Transformation and application of frequency conversion energy-saving technology on traditional air compressor

The false twisting machine (elastic wire machine) is a device for curing the pre-oriented yarn of polyester. In addition to the process of preparing compressed air for the production process, it is also necessary to provide network pressure for the process needs in different types of processing. The air flow with a certain pressure changes the structural effect of the fiber to produce different yarn characteristics. The use of compressed air has broadly expanded the range of machine processing to a certain extent.

There are many dense areas in the area along the Yangtze River in Jiangsu Province. Many of them are limited in size due to the small scale, and there are many energy wastes caused by unreasonable investment. With the increasing use of electrical equipment and the increasing tension of energy, the contradiction of insufficient power is becoming more and more obvious. As a result, more and more regions have experienced peak power cuts, which has made more companies realize the importance of saving energy. In turn, it turned to consider energy-saving renovations for “power-hungry households” such as air compressors.

2 The necessity of retrofitting analysis The traditional control method of air compressor (referred to as air compressor) is like adding one unloading air supply control, that is, when the storage pressure reaches the upper limit, the intake valve is closed, and the compressor enters the unloading operation state; the pressure arrives. When the lower limit is set, the intake valve is opened and the compressor enters full load operation. In actual work, due to the constant change of the consumption of air pressure, the air compressor always works in the repeated ''full load-unloading' working state. The idle current during unloading is about 30%~50% of the rated motor current, this part The power consumption becomes the idle loss of the machine at the rated speed. Therefore, long-term no-load operation seriously wastes power.

When the power frequency starts, the current of the motor is about 7~8 times of the rated current. Even if the YA step-down is used, the current at the start is still 2~3 times of the rated current. The power interference caused by the power supply affects the stability of the power grid and other The operation of the electrical equipment is safe.

From the mechanical analysis, the air compressor has a large wear of the motor bearing under the long-term high-speed operation state, and also causes a large amount of maintenance of the equipment.

3 The design of the transformation plan The control goal of the air compressor site is to maintain the constant pressure of the pipeline, that is, the constant pressure gas supply requirement. According to the customer scale and the actual situation on site, we have set two transformation schemes: simple open loop variable frequency control and closed loop feedback type variable frequency control. Users can choose according to the actual requirements of the site.

3.1 Open-loop variable-frequency control Open-loop variable-frequency control flow chart As simple open-loop variable-frequency control transformation program debugging and use: Initially set the operating frequency of the inverter f to close the air compressor intake valve to start, the inverter drives the motor It starts almost smoothly at no load, so the load torque is small. After starting, open the intake valve. After the pressure-up process, check whether the air pressure meets the requirements of production gas supply through the pressure gauge. If the pressure is too small or decreases during use, the gas supply is less than the gas consumption, and the working frequency needs to be increased appropriately. If the pressure is too high or rising, the gas supply is greater than the gas consumption, and the operating frequency needs to be appropriately reduced. During the use process, the user can reduce the consumption frequency of the inverter by directly changing the operating frequency f of the inverter through the operation panel or frequency adjustment knob of the inverter until the pressure does not fluctuate.

The open loop control method has the advantages of fewer peripheral circuits, simple modification, low cost, and the like, and can effectively maintain the constant air pressure. This kind of transformation method is “small investment and quick effect”. It is simple, intuitive, easy to operate and easy to maintain. It is very suitable for enterprises with small scale and weak technical strength. The disadvantage is that the working frequency should be manually adjusted before each large gas consumption change. It is necessary to manually check the air pressure condition, and it is necessary to pay attention to whether the new large-capacity gas equipment is put into use or whether there is a gas leakage phenomenon, so as to avoid the air pressure. Large changes.

3.2 Closed-loop feedback type variable frequency control Closed-loop feedback type frequency conversion control, that is, adding a set of pressure sensing equipment based on open loop control. The pressure transmitter converts the exhaust pressure monitored by the pressure sensor into an electric signal and feeds it back to the internal PID regulator of the inverter, compares it with the pressure reference value (PI percentage setting, etc.), and controls according to the predetermined PID according to the magnitude of the difference. The mode is operated, and the inverter adjusts the working voltage output according to the real-time pressure condition, and changes the rotation speed of the motor, so that the actual pressure is always maintained within the allowable range of the given pressure. Therefore, the air supply flow rate of the air compressor can be changed with the change of the gas flow rate to achieve a true balance between supply and demand, and the entire system can achieve the best working efficiency while saving energy. The control block diagram is as shown.

Variable-frequency speed control closed-loop feedback control block diagram The advantages of closed-loop control are accurate control, automatic monitoring instead of manual inspection, high efficiency of the system, suitable for large and medium-sized workshops or the transformation of high pressure fluctuations in production. The disadvantage is that the transformation process is more complicated than the open loop method. It is necessary to test the parameters of the PID and other parameters several times. Therefore, the technician needs to perform the test several times and summarize the optimal setting result.

