Pressure control method for once-through steam generator under large-load-transient operating condition

Abstract

The present invention relates to a pressure control method for a once-through steam generator (OTSG) under a large-load-transient operating condition. The method comprises: using a fast control mode in which a memory channel and an actual measurement channel are combined for fast control, and pressure deviation is used as a core parameter when a large-load transient occurs. Firstly, real-time monitoring is performed to rapidly determine whether a preset condition is met; if the condition is met, an actually measured pressure deviation value at an initial moment is used to rapidly regulate a feedwater flow rate; and if the condition is not met, regulation is performed on the basis of a current actually measured pressure deviation value, thereby ensuring the accuracy and timeliness of control. Secondly, by means of taking into consideration the actual pressure response of an OTSG, the control strategy uses a flexible regulation mechanism, so that the dependence on conventional PID control is reduced, thereby enhancing the stability and reliability in the face of complex and rapidly changing operating conditions. Finally, by means of optimizing control logic, frequent regulation of a feedwater valve due to rapid pressure changes is reduced.

Description

Method for controlling pressure of once-through steam generator under large load transient condition TECHNICAL FIELD

[0001] The present application relates to the technical field of nuclear power plant piping, in particular to a method for controlling pressure of once-through steam generator under large load transient condition. BACKGROUND

[0002] In nuclear power generation, the occurrence of large load transient signal is often accompanied by a sharp deviation between nuclear power and secondary circuit load, which can cause serious imbalance of primary and secondary side heat transfer process of OTSG (once-through steam generator). Due to the existence of vapor-liquid two-phase fluid in the OTSG secondary side heat transfer pipe, this heat transfer imbalance can quickly cause a sharp fluctuation of the pipe pressure and steam-water flow. In the face of such rapid and complex working condition changes, the traditional multi-channel PID control often has difficulty in responding effectively, and if not properly adjusted, it may even trigger the protection shutdown mechanism, seriously threatening the safe and stable operation of the nuclear power plant.

[0003] The multi-channel, PID control method proposed in the "Method for controlling pressure of once-through steam generator" can achieve accurate control of the OTSG pressure, but it is relatively complex and difficult to cope with large load transient conditions. Based on this, the technology "A rapid control method for pressure of once-through steam generator" generates flow demand directly from power in the large load transient condition, which will cause rapid changes in feedwater, but in this process, the actual response of the OTSG pressure does not participate in the control of the feedwater demand, and the robustness of the control is poor. In addition, in the large load transient condition, the response of the OTSG pressure is fast and sensitive, which will cause rapid fluctuations of the feedwater valve, and the requirement for the feedwater valve is high, and the robustness of the control needs to be improved. SUMMARY

[0004] The present application provides a method for controlling pressure of once-through steam generator under large load transient condition, which can solve the problem of instability of the traditional control method.

[0005] In order to solve the above technical problems, the method comprises: detecting whether a large load transient condition occurs;

[0006] If the large load transient condition occurs, obtaining pressure measurement data of the outlet of the once-through steam generator, and determining a measured pressure value according to the pressure measurement data;

[0007] Detecting a secondary circuit load value, and determining a target pressure value of the once-through steam generator according to the secondary circuit load value;

[0008] Calculating a measured pressure deviation value of the once-through steam generator according to the measured pressure value and the target pressure value;

[0009] If the preset condition is met, the feedwater flow control of the once-through steam generator is performed according to a memory pressure deviation value, which is a measured pressure deviation value at an initial moment of the large load transient condition; if the preset condition is not met, the feedwater flow control of the once-through steam generator is performed according to a current measured pressure deviation value.

[0010] In an embodiment, the once-through steam generator drives a turbine by using heat energy generated by a reactor, and the detection of whether the large load transient condition occurs includes:

[0011] The nuclear power is obtained according to the flux of the neutrons in the reactor core in a plurality of power range detection channels of the reactor;

[0012] The two-loop load value is obtained according to the pressure values of a plurality of first-stage pressure measurement channels of the turbine;

[0013] The two-loop load deviation is obtained according to the nuclear power and the two-loop load value, and the large load transient condition is detected according to the two-loop load deviation.

[0014] In an embodiment, the two-loop load value is obtained according to the pressure values of a plurality of first-stage pressure measurement channels of the turbine, and the method includes:

[0015] The average value of the plurality of pressure values is calculated to obtain a pressure average value;

[0016] The pressure average value is input into a first function generator to obtain the two-loop load value; wherein the first function generator is used to convert the pressure value into the corresponding two-loop load value.

