A natural circulation to forced circulation conversion method and conversion system based on OTSG grouping coordination and circulating pump control

Abstract

The application discloses a natural circulation to forced circulation conversion method and a conversion system based on OTSG grouping coordination and circulating pump control, belongs to the technical field of reactor thermal hydraulic and operation control, and solves the problems that in the existing conversion process under a low load condition, a circulating pump speed-up, a direct-flow steam generator pressure control and a two-loop matching control lack unified linkage criteria, and the problems of abnormal increase of the direct-flow steam generator pressure, fluctuation of the circulating pump flow and insufficient two-loop heat exchange matching are easily caused. The application obtains circulating pump, OTSG and two-loop operation parameters to judge the conversion condition, divides the OTSG into a pressure rise limiting group, a normal matching group and a response lag group and uses the groups as common criteria of two types of control, dynamically selects four speed-up modes of the circulating pump, differentiates and corrects two-loop parameters according to the grouping and forms a closed-loop linkage control, and is suitable for start-stop and load regulation processes of a nuclear power device under a low load condition.

Description

Technical Field

[0001] This invention belongs to the field of reactor thermal hydraulics and operation control technology, and in particular relates to a method and system for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control. Background Technology

[0002] During low-load operation or start-up and shutdown phases, nuclear power plants typically rely on the density difference between the hot and cold coolants in the primary coolant loop to create natural circulation flow, thereby removing core heat at low power levels. Low-load conditions can include operating states where reactor power is below a preset power threshold or natural circulation flow rate is below a preset flow rate threshold. When the operating conditions change or the load needs to be increased, the system must be switched from natural circulation to forced circulation. This is achieved by starting the circulation pumps and gradually establishing a stable forced circulation flow rate, thereby improving the flow regulation capability of the primary coolant and meeting the heat exchange requirements at higher power levels.

[0003] During the transition from natural circulation to forced circulation, the increase in circulation pump speed alters the primary loop flow rate and pressure drop distribution, enhancing heat transfer from the reactor core outlet coolant to the Once-Through Steam Generator (OTSG). The OTSG serves as both a heat exchanger for transferring heat from the primary loop to the secondary loop and a crucial link between primary loop flow rate changes and secondary loop pressure, feedwater, and load response. If the feedwater flow rate, pressure regulation, and load regulation on the secondary side of the OTSG fail to match the increase in primary loop flow rate during the circulation pump speed-up process, it can easily lead to increased OTSG pressure, a higher rate of pressure change, and a delayed secondary loop feedwater response.

[0004] Currently, the control for the transition from natural circulation to forced circulation generally employs control methods based on fixed thresholds, fixed operating times, or manual experience. Under this control mode, there is a lack of unified linkage criteria between the circulation pump's acceleration process and the pressure changes, pressure change rate, and secondary loop feedwater response status of the DC steam generator. This makes it impossible to dynamically adjust the control strategy based on the real-time operating status of the system. Especially under low-load conditions, the circulation pump inlet pressure margin is inherently small, and the adjustment margin for secondary loop feedwater flow and load is also relatively limited. If the circulation pump accelerates too quickly, or if the pressure risk differences and feedwater response differences between different DC steam generators are not addressed specifically, it can easily lead to significant fluctuations in circulation pump flow, abnormally excessive DC steam generator pressure, and insufficient secondary loop heat exchange matching. In severe cases, this can even threaten the operational safety of the nuclear power plant. Therefore, there is an urgent need to develop a method for transitioning from natural circulation to forced circulation that can adapt to the characteristics of low-load conditions and achieve coordinated linkage between circulation pump control, DC steam generator pressure control, and secondary loop matching control. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method and system for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, in order to solve the problem that there is no unified linkage criterion between circulating pump speed-up, DC steam generator pressure control and secondary loop matching control during the conversion from natural circulation to forced circulation under existing low-load conditions, which easily leads to abnormal increase in DC steam generator pressure, fluctuation in circulating pump flow and insufficient heat exchange matching in the secondary loop.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, comprising the following steps: S1. Under low-load natural circulation conditions, obtain the operating parameters of the circulating pump, the operating parameters of the DC steam generator, and the operating parameters of the secondary loop; the operating parameters of the circulating pump include the inlet pressure of the circulating pump, the speed of the circulating pump, and the flow rate of the circulating pump; the operating parameters of the DC steam generator include the pressure and pressure change rate of each DC steam generator; the operating parameters of the secondary loop include the feedwater flow rate and load parameters of the secondary loop corresponding to each DC steam generator. S2. Based on the changes in the inlet pressure of the circulating pump, the flow rate of the circulating pump, the pressure change of the DC steam generator, and the response status of the secondary circuit water supply, determine whether the conditions for switching from natural circulation to forced circulation are met. S3. When the conversion conditions are met, the DC steam generators are divided into pressure rise limit group, normal matching group and response lag group according to the pressure deviation, pressure change rate and corresponding secondary loop feedwater response status of each DC steam generator. The grouping results are used as the common criterion for selecting the circulating pump control mode and adjusting the secondary loop feedwater flow and load parameters. S4. Based on the circulating pump inlet pressure, the circulating pump flow rate change rate and the grouping results, control the circulating pump to enter at low speed, and dynamically select the circulating pump speed-up mode from four modes: rapid speed-up, slow speed-up, maintaining speed, and reversing speed-down. S5. During the speed-up process of the circulating pump, the feedwater flow rate setpoint and load parameters of the corresponding second loop are corrected according to the different DC steam generator groups, and the circulating pump control mode is updated according to the corrected second loop feedwater response status.

