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The Solution for Temperature Rise of Permanent Magnet Rotor

1. The use of injection-molded permanent magnets: The injection-molded permanent magnets can greatly reduce eddy current loss and reduce the temperature rise of the permanent magnet rotor due to their high electrical resistivity.

2. Increase the air gap: For asynchronous motors, increasing the air gap will increase the magnetic leakage, increase the excitation current and reduce the efficiency. For rare earth permanent magnet synchronous motors, adding an air gap can increase the magnetic reluctance and harmonic leakage reactance of the high-order harmonic air gap, reduce the degree of flux linkage, weaken the harmonic current, and reduce the surface of the stator and rotor. Loss and harmonic loss, etc., so as to reduce the temperature rise.

3. The rotor adopts semi-closed El slot or closed slot: it can reduce the surface loss of the PM rotor core and the pulsation loss in the tooth, and reduce the effective air gap length, improve the power factor, and reduce the air gap permeability harmonics. Pulse amplitude value to reduce the harmonic loss caused by magnetic flux harmonics.

4. Choose the appropriate slot fit: the lower the harmonic order, the more the rotor slot number, the greater the loss; when the stator and rotor slot number ratio is close to 1, the loss is the smallest, so choose the near-slot fit as much as possible.

5. Stator winding double-layer short-distance distributed winding: Double-layer short-distance distributed winding can choose different spans according to needs, which can reduce high-order harmonics, but also makes the fundamental electromotive force small, thereby effectively improving the waveform of the air gap magnetic field , Reduce harmonic loss and reduce temperature rise.

This article analyzes and proposes methods to reduce the temperature rise of the permanent magnet rotor. After replacing the permanent magnet brand on the original prototype, the test shows that the eddy current loss of the permanent magnet has a great influence on the rotor temperature. Therefore, if injection-molded permanent magnets with higher resistivity can be used in the motor manufacturing process, the temperature rise of the rotor will be reduced.