Research On Direct Torque Control Of Coil Assisted Excitation Brushless DC Motor

Reluctance motor has many advantages,such as simple structure of stator and rotor,independent operation of each phase winding,large starting torque,small starting current,strong adaptability and low loss,etc.It has attracted wide attention in recent years.Therefore,this thesis proposes a new type of Coil Assisted Excitation Brushless DC Motor(CAE-BLDCM),which is improved from the traditional switched reluctance motor.However,because the magnetic circuit of CAE-BLDCM is always saturated during its operation,the CAE-BLDCM system has strong non-linearity,and the turn-on and turn-off of power converter will also result the large torque ripple occurs in the middle of two-phase electrification,which makes the CAE-BLDCM produce large torque ripple and vibration noise during operation.These shortcomings make the CAE-BLDCM unsuitable for operation under specific operating conditions,which limits the scope of application of the motor in industry.At the same time,because it is difficult to get the precise mathematical model of the CAE-BLDCM,it is very difficult to analyze the cause of torque ripple and design the method to reduce it.In order to reduce the torque ripple and improve the operation efficiency of the system,the direct torque control system of the CAE-BLDCM is studied in this thesis.By introducing the direct torque control technology into the control process of the CAE-BLDCM,the torque ripple of the motor is effectively reduced.Firstly,the structure and operation principle of CAE-BLDCM are analyzed,the mathematical model of the motor is established,and three basic control strategies of CAE-BLDCM are introduced.On this basis,the direct torque control method of CAE-BLDCM is studied in this thesis.In order to improve the system efficiency,DTC method based on the torque sharing function is designed,the torque sharing function is improved,the system efficiency is further improved,and the influence of the central coil on the torque is added to make a more reasonable design.Thus,the torque ripple of the CAE-BLDCM can be improved.Secondly,the flux characteristics of CAE-BLDCM are measured by experimental measurement,and the mathematical model of the motor is deduced.The simulation diagram of direct torque control system is built in MATLAB/Simulink.The direct torque control methodsof different torque sharing functions(linear TSF and cosine TSF,with and without central coil)are compared and analyzed.Finally,a three-phase 9/6 pole CAE-BLDCM motor control system experimental platform.The hardware of the system includes control circuit,IGBT driving circuit,power converter circuit,current and voltage detection and position detection circuit.And the software design process is given.