[0007] Furthermore, step S1 includes the following steps: S11. Obtain the inlet pressure, rotational speed, and flow rate of the circulating pump, and calculate the rate of change of the circulating pump flow rate based on the current sampling time and the historical sampling time. S12. Obtain the pressure of each DC steam generator, and calculate the pressure change rate and pressure deviation of each DC steam generator based on the pressure values ​​at the current sampling time and the historical sampling time. S13. Obtain the feedwater flow rate, feedwater flow rate setpoint, and load parameters of the corresponding secondary circuit for each DC steam generator, and calculate the feedwater response status of the secondary circuit based on the feedwater flow rate and feedwater flow rate setpoint.

[0008] Furthermore, in step S2, the conditions for transitioning from a natural cycle to a forced cycle must simultaneously meet the following four requirements: The inlet pressure margin of the circulating pump is greater than the minimum inlet pressure margin threshold, which satisfies the inlet pressure condition for low-speed integration. The circulating pump is in a shutdown or low-speed waiting-to-start range, and the rate of change of the circulating pump flow rate is less than the preset flow rate change rate threshold, and it is in a state where it can be connected at low speed. The pressure of all DC steam generators did not exceed the corresponding pressure setting range, and the pressure change rate was less than the preset pressure change rate threshold, and the pressure status was within the allowable transition range; All DC steam generators have feedwater response deviations in their corresponding second loops that are less than the preset feedwater response deviation threshold, and the load parameters are within the allowable adjustment range. The second loop has an adjustment margin to match the flow rate increase of the first loop.

[0009] Furthermore, the grouping process of the DC steam generator in step S3 is as follows: S31. Calculate the pressure risk coefficient of the i-th DC steam generator. The formula for calculating the pressure risk coefficient is: in For the first Pressure risk factor of a DC steam generator For the first The pressure of a DC steam generator The corresponding pressure setting value, To allow for pressure deviation, The rate of change of pressure, To allow for the rate of pressure change, and These are the weighting coefficients; Calculate the feedwater response deviation of the second loop corresponding to the i-th DC steam generator. The formula for calculating the feedwater response deviation is: in For the first The feedwater response deviation of the two loops corresponding to each DC steam generator Set the water supply flow rate. This refers to the actual water supply flow rate. S32. When the pressure risk coefficient of the i-th DC steam generator is greater than or equal to the first risk threshold, or the pressure change rate is greater than or equal to the preset pressure change rate threshold, it is classified into the pressure rise limit group. S33. When the pressure risk coefficient of the i-th DC steam generator is less than the first risk threshold, the pressure change rate is less than the preset pressure change rate threshold, and the feedwater response deviation is less than the preset feedwater response deviation threshold, it is classified into the normal matching group. S34. When the feedwater response deviation corresponding to the i-th DC steam generator is greater than or equal to the preset feedwater response deviation threshold, or when the corresponding second-loop feedwater regulation or load regulation reaches the preset regulation boundary, it is classified as a response lag group.

