JPS58140498A - Operation control method for screw compressor - Google Patents

Abstract

PURPOSE:To permit to prevent waste of energy by a method wherein an automatic and the most optimized method for the control of a suction choking valve, ON-OFF control and the control of stopping a motor is selected. CONSTITUTION:Compressed gas in an oil retrieving device 8 is released into atmosphere by a releasing valve. Pressurized gas in a gas cooling device is supplied into piston rod side chambers 7a, 7b to operate the suction choking valve 6. Input signals of a pressure in the gas cooling device and the input power of a motor 3, detected by a pressure dtector 24A and the same 25, are inputted into a control unit 23 to select the most proper means, therefore, the waste of energy for the screw type compressor may be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION 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.

Conventionally, one method for controlling the capacity of a screw soil compressor is to use a combination of suction throttling type control and on/off type control for volume control. The suction throttle control described above is to control the opening If of the suction throttle valve according to the discharge pressure.
Further, the on-off type control is to control the suction throttle and the discharge valve on and off according to the discharge pressure.

In the conventional control method for woodcutter, the procedure for determining whether suction throttling control or on-off control is more advantageous is to actually operate the screw compressor using both types of control, and during this operation, control The screw compressor was controlled by measuring the power consumption, air cover, and discharge pressure, and by comparing these measured values, it was determined whether to select either of the two controls described above. , since it requires trials for judgment, it lacks continuity. Also,
Although it is temporary, the screw compressor will be operated under the control with less energy saving effect, resulting in energy loss.

An object of the present invention is to provide a screw compressor operation control method 1 that can improve the energy saving effect.

A feature of the present invention is that three types of control, suction throttling control, on-off control, and motor stop control, are switched using state quantities, and the state quantities obtained from the control currently in operation and the characteristics of other controls are used. From the formula, the state quantities for operation with other controls are calculated, and by comparing these state quantities, one of the three controls is determined and that control is executed, and the response of the control is This improves performance and energy saving effects.

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 implementing 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 throttle valve provided in the suction pipe 4, and this suction The throttle valve 6 is opened and closed by a cylinder 7. 8 is an oil recovery device, 9 is a 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.

The suction gas passes through the suction throttle ff6 and enters the suction pipe 4 of the compressor 1.
It is sucked into the compressor 1 and pressurized. This pressurized suction gas passes through the discharge t5 and the check valve 13 to the oil recovery device 8.
The oil in the waste is separated and stored in the lower part of the oil recovery device 8. The compressed gas from which the oil has been separated passes through an oil separation filter 14i provided at the outlet of the oil recovery device 8, passes through a pressure regulator 4P15, passes through a gas cooler 10, and is supplied to the load side through an air storage tank 11 and a supply pipe 12. The oil in the oil collector 8 is cooled by an oil cooler 16, filtered by an oil filter 17, and then supplied to the compressor. The pressure a-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 supplied to the piston rod side chamber 7m of the cylinder 7 through a pressure reducing valve 18 and a three-way solenoid valve 19, and to the opposite piston rod side chamber 7b of the cylinder 70 through a pressure regulating valve 20 and a solenoid valve 21. be done. As a result, the suction throttle valve 6 is moved, and the amount of waste suctioned into the compressor 1 can be adjusted.

The aforementioned three-way solenoid valve 19 switches and communicates the S boat with the Q port or the R boat. These three-way solenoid valve 19, solenoid valve 21. The discharge valve 9 and the electromagnetic switch 22 of the motor 3 are operated by commands from the control device 23. Control device 2
Input signals of the output of the gas cooler 10 detected by the pressure detector 24A and the input power of the motor 3 detected by the detector 25 are added to 3. 24B indicates a flow rate sensor that detects the amount of air used.

