Based on the magnet steel eddy current loss analysis, this paper discusses on the effect of permanent magnet motor rotor temperature rise and improvement measures

Rare earth permanent magnet synchronous brushless motor (REPMSM)With small volume, light weight, high efficiency, etc. In theory the rotor without loss of fundamental wave, the rotor temperature rise should be low, but the reality does not.



with the authors developed a type of increasing safety of rare earth permanent magnet synchronous motor as an example, there was a rotor temperature rise test up to 1, 25 & deg; The phenomenon of C. The rotor temperature is too high, can cause danger of demagnetization of ndfeb permanent magnet, affect the normal work of the motor.



this paper analyzes the possible reasons for the rotor temperature rise is too large, puts forward the measures to reduce temperature rise.



1: rotor structure of REPMSM stator in asynchronous motor stator, it generally refers to the structure of the rotor structure.



article by the squirrel-cage asynchronous starting of REPMSM rotor, shaft and rotor core and permanent magnet rotor core composed of plate laminate, and fill in the ndfeb permanent magnets in rotor core, cast aluminum form cage at the same time, as shown in figure 1.



it with asynchronous motor starting process, when the armature winding of the stator zhongtong people balanced three-phase alternating current (ac), forming a circular pattern of rotating magnetic field the rotor static, turn the mouse cage, cutting lines, and induced the alternating current (ac) form the alternating magnetic field, with the stator magnetic field, rotor began to turn.



when the rotor speed close to synchronous speed, no longer produce induced current in the cage bar, but with the constant magnetic field formed by the permanent magnet synchronous rotation, the stator magnetic field into the normal operation.



2 rotor temperature rise reason: when the motor running fever, from the loss of the machine. REPMSM synchronous operation, including the permanent magnet rotor loss loss and harmonic loss, etc.



2. 1)Loss of permanent magnets: summary of resistivity is (1. 44报; l0ˉ)Ω·M, have a certain electrical conductivity, will produce eddy current loss in the alternating magnetic field. Summary of thermal conductivity of 7. 7卡路里/ m. h . ° C, poor heat transfer. Ndfeb magnet is easy to rust, oxidation, make the heat conduction outward, fuelled the rise of temperature of the rotor.



2. 2)Harmonic loss: affected by the factors such as the cogging effect, the stator magnetic field, the harmonic of motor air gap magnetic field is very complex. The harmonic magnetic field in different speed in the air gap relative to the rotor motion, induced current in the rotor core and rat cage bar, resulting in a harmonic losses, make the rotor temperature rise.



3 lower temperature measures: by the above analysis, puts forward the methods to solve these problems are as follows:



3. 1)Permanent magnet segmented, layered: the placement of permanent magnet is no longer the entire length of the material, but a permanent magnets can be divided into several small pieces or more layers, as shown in figure 2. (and to the permanent magnetsLayer)Surface electrophoresis treatment, to reduce the eddy current loss, lowering the temperature rise of the rotor.



3. 2)Augmenting the gap: for asynchronous motor, augmenting the gap will increase magnetic flux leakage, make field current increases, lower efficiency. For the rare earth permanent magnet synchronous motor, increase the air gap, and can increase the higher harmonic air-gap magnetic field magnetic resistance and harmonic leakage resistance, reduce the flux of the cross-linking degree, weaken the harmonic current, reduce, the surface of the rotor loss and harmonic loss and so on, which have the effect of lower temperature rise.



3)Rotor USES half closed El slot or closed slot: so we can reduce the surface of the rotor core loss and pulse vibration within the tooth loss, and make the effective length of air gap decreases, and improve the power factor, and decrease the air gap permeance harmonic pulse amplitude value, reduce permeance harmonic caused by harmonic losses.



4)Select the appropriate slot coordination: the lower the harmonic frequency, rotor slot number, the more the greater the loss; Calm, rotor slot number than close to 1, minimum loss, so as far as possible choose close groove cooperates.



5)Stator winding double winding short distance distribution: double winding short distance distribution according to need to choose different span, can reduce the high order harmonic, and reduce the fundamental electromotive force is not big, so as to effectively improve the waveform air-gap magnetic field, reduce the harmonic losses, reduce the temperature rise.



6)Selects the high quality of ndfeb permanent magnets: found in the actual application, different manufacturers of the same brand of ndfeb permanent magnet performance have bigger difference. Ndfeb different grades, different sizes, eddy current loss and thermal conductivity also differ. Choose the larger thermal conductivity on the high performance ndfeb permanent magnet materials, is advantageous to the heat conduction on the magnetic steel, thus lowering the temperature rise of the rotor.



4 prototype the improvement measures and the effect of the rotor temperature rise: from the above analysis, ndfeb permanent magnets used in the prototype brand, by the previous 40 sh in 33 uh, a new temperature rise test, as a result of the stator core is 80 ℃, temperature, temperature rise of 51 ℃, the temperature of the rotor core is 140 ℃, temperature is 110 ℃. Change after the permanent magnet rotor core temperature decreased by 10 ℃, is a great influence on the temperature rise of the rotor permanent magnet eddy current loss.



5 epilogue: this article discusses the reasons of rare earth permanent magnet synchronous motor rotor temperature rise too high, and put forward the analysis method of lowering the temperature rise of the rotor. After the permanent magnet brand of the original prototype to test and show that permanent magnet eddy current loss had a great influence on the rotor temperature. So, if can take permanent magnets in the motor manufacturing process segment or layered measures, such as rotor temperature rise will be declined.