experiment proves the correctness of the theory and completes the research of vector control strategy of BLDCM. |
