With the emergence of Nd-Fe-B rare earth magnetic steel, permanent magnet motor has developed rapidly. Permanent magnet variable frequency motor speed regulation system has entered all walks of life, which has the potential to replace asynchronous motor variable frequency system. The application of permanent magnet motor + special frequency converter in air compressor system has achieved good energy-saving effect.

At present, most air compressors adopt the control mode of asynchronous motor + frequency converter to reduce the working pressure of the air compressor by adjusting the motor speed and ensuring the constant working pressure. It saves about 15% - 20% of the rated power and energy loss of the air compressor system controlled by the contactor due to the "idle" period of the motor. At the same time, the reduction of working pressure reduces the power loss during work, so as to achieve the purpose of better energy saving. According to the different pause time of the air compressor system, the frequency conversion speed regulation mode is better than the contactor control mode, and the power saving rate is 20 ~ 40%.

However, the cost of this type of air compressor system is high, and the efficiency of the asynchronous motor for driving will decline rapidly with the decline of working speed. Especially in low-frequency operation, the efficiency of the motor will be greatly reduced.

Because the permanent magnet variable frequency motor itself has magnetic steel and the excitation magnetic field is provided by the permanent magnet, it does not need to absorb reactive excitation power from the power grid. Therefore, the power factor of the permanent magnet variable frequency motor is very high up to more than 0.93. Therefore, the permanent magnet variable frequency motor can be made into more poles, shorten the winding end, reduce copper loss and improve the efficiency of the permanent magnet variable frequency motor, There is no need to worry about the low power factor.

Take the special motor for kyt180 air compressor produced by Shandong lijiu Special Motor Co., Ltd. as an example, with rated power of 22KW and rated speed of 3600 rpm. When the rated torque is 600 rpm, the efficiency is more than 85%. So that the motor does not need fan cooling. Under the condition of self-contained fan, the temperature rise is 2 ° lower than that under rated conditions.

Compared with asynchronous variable frequency motor, when starting at low frequency, the main magnetic field of asynchronous variable frequency motor is weak and the power factor is low. The rated torque can be reached only when the starting current is 1.5 ~ 2 times of the rated current. The main magnetic field of permanent magnet variable frequency motor is constant, the stator current is almost all active current, and the rated torque can be reached when the starting current is twice the rated current. With a small starting current, a large starting torque can be obtained, and the speed of the system increases quickly, which reduces the pressure fluctuation of the air storage tank and ensures the stable and reliable operation of the system.