Research On The Electromagnetic And Thermal Problems Of Compound-structure Permanent-magnet Synchronous Machine Used For Electric Vehicles

With the rapid industry development of electric vehicles, the hybrid drive system attracts more and more attention. The series-parallel hybrids are becoming research hotspot due to their satisfactory driving performance and fuel consumption. However, the planetary gear unit used by most series-parallel hybrids is a precision mechanical component that requires regular lubricating, leading to disadvantages such as high manufacture and matainance cost, additional transmission loss and operation noise. The compound-structure permanent-magnet synchronous machine (CS-PMSM) studied in this paper simplifies the configuration of series-parallel hybrids while implementing the same power-split function as planetary gear unit. Hence, the CS-PMSM is considered as a promising electric variable transmission solution to substitute planetary gear unit. This paper focuses on the problems of CS-PMSM such as comparison of structural topologies, magnetic decoupling design, cooling system and experimental test of prototype machine.By investigating the speed, torque and power correlations of the internal combustion engine (ICE), double rotor machine (DRM) and stator machine (SM) in a hybrid drive system, the optimal energy transducing configuration for CS-PMSM is proposed. Meanwhile, features of the six CS-PMSM topologies such as the torque density, facility of manufacture process, thermal performance and magnetic coupling, are compared to make comprehensive evaluation of various schemes. Furthermore, the selection rules of CS-PMSM for HEV system are proposed, which provides reference for the initial scheme design of CS-PMSM.Principles for the magnetic system design of CS-PMSM are researched. Considering the typical magnetic coupling and cooling problems, as well as the facility of manufacture and practical applicability, the radial-radial flux CS-PMSM is selected for further investigation. The magnetic system of the CS-PMSM is designed for comparable overall specifications with Toyota Prius. The thickness matching rules of permanent magnets (PMs) and outer rotor yoke are studied to enable magnetic decoupling when the power ratings of the two machines and thicknesses of inner and outer PMs are significantly different. Besides, armature reaction is investigated for magnetic decoupling. Important reference is provided for magnetic system design of CS-PMSM.The thermal problem and precise temperature measurement of CS-PMSM are researched. Considering the facility of experimental validation, thermal analysis is carried out based on the developed prototype CS-PMSM. Thermal field model is built up by finite-element method (FEM) software Fluent, and thermal distributions under different cooling conditions are calculated to study the laws of temperature rise and principles of selecting cooling system. To guarantee the safe operation of CS-PMSM, a precision multi-point real-time temperature measuring system is investigated. Problems introduced by sensor wiring resistance, component precision and electromagnetic interference (EMI) are solved, and usable circuit is designed. Hence, methods and references for the selection of cooling system and reliable operation of CS-PMSM are provided.A prototype machine is manufactured and experiments are conducted to test the electromagnetic, thermal and system performance. Considering the limitation of laboratory test equipment, the prototype CS-PMSM is developed with low power rating. The back EMF, torque-current curve, efficiency and thermal performance of the machine are tested and compared with theoretically simulated data. The experimental and simulated results are proved to have satisfactory agreement. A test bench is set up for the prototype machine and the New York City Cycle (NYCC) is used for the experimental evaluation of CS-PMSM system. Consequent system test results indicate well consistency with simulations. Moreover, by Advisor, the same drive cycle is simulated for Toyota Prius and conventional vehicle, respectively, and the CS-PMSM system is proved to have similar fuel efficiency with Toyota Prius, saving more than 40% fuel compared with the conventional vehicle, which validates the advantage of CS-PMSM system.