JPH0134316B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the capacity of a screw compressor, and more particularly to a method for controlling the capacity of a screw compressor that can achieve energy savings.

[Conventional technology]

As a capacity control method used in a screw compressor, there is a combination of suction throttling type control and on/off type control, as described in, for example, Japanese Patent Application Laid-Open No. 52-136406. In the suction throttle type capacity control, the amount of suction gas is adjusted by continuously opening and closing the suction throttle valve, which is operated by inputting pressure fluctuations in the discharge side conduit including the air storage tank. In addition, the on-off type capacity control fully closes the suction throttle due to the pressure increase in the discharge side pipe when the no-load condition occurs, and opens the release valve that operates based on pressure fluctuations to reduce the compression in the oil recovery device. If the gas is released and the compressor is operated at minimum load, and the pressure in the discharge line is reduced,
The suction throttle valve is fully opened and the exhaust valve is closed to operate at full load, and these operating conditions are alternated.

[Problem to be solved by the invention]

In capacity control using a combination of suction throttling control and on-off control, the suction throttling control and on-off control have different power consumption characteristics with respect to the amount of air used by the load. That is, when comparing the two, the suction throttle type control has an energy saving effect in a region where the amount of air used is large, and the on-off type control has an energy saving effect in a region where the amount of air used is small.
In this type of capacity control, the switching point for switching from suction throttle type control to on-off type control, or vice versa, is fixed in advance according to specifications or the like. For this reason,
When the capacity of the connected piping system changes, it is impossible to change the switching point described above, so the power consumption increases when used. Therefore, good operation was not carried out from the viewpoint of energy saving.

The present invention has been made based on the above-mentioned issues, and enables energy-saving operation by changing the switching point between suction throttling type control and on-off type control depending on the volume of the piping system connecting to the screw compressor. An object of the present invention is to provide a capacity control method for a screw compressor.

[Means to solve the problem]

The features of the present invention include suction throttling type control using a suction throttle valve provided on the suction side of the screw compressor, and on/off type control using the suction throttling type control and a discharge valve provided on the discharge side of the screw compressor. In a screw compressor that performs capacity control by switching between the two controls, both controls are executed using a temporary set value for temporarily determining the switching point of the control, and the screw compressor is measured by executing both controls. The input power of the motor,
Compare the state quantities of any one of the state quantities such as air usage amount and discharge pressure, and when those measured values match, that state quantity is stored as the setting value for the switching point of both controls. Then, if the state quantity is above a set value, suction throttling type control is performed, and if it is less than that, capacity control operation is performed using on/off type control.

[Effect]

When the volume of the piping system connected to the screw compressor changes, on-off type control and suction throttle type control are respectively executed. Compare any one of the state quantities of the screw compressor's motor input power, air volume, air volume ratio, discharge pressure, etc. measured by the execution, and when the measured values match, , the state quantities are stored as set values for the switching points of both controls. In this way, an appropriate switching point can be obtained in response to changes in the volume of the piping system connected to the screw compressor. Thereafter, with this set value as a reference, if the measured state quantity is greater than or equal to the set value, the suction throttling type control is used, and if it is less than that, the on/off type control is used.

〔Example〕 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a control system diagram of a screw compressor for carrying out the method of the present invention. In the figure, 1 is a screw compressor, 2 is a screw rotor of the screw compressor 1, 3 is a motor that rotates the screw rotor 2, 4 is a suction pipe of the screw compressor 1, 5 is a discharge pipe, and 6 is a suction installed in the suction pipe 4. This suction throttle valve 6 is a throttle valve and is opened and closed by a cylinder 7. 8 is an oil recovery device, 9 is an air release valve provided in the oil recovery device 8, 10 is a gas cooler, 11 is an air storage tank, and 12 is a supply pipe.

