Application of frequency inverter in air compressor transformation

1 Brief description of the working principle of screw air compressor

The screw air compressor is composed of a pair of parallel yin and yang rotors (or screws) rotating in the cylinder, 

so that the air between the rotor teeth continuously produces periodic volume changes, 

and the air is transported from the suction side to the output side along the rotor axis, realizing the whole process of suction, 

compression and exhaust of the screw air compressor. The air inlet and outlet of the air compressor are located at both ends of the shell, 

and the slots of the yin rotor and the teeth of the yang rotor are driven by the main motor to rotate.

2 Problems existing in the operation of the air compressor

Although the main motor adopts Y-△ step-down starting, the current at starting is still very large, and there is a certain starting time. 

The energy consumed during this period cannot be ignored.

The main motor often works at full load, but the energy is wasted on the outlet valve, which is uneconomical operation and serious waste of electricity.

The main motor operates at industrial frequency, causing the air compressor to make a lot of noise when running.

The impact of the main motor frequency starting equipment is large, and the motor bearing wear is large, so the mechanical work is large during equipment maintenance.

3 Energy-saving principle of air compressor frequency conversion

The control principle is: the pipeline pressure value measured by the pressure transmitter is compared with the set value of the pressure to obtain the deviation, 

and the frequency value of the frequency converter acting on the asynchronous motor is calculated by the PID regulator. 

The frequency converter outputs the corresponding frequency and amplitude of the alternating current to adjust the speed of the motor, 

and the air compressor outputs the corresponding compressed air to the air tank to change the pressure until the pipeline pressure is 

the same as the given pressure value.

4 Benefits of air compressor frequency conversion transformation

Save energy, reduce operating costs, improve pressure control accuracy, extend the service life of the compressor, 

and reduce the noise of the air compressor.

5 Frequency converter transformation requirements

On-site air compressor power: 30KW, maximum working current 59A.

Design requirements: The main motor inverter keeps the outlet pressure of the gas tank stable during operation, 

and the pressure fluctuation range does not exceed ±0.01Mpa; maintain the original power frequency control

 system to ensure that when the inverter is abnormally protected, it can directly cut into the power frequency 

without affecting production; when the gas consumption is small, the inverter is in low-frequency operation or 

enters a dormant state, and the motor winding temperature should be guaranteed not to exceed the allowable range.

According to the site conditions: select SOWAKAM series SW200-030G3B inverter; rated current: 60A; overload capacity: 

inverter rated output current 150%, 1min.