Core Loss Calculation in a Variable Flux Permanent Magnet Machine for Electrified Transportation

The paper is focused on the modeling and measurement of core losses in an AlNiCo-based variable flux permanent magnet machine. The application of AlNiCo as a low coercivity magnet provides the ability of the magnet flux control using short-time d-axis current pulses. This allows a reduction in the machine core losses under high-speed conditions, thus improving the machine efficiency. In order to identify the machine efficiency gains, the core losses have to be accurately modeled at different magnetization levels. An advanced core loss model for the variable flux machine (VFM) is first presented. This model is based on the calculation of an equivalent sinusoidal waveform of nonsinusoidal magnetic flux density. The model is then utilized to calculate the core losses in a tangentially magnetized VFM using finite-element simulation. In order to validate the developed model experimentally, a measurement method is developed to segregate the mechanical losses and the no-load core losses at different speeds and magnetization levels for a 5-hp VFM. Finally, the proposed model accuracy is verified through a comparison with the experimentally measured core losses under a no-load condition.