Suction gas is sucked into the compressor 1 from the suction pipe 4 of the compressor 1 through the suction throttle valve 6 and is pressurized. This pressurized suction gas is transferred to the discharge pipe 5 and the check valve 13.
The gas enters the oil recovery device 8 through the gas, and the oil component in the gas is separated and stored in the lower part of the oil recovery device 8. The compressed gas from which oil has been separated passes through an oil separation filter 14 provided at the outlet of the oil recovery device 8, passes through a pressure regulating valve 15, passes through a gas cooler 10, and is supplied to the load side through an air storage tank 11 and a supply pipe 12. Further, the oil in the oil recovery device 8 is cooled by an oil cooler 16, filtered by an oil filter 17, and then supplied to the compressor. The compressed gas in the oil recovery device 8 is released to the atmosphere by a release valve. The pressure gas in the gas cooler 10 is controlled by a pressure reducing valve 18 and a three-way solenoid valve 1.
9 to the piston rod side chamber 7a of the cylinder 7.
In addition, it is supplied to the opposite-piston rod side chamber 7b of the cylinder 7 through the pressure regulating valve 20 and the electromagnetic valve 21. Thereby, the suction throttle valve 5 is moved, and the amount of gas sucked into the compressor 1 can be adjusted. The aforementioned three-way solenoid valve 19 switches its S port to the Q port or R port for communication. The three-way solenoid valve 19, the solenoid valve 21, the discharge valve 9, and the solenoid switch 22 of the motor 3 are operated by commands from the control device 23. The control device 23 includes the pressure of the gas cooler 10 detected by the pressure detector 24 and the pressure detected by the pressure detector 24.
An input signal of the input power of the motor 3 detected at 5 is added. The input power of this motor 3 represents the power consumption of the compressor.

Next, the suction throttle type control operation according to the present invention will be explained.

In response to a command from the control device 23, the air release valve 9 and the solenoid valve 21 are opened, and the three-way solenoid valve 19 communicates its S port with the Q port. This results in
The pressure gas in the gas cooler 10 is reduced to a constant pressure by the pressure reducing valve 18 and guided to the piston rod side chamber 7a of the cylinder 7. The pressure regulating valve 20 generates a secondary pressure according to the change in the pressure of the gas cooler 10 from the time when the set pressure P _d is exceeded. This secondary pressure is then led to the side chamber 7b of the cylinder 7 opposite to the piston rod. The action of the pressure gas on the cylinder 7 causes the cylinder 7 to operate in response to changes in the pressure of the gas cooler 10, thereby continuously controlling the amount of gas sucked by the suction throttle valve 6. FIG. 2 shows the characteristics of this suction throttle type control and the on/off type control described later.
In the figure, the horizontal axis shows the air usage ratio, and the vertical axis shows the power consumption ratio. Characteristic line a shows the characteristics of the suction throttling type control, and characteristic line b shows the characteristics of the on-off type control. The intersection c of the characteristic lines a and b becomes the switching point for both controls.

Next, the on/off type control operation according to the present invention will be explained.

When the solenoid valve 21 is closed by a command from the control device 23 and the pressure detected by the pressure detector 24 rises to the upper limit set pressure P _u , the control device 23
The three-way solenoid valve 19 closes the S port to R.
Connect to the port. As a result, the pressure gas in the gas cooler 10 acts on the side chamber 7b of the cylinder 7 opposite to the piston rod, so that the cylinder 7 is connected to the suction throttle valve b.
fully closed. At the same time, the air release valve 9 is opened in accordance with a command from the control device 23 to release the compressed gas in the oil recovery device 8 to the atmosphere, and the operating state of the compressor 1 is set to no load. After that, when the pressure inside the gas cooler 10 decreases and reaches the lower limit set value P _L , the three-way solenoid valve 1
9 is switched to communicate its S port with the Q port, so that the pressure gas in the gas cooler 10 is applied to the piston rod side chamber 7a of the cylinder 7. Therefore, the cylinder 7 fully opens the suction throttle valve 6,
The operating state of the compressor 1 is set to full load. At the same time, the air release valve 9 is fully closed to stop air release. In this way, no-load operation and full-load operation are repeated alternately. The characteristic of this on-off type control is shown by characteristic line b in FIG. Further, FIG. 3 shows the state changes of each part during this on-off type control. In FIG. 3, the characteristic line d shows the pressure change in the gas cooler 10, the characteristic line e shows the pressure change in the oil recovery device 8, and the characteristic line f shows the power change in the motor 3. T _d is no-load operation time, T _u
is the full load operating time, and T _p is the compression time in the oil recovery device 8.

Next, the configuration of the control device 23 for executing the above-described suction throttle type control and on/off type control will be explained with reference to FIG. 4. In this figure, the same reference numerals as in FIG. 1 are the same parts. 26 is detector 2
An A/D converter converts the analog signals from 4 and 25 into digital signals, 27 is a central processing unit that processes the captured signals according to a pre-stored processing procedure, and 28 is an external device that transmits the processed results. 29 is a read-on memory (ROM) for storing processing procedures of the central processing unit 27, and 30 is a random access memory (RAM) for temporarily storing calculation results and the like.

