JPS6142013A - Pi controller for liquid level control - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a PI control device for liquid level control for controlling the liquid level in a liquid storage part of a tank tower @ to a constant level.

[Technical background of the invention and its problems]

For example, in order to provide a stable supply of liquid, a tank tower is provided in the liquid distribution system, the liquid is temporarily stored there, and the stored liquid is supplied to the mlj side.

In order to keep the liquid level in the tank tower constant, as shown in Figure 4, a level detector 2 is installed in the tank tower 1 to detect the liquid level in the tank tower 1, and , give the detection output to the level indicating controller 3,
It compares with the base fs value, obtains a manipulated variable according to the difference, and gives this manipulated variable to the flow rate indicating controller 4. In the case of the device shown in Figure 4, the inflow system line is constant, and the outflow system V (flow rate detection b
5 and a control valve 6 that can be automatically adjusted by electrically controlling the valve opening for regulating the flow rate of the pipe line at the subsequent stage to control the outflow amount]. This method keeps the liquid level constant. Therefore, in this device, the output of the flow rate detector 5 and the operating output MY output from the level indicating controller 3 are input to the flow rate indicating controller 4, and the flow rate indicating controller 4 determines the flow rate using the operating output MY as a reference value. A difference output between the detection outputs of the detector 5 is obtained, which is used as an operational output, and is applied to the control valve 6 to control the opening and maintain the liquid level in the tank tower 1 within a predetermined value.

In this way, liquid level control is normally performed by adjusting the inflow or outflow amount according to the liquid level, but if the control system is made to respond sensitively to overflow, it will cause a hunting phenomenon. In the case of a system in which there is little problem even if there is a slight response delay, a control algorithm (hereinafter referred to as this) that sets a certain tolerance value (gap) for the liquid level and does not respond when it is within this level, in other words, it is a dead zone. (referred to as gap PI control).

Gear, GuP! The control is as shown in FIG.
The control deviation In' is determined using nXKp (f in), and PI sub-control is performed.

However, since this control sets a linear dead zone, when the deviation n is within GP, the control deviation n' becomes zero. In this case, it is good when the liquid level changes slowly, but the liquid level When the level changes suddenly, no manipulated output is generated if it is within the GP, and the manipulated output is generated only when the deviation exceeds the GP, so the response to sudden changes in the liquid level is extremely poor. There are drawbacks.

[Object of the invention,]

The present invention has been made in view of the above circumstances, and is designed to enable control to be performed in accordance with the amount of change in the liquid level when the liquid level changes suddenly even within the gap in PI control. P for liquid level control with improved response! The purpose is to provide a control device.

[Summary of the invention]

That is, in order to achieve the above object, the present invention monitors changes in the volume of the stored liquid, and when the volume is within a predetermined range, it is used as a dead zone for control, and when the volume is outside the above range, the flow rate is adjusted according to the amount of change. means for obtaining the volume detection output and monitoring the amount of change thereof; and, when the amount of change exceeds a reference value, the amount of change is corrected by multiplying the amount of change by a predetermined correction coefficient. A means for generating an output and a means for adding this corrected amount of change to generate a control amount are provided, and the amount of change in volume is monitored and a predetermined correction is made to the amount of change depending on the magnitude of the amount of change. By giving the control amount to the control amount generating means, the deviation is caused by the gear.

Even if the liquid level is within the dead zone, when the liquid level suddenly changes, the liquid level can be controlled according to the amount of change to improve responsiveness.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a professional diagram showing the configuration of the device of the present invention. In the figure, reference numeral 11 represents a deviation calculator, and this deviation calculator 11 is preset to the detection output pv output by the level detector 2. It has a function of receiving the reference value SV, comparing the detection output pv with the reference value Sv, and outputting the deviation en. Reference numeral 12 denotes a comparator. This comparator 12 receives this deviation/n and a preset gear and f-value GP, compares the two, calculates the magnitude, and outputs the determination result. is s 13d
, a two-manpower selector is used, and the deviation en is determined by the gear knob value GP according to the determination result of the two-manpower selector 13d and the comparator 12.
It has a function to select and output 0 when it is within the range, and select and output the three-company deviation en when it is outside the gear and value GP. Reference numeral 14 denotes a deviation calculator, and this deviation calculator 14 calculates the deviation e outputted via the two-man power selector 13 based on the gear and pull value GP.
n and generate the difference output. 15 is a multiplier, and this multiplier 15 multiplies the deviation gain KP by the output of the deviation calculator 14. Reference numeral 16 denotes a rate of change calculator, and this rate of change calculator 16 receives the detection output p.
It has a function of receiving v and calculating its change rate value Δpv.

17 is a comparison calculator), and this comparison calculator 17 compares the change rate value Δpv and a preset change rate limit ΔGP.
The size is determined by comparing it with 1m. 1
This two-man power selector 18 is a two-man power selector from eight companies, and this two-man power selector 18 determines the change rate value Δpv to be 0 when it is within the change rate limit ΔG P 1 ml, and the change rate value according to the determination result of the comparator 17. It has a function of selecting and outputting the change rate value ΔGP when it is outside the value lGP.

19 is a multiplier, and this multiplier 19 applies a change rate gain K P' set in advance to the output of the two-man power selector 18.
Multiply and output. Numeral 20 is an adder/subtractor 20 which subtracts the output of the multiplier 15 and the multiplier U unit 16 and outputs the result as the control deviation en'.

21 is a PID calculator, and this ID calculator 2 outputs 3iL as a manipulated variable Mv' for controlling the opening of the operating valve 6 based on the control deviation n' output from the adder/subtractor 20. This outputs the following.

Next, the operation of this device having the above configuration will be explained.

As shown in Fig. 1, this device has a deviation an and a gap value G.
Components 11 to 15 that calculate the control deviation n' using P, and a component 16 that calculates the correction amount for the control deviation n' by changing the rate of change Δpv and the rate of change limit value ΔPV1n.
~19, the control deviation 11 fi', and the correction amount are added and subtracted,
It is roughly divided into components 20 and 21 that perform PID calculations.

The rate of change speed and deviation components each operate independently.

- Upon receiving the detection output pv output from the level detector 2 and the preset reference value SV, the deviation detector 11 compares the detection output Pv with the reference value SV and calculates the deviation.
Output n. Then, this output is given to a comparator 12 and a two-man selector 13. Then, the comparison calculator 12 receives this deviation @n and the preset gap value CP, compares the two, calculates the magnitude thereof, and outputs the determination result. This discrimination result is given to the two-manpower selector 13, and the two-manpower selector 13, based on the discrimination result of the comparator 12, selects Hiro 0 when the deviation on is within the gear knob value GP.
Also, when the value is outside the GP, the deviation/exit is selected and output. This output is given to a deviation calculator 14, which compares this deviation/n given via the two-man power selector 13 with the gear and gear value GP as a reference.
Generate the difference output. And this difference output is multiplier 1
5, and this multiplier 15 inputs r in KP for the deviation.
is multiplied by

On the other hand, the rate of change calculator 16 that receives the detected output pv calculates a rate of change value Δpv of the detected output pv. Then, this is given to the comparator 17.

The comparison calculator 17 compares the given rate of change value Δpv with a preset rate of change I7 ΔGrim to determine its magnitude. Then, this discrimination result is given to the two-manpower selector 18. Then, this two-man power selector 18 determines that the change rate value Δpv is change rate +7), 0 when the change rate value Δpv is within ΔGP1m, and 0 when the change rate value Δpv is outside the change rate lGP, based on the determination result of the comparator 170. Select and output. This output is given to a multiplier 19, which multiplies the output of the two-manpower selector 18 by a preset change rate gain KP' and outputs the result. This output is given to the adder/subtractor 20 together with the output of the multiplier 15, where it is multiplied by the output of the multiplier 15! The output of a16 is subtracted and the result is output as a control deviation/n' and is given to the PID calculator 21. and,
Based on the control deviation output from the PIDID calculator 2 and the adder/subtractor 20, the operation amount MY for controlling the opening of the operation valve 6 is calculated and given to the operation valve 6, and the valve opening is adjusted. controlled.

The above is a general explanation of the control operation. Next, the operation when the liquid level is within the gear, which is a feature of the device of the present invention, will be explained.

It is now assumed that the detected output pv of the liquid level detector 2 is at the level within the gear f and exhibits a change as shown in FIG.