[0017] In an embodiment, the detection of whether the large load transient condition occurs according to the two-loop load deviation includes:

[0018] The load change rate is calculated according to the two-loop load deviation and a preset coefficient;

[0019] If the load change rate exceeds a first threshold value, it is determined that the large load transient condition occurs;

[0020] In an embodiment, the calculation of the load change rate according to the two-loop load deviation and the preset coefficient includes:

[0021] The two-loop load deviation and the preset coefficient are calculated by a preset formula to obtain the load change rate, wherein the preset formula is:

[0022]

[0023] wherein, is the preset coefficient; R is the load rate of deviation for primary and secondary loop loads.

[0024] In an embodiment, the obtaining the pressure measurement data of the outlet of the once-through steam generator, and determining a measured pressure value according to the pressure measurement data comprises:

[0025] obtaining pressure measurement data of multiple pressure measurement points of the outlet of the once-through steam generator;

[0026] selecting the maximum pressure measurement data from the multiple pressure measurement data as the measured pressure value.

[0027] In an embodiment, the calculating a measured pressure deviation value of the once-through steam generator according to the measured pressure value and the target pressure value comprises:

[0028] filtering the measured pressure value to obtain a processed measured pressure value;

[0029] obtaining the measured pressure deviation value according to a difference between the processed measured pressure value and the target pressure value.

[0030] In an embodiment, the preset condition comprises:

[0031] the current measured pressure deviation value is within a first preset range, or the current time is within a second preset range from an initial time of a large load transient condition.

[0032] In an embodiment, the water flow control of the once-through steam generator according to the memory pressure deviation value comprises:

[0033] obtaining the memory pressure deviation value as an input signal to a second function generator, and converting the memory pressure deviation value into a water flow demand through the second function generator;

[0034] the water flow control of the once-through steam generator according to the current measured pressure deviation value comprises:

[0035] obtaining the current measured pressure deviation value as an input signal to a second function generator, and converting the current measured pressure deviation value into a water flow demand through the second function generator; wherein the second function generator is configured to convert the pressure deviation value into a corresponding water flow adjustment amount.

[0036] In an embodiment, the water flow demand is converted into a water valve opening degree demand signal through a third function generator, and the water valve opening degree demand signal is used to adjust the opening degree of the water valve of the once-through steam generator.

[0037] The implementation of the present application has the following beneficial effects: by monitoring in real time and quickly judging whether the preset condition is reached, the initial measured pressure deviation value is used to quickly adjust the feedwater flow once the condition is met; if not, the adjustment is made according to the real-time measured pressure deviation value, ensuring the accuracy and timeliness of the control. Secondly, the control strategy considers the actual pressure response of the OTSG and uses a flexible adjustment mechanism, reducing the dependence on traditional PID control, thereby enhancing the stability and reliability when facing complex and rapidly changing working conditions. Finally, by optimizing the control logic, the frequent adjustment of the feedwater valve due to rapid pressure changes is reduced, which not only reduces the mechanical pressure of the valve and prolongs its service life, but also reduces the maintenance cost and potential risks caused by valve failure. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the drawings needed to be used in the description of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0039] Figure 1 is a flowchart of a method for controlling the pressure of a once-through steam generator under large load transient conditions according to an embodiment;

[0040] Figure 2 is a logic diagram of large load transient signal generation according to an embodiment;

[0041] Figure 3 is a logic diagram of OTSG measured pressure signal generation according to an embodiment;

[0042] Figure 4 is a flowchart of OTSG pressure fast control according to an embodiment;

[0043] Figure 5 is a logic diagram of OTSG pressure fast control according to an embodiment. DETAILED DESCRIPTION

[0044] The present application will be described in further detail below in conjunction with the drawings and embodiments. It is particularly pointed out that the following embodiments are only used to illustrate the present application, but do not limit the scope of the present application. Similarly, the following embodiments are only some embodiments of the present application, not all embodiments, and all other embodiments obtained by those skilled in the art without creative labor are within the scope of the present application.

[0045] Reference to“an embodiment” herein means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of the phrase“in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all referring to a common embodiment, or an embodiment that is independent of other embodiments. One of ordinary skill in the art will recognize that the embodiments described herein with reference to particular examples can be combined, can be replaced by other technologies and techniques, and can be applied to other examples.