Next, an example of a procedure for performing suction throttling type and on/off type capacity control by the control device 23 will be described with reference to FIG.

Here, the power consumption (input power) of the motor is used as the state quantity for determining the switching point of both control methods.

At the start of startup, in step P1, the setting value M as the power consumption at the switching point of both control methods is set to a provisional value, that is, the power consumption when the air usage ratio is 100%.
Next, the compressor is started with suction throttling control. (You can also start with on-off type control.) Suction throttle type control first opens the solenoid valve 21 in step P2, and opens the three-way solenoid valve 19 in step P3.
Connect the port and Q port. Close the release valve 9 in step P4, and close the electromagnetic switch 22 in step P5.
and start motor 3. As a result, suction throttling type capacity control is performed. And step
A/D shows the power consumption of motor 3 at P6 as shown in Figure 4.
The converter 26 inputs the data into the memory 30 at every sampling time Δt. In step P7, it is determined whether the number of samples of the sampled power consumption W _o has reached K, and if the number of samples is <K, step P7 is executed.
Continue suction throttle control for P2 to P7. When the number of samples reaches K, the process moves to step P8. At step P8 is calculated and stored as the power consumption M ₁ of the intake throttle type control at the current air usage state. Step P9
compares the power consumption _M1 of this suction throttling type control with the provisional set value M, and if _M1 > M, the suction throttling type control of steps P2 to P9 is continued. If M ₁ <M, the process moves to on/off type control after step P10.

The on-off type control first executes the on operation of steps P10 to P14, that is, full load operation. The solenoid valve 21 is closed in step P10, and the S port and Q port of the three-way solenoid valve 19 are communicated with each other in step P11.
In step P12, close the air release valve 9 and close the gas cooler 1.
Increase the pressure within 0. In step P13, the power consumption of motor 3 is sampled every Δt, and
The sample value W _o is memorized. In step P14, it is determined whether the pressure inside the gas cooler 10 has reached the upper limit pressure P _u . Gas cooler 10 pressure <P _u
If so, continue the on operation in steps P10 to P14.
When the pressure of the gas cooler 10 rises to > P _u , the process moves to the off operation, that is, the no-load operation of steps P15 to P18. In step P15, the S port and R port of the three-way solenoid valve 19 are brought into communication, and the suction throttle valve 6 is fully closed. In step P16, the air release valve 9 is opened to release the compressed gas in the oil recovery device 8, thereby reducing the pressure in the gas cooler 10. This causes the compressor to enter a no-load operating state. Step P17 samples the power consumption of the motor 3 every Δt, and stores the sampled value W _o . In step P18, it is determined whether the pressure inside the gas cooler 10 has reached the lower limit pressure P _L. If the gas cooler 10 pressure> _PL , the off operation in steps P15 to P18 is continued, and if the gas cooler 10 pressure < _PL , the process moves to step P19. Step P19 performs on/off operation 2
This is a judgment function for executing the process twice, and after executing the process twice, the process moves to step P20. Step P20 determines and stores the average power consumption _M2 of the motor 3 consumed during full load operation and no load operation.

This is the step during the second on/off operation.
The average power M ₂ is calculated from the power consumption W _o sampled at every Δt in P13 and P17 using equation (2). Here, T _d indicates the no-load operating time in FIG. 3, and T _u indicates the full-load operating time. Further, K indicates the number of samples.

However, K = T _d + T _u /Δt Using the power consumption M ₁ and M ₂ of both control methods at the current air usage state obtained in this way,
In step P21, M ₁ and M ₂ are compared in order to find the switching point (M ₁ =M ₂ ) between both control systems.

This comparison result shows that if M ₁ <M ₂ , the current amount of air used by the compressor is on the right side of the switching point C of the air amount characteristics in FIG. Furthermore, it is shown that when the power consumption is _M1 or more, the energy saving effect is greater when operating with suction throttling control. However, since M ₁ is not yet the optimal switching point, the operation to find the switching point is performed again.
In step P22, the temporary set value _M1 is changed to a value smaller than M1, that is, a value _M1 -Δw closer to the switching point, and the suction throttling type control in steps P2 to P9 is executed. Here, Δw is a constant value and is adjusted depending on the capacity characteristics of the compressor.

