CN205136018U - Air compressor economizer system based on PID frequency conversion - Google Patents

Abstract

The utility model provides an air compressor energy-saving system based on PID frequency conversion regulation, comprising: a group of air compressor systems, a frequency converter controlled by a PID program module in a PLC control system; an output terminal of the air compressor system Connected with the main network gas storage tank, a pressure sensor is used to detect the current output total pressure value of the group of air compressor systems, and feed back the current output total pressure value to the PID program module in the PLC control system; the air compressor system Each air compressor in the air compressor is connected to the frequency converter through the frequency conversion contactor, and is connected to the power frequency power supply through the power frequency contactor; the PID program module in the PLC control system makes the air compressor system One air compressor works in the frequency conversion mode, and the rest of the air compressors work in the power frequency mode, so as to adjust the total output power in real time, so that the total output power of the air compressors can be maintained in a roughly constant range.

Description

An air compressor energy-saving system based on PID frequency conversion regulation

technical field

The utility model relates to an energy-saving system of an air compressor.

Background technique

In the glass industry, the production gas has high requirements on the pressure and flow rate of compressed air, and the air compressor station is the place for making and supplying gas for float glass. In the air compressor station, the air compressor is the main equipment for gas production and supply. In recent years, with the large-scale application of air compressors in industrial and mining enterprises, their energy consumption accounts for a large proportion of the daily consumption of enterprises. The efficiency of air compressors in actual use is low. The efficiency of air compressors in most factories and mines is between 60% and 70%, resulting in high energy loss and high maintenance costs.

There are two reasons why the air compressor is not energy-saving: one is that the selection of the model is unreasonable, resulting in an excessive margin; The pressure of the main pipe at the outlet of the compressor is constant, and the air compressor will continuously adjust the pressure of the air compressor by loading and unloading, resulting in large fluctuations in the air supply pressure of the main pipe, which cannot meet the needs of users.

In order to stabilize the main pipe pressure and reduce the fluctuation of the air supply volume, the user can only realize the long-term loaded operation of the air compressor by evacuating. The traditional air compressor will cause a lot of waste during use, and also increase the maintenance cost of the equipment.

Utility model content

The main technical problem to be solved by the utility model is to provide an energy-saving method for an air compressor, by adjusting the output power of a compressor in the air compressor group through a frequency converter, so that the total output power of the air compressor can be adjusted in real time, Keep the total output power of the air compressor within a roughly constant range.

In order to solve the above-mentioned technical problems, the utility model provides an air compressor energy-saving system based on PID frequency conversion regulation, including: a group of air compressor systems, a frequency converter controlled by a PID program module in the PLC control system;

The output end of the air compressor system is connected to the main network gas storage tank, and a pressure sensor is used to detect the current output total pressure value of the group of air compressor systems, and feed back the current output total pressure value to the PID in the PLC control system program module;

Each air compressor in the air compressor system is connected to the frequency converter through a frequency conversion contactor, and is connected to a power frequency power supply through a power frequency contactor; the PID program module in the PLC control system makes the One air compressor in the air compressor system works in variable frequency mode, and the rest of the air compressors work in industrial frequency mode.

In a preferred embodiment: the PID program module in the PLC control system is connected to a man-machine interaction interface, and a target output total pressure value is input to the PID program module through the man-machine interaction interface.

In a preferred embodiment: a hard-wired electrical interlock is used between the air compressor and the frequency conversion contactor.

In a preferred embodiment: the frequency converter adjusts the speed of the asynchronous motor of the air compressor working in the frequency conversion mode according to the relationship between the current total output pressure value of the group of air compressors and the target output total pressure value, Thereby changing the output pressure value of the air compressor working in variable frequency mode.

In a preferred embodiment: when the target total output pressure value is greater than the current total output pressure of the group of air compressors, the frequency converter increases the speed of the asynchronous motor of the air compressor working in the frequency conversion mode, thereby making the When its output pressure value rises, the current total output pressure of this group of air compressors also rises accordingly;

When the target output total pressure value is less than the current output total pressure of the group of air compressors, the frequency converter reduces the speed of the asynchronous motor of the air compressor working in the variable frequency mode, thereby reducing its output pressure value, and the group The current output total pressure of the air compressor is also reduced accordingly.