[0010] Furthermore, the control process of the circulating pump in step S4 is as follows: S41. Calculate the inlet pressure margin of the circulating pump based on the inlet pressure of the circulating pump and the preset lower limit of the inlet pressure, and calculate the rate of change of the circulating pump flow rate in real time. S42. When the conversion conditions are met and the inlet pressure margin of the circulating pump is greater than the minimum inlet pressure margin threshold, control the circulating pump to start at a low speed according to the preset low speed start value to establish the initial forced circulation flow. S43. When the inlet pressure margin of the circulating pump is greater than the rapid speed-up pressure margin threshold, the flow rate change rate of the circulating pump is less than the preset flow rate change rate threshold, and the DC steam generator is in the normal matching group, control the circulating pump to execute the rapid speed-up mode. S44. When the inlet pressure margin of the circulating pump is between the minimum inlet pressure margin threshold and the rapid speed-up pressure margin threshold, or when the DC steam generator is in the pressure rise limit group, control the circulating pump to execute the slow speed-up mode. S45. When the rate of change of the circulating pump flow is greater than or equal to the preset rate of change of the flow, or when the DC steam generator is in the response lag group, control the circulating pump to execute the speed holding mode. S46. When the inlet pressure margin of the circulating pump is less than or equal to the minimum inlet pressure margin threshold, or the pressure risk coefficient of the DC steam generator is greater than or equal to the second risk threshold, control the circulating pump to execute the reversal speed reduction mode.

[0011] Furthermore, step S5 includes the following steps: S51. Feedforward correction is made to the setpoint of the secondary circuit water supply flow rate based on the change in the speed of the circulating pump. The setpoint of the secondary circuit water supply flow rate is determined based on the water supply flow rate during the low-load natural circulation stage, the water supply adjustment coefficient, the change in the speed of the circulating pump, and the advance adjustment time. S52. When the DC steam generator is in the pressure rise limit group, the speed increase of the circulating pump is limited, and the corresponding secondary loop load parameters are corrected so that the pressure change rate of the corresponding DC steam generator is lower than the preset pressure change rate threshold. S53. When the DC steam generator is in the normal matching group, the corresponding secondary circuit water supply flow rate set value is synchronously corrected according to the change in the circulating pump speed, and the secondary circuit matching control is maintained according to the adjustment direction of the current load parameters. S54. When the DC steam generator is in the response lag group, the corresponding secondary circuit feedwater flow rate set value is corrected in advance; when the feedwater response deviation is still greater than or equal to the preset feedwater response deviation threshold, the circulating pump is controlled to switch to slow speed-up mode or maintain speed mode. Furthermore, the correction formula for feedforward correction of the secondary circuit feedwater flow rate setpoint based on the change in circulating pump speed is as follows: in, This is the setpoint for the feedwater flow rate of the second loop corresponding to the i-th DC steam generator. The corresponding secondary circuit water supply flow rate during the low-load natural circulation phase is... This is the water supply regulation coefficient. Adjust the timing of the second circuit in advance.

[0012] Furthermore, when the circulation pump flow rate reaches the preset forced circulation flow rate range, the DC steam generator pressure change rate is lower than the preset pressure change rate threshold, and the feedwater response deviation is less than the preset feedwater response deviation threshold, the transition from natural circulation to forced circulation is determined to be complete.

[0013] Furthermore, after the circulating pump executes the reversal speed reduction mode, the natural circulation to forced circulation conversion condition judgment step and the DC steam generator grouping criterion step are re-executed to determine whether the conversion condition is met and update the grouping results.

