JPH05333196A - Reactor water level control device - Google Patents

Abstract

PURPOSE:To effectively suppress the reactor water level fluctuation when the output is changed by the core flow action. CONSTITUTION:A reactor water level control device is provided with a feed- forward controller 15a inputted with the output signal URFC13 of a recirculation flow control device 5, estimating the main steam quantity change by the core flow change, and calculating the water feed flow adjustment signal UFF offsetting the main steam quantity change, a feedback controller 16 inputted with the reactor water level signal 7, calculating the drift from the reactor water level preset value, calculating its proportional integral, and outputting the water feed flow adjustment signal UFB, and an adder 18 adding the output signal UFF of the feed-forward controller 15a and the output signal UFB of the feedback controller 16 and outputting the final water feed flow adjustment signal UFWC 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water level control device for a BWR plant which suppresses fluctuations in reactor water level during power change operation by operating core flow rate.

[0002]

2. Description of the Related Art FIG. 2 shows an outline of a BWR control system. The steam generated in the reactor 1 passes through the main steam pipe 2,
Drive a turbine (not shown). Water supply to the reactor is
It is adjusted by the reactor water level control device 4 which gives a rotation speed command (supply water flow rate adjustment signal) to the water supply pump (RFP) 3. On the other hand, the recirculation flow rate controller (RFC) 5 controls the reactor power by adjusting the rotation speed of the recirculation pump 6 and changing the core flow rate (recirculation flow rate).

As shown in FIG. 8, a conventional reactor water level control device 4 feeds back a reactor water level signal 7 to obtain a deviation from a reactor water level set value 8, and the reactor water level deviation is supplied with a feed water flow rate signal 9. A value obtained by processing the difference with the main steam flow rate signal 10 by the mismatch calculation section 11 is applied, and proportional integral (PI) calculation is performed and this is output as a feed water flow rate adjustment signal.

[0004]

In the above-mentioned nuclear reactor, for example, when the reactor power output drops, the load setting signal 12
Or a manual change, the core flow rate is reduced by the recirculation flow rate control device 5 which outputs the core flow rate adjustment signal 13 to the recirculation pump. When the core flow rate is reduced, the reactor water level rises due to the effects of these two phenomena, that is, an increase in voids in the reactor and a mismatch in mass balance with the feed water flow rate due to a decrease in steam flow rate.

In such a state, the conventional reactor water level control device 4 receives feedback of the decreasing steam flow rate signal 10 and the rising reactor water level signal 7, and adjusts the feed water flow rate calculated based on these feedback signals. The signal reduces the rotation speed of the feedwater pump to suppress the rise in reactor water level. In this case, the higher the gains of the mismatch calculation unit 11 and the proportional-plus-integral calculation unit 14 are, the greater the effect of suppressing the rise in the water level is. However, in practice, the control gain cannot be set excessively high because of the stability of the control system. However, there is a limit to the effect of suppressing the rise in water level.

The present invention has been made in consideration of the above point, and an object of the present invention is to provide a reactor water level control device capable of effectively suppressing fluctuations in the reactor water level when the output is changed by operating the core flow rate. To do.

[0007]

That is, the present invention provides a reactor water level control device for controlling the reactor water level by adjusting the core flow rate to control the reactor power and adjusting the feed water flow rate to the reactor. , A feedback control unit that calculates the feed water flow rate adjustment amount based on the deviation between the reactor water level set value and the reactor water level signal, and predicts the steam flow rate change based on the core flow rate signal or the signal that determines the core flow rate, A feedforward control unit that calculates a feedwater flow rate adjustment amount that cancels out a flow rate change, and outputs the sum of the output signal of the feedback control unit and the output signal of the feedforward control unit as a final feedwater flow rate adjustment signal. It is characterized by

[0008]

In the reactor water level control device having the above structure, the feedforward control section inputs a signal for determining the core flow rate, such as a core flow rate signal or an output signal of the recirculation flow rate control device, and the steam flow rate due to fluctuations in the core flow rate. A feedwater flow rate adjustment amount that predicts a change and cancels it out is calculated. The feedback control unit uses the reactor water level signal as a feedback signal, performs proportional integral calculation of the deviation from the reactor water level set value, and outputs a feedwater flow rate adjustment signal. The rotation speed of the water supply pump is adjusted by the sum of the water supply flow rate adjustment signal output from the feedforward control unit and the water supply flow rate adjustment signal output from the feedback control unit.