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

Based on the command from the control device 23, the air release valve 9 and the solenoid valve 21 are activated.
Open, three-way 11 solenoid valve 19v Yusono S bow ) t
- Connected to Q boat. As a result, the pressure gas in the gas cooler lO is reduced to a constant pressure by the Sakaide box 18, and is guided to the anti-piston rod chamber 7b of the cylinder 7. The pressure regulating valve 20 generates a secondary pressure fC in response to a change in the pressure of the gas cooler 10 from the moment the set pressure Pat- is exceeded. Then, this secondary pressure is guided to the cylinder 70 side chamber 7a 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 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, the joint axis shows the consumption power ratio, the characteristic +@a shows the characteristic of the suction throttling type control, and the characteristic line 1 shows the characteristic of the on-off type control. This time ma
The intersection C of tb becomes the optimal switching point for both controls. The assistance when the motor stops becomes zero as shown by symbol P.

Next, the on/off control operation according to the present invention will be explained using diagram M1.

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, the three-way solenoid valve 19 is closed by the command from the control device 23. to the R boat. As a result, the pressure gas in the gas cooler lO acts on the chamber 7b on the side opposite to the piston rod of the cylinder 70, so that the cylinder 7 completely closes the suction throttle valve. At the same time, the air release valve 9 is opened by 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 1O decreases and reaches the lower limit set value PL, the three-way solenoid valve 19 is switched and communicates with the S boat'grQ boat, so that the gas cooler 1
The pressure gas inside 0 is in the piston rod side chamber 7m of cylinder 7.
added to. Therefore, the cylinder 7 fully opens the suction throttle valve 6, and 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 characteristics of this on-off type control are shown in the characteristic line of FIG. In FIG. 2, the horizontal axis indicates the air usage ratio Q, and the vertical axis indicates the power consumption ratio. 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 of the gas cooler 10, and the characteristic line #e
Characteristic @f shows the change in the pressure of the oil recovery device 8, and the characteristic @f shows the change in the power of the motor 3. T- is the no-load operating time, T11 is the full-load operating time, and T, fl is the compression time in the oil recovery device 8.

Next, motor stop control according to the present invention will be explained.

FIG. 4 shows the control operation. In FIG. 4, parts with the same reference numerals as those in FIG. During on-off type control, the no-load operation time T4 is the time limit T.

When it becomes equal to , the motor 3 is completely stopped.

When the pressure (discharge pressure) d of the gas cooler 10 reaches PLK, the motor 3 is started.

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

Next, an example of an energy-saving operation execution procedure in which the control device 23 automatically switches among the three control methods of suction throttling control, on-off control, and motor stop control according to the load condition is shown in the flowchart shown in FIG. This is explained by:

First, in order to start the compressor motor 3, step 6
Open the solenoid valve 21 at 10, and open the 8 boat t of the three-way solenoid valve 19.
- Connect to the R boat and close the air release valve 9. In step 611, the electromagnetic switch 22t is turned on and the motor 3 is energized. Step 612 confirms that the motor has started. Next, at Stella 7'620, the three-way solenoid valve 19 (bow) 8t-9 is communicated with the boat, and an on-off control compression operation is started. In step 621, it is determined whether the discharge pressure (pressure of the gas cooler 10) has increased to P or not.

If the pressure is Psl, step 630 is executed. From step 630 onwards, an on-off control air release operation is entered. First, in step 63cf, the three-way solenoid valve 19 is connected to the StR boat, and the air discharge ff9 is opened. In step 631, measurement of the air release time T- is started. In step 632, it is determined whether the air release time T4 has reached the limit time T. If Ta>T-, the process moves to motor stop control and step 64o.

641t - Execute. - 10,000, T in step 632
If a < T, step 633 is executed.

In this step 633, it is determined whether the discharge pressure (pressure of the gas cooler 10) has fallen to PL. If the pressure is PL, step 650t--execute. Steps 650 to 662 show the on-off control procedure.

In step 650, the 8 ports of the three-way solenoid 19 are communicated with the Q boat, and the release valve 9t is closed. This causes the compressor to perform expanded compression operation. At step 651, the total power consumption of the motor is started at 11 J't, and at the same time, the measurement of the compression time T is started. Here, the motor power consumption is determined by measuring the power consumption value at every time Δt, as shown in FIG.
1. Measurement of motor power consumption up to l1la0 to a are added.

