JPH0152595B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the operation of a screw compressor, and more particularly to an energy-saving operation control method.

[Conventional technology]

Conventionally, a capacity control method controls the capacity of a screw compressor by switching between on-off control that opens and closes the intake duct, motor stop control that starts and stops the compressor drive motor, and suction throttling control. is known. This type of technology was developed in Japanese Patent Application Laid-open No.
It is disclosed in Publication No. 155405.

The suction throttle control controls the opening degree of the suction throttle valve according to the discharge pressure, and the on-off type control turns on and off the suction throttle valve and the exhaust valve according to the discharge pressure.

[Problem to be solved by the invention]

By the way, in the above conventional technology, in order to reduce the power consumption of the motor during operation of the compressor, it is difficult to determine which of the three operating methods should be selected in response to fluctuations in the amount of air used and load capacity during actual operation. However, sufficient consideration has not been given to this point, and it cannot be said that optimal operation from the viewpoint of energy savings is achieved in response to changes in load.

An object of the present invention is to provide a method for controlling the operation of a screw compressor that can improve the energy saving effect.

[Means to solve the problem]

The above purpose is to operate a screw compressor while switching between suction throttling type control, on-off type control, and motor stop control. Memorize the power consumption characteristics in advance, measure the power consumption of the compressor drive motor, the no-load operating time T _d , and the full-load operating time T _u during the actual operation period, and calculate T _d and T _u . _The air usage ratio Q _h in the on _- off type _control is _determined using Perform stop control, measure the discharge pressure in the motor stop control, and when the discharge pressure reaches the set value P _L , switch to on-off type control and operate. When the comparison result between the operating time T _d and the control time T _n is T _d <T _n , the measured power consumption L _h of the motor, the motor power consumption characteristics in the suction throttling type control, and the air usage ratio Q _h Compare the expected _{motor consumption power L s when performing suction} throttling type control obtained _from When the suction throttling type control is operated, the suction throttling type control is operated, and when the suction throttling type control is operated, the motor consumption power characteristic in the on-off type control and the motor consumption power characteristic in the suction throttling type control are intersected. Compare the motor power consumption L _k with the measured motor power consumption L _s during suction throttling control, and when L _s L _k , operation is continued with suction throttling control, and L _s < L _k . This is achieved by switching to the on-off type control when operating.

[Effect]

First, prior to control, the motor consumption power characteristics in the on-off type control and the motor consumption power characteristics in the suction throttle type control are stored. When actual operation begins, the screw compressor is operated with on-off control or suction throttling control depending on the amount of air used. Note that if the amount of air used is extremely low, motor stop control is performed to stop the motor for driving the compressor.

If the actual operation is an on-off type control operation, the actual motor power consumption L _h is measured, as well as the full load operation time T _u and the no load operation time T _d . The air usage ratio Q _h is calculated from these T _u and T _d . Then, T _d is compared with the time limit T _n , and when T _d T _n , it is determined that the amount of air used is very low, and the process moves to motor stop control to stop the motor. In motor stop control, the discharge pressure is measured, and when the discharge pressure reaches the set value P _L , the control shifts to on-off type control. Now, during on-off type control operation, when the comparison result between the no-load time T _d and the limit time T _n is T _d < T _n , the motor consumption power characteristics in suction throttle control stored in advance and the calculated From the air usage ratio Q _h , the expected motor power consumption L _s is calculated if suction throttling control is currently being performed. Then, the calculated motor power consumption L _s is compared with the motor power consumption L _h actually measured in the on/off control operation, and it is determined which control mode consumes less energy. As a result, when L _h < L _s , operation continues under on-off type control, and L _h L _s
In this case, switch to suction throttle control. In this way, in reality, while performing on-off type control, the situation with suction throttle type control is estimated, and it is determined which of the two types of control will save energy, and the continuation or switching is performed. There is no need to try suction throttle control.