As described above, the reactor water level control device of the present invention predicts a change in the steam flow rate due to the operation of the core flow rate, and performs the feed water flow rate operation in advance to cancel the fluctuation in the reactor water level based on the change in the steam flow rate. At the same time, the fluctuation of the reactor water level deviated from the prediction is suppressed by the feedback control, so that the fluctuation of the reactor water level at the time of changing the output due to the operation of the core flow rate can be promptly suppressed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In all of the drawings, the same parts are designated by the same reference numerals, and parts having the same names and slightly different functions are designated by the same reference numerals with suffixes a, b, ....

FIG. 1 shows a reactor water level controller 4a according to a first embodiment of the present invention. This reactor water level control device 4a uses the output signal u _RFC 1 of the recirculation flow rate control device 5.
3 is input to predict a change in the main steam flow rate due to a change in the core flow rate, and a feed water flow rate adjustment signal u that cancels the change in the main steam flow rate.
_The feedforward control unit 15a for calculating _FF and the reactor water level signal 7 are input to obtain the deviation from the reactor water level set value,
The feedback control unit 16 that performs proportional-plus-integral calculation on this to output the feedwater flow rate adjustment signal u _FB , the output signal u _FF of the feedforward control unit 15 a, and the feedback control unit 16
Output signal u _FB of
_It is composed of an adder 18 which outputs an _FWC 17.

In the above configuration, the recirculation flow rate control device 5
Output u _FWC 17 from the output signal u _RFC 13 dynamic characteristics to the main steam flow rate W _S of W _S (s), the reactor water level controller 4a
When the dynamic characteristic from the flow rate to the feed water flow rate W _F is W _F (s), the transfer function C _FF (s) of the feedforward control unit 15a is set as follows. Here, s represents a Laplace operator.

C _FF (s) = W _S (s) / W _F (s) (1) For example, when W _S (s) and W _F (s) are identified by the first-order delays shown in the following equations, respectively. , W _S (s) = K _S / (1 + T _S・ s) (2) W _F (S) = K _F / (1 + T _F・ s) (3) From the formula (1), C _FF (s) Is C _FF (s) = K _FF (1 + T _F · s) / (1 + T _S · s) (4). Here, K _FF = K _S / K _F. in this case,
Since W _S and W _F can be measured, K can be calculated from u _RFC and u _FWC .
_S , K _F , T _S , and T _F can be obtained by fitting.

In the sampling system, the sampling time Δ
where t is the predicted value W _{S ′} (t) of the main steam flow rate and the output u _FF (t) of the feedforward control unit 15a is described as follows.

[0015] Since the reactor water level L can be approximated by the following formula of mass balance of feed water / main steam, Feedforward control unit 16a set by equation (1)
, DL / dt = 0 is established as an equality, and the water level fluctuation is 0.
become. However, this is the time when the approximate expressions relating to the plant dynamic characteristics of the expressions (2), (3), and (8) hold as an accurate model expression. When it deviates from the approximation, it appears as reactor water level fluctuation. The reactor water level fluctuation can be compensated by the feedback control unit 16.

Next, the movement of the plant variable when the output is changed will be described with reference to FIG. FIG. 3 shows plant variables when the load setting is lowered (recirculation flow controller output u _RFC , core flow rate, main steam flow rate, reactor water level controller output u _FWC ,
It shows the response of feed water flow rate, feedback control unit output u _FB , reactor water level). The response by the control of this embodiment is shown by a solid line, and the response by the control of the conventional example is shown by a broken line.

