| After being regulated its structure,the conventional permanent magnet machine is added with the field winding and then developed into the hybrid excitation machine(HEM).In the HEM,the different magnetic path type between the two kinds of magnetomotives force,from the permanent magnet(PM)and the field winding,can be designed like the series,parallel and isolation mode.In addition to the good magnetic flux-regulating ability,the HEM combines the characteristic of the high power density and high efficiency of PM machine,meaning its bright future in some areas such as aerospace,aviation,wind power generation and automobile.This dissertation pays attention to a tangential/radial magnetic path hybrid excitation synchronous machine(T/R-HESM),with the parallel magnetic path mode.Following the introduction of the basic characteristic of T/R-HESM,the research focuses on the scheme choice of brushless excition,operating characteristic,loss calculation,efficiency analysis and temperature distribution.For the brushless excitation of T/R-HESM,the qualitative analysis of electromagnetic property is made and the three-stage scheme in electrically excited synchronous machine,widely used in aircraft power,is referenced and improved.Considering there is some amount of the air-gap magnetic field,coming from the PM,in T/R-HESM without field current,the three-stage scheme is modified into a two-stage scheme by removing its auxiliary PM exciter.Hence the studied machine in the dissertation is also called as two-stage brushless hybrid excitation synchronous machine(T-BHESM),which is composed of main machine,exciter and rectifier.The T/R-HESM and the revolving-armature type alternator are acted as the main machine and the exciter,respectively.At work,by the rotating rectifier,AC voltage of the exciter is rectified into DC voltage to supply the main machine,namely T/R-HESM.In view of the structure feature of the studied machine,2-D finite element method(FEM)is adopted to solve the electromagnetic field.First,distribution and regulating characteristic of the magnetic field is computed through FEM.The stator skew slot and the rotor shape are respectively discussed to improve the output voltage waveform quality.On one hand,the harmonic contents of phase back-electromotive force(emf),before and after skew slot is adopted,are compared.On the other hand,the harmonic contents of air-gap magnetic field are analysed in T/R-HESM,and then the influence of rotor shape on the air-gap magnetic field is also studied.Depending on the exciting requirement of the main machine,structure size of the exciter is obtained,and then via FEM,the exciter is computed for its electromagnetic field,more concern on the current amplification ability.Furthermore,in order to knowing the influence of design size on the exciting ability,the change regularity of electromagnetic parameter,such as air-gap magnetic field and rectified voltage,with the structure variables of exciter,such as pole-arc coefficient and air-gap length,is also investigated.Due to the high coupling between the tangential magnetic path and the radial part,serious magnetic saturation happens in the rotor of T/R-HESM,which is different from conventional machine.Thus,the FEM based on the frozen permeability is used to solve the magnetic-saturation problem mentioned above,and accordingly the nonlinear magnetic problem is changed into a linear one.The magnetic-saturation degree is subjected to the magnetomotive force from stator armature winding,exciting coils and PM,so the influence of exciting and load current on the d-axis and q-axis inductance of armature winding is studied,as well as analysis of self-and mutual inductance.On the basis of the calculated inductances value,the mathematical model for the studied machine is built to aim at its external characteristic.The loss of T-BHESM is explored with the goal of evaluating the efficiency.First,the type of loss and the relevant causes are analyzed,and then the influence of exciting intensity,rotation speed,load current size and load type on the iron loss is computed with the help of FEM,as well as the frequency trait of the iron loss in T/R-HESM.Secondly,two different segment methods of PM,used to reduced the eddy current loss,are discussed.The solved data show the iron loss is main body of the machine loss with light load,and copper loss gradually becomes another major part of loss with increase of the load current.At low rotation speed,for the main machine,the copper loss of exciting winding accounts for the large percentage of rotor loss.However,the iron loss and the eddy current loss gradually turn into a significant portion of rotor loss with the increase of rotation speed of the machine.Efficiency is calculated according to the above-obtained loss data,showing the machine can operate with an efficiency of more than 90% at the rated condition.The temperature field of T-BHESM is solved via FEM.First,the heat transfer path of T-BHESM is qualitatively analysized.Considering its structural feature,only one quarter model of the machine is created to save computing time.Subsequently,the above-mentioned loss is served as heat source to calculate the temperature field.Relationships between temperature rise and working condition,such as the rotation speed,exciting current intensity,load size and loss type,are shown.Research results show that,compared with the PMs in the permanent magnet machine,the PMs of the studied machine work in the relatively harsh environment due to heat resulting from the field windings.In addition,the influence of some conditions,such as the shell surface wind speed,the insulation factors of winding and the cooling fin,on temperature rise is also given.This project is supported by National Natural Science Foundation of China,named “basic study of brushless variable frequency hybrid excitation synchronous machine with tangential/radial magnetic path(No.50977044)”,and Joint Foundation of Production and Research of Jiangsu province,named “power direct-driven system and control technology of urban rail transport(No.BY2014003-09)”. |
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