Energy saving of screw air compressor

Using a pressure variable automatic frequency converter to regulate continuous operation is more economical and has minimal impact on the service life of the equipment.

I want to know the impact on the oil circulation system and cooling system after frequency conversion (lower than the power frequency), and I hope for the answer. A big reward for a reasonable reply that does not duplicate the answer above!

I have found some information on the Internet before and see if it is useful. * Working Principle of Screw Air Compressor A screw air compressor consists of a pair of male and female rotors (or screws) that mesh in parallel with each other and rotate in the cylinder, causing the air between the rotor tooth slots to continuously produce periodic volume changes. The air is transported from the suction side to the output side along the rotor axis, realizing the entire 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 housing. The slots of the female rotor and the teeth of the male rotor are driven by the main motor to rotate. * Working principle of piston air compressor: The electric motor drives the pulley to directly drive the crankshaft through the coupling, driving the connecting rod and piston rod to make the piston reciprocate in the compressor cylinder to complete the suction, compression, discharge and other processes. It boosts the pressure of unpressurized or low-pressure gas and outputs it to the pressure storage tank. Among them, the piston assembly, the piston, the inner wall of the cylinder and the cylinder head form a working chamber with variable volume. Driven by the crank connecting rod, it reciprocates in the cylinder to achieve compression of the gas in the cylinder. The air compressor system controls the main motor operation mode of the air compressor to run at full pressure after starting with star-angle pressure reduction. The specific working process of the air supply system is as follows: When the start button is pressed, the control system turns on the starter coil and opens the oil cut-off valve. The air compressor starts in the unloading mode. At this time, the air inlet valve is in the closed position and the bleed valve opens to discharge the pressure in the oil and gas separator. After waiting for pressure reduction for n seconds (controlled by time relay), the air compressor starts to load and run, and the system pressure begins to rise. If the system pressure rises to the upper limit of the pressure switch, that is, the jump pressure, the controller closes the inlet valve, bleeds the oil-gas separator, and runs the compressor without load. Until the system pressure drops to the lower limit of the pressure switch, that is, under the rebound pressure, the controller opens the inlet valve, closes the oil-gas separator bleed valve, opens the compressor, closes the oil-gas separator bleed valve, and runs the compressor at full load. Energy Saving Analysis of Air Compressor System In the pipeline air supply system, the most basic control object is flow, and the basic task of the air supply system is to meet the user's demand for flow. At present, the common gas flow control methods include adding and unloading gas supply control methods and speed control methods. * Adding and unloading air supply control The adding and unloading air supply control method is the air inlet valve switch control method, that is, when the pressure reaches the upper limit, the valve is closed and the compressor enters light load operation. ； When the pressure reaches the lower limit, the valve opens and the compressor enters full load operation. Since the air compressor cannot rule out the possibility of long-term operation at full load, the capacity of the motor can only be determined according to the maximum need, and the design margin is generally too large. The impact when starting the equipment at power frequency is large, and the motor bearings are greatly worn, so the maintenance of the equipment is heavy. Although they are all reduced-voltage starts, the current at start-up is still very large, which will affect the stability of the power grid and the operation safety of other electrical equipment, and most of them run continuously. Since the driving motor of the general air compressor itself cannot adjust the speed, it cannot directly use changes in pressure or flow to match the speed-down adjustment output power. The motor is not allowed to start frequently, resulting in the motor still running without load when the air consumption is small, resulting in a huge waste of electrical energy. 　　Frequent unloading and loading lead to frequent changes in the pressure of the entire gas network, which cannot maintain a constant working pressure and extend the service life of the compressor. Even when the required flow rate is small due to some adjustment methods of the air compressor (such as adjusting the valve or adjusting the unloading, etc.), since the motor speed remains unchanged, the motor power decreases to a relatively small extent. 　 * Speed ​​control adjusts the flow rate by changing the speed of the air compressor, while the opening of the valve remains unchanged (generally maintaining the maximum opening). When the air compressor speed changes, the lift characteristics of the air supply system change accordingly, while the pipe resistance characteristics remain unchanged. Under this control method, the speed of the air compressor motor is changed through frequency conversion speed regulation technology. The air supply flow of the air compressor can change with the change of air flow to achieve a true balance between supply and demand. While saving energy, the entire system can also achieve optimal working efficiency. The frequency converter is based on the AC-to-AC power conversion principle and can output AC voltage with continuously adjustable frequency according to the needs of the controlled object. The motor speed is proportional to the power frequency. Therefore, using the frequency converter output AC voltage with adjustable frequency as the power supply voltage of the air compressor motor can easily change the air compressor speed. Principle of energy saving in air compressor system It is a more scientific control method to use frequency converter to control the speed of air compressor to achieve energy saving. According to the operating characteristics of the air compressor: Q1 / Q2 = n1 / n2 H1 / H2 = ( n1 / n2 ) 2 P1 / P2 = ( n1 / n2 ) 3 where Q——air volume of air compressor supply pipe network ； H————pipe network pressure ； P————Motor power consumption ； n——air compressor speed. It can be seen from the above formula that when the motor speed drops to 80% of the rated