As the load setting a is lowered, the core flow rate adjustment amount b is reduced, and the core flow rate c is reduced accordingly. Due to the decrease in the core flow rate c, voids in the core increase, the reactivity decreases, the reactor output decreases, and the steam flow rate (main steam flow rate d) taken out from the reactor also decreases. The feedforward control unit 15a predicts the decrease in the main steam flow rate and the delay in the feed water flow rate, and outputs the output u according to the equations (6) and (7).
Calculate _FF . The command (u _FWC ) e to the water supply pump is given as a superposition signal of this output u _FF and the output signal (u _FB ) g of the feedback control unit described later. The command e ′ to the water supply pump by the conventional control is equal to the output signal g ′ of the reactor water level control device 4 whose main component is feedback control, which will be described later.

As shown in FIG. 3, the water supply command signal e according to the present invention can output a water supply narrowing command faster than the conventional control signal e '. Therefore, the feed water flow rate f adjusted according to the present invention can respond faster than the feed water flow rate f'adjusted in the conventional example, so that the fluctuation of the reactor water level is small as shown by the solid line h. On the other hand, in the conventional control, the narrowing of the feed water flow rate is delayed as indicated by the broken line f ′ with respect to the decrease of the main steam flow rate d.
As shown in, the fluctuation of the reactor water level becomes large.

The output signal of the feedback control unit 15a of this embodiment shown by the solid line g is calculated only from the reactor water level deviation, whereas the output signal u _FB of the conventional control shown by the broken line g'is It is calculated by reflecting the mismatch between the main steam flow rate signal and the feed water flow rate signal together with the reactor water level deviation.

In the above embodiment, the mismatch gain calculating section 11 for feeding back and calculating the mismatch between the main steam flow rate signal and the feed water flow rate signal as described in the conventional example is not shown because it is not an essential component, but FIG. The same effect can be obtained even if the mismatch gain calculator is provided in the feedback controller 16 shown in FIG.

FIG. 4 shows a reactor water level control device 4b according to a second embodiment of the present invention. The difference from the reactor water level control device 4a described above is that the feedforward control section 15b is used.
The input signal of is not the core flow rate adjustment signal u _RFC but the core flow rate W _C. In this case, the dynamic characteristic from the output u _RFC 13 of the recirculation flow rate control device 5 to the core flow rate W _C is W _C (s), and the dynamic characteristic from the core flow rate W _C to the main steam flow rate W _S is W ′ _S. expressed in (s), the transfer function C of the feedforward control unit 15b _'FF (s) is C' are set to _{FF (s) = W 'S} (s) / W F (s) ... (9).

In the above-mentioned structure, similarly to the first embodiment, based on the core flow rate signal 19, according to the equation (9),
Predictive advance control is performed.

Therefore, also in this embodiment, it is possible to predict the change in the main steam flow rate due to the change in the core flow rate, and to control the water level fluctuation accompanying it in advance.

FIG. 5 shows a reactor water level control device 4c according to a third embodiment of the present invention. In this embodiment, an MG set generator 20 is used as a frequency conversion device for a recirculation pump motor.
And a MG set generator speed controller 21 for controlling the speed of the MG set generator 20 are installed. That is, in the present embodiment, the input signal of the feedforward control unit 15c is the MG signal.
The set generator speed signal 22 is used.

The transfer function C ″ _FF (s) of the feedforward controller 15c is set as follows, where W ″
_S (s) represents the dynamic characteristics from the MG set generator speed to the main steam flow rate W _S.