4 Implementation of the scheme 4.1 Selection of the device The selection of the inverter is selected according to the rated power of the matching motor and the appropriate capacity is reserved. It is recommended to use the speed sensorless vector inverter to improve the starting effect; the inverter has built-in PID adjustment. Function and 4 ~ 10VDC analog signal interface (for the input and input of pressure sensing signal); the inverter needs to be equipped with digital operation / display panel or frequency adjustment knob; the inverter has good quality and reliable operation.

No. output, short hysteresis time, accurate measurement and reliable quality products, it is recommended to select current type signal output for consideration of on-site interference prevention.

It is recommended that the peripheral circuit be equipped with a start/stop button, emergency stop protection button, motor overheat protection, and reduce the inverter harmonic interference AC reactor/filter and other peripheral devices. All factors that may involve personal safety should be first Focus on consideration.

4.2 The implementation of the transformation is equipped with a piston compressor, the rated power of the main motor is 130kW. The air compressor is in full load and unloading operation for a long time, and the energy is wasted greatly. The Delixi CDI9000-G series 132kW inverter is used for open loop. The method is controlled and modified. The average current is about 40A when the minimum demand pressure and air supply are measured, which is 20A lower than before the transformation; the average working current is about 120A when the maximum demand pressure and air supply is required, which is 40A lower than before the transformation. According to different varieties of production, the average monthly energy can be saved by 25%~30%, and the annual electricity cost saved is about 70,000 yuan. It has been used for nearly 3 years after the transformation and is working well.

4.3 Remarks in the use of the transformation In the actual use of the process should pay attention to the following aspects: 4.3.1 The actual operating frequency of the inverter is not set as small as possible. Because some inverters are not ideal for low-frequency control performance, when the frequency is low, there will be insufficient torque, and an alarm such as inverter overload will cause shutdown. Moreover, the air compressor should not be operated in the low frequency state for a long time, and the working stability of the air compressor is deteriorated due to the low rotation speed. On the other hand, the lubrication effect of the cylinder body is deteriorated, and the wear will be accelerated, so the overall situation is improved. The recommended operating frequency should be no less than 20Hz, and the recommended minimum frequency is around 25Hz.

4.3.2 Most of the inverters are designed with a torque compensation function to increase the output voltage at low frequencies. However, the saturation of the magnetic flux will cause the excitation current to be too large, the motor windings will overheat, and the motor will be damaged in severe cases, so the compensation value should not be set too large.

4.3.3 Since the main motor is running at a lower power frequency, the heat dissipation effect will be worse for the motor that is self-heating by the fan blades mounted on the motor shaft. Therefore, it should be noted whether the temperature rise of the motor is In the safety allowable range, external heat dissipation measures should be added as necessary.

5 Conclusions The traditional air compressors of the traditional drag mode have lower investment costs than the inverter air compressors, but their operating costs are far greater than the inverter air compressors, which generate a lot of energy waste during the operation. Through the control transformation of the AC frequency converter, it is possible to effectively save operating energy consumption and reduce standard testing. 55 and time advance, actively explore, do a good job in enterprise standardization work Zhang Lu (Beijing Zhongli Machine Engineering Technology Co., Ltd. 101111) to determine the enterprise information base, enterprise informationization to promote the development of standardized thinking analysis and some experience .

1 Introduction Standardization is a supporting technology for advanced production models and advanced manufacturing technologies. With the rapid development of science and technology, the emergence of new management models to adapt to the market economy, how to diligently think about and advance the standardization work of enterprises is the responsibility of our standardization workers. Let's share some of our experiences with you.

2 concentrating on research products, understanding production requirements, and corporate standards are closely linked to the market. 2.1 Company products and production characteristics Beijing Zhongli Company (formerly Beihua Machine) is the largest chemical fiber manufacturing base in China with polyester, acrylic and nylon civilian yarns and industrial Spinning process, engineering of direct spinning, slicing, and non-woven fabrics of filaments, differential products, etc.; large-scale complete sets of technology and equipment; high-speed winder technology and manufacturing of various specifications. The biggest feature of chemical fiber equipment is that users have flexible and varied requirements for finished silk according to market conditions.

In order to meet the process requirements, each component or even a part of the equipment will be produced in one piece due to changes in one or more parameters.

In production, it is basically based on the requirements of the user contract. The products belong to many varieties and small batches. To truly realize product standardization and modularization, it is necessary to do a lot of improvement work.

2.2 Innovative drawing number and part number preparation method, establish the component type spectrum, and produce the low-cost operation cost, and also realize the constant pressure gas supply requirement of the factory. Nowadays, more and more variable frequency air compressors are accepted by large and medium-sized users. However, for enterprises with smaller investment scales and enterprises with earlier investment in equipment, it is a better solution to carry out skill transformation through frequency conversion control. Method.

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