Superior Efficiency Under PWM Harmonic Current in an Axial-Flux PM Machine for HEV/EV Traction: Comparison With a Radial-Flux PM Machine

This paper evaluates the harmonic current caused by a pulse width modulation (PWM) inverter and how it affects the efficiency of a novel axial-flux permanent-magnet machine using a ferrite permanent magnet (AF-FePM) in traction applications. First, differences between the finite element analysis (FEA) and experimental results are discussed using a prototype of the proposed AF-FePM. Second, the AF-FePM is compared with a commercially available radial-flux permanent-magnet machine using a Nd-sintered magnet (RF-NdPM). For both machines, the efficiency and loss are calculated using FEA when applying the sinusoidal and harmonic currents. Additionally, we present the superior efficiency of the AF-FePM under the PWM harmonic current during a WLTC driving cycle because the designed model employs the ferrite magnet and a round copper wire, unlike the RF-NdPM. Finally, motor and inverter losses at different switching frequencies are also evaluated. This paper eventually shows that the proposed AF-FePM would be one of the suitable candidates to enhance high efficiency under PWM harmonic current condition based on comprehensive discussion.