In the commercial frequency air compressors currently in operation, a large part of the time is entered under non-full load conditions. The drawbacks of the traditional power frequency control cause a large amount of energy waste, resulting in low efficiency. Delta inverter is applied in the modification of air compressor. It can automatically adjust the speed according to the pressure feedback condition, ensure the output pressure is set, improve the ft efficiency and supply quality, and achieve real energy saving. According to statistics, 60% of China's electric energy is consumed by fans and pumps widely used in various industries, while air compressors account for about 15% of 60%, that is, air compressors consume 9% of electricity consumption in China. %. The air compressor has a long running time and is equipped with a large motor power. If it can reduce the power consumption of the air compressor and improve the economic operation of the air compressor, it has a certain meaning for energy saving. After the transformation, the inverter is used to drive the motor. The inverter can automatically adjust the speed according to the user's gas consumption, maintain the gas storage pressure unchanged, the motor input power is greatly reduced, and the pressure closed-loop control is used to realize the air supply pressure of the air compressor. Dynamic matching of the speed reduces the actual input power of the motor to achieve energy saving. 2 working frequency screw air compressor working principle The screw air compressor is rotated by the screw in the cylinder, so that the air between the rotor slots continuously produces a periodic volume change, and the air is transported from the suction side to the output along the rotor axis. On the side, the whole process of suction, compression and exhaust of the screw air compressor is realized. The air inlet and the air outlet of the air compressor are respectively located at both ends of the housing, and the slots of the female rotor and the male rotor teeth are driven to rotate by the main motor as shown. First of all, the shaft power required on the drive shaft of the air compressor has a direct relationship with the exhaust pressure and the air compressor speed. That is, in actual operation, the air compressor is not changed frequently due to the use of compressed air. Operating under rated conditions, and the pressure of the air compressor exhaust pressure directly affects the actual shaft power. The higher the yin and yang rotor of the exhaust pressure screw air compressor, the greater the required shaft power. Secondly, in order to meet the requirements of the change of gas consumption, the gas in the gas storage tank must maintain a certain pressure. At present, most air compressors use a cut-off air intake adjustment method to change the amount of air discharged to the air tank. The relationship between the supply and demand of the air compressor air volume is the change of the exhaust pressure. When the air compressor exhaust volume meets the production gas demand, the gas storage pressure remains unchanged. If this state can be maintained, it is of course the best, but actually The gas consumption is changed at any time, and the design redundancy is large, so the air compressor exhaust volume must be greater than the gas consumption. If the air compressor is still running at a constant speed, the gas in the gas storage tank will accumulate more. When the pressure in the tank rises to the set pressure, two methods are generally used: one is the unloading operation of the air compressor, the compressed gas is not generated, the motor is in no-load operation, and the power consumption is still full load 30- 60%, this part of the power is abolished by white waves; another way is to stop the air compressor operation, so it seems that the energy wasted by the air compressor idling or venting is eliminated, but if there is no large volume of gas storage tank It will bring frequent start of the motor. The no-load starting current of the air compressor is about 57 times of the rated current. It will have a greater impact on the power grid and other electrical equipment, and the service life of the air compressor will also be shortened. 3 Power frequency control screw air compressor problems After analysis, power frequency control screw air compressor mainly has the following four major problems: (1) power frequency screw air compressor generally adopts direct start or star-angle start, although star - The angle start is decompression start, but the starting current is very large, which will affect the stability of the power grid and the safety of other electrical equipment. (2) The power frequency screw air compressor motor work is divided into two types, one is lower than The lower limit of pressure starts, stops above the upper limit of pressure, and this type of operation has frequent start; the second type is that the motor runs all the time, and the loading and unloading of the machine head is controlled by the loading valve, both of which have a large amount of waste of electric energy; 3) The power frequency start has a great impact on the equipment, and the motor bearing wears a large amount, so the equipment maintenance workload is large; (4) The air compressor operating at the power frequency has a large noise operation. 4 frequency conversion transformation scheme 4.1 simple transformation scheme The drive of the motor is driven by the frequency converter. The gas storage tank needs to connect the pressure type of the analog output to the frequency converter, and the PID control is completed by the frequency converter itself. The original controller is reserved for processing some status signals of the original air compressor as shown. 