Abstract : This paper analyzes the problems existing in changing the air supply method during the operation of air compressors, and introduces the advantages, energy-saving principle and energy-saving effect of variable frequency technology in compressed air systems. Keywords : Air compressor; adjustment method; variable frequency drive; energy saving. Air compressors are important equipment in mines, with long operating times and large motor power. Therefore, high performance and high reliability are required. Although we have strengthened daily operation management, reduced leakage, reasonable lubrication, and regular maintenance, their inherent energy-saving potential has not been fully explored. The following discusses the economical operation of air compressors, that is, obtaining reasonable air demand with the least amount of electricity. 1 Analysis of Adjusting and Changing the Air Supply Method In the past, the air supply was changed by cutting off the intake air. The supply and demand relationship of air compressors is reflected in the change of exhaust pressure. When the exhaust volume of the air compressor just meets the requirements of the air consumption location, the air storage pressure remains unchanged. If this state can be maintained, it is of course the best. However, in reality, the air consumption changes all the time, and the design has a large margin. Therefore, the air compressor's discharge capacity must be greater than the air consumption. If the air compressor continues to operate at a constant speed, the gas in the storage tank will accumulate. When the pressure in the tank rises to the set pressure, two methods are generally used: ① The air compressor is unloaded and no compressed gas is produced. The motor runs under no-load conditions, but its power consumption is still 30% to 60% of the full load, and this part of the electrical energy is wasted; ② The air compressor is stopped. However, if there is no large-capacity storage tank, it will lead to frequent motor starts. The motor starting current is about 4 to 7 times the rated current, which has a significant impact on the power grid and other electrical equipment, and also shortens the service life of the air compressor. 2 Application of Variable Frequency Technology In recent years, variable frequency drive (VFD) speed regulation technology has been widely used. It has high efficiency, wide speed range, high precision, good linearity, good energy saving effect, stable pressure, and no impact on equipment and power grid. Using a frequency converter for speed regulation can ensure operation at the lowest pressure required for production, greatly reducing the input power of the motor. With the aid of pressure closed-loop control, dynamic matching of the air compressor's supply pressure and speed is achieved, reducing the actual power of the motor and achieving energy saving. (1) Control mode of the frequency converter. The frequency converter consists of a frequency converter, a pressure regulator, and a control circuit to form a closed-loop automatic regulation mode. When the air compressor starts, the air consumption at the air consumption point increases or decreases. The pressure sensor set on the outlet of the air compressor system transmits the pressure signal to the frequency converter to change the speed of the air compressor and adjust the supply pressure to achieve constant pressure air supply. (2) Energy saving principle. According to the principle of fluid mechanics, the air supply is proportional to the speed of the motor, and the input power of the motor is proportional to the cube of the speed, that is: Q1/q2=n1/n2, P1/P2=(n1/n), (Q is the air production, n is the speed, and P is the power). Therefore, changing the speed of the air compressor can change the air supply. After changing the speed, the input power changes significantly and decreases at a rate of cubic. For example, when the air supply decreases by 80%, the speed also decreases by 80%, and the input power decreases to 51.2% of the original operating power, reducing the actual input power of the motor and achieving the purpose of saving electricity. That is, the speed of the motor is controlled by the air supply pressure, and the power required by the compressor is the same as the output power of the motor. In addition, the air compressor stops idling and there is no light load operation, so the power saving effect is obvious. (3) Control points. Without changing the original control method and structure, the original electrical control can be used when the frequency converter is stopped. The wiring is simple and does not affect production (Figure 1). Since the air compressor starts under load (there is a small amount of air inside), the frequency converter needs to respond quickly during starting and acceleration/deceleration. Therefore, the power of the frequency converter should be greater than the power of the motor. (4) Advantages of using frequency converter. It achieves soft start of the air compressor, with no peak current, smooth start-up, significantly reduced air compressor noise, and smooth operation. The air compressor's discharge volume is controlled by the motor speed. The valve plates in the cylinder no longer repeatedly open and close, extending the service life of the air compressor, reducing maintenance, ensuring constant air supply pressure, improving air supply quality, and saving a lot of electricity.