Measures to Suppress Eddy Current Loss in Permanent Magnets of Tangential Permanent Magnet Synchronous Motors Based on Slot-Pole Ratio Selection
To suppress the permanent magnet eddy current losses in tangential permanent magnet synchronous motors,an estimated model for permanent magnet eddy current losses is constructed based on Maxwell equation and constitutive equation with approximate assumptions on the shape of the permanent magnet.A magnetic conductance function based on Carter coefficient concept is employed to estimate the change in magnetic flux density under the slot due to stator slotting.The conclusions of the theoretical analysis are verified based on five motor designs with slot-pole ratios of 1.05,1.20,1.30,2.40,and 3.60,respectively.The permanent magnet losses are analyzed at load current and double load current to obtain the radial air-gap magnetic flux density curve and its harmonic content for each motor.Considering the weakening effect of increasing the slot-pole ratio on stator iron losses and permanent magnet eddy current losses,a motor slot-pole ratio selection strategy is proposed.The results show that increasing the slot-pole ratio can decrease the variation in magnetic flux density stator slot,thus suppressing low-order harmonic content in the air-gap magnetic field and reducing permanent magnet eddy current losses,enhancing the motor's operational reliability,but it also introduces more high-order harmonics,which increases the stator iron consumption.
permanent magnet synchronous motorpermanent magnet eddy current lossslot-pole ratioradial air-gap magnetic flux density
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