[0014] The present invention also provides a natural circulation to forced circulation conversion system based on OTSG group coordination and circulating pump control. The conversion system uses the above-mentioned conversion method and includes a data acquisition module, a conversion condition judgment module, a DC steam generator grouping criterion module, a circulating pump control module, and a two-loop matching control module. The data acquisition module is used to acquire the operating parameters of the circulating pump, the operating parameters of the DC steam generator, and the operating parameters of the secondary loop in real time under low-load natural circulation conditions, and output them to the conversion condition judgment module. The conversion condition judgment module is used to determine whether the conversion condition from natural cycle to forced cycle is met based on the received parameters. If the condition is met, it outputs a conversion permission signal to the DC steam generator grouping criterion module. If the condition is not met, it outputs a signal to maintain the natural cycle state. The DC steam generator grouping criterion module is used to receive the allowable conversion signal, divide the DC steam generator into a pressure rise limit group, a normal matching group, and a response lag group, and output the grouping results to the circulating pump control module and the second loop matching control module in parallel, as a common control criterion for the two modules. The circulating pump control module is used to control the circulating pump to enter at low speed and dynamically select the speed-up mode based on the circulating pump inlet pressure margin, the circulating pump flow rate change rate and the received grouping results, and at the same time output the circulating pump speed change to the second loop matching control module. The dual-loop matching control module is used to correct the feedwater flow rate setpoint and load parameters of the corresponding dual loop according to the received grouping results and the change in the speed of the circulating pump, and at the same time, it feeds back the feedwater response status of the dual loop to the circulating pump control module to realize the dynamic update of the circulating pump speed-up mode.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention establishes a unified linkage mechanism between the grouping result of the DC steam generator and the secondary loop matching control by using the grouping result of the DC steam generator as a common criterion for the control of the circulating pump and the secondary loop matching control. This fundamentally solves the problems of the lack of a unified criterion between the circulating pump speed-up process and the DC steam generator pressure change and the secondary loop feedwater response state in the prior art, as well as the insufficient coordination of various control links, thus avoiding system operation abnormalities caused by control disconnection.

[0016] This invention classifies each DC steam generator into three groups—pressure rise limiting group, normal matching group, and response lag group—based on their pressure risk coefficient, pressure change rate, and secondary loop feedwater response deviation. This differentiated approach addresses the shortcomings of failing to differentiate and address pressure risk and feedwater response differences among different DC steam generators. For DC steam generators with high pressure rise risk, abnormal pressure increases are effectively suppressed by limiting the circulation pump speed increase and correcting the corresponding secondary loop load parameters. For DC steam generators with lag in feedwater response, the lag in secondary loop regulation is compensated for by pre-correcting the secondary loop feedwater flow rate setpoint. For DC steam generators in normal condition, the feedwater flow rate is synchronously matched to ensure heat exchange efficiency, comprehensively improving the consistency and stability of the operating status of each DC steam generator during the conversion process.

[0017] This invention provides four dynamic control modes for the circulating pump: rapid acceleration, deceleration, speed maintenance, and speed reduction. By combining the inlet pressure margin and flow rate change rate of the circulating pump in real time to adjust the acceleration strategy, it can accelerate the conversion process when the system condition allows, and promptly decelerate, maintain, or even reduce the speed when the inlet pressure margin is insufficient, the flow rate fluctuates too much, or the DC steam generator is in an abnormal state. This effectively avoids problems such as low inlet pressure and large flow fluctuations caused by excessively rapid acceleration of the circulating pump under low load conditions, ensuring the safe operation of the circulating pump and the smooth transition of the primary loop flow.

[0018] This invention employs a feedforward correction method for the secondary loop feedwater flow rate based on changes in the circulating pump speed. Combined with the grouping status of different DC steam generators, it implements differentiated feedwater and load regulation strategies, enabling the secondary loop to respond proactively to changes in the primary loop flow rate. This significantly improves the heat exchange matching degree between the secondary and primary loops, reducing pressure fluctuations in the DC steam generator and abnormal secondary loop parameters caused by heat exchange mismatch. Simultaneously, by feeding back feedwater response deviations and load regulation boundary states to the circulating pump control module through the secondary loop matching control module, a closed-loop linkage control is formed. This allows for dynamic updates to the control strategy based on the real-time operating status of the system, further enhancing the adaptive capability and control accuracy of the transition process.

