| In the past 20 years, the greatest economy development happened in our country; however the unhealthy economic structures did great harm to the environment. With the intensification of the environmental pollution, oil crisis and the requirement of a better living environment, new energy technology came into people’s sight. As is well known, wind power and electric vehicle are the important components of new energy technology and in both of them the high performance low-speed direct-drive electric machines play an important role. Of all kinds of electric machines, permanent magnet machines, which have high efficiency, high torque density and good speed adjustment capability are the hot point of investigation. However, under the condition that there is no breakthrough in energy storage technology, people have to release more potential from electric machines which is used in electric vehicles and winding power to achieve longer duration and larger propulsion, therefore, the desire to find new type electric machines which have higher power density has becomed more and more imperative. During recent years, a lot of new structures has been used in electric machine, such as switch reluctance machine, flux switch machine, transverse flux machine and axial flux machine, among these machines, transverse flux machines which have high power density and good low speed performance are more adaptable to the application of wind power and electric vehicles. However, most transverse flux machines used expensive materials such as soft magnetic composite (SMC) and very complex structures which lead to the difficult manufacture process and high manufacturing costs in machine production. Axial flux machine is another kind of machines which have high power density and high efficiency, investigations on this kind of machines are easily to seek in academic journals and conferences, yet there are not so much study in the flux leakage of this kind of machines, in addition, the flux path of axial flux machines is 3D structure which is similar to that in transverse flux machines, that means some of the conclusions are also applied to the analysis of transverse flux machines. In this dissertation, a novel axial-transverse flux machine which combine the advantages of fractional slots machine, axial flux machine and transverse flux machine is presented, we started from the leakage flux of normal axial flux PM machine, designed a prototype of novel machine using the flux leakage factor calculated by normal machine and analyzed the no-load and load characteristics of transverse flux machine, the main contents of this study are divided as follows:(1) A novel axial-transverse flux PM machine was proposed, its principle and characteristics was introduced.A novel axial-transverse flux machine is proposed combining the advantages of normal fractional slots concentrated winding machines, axial flux machines and transverse flux machines. This machine consists of 10 fan-shaped permanent magnet poles,12 "C" shaped stator cores and 12 coils wound on the cores, the 12 stator cores are arranged in the circumferential direction uniformly and the 12 coils are connected each other using the same way in the 12 slots 10 poles fractional slots concentrated winding machines. It is obviously that the flux in the air gap of this machine is along the axial direction, the winding arrangement is typical fractional slots concentrate winding, the "C" shaped stator core is similar to transverse flux machine, and of course, this machine has the advantages of all those three machines.(2) An accurate 3D magnetic circuit of normal axial flux PM machine was created, the analysis expression of the flux leakage factor was obtained by this model and the result was verified by 3D FEM.Axial flux permanent magnet machines have the advantages of both disc machines and permanent magnet machines and has the advantages of high torque/inertia ratio, high efficiency and high power density, thus it is widely used in battery energy storage system, electric vehicle system and new energy power systems. The investigation about axial flux machines focused on comparison of the performance with other kinds of machines, electromagnetic designs and structure optimizations, however the key factor of machine design-flux leakage did not draw enough attention, in addition, most of those studies about axial flux machine used 3D FEM or equivalent 2D model,3D accurate model was not widely used.3D FEM is usually used to analyze axial flux machines, but as we know,3D FEM will cost a lot of time to build model and to calculate which is obviously not fit for the initial design and optimized design of machines. Therefore, flux path calculation is used in the initial and optimized design of axial flux machine and the FEM is used to verify the results, In any kind of machines, flux leakage factor has to be determined for the flux path calculation, the flux path in axial flux machine is three dimensional path and the leakage flux between magnet poles and the leakage flux of the edge of the magnet are similar to those in axial flux machines, which means it can be used in the flux path calculation of novel machines either, In this dissertation, a 3D accurate equivalent magnetic circuit of normal axial flux PM machine was created, the analysis expression of the flux leakage factor was obtained based on the magnetic circuit and the result was verified by FEM.(3) The no-load dynamic performance of the axial-transverse flux machine was analyzed; the no-load back EMF waveform of the machine was obtained by the integration of the volume of magnet and the waveform was optimized using bacterial foraging algorithm (BFA).No-load permanent magnet back EMF occupies a very important place in permanent magnet machine design; the waveform of permanent magnet back EMF reflects many key factors in PM machines. In electric machine design, the PM back EMF can be obtained by FEM or analytical method, analytical method costs less time but has low accuracy compared to FEM, but as a 3D flux path machine, analytical method is a better candidate because it has high calculation efficiency. During the analytical calculation methods, differential equation is usually used to solve the flux problem in permanent magnet machines, but 3D differential equations are very difficult to be solved, in addition, the boundary condition of the machine discussed in this dissertation is very hard to determine which will result in a difficult process to solve the equations. In order to obtained the PM back EMF waveform quickly, a new analytical method base on the integration of permanent magnet volume was used to calculate the no-load back EMF waveform of the novel machine,3D FEM was used to verify the correctness of the analytical method, and finally bacterial foraging algorithm was used to optimize the waveform.(4) The load dynamic performance of the axial-transverse flux machine was analyzed by dynamic magnetic circuit, the waveform of load flux linkage and torque were obtained.In the study of load characteristic, the flux linkage of coils is still the key point; it is different from the calculation of no-load flux linkage in which the current in windings can be neglected. Dynamic magnetic circuit method is a suitable method which is usually used to analyze the problems in salient pole machines, but in order to build a suitable coordinate system in the machine studied in this dissertation, a simplified model is used, In this part, the principle of dynamic magnetic circuit is introduced firstly, then the simplified model is discussed by listing the magnetic circuit and the reluctances at different rotor position, finally the waveform of flux linkage and torque was obtained.(5) The sizing equation of the machine is derived, by sizing equation and flux path calculation, a prototype was manufactured and tested, the experiment verified the rationality of the design strategy.The relationship between the machine output power and its efficiency, speed, electromagnetic load and size was derived, the steps of flux path calculation was also given in this part. The initial geometry size was obtained by estimating the efficiency, electromagnetic load and power factor etc. Verified by FEM, a prototype is manufactured; a 2.2kW induction motor is used to drive the prototype and the back EMF which is got from the oscilloscope confirmed the availability of this motor; a frequency converter is used to drive the prototype directly, tested by the power tested machine, the output power is satisfied the design specification. |
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