How to improve the efficiency of permanent magnet motors

Permanent magnet synchronous motor is mainly composed of stator, rotor and housing parts. Like ordinary AC motors, the stator core is a lamination structure to reduce the iron loss due to eddy current and hysteresis effects when the motor is running; the windings are usually three-phase symmetrical structures, but the selection of parameters is quite different. The rotor part has various forms, including a permanent magnet rotor with a starting squirrel cage, and an embedded or surface-mounted pure permanent magnet rotor. The rotor core can be made of solid structure or laminated. The rotor is equipped with permanent magnet material, which is commonly called magnet steel.

Under normal operation of the permanent magnet motor, the rotor and stator magnetic fields are in a synchronized state, and 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 heat generation. Generally, the permanent magnet motor is powered by a special frequency converter, and naturally has a soft start function. In addition, the permanent magnet motor belongs to the synchronous motor, which has the characteristics of adjusting the power factor of the synchronous motor through the excitation strength, so the power factor can be designed to a specified value.

From the perspective of starting, 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 easy to achieve; similar to the starting of the variable frequency motor, it avoids the starting defect of the ordinary squirrel asynchronous motor.

In short, the efficiency and power factor of the permanent magnet motor can be very high, and the structure is very simple, and the market has been very popular in the past ten years.

However, the demagnetization fault is an unavoidable problem of the permanent magnet motor. When the current is too large or the temperature is too high, the temperature of the motor winding will rise instantaneously, the current will increase sharply, and the permanent magnet will lose its magnetization rapidly. In the control of the permanent magnet motor, an overcurrent protection device is set to avoid the problem of the motor stator winding being burned, but the resulting loss of magnetism and equipment shutdown are inevitable.

Compared with other motors, the application of permanent magnet motors in the market is not very popular. Whether for motor manufacturers or users, there are some unknown technical blind spots, especially when it comes to matching with frequency converters, which often lead to design problems. The value is seriously inconsistent with the experimental data and must be repeatedly verified.