Electromagnetic Design And Characteristic Analysis Of Dual-Stator Brushless Doubly-Fed Wind Power Generator With Cage-Barrier Rotor

Taking the project supported by National Natural Science Foundation of China as background,this thesis proposes a novel MW dual-stator brushless doubly-fed wind power generator(DSBDFWPG)with cage-barrier rotor.The DSBDFWPG is a kind of double air-gap and double field modulation machine with special structure.There are two kinds of three phase windings with different number of pole pairs in outer/inner stator,namely power winding(PW)and control winding(CW).These windings are carried out magnetic field modulation and coupling through cage-barrier rotor to achieve electromechanical energy conversion.In this thesis,theoretical analysis,electromagnetic design and experimental research will be carried out on the DSBDFWPG with cage-barrier rotor.The main research contents include the following aspects:(1)Aiming at DSBDFWPG with cage-barrier rotor,its principle and structure are quite different from conventional brushless doubly-fed generator(BDFG).Because the existing theories and methods can not be directly applied to DSBDFWPG,it is necessary to study the magnetic field modulation theory of DSBDFWPG in this thesis.Through the analysis of winding magnetomotive force and air-gap permeability function,a useful air-gap magnetic density component of the DSBDFWPG to achieve electromechanical energy conversion is derived.Based on the basic electromagnetic relationship and doubly-fed operation mode of electric machine,the steady-state coupling circuit of DSBDFWPG is derived.Meanwhile,the voltage equation,current equation and electromagnetic torque of DSBDFWPG,which is derived.On this basis,the steady-state equivalent circuit(EC)of DSBDFWPG is derived.At the same time,the winding function method is used to calculate the self-induction and mutual inductance of windings,and the slot leakage permeances of stator and rotor windings are calculated by energy method.The performance of DSBDFWPG is calculated by the EC.The results are verified by experimental testing.Based on the EC of electric machine,the active power and the reactive power of DSBDFWPG are deduced through the voltage equation.(2)Aiming at the complex magnetic field of DSBDFWPG,a hierarchical analytical model of DSBDFWPG is established.On this basis,the winding equivalent current density and analytical magnetic field of DSBDFWPG are studied.The magnetic flux density of DSBDFWPG is derived.Based on the special structure and assumptions of DSBDFWPG,the hierarchical analytical model of DSBDFWPG is proposed.Due to two sets of three-phase windings with different pole pairs number in stator and complex magnetic field of the electric machine,the equivalent current density of the PW,CW and cage-bar is respectively calculated according to the actual situation by the groove-by-groove method,respectively.Based on the hierarchical analytical model and the winding equivalent current density of DSBDFWPG,the vector magnetic potential of each area of DSBDFWPG is derived by separated variable method.Combined with the boundary conditions of the electric machine,the magnetic flux density of each area of DSBDFWPG under the PW excitation and CW excitation is respectively derived.Then the magnetic flux density of each area of DSBDFWPG under various excitation is superimposed.On this basis,taking 3MW DSBDFWPG as the research object,the air-gap magnetic flux density of DSBDFWPG is analyzed,and the results are verified by finite element method(FEM).(3)In order to improve the torque density of the DSBDFWPG and reduce the electromotive force(EMF)distortion ratio of winding,the power distribution principle of outer and inner unit electric machine,main dimensions determination method,slot-pole combination rule,stator winding arrangements and winding connection modes,which is deeply studied for the DSBDFWPG.The design principle and methods of DSBDFWPG are concluded.Based on the power relationship and design requirements of DSBDFWPG,the relationship between the output power ratio of outer and inner unit electric machine and the diameter of outer and inner stator is derived.The main dimensions of DSBDFWPG are determined according to the technical requirements and major dimension relationships of the electric machine.On this basis,taking 3MW DSBDFWPG as the research object,the FEM is used to analyze the influence of different slot-pole combinations on the DSBDFWPG performance,such as winding EMF distortion rate,rotor coupling capacity and air-gap magnetic density.The relationship between stator/rotor slot number and PW pole pairs number and CW pole pairs number is summarized.Meanwhile,in order to ensure the electromagnetic characteristics consistency of outer and inner unit electric machine and improve the efficiency of DSBDFWPG,the influences of winding layers number,winding positions and winding connection modes on the performance of electric machine are studied.It is concluded that the PW located at the slot opening and the CW located at slot bottom can reduce the EMF distortion ratio of winding and voltage regulation factor of electric machine.Meanwhile,the characteristics of winding connections are concluded.At last,based on the above-mentioned design principles and methods of electric machine,a 3MW DSBDFWPG is designed,and the performance of DSBDFWPG is analyzed and calculated by analytic method and FEM.Meanwhile,a CAD software platform for performance calculation of the DSBDFWPG is developed.(4)Aiming at the low coupling capability of the existing rotor structure,a new type of cage-barrier rotor structure is proposed.The rotor topological structure and the rotor structure parameters are studied,and the change rules of the influence of the rotor structure parameters on the rotor coupling capability are revealed.By analyzing the influence of different the rotor magnetic-barrier structure and rotor cage-bar structure on the rotor coupling capability,the rotor magnetic barrier and cage-bar structure are determined.Based on the determined rotor structure,the influences of rotor pole arc coefficient,magnetic permeability layer number,width ratio of magnetic permeability layer to non-magnetic permeability layer and cage bar number on rotor coupling capability are analyzed by the FEM.The selective principle and method of the rotor structure parameters are concluded.On this basis,3MW DSBDFWPG is taken as the research object to determine a better scheme for selecting the rotor structure parameters,and the rotor coupling capability is analyzed.(5)Based on the design principle and method of MW DSBDFWPG,a 50 kW prototype is designed and manufactured.Meanwhile,the experimental platform of prototype is built,and the methods of parameter testing and performance experiment of prototype are studied.The winding resistance and induction of the prototype are measured by bridge method and static testing method,respectively.The results are verified the correctness and effectively of the parameter analysis method.In order to verify the design principles and analysis methods proposed for MW DSBDFWPG,the no-load and load operations of the prototype under different speeds and different excitation are measured and analyzed.The experimental results are consistent with the results of the finite element simulation and the theoretical analysis.It is verified that the theoretical analysis and research methods are correct and effective.