[0019] Through the aforementioned control mechanism, this invention effectively shortens the transition time from natural circulation to forced circulation while ensuring the safe operation of the nuclear power plant. It also improves the reliability and stability of the transition process, avoids equipment damage and operational risks caused by abnormalities in the transition process, and is applicable to the start-up, shutdown, and load regulation processes of nuclear power plants under low-load conditions. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is an overall flowchart of a method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, as described in this invention. Figure 2 This is a flowchart of the data acquisition process for a method of converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, as described in this invention. Figure 3 This is a flowchart illustrating the conversion condition judgment process for a natural circulation to forced circulation conversion method based on OTSG group coordination and circulating pump control, as described in this invention. Figure 4 This is a flowchart of the OTSG grouping criterion for a method of converting natural circulation to forced circulation based on OTSG grouping coordination and circulating pump control, as described in this invention. Figure 5 This is a flowchart of the circulating pump control mode selection method for the natural circulation to forced circulation conversion method based on OTSG group coordination and circulating pump control described in this invention. Figure 6 This is a flowchart of a two-loop matching control method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, as described in this invention. Figure 7 This is a block diagram of a system for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, as described in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0022] Reference Figure 1 As shown, a method for converting natural circulation to forced circulation based on OTSG grouping coordination and circulating pump control is presented. This method combines low-speed integration control of the circulating pump, OTSG grouping criteria, and second-loop matching control, so that the OTSG grouping result can be used as a common criterion for selecting the circulating pump control mode and adjusting the second-loop feedwater flow and load parameters.

[0023] In this embodiment, when the reactor power meets the requirements... Or natural circulation flow meets At that time, the system is determined to be in a low-load natural circulation state. Among these, This represents the current power of the reactor. To preset the power threshold, For natural circulation flow, The preset natural circulation flow threshold is used.

[0024] The method described in this embodiment includes the following steps: S1. Obtain the operating parameters of the circulating pump, OTSG, and secondary circuit under low-load natural circulation conditions; S2. Based on the changes in circulating pump inlet pressure, circulating pump flow rate, OTSG pressure, and secondary circuit water supply response, determine whether the conditions for switching from natural circulation to forced circulation are met; if the switching conditions are not met, maintain the current natural circulation state. S3. When the conversion conditions are met, the OTSG is grouped according to the OTSG pressure deviation, pressure change rate and secondary loop water supply response status, and the grouping results are used as the common criteria for circulating pump control and secondary loop matching control. S4. Based on the circulating pump inlet pressure, circulating pump flow rate change rate and OTSG grouping results, control the circulating pump to enter at low speed and select the rapid speed-up, slow speed-up, speed maintenance or speed reduction mode. S5. During the speed-up process of the circulating pump, the set value of the secondary circuit water supply flow and the load parameters are corrected according to different OTSG groups; when the circulating pump flow, OTSG pressure change rate and secondary circuit water supply response deviation all meet the preset range, the conversion is determined to be complete.

[0025] In the above process, the OTSG grouping result output by S3 is simultaneously input to S4 and S5, so that the circulating pump speed-up control and the two-loop matching control use the same grouping criterion.

[0026] Reference Figure 2 As shown, in this embodiment, S1 includes the following steps: S11. Obtain the circulating pump inlet pressure, circulating pump speed, and circulating pump flow rate, and calculate the circulating pump flow rate change rate based on the circulating pump flow rate at the current sampling time and the historical sampling time: in, The rate of change of the circulating pump flow rate, The current flow rate of the circulating pump at the current sampling time. The flow rate of the circulating pump at the previous sampling time. The sampling period is specified. The circulating pump inlet pressure is used to calculate the inlet pressure margin, the circulating pump speed is used to determine the current connection status, and the circulating pump flow rate change rate is used for subsequent circulating pump speed-up mode selection.

[0027] S12, Obtain the first Each OTSG pressure is calculated, and the pressure change rate is calculated based on the pressure values ​​at the current sampling time and the historical sampling times. Simultaneously calculate the OTSG pressure deviation: in, For the first OTSG pressure change rate, The pressure at the current sampling moment, The pressure at the previous sampling time, For pressure deviation, This corresponds to the pressure setpoint. The pressure change rate and pressure deviation are used as criteria for subsequent OTSG grouping.

[0028] S13, Obtain the... Each OTSG corresponds to the secondary circuit water supply flow rate, water supply flow rate setpoint, and load parameters, and calculates the secondary circuit water supply response deviation: in, For water supply response deviation, Set the water supply flow rate. This represents the actual water supply flow rate. Load parameters. Used to determine whether the load regulation of the secondary circuit has reached the preset regulation boundary: in, and These are the lower and upper limits of the allowable adjustment range for the load parameters, respectively.