Subsequently, when the actual operation is suction throttling control operation, the actual motor power consumption L _s is measured. Then, from the motor consumption power characteristic in the on-off type control and the motor consumption power characteristic in the suction throttling type control, which are stored in advance, the intersection point of both characteristics, that is, the motor consumption power L _k at the temporary switching point is determined.
This L _k is compared with the measured L _s to determine which method of operation consumes less energy. That is, when L _s L _k , suction throttling type control is continued, and when L _s < L _k , it is switched to on-off type control. In this way, it is actually possible to determine which of the two types of control is more advantageous in terms of energy saving while executing the suction throttling type control without trying the on-off type control.

In this way, it is possible to reliably determine the control method that consumes the least energy depending on the amount of air used while the current control is being executed.

〔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 pressurized into a 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 6 is moved, and the amount of suction gas to 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 a pressure detector 24A.
Input signals of the pressure of the gas cooler 10 detected by the detector 25 and the input power of the motor 3 detected by the detector 25 are added. 24B indicates a flow rate sensor that detects the amount of air used.

Next, the suction throttle type control operation will be explained.

In response to a command from the control device 23, the air release valve 9 is closed, the solenoid valve 21 is opened, and the S port of the three-way solenoid valve 19 is communicated with the Q port. As a result, the pressure gas in the gas cooler 10 is removed from the pressure reducing valve 18.
The pressure is reduced to a constant pressure by the piston rod side chamber 7a of the cylinder 7. Pressure regulating valve 20
generates a secondary pressure according to the change in 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. Due to the action of pressure gas on the cylinder 7, the cylinder 7 operates in response to changes in the pressure of the gas cooler 10, and continuously controls the amount of gas sucked by the suction throttle valve 6. FIG. 2 shows the characteristics of this suction throttling type control, the on/off type control described later, and the motor stop control. 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 suction throttling control, and characteristic line b
is a characteristic of on-off type control. This characteristic line a,
The intersection point c of b is the optimal switching point for both controls. The power when the motor is stopped becomes zero as shown by symbol P.

Next, the on/off type control operation will be explained using FIG. 1.

When the solenoid valve 21 is closed by a command from the control device 23 and the pressure detected by the pressure detector 24A rises to the upper limit setting pressure P _u , the three-way solenoid valve 19 is closed by the command from the control device 23. is connected to the R port. As a result, the pressure gas in the cooler 10 acts on the side chamber 7b of the cylinder 7 opposite to the piston rod, so that the cylinder 7
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. In FIG. 2, the horizontal axis shows the air usage ratio Q, and the vertical axis shows the power consumption ratio L.
Further, FIG. 3 shows the state changes of each part during this on-off type control. In FIG. 3, the characteristic line d represents the pressure change in the gas cooler 10, and the characteristic line e represents the oil recovery device 8.
The characteristic line f shows the change in the power of the motor 3. T _d is no-load operation time, T _u is full-load operation time,
T _p is the compression time in the oil recovery device 8.

Next, motor stop control will be explained.

FIG. 4 shows the control operation. In FIG. 4, the same reference numerals as in FIG. During the on-off type control, if the no-load operation time T _d becomes equal to the limit time T _n , the motor 3 is stopped. When the pressure (discharge pressure) d of the gas cooler 10 reaches P _L , the motor 3 is started.

Next, the configuration of the control device 23 for executing the above-mentioned suction throttle type control, on/off type control, and motor stop control will be explained with reference to FIG. In this figure, parts with the same reference numerals as those in FIG. 1 are the same. 26 is an A/D converter that converts the analog signals from the detectors 24A and 25 into digital signals; 27 is a central processing unit that processes the captured signals according to a pre-stored processing procedure; 28
29 is a D/A converter that outputs the processed result to an external device; 29 is a read-only memory (ROM) that stores the processing procedure of the central processing unit 27; 30
is a random access memory (RAM) that temporarily stores calculation results.

Next, the control device 23 performs suction throttling control.
An example of an energy-saving operation execution procedure in which three control methods, on-off control and motor stop control, are automatically switched according to the load condition will be explained with reference to the flowchart shown in FIG.