speed, the air volume supplied by the air compressor to the pipe network drops to 80%, the pipe network pressure drops to (80%) 2, and the motor power consumption drops to (80%) 3, or 51.2%. After removing the effects of motor mechanical losses and motor copper and iron losses, the energy saving efficiency is also close to 40%. This is the principle of speed regulation and energy saving. Long-term practice has proven that by connecting a variable frequency energy-saving system to the gas supply system and using variable frequency technology to change the speed of the air compressor to adjust the flow in the pipeline instead of the valve adjustment method, significant energy-saving effects can be achieved. Generally, the energy-saving rate is above 30%. In addition, the soft start function and smooth speed regulation of the frequency converter can achieve smooth adjustment of flow, while reducing startup shock and extending the service life of the unit and pipe set. Air compressor frequency conversion modification plan * Notes on air compressor frequency conversion modification 1) Air compressors are large rotational inertia loads. This starting characteristic can easily cause the V/F control inverter to have skip current protection when starting. It is recommended to select a speed sensorless vector inverter with high starting torque to ensure the continuity of constant pressure air supply and the reliable and stable operation of the equipment. ； 　　2) The air compressor is not allowed to operate at low frequency for a long time. When the speed of the air compressor is too low, on the one hand, the working stability of the air compressor will be deteriorated. On the other hand, the lubrication of the cylinder will be deteriorated, which will accelerate wear. Therefore, the lower limit frequency of operation should not be less than 20Hz ； 　　3) In order to effectively filter out the high-order harmonic components in the inverter output current and reduce the electromagnetic interference caused by high-order harmonics, it is recommended to use an output AC reactor. It can also reduce the motor operating noise and temperature rise, and improve the stability of the motor. * The energy-saving principle of constant pressure air supply is as mentioned above. Flow is the basic control object of the air supply system, and the air supply flow needs to meet the air consumption flow at all times. In the gas supply system, the air pressure in the gas storage pipe can fully reflect the relationship between gas supply capacity and gas demand.: If the gas supply flow rate > the gas flow rate → the gas storage pipe pressure rises; if the air supply flow < the gas flow rate → the gas storage pipe pressure drops; if the air supply flow rate = the gas flow rate → the gas storage pipe pressure remains unchanged. Therefore, keeping the air pressure in the pipeline constant can ensure that the air supply capacity there just meets the gas demand. This is the purpose of the constant pressure gas supply system. When the air compressor uses variable frequency speed regulation technology for constant pressure air supply control, the system principle block diagram is shown in Figure 1. The frequency conversion speed regulation system takes the pipe network pressure as the control object. The pressure transmitter installed at the outlet of the gas storage pipe converts the pressure of the gas storage tank into an electrical signal and sends it to the PID regulator inside the frequency converter. It is compared with the pressure given value and operates according to the established PID control mode based on the difference. The control signal is generated to control the output voltage and inverter frequency of the frequency converter and adjust the motor speed, so that the actual pressure is always maintained at the given pressure. In addition, after adopting this solution, the air compressor motor can be soft-started by the frequency converter from standstill to stable speed, avoiding the large current at startup and the mechanical impact caused by startup to the air compressor. Under normal circumstances, the air compressor works in the frequency converter speed control mode. Once the frequency converter fails, the production process does not allow the air compressor to shut down. Therefore, the system is equipped with a switching function between industrial frequency and variable frequency. In this way, when the frequency converter fails, the industrial frequency power supply can directly supply power through the contactor, so that the air compressor can work as usual. The entire control process is as follows: Air demand ↑ —— Pipeline air pressure ↓ —— The difference between the pressure setting value and the feedback value ↑ —— PID output ↑ —— Inverter output frequency ↑ —— Air compressor motor speed ↑ —— Air supply flow ↑ —— Pipeline air pressure tends to be stable. Pay special attention to that within the pressure tolerance range, the PID of the inverter is not adjusted, that is, the output frequency remains unchanged. Figure 3 The frequency conversion electrical control diagram of the air compressor is shown in Figure 3. The circuit of the air compressor motor is equipped with "mains" and "power-saving" contactors, so that there are two working modes to choose from: "mains operation" and "power-saving operation": In mains operation mode, the frequency converter does not work, and the entire system starts and stops manually and operates at power frequency in the original way. ； In the energy-saving operation mode, the air compressor is directly driven by the frequency converter. The system automatically adjusts the motor speed of the air compressor according to changes in air consumption, so that the air storage tank always maintains a constant pressure air pressure output. Summary: Introducing variable frequency speed regulation technology into the field of air compressors has been an important research topic for various air compressor manufacturers in recent years. All major professional air compressor suppliers have launched their own variable frequency air compressor products, and they have quickly performed very well in their high-end markets. But at present, a large number of power frequency air compressors are widely used. Therefore, the market for air compressor modification is very huge. I sincerely hope that this air compressor frequency conversion transformation solution can help the majority of system integrators, air compressor end users, and electrical automation enthusiasts, or provide them with a new idea.

1# zhx7540 The solution is very good. My company also has a screw air compressor. It is worth learning.* , we also adopt this plan to transform