[0026] _{C 'FF (s) = W} "S (s) / W F (s) ... (10) This example is for performing predictive preceding control based on the MG set generator speed signal 22, the According to an embodiment, M
Regardless of the control parameter of the G set generator speed controller 21, it is possible to suppress the fluctuation of the reactor water level when changing the MG set generator speed and changing the output. Since the MG set generator speed signal has a lower noise level than the core flow rate signal,
There is an advantage that a high frequency unnecessary operation signal is rarely given to the water supply pump. ..

FIG. 6 shows a reactor water level control device 4d according to a fourth embodiment of the present invention, in which the feedback control unit 1 is used.
6, a feedforward control unit 15d that performs a neural network operation based on the output signal u _RFC 13 of the recirculation flow rate control device 5, and a learning unit 23 that determines the weighting coefficient of this neural network.

FIG. 7 shows the neural network structure. At time t, the output signal u _RFC (t) is fetched and u _RFC (t-Δt), u already fetched and stored
_RFC (t-2Δt), ..., u Output using _RFC (tnΔt) u
Calculate _FF (t). The output of a single neuron that is a component of the neural network is expressed by the following equation.

Y = f (Σw _i x _i ) (11) The function f (X) is a logistic function f (X) = 1 / {1 + exp
(-x + θ)} or the like is used. w _i is a weighting factor and can be determined by learning.

The learning unit 23 learns the weighting coefficient w _i . The teaching signal is used as the water supply command u _FWC and compared with the output u _FF of the feedforward control unit 15d, and the weight coefficient w _i is corrected so that the two signals match. For this learning method, for example, the backpropagation method as shown in the literature (Hideki Aso: "Neural network information processing" industry book) is used.

By using the neural network for the feed-forward control, it becomes easy to determine a predictive model and a preceding control law for a complex plant, a plant that cannot be expressed linearly.

[0032]

As is apparent from the above description, according to the present invention, a change in the steam flow rate due to the operation of the core flow rate is predicted, and the feed water flow rate operation is performed to cancel the fluctuation of the reactor water level based on the change in the steam flow rate. In addition to the above, the fluctuation of the reactor water level deviated from the prediction is suppressed by the feedback control, so that the fluctuation of the reactor water level when the output is changed by the core flow rate operation can be suppressed promptly.

[Brief description of drawings]

FIG. 1 is a block diagram showing a reactor water level control system according to a first example of the present invention.

FIG. 2 is a diagram showing an outline of a BWR control system.

FIG. 3 is a graph showing the response of the plant when the load set point is lowered in the first example and the conventional example.

FIG. 4 is a block diagram showing a reactor water level control device according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a reactor water level control device according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing a reactor water level control system according to a fourth example of the present invention.

FIG. 7 is a diagram showing a structure of a neural network according to a fourth embodiment.

FIG. 8 is a block diagram showing a conventional reactor water level control device.

[Explanation of symbols]

3 ... Feed pump 4 ... Reactor water level controller 5 ... Recirculation flow rate controller 7 ... Reactor water level signal 8 ... Reactor water level set value 12 ... Load setting signal 13 ... … Reactor flow rate adjustment signal 14 ……… Proportional and integral calculation section 15 ……… Feed forward control section 16 ……… Feedback control section 17 ……… Feed water flow rate adjustment signal (reactor water level controller output) 18 ……… Adder 19 ……… Core flow rate signal 20 ……… MG set generator 21 ……… MG set generator speed controller 22 ……… MG set generator speed signal 23 ……… Learning section

Claims (1)

[Claims] 1. A reactor water level control device for controlling a reactor water level by adjusting a reactor core flow rate to control a reactor power and adjusting a feed water flow rate to the reactor. A feedback control unit that calculates the feed water flow rate adjustment amount based on the deviation from the water level signal, and predicts the steam flow rate change based on the core flow rate signal or the signal that determines the core flow rate, and cancels this steam flow rate change amount. And a feedforward control unit for calculating, and outputting a sum of an output signal of the feedback control unit and an output signal of the feedforward control unit as a final feedwater flow rate adjustment signal. apparatus.