[0029] The circulating pump inlet pressure, circulating pump speed, circulating pump flow rate change rate, OTSG pressure change rate, pressure deviation, secondary circuit water supply response deviation, and load parameter adjustment status are obtained through S11 to S13, and the above data are input into S2, S3, S4, and S5.

[0030] Reference Figure 3 As shown, in this embodiment, S2 includes the following steps: S21. Calculate the circulating pump inlet pressure margin based on the circulating pump inlet pressure and the preset lower limit of the inlet pressure: when If the condition is met, the circulation pump is determined to meet the inlet pressure condition for low-speed integration; otherwise, the current natural circulation state is maintained, and S1 is re-executed.

[0031] S22. Based on the current speed, flow rate, and rate of change of the circulating pump, determine whether the circulating pump is in a state where it can be connected at low speed. When the circulating pump is stopped or in a low-speed waiting-to-start range, and the following conditions are met: At that time, it is determined that the circulating pump is in a state where it can be connected at low speed.

[0032] S23. Based on the OTSG pressure, pressure setpoint, and pressure change rate, determine whether the OTSG pressure status is within the allowable transition range. When the OTSG pressure does not exceed the corresponding pressure setpoint and meets the following conditions: When the OTSG pressure state meets the switching requirements, it is determined that the OTSG pressure state is satisfied.

[0033] S24. Based on the secondary circuit water supply flow rate, water supply flow rate setpoint, water supply response deviation, and load parameter adjustment boundary, determine whether the secondary circuit has an adjustment margin. When the following conditions are met: And it satisfies: At that time, it is determined that the second circuit has an adjustment margin to match the flow increase of the first circuit.

[0034] S25. When all of S21 to S24 meet the preset conditions, it is determined that the conditions for the transition from natural loop to forced loop are met. The comprehensive criterion is as follows: If any of the above conditions are not met, the command to integrate the circulation pump at low speed will not be executed, and the current natural circulation state will be maintained.

[0035] in, This is the inlet pressure margin of the circulating pump. This refers to the inlet pressure of the circulating pump. To preset the lower limit of inlet pressure, This is the minimum inlet pressure margin threshold. The rate of change of the circulating pump flow rate, The threshold for the rate of change of the circulating pump flow rate. For the first OTSG pressure change rate, To preset the pressure change rate threshold, For water supply response deviation, The threshold for water supply response deviation. For load parameters, and These are the lower and upper limits of the allowable adjustment range for the load parameters, respectively.

[0036] Reference Figure 4 As shown, in this embodiment, S3 includes the following steps: S31, according to the... Calculate the pressure risk coefficient for each OTSG based on its pressure, pressure setpoint, allowable pressure deviation, pressure change rate, and allowable pressure change rate. The water supply response deviation is calculated based on the corresponding secondary circuit water supply flow setpoint and the actual water supply flow: S32. When the following conditions are met: Or satisfy: At that time, the corresponding OTSG will be classified into the pressure rise limit group.

[0037] S33, When the following conditions are met: When this happens, the corresponding OTSG will be classified as a normal matching group.

[0038] S34. When the following conditions are met: Alternatively, when the corresponding secondary circuit water supply regulation or load regulation reaches the preset regulation boundary, the corresponding OTSG will be classified as a response lag group.

[0039] The grouping results of the pressure rise limit group, normal matching group, and response lag group are simultaneously input into the S4 circulating pump control process and the S5 second-loop matching control process, serving as a common criterion for selecting the circulating pump speed-up mode, correcting the second-loop feedwater flow setpoint, and adjusting the load parameters.

[0040] in, For the first The pressure risk coefficient of each OTSG For the first OTSG pressure, The corresponding pressure setting value, To allow for pressure deviation, The rate of change of pressure, To allow for the rate of pressure change, and These are the weighting coefficients. The first risk threshold, To preset the pressure change rate threshold, For water supply response deviation, This is the preset water supply response deviation threshold.

[0041] Reference Figure 5 As shown, in this embodiment, S4 includes the following steps: S41. Calculate the circulating pump inlet pressure margin based on the circulating pump inlet pressure and the preset lower limit of the inlet pressure: The rate of change of circulating pump flow rate is calculated based on the sampled value of circulating pump flow rate.

[0042] S42. When the conditions for the transformation from a natural cycle to a forced cycle are met, and the following conditions are also met: At that time, the control circulation pump is connected at a low speed according to the preset low speed start value to establish the initial forced circulation flow.