In FIG. 6, the control is roughly divided into on-off type control, suction throttle type control, and motor stop control. Then, while executing any of these three controls, the one that is more advantageous in terms of energy saving is selected to perform capacity control.

The information and programs necessary to perform the processing shown in Fig. 6 are stored in the ROM 29 shown in Fig. 5 or
Store it in RAM30. Specifically, the necessary information includes motor consumption power characteristics in on-off type control, motor consumption power characteristics in suction throttle type control, and a constant for judgment (time limit T _n ). Formulas for calculations are built into the program.

In FIG. 6, the screw compressor is first started to operate under on-off control. The on/off type control is performed in steps 610 to 633 and steps 650 to 633.
It consists of 662. As will be described later, the formulas used here are the formula (1) for determining the average motor power consumption L _h shown in Figure 7, the formula (3) for determining the air usage ratio Q _h , and the predicted value. This is equation (6) for determining the motor power consumption L _s during suction throttle control. The things to be measured are the sample value a _k of the motor power consumption shown in Figure 8, the motor power consumption L ₁₀₀ at the time of 100% air usage ratio shown in Figure 7, and the full load operating time shown in Figure 3. T _u and no-load operating time
It is T _d . Note that L ₁₀₀ may be a constant in advance.

Now, in the on-off type control operation, first,
Step 6 to start the compressor motor 3
At step 10, the solenoid valve 21 is closed, the S port of the three-way solenoid valve 19 is communicated with the R port, and the release valve 9 is closed. In step 611, the electromagnetic switch 22 is turned on and the motor 3 is energized.

This has the effect of lowering the starting current of the motor by fully closing the suction throttle valve and causing no-load operation.

At step 612, it is confirmed that the motor has started. Next, in step 620, the port S of the three-way solenoid valve 19 is communicated with the port Q, and an on-off control compression operation begins. In step 621, it is determined whether the discharge pressure (pressure of the gas cooler 10) has increased to P _u . If the pressure is P _u , step 630 is executed. Step 630
Below, we will enter the no-load operation of on-off type control. First, in step 630, the port S of the three-way solenoid valve 19 is communicated with the R port, and the air release valve 9 is opened. In step 631, measurement of the no-load operation time _Td is started. In step 632, it is determined whether the no-load operation time _Td has reached the time limit _Tn . T _n is a set value to be memorized. If T _d
When T _n is reached, the control shifts to motor stop control and steps 640 and 641 are executed. on the other hand,
If T _d <T _n in step 632, step 633 is executed. In this step 633,
It is determined whether the discharge pressure (pressure of the gas cooler 10) has fallen to P _L. If the pressure is P _L
If so, step 650 is executed.

In step 650, the S port of the three-way solenoid valve 19 is communicated with the Q port, and the air release valve 9 is closed. This causes the compressor to perform a compression operation. Step 65
At step 1, measurement of the motor power consumption is started, and at the same time, measurement of the full load operating time T _u is started. Here, the motor consumption power is determined by the time Δt as shown in FIG.
The power consumption value is measured at each time, and the measured values of the motor power _consumption from time T _p to t _{o are} added.

In step 652, the discharge pressure (gas cooler 1
0 pressure) has become P ₁₀₀ .
If the pressure reaches P ₁₀₀ , step 653 is executed and this value is stored for calculating the motor power consumption characteristic. In other words, at this time, the measured motor power consumption is the air usage ratio (q) 100
Corresponds to the power consumption L ₁₀₀ for %. Step 6
54, the discharge pressure (pressure of the gas cooler 10) is
Determine whether P _u has risen. If the pressure reaches P _u , step 655 is executed.

