The New Permanent Magnet Switching Flux From The Generator

Integrated starter generator (ISG) is an electric subsystem in which the functions of starting an internal combustion engine and generating electric power are fulfilled with one electric machine onboard vehicle, instead with two separated machines in a traditional automotive vehicle. Due to its significant advantage over the separated machines for cold cranking and battery charging, ISG attracts considerable interest in modern automobiles and mild hybrid electric vehicles. On the other hand, novel doubly salient motors developed from switched reluctance motor have been extensively studied and utilized since the switched reluctance motor was invented. These novel doubly salient motors have coils or permanent magnet in the stator, but not in the rotor, so the structures of the motors are simple and the manufacture cost is low. Permanent magnet flux-switching machine(PMFSM), a novel doubly salient machines is studied in this paper for application of automotive ISG. The PMFSM which has a magnet imbedded in each stator pole combine the merits of both switched reluctance motor and PM brushless motor, such as simple and robust structure, fault tolerance, high efficiency, etc. In the PMFSM, the PM-excited flux always exists and has a constant direction in the magnets. However, the flux path changes with the rotor position, resulting in variation of both amount and direction of the flux-linkage in the stator coil, and thus inducing back-EMF. The machines can be driven as a brushless DC(BLDC) or brushless AC(BLAC) machine.The phase back- EMF, cogging torque and static torque of a 12/10-pole PMFSM which are computed with the finite element analysis(FEA) software are considered in optimal design. The FEA results of the machines with different geometric variables are comparatively studied. The balance of these features is investigated for the ISG application. The on-load performance simulation results are obtained and analyzed. The performance specification of the ISG requires a constant output voltage over a very wide speed range for battery charging, as well as a very high starting torque for cold cranking. By advancing the inverter firing angle and changing windings connection, the machine can reach higher speed under constant power operation, verifying the flux-weakening capability of the machine.Finally, other two novel structures of FSPM are investigated with comparison with the 12/10 structure with Back-EMF. The related factors of the Back-EMF of a PMFSM are given to guide future research.