Research On Axially Laminated Anisotropic Rotor Brushless Doubly-Fed Machine

Brushless Doubly-Fed Machine(BDFM)has a novel structure,it runs reliably and the inverter has small capacity.When it is used as motor,frequency conversion speed regulation can be realized.As a generator,it can be used for variable speed constant frequency power generation.The performance of BDFM is largely dependent on rotor structure.There are three kinds of rotor structures: the special cage,wound-rotor and reluctance structure.The special cage structure is suitable for large capacity motor,but the air gap magnetic field harmonic content is large and the efficiency is low;The rotor winding of the wound-rotor structure can be designed flexibly,the harmonic content of the air gap magnetic field is small and the efficiency is high.Now it has entered actual usage status,but the motor may be unstable at some operating points.The reluctance rotor motor has the advantages of low loss and high efficiency,which is suitable for high speed operation,but it is difficult to design,and the method to weaken the harmonic component of the air gap magnetic field is limited.To further understand the characteristics of this kind of motor,in this dissertation,a kind of reluctance structure: axially laminated anisotropic(ALA)rotor BDFM is studied and focus on researching the internal electromagnetic relationship and the influence of the rotor parameter variation.Through the analysis of rotor parameters,the measures that can be taken to optimize the performance of this motor are illustrated.In order to facilitate further research in the future,the finite element software is used to verify the conclusion.The main contents of this paper include:Firstly,This paper briefly reviews the development history of BDFM and the main work done by domestic and foreign scholars and the structure of stator and rotor of the BDFM is introduced.Its working principle and several common operating modes is also introduced.Secondly,on the basis of simplifying the motor structure of ALA rotor BDFM,the expression of the air gap magnetic flux density distribution in the unsaturated state is derived by mathematical method.Through on the analysis of air gap magnetic flux density,the angle relationship between the fundamental flux density with the same pole pairs produced by both winding is explained.Furthermore,the expressions of inductance and torque are obtained.At the same time,the voltage equation and power distribution are also analyzed in detail.Thirdly,the stator winding of a 4/2 pole-pairs ALA rotor BDFM is designed and the harmonic analysis results.are given.Furthermore,based on the mathematical expression of the air gap magnetic flux density,the rotor structure of the 4/2 pole-pairs ALA rotor BDFM is analyzed and the key factors which affect the fundamental components of the air gap magn.etic flux density and the coupling ability between the two windings of the stator are found.The measures that can be taken to optimize the performance of the motor are proposed by the mentioned analysis.Meanwhile the contradiction between these measures are explained.Finally,the finite element simulation analysis of a 4/2 pole-pairs ALA reluctance rotor BDFM is carried out.By simulation,the expression of the air gap magnetic flux,the inductance,the torque and the power distribution are verified.Through the analysis of the inductance values obtained under different conditions,the correctness of the proposed measures is verified,and the problems in the research process are explained,which lays the foundation for future research.