Compared with the traditional electric excitation motor, the rare earth permanent magnet motor has the advantages of simple structure and reliable operation; small size and light weight; low loss, and high efficiency; the shape and size of the motor can be flexible and diverse, and the application range is extremely wide.
2. Advantages of permanent magnet motors
(1) High-efficiency permanent magnet synchronous motor does not need reactive excitation current, which can significantly improve power factor, reduce stator current and stator resistance loss, and have no rotor copper loss during stable operation, thereby reducing fan and corresponding wind friction. The loss and efficiency can be increased by 2 to 8 percentage points compared with the induction motor of the same specification. Moreover, the permanent magnet synchronous motor can maintain high efficiency and power factor within the range of 25% to 120% of the rated load, which makes the energy-saving effect more significant during the light load operation. This type of motor is generally equipped with a starting winding on the rotor, which has the ability to start directly at a certain frequency and voltage.
(2) The pm motors can achieve continuous operation at low speed and high torque, which cannot be achieved by asynchronous motors and DC motors, and the permanent magnet synchronous motor can have an ultra-high efficiency of more than 90% under the load range of 25%-120%. The peak current at startup is small, the startup is stable, and it can better protect other equipment in the power grid system, and can well adapt to various working conditions of the air compressor.
3. Application of permanent magnet motor in the air compressor industry
1. The exhaust pressure of the permanent magnet variable frequency air compressor is stable
The frequency converter screw air compressor adopts the stepless variable speed characteristic of the frequency converter and realizes a smooth start through the internal controller or PID regulator. When there is a large fluctuation in the gas consumption, the operation can be adjusted quickly. Compared with the power frequency lower limit switch control, the system has higher stability.
2. Low noise permanent magnet variable frequency air compressor
Most of the working state of the inverter is below the rated speed, which reduces the mechanical noise and wear of the host, and prolongs the maintenance and service life. If the fan also adopts frequency conversion speed regulation, the noise of the air compressor during operation can be significantly reduced.
3. The permanent magnet variable frequency air compressor has no starting impact
Because the inverter itself has the function of a soft starter, the starting current can be controlled within 1.2 times the rated current. In comparison, the power frequency starting current is usually more than 6 times, so the permanent magnet variable starting shock is small.
4. Variable flow control of permanent magnet variable frequency air compressor
The power frequency air compressor can only work under the specified exhaust, and the exhaust of the variable frequency air compressor can be adjusted within a large range. The frequency conversion speed regulation can adjust the speed of the motor in real-time according to the actual gas consumption, and adjust and control the exhaust. The air compressor can automatically sleep when the air consumption is low, which greatly reduces the energy consumption. Improve the control method to further improve the energy-saving effect.
Because the frequency converter adopts over-modulation technology (converting the baseband signal into a transmission signal), even if the AC power supply voltage is slightly lower, it can output enough torque to drive the motor to work. When the voltage is slightly higher, the voltage output to the motor will not be too high. For self-generating enterprises, variable frequency speed regulation can give full play to its advantages. According to the characteristics of the motor frequency converter (the variable frequency air compressor works in energy saving under the rated voltage), it has an obvious effect on the places with the low grid voltage.