Rotor temperature rise has not attracted enough attention in the initial designing of low power permanent magnet synchronous motors (PMSMs). Slot effect of stator windings, magnetomotive force of non-sine windings, or harmonic electrodynamic force caused by harmonic current will generates eddy current losses in the rotor magnets and rotor yoke. Eddy current loss of rotor is relatively small in comparison with stator’s copper loss and iron loss. With the increase in motor power, rotation speed, and permanent magnet’s volume, eddy current in permanent magnets will result in the higher temperature rise, then lead to the demagnetization and then decrease motor performance. Lifetime of permanent magnets in the rare earth permanent magnet motor is mainly determined by electrical resistivity, but those magnets are always having high conductivity and low heat resistance. Samarium Cobalt magnets still have irreplaceable high temperature performance and stability compared with Neodymium magnets. Laminated magnets are proven to reduce eddy current losses in high efficiency motors besides some conventional solutions, then the combination of Samarium Cobalt magnets and magnet segmentation technology, laminated SmCo magnet, undoubtedly become the ideal choice for high temperature rotating machinery.
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