Transformation project of frequency converter to air compressor

Transformation project of frequency converter to air compressor

1. Brief description of working principle of air compressor:

　　 The working principle is that a pair of male and female rotors (or screws) that are toothed parallel to each other rotate in the cylinder, so that the air between the rotor teeth continuously produces periodic volume changes, and the air is transported from the suction side along the rotor axis. To the output 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 casing, and the slots of the female rotor and the teeth of the male rotor are driven to rotate by the main motor.

　　 　　The operation mode of the main motor of the original air compressor is star-angle or automatic decompression start, which is more important than post full pressure operation. The specific operation procedure is: press the start button, the control system turns on the starter coil and opens the oil cutoff valve, the air compressor starts in the unloading mode, at this time the intake valve is in the closed position, and the air release valve is opened to discharge the oil and gas separation The pressure inside the device. After 2 seconds of depressurization, the air compressor starts to load and the system pressure starts to rise. If the system pressure rises to the upper limit of the pressure switch, that is, the take-off pressure, the controller closes the intake valve, deflates the oil and gas separator, and the compressor runs without load until the system pressure drops to the lower limit of the pressure switch, that is, it rebounds. Under pressure, the controller opens the intake valve, closes the gas separator bleed valve, opens the compressor, closes the gas separator bleed valve, and the compressor runs at full load.

　　 2. Problems in the original system operating conditions

　　 1. Although the main motor starts at star-angle decompression, the current at starting is still large, which will affect the stability of the power grid and the safety of other electrical equipment.

　　 2. The main motor often runs at no-load, which is non-economical operation and wastes electricity.

　　 3. The main motor power frequency operation causes the air compressor to run very loudly.

　　 4. The main motor power frequency starting equipment has a large impact, and the motor bearings have large wear and tear, so there is a large amount of machinery during equipment maintenance.

Frequency conversion transformation plan:

1. Energy saving principle and effect

We know that the air supply can also be adjusted by adjusting the motor speed. Since the air compressor is basically a constant torque load, the use of frequency conversion speed regulation to adjust the air supply can make the output power of the motor basically proportional to the speed (air supply), achieving a good energy saving effect. We use the AMB inverter with vector control function, which enables the motor to provide the torque required by the load even at low speeds. At the same time, the automatic energy-saving mode of the AMB inverter enables the motor to run at the minimum current while meeting the load torque requirements, achieving better power-saving effects.

The effects brought by the constant pressure air supply frequency conversion control system are as follows:

(1) All the air outlet release valves are closed, and the way of adjusting the air supply volume with the air outlet release valve is cancelled to avoid the resulting waste of electricity. Instead, the frequency converter is used to adjust the speed of the motor to adjust the gas flow, so that the output power of the motor is basically proportional to the flow demand, and the motor is always operated with high efficiency to achieve obvious power saving effects. For example, when the gas consumption is 50% of the rated gas supply, the power saving rate can reach more than 40%;

(2) Using the energy-saving mode of the inverter, the motor can run at the highest efficiency under light load and reduce unnecessary power loss;

(3) According to strict EMS standards, high-efficiency PWM inverters use high-speed and low-consumption IGBTs to reduce harmonic distortion and motor power loss.

(4) It can make the current of the motor start up and load smoothly without any impact; it can realize the soft stop of the motor, avoid the harm caused by the reverse current, and help to extend the service life of the equipment; avoid the current peak Fines from power companies;

(5) After the frequency conversion control system is adopted, the pressure of the gas in the gas supply pipeline can be monitored in real time, so that the pressure of the gas in the gas supply pipeline can be kept constant, and the production efficiency and product quality can be improved;

(6) Because the motor runs in a high-efficiency state, the power factor is high, which reduces reactive power loss and saves a lot of electrical energy.

(7) Save the original release valve system, and adjust it when necessary to enhance the reliability of the system.

In short, after adopting the intelligent control system for constant pressure air supply, not only can the electricity cost be saved by 30-40%, the service life of the compressor can be prolonged, and the purpose of "constant pressure air supply" can be realized, and the production efficiency and product quality can be improved.

　 3. Design principles of frequency conversion transformation scheme

According to the existing problems of the original working conditions and combined with the requirements of the production process, the air compressor system after frequency conversion transformation should meet the following requirements:

　　 1. The motor frequency conversion operation state keeps the outlet pressure of the gas storage tank stable, and the pressure fluctuation range cannot exceed ±0.02Mpa.

　　 2. The system should have two sets of control loops: variable frequency and industrial frequency.

　　 3. The system has two sets of control loops, open loop and closed loop.

　　 4. One inverter can control two air compressor units, which can be switched by a change-over switch.

　　 5. According to the operating conditions of the air compressor, the system should ensure that the motor has constant torque operation characteristics.