In the next step P2 to P9 suction throttle control,
Since the set value M has become M ₁ −Δw, the power consumption has decreased.
Suction throttling control continues until M ₁ −Δw or less, reducing the amount of air used by the load and reducing power consumption by M ₁
-Δw or less, the compressor is operated using on-off control in steps P10 to P20, and the power consumption at this time is
Find _M2 .

In this way, the power consumption of both control methods is determined when the amount of air used is smaller than the previous time, and the step
At P21, similarly to the above, it is determined whether it is a switching point. Through such a procedure, control is performed so that the switching point is determined by repeatedly changing the temporary setting value M of the switching point by Δw.

On the other hand, if the comparison result in step P21 is M ₁ >M ₂ , this indicates that the current amount of air used by the compressor is on the left side of the switching point C of the capacity characteristics in FIG. If the power consumption is less than _M1 , operating with on-off control will have a greater energy saving effect.

However, since the power consumption M ₁ found here is not the optimal switching point, the operation to find the switching point is performed again. In step P23, a value larger than the provisional setting value _M1 , that is, a value _M1 + that is close to the switching point is set.
Δw and performs on/off type control in steps P24 to P25. In step P25, the power consumption _M2 of the on-off type control is compared with the provisional setting value M, and the on-off type control is continued until the power consumption becomes equal to or greater than M. Then, when the load condition changes and the power consumption becomes equal to or greater than M, the suction throttling type control in step P26 is executed to find the power consumption _M1 at that time.

In this way, the power consumption of both control methods is determined when the amount of air used is larger than the previous time, and the step
At P21, similarly to the above, it is determined whether it is a switching point. Through such a procedure, control is performed so that the switching point is determined by repeatedly changing the temporary setting value M of the switching point by Δw.

Now, if the comparison result in step P21 matches M ₁ = M ₂ or falls within the allowable range, then step P27
Then, the power consumption at that time is stored as the switching point C set value _M3 . In subsequent control, step
If the power consumption in each control method is equal to or greater than the set value _M3 in P28, step P30
If it is less than that, select the on-off control in step P29. Note that the description of the suction throttling type capacity control in steps P26 and P30 indicates the procedure of steps P2 to P8.
The description of the on-off type capacity control in steps P24 and P29 shows the procedure of steps P10 to P20.

In this way, the capacity control method that provides the most energy saving effect can be automatically selected depending on the state of the amount of air used by the load.

Next, another example of the switching execution procedure between the suction throttle type control and the on/off type control will be explained with reference to FIG.

In this example, the temporary setting value M _A for the switching point from suction throttle type control to on-off type control, and the temporary set value M _B for the switching point from on-off type control to suction throttle type control are set in advance. It is stored in memory. The stored value in this case is the power consumption of the motor 3. Then, it starts with suction throttle control,
The power consumption M ₁ of the motor 3 at that time is compared with the provisional setting value _MA , and if the power consumption M ₁ becomes equal to or less than the provisional setting value _MA , the control shifts to on-off type control. Similarly power consumption M ₂
and the provisional setting value M _B , and if the power consumption M ₂ is greater than or equal to the provisional setting value M _B , the suction throttling type control is performed. In this way, it is also possible to separately set temporary set values for the suction throttle type control and the on/off type control.

In order to reduce the switching fatigue of each valve that occurs during the on-off type control in the above-mentioned embodiment, a timer limit is set for the suction throttle type control and the on-off type control as shown in Fig. 7, so that when the control is switched, This switching control can also be operated for a certain period of time by using a timer. This timer planning is done based on the program processing time. It is also possible to start an external timer and perform interrupt control. Furthermore, as shown in Fig. 8, a limit value is set for the number of times the exhaust valve 9 and suction throttle valve 6 operate under on-off type control, and if the number of valve operations exceeds the limit value, suction throttle type control is applied. It may be possible to move to on/off type control for a certain period of time and disable transition to on/off type control for a certain period of time.

Although the above embodiment has been explained using the input power of the motor 3 as the state quantity for controlling the capacity of the compressor, state quantities such as the input current of the motor 3, the amount of air used, the air amount ratio, the discharge pressure, etc. can also be used. The amount of air used is determined by the relationship between the amount of air used during compressor operation and the power consumption.
Since there is a functional relationship, power consumption can be calculated from this amount of air used, and the discharge pressure of the compressor changes depending on the amount of air used. That is, as the amount of air used increases, the pressure decreases, and as the amount of air used decreases, the pressure increases, so this discharge pressure can also be used as an element of power consumption. In addition, as a means for opening and closing the suction throttle valve 6, a rack 31 and a pinion 32 are used as shown in FIG.
It can also be driven by In this case, the pinion 32 will connect the pulse motor. Further, although a microcomputer is used as the control device 23, a combination of other analog circuits and digital circuits may also be used.