[0046] It should be noted that the terms“first”,“second” in the present application are used only for descriptive purpose, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with“first”,“second” explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of“multiple” is at least two, such as two, three, etc., unless otherwise specifically limited. All directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture (as shown in the drawings), and if the certain posture changes, the directional indications also change accordingly. In addition, the terms“include” and“have” and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product or device.

[0047] OTSG (once-through steam generator) is a key equipment connecting the primary and secondary loops of the reactor, which functions to transfer heat between the primary and secondary loops. The OTSG drives the steam turbine using the heat generated by the reactor, specifically: the heat generated by the reactor is transferred to the OTSG through the primary loop, the OTSG transfers the heat to the water in the secondary loop, causing the water to become steam, the steam enters the steam turbine, driving it to rotate and generating electricity. The matching of nuclear power and target load of the steam turbine can be achieved by OTSG pressure control.

[0048] As shown in FIG. 1, in one embodiment of a method for OTSG pressure control in a large load transient condition, the method comprises: S1: detecting whether a large load transient condition occurs; the method is used to achieve rapid control and stable control of OTSG pressure when a large load transient condition occurs, to ensure the safe and stable operation of the nuclear power plant.

[0049] Specifically, S11: obtaining the nuclear power according to the flux of the neutrons in the core in the reactor in multiple power range detection channels, specifically, obtaining the nuclear power by taking the maximum value of the multiple fluxes according to the flux of the neutrons in the core in the reactor in multiple power range detection channels.

[0050] As shown in Figure 2, nuclear power monitoring specifically includes: n power range detection channels (n is an integer greater than 1) in the reactor, used to monitor the neutron flux rate in the reactor core in real time. The neutron flux rate in the reactor core is obtained through these n channels, denoted as φ1, φ2, ..., φ n The maximum value among these injection rates is selected, i.e., max(φ1, φ2, ..., φ). n The maximum value is used as the current nuclear power. This is because, under high-load transient conditions, the highest neutron flux rate in the reactor core most directly reflects the intensity of the nuclear reaction.

[0051] S12. Based on the pressure values ​​of multiple first-stage pressure measurement channels of the steam turbine, obtain the primary and secondary loop load values. Specifically, calculate the average value of multiple pressure values ​​to obtain the pressure average value; input the pressure average value into the first function generator to obtain the secondary loop load value; wherein, the first function generator is used to convert the pressure value into the corresponding secondary loop load value.

[0052] The secondary loop load monitoring is as follows: The steam turbine has i first-stage pressure measurement channels (i is an integer greater than 1) to monitor pressure changes at the turbine inlet. The pressure values ​​of the first stage of the steam turbine are obtained through these i channels, denoted as P1, P2, ..., P... i Calculate the load values ​​for the second circuit: First, calculate the average of these pressure values, i.e., Average(P1, P2, ..., P...). i Then, this average value is converted into a secondary loop load value using a preset first function generator. The first function generator contains a pre-set calculation formula. This conversion process considers the specific relationship between pressure and load, ensuring an accurate reflection of the actual load conditions of the secondary loop.

[0053] S13. Calculate the load deviation between the primary and secondary loops based on the nuclear power and the secondary loop load value, and detect whether a large load transient condition has occurred based on the load deviation between the primary and secondary loops. Specifically, detecting the occurrence of a large load transient condition based on the load deviation between the primary and secondary loops includes: calculating the load change rate based on the load deviation between the primary and secondary loops and a preset coefficient; if the load change rate exceeds a first threshold, a large load transient condition is determined to have occurred; specifically, the load change rate is calculated using a preset formula based on the load deviation between the primary and secondary loops and the preset coefficient. The preset formula is:

[0054]

[0055] in, These are preset coefficients; R represents the load deviation between the first and second circuits; R is the load change rate.

[0056] In an embodiment, the difference between the nuclear power and the secondary circuit load is substituted into a preset formula to obtain a secondary circuit load deviation The change rate is calculated by the preset formula, wherein the coefficient τ for solving the change rate is determined according to argument analysis. The processed change rate signal is subjected to threshold comparison, and the large load transient signal is generated when the change rate is greater than the threshold.

