Research On A Radial-radial Flux Compound-structure Permanent-magnet Synchronous Machine Used For Hybrid Electric Vehicles

The power-split hybrid drive system which employs the plenetary gear and two electric machines is the most advanced and successfuel electric drive system among hybrid systems at present. It provides the function of the high-performance electronic continuously variable transmission (E-CVT). Another power-split hybrid system which gets rid of the plenetary gear and integrates two electric machines (we call it compound-structure electric machine system in this thesis) could realize the same function as E-CVT and also gain the advantages of compact structure, low cost and flexible control stategies. It has become a new development direction in the field of hybrid systems. This thesis makes an intensive study of a radial-radial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), which belongs to one kind of the compound-structure electric machines, and the main research work is as follows.First of all, the issue of magnetic coupling caused by special structure of the radial-radial flux CS-PMSM is investigated. The design principle to realize magnetic decoupling is proposed, and the design method to mimimum the yoke thichness of the outer rotor and to improve power desity as well as to ensure magnetic decoupling is further investigated. A 20kW prototype machines is designed based on the proposed method, and the degree of the magnetic-field interference is evaluated by finite-element-method (FEM) calculations, which validates the proposed design method. Based on the feasibility of the magnetic decoupling, the mathematical model according with the electromagnetic and electromechanical relations of the CS-PMSM and considering the effect of the cross-magnetization phenemenon is established, which lays the foundation of controlling the CS-PMSM accurately.Secondly, the performance of the CS-PMSM is calculated and validated with FEM, as well as the inductance parameter is accurately calculated and the magnetic-field characteristic is analyzed. The performance is calculated with the method of multi-slice two dimentional (2D) FEM, which makes use of 2D FEM calculations to avoid problems of the harsh requirement for computer hardware, time consuming, limited calculation accuracy caused by three dimentional (3D) FEM calculations. The results show good working performance of the CS-PMSM. Furthermore, the method and step to calculate the d- and q-axis self and mutual inductances which could consider the saturation and cross-magnetization phenomenon are presented. The inductance parameter of the stator machine (SM) and double-rotor machine (DRM) is calculated, and the magnetic-field characteristic of the two machines is further investigated based on the calculated results, which provides a reference for accurate control.Thirdly, the 2D FEM thermal model is established and the temperature distribution is calculated, which show the hot spot of the CS-PMSM. The water and forced-air cooling are employed to cool the machine, and the effect of the two cooling method on different regions and their effectiveness are analyzed. Moreover, the discipline of the cooling-fluid parameter's effect on the cooling effectiveness is investigated, which provides a theoretical reference for properly chosing the fluid parameter, reversely deducing the design index of the cooling system, optimizing the cooling-system design and improving the system effeciency.Lastly, a prototype machine of the radial-radial flux CS-PMSM was manufactured, and the experimental test and its functional validation was performed. The tested results validate the proposed design and calculation methods, and further optimization of the prototype machine was suggusted. Moreover, the features and operation modes of the CS-PMSM system used in hybrid electric vehicles (HEVs) are analyzed, and the operation modes of the hybrid system were simulated and tested on the test bench. The tested results validate the fuctions of the CS-PMSM as the starter motor, generator, and continuously variable transmission used to adjust speed and torque, which provides an important reference for the practical application of the CS-PMSM system used in HEVs.