1 Working principle of air compressor The working principle of the screw air compressor, the air is sucked through the air filter and the suction regulating valve. The regulating valve is mainly used to adjust the compression chamber formed by the cylinder, the rotor and the sliding piece, and the rotation of the female and male rotors is eccentric with respect to the cylinder. The way it works. The slide is mounted in the groove of the rotor and pushes the slide to the cylinder wall by centrifugal force. The efficient oil filling system ensures good cooling of the compressor and minimum comfort consumption of the lubricant, and a thin layer formed on the cylinder wall. the oil film prevents direct contact between the wear caused by the metal member. The compressed air has a higher temperature, which is mixed with a certain amount of oil and gas, and is separated by the oil separator. After that, the oil and gas are cooled by the oil cooler and flowed back to the storage tank through the oil filter, and the air passes through the gas aftercooler (air The cooling device is cooled to enter the gas storage tank. 2 Air compressor frequency conversion energy saving principle The basic operation mode of the screw air compressor is the loading and unloading mode. When the load is reduced, the motor is idling, and the energy is wasted. If the inverter is used to adjust the speed by changing the frequency of the motor, the inverter control controls the air volume per unit time of the air compressor by changing the speed of the motor, thereby achieving the pressure of the control pipeline. Has obvious energy saving effect. The schematic diagram of the air compressor frequency conversion energy-saving system is shown in Figure 2. The principle is as follows: the pressure value of the pipe network measured by the pressure transmitter is compared with the set value of the pressure, and the deviation is obtained, and the frequency value of the frequency converter acting on the asynchronous motor is calculated by the PID regulator. The AC frequency of the corresponding frequency and amplitude output by the inverter gets the corresponding speed on the motor. Then the compressed air output from the air compressor is output to the gas storage tank, and the pressure is changed until the pipe network pressure is the same as the given pressure value. (1) The air compressor is a large moment of inertia load. This kind of starting characteristic can easily cause the inverter to skip the flow protection during startup. It is recommended to use a speedless vector inverter with high starting torque to ensure that it can be realized. The continuity of constant pressure air supply ensures reliable and stable operation of the equipment. (2) The air compressor is not allowed to run at low frequency for a long time, and the air compressor speed is too low. On the one hand, the stability of the air compressor is deteriorated, and on the other hand, the lubrication degree of the cylinder is deteriorated, which will accelerate wear. Therefore, the working limit should be no less than 20Hz. (3) It is recommended to use a frequency converter with a power rating higher than that of the air compressor to avoid frequent tripping of the air compressor. (4) In order to effectively filter out the higher harmonic components in the inverter output current and reduce the electromagnetic interference caused by higher harmonics, it is recommended to use the output AC reactor to reduce the noise of the motor operation and improve the stability of the motor. Sex. (5) The designed system should have two sets of control loops, frequency conversion and power frequency, to ensure that the inverter has abnormal jump protection without affecting production. 3.1 system principle design The control system consists of the following components: frequency converter, programmable controller, frequency converter cabinet, reactor, pressure transmitter, oscillating sensor, contactor, air switch, cable, ammeter, voltmeter, button, transformer, etc. The PLC consists of a touch screen, a power supply, a CPU, an analog output module, a digital input, and an output module. Among them, PLC is used to realize the control of the electrical part. It consists of five parts: start, run, stop, switch, alarm and fault self-diagnosis. Start: Take two motors M1, M2 as an example, you can select the inverter / power frequency start through the transfer switch. Operation: Normally, the motor M1 is in the variable frequency speed regulation state, and the motor M2 is in the shutdown state. The on-site pressure transmitter detects the outlet pressure of the pipe network and compares it with the given value. After the PID command is calculated, the frequency signal is obtained, and the rotational speed is adjusted to reach the required pressure. Stop: Press the stop button, the PLC controls all contactors to open and the inverter stops working. Switching: realize M1, M2 power frequency and frequency conversion. Alarm and fault self-diagnosis: There are generally four quantities to be monitored inside the air compressor: cooling water pressure monitoring, lubricating oil monitoring, body temperature monitoring, and gas tank pressure monitoring. Take a factory air compressor as an example. The parameters tested before the transformation are as follows: motor power 110KW, outlet pressure is 5.9-6.5MPa, running time is 12 hours/day, 320 days in a year, loading time is 15 seconds, load shedding time is 15 seconds; loading current is 190A, The load shedding current is 90A. After testing, the power saving rate is above 30%. The annual electricity saving (according to 30%) is calculated as follows: W electricity consumption = 12 × 320 × 110 × 30% = 1.27 × 105 (kWh) It can be seen that the power saving effect is obvious. In addition, the system has other advantages after the transformation. First of all, the noise of the machine is reduced. The PLC and the frequency converter realize the soft start and soft stop of the machine, which avoids the impact on the power grid when the air compressor starts, and reduces the maintenance amount of the equipment. Second, two sets of control loops ensure normal and safe operation of the system. Finally, the degree of automation is high, overcoming the shortcomings of manual adjustment of the original system. Starch Ether,Hydroxypropyl Starch Ether HPS,Starch Ether HPS,Starch Ether HPS For Tile Adhesive Shijiazhuang Shangzu Building Materials Technology Co.,Ltd. , https://www.shangzuchem.com
2.3 frequency conversion transformation considerations
3 PLC-based air compressor frequency conversion control system
3.2 Case Analysis