Research On Basic Theory Of Permanent Magnet Flux Switching Dual Rotor Motor In Hybrid Power System

With the development of the hybrid electric vehicles (HEVs), an electromagnetic hybrid driving system adopting double-rotor machine (DRM) is proposed and receives much attentions. Compared with traditional automobile’s driving system, it can realize higher fuel economy, and continuously variable transmission and dynamic coupling with more efficiency. And compared with the mechanical hybrid driving system adopting planetary gear, it has more compact structure, and the DRM can replace the starter/generator, motor, and planetary gear to realize the power coupling and split. Hence, it has been one of the development directions of hybrid driving system.For HEV applications, the DRM should has high torque density and low torque ripple. To realize the needs, and reduce the magnetic couple in the DRM, a stator-PM DRM type—the flux-switching permanent-magnet double-rotor machine (FSPM-DRM) is proposed and investigated in this paper. The main points are as follows:1. To meet the demand of the small bulk and light weight electrical machine used for HEV, the DRM concept is integrated into the flux-switching permanent-magnet machine(FSPM) structure which has high torque density, high power density, and high efficiency, as well as large cogging torque, thus the resulting FSPM-DRM is proposed. To minimized the cogging torque, the stator and rotor pole combination is optimized at first, and the 3-phase 12/22/12-pole FSPM-DRM topology is selected. Based on it, the general power equation for FSPM-DRM design is presented, and the detail design and optimization process of the FSPM-DRM is introduced. To verify the design results, the FSPM-DRM’s electromagnetic performances and the magnetic coupling are analyzed using finite element method (FEM), and the losses considering eddy current losses in windings and efficiencies in the FSPM-DRM are investigated, which lay a foundation for FSPM-DRM’s precise control and thermal analysis.2. To analysis the temperature distributions in the FSPM-DRM, the lumped parameter thermal network method and 3-D FEM are used for thermal analysis of FSPM-DRM at various operational modes and loads. The calculation results from two methods both show that the hot spots at various working conditions locate in the end-windings, and the temperatures of windings at high speed and high load operations can exceed the allowable temperature of the winding’s insulation grade. Based on above analysis, two cooling systems, the double-fan cooling system and the water-duct cooling system, of the FSPM-DRM are designed and compared using FEM. The results display that both can effectively reduce the temperature rise in FSPM-DRM, and the water-duct cooling system shows better cooling effect. At last, the electromagnetic-thermal coupling is investigated, in which the influence of the temperature rise on the FSPM-DRM electromagnetic performance is analyzed, and the eddy current loss in windings and its interaction with temperature rise are also investigated and proved that the eddy current loss in windings cannot be ignored in loss analysis.3. To prove the effective of the FSPM-DRM used for hybrid driving system, the Matlab simulation models of the FSPM-DRM vector-controlled system and the whole hybrid driving system are built. Firstly, based on the FEA conclusion that the magnetic coupling is very small and the FEM simulated flux linkage, inductances, and cogging torque in FSPM-DRM, the vector-controlled system of the FSPM-DRM is set up and simulated at different operation modes, in which the FSPM-DRM shows quick dynamic response and high static performance. Secondly, the whole hybrid driving system’s simulation model, including the engine module, battery module, FSPM-DRM control system module, the automobile module, and the energy management module, is put up, and based on it the 10.15 city driving cycle and the NEDC driving cycle are simulated and the fuel economies are calculated. The results display that the FSPM-DRM can operate at different working conditions and realize power coupling and split in hybrid driving system, and for two driving cycles the fuel economies of the FSPM-DRM are apparently improved compared with the traditional automobile.4. According to the design parameters of the FSPM-DRM, a 2kW principle prototype is manufactured, and the test bench of the FSPM-DRM control system based on TMS320F28335 DSP is built. Several tests are made on FSPM-DRM’s performance evaluation and its effective run at different operational modes. The results validate the correctness of the theoretical analysis, and the reasonableness of the FSPM-DRM design and its control strategy. It also provide theory and technology support for further FSPM-DRM’s practical application in hybrid driving system.