In step 655, the S port of the three-way solenoid valve 19 is communicated with the R port, and the air release valve 9 is opened. This causes the compressor to perform an air release operation. In step 656, the value of the full load operating time T _u is stored in the memory, and measurement of the no load operating time T _d is started. In step 657, the no-load operation time is
Determine whether T _d has reached the time limit T _n .
If the no-load operation time _Td reaches the limit time _Tn , the motor stop control is performed and steps 640 and 641 are executed. On the other hand, step 65
At step 7, if T _d <T _n , step 658 is executed. In step 658, it is determined whether the discharge pressure (pressure of the gas cooler 10) has reached P _L. If the pressure is P _L , step 659 is executed. In step 659, the value of the no-load operation time _Td is stored in the memory. Next, in step 660, the average motor power consumption L _h ,
Calculate the air usage ratio Q _h . These are calculated using the following calculation method. That is, the average motor power consumption L _h is calculated by the following equation (1) (see Figure 8).

where a _k : sampling value of motor power n : number of measurements The on-off time T _h is calculated by the following equation (2).

T _h = T _u (full load operation time) + T _d (no load operation time) ...(2) The air usage ratio Q _h is calculated by the following formula (3).

Q _h = T _u − T _p /T _h ×100 (%) Here, T _p is very small compared to T _u , so it will be omitted.

Q _h =T _u /T _h ×100 (%) (3) Next, in step 661, the motor power consumption L _s during suction throttling type control is calculated. Calculation of this motor power consumption _Ls will be explained using the capacity characteristics of the suction throttling type control and the on/off type control shown in FIG.

The following method can be used to calculate the motor power consumption _Ls . One method is to measure the suction throttle characteristic a shown in Figure 7 in advance, and use this characteristic as the air usage ratio q.
and power consumption l as a function f _s (q, l). Then, the motor power consumption L _s during suction throttling control is calculated using the following equation (4) consisting of this characteristic equation and the amount of air used Q _h .

L _s = f _s (q, l) ...(4) However, q is assumed to be Q _h .

Another method uses the suction throttle characteristics shown in Figure 7,
Motor power consumption at 100% of air usage ratio q
It is expressed by an equation that passes through the coordinate points L ₁₀₀ and motor consumption power L _sp =L ₁₀₀ ×K ₁ at 0% of the air usage ratio q, that is, equation (5). However, K ₁ is the air usage ratio q.
Give as a percentage of 100%. Further, as the motor power consumption _L100 , the value measured in step 653 of the flowchart shown in FIG. 6 is used.

l = L ₁₀₀ × (1 - K ₁ ) / 100q + K ₁・L ₁₀₀ ... (5) The motor during suction throttle control is obtained by the following equation (6) obtained by substituting Q _h for q in the above equation. Find the power consumption L _s .

L _s = L ₁₀₀ × (1−K ₁ )/100Q _h +K ₁ ·L ₁₀₀ (6) The motor power consumption L _s during suction throttling control can be calculated using the method described above. The latter method is characterized in that it can be applied as is even if the capacities of the motor 3 and compressor change.

Motor consumption power L _s during suction throttling type control and motor consumption power during on-off type control determined in this way
L _h is compared in step 662 of the flowchart shown in FIG. And this step 66
If L _h <L _s in step 2, the process returns to step 650 and on/off type control is executed. Also, L _h ≧ L _s
If so, the process advances to step 670 and suction throttling control is executed.

Next, in the suction throttle control, step 6
Processes 70 to 674 are executed. First, in step 670, the solenoid valve 21 is opened and the three-way solenoid valve 1 is opened.
It communicates with the S port Q port of 9, and further connects to the air release valve 9.
is closed. In step 671, the values of the motor power consumption L _sp and L _hp when the air usage ratio q of the suction throttling type control and the on/off type control are 0% are calculated.

The motor power consumption L _sp when the air usage ratio q of suction throttle type control is 0% is determined by the following equation (7).

L _sp = L ₁₀₀ × K ₁ (7) The motor power consumption L _hp when the air usage ratio q of the on-off type control is 0% is determined by the following equation (8).

L _hp = L ₁₀₀ × K ₂ …(8) However, both K ₁ and K ₂ are given as a ratio to 100% of the amount of air used.

In step 672, the motor power consumption L _k at the switching point of the control where the characteristics of the suction throttling type control and the on-off type control match is calculated. This motor consumption power
There are the following methods to calculate L _k .

