Analysis And Design Of Dual-stator HTS Exciting Field Modulation Machine

Compared with conventional electrical machines,the superconducting(SC)electrical machines owning the higher electrical loading and magnetic loading have the advantages of high power density and high efficiency,due to the use of SC materials.The SC electrical machines have promising application prospects in the fields of high-torque density propulsion motor,highpower direct-drive wind generation and rail linear propulsion system.However,most of the SC electrical machines currently developed are based on the topology of the electrically-excited synchronous electrical machine,called as SC excited synchronous electrical machine(SCESM).The SC windings are located on the rotor or stator in this type of SCESM,resulting in the use of brush-slip ring,rotating seal coupler and torque tube.These components not only require regular maintenance but also reduce the reliability of SC electrical machines.For high-temperature superconducting(HTS)electrical machine with extremely high reliability requirements,removing brush-slip ring and torque tube,realizing stationary seal of the coolant,improving the reliability of the HTS electrical machine,and reducing operation & maintenance costs will be the development trend in the future.A dual-stator HTS exciting filed-modulation machine(DSHTS-FMM)is proposed based on the airgap magnetic field modulation theory in the thesis.Both the SC field winding and the copper/SC armature winding are located on the stators in the proposed topology,which not only realizes the stationary seal of the coolant but also realizes the brushless transmission of the current and reduces the design difficulty of the torque tube as well.The thesis takes the DSHTSFMM as the research object,proposes and analyzes the topologies of the dual-stator stationaryseal SC electrical machine,reveals the special influences of the armature reaction field on the SC winding in the field-modulation SC electrical machines(FMSCM),further proposes a kind of composite harmonic shielding method,builds the design method of the DSHTS-FMM based on the airgap magnetic field modulation theory.Finally,a 10 k W prototype is fabricated,and the corresponding experimental research is conducted.The test results validate the correctness of the proposed analysis and design methods of the DSHTS-FMM.In addition,the conceptual design of the 10 MW dual-stator HTS field-modulation direct-drive generator(DSHTS-FMDDG)is carried out.The main research content and fruits of the thesis are as follows:1.The DSHTS-FMM is proposed.The innovation motivation and working mechanism to the DSHTS-FMM is explained based on the airgap magnetic field modulation theory,and the advantages of the DSHTS-FMM are shown in terms of high power density and the SC magnets self-protection.2.The special influences of the armature reaction field on the SC winding in the FMSCM are revealed,mainly including three aspects: the fundamental harmonic of the armature reaction field is a low-frequency large-magnitude alternating external magnetic field relative to the SC winding;there are abundant moving harmonics relative to the SC winding in the air gap after the armature reaction field is modulated;these moving harmonics will generate high induced voltages in the SC windings,which is not only easy to cause the fluctuation of the excitation current and increase the AC loss in the SC winding,but also affect the voltage monitor of the SC winding.In order to inhibit these negative influences,a composite electromagnetic shielding system consisting of a squirrel-cage damper and a copper shielding layer is proposed based on the dual-stator topology,suppressing the low-frequency large-magnitude harmonics and the high-frequency low-magnitude harmonics,respectively.3.The mathematical analysis model of DSHTS-FMM is established based on the airgap magnetic field modulation theory.This novel theory points out that the electromagnetic performances of any electrical machine can be characterized by three elements of “magnetic source”,“modulator” and “selector”.According to these cognitions,the mathematical expression of the excitation magnetic field source and the armature-reaction field source are given,and a characterization method of the outer stator modulator,the rotor modulator and the inner stator modulator based on the infinite deep slot model is proposed.The established mathematical analysis model can basically meet the requirements of the initial design stage,and have faster calculation speed than the finite element method.4.The design and manufacturing method of the DSHTS-FMM is established,and a 10 k W prototype is fabricated.The design method of initial electromagnetic parameters of the DSHTS-FMM is proposed based on the airgap magnetic field modulation method.According to the design requirements of power,speed,volume,et al.,the magnetomotive force of the field winding,the turns number of the armature winding,and the wire scale can be easily determined.The initial design scheme can provide reference for the following finite element analysis and optimal design.In addition,a SC coil design method based on the carryingcurrent test results of a SC short samples is proposed.Based on the magnetomotive force determined in the electromagnetic design stage,the turns number and working current of the SC coil can be designed to ensure the SC coils working safely.5.The generation test platform of the DSHTS-FMM is built,including the cooling system,the excitation and test system of the SC coils,drag motor,etc.The no load and load experiments of 10 k W prototype can be conducted by adjusting the speed of drag motor and the load,to validate the correctness of the proposed analysis and design methods.6.Two 10 MW DSHTS-FMDDG conceptual prototypes are designed,one is semi-SC DSHTSFMDDG,the other is full-SC DSHTS-FMDDG.As far as the power density per volume,the semi-SC DSHTS-FMDDG is about 1.83 times higher than the PMDDG,and the full-SC DSHTS-FMDDG is about 2.62 times higher than that of the PMDDG.From the point view of the power density per mass,the semi-SC one with magnetic inner stator has no obvious advantages relative to the PMDDG,however,if the inner stator made of nonmagnetic material is adopted,the power density per mass of the semi-SC one can improve about 28.4%higher than that of the PMDDG.In addition,the power density performance of the full-SC one is better than the semi-SC one.Compared with the PMDDG,the power density per mass of the full-SC one with magnetic inner stator can improve 34.8%.If using the nonmagnetic inner stator,the full-SC one can increase 62% higher than that of the PMDDG.In general,the power density of the DSHTS-FMDDG can basically match with the superconducting direct drive generator(SCDDG)based on the topology of the electrically-excited synchronous machine.However,the DSHTS-FMDDG can overcome the difficulty of rotating seal,brushslip ring and torque tube.Therefore,from the perspective of the reliability of the SC electrical machine system and the cost of the full lifetime,the DSHTS-FMDDGs have advantages over the SCDDG.