　　 6. In order to prevent non-sinusoidal waves from interfering with the air compressor controller, there should be effective measures to suppress electromagnetic interference at the input of the inverter.

　　 7. In the case of low electrical consumption, when the inverter is running at low frequency, it should be ensured that the motor winding temperature and motor noise do not exceed the allowable range.

　　 8. Considering the future expansion of the system, the inverter should meet the requirements for future expansion of working conditions.

Fourth, the selection of the inverter

　　 According to the above principles, after many investigations and comparisons, we finally chose the G9 series general-purpose inverter produced by Anbangxin Company, so that the system can meet the requirements of the above working conditions.

　　 1. The frequency accuracy of G9 inverter: digital setting is ±0.01%; analog setting is ±0.2%. The pressure fluctuation range can meet the design requirements.

　　 2. The system is designed with two main circuits of frequency conversion and industrial frequency.

　　 3. The system has designed two sets of control loops, closed loop and open loop.

　　 4. Using the change-over switch, the inverter can control one of the two air compressor units at will.

　　 5. G9 type inverter is suitable for load with constant torque characteristics. The inverter also has functions of torque compensation and boost.

　　 6. An input reactor is added to the upper end of the inverter to effectively restrain the inverter's interference to the power grid.

　　 7. An output reactor is installed at the lower end of the inverter to ensure that the motor temperature noise does not exceed the allowable range during low-frequency operation.

Five, the principle of the transformation plan

　　 The pressure closed-loop control system composed of frequency converter, pressure transmitter, motor, and spiral rotor automatically adjusts the motor speed to stabilize the air pressure in the air tank within the set range and perform constant pressure control.

　　 The feedback pressure is compared with the set pressure, and the output step of the inverter is controlled in real time to adjust the motor speed to stabilize the air pressure in the air tank at the set pressure.

Sixth, the benefits of air compressor after frequency conversion transformation

　　 1. Save energy

　　 Compared with traditionally controlled compressors, inverter-controlled compressors have the most practical significance in energy saving. The compressor operating conditions supplied according to the air volume demand are economical.

　　 2. Operation cost reduction

　　 The operating cost of a traditional compressor consists of three items: initial purchase cost, maintenance cost and energy cost. The energy cost accounts for about 77% of the compressor operating cost. The energy cost is reduced by 44.3%, coupled with the reduction of the impact on the equipment after the frequency conversion start, the maintenance and repair volume will also be reduced, so the operating cost will be greatly reduced.

　　 3. Improve pressure control accuracy

　　 The frequency conversion control system has precise pressure control capability. Make the air pressure output of the compressor match the air volume required by the user's air system. The output air volume of the inverter controlled compressor changes with the change of the motor speed. Because the accuracy of the frequency conversion control motor speed is improved, it can keep the system pressure change of the pipe network within the range of 3pisg, that is, within the range of 0.2bar, which effectively improves the quality of the working conditions.

　　 4. Extend the service life of the compressor

　　 The frequency converter starts the compressor from 0HZ, and its starting acceleration time can be adjusted, thereby reducing the impact on the electrical and mechanical parts of the compressor when starting, enhancing the reliability of the system and extending the service life of the compressor. In addition, the frequency conversion control can reduce the current fluctuations when the unit starts. This fluctuating current will affect the power consumption of the grid and other equipment. The frequency converter can effectively reduce the peak value of the starting current to the minimum.

　　 5. Reduced the noise of the air compressor

　　 According to the working conditions of the compressor, after the frequency conversion speed regulation reformation, the motor running speed is obviously slowed down, so the noise of the air compressor is effectively reduced. Field measurements show that the noise is reduced by about 3 to 7 decibels compared with the original system.

　 Investment Analysis

1. Project cost

The cost of air compressor power saving transformation: XXXXXX yuan

2. Analysis of investment return

The monthly electricity consumption of a single air compressor in the bottle-making workshop is about:

160KW×24 hours/day×30 days/month×0.8=XXXXKWH

The air compressor power saving rate can reach: fluctuates between 20-30%, and the monthly average value is: 25%; the electricity price is 0.52 yuan XXX/KWH then:

Monthly electricity saving fee for air compressor: XXXXWH×25%×XX yuan/KWH=XXX yuan

Investment payback period = total investment / monthly savings = XXXX≈21 months

The investment in power-saving transformation will be fully recovered within XXXX months.

Concluding remarks

With the advent of the era of popularization of frequency converter applications, expanding the application of frequency converters to the field of traditional air compressor transformation has not only expanded the application market of frequency converters, but also proposed new issues for the air compressor manufacturing industry. It is expected that in the near future, due to the intervention of frequency conversion technology, air compressors will truly enter the era of economic operation.