4.2 Simple transformation analysis (2) Need to increase the pressure transmitter, provide pressure analog signal to the inverter to do P1D pressure feedback; standard pressure value; fan, after the frequency conversion motor running speed is reduced, the motor cooling effect is not good, you can set the lower limit The frequency ensures the heat dissipation of the motor; sleep can automatically wake up. 4.3 Complex retrofit scheme Frequency conversion retrofit scheme In order to ensure uninterrupted air supply, it can be switched to the power frequency state when the inverter is faulty. The air compressor that needs to be modified has the work/frequency conversion function. There are two implementation methods. In order to replace the air compressor controller, the controller with the work/change switching function is adopted; the second method is to replace the air compressor controller, and the control loop needs to be redesigned to realize the work/variable control, which needs to be based on the customer's existing The control circuit is designed. As shown. 4.4 Complex transformation analysis (1) To increase the frequency conversion function, it is necessary to change the control mode, the modification of the original control panel is large, and the cost will increase a lot; (2) The gas storage tank is also required to provide the pressure analog signal to the inverter to achieve voltage regulation. PID control; (3) Applicable to occasions where the air source cannot be interrupted; (4) After the transformation, when the inverter is out of line fault, it should be able to automatically switch to the power frequency after a delay; (5) due to the original motor cooling fan For the axial flow fan, the motor running speed is reduced after the frequency conversion, the motor heat dissipation effect is not good before, the lower limit frequency can be set to ensure the heat dissipation of the motor; (6) the system does not need gas for a long time, the system automatically enters sleep and can automatically wake up. External signal|Pressure feedback signal controller output signal main circuit control chart attached table different power saving data characteristics 5.1C2000 product features (2) induction motor and synchronous motor control integration; line editing; output current 120% / min; heavy load Rated output current 150% / min; upper), brake braking unit (30kW or less); enjoy the protection level; 5.2CP2000 product features (4) long life design and life detection of important parts; acceptability; 50° C ambient temperature environment, automatically adjust the output rating to maintain high-efficiency operation of the inverter; 6 the dominant value current of the inverter air compressor, start smoothly; (2) greatly reduce the noise of the compressor system; and self-protection, no need for special care; In the case of longevity, reduced maintenance, and gas quality; the energy saving effect is more obvious. 7 Benefit Analysis after Frequency Conversion Reconstruction 7.1 Energy Saving Air Compressor The original purpose of the transformation is to save energy consumption. According to the amount of gas used in the field, the maximum energy saving is about 40%. Energy saving mainly comes from two aspects, one is to automatically adjust the speed according to the amount of gas used; the other is the energy saving effect brought by the constant pressure. 7.2 Maintenance cost reduction Because the frequency converter is soft start, the impact on the whole equipment is reduced at startup, so the cost of shutdown maintenance is greatly reduced, and the service life of the compressor can be prolonged. 7.3 Improve Pressure Control Accuracy The frequency converter has precise pressure control capability, and the air pressure output of the compressor matches the air volume required by the user air system. The output air volume of the inverter controlled compressor changes as the motor speed changes. Since the accuracy of the variable speed control motor speed is increased, it can keep the system pressure variation of the pipe network substantially unchanged. 7.4 Reduce the noise of the air compressor operation After the frequency conversion, the running speed of the motor is reduced, which greatly reduces the noise of the air compressor operation. 8 variable-frequency air compressor power-saving calculation example The average gas production only accounts for 70% of the rated exhaust gas, 4000 hours a year, 0.7 yuan / kWh, and the power consumption of the inverter air compressor: a) no-load Loss: 30% unloading time * hourly no-load loss during unloading) X The above data can be found in the total multi-power consumption schedule. 9 Conclusion For the transformation of screw air compressor, according to the customer's gas situation, the maximum energy saving reaches 40%. At the same time, the screw air compressor after the transformation, because the system impact is small, the operation is more stable, providing users with a reliable gas source. It is a reliable choice for customers. Beijing University of Science and Technology, majoring in industrial automation, is currently a senior application engineer in the inverter product department of Zhongda Dentsu Co., Ltd., engaged in the testing and promotion of Delta inverter products, with rich experience and comprehensive knowledge. As a professional heat pump water heater manufacturer, NEW ENERGY provides different kinds of residential and commercial water heater products. 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