Back EMF, Torque–Angle, and Core Loss Characterization of a Variable-Flux Permanent-Magnet Machine

An appropriate torque–angle selection can improve the torque-to-current ratio of a machine, converter size, and provide an optimal motor operation. A precise information of the back electromotive force (EMF) helps estimating the magnet flux linkage. An accurate determination of the core loss leads to a better machine design and efficiency estimation. This paper presents the back EMF, flux linkage, torque–angle, and core loss characterization of a variable-flux permanent-magnet machine. The magnetic properties of AlNiCo 9 magnet and the process of magnetization and demagnetization are also described. The no-load back EMF, torque–angle curves, and no-load core losses are measured and simulated for a 7.5-hp variable-flux machine for three different magnetization levels. Static torque–angle curves are obtained by varying the current advance angle and the rotor position. Simulations are performed using three different machine design softwares to validate the design, software accuracy, and machine models. The core losses are also obtained using an analytical method, which is first utilized to calculate losses in M19G29 laminations, and then implemented to estimate the core losses of the prototyped variable-flux machine. The experimental results are found to be in a good agreement with the simulation and the core losses compared well with the analytical data.

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