[0043] S43. When the following conditions are met: Furthermore, when the OTSG is in the normal matching group, the control circulation pump executes the rapid acceleration mode.

[0044] S44. When the following conditions are met: Or satisfy: At that time, the circulating pump is controlled to execute a slow-up speed mode.

[0045] S45. When the following conditions are met: Or satisfy: At that time, the circulating pump is controlled to maintain a constant speed mode.

[0046] S46. When the following conditions are met: Or satisfy: At that time, the circulating pump is controlled to execute the reversal speed reduction mode.

[0047] The circulating pump speed is updated according to the following formula: in, This is the normalized speed coefficient of the circulating pump. This represents the adjustment amount of the circulating pump speed within the current control cycle.

[0048] The adjustment amount of the circulating pump speed is determined according to the following formula: in, , , , These correspond to rapid acceleration, slow acceleration, maintaining speed, and reversal deceleration modes, respectively. This is the minimum inlet pressure margin threshold. The rapid acceleration pressure margin threshold, The threshold for the rate of change of the circulating pump flow rate. and This is the threshold for stress risk classification. This is the water supply response deviation threshold.

[0049] After the circulating pump executes the reversal speed reduction mode, the S2 transition condition judgment and the S3 OTSG grouping criterion are re-executed.

[0050] Reference Figure 6 As shown, in this embodiment, S5 includes the following steps: S51. Feedforward correction of the secondary circuit feedwater flow rate setpoint based on the change in circulating pump speed: in, For the first Each OTSG corresponds to the setpoint for the secondary circuit water supply flow. The corresponding secondary circuit water supply flow rate during the low-load natural circulation phase is... This is the water supply regulation coefficient. Adjust the timing of the second circuit in advance.

[0051] S52. When the OTSG is in the pressure rise limit group, limit the speed increase of the circulating pump and correct the corresponding secondary circuit load parameters to meet the following requirements: If it still satisfies after correction If so, the circulating pump will switch to a reversing speed reduction mode.

[0052] S53. When the OTSG is in the normal matching group, the corresponding secondary circuit feedwater flow rate setpoint is synchronously corrected according to the change in the circulating pump speed, and the current load parameter adjustment direction is maintained so that the feedwater response deviation meets the following requirements: S54. When the OTSG is in the response lag group, the corresponding secondary circuit water supply flow rate setpoint should be corrected in advance; if the correction still satisfies: The water supply response deviation will then be fed back to the circulating pump control process, causing the circulating pump to switch to either a slow-up mode or a speed-maintaining mode.

[0053] S55. When the circulating pump flow rate, OTSG pressure change rate, and secondary loop feedwater response deviation simultaneously meet the following conditions: If the natural cycle transition to the forced cycle is complete, then the process is considered complete; otherwise, the data acquisition, grouping criteria, and circulation pump control mode update will continue.

[0054] In the above process, the second-loop matching control module receives the OTSG grouping results and feeds back the water supply response deviation and load parameter adjustment boundary state to the circulating pump control module as input for updating the circulating pump speed-up mode.

[0055] Reference Figure 7 As shown, this embodiment is a natural circulation to forced circulation conversion system based on OTSG group coordination and circulating pump control, including a data acquisition module, a conversion condition judgment module, a DC steam generator grouping criterion module, a circulating pump control module, and a two-loop matching control module.

[0056] The data acquisition module is used to acquire the operating parameters of the circulating pump, the OTSG, and the secondary loop.

[0057] The conversion condition judgment module is used to determine whether the conditions for switching from natural circulation to forced circulation are met based on the inlet pressure margin of the circulating pump, the rate of change of the circulating pump flow, the rate of change of the OTSG pressure, and the response deviation of the secondary loop feedwater. When the conversion conditions are met, it outputs a signal to allow the conversion to the DC steam generator grouping criterion module. When the conversion conditions are not met, it outputs a signal to maintain the natural circulation state and returns to the data acquisition module to reacquire the operating parameters.

[0058] The DC steam generator grouping criterion module is used to divide the OTSG into a pressure rise limit group, a normal matching group, or a response lag group based on the OTSG pressure risk coefficient, pressure change rate, and secondary loop feedwater response deviation after receiving the allowable conversion signal. The grouping results are simultaneously output to the circulating pump control module and the secondary loop matching control module.