[0057] Specific steps include: a preset formula is used to calculate the load change rate R. Next, the calculated load change rate R is compared with a preset threshold to determine whether a large load transient condition occurs. If R exceeds the threshold, a large load transient condition is confirmed, and corresponding signals are generated accordingly. These signals immediately trigger a series of preset emergency response measures, including but not limited to adjusting the feedwater flow, changing the steam discharge strategy, and starting the standby equipment.

[0058] Further, S2: if a large load transient condition occurs, the pressure measurement data of the outlet of the once-through steam generator is obtained, and the measured pressure value is determined according to the pressure measurement data. Specific steps include: if a large load transient condition occurs, the pressure measurement data of multiple pressure measurement points of the outlet of the once-through steam generator is obtained, and the maximum pressure measurement data is selected from the multiple pressure measurement data as the measured pressure value.

[0059] As shown in FIG. 3, specifically, j pressure measurement points (j is an integer greater than 1) can be set for the OTSG outlet, and the maximum value of the j measurement values represents the measured pressure of the OTSG.

[0060] S21: At the moment when the large load transient condition is confirmed, the all-around monitoring of the OTSG outlet pressure is performed, and through the j pressure measurement points pre-set at the OTSG outlet, j pressure measurement values reflecting different positions and different time points can be captured and collected in real time. In order to accurately grasp the pressure state, the maximum value is selected from these measurement values. The measured pressure value is subjected to filtering processing to ensure the accuracy and reliability of the data to obtain the processed measured pressure value; and according to the difference between the processed measured pressure value and the target pressure value, a measured pressure deviation value is obtained.

[0061] Further, S3: the secondary circuit load value is detected, and the target pressure value of the once-through steam generator is determined according to the secondary circuit load value.

[0062] As shown in FIG. 4, specifically, according to the real-time detected secondary loop load value, the target pressure value of the OTSG under the current working condition is determined through a preset algorithm or a lookup table. The secondary loop load deviation change rate is continuously monitored, and once the change rate exceeds a preset threshold, a large load transient signal is triggered, and the pressure quick control mode of the OTSG is activated. This mode includes two control paths of a measured channel and a memory channel, and the determination of the target pressure value is still a key parameter to ensure stable operation and safety.

[0063] Further, S4: the measured pressure deviation value of the once-through steam generator is calculated according to the measured pressure value and the target pressure value.

[0064] Specifically, first, the measured pressure value of the OTSG obtained in the S2 stage (after filtering to eliminate noise) is subtracted from the target pressure value at the same time determined in the S3 stage to obtain the measured pressure deviation value.

[0065] Further, S5: it is judged whether the preset condition is met at present, if yes, the feedwater flow control of the once-through steam generator is performed according to the memory pressure deviation value, and the memory pressure deviation value is the measured pressure deviation value at the initial moment of the large load transient working condition; if no, the feedwater flow control of the once-through steam generator is performed according to the current measured pressure deviation value. The preset condition includes that the current measured pressure deviation value is within a first preset range, or the current time distance from the initial moment of the large load transient working condition is within a second preset range. Specifically, if the current preset condition is met, the current measured pressure deviation value is greater than or equal to a second threshold, or the current time distance from the initial moment of the large load transient working condition is less than or equal to a third threshold.

[0066] If the current preset condition is not met, the current measured pressure deviation value is less than the second threshold, and the current time distance from the initial moment of the large load transient working condition is greater than the third threshold.

[0067] S51: if the current preset condition is met, the memory pressure deviation value is obtained as an input signal to the second function generator GF3, and the second function generator GF3 is used to convert the pressure deviation value into a feedwater flow demand; if not, the current measured deviation value is obtained as an input signal to the second function generator GF3, and the second function generator is used to convert the pressure deviation value into a feedwater flow demand. Wherein, the second function generator is used to convert the pressure deviation value into a corresponding feedwater flow adjustment amount. If the current preset condition is not met, the current measured pressure deviation value is obtained in real time, and is input as an input signal to the second function generator GF3. The second function generator GF3 calculates the corresponding feedwater flow demand through the algorithm built therein.

[0068] S52: convert the feedwater flow demand into a feedwater valve opening demand signal through the third function generator GF4, and the feedwater valve opening demand signal acts on the feedwater valve of the once-through steam generator to adjust the opening.