In step 652, the discharge pressure (pressure of the gas cooler 10) is Pl. Determine whether it has become 0. If the pressure is P, . If so, step 653 is executed. That is, at this time, the measured motor power consumption is power consumption L1° with respect to the usage air amount ratio (Q) 100%. corresponds to In step 653, it is determined whether the discharge pressure (pressure of the gas cooler 1o) has increased to Pl. If the pressure becomes Pl, d-step 655 is executed.

In step 655, the 8th boat of the three-way solenoid valve 19 is communicated with the R boat, and the casing is opened.

This causes the compressor to perform an air release operation. Step 656
Then, the value of the compression time T is stored in the memory, and the measurement of the air release time Ta is started. In step 657, it is determined whether the air release time 1'- is a limited time 1p or not. If the air release time T- reaches the limit time 1'', the process moves to motor stop control, and steps 640 and 6
Execute 41 gold.

On the other hand, in step 657, if T4<T-, step 658t- is executed. In step 658, it is determined whether the discharge output (pressure of the gas cooler 10) has reached PL. If the pressure is PL, step 6
Execute step 59. In step 659, the value of frame air release time T4 is stored in memory. Next, in step 660,
Average motor power consumption Lb, on/off time T b s air usage ratio Q- are calculated. This is done using the following calculation method. That is, the average motor power consumption Lm is calculated by the following equation (1) (see FIG. 8).

ak Lh =□ ・・・・・・・・・・・・・・・ (1)
However, ak: sampling value of motor power n: number of measurements On/off time T- is calculated by the following equation (2).

Th = T - (compression time) + Ta (air release time)...
(2) The air usage ratio 9 is calculated using the following equation (3).

Next, in step 661, the motor power consumption during suction throttling control is calculated. This motor consumption power is
The calculation of t- 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 is available for calculating the motor power consumption. One of them is the suction throttle characteristic a shown in Figure 7.
This characteristic is expressed as a function f, (q, l) of the air usage ratio q and the power consumption t. and,
The following equation (4
), the motor power consumption during suction throttle control, t-
calculate.

Ll = f, (q, l...
・(4) However, let q be Q-.

Another method is to use the suction throttle characteristics shown in FIG. 7 as the motor power consumption at the time of 100% of the air usage ratio (Q). . and the motor power consumption at θ% of the air usage ratio (Q).

=I1. . . It is expressed by a formula passing through both coordinate points of XK, that is, formula (5). However, K1 is defined as the ratio to 100% of the air usage ratio (Q). The power consumed by the motor. . uses the value measured in step 653 of the flowchart shown in FIG.

・・・・・・・・・・・・・・・(5) Qb for q in the above formula
The motor power consumption during suction throttle control is determined by the following equation (6) obtained by substituting k.

(6) By the method described above, it is possible to calculate the motor power consumption (t) during suction throttling type control. The latter method is characterized in that it can be applied up to a time even when the capacities of the motor 3 and the compressor change.

The motor power consumption during suction throttling type control obtained in this way, and the motor power consumption during on-off large control, I, -, are expressed as follows:
A comparison is made in step 662 of the flowchart shown in FIG. If Lh<L= in step 662, the process returns to step 650 and executes the on-off type control. If Lh>L, the process advances to step 67G and suction throttling control is executed.

In step 670, the solenoid valve 21 is opened, the 8 boats of the three-way solenoid valve 19 are connected to the Q boat, and the air release valve 9t is opened.
- Closed. In step 671, the values of the motor power consumption L s6 and L ha when the air usage ratio (Q) of the suction throttle type control and the on-off type control are 0% are calculated.The air usage ratio (Q) of the suction throttle large control is calculated. The motor power consumption when is 0%. is determined by the following equation (7).

L. “LIOoXK,・・・・・・・・・・・・・・・
- (7) Motor consumption power Lhou when the air usage ratio (Q) of on-off type control is 0% is determined by the following equation (8).

L b6 L: L 1°. XK......
・・・・・・・・・(8) However, K1. Both can be expressed as a ratio to 100% of usage.

In step 672, the motor consumption power Lh at the control switching point where the characteristics of the large suction throttle control and the on-off type control match
Calculate. The following method is available as a method for calculating this motor power consumption Lht=.

