1、 Working principle of air compressor

u Screw type air compressor working principle

Screw type air compressor is composed rotated of by a pair of parallel meshing rotors (or screws rotation) in the cylinder, the volume change of the rotor slot between the air continuously produce periodic air so that the air between the rotor teeth continue to produce periodic volume changes, along the axis of the rotor by the suction side is transmitted to the output side, realize the whole process of screw type air compressor suction, compression and exhaust. The air inlet and the air outlet of the air compressor are respectively arranged located at both ends of the shell, and the grooves of the negative rotor and the teeth of the positive rotor are driven and rotated by the main motor.

u Piston type air compressor working principle

Piston type air compressor is driven by the motor pulley through the coupling of direct drive crankshaft drives the connecting rod and the piston rod, the piston reciprocates in the compressor cylinder, suction, compression, complete discharge process, no pressure or low pressure gas booster, and output to the pressure storage tank. Wherein, the piston assembly, the piston and the cylinder wall and the cylinder cover form a variable volume working chamber, and under the drive of the crank connecting rod, the reciprocating motion is carried out in the cylinder to realize the compression of the gas in the cylinder.

2、 Inverter control scheme

 (1) Control principle

Variable frequency speed regulation system of pipeline pressure as the control object, installed in the gas tube pressure transmitter port will change the pressure of the gas tank into electrical signals sent to the inverter internal PID regulator, compared with the given pressure value, and according to the difference of size according to the established PID control mode of operation, generating a control signal to control the inverter the output voltage and the inverter frequency, adjust the motor speed, so that the actual pressure maintained at a given pressure. In addition, after adopting the scheme, the air compressor motor can realize soft starting by the inverter from the stationary to the steady speed, thus avoiding the large current at starting and the mechanical impact caused by the start to the air compressor. Under normal circumstances, the air compressor works in the frequency converter speed control mode. The inverter when failure occurs, the production process is not allowed to air compressor stops, so the system has set up frequency and frequency switching function, so that when the inverter fault occurs, the power supply through the direct power supply contactor, the air compressor to work as usual.

The air compressor adopts frequency conversion timing technology to control the constant pressure air supply. The system principle block diagram is shown below

Figure 3-1

Figure 3-2

The whole control process is as follows:

Gas demand increase——pressure down——pressure set value and feedback value of stable up——PID output up——the inverter output frequency up —— air compressor motor speed up——flow up——pressure tends to be stable;

Inverter fault —— inverter relay Y2 closed ——contactor KM1 disconnect —— contactor KM2 closed ——air compressor grid power operation.

Note: 18.5KW and above power section of the motor, in Power spare, it is best better to take star delta buck start, this reference map does not provide star delta step-down start circuit diagram.

1、 Control features

u  It can realize smooth soft starting, avoid electrical and mechanical shock, and prolong the service life of the compressed motor and parts;

u The Realize energy-saving operation is realized, and the energy saving is realized while the automatic control is fine;

u It reduces the noise of the air compressor;

u It has the functions of short circuit, no phase loose, over current, over voltage, over load and under voltage;

u The circuit of the motor of the air compressor is equipped with "city electricity" and "electricity saving" contactor, so that there can be two modes of operation, namely, city power operation and power saving operation, and the has corresponding indicator lamp.

5、 The main parameter settings