[0069] Specifically, for the feedwater flow control strategy of the OTSG, firstly, it is evaluated whether the preset condition is met or not. The preset condition mainly includes two aspects: one is whether the measured pressure deviation value exceeds a preset threshold, and the other is whether the current time distance from the initial time of the large load transient condition is less than or equal to another preset time limit.

[0070] As shown in FIG. 5, specifically, if the preset condition is met (the current measured pressure deviation value is greater than or equal to the second threshold, or the current time distance from the initial time of the large load transient condition is less than or equal to the third threshold), it is judged that the current is in the transient initial stage which needs fast response and stable control. In order to effectively avoid the violent oscillation of the feedwater valve and stabilize the feedwater flow, the control mode of the memory channel is selected. At this time, the memory pressure deviation value recorded at the initial time of the large load transient condition is used as the input signal. This memory pressure deviation value is then input into the second function generator GF3, and through a specific algorithm or mapping relationship, the second function generator GF3 converts it into the corresponding feedwater flow demand. Then, this feedwater flow demand is further processed by the third function generator GF4 to convert it into the opening demand signal of the feedwater valve, so as to realize the accurate control of the feedwater valve.

[0071] If the preset condition is not met (the current measured pressure deviation value is less than the second threshold and the current time distance from the initial time of the large load transient condition is greater than the third threshold), it is considered that the current is in the relatively stable or normal regulation range. At this time, the control mode of the measured channel is switched to. In the measured channel, the current measured pressure deviation value is obtained in real time and input into the second function generator GF3 as the input signal. The second function generator GF3 calculates the corresponding feedwater flow demand through its built-in algorithm. Subsequently, this feedwater flow demand also passes through the third function generator GF4 to convert it into the opening demand signal of the feedwater valve. Unlike the memory channel, the measured channel continuously and dynamically obtains the measured data and adjusts to ensure that it can adapt to the changes of the actual working condition at any time.

[0072] The application also provides a computer storage medium storing a computer program, which realizes the steps of any one of the above-mentioned methods for controlling the pressure of the once-through steam generator under the large load transient condition when executed by a processor.

[0073] In an embodiment of the computer storage medium provided by the application, a computer program is stored thereon, and the computer program is executed by a processor to implement the steps of the method for controlling the pressure of the once-through steam generator under the large load transient condition. Specifically, it needs to be noted that the computer readable medium of the application can be a computer readable signal medium or a computer readable storage medium or any combination of the two. The computer readable storage medium may, for example, but is not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor device or device, or any combination thereof. More specific examples of the computer readable storage medium can include, but are not limited to, an electrical connection with one or more conductive wires, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof. In the application, the computer readable storage medium can be any tangible medium containing or storing a program that can be used or combined with an instruction execution device or device. In the application, the computer readable signal medium can include a data signal propagating in a baseband or as part of a carrier wave, which carries computer readable program code. Such a propagating data signal can take many forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. The computer readable signal medium can also be any computer readable medium other than the computer readable storage medium, which can send, propagate or transmit a program for use by or in combination with an instruction execution device or device. The program code contained in the computer readable medium can be transmitted by any suitable medium, including but not limited to: wire, cable, RF (radio frequency), etc., or any suitable combination thereof.

[0074] The above computer readable storage medium can be contained in the above computer device; or can exist separately without being assembled into the computer device.

[0075] The scheme of the application adopts a fast control combining a memory channel and a measured channel, and a fast control mode with the measured pressure deviation as a core parameter when the large load transient occurs. When the measured pressure deviation value is greater than or equal to a threshold value or is less than or equal to a time limit from the initial moment of the large load transient, the initial OTSG pressure deviation of the transient initial stage is recorded and fixed by using the memory channel, the stable feedwater flow demand is set, the valve overshoot is avoided, and the smooth transition is ensured; then, when the measured pressure deviation value is less than the threshold value and is greater than the time limit from the initial moment of the large load transient, the measured channel is automatically switched to, the real-time pressure deviation is dynamically adjusted according to the feedwater flow, the precise and flexible control is realized, the OTSG heat transfer imbalance and pressure fluctuation under the large load transient are effectively solved, and the safe and stable operation of the nuclear power plant is ensured.

