Screw air compressor is widely used in industrial production, and a load-unload valve is used in its control to control the air supply of the air compressor. Due to the working cycle of the gas equipment or the difference in the production process, the gas consumption fluctuates, which sometimes causes the air compressor to be frequently loaded and unloaded. After the air compressor is unloaded, the motor still runs at a power frequency, which not only wastes electric energy but also increases the mechanical wear of the equipment; the loading process of the air compressor is suddenly loaded, which also causes a great impact on the equipment and the power grid. Therefore, the frequency conversion transformation of the air compressor has the effects of improving the starting and running mode of the motor, reducing the mechanical wear of the equipment, and saving electric energy within a certain range. First, the working principle of the screw air compressor The single screw air compressor is taken as an example to illustrate the working principle of the air compressor. Figure 1 shows the structural schematic diagram of the single screw air compressor. The working process of screw air compressor is divided into four processes: suction, sealing and conveying, compression and exhaust. When the screw rotates in the housing, the screw meshes with the groove of the housing, the air is sucked in by the air inlet, and the oil is also sucked in, and the sucked oil is sealed and transported to the exhaust port due to the rotation of the meshing surface; During the process, the meshing gap of the tooth groove gradually becomes smaller, and the oil and gas is compressed; when the meshing surface of the tooth groove rotates to the exhaust port of the casing, the higher pressure oil and gas mixed gas is discharged from the body. Second, the composition of the compressed gas supply system and the control principle of the air compressor 1. The compressed air supply system consists of a factory air compressed gas supply system generally consists of an air compressor, a cold dryer, a filter, a gas storage tank, a pipeline, and a valve. And gas equipment. Figure 2 shows the schematic diagram of the composition of the compressed gas supply system. 2. Control principle of air compressor In the air compressor control system of the factory, the pressure relay installed on the rear pipeline is generally used to control the operation of the air compressor. When the air compressor is started, the loading valve is in the inoperative state, the loading cylinder does not move, the air inlet of the air compressor head is closed, and the motor is started without load. When the air compressor starts running, if the back-end equipment uses a large amount of gas, and the pressure of the compressed gas in the gas storage tank and the rear-end pipeline does not reach the upper pressure limit, the controller acts to load the valve, open the intake port, and the motor load Run, continuously producing compressed air to the rear line. If the gas is stopped by the gas equipment at the back end, the pressure of the compressed gas in the rear end pipeline and the gas storage tank gradually increases. When the pressure upper limit setting value is reached, the pressure controller issues an unloading signal, and the loading valve stops working, and the intake port Off, the motor runs at no load. Figure 3 is a schematic diagram of the system of a brand of air compressor. Third, screw air compressor frequency conversion transformation air compressor power frequency operation and frequency conversion operation comparison: air compressor motor power is generally larger, the start mode is mostly no-load (unload) star-delta start The loading and unloading methods are all instantaneous. This makes the air compressor have a large starting current when starting, and the mechanical impact on the equipment is large when loading and unloading; not only causing fluctuations in the power supply voltage, but also causing large fluctuations in the compressed air source; It also accelerates wear and tear on the equipment and reduces the life of the equipment. The frequency conversion of the air compressor can make the motor soft start and soft stop, reduce the starting impact and prolong the service life of the equipment. At the same time, due to the variable operating frequency of the motor, the air compressor can automatically adjust the motor speed according to the amount of gas used. The frequent loading and unloading of the motor is reduced, so that the air pressure of the air supply system is maintained constant, and the power is saved to a certain extent. Frequency conversion of the main circuit and control circuit of air compressor: Take a brand air compressor as an example, Figure 4 is its circuit schematic. It can be seen that the air compressor of the brand model adopts the star-delta start mode. When the main circuit is modified, the inverter is serially connected into the original power supply line; the original load valve control circuit is disconnected, and the original load valve is controlled. The output is changed to a time relay JS. The coil end of the time relay is connected to the zero line of the 220V control circuit, and the other end is connected to the loading output point of the PLC. The one end of the loading valve is directly connected to the zero line of the 220V control circuit, and the other end is passed. A pair of normally open contacts of the time relay JS is connected to the live line of the 220V control circuit, and the loading time is extended by the time relay. The forward rotation signal terminal FWD of the inverter is connected to the common control terminal CM of the inverter through a pair of normally open contacts of the AC contactor KM1 on the main circuit of the motor. The analog feedback signal C1 and GND terminals of the inverter are connected to the pressure sensor on the compressed gas delivery line. Figure 5 is a schematic diagram of the circuit after the frequency conversion. This article is edited by China DSNEAIR Compressor Manufactory (https://air-compressor.net). Please indicate