Core Losses and Machine Design for Electric/Hybrid Vehicles

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The area of core losses in electrical machines is of growing interest as higher speed machines are being designed with complicated geometries, leading to complex flux patterns. The fluxes may be primarily alternating, but a significant portion of the machine experiences a rotational loss, an area in which very little work has been done. The work proposed is divided into three sections.** The first is to develop more accurate models for waveforms that are primarily pulsating. The applicant has found that fundamental errors are being made in the separation of losses into eddy currents and hysteresis because of how the measurements are made. In typical Epstein specimens the entire flux is measured flowing in the lamination, yet as frequency increases, skin effect takes over and there is a variation in the magnitude and phase of flux density within the thickness of the lamination. More accurate modeling has allowed this variation to be taken into account, but this must still be translated into more accurate calculations of the actual losses.** Some fundamental work in the measurement of rotational iron losses in machines have been done recently. A new test fixture has been designed and built and limited tests have been conducted. The purpose of this task is to advance the measurement to include non-sinusoidal excitations, while the flux is rotating and to include a wider range of materials and gauges. On the modeling side, fundamental work needs to be done on developing a formula for hysteresis and eddy current losses while the flux is rotating, similar to what has been done for pulsating fluxes.** The third task is to use the results in the core loss modeling to design a new synchronous reluctance motor with low torque ripple, without the need for skewing. Skewing of the stator or rotor increases the manufacturing complexity. Also the average flux density is reduced. A new technique related to the orientation of the ribs in the rotor is proposed which can allow torque ripple minimization in the absence of skewing.****