One method is to measure the on-off type characteristic b shown in FIG. 7 in advance and give this characteristic as a function of f _h (q, l). The motor power consumption L _k is obtained from the intersection of this characteristic equation and the above equation (4) or (5). In this case, the motor power consumption L _k is at point c in FIG. 7.

The other one is from the on-off type control shown in Fig. 7,
It is expressed by an approximate equation that passes through the operating points Q _h and L _h of the on-off type characteristic b at the time of switching to suction throttle type control and the operating points O and L _hp when the usage air amount ratio is q0%. This approximate formula is shown in equations (9) and (10). From the intersection of this approximate equation (9), equation (10) and the above equation (4) or equation (5), motor consumption power L _k
seek.

l=L _h −L _hp /Q _{h ・}q+L _hp …(9) Or by substituting equation ( ₈ ) into equation (9), l=L _{h −K 2}・L ₁₀₀ /Q _h・q+K ₂・L ₁₀₀ …(10) Also, L _k can be calculated from equations (5) and (10).

L _k = 100L _sp (L _h −L _hp )−Q _h L _hp (L ₁₀₀ −L _sp )/100(
L _h −L _hp )−Q _h (L ₁₀₀ −L _sp ) …(11) However, L _sp = L ₁₀₀ ·K ₁ and L _hp = L ₁₀₀ ·K ₂ .

In addition, if the load capacity of the compressor changes, the seventh
The on-off type control characteristic b shown in the figure changes. Therefore, it is necessary to find the control switching point c.

The former L _k calculation method can be applied when the load volume is constant, and if the on-off type control characteristic b is given in advance, L _k can be found as the switching point.

In addition, the latter method can be applied when the load volume changes and the on-off type control characteristic b is not determined, and if the motor consumption power L _hp when the air usage ratio is 0% is given in advance, The feature is that L _k is obtained as a temporary setting value of the switching point.

In the flowchart of Figure 6, the measured values during suction throttle control are the motor power consumption L _s shown in Figure 7 and the motor power consumption of on-off control at the time of switching from on-off control to suction throttle control.
L _h and the air usage ratio Q _h .

In addition, the calculation formulas and values to be calculated in memory are the formula (7) for calculating L _sp , the formula (8) for calculating L _hp , and the formula (8) for calculating L _k shown in Figure 7.
This is equation (11) to find. Note that L _sp and L _hp may be given in advance as constants.

Next, in step 673, the motor consumption power L _s of suction throttling type control is measured. In step 674, the motor power consumption _Lk at the switching point is compared with the motor power consumption _Ls in the suction throttling type control. And L _s ≧L _k
If so, continue suction throttle control. Also, L _s <
If L _k , to perform on-off type control,
Step 621 is executed.

Next, motor stop control will be explained.

In step 640 shown in FIG.
2 and stop the motor 3. Step 6
41, the discharge pressure (pressure of the gas cooler 10) is
Determine whether you have become P _L. If this pressure is P _L , steps 610, 611, 61
After executing Step 2 to start the motor 3, the compression operation of Step 620 is executed.

In the above-mentioned embodiment, the state quantities obtained from the control currently in operation and the state quantities obtained from other control operations are calculated based on the characteristic expressions of the other controls, and control switching is determined based on these. Control responsiveness and energy saving effects are improved.

Next, another embodiment of the present invention will be described with reference to FIG. In this embodiment, a step 663 for comparing on-off times is added to the procedure in the flowchart shown in FIG. Then, if the on-off time T _h > T _o (time limit), the on-off control is continued. If T _h ≦ T _o , step 670
Execute and switch to suction throttle control. T _o is a setting value to be memorized.

