Research On Power Factor Control Technology Of Brushless Double-Fed Motor

The brushless doubly-fed variable frequency speed control system is mainly applied to loads such as high-power fans and pumps,and concentrates on the advantages of various motors.The inverter capacity required for variable frequency speed regulation is only a small part of the total power.From the perspective of economic cost,other variable frequency speed control systems are unparalleled.In terms of motor structure,the rotor structure eliminates the brush and the slip ring,which greatly improves the structural stability and reduces the maintenance cost.It is more suitable for the harsh environment.At the same time,the control winding of the stator is connected to the low-voltage inverter to control the high voltage.Motor.However,the structure of the brushless doubly-fed motor is special structure,which results in the internal harmonic content of the motor is larger than that of the traditional AC motor,so the reactive power will increase and the power factor will decrease.A detailed analysis of the power factor of the brushless doubly-fed motor is carried out.In order to decrease the reactive power and improve the power factor,this thesis proposes a power factor vector control strategy based on power winding.Firstly,through the overall introduction of the structure and operation mode of the brushless doubly-fed motor,the principle of electromechanical energy conversion is analyzed.As a new type of magnetic field modulation motor,the brushless doubly-fed motor is quite different from the traditional motor.According to the magnetic field modulation mechanism,the interaction of the air gap magnetic field inside the motor is analyzed,and the process of electromechanical energy conversion is expounded.Secondly,taking the power winding power factor as the research object,the definition of power factor angle is introduced,and the variables affecting the power factor are analyzed.In order to improve the power factor,the effective magnetic field component is modulated from the magnetic field to study the air gap magnetic field of the power winding.The power winding and the control winding current vector are decoupled,which lays a foundation for the power factor control method.Thirdly,the mathematical model of the power winding power factor is established,and the vector control method is introduced to perform the magnetic field orientation.The control winding current is vector controlled.The relationship between the reactive power of the power winding and the excitation component of the control winding current is established,and the system is simulated.,the power factor control of the power winding is realized.Finally,the experimental verification of the power winding power factor control strategy proposed in this thesis is carried out.A related experimental study was carried out with a reluctance rotor brushless doubly-fed motor.Taking the power winding power factor as the core,the V/F control method and the vector control method are compared and the variables affecting the power factor are tested.The results show the correctness of the proposed control strategy.