One of them is to measure the on-off type characteristics shown in Figure 7, and give this characteristic as a function of fb (Q, t). The motor power consumption Lh is obtained from the intersection of this characteristic equation and the above-mentioned equation (4) or equation (5). In this case, the motor power consumption Lht1 is 0 point in FIG.

The other is the on-off type characteristic bl shown in Fig. 7, and the operating point (Q, b, L
h) and the operating point when the air usage ratio (q) is 0% (0=L
be). This approximate formula is Equation (9)
It is shown in the formula 0 (lO). This approximation formula (9).

Motor consumption power Lh is determined from the intersection of equation (10) and equation (4) or equation (5).

Or... (10) Next, in step 673, the motor power consumption of the suction throttle p-type control is measured. In step 674, the motor consumption power Lm at the switching point
Compare the power consumption of the motor with the large suction throttle control.

And...

If ≧Lk, the suction throttle type 9 control is continued. Also, L,
If <Lk, step 6o is executed for the friend who executes on-off type control.

Next, motor stop control will be explained.

In step 640 shown in FIG. 6, the electromagnetic switch 22? l-
disconnect and stop motor 3. In step 641, it is determined whether the discharge pressure (pressure of the gas cooler IO) is close to PL. If the pressure is 6 (Pt), step 621 is executed to start the motor 3, and then on/off type control is executed.

In the above-mentioned embodiment, the state quantity tV obtained from the other control operation is calculated based on the state quantity obtained from the control currently in operation and the characteristic expression of the other control, and control switching is determined based on these. The responsiveness and energy saving effect of the system 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 time eclipses is added to the procedure in the flowchart shown in FIG. If the on-off time Tb>T (time limit), the on-off control is continued. If T-≦T, step 670 is executed to switch to large suction throttle control.

Next, still another embodiment of the present invention will be explained with reference to FIG. In this embodiment, steps 664, 665 and 675 of timer control are added to the procedure of the flowchart shown in FIG. 6 to limit the operation time of the large suction throttle control. When the control is switched from on-off control to large suction throttle control, that is, when switching from the motor consumption power comparison in step 662 in the on-off control to large suction throttle control, in step 665, the timer value T is set to T. . In addition, when switching to suction throttle large control from step 6630 ON/OFF time comparison, step 66
4, the timer values T and tT* are set. In the suction throttle large control, step 675 is inserted between step 673 and step 674 to detect the elapsed time of the timer. If the timer value T,=0 in step 675, the operation is switched to on-off type control. The switching from the step 664 side described above is performed using the solenoid valve 1 under on-off type control.
9,21. On/off operation of filter 17, suction throttle valve 6, etc. This is to alleviate the j1 degree.

In addition, the switching from step 665 is based on the operating state of the compressor, etc. (changes in the output of the compressor and motor due to oil viscosity, etc.) ,. . This is the tth time to measure 01lli.

Note that the above embodiment was explained using the power consumption of the motor 3 as the state quantity for energy saving control of the compressor.
The input 11L flow of motor 3 can also be used. In addition, the amount of air used Q was calculated from hk on-off time, but the first
It is possible to use the flow rate unit 24 Bt shown in the figure. Further, although a microcomputer is used as the control device 23, a combination of other analog circuits and digital circuits may be used.

As described in detail above, according to the present invention, there are three controls: suction throttle control, on-off control, and motor stop control.
To 22! Since the optimum control method can be automatically selected depending on the air usage status, the energy saving effect is improved.