Compared with the prior art, the technical solution of the utility model has the following beneficial effects:

(1) The power saving effect is obvious. According to the statistics of power consumption before and after using frequency conversion control, the average daily power consumption of a 355KW air compressor before using frequency conversion control is 7781 kWh, and after using frequency conversion control, the average daily power consumption is 4400 kWh, which saves a single day after using frequency conversion control The power consumption is 3381 degrees. Calculated according to the average electricity price of China Southern Power Grid of 0.73 yuan/kWh, the energy-saving transformation of the company's air compressors can save electricity costs of 900,800 yuan per year.

(2) The air supply pressure is stable. Using the PID adjustment mode controlled by PLC, the system automatically adjusts the operating frequency of the inverter according to the pressure fed back by the pressure sensor, controls the output air volume of the air compressor, and ensures the stability of the air supply pressure.

(3) Reduced equipment loss. The air compressor runs below the rated frequency for a long time, which reduces the speed of the air compressor, and at the same time avoids the frequent loading and unloading of the air compressor to balance the pressure of the pipe network when the power frequency is running, reducing equipment wear and saving maintenance funding.

(4) The impact of starting current is reduced. The method of frequency conversion starting reduces the starting current. Compared with star-delta step-down starting, this system minimizes the impact of starting current on the system.

Description of drawings

Fig. 1 is a schematic diagram of an air compressor energy-saving system based on PID frequency conversion regulation in a preferred embodiment of the present invention.

detailed description

The utility model will be further described below in conjunction with the accompanying drawings and specific embodiments.

With reference to Fig. 1, a kind of air compressor energy-saving system based on PID frequency conversion regulation, comprises: a group of air compressor systems, the frequency converter controlled by the PID program module in the PLC control system; The compressor system includes two screw air compressors.

The output end of the screw air compressor system is connected to the main network gas storage tank, and a pressure sensor is used to detect the current output total pressure value of the group of screw air compressor systems, and feed back the current output total pressure value to the PLC control system The PID program module;

The two screw air compressors in the screw air compressor system are respectively connected to frequency converters through frequency conversion contactors, and the screw air compressors and frequency conversion contactors are electrically interlocked by hard wiring. The two screw air compressors are also respectively connected to the power frequency power supply through the power frequency contactor; the PID program module in the PLC control system makes one screw air compressor in the screw air compressor system work in the frequency conversion mode, The other air compressor works in power frequency mode.

The PID program module in the PLC control system is connected to a man-machine interaction interface, and a target output total pressure value is input to the PID program module through the man-machine interaction interface.

The principle of frequency conversion regulation is as follows: the frequency converter adjusts the speed of the asynchronous motor of the screw air compressor working in the frequency conversion mode according to the current total output pressure value of the group of air compressors and the target output total pressure value, thereby Change the output pressure value of the screw air compressor working in variable frequency mode.

Specifically: when the target output total pressure value is greater than the current output total pressure of the group of air compressors, the frequency converter increases the speed of the asynchronous motor of the screw air compressor operating in the frequency conversion mode, thereby making its output As the pressure value rises, the current output total pressure of the group of screw air compressors also rises accordingly;

When the target total output pressure value is less than the current total output pressure of the group of air compressors, the frequency converter reduces the speed of the asynchronous motor of the screw air compressor working in the frequency conversion mode, thereby reducing its output pressure value, the The current output total pressure of the group screw air compressor is also reduced accordingly.

The reason why the output pressure value of the screw air compressor working in the variable frequency mode can be changed by adjusting the speed of the asynchronous motor of the screw air compressor working in the variable frequency mode is because the screw air compressor is a constant torque load, and its The output power has a linear relationship with the speed of the asynchronous motor, and its derivation formula is as follows:

According to the principle of mechanics, the pulling force F and the frictional force f are equal in magnitude and opposite in direction, and F pulls the object to move in a straight line within a unit time t, and the displacement is s. Then the work done by F in unit time t is P:

$P=\frac{W}{T}=\frac{f\×\mathrm{the\; s}}{T}=f\mathrm{\ν}=f\mathrm{\ν}$ (Formula 1)

Substituting the friction formula f=μFn into Equation 1, we can get:

P=μF _n ν(Formula 2)

Note: μ is the coefficient of sliding friction, and Fn is the normal pressure between objects that generate friction.

