Researcch On Electromagnetic Design Method Of The Cage Rotor Brushless Doubly-Fed Machine

At present,there are two main types of VSCF motors,including brush doubly-fed motor and permanent magnet synchronous generator.Brushless doubly-fed motor requires a small frequency converter capacity,adjustable power factor,but the motor itself has a brush and slip ring structure,low reliability,high maintenance cost;Permanent magnet synchronous motor requires large frequency converter capacity and high total system cost.Compared with the former two,the brushless doubly-fed motor saves the brush and slip ring,improves the reliability,reduces the maintenance cost,and requires a small frequency converter capacity,the total cost of the system is low.Because of these advantages,brushless doublyfed motor has a wide application prospect in the field of wind power generation.In recent years,many scholars at home and abroad have conducted in-depth research on the electromagnetic design,mathematical model,control strategy and motor structure optimization of brushless doubly-fed motor.Although fruitful results have been achieved,the design method of brushless doubly-fed motor is still immature,which requires further in-depth research.The design methods of the motor are mainly based on "field" and "path".The calculation method based on "field" has high accuracy,but its calculation time is long and the physical concept is not clear.The calculation method based on "path" has clear physical concept and simple process,but the calculation progress is lower.Therefore,"path" is widely used in motor design.The structure of brushless doubly-fed motor is complex,and the calculation error of traditional "path" calculation method is very large,so this paper proposes an improved "path" calculation method that subdivides the motor core magnetic circuit more accurately,which can accurately calculate the parameters and performance of brushless doubly-fed motor.This paper studies the brushless double-fed motor with cage rotor based on this method as follows:1.Parameter calculation of brushless doubly fed machineThis paper improves the original laboratory brushless doubly-fed motor equivalent magnetic circuit model,proposed a based on this model can reflect the motor internal magnetic circuit calculation method,the solution of the "path" calculate method can accurately between the motor stator and rotor inductance parameters,by means of finite element simulation,winding function method,and the "path" between the results of numerical method,effectively prove the validity of the equivalent magnetic circuit calculation method based on the new.The inductance parameters of power winding and control winding are also calculated.2.Calculation of rotor short loop current of brushless doubly fed machineBased on the analysis of cage of internal magnetic field Angle of brushless doubly-fed motor,brushless doubly-fed motor in steady state is derived when the rotor induced voltage analytical expression,the combination of rotor inductance parameters of the equivalent magnetic circuit calculation and generation of the mathematical model of multi loop using the semi-analytical method to solve the cage rotor brushless doubly-fed motor short circuit ring current amplitude and phase,compared with the finite element simulation results,proved that the semianalytical method can accurately calculate the rotor end ring current amplitude and phase,the cage rotor brushless doubly-fed motor design provides a theoretical basis.3.Air gap magnetic density calculation and harmonic analysis of brushless doubly-fed motorKnown in two sets of stator windings is calculated in the input current and through the equivalent magnetic circuit of rotor end ring current situation,again using the equivalent magnetic circuit model,according to the magnetomotive force and the current,the magnetomotive force and the relationship between the magnetic flux,calculate the air-gap magnetic field of the stator winding produce,air-gap magnetic field of rotor end ring and synthesis,the air-gap magnetic field of the rotor,using the finite element simulation demonstrate the validity of the semi analytical calculation results.The harmonic components of air gap magnetic density are obtained by Fourier decomposition,and the source of harmonic components is analyzed,which provides a theoretical basis for optimizing the structure of stator rotor.4.Calculation of iron loss and electromagnetic power of brushless doubly-fed motorThis paper analyses the composition of brushless doubly-fed motor iron loss,based on the equivalent magnetic circuit model can exactly solve any point in the core of magnetic time waveform,according to the calculation method of each part of the iron in the core consumption respectively to calculate the stator,rotor loss of teeth and yoke,effective considering the rotation of the motor loss and higher harmonic loss,compared with the finite element simulation results,verify the semi-analytical method to calculate the accuracy of the brushless doubly-fed motor iron loss.5.Matlab program writingThe calculation program of the above semi-analytical method is written by Matlab software.The new parameters and performance can be obtained by changing the input parameters of the motor.The calculation method is applicable to all cage rotor brushless doubly-fed motors,and is provided for the cage rotor brushless doubly-fed machine.The "path" calculation design program.