The brushless motor runs in an automatic control mode, and will not add a starting winding to the rotor like a synchronous motor started under heavy load under variable frequency speed regulation, nor will it cause oscillation and out-of-step when the load changes suddenly. What is the reason for its rotor eddy current loss?
With the continuous improvement of the power and speed of the brushless motor, the permanent magnet overheating and demagnetization caused by the rotor eddy current loss has become a key factor restricting the high power density of the brushless DC motor. This is because the rotor and stator conduct heat and dissipate heat through the air gap. The conditions are poor, causing the rotor temperature to be higher than the stator temperature. The large eddy current loss of the rotor can easily lead to high rotor temperature and increase the risk of overheating and demagnetization of the permanent magnets on the rotor.
Therefore, reducing the eddy current loss of the rotor to reduce the heating of the rotor, and reducing the copper loss to reduce the temperature of the stator to facilitate the heat dissipation of the rotor, which is beneficial to improve the power density of the brushless DC motor.
The time harmonic of the armature current is the main factor that causes the rotor eddy current loss and the effective value of the current to increase. Compared with the sine wave drive mode, the square wave drive mode will bring greater current time harmonics. The discontinuous commutation of the stator current is an important reason for the time harmonics of the current, which leads to the heating of the rotor. The current research methods on the rotor eddy current loss and copper loss of the brushless DC motor mainly include the research on the rotor structure that changes the eddy current induction path and the research on the driving method to reduce the time harmonics of the armature current.
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