According to the relationship between linear velocity ν and angular velocity ω, the following formula can be obtained:

ν=ωρ=2πfr (Formula 3)

Note: f in formula 3 is the rotation frequency of the rotating body.

Substituting Equation 3 into Equation 2, the following formula can be obtained:

P=μF _n ν=μF _n ωr=μF _n 2πrf (Formula 4)

From Equation 4, it can be concluded that the rotors of the screw air compressor rotate at a constant speed against the friction force, and the mechanical power that the motor needs to provide is calculated according to Equation 4 (neglecting the loss of mechanical efficiency η, and setting η to 1).

To sum up, it can be approximately considered that the output power P of the screw air compressor has a linear relationship with the frequency of the screw air compressor motor. Therefore, changing the speed n of the asynchronous motor of the screw air compressor can change the output power of the screw air compressor, thereby controlling the output flow and pressure of compressed air, thereby achieving the purpose of energy saving. The frequency converter has the ability of stepless speed regulation, and its frequency change has a linear relationship with the speed. According to the speed formula of the asynchronous motor:

$\mathrm{no}=\frac{60f}{P}(1-\mathrm{the\; s})$ (Formula 5)

In formula 5, n is the asynchronous speed of the motor, f is the power frequency of the motor, s is the slip rate of the motor, and P is the number of pole pairs of the motor.

When P and s are determined, the output speed of the motor has a linear relationship with the power frequency of the motor. Therefore, changing the frequency of the motor can change the output speed n of the motor, thereby realizing frequency conversion speed regulation.

In order to maintain the constant pressure of the compressed air main pipe, the PLC controls the output frequency of the inverter by detecting the data fed back by the pressure sensor, and reaches and stabilizes the target output total pressure value input by the operator through the man-machine interface. Technicians can realize this function by programming the PID program block inside the PLC.

Setting the correct PID parameters can make the frequency conversion speed regulation system of the screw air compressor run stably and efficiently. A crucial issue in PID control is the setting of proportional coefficient, integral time and differential time. In this program, Siemens S7-200PLC with PID parameter self-tuning is selected to realize the automatic speed regulation of the frequency converter.

Siemens S7-200 programming software STEP7-Micro/WIN4.0 provides PIDWizard (PID command wizard) wizard, which can help users easily generate a PID algorithm for a closed-loop control process. This wizard can complete the automatic programming of most PID calculations. The user only needs to call the subroutine generated by the PID wizard in the main program and complete the setting of the PID controller parameters to complete the PID control task.

After the written program is downloaded to the PLC through the host computer, switch the PLC to the RUN state, open the PID control panel in the programming software STEP7-Micro/WIN4.0, and debug the frequency and The trend graph of the actual pressure change is used to debug the feedback, output, target value stabilization and PID response speed in the PID program block.

When starting debugging, start the inverter first, and choose to manually adjust the PID parameters. The purpose of manual adjustment is mainly to avoid system self-tuning at the beginning, and the system may fail to tune. After tuning the parameters, select PID parameter auto-tuning.

1) First set the proportional coefficient K _c , that is, the integral time T _i is INF, the differential time T _D is 0, and the value of K _c is continuously increased from 1.0, and when there is a tendency of oscillation during the debugging process, it is properly reduced _Kc value until the system output stabilizes.

2) Set the integral time T _i again, the integral time T _i determines the rate of change of the output frequency of the PID controller. If the integral time is too short, the deviation between the given value and the feedback value will be corrected faster; if the integral time is too long, the controller will have no integral function. Therefore, in the tuning process, first set the integral time T _i to 0, introduce a strong integral action to make the system oscillate, and then increase the integral time continuously until the system can eliminate the static error, so that the output does not oscillate and tends to Stablize.

