Optimization of outer-rotor hybrid excitation FSM for in-wheel direct drive electric vehicle

Research on flux switching machines (FSMs) has been an attractive topic recently due to tremendous advantages of robust rotor structure, high torque, and high power capability that suits for intense applications. However, most of the investigations are focusing on inner rotor structure which incongruous for direct drive applications. In this paper, the design optimization and performance analysis of 12Slot-14Pole hybrid excitation flux switching machine (HEFSM) with outer-rotor configuration are conducted for in-wheel direct drive electric vehicle (EV). Similar with conventional inner-rotor HEFSMs, two magnetic flux sources of permanent magnet (PM) and field excitation coil (FEC) have extra advantage of variable flux control capability, while the outer-rotor configuration has ability to provide much higher torque and power density suitable for in-wheel EV drives. Based on some design restriction and specification, design refinements are conducted on the initial design machine by using deterministic optimization approach. The final design machine has achieved maximum torque and power density of 335.08Nm and 5.93kW/kg, respectively, slightly better than inner rotor HEFSM and interior permanent magnet synchronous machine (IPMSM) design for EV.