〔Effect of the invention〕

As detailed above, the present invention allows the switching point between the suction throttling type control and the on-off type control to be selected in accordance with the amount of air used by the load, so that an energy saving effect can be obtained. Even if the volume of the piping system changes, the capacity of the compressor can be controlled using either suction throttling type control or on-off type control, which is more energy-saving.

[Brief explanation of drawings]

FIG. 1 is a control system diagram of a screw compressor for carrying out the capacity control method of the present invention, and FIG. 2 is a characteristic diagram of the suction throttling type control and on-off type control of the present invention.
FIG. 3 is a diagram showing state changes of each part during on-off type control of the present invention, FIG. 4 is a diagram showing an example of the configuration of a control device used in the method of the present invention, and FIGS.
FIG. 8 is a flowchart showing an example of the execution procedure of the capacity control method of the present invention, and FIG. 9 is a diagram showing another example of the suction throttle valve driving means used in the method of the present invention. DESCRIPTION OF SYMBOLS 1... Screw compressor, 2... Screw rotor, 3... Motor, 4... Suction pipe, 6... Suction throttle valve, 8... Oil collector, 9... Discharge valve, 10...
Gas cooler, 11... air storage tank, 12... supply pipe,
16... Oil cooler, 19... Three-way solenoid valve, 21...
... Solenoid valve, 23 ... Control device, 24 ... Pressure detector, 25 ... Detector.

Claims (1)

[Scope of Claims] 1. Switching between suction throttle type control using a suction throttle valve provided on the suction side of the screw compressor and on/off type control using the suction throttle valve and a discharge valve provided on the discharge side of the screw compressor. Then, in the screw compressor that performs capacity control, both controls are executed using the temporary setting values for temporarily determining the capacity control, and the input power and input current of the screw compressor motor are measured by executing these two controls. , the amount of air used, the air amount ratio, the discharge pressure, etc., and when the measured values match, that amount of state is used as the switching point for both controls. A capacity control method for a screw compressor, characterized in that the state quantity is stored as a set value, and thereafter, if the state quantity is above the set value, suction throttling type control is performed, and if it is less than that, capacity control operation is performed using on-off type control. . 2 Compare any one of the state quantities measured during suction throttle control operation and on-off type control operation, and if the measured value under suction throttle control is smaller, perform suction throttle control. 2. A capacity control method for a screw compressor according to claim 1, wherein the provisional setting value temporarily determined for the switching point is changed to a smaller value than before. 3 Compare any one of the state quantities measured during suction throttling type control operation and on-off type control operation, and if the measured value in on-off type control is smaller, perform on-off type control and 2. A capacity control method for a screw compressor according to claim 1, wherein the temporary setting value temporarily determined for the switching point is changed to a larger value than before. 4 Compare the state quantity measured during suction throttling type control operation with the set value, and if the measured value in suction throttling type control is smaller, perform suction throttling type control, and
A capacity control method for a screw compressor according to claim 1, characterized in that the temporary set value temporarily determined for the switching point is changed to be smaller than before. 5 Compare the state quantity measured during the on-off type control operation with the set value, and if the measured value in the on-off type control is smaller, perform the on-off type control, and
2. A capacity control method for a screw compressor according to claim 1, wherein the provisional setting value provisionally determined for the switching point is changed to a larger value than before. 6. According to any one of claims 2 to 5, the change value of the provisional set value is changed according to the difference in the measured value of the state quantity between the suction throttling type control and the on/off type control. The capacity control method of the screw compressor described. 7. Any one of claims 1 to 5, characterized in that temporary set values are set separately for suction throttle type control and on-off type control, and the control is switched and executed using each temporary set value. A method for controlling the capacity of a screw compressor described in . 8 During control operation after determining and memorizing the switching point, if a difference occurs in the measured value difference between each control during switching, and if the difference is greater than the allowable range, set the set value to obtain the optimal switching point. A capacity control method for a screw compressor according to any one of claims 1 to 6, characterized in that: