JPH04115195A - Fuzzy method for controlling water level of steam drum - Google Patents

Abstract

PURPOSE:To improve an operation control performance by a method wherein the amount of adjustment of the opening of a feed water adjusting valve is inferred discretely by a three kinds of fuzzy inference elements on the basis of a steam drum water level deviation, a water level change rate, etc. and a weighting synthetic computation is executed therefor in accordance with the state of a plant. CONSTITUTION:Receiving a steam drum water level deviation etc. as inputs, a first fuzzy inference element 51 of a steam drum system infers the amount of operation of a valve according to such a control rule that 'the valve is closed in a large degree when a level difference is positive and large and when a level change rate is large', for instance. When a flow rate evaluated from the opening of a main valve etc. is inputted, a second fuzzy inference element 52 of a steam-feed water flow rate system infers the amount of operation of the valve according to such a control rule that 'the valve is closed when the flow rate deviation shows that feed water is somewhat excessive', for instance. Receiving as an input a flow rate deviation of an actual feed water flow rate from an optimum feed water flow rate, which is evaluated from a reactor output, a third fuzzy inference element 53 of a reactor output system infers the amount of operation of the valve according to such a control rule that 'the valve is closed in a large degree when the flow rate deviation shows that the feed water is excessive', for instance. Such three discrete inferences as statd above are executed, a weighting synthetic computation is executed and thereby the opening of a feed water adjusting valve is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for automatically controlling the liquid phase water level in a steam drum in a nuclear power plant or the like. To explain in more detail, for example, in the low power region of the nuclear reactor,
The present invention relates to a method of controlling the water level in a steam drum that separates steam-water mixed fluid generated in a nuclear reactor using fuzzy inference techniques.

[Conventional technology] The following is an explanation using a new converter reactor power plant as an example.

The steam drum in the new converter reactor power plant collects the coolant mixture of steam and water generated from the nuclear reactor, separates the steam and water, and sends only the steam to the turbine system, while the water is mixed with the feed water returned from the turbine system. This is a device whose role is to feed the reactor back into the reactor. At this time, the steam drum water level must be maintained within an appropriate range in order to ensure heat removal from the fuel in the reactor and to prevent water carryover to the turbine. Therefore, the water supply flow rate is controlled to maintain the steam drum water level at a set value. In order to control this water level to be constant, in principle, the flow rate of the water supply should be controlled by the water supply control valve so that the flow rate of the separated steam matches the flow rate of the water supply. By the way, in the water supply system from the turbine system to the steam drum, two types of water supply control valves with different capacities are usually installed in parallel, and one of these two types of valves is used depending on the reactor output. Among these, in the high power region (high flow region) where the reactor output is approximately 18% or more, the three elements of the water level signal, steam flow rate signal, and feed water flow rate signal can be measured with high accuracy. The three-element PI (proportional-integral) control system is adopted for the water supply control valve (one water supply control valve).

However, in the low power region (low flow region) where the reactor output is 18% or less, the low flow water supply ms valve (smaller capacity water supply control valve) uses a one-element PI control method using only the steam drum water level signal. . This is mainly due to the inability to measure the steam flow rate and feed water flow rate with high accuracy, and the fact that the flow rate outflow from the steam drum other than the steam flow rate is relatively large, so the steam flow rate and the feed water flow rate cannot be considered equal. be.

[Problem to be solved by the invention] One element PI using only the steam drum water level signal as described above
In the control system, the opening of the feedwater control valve is not adjusted until after the steam drum water level has changed, so large water level fluctuations tend to occur when the reactor output changes.

For this reason, certain limits are set on the rate of change in reactor output,
Operators responded by making manual adjustments as necessary. In other words, it was necessary for skilled operators to constantly monitor the reactor output and various valve openings, and then make appropriate manual corrections.

For example, when switching the water supply control valve, after operating the main water supply control valve, the low flow rate water control valve is immediately operated by the corresponding amount to prevent the water supply flow rate from changing. At this time, if the reactor output changes, it will be necessary to adjust it accordingly.

The purpose of the present invention is to improve plant operation control performance, reduce the burden on operators, and save labor by automatically controlling the steam drum water level control method that was conventionally performed by operators using fuzzy reasoning. It's about trying.

[Means for Solving the Problems] The present invention separates a mixed fluid of steam and water generated from a furnace, sends only the steam to a turbine system, and returns water from the turbine system through a water supply control valve. In this method, the water level in the low flow rate region of the steam drum, which is mixed with incoming feed water and sent to the furnace again, is controlled by adjusting the opening degree of the feed water control valve using a fuzzy control method.

In order to achieve the above object, the present invention adjusts the opening degree adjustment amount of the feedwater control valve based on the steam drum water level deviation and the water level change rate (a first fuzzy inference part and a first fuzzy inference part based on the feedwater-steam flow rate deviation). The second fuzzy inference section and the third fuzzy inference section based on the reactor output perform separate inferences, weighting according to the plant state, and performing a composite calculation to determine the results.

In addition, in the present invention, "steam tram J" refers to a device that separates steam and water from a mixed fluid of steam and water, and is used in steam drums of nuclear reactors, as well as steam separators and steam separators in various similar cooling systems. This also includes generators.

[Effect: Since it is not possible to accurately measure the feed water flow rate or steam flow rate in the low flow rate region, the operation of adjusting the opening degree of the feed water control valve so as not to change the steam drum water level is all done by the operator's intuition or by comprehensive evaluation of many parameters. has been achieved by. The fuzzy control method used in the present invention is suitable for creating a control system that effectively incorporates such control know-how based on the knowledge and experience of operators.

In a plant like the one in the present invention, several process data including the steam drum water level are input, but if control rules are to be created for all of these condition inputs, a very large number of rules will be required. Therefore, the fuzzy inference section is divided into three inference sections and inference is performed individually, and the inference results of each section are weighted according to the plant state and combined, and an optimal conclusion is drawn.

[Example] Fig. 1 is a conceptual diagram showing an example of a subdivision system in which the method of the present invention is applied to a new type converter plant. First, the overall configuration of the plant will be briefly explained.

A coolant mixture of steam and water generated in the nuclear reactor 10 enters the steam drum 12 and is separated from air and water. The separated steam passes through a steam isolation valve 14, a steam stop valve 16 and a steam control valve 18.
It passes through the turbine 20, drives the generator 22, and reaches the condenser 24. A portion of the steam from steam isolation valve 14 passes through turbine bypass valve 26 to condenser 24 . Water in the condenser 24 returns to the steam drum 12 through a condensate pump 28, a feedwater heater 30, a feedwater pump 32, and a feedwater control valve 34. This feed water is mixed with the separated water in the steam tram 12 and returned to the reactor 10 through the lower header 38 by a recirculation pump 36. Here, the water supply control valve 34 is a low-flow water supply control valve, and to simplify the explanation, the main water supply control valve provided in parallel thereto is not shown.

In this embodiment, a neutron detector 40 for measuring the output of the nuclear reactor 10, a drum water level detector 42 for measuring the water level of the steam tram 12, and a fuzzy control section 44 are provided. A steam drum water level signal, a turbine bypass valve opening signal, a feedwater control valve opening signal, a reactor output signal, etc. are input to the fuzzy control unit 44, and an output from the fuzzy control unit 44 (feedwater control valve opening request signal) to control the opening degree of the water supply control valve 34.

FIG. 2 shows the calculation flow of the fuzzy control system according to the present invention. In the present invention, the opening degree adjustment amount of the water supply control valve 34 is individually inferred by three fuzzy inference parts. A first fuzzy inference unit 51 for the steam drum system which processes the various process signals as described above from the plant based on the steam drum water level deviation and water level change rate, and a feed water-steam flow rate system based on the feed water-steam flow rate deviation. Based on the reactor power (a third fuzzy inference part 53 of the reactor power system),
Inference is made individually using the respective control rule bases 54, 55, and 56, weighting is performed according to the plant state, and a composite calculation is performed.

First to third fuzzy inference units 51. The contents of the control rules in . . . , 53 are as follows.

Note that any number of these control rules may be set, and any generally known inference method may be used as the fuzzy inference method.

When the steam drum water level deviation (actual water level - set water level) and water level change rate are input, the first fuzzy inference unit 51 of the steam drum system infers the valve operation amount according to the following control rule.

・If the water level deviation is positive and large, and the water level change rate is positive and large, close the valve.

・If the water level deviation is positive and large and the water level change rate is zero,
Close the valve slightly.

- If the water level deviation is positive and large and the water level change rate is negative and large, the valve will not operate.

The second fuzzy inference unit 52 of the steam-feed water flow rate system calculates the flow rate deviation (feed water flow rate - steam flow rate) evaluated from the main valve opening degree, etc.
When input, the valve operation amount is inferred using the following control rule.

・If the flow rate deviation is slightly excessive, close the valve slightly.

- If the flow deviation is zero, the valve will not move.

・If the flow rate deviation is significantly insufficient for water supply, open the valve wide.

If the reactor power increases, the amount of steam generated will increase, so it is necessary to increase the flow rate of water supply. Generally, the appropriate feed water flow rate for the reactor power is proportional to the reactor power. Therefore, when the third fuzzy inference unit 53 of the reactor power system inputs the flow rate deviation between the optimum feed water flow rate evaluated from the reactor output and the actual feed water flow rate (feed water flow rate - optimal feed water flow rate), the following control rule is created. The amount of valve operation is inferred by

・If there is a flow deviation or a significant excess of water supply, close the valve wide.

- If the flow deviation is zero, the valve will not move.

・If there is a flow deviation or a slight shortage of water supply, open the valve slightly.

Here, since the steam flow rate and feed water flow rate cannot be measured with high accuracy, for example, in the case of a new converter plant with two feed water-steam systems (referred to as A loop and B loop) shown in Figure 3, calculations are performed as follows. Calculated by

The second inference part uses the deviation between the feedwater flow rate and the output flow rate from the steam drum, such as the steam flow rate. If the flow rate deviation is ΔF2A(t), it can be expressed as in equation (1).

ΔF2A (t) =FEEDA (t) 1CUWR
A(t) +RCPSA(t)-TBA(t)-CO
W A (t) ... (11 Here, FEEDA (t): A loop water supply flow rate CUWRA
(t): A-loop reactor purification system return flow rate RCPSA (
t): A-loop recirculation pump seal water injection flow rate TBA(t): Steam flow rate from the A-loop side of the turbine bypass valve flow rate C[JW A(t): Furnace purification system water intake flow rate from the A-loop. Among these, CUWRA(t), TBA(t)
and CIJIV A(t) are not measured. However, if the unbalance between the A loop and the B loop is ignored, the equation (]) can be simplified as follows.

ΔF2A(i) = FEED, (t) −(TB(t
)+BLOW(t,)) /2
... (2) Here, TB(t): Turbine bypass valve flow rate BLOW(
t): Blowdown flow rate from the furnace purification system to the condenser. In equation (2), BLOW(t) has been measured, but TB(t) has not. Also, FEBDA (
t) cannot be used due to poor measurement accuracy. Therefore, F.E.
EDA(t) and TB(t) are determined from each valve opening using the following formula.

FEEDA (t) = FFLov (FV LovA
(t))+FFp*+ (FV□+A(t))
... (3) TB(t) = FL
(TVI(t))+FL(TV2(t))−(4)
Here, FFt, ov (FV LovA(t)): Function that gives the water supply flow rate for the A-loop low-flow water supply control valve opening FVLovA(t) PPp*+ (FV pt+A(t)): A-loop main water supply Functions that give the water supply flow rate for the control valve opening FV□1A (1) FL (TVI (t)), FL (TV2 (t)): Opening degrees TVI (t) and TV of turbine bypass valves 1 and 2
2(t). The above-mentioned function that gives the flow rate from the valve opening degree may be used by determining an optimal fitting curve based on the correlation data between the two. However, regarding the water supply flow rate, the differential pressure before and after the water supply control valve changes greatly as the plant starts up.
Fitting is impossible with the above one type of function.

Therefore, as another method, there is a method of calculating the flow rate using the following equation using the 07 curve of the valve.

FEBDA(t') = ρX (P, -P, -P, -P
,)””X (CVLONIA(FV LovA(t
)) + CVPRIA(FV PRIA(1)))
... (3)' where, ρ fluid density P, : feed water pump outlet pressure P2 : steam drum pressure P2 , hydrostatic head from the center of the steam drum to the feed water control valve P4 fluid friction loss from the feed water control valve to the steam drum CVLowA(FV,,owA(t)): A)
Function CVPIIA (FV p*IA(t)) that gives the ov value for the low flow rate water supply control valve opening FVLovA(t) of Lt-bu: ov for the main water supply control valve opening FVpi+A(t) of the A loop
It is a function that gives a value. That is, equation (3) or (3)
By applying equations ' and (4) to equation (2), the deviation between the feed water flow rate and the steam flow rate can be estimated by calculation.

Next, the third inference section infers the operation amount of the low flow rate feed water control valve opening based on the reactor output, which is based on the correlation between the reactor output and the feed water flow rate in cases where good steam drum water level control has been performed in the past. An optimal fitting curve is determined from the actual data, and this curve is used to set the optimal water supply flow rate commensurate with the input reactor output, and this is done according to the control rules described above based on the deviation between this and the actual water supply flow rate. That is, the deviation ΔF3A(t) between the actual water supply flow rate and the optimal water supply flow rate
is calculated using the following formula.

ΔF3A(t) =FEEDA(t) −FF3 Lo
v(PO(t))... (5) Here, FF3 Lo, (PO(t)): Reactor output PO
(t) is a function that gives the optimal water supply flow rate.

In this way, in the present invention, independent inferences are made from the three most noteworthy aspects regarding steam drum water level control, and the determined value W1. The system obtains W2 and W2, integrates them by weighted composition calculation, and outputs them to control the opening degree of the water supply control valve (see Fig. 2). Here, the weight gain (m + + m
! + mz) increases the weight of the steam drum water level system in areas where the change in steam flow rate is small, such as during reactor core heating, and increases the weight of the steam drum water level system in areas where changes in steam flow rate or feed water flow rate are large, such as after reaching rated pressure. By automatically setting the weights of the steam flow rate system and the reactor power system to be large, it is possible to freely set a variety of characteristics by switching according to the state of the plant using upper-level meta rules.

Figure 4 shows the results of a functional confirmation test of the method of the present invention in a new converter plant. This is a comparison between the steam drum B water level which is automatically controlled by a PI controller based on one-element input of only the steam drum water level signal, and the steam tram A water level which is controlled based on the information of the inference results of the method of the present invention. This confirmed that steam tram A controlled by the method of the present invention exhibited better controllability in suppressing water level fluctuations to a smaller level.

[Effects of the Invention] Since the present invention is a steam drum water level control method using fuzzy control as described above, steam drum water level fluctuations can be prevented even in low flow areas where conventional three-element PI control methods could not be adopted and one-element PI control was relied upon. The width can be reduced to about 1/2 to 1/6 of that of the conventional technology, and control performance is significantly improved.

In addition, in the present invention, the results of inference from three types of aspects are combined and calculated by changing the weighting according to the state of the plant, so the number of control rules can be reduced, and characteristics suitable for each state of the plant can be easily determined. It is possible to have it in the control system.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram showing an example of a new type converter plant to which the method of the present invention is applied, Fig. 2 is a calculation flow diagram of the fuzzy control system, and Fig. 3 is a schematic diagram of the water supply-steam system of an example of the new type converter plant. 4 are graphs showing the fuzzy control system function confirmation results. 10...Nuclear reactor, 12...Steam drum, 20...
Turbine, 34... Water supply control valve, 40... Neutron detector, 42... Drum water level detector, 44... Fuzzy control unit, 51... First fuzzy inference unit, 52...
- Second fuzzy inference section, 53...Third fuzzy inference section. Patent Applicant Power Reactor and Nuclear Fuel Development Corporation Ri Hitoshige Miyuma (Min) Procedural Amendment (,8) l. 2゜3゜4゜Indication of the case Patent application No. 235108 of 1990 Name of the invention Fuzzy control method for steam drum water level Relationship to the case Patent applicant address 1-9-13 Akasaka, Minato-ku, Tokyo Name: Representative, Power Reactor and Nuclear Fuel Development Corporation Address: 2nd floor, Onozuka Building, 2-10-4 Shibakoen, Minato-ku, Tokyo 105 Phone: 433-37997 Contents of amendment (1) Line 3, page 14 of the specification Equation (3)' on the fifth line is corrected as follows. rFEEDA(t) = ρX (PI −P2 −
P3-P4)”2X (CVLowx(FV,,
ovA(j)) +CVIIIA(FV PRIA(
t))) /1.17 °−(31
j or more

Claims (1)

[Claims] 1. Separate the mixed fluid of steam and water generated from the furnace,
Only the steam is sent to the turbine system, and the water is mixed with the feed water that returns from the turbine system through the feed water control valve and sent back to the furnace. In a method of controlling by adjusting,
The opening adjustment amount of the feed water control valve is determined by a first fuzzy inference unit based on the steam drum water level deviation and the water level change rate;
A second fuzzy inference unit based on a steam flow rate deviation and a third fuzzy inference unit based on a reactor output perform separate inferences, perform weighting according to the plant state, and perform a combined calculation to determine the steam. Fuzzy control method for drum water level.