3) Set the differential time T _D on the basis of the previous two steps. The differential action is equivalent to the predictive adjustment of feedback changes. If the differential time T _D is set to 0, the PID controller is equivalent to no differential action. Therefore, first set T _D is set at a larger value to allow the output to oscillate, and then gradually decrease to find the critical oscillation value and improve the dynamic performance of the system.

After the self-tuning is completed, the frequency change of the inverter tends to be stable, and the error between the output and feedback frequency values is small, which can fully meet the needs of the production process.

This system has the functions of manual/automatic switching and industrial frequency/variable frequency switching, and the operator only needs to select the corresponding function on the control panel. When the 1# screw air compressor runs with frequency conversion, the 2# screw air compressor can only choose power frequency operation, and vice versa.

When the system is running in the automatic state, the operator only needs to input the required target output total pressure value on the man-machine interface, and the PLC will automatically adjust the frequency converter according to the comparison between the set target output total pressure value and the pressure value fed back by the pressure sensor At the same time, the current, voltage and frequency of the inverter during operation are fed back to the PLC, and the PLC displays the relevant values and operating status on the man-machine interface in real time. When a fault occurs, the system analyzes whether the equipment is a minor fault or a major fault. In the case of a minor fault, the system will alarm and record the fault information. The operator will notify the equipment maintenance personnel to overhaul and start the spare screw air compressor; Stop the operation of the equipment, and the operator starts the standby equipment immediately and notifies the maintenance personnel to overhaul.

To sum up, this system has high redundancy performance, which ensures the continuous operation of the frequency conversion system, improves the energy saving efficiency, and also ensures the safety of equipment operation. The adoption of man-machine interface is not only friendly in operation, but also simple in maintenance.

The above is only a preferred embodiment of the utility model, but the scope of protection of the utility model is not limited thereto, and any person familiar with the technical field can easily think of All changes or replacements should fall within the protection scope of the present utility model. Therefore, the protection scope of the present utility model should be based on the protection scope of the claims.

Claims (5)

1. based on an air compressor energy conserving system for PID variable frequency adjustment, it is characterized in that comprising: one group of air compressor system, the frequency variator controlled by the PID program module in PLC control system;

The output terminal of described air compressor system is connected with supervisor's net gas holder, and current output stagnation pressure force value for detecting this group air compressor system current output stagnation pressure force value, and is fed back to the PID program module in PLC control system by a pressure transducer;

Each air compressor in described air compressor system to be connected with frequency variator respectively by frequency conversion contactor and to be connected with power frequency supply respectively by power frequency contactor; PID program module in described PLC control system makes in described air compressor system air compressor be operated in variable mode, and remaining air compressor is operated in power frequency pattern.

2. a kind of air compressor energy conserving system based on PID variable frequency adjustment according to claim 1, it is characterized in that: the PID program module in described PLC control system connects a man-machine interaction interface, by man-machine interaction interface, one target is inputted to PID program module and export stagnation pressure force value.

3. a kind of air compressor energy conserving system based on PID variable frequency adjustment according to claim 1, is characterized in that: adopt hardwire electrical interlocks between described air compressor and frequency conversion contactor.

4. a kind of air compressor energy conserving system based on PID variable frequency adjustment according to claim 2, it is characterized in that: described frequency variator also adjusts the rotating speed of the asynchronous motor of the air compressor being operated in variable mode according to the magnitude relationship that the current output stagnation pressure force value of this group air compressor and target export stagnation pressure force value, thus changes the delivery pressure value that this is operated in the air compressor of variable mode.

5. a kind of air compressor energy conserving system based on PID variable frequency adjustment according to claim 4, it is characterized in that: when described target export stagnation pressure force value be greater than this group air compressor current output total pressure time, frequency variator makes the rotating speed of the asynchronous motor of the air compressor being operated in variable mode raise, and then its delivery pressure value is raised, the current output total pressure of this group air compressor also increases;

When described target export stagnation pressure force value be less than this group air compressor current output total pressure time, frequency variator makes the rotating speed of the asynchronous motor of the air compressor being operated in variable mode reduce, and then its delivery pressure value is reduced, the current output total pressure of this group air compressor also decreases.