Next, still another embodiment of the present invention will be described with reference to FIG. This embodiment includes timer control steps 664 and 66 for controlling the operation time of the suction throttling control in the flow chart shown in FIG.
5,675. When the control is switched from on-off control to suction throttle type control, that is, when switching from the motor consumption power comparison in step 662 in on-off control to suction throttle type control, in step 665, the timer value T _p is set.
Set to T ₁ . Furthermore, when switching to suction throttling type control from the on/off time comparison in step 663, the timer value T _p is changed to T ₂ in step 664.
Set to . Step 67 for suction throttle control
Step 675 is inserted between step 3 and step 674 to detect the elapsed time of the timer. If the timer value T _p =0 in this step 675,
Switch operation to on/off type control. No. 9 mentioned above
Switching to suction throttle type control from the step 663 side in Fig.
9, 21, the filter 17, the suction throttle valve 6, etc., to reduce the frequency of on/off operations. In addition, the switching from step 665 corresponds to the operating state of the compressor, etc. (changes in output of the compressor and motor due to oil viscosity, etc.), and after the compressor enters stable operation, the above-mentioned air usage ratio is increased to 100. This is to measure the value of motor power consumption L ₁₀₀ at the time of %.

In addition, although the above-mentioned Example was demonstrated using the power consumption of the motor 3 as a state quantity for energy saving control of a compressor, the input current of the motor 3 can also be used. In addition, the amount of air used Q _h was determined from the on-off time, but the flow rate sensor 24B shown in Fig.
can be used. Further, although a microcomputer is used as the control device 23, a combination of other analog circuits and digital circuits may be used.

〔Effect of the invention〕

As described in detail above, according to the present invention, the three types of control, suction throttling control, on-off control, and motor stop control, can be automatically selected as the optimal control method depending on the air usage state. Therefore, the energy saving effect is improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a control system diagram of a screw compressor controlled by the control method of the present invention, and FIG.
The figure is a characteristic diagram of each control method of suction throttling type control, on-off type control, and motor stop to explain the control method of the present invention. FIG. 4 is a diagram showing changes in the state of each part during motor stop control to explain the control method of the present invention. FIG. 5 is a diagram showing an example of the configuration of a control device used in the present invention. 6 is a flowchart showing an example of the execution procedure of the control method of the present invention, and FIG. 7 is a characteristic showing the relationship between the used air amount ratio and power consumption for parameter calculation in the control method of the present invention. figure,
FIG. 8 is a characteristic diagram for explaining the method of calculating the average motor power consumption during on/off control in the control method of the present invention, and FIGS. 9 and 10 are flowcharts showing other execution procedures of the control method of the present invention. It's a chat. 1...Screw compressor, 2...Screw rotor, 3
…Motor, 4…Suction pipe, 6…Suction throttle valve, 8…Oil recovery device, 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, 2
4A...Pressure detector, 25...Input power detector to motor 3.

Claims (1)

[Claims] 1. 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. , a method for controlling the operation of a screw compressor in which a stop control of a motor that drives the screw compressor is selected and switched according to the load condition, the motor power consumption characteristics in on-off type control and suction throttling type control. _Store in advance _the power consumption characteristics _{of the} motor at Determine the air usage ratio Q _h in the on-off type control, and when the no-load operation time T d and the limit time T _n are compared with the no-load operation time T _d and the limit time T _n during the on- _off type control operation, the stop control of the motor is performed. In the motor stop control, the discharge pressure is measured, and when the discharge pressure reaches the set value P _L , the operation is switched to on-off type control, and during the on-off type control operation, the no-load operation time T When the comparison result between _d and the limit time T _n is T _d < T _n , it is determined from the measured power consumption L _h of the motor, the motor power consumption characteristic in the suction throttling type control, and the air usage ratio Q _h . When L _h < L _s , operation is continued under on-off control, and when L _{h L s is} reached, the suction throttle control is Operation is performed by switching to throttle type control, and when the suction throttle type control is operating, the motor power consumption at the intersection point of the motor consumption power characteristics obtained from the motor consumption power characteristics in the on-off type control and the motor consumption power characteristics in the suction throttle type control. Compare L _k with the measured motor consumption power L _s during suction throttling control, and when L _s L _k , operation is continued with suction throttling control, and when L _s < L _k , the above-mentioned on-off type A method for controlling the operation of a screw compressor, characterized in that the operation is performed by switching to a control mode.