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Advantages and disadvantages of rare earth permanent magnet synchronous motor compared with squirrel-cage asynchronous motor


A ：high efficiency and energy saving
1) no slip error, no fundamental wave loss of iron and copper on the rotor;
2) the rotor permanent magnet is used for excitation, and the power factor can reach 1, saving the reactive power. On the other hand, the stator current decreases, the stator copper loss decreases, and the efficiency increases.
3) the polar arc coefficient is generally greater than the polar arc coefficient of the asynchronous motor. When the power supply voltage and the stator structure are fixed, the average magnetic density is smaller than the asynchronous motor and the iron loss is smaller.
4) stray loss of rare earth permanent magnet synchronous motor: it is generally believed that the non-sinusoidal magnetic field of the permanent magnet increases the stray loss, but on the other hand, the large air gap of the rare earth permanent magnet synchronous motor reduces the stray loss.

B ：small size, light weight, high power density
1) analysis from the perspective of electromagnetic load: the calculated polar arc coefficient is larger than that of asynchronous motor, and the volume and weight decrease under the same condition of electrical load and air gap magnetic density.
2) from the perspective of thermal load, due to its high efficiency and low heat, the electrical load and air-gap magnetic density can be appropriately improved, and the effective volume of the motor can be reduced.

C ： excellent speed regulation performance
1) the feature that the speed is strictly proportional to the frequency is very suitable for the system with constant speed and accurate synchronization.

D ：deficiency
1) compared with asynchronous motor, rare earth permanent magnet synchronous motor has complex structure, high cost and difficult starting.


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