In this device, the change rate calculator 16 that receives the change rate value detection output pv extracts the detection output pv at predetermined time intervals, and
A change rate value Δpv of the detected output is calculated based on the level difference between the outputs. Then, this is given to the comparator 17. This given rate of change value Δpv is the rate of change limit ΔP
Since V1m is smaller than V1m, the comparator 17 compares the two and determines that the rate of change value Δpv is small. Therefore,
Upon receiving this, the two-man power selector 18 outputs 0, and therefore, control is performed only by the outputs of the components 11 to 15, that is,
This is gap PI control.

In the case of FIG. 3, the change rate value ΔpvH1 of the detection output calculated by the change rate calculator 16 based on the level difference between the detection output Pvt and the original value extracted at predetermined time intervals, the change rate limit, Since it is larger than ΔPV1m, the comparator 1'7 compares the two and determines that the change rate value Δpv is large. Therefore, the two-man power selector 18 receiving this is Δp
Therefore, a correction valve of .n' corresponding to ΔPV is determined and output. Then, add this to component 11
Since it is added to the output on the ~15 side, it is a gear.

Even if there is a variation within f, the PI sub-control is performed in accordance with ΔPv regardless of this.

In this way, even if there is a fluctuation within the gear or f, if the fluctuation range is large, PI sub-control will be performed, so even if a sudden change in liquid level occurs within the gear or f, the flow rate will be controlled in advance. It is possible to improve the responsiveness of liquid level control.

In the above embodiment, the rate of change value ΔPv of the liquid level was obtained by sampling it at a predetermined period, but this was continuously detected and the signal was differentiated, and the state of change was determined by calculating the slope of the change. By monitoring changes, it becomes possible to detect and respond to sudden changes during the sampling period that could not be detected with periodic sampling.

In addition, the time required for the assimilation rate value ΔPv to reach a certain level is determined, and the gears are adjusted accordingly.

7' It is also possible to determine whether to maintain PI control or to shift to PI sub-control. .

Note that there are the following methods for determining a correction value for the level change speed.

(1) The level change speed, the change speed, and the value (ΔP
A method of subtracting V1m) and multiplying Δpv−ΔPv1rp by the change rate gain (K p').

This method requires less correction due to level change speed, so
Although the responsiveness deteriorates somewhat, the change in outflow amount can be suppressed.

(2) A method in which the volume of the tank tower is calculated based on the level change rate, and the set value of the outflow amount is calculated based on this calculated volume.

There are two methods for calculating the volume: a method of approximation using a polygonal line, and a method of using calculation formulas and tables (constants) depending on the level position.

〔Effect of the invention〕

As described in detail above, in the gear and gear PI control in which a dead band is provided that does not respond to the level change according to the present invention, if a sudden change occurs within the dead band, PI sub-control is performed in accordance with the change. As a result, even if there is a sudden change in the liquid level within the dead zone, there is no longer a need to immediately enter control after crossing the dead zone, as was the case in the past, so there is no response delay. It is possible to provide a PI control device for liquid level control that can perform extremely good gap PI control that combines the advantages of gap PI control and PI sub-control.

[Brief explanation of drawings]

Fig. 1 is a professional diagram showing an embodiment of the present invention;
FIG. 3 is a characteristic diagram for explaining the present invention in detail, FIG. 1 is a system diagram of basic liquid level control, and FIG. 2 is a control characteristic diagram of conventional gap PI control. 1...tank tower, 2...level detection a, 3...
・Level indicating controller, 4...Flow rate indicating controller, 5...
・Flow rate detector, 6... Control valve, 11.14... Deviation calculator, 12.17-... Comparison calculator, 13.18...
・Two-man power selector, 15.19... Multiplier, 16...
Assimilation rate calculation unit, 20...addition/subtraction unit, 2no...PID
Drummer. Patent attorney Suzue Takehiko Diagram 1

Claims (3)

[Claims] (1) In a system that monitors changes in the volume of the stored liquid and uses it as a dead zone for control when the volume is within a predetermined range, and controls the flow rate in accordance with the amount of change when the volume is outside the range, means for obtaining the volume detection output and monitoring the amount of change thereof, and when the amount of change exceeds a reference value;
A PI control device for liquid level control, comprising means for generating a corrected change output by multiplying the change amount by a predetermined correction coefficient, and means for generating a control amount by adding the corrected change amount. (2) The PI control device for liquid level control according to claim 1, wherein the amount of change is periodically monitored. (3) The amount of change is continuously monitored, and when the tendency of the change exceeds a reference value, the amount of change is corrected with a correction coefficient to provide a corrected amount of change output. PI control device for liquid level control as described in .