The permanent magnet synchronous motor is mainly composed of a stator, a rotor and a housing. Like ordinary AC motors, the stator core is a laminated structure to reduce iron loss due to eddy current and hysteresis effects during motor operation; the winding is usually a three-phase symmetrical structure, but the parameter selection is quite different. The rotor part has various forms, including permanent magnet rotors with starting squirrel cages, and embedded or surface-mounted pure permanent magnet rotors. The rotor core can be made into a solid structure or laminated. The rotor is equipped with permanent magnet material, which is usually called magnetic steel.
When the magnetic motor is working normally, the rotor and stator magnetic fields are in a synchronous state, there is no induced current in the rotor part, no rotor copper loss, hysteresis, and eddy current loss, and there is no need to consider the problem of rotor loss and heating. Generally, permanent magnet motors are powered by special inverters and naturally have a soft start function. In addition, permanent magnet motors are synchronous motors, which have the characteristics of synchronous motors that adjust the power factor by the strength of the excitation, so the power factor can be designed to a specified value.
From the starting perspective, due to the fact that the permanent magnet motor is started by a variable frequency power supply or a matching inverter, the starting process of the permanent magnet motor is very easy to implement; similar to the starting of a variable frequency motor, it avoids the starting defects of ordinary cage-type asynchronous motors.
In short, the efficiency and power factor of permanent magnet motors can be very high, the structure is very simple, and the market has been very hot in the past decade.
However, demagnetization failure is an unavoidable problem for permanent magnet motors. When the current is too large or the temperature is too high, the motor winding temperature will rise instantly, the current will increase sharply, and the permanent magnet will lose magnetism quickly. In the control of permanent magnet motors, an overcurrent protection device is set to avoid the problem of the motor stator winding being burned, but the resulting demagnetization and equipment shutdown are inevitable.
Compared with other motors, permanent magnet motors are not very popular in the market. Both motor manufacturers and users have some unknown technical blind spots, especially when it comes to matching with frequency converters, which often leads to serious discrepancies between design values and test data and must be repeatedly verified.
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