Influence of Eddy Current Loss of Magnetic Steel on Rotor Temperature Rise of Permanent Magnet Motor

The rare earth permanent magnet synchronous motor (REPMSM) has the characteristics of small size, light weight and high efficiency. Theoretically, the rotor has no fundamental loss, and the rotor temperature rise should be low, but the actual situation is not. Taking an increased safety rare earth permanent magnet synchronous motor as an example, the rotor temperature rises up to 125°C during the test. If the rotor temperature is too high, it will cause demagnetization danger to the NdFeB permanent magnet and affect the normal operation of the motor. This paper analyzes the reasons that may lead to excessive temperature rise of the rotor, and puts forward measures to reduce the temperature rise. 1. Rotor structure The stator of REPMSM takes the stator of an asynchronous motor, and its structure generally refers to the structure of the rotor. Different

Rare earth permanent magnet synchronous motor (REPMSM) has the characteristics of small size, light weight and high efficiency. Theoretically, the rotor has no fundamental wave loss, and the rotor temperature rise should be low, but the actual situation is not the case..

to Take a Zeng'an rare earth permanent magnet synchronous motor as an example, the rotor temperature rises up to 1 25°C during the test. If the rotor temperature is too high, it will cause demagnetization of the NdFeB permanent magnet and affect the normal operation of the motor .

This paper analyzes the reasons that may lead to excessive temperature rise of the rotor, and puts forward measures to reduce the temperature rise..

1. rotor structure

The stator of REPMSM takes the stator of an asynchronous motor, and its structure generally refers to the structure of the rotor. The rotor of asynchronous start REPMSM is composed of squirrel cage bar, rotating shaft, rotor iron core and permanent magnet. The rotor iron core is laminated by punching sheets, and NdFeB permanent magnet is filled in the rotor iron core, and aluminum is cast to form a squirrel cage, as shown in Figure 1.

Figure 1 Schematic diagram of rotor structure

The starting process is the same as that of an asynchronous motor. When three-phase symmetrical alternating current flows through the stator armature winding, a circular rotating magnetic field is formed. At this time, the rotor is stationary, and the rotor squirrel cage cuts the magnetic lines of force, and induces alternating current to form an alternating magnetic field, which interacts with the stator magnetic field., The rotor starts to rotate.

When the rotor speed is close to the synchronous speed, the induced current is no longer generated in the squirrel cage bar, but the constant magnetic field formed by the permanent magnet rotates synchronously with the stator magnetic field and enters normal operation.

2. Causes of rotor temperature rise

The heating of the motor during operation comes from the loss of the motor. When REPMSM operates synchronously, the rotor loss includes permanent magnet loss and harmonic loss.

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