[Brief explanation of the drawing]

1. Fig. 1 is a diagram showing an example of a control system diagram of a Sufuryu compressor controlled by the control method of the present invention, and Fig. 2 is a drawing showing an example of a control system diagram of a suction throttling type control, on/off, to explain the control method of the present invention. Characteristic diagrams of each control method of type control and motor stop; Figure 3 is a diagram showing state changes of each part during on-off type control to explain the control method of the present invention; Figure 4 shows the control method of the present invention. 5 is a diagram showing an example of the configuration of a control device used in the present invention. FIG. 6 is an example of an execution procedure of the control method of the present invention. FIG. 7 is a characteristic diagram showing the relationship between the used air amount ratio and consumed power for parameter calculation in the control method of the present invention, and FIG. 8 is the average motor during on-off control in the control method of the present invention. A characteristic diagram for explaining how to calculate the power consumption, and FIG. 9 and FIG. 1O are flowcharts showing other execution procedures of the control method of the present invention. 1... Screw compressor, 2... Screw rotor, 3
...Motor, 4...Suction pipe, 6...Suction throttle valve,
8... Oil recovery device, 9... Air release valve, 10... Gas cooler, 11... Air storage tank, 12... Supply pipe, 16...
・Oil cooler, 19...three rice 2 121 d spear 31 month year 5I21 o 7 evil talent δ figure o'l IZI

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 and compression using the suction throttle valve and a discharge valve provided on the discharge side of the compressor. In the operation control of a screw compressor, which selects and switches three controls according to the load condition: stopping the motor that drives the machine + h rice reduction, the state quantities obtained during operation of each of the above controls and this condition are A screw compressor characterized by calculating the state quantity when operated with other controls based on wAfl, and comparing these state quantities to select the control with the greatest energy saving effect. Operation control method. 2 During on-off type control operation, air usage Qh) motor power consumption L-, on-off time T- = T, (compression time)
+T4 (air release time) is detected, and the used air I is determined from the relational expression between the used air amount ratio during suction throttle control and the motor consumption power.
Calculate motor power consumption Ll during suction throttle control corresponding to Q j, , If power consumption Lm<L, continue on-off control; if Lh>L, switch control to suction throttle control. The method for controlling the operation of a screw compressor according to claim 1, wherein the t% characteristic is expressed as t%. 3. During on-off type control operation, air release time Ta<T, (
If the key is ≧T, then the on-off type control is continued, and if the key≧T, the motor is stopped by switching to the motor stop control. Operation control method for screw compressor. 4. During suction throttling type control operation, the motor power consumption during this control is detected, and control obtained by the relationship between the air usage ratio and motor power consumption during suction throttling type control and on-off type control. Calculate the motor power consumption Lh at the switching point, and if these consumption dynamics Lh and L-point, >Lk, continue the suction throttling type control, and if L-<Lk, switch to the on-off type control. 2. The method of controlling the operation of a screw compressor according to claim 1, wherein the method comprises switching the compressor. 5. The motor consumption power Lhkj, which is the control switching point during large suction throttle control, An approximate formula that passes through the operating point (Q, h, T, -) of the on-off type control at the time of switching and the air release operating point (0, Lbo) when the air usage ratio in the on-off type control is zero. 5. A method for controlling the operation of a screw compressor according to claim 4. 6. The method for controlling the operation of a screw compressor according to claim 2 or 4, characterized in that the used air amount is used instead of the used air amount ratio. 7. Detect the relational expression between the motor power consumption and the air flow ratio during on-off control operation, corresponding to the discharge pressure when the air flow ratio is 100% during on-off control operation, and calculate the motor power consumption. ,. . And the power consumption of the motor when the amount of air used is zero during large intake throttle control. =L. . 5. The method of controlling the operation of a screw compressor according to claim 4, wherein f% is used as an equation passing through both coordinate points of XK (ratio to 100% air usage). 8. Claim 2, characterized in that motor current consumption is detected instead of motor consumption power and used for control.
The method for controlling the operation of a screw compressor according to any of the above items. 9. The air usage ratio in on-off type control is T, /T,
Obtaining from +T- 1j- The method for controlling the operation of a screw compressor according to claim 6 or 7, characterized in that: +T-. During the 1α on-off type control operation, the on-off time Tk is Th
>T- (time limit), continue on-off type control,
3. The method of controlling the operation of a screw compressor according to claim 1, wherein if Th<T-, the control is switched to suction throttling control. 11. When switching from on-off type control to suction throttle type control, the operating time T is measured by a timer, and this time T1
The method for controlling the operation of a screw pressure machine according to claim 1, characterized in that when Ts=Tp (time limit), the control is switched to suction throttling type control.