[0076] It can be understood that the above embodiments only express the preferred embodiments of the present application, which are described in a more specific and detailed manner, but cannot be understood as a limitation to the patent scope of the present application; it should be pointed out that, for ordinary skilled in the art, the above technical features can be freely combined without departing from the concept of the present application, and several modifications and improvements can be made, which all belong to the protection scope of the present application; therefore, any equivalent transformation and modification made to the patent claim scope of the present application shall belong to the coverage of the patent claim of the present application.

Claims

1. A method for pressure control of once-through steam generators under heavy load transient conditions, characterized by, The method comprises the following steps: detecting whether a large load transient condition occurs; if the large load transient condition occurs, obtaining pressure measurement data of the outlet of the once-through steam generator, determining a measured pressure value according to the pressure measurement data; obtaining a two-loop load value, and determining a target pressure value of the once-through steam generator according to the two-loop load value; calculating a measured pressure deviation value of the once-through steam generator according to the measured pressure value and the target pressure value; judging whether a preset condition is met, and if yes, performing feedwater flow control of the once-through steam generator according to a memory pressure deviation value, the memory pressure deviation value being a measured pressure deviation value at an initial moment of the large load transient condition; if not, performing the feedwater flow control of the once-through steam generator according to a current measured pressure deviation value.

2. The method of claim 1 for pressure control of once-through steam generators under large load transient conditions, the once-through steam generators driving a turbine using heat energy generated by a nuclear reactor, characterized in that, The detection of whether the large load transient condition occurs comprises: obtaining a nuclear power according to a neutron fluence rate of a plurality of power range detection channels of a reactor core; obtaining a two-loop load value according to pressure values of a plurality of first-stage pressure measurement channels of a steam turbine; obtaining a one-two loop load deviation according to the nuclear power and the two-loop load value, and detecting whether the large load transient condition occurs according to the one-two loop load deviation.

3. The method for direct flow steam generator pressure control during large load transient conditions of claim 2, wherein, The obtaining of the two-loop load value according to the pressure values of the plurality of first-stage pressure measurement channels of the steam turbine comprises: calculating an average value of the plurality of pressure values to obtain a pressure average value; inputting the pressure average value into a first function generator to obtain the two-loop load value; wherein the first function generator is used to convert the pressure value into a corresponding two-loop load value.

4. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 2 wherein, The detection of whether the large load transient condition occurs according to the one-two loop load deviation comprises: calculating a load change rate according to the one-two loop load deviation and a preset coefficient; if the load change rate exceeds a first threshold value, it is determined that the large load transient condition occurs.

5. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 4 wherein, The calculation of the load change rate according to the one-two loop load deviation and the preset coefficient comprises: calculating the load change rate according to the one-two loop load deviation and the preset coefficient through a preset formula, wherein the preset formula is: , wherein are preset coefficients; wherein, ΔP is the one-two loop load deviation, and R is the load change rate.

6. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 1 wherein, The obtaining of the pressure measurement data of the outlet of the once-through steam generator and the determination of the measured pressure value according to the pressure measurement data comprise: obtaining pressure measurement data of a plurality of pressure measurement points of the outlet of the once-through steam generator; selecting the maximum pressure measurement data from the plurality of pressure measurement data as the measured pressure value.

7. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 1 wherein, The calculation of the measured pressure deviation value of the once-through steam generator according to the measured pressure value and the target pressure value comprises: performing filtering processing on the measured pressure value to obtain a processed measured pressure value; obtaining the measured pressure deviation value according to a difference between the processed measured pressure value and the target pressure value.

8. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 1 wherein, The preset condition comprises: the current measured pressure deviation value is within a first preset range, or a current time distance from an initial moment of the large load transient condition is within a second preset range.

9. The method for direct flow steam generator pressure control during large load transient conditions as claimed in claim 1 wherein, The feedwater flow control of the once-through steam generator according to the memory pressure deviation value comprises: The obtained memory pressure deviation value is an input signal transmitted to a second function generator, and the second function generator is used to convert the input signal into a feedwater flow demand. The feedwater flow control of the once-through steam generator according to the current measured pressure deviation value comprises the following steps: The obtained current measured pressure deviation value is an input signal transmitted to a second function generator, and the second function generator is used to convert the input signal into a feedwater flow demand.

10. The method for direct flow steam generator pressure control during large load transient conditions of claim 9, wherein, The feedwater flow demand is converted into a feedwater valve opening degree demand signal by a third function generator, and the feedwater valve opening degree demand signal is used to adjust the opening degree of the feedwater valve of the once-through steam generator.

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