Measures to reduce temperature rise:
From the above analysis, the corresponding solutions are proposed as follows.
3.1) Segmentation and delamination of permanent magnets: the placement of permanent magnets is no longer a whole piece of material, but a permanent magnet is divided into a plurality of small segments or layers, and the surface of the permanent magnet segments (layers) is subjected to electrophoresis treatment. In order to reduce the eddy current loss, reduce the rotor temperature rise.
3.2) Increase the air gap: For asynchronous motors, increasing the air gap will increase the leakage current, so that the excitation current will increase and the efficiency will decrease. For the rare earth permanent magnet synchronous motor, the air gap can increase the magnetic resistance and harmonic leakage resistance of the high-order harmonic air gap magnetic field, reduce the cross-linking degree of the flux linkage, weaken the harmonic current, and reduce the surface of the stator and rotor. Loss and harmonic losses, etc., thereby reducing the temperature rise.
3) The rotor adopts a semi-closed El slot or closed slot: this can reduce the surface loss of the rotor core and the pulse vibration loss in the tooth, reduce the effective air gap length, improve the power factor, and reduce the pulse amplitude of the air gap harmonics. Value, reducing harmonic losses caused by magnetic flux harmonics.
4) Select the appropriate slot fit: the lower the harmonic order, the more the number of rotor slots, the greater the loss; the fixed and rotor slot 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 windings can select different spans according to requirements, which can reduce high-order harmonics and reduce the fundamental electromotive force, thus effectively improving the waveform of the air-gap magnetic field. Reduce harmonic losses and reduce temperature rise.
6) Selection of high-quality NdFeB permanent magnets: In practical applications, it has been found that the performance of the same brand NdFeB permanent magnets produced by different manufacturers is quite different. Unlike the NdFeB grades, the eddy current losses are different and the thermal conductivity is also different. Selecting a high-performance NdFeB permanent magnet material with a relatively high thermal conductivity is beneficial to the conduction of heat on the magnetic steel, thereby reducing the temperature rise of the rotor.
4 improved measures and effects of rotor temperature rise:
From the above analysis, the NdFeB permanent magnet grade used in the prototype was changed from the previous 40SH to 33UH, and the temperature rise test was repeated. The result was that the stator core temperature was 80 ° C, the temperature rise was 51 ° C, and the rotor core temperature was 140 ° C. The temperature rise is 110 °C. After the permanent magnet is replaced, the temperature rise of the rotor core drops by 10 °C. It can be seen that the eddy current loss of the permanent magnet has a great influence on the temperature rise of the rotor.
5 Conclusion:
In this paper, the causes of excessive temperature rise of rare earth permanent magnet synchronous motor rotor are discussed, and the method of reducing rotor temperature rise is proposed. After testing the permanent magnets of the original prototype, it is shown that the eddy current loss of the permanent magnet has a great influence on the rotor temperature. Therefore, if the permanent magnet segmentation or delamination can be taken during the motor manufacturing process, the rotor temperature rise will decrease.