[0059] The circulating pump control module is used to control the circulating pump to enter at low speed based on the circulating pump inlet pressure margin, the circulating pump flow rate change rate and OTSG grouping results, and to select a mode of rapid speed increase, slow speed increase, maintaining speed or reversing speed decrease.

[0060] The two-loop matching control module is used to correct the set value of the secondary loop water supply flow and load parameters based on the change in the speed of the circulating pump and the OTSG grouping results. Among them, the pressure rise limit group is used to correct the load parameters and limit the speed of the circulating pump, the normal matching group is used to correct the set value of the water supply flow synchronously, and the response lag group is used to correct the set value of the water supply flow in advance and provide feedback on the water supply response deviation.

[0061] In this embodiment, the circulating pump control module outputs the circulating pump speed change to the second-loop matching control module, and the second-loop matching control module feeds back the water supply response deviation and load parameter adjustment boundary state to the circulating pump control module, so that the circulating pump speed-up mode and the second-loop matching adjustment amount are updated according to the same OTSG grouping result.

[0062] The specific embodiments of the present invention disclosed above are merely illustrative of the invention. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, characterized in that: Includes the following steps: S1. Under low-load natural circulation conditions, obtain the operating parameters of the circulating pump, the operating parameters of the DC steam generator, and the operating parameters of the secondary loop; the operating parameters of the circulating pump include the inlet pressure of the circulating pump, the speed of the circulating pump, and the flow rate of the circulating pump; the operating parameters of the DC steam generator include the pressure and pressure change rate of each DC steam generator; the operating parameters of the secondary loop include the feedwater flow rate and load parameters of the secondary loop corresponding to each DC steam generator. S2. Based on the changes in the inlet pressure of the circulating pump, the flow rate of the circulating pump, the pressure change of the DC steam generator, and the response status of the secondary circuit water supply, determine whether the conditions for switching from natural circulation to forced circulation are met. S3. When the conversion conditions are met, the DC steam generators are divided into pressure rise limit group, normal matching group and response lag group according to the pressure deviation, pressure change rate and corresponding secondary loop feedwater response status of each DC steam generator. The grouping results are used as the common criterion for selecting the circulating pump control mode and adjusting the secondary loop feedwater flow and load parameters. S4. Based on the circulating pump inlet pressure, the circulating pump flow rate change rate and the grouping results, control the circulating pump to enter at low speed, and dynamically select the circulating pump speed-up mode from four modes: rapid speed-up, slow speed-up, maintaining speed, and reversing speed-down. S5. During the speed-up process of the circulating pump, the feedwater flow rate setpoint and load parameters of the corresponding second loop are corrected according to the different DC steam generator groups, and the circulating pump control mode is updated according to the corrected second loop feedwater response status.

2. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 1, characterized in that: Step S1 includes the following steps: S11. Obtain the inlet pressure, rotational speed, and flow rate of the circulating pump, and calculate the rate of change of the circulating pump flow rate based on the current sampling time and the historical sampling time. S12. Obtain the pressure of each DC steam generator, and calculate the pressure change rate and pressure deviation of each DC steam generator based on the pressure values ​​at the current sampling time and the historical sampling time. S13. Obtain the feedwater flow rate, feedwater flow rate setpoint, and load parameters of the corresponding secondary circuit for each DC steam generator, and calculate the feedwater response status of the secondary circuit based on the feedwater flow rate and feedwater flow rate setpoint.

3. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 1, characterized in that: In step S2, the conditions for transitioning from a natural cycle to a forced cycle must simultaneously meet the following four requirements: The inlet pressure margin of the circulating pump is greater than the minimum inlet pressure margin threshold, which satisfies the inlet pressure condition for low-speed integration. The circulating pump is in a shutdown or low-speed waiting-to-start range, and the rate of change of the circulating pump flow rate is less than the preset flow rate change rate threshold, and it is in a state where it can be connected at low speed. The pressure of all DC steam generators did not exceed the corresponding pressure setting range, and the pressure change rate was less than the preset pressure change rate threshold, and the pressure status was within the allowable transition range; All DC steam generators have feedwater response deviations in their corresponding second loops that are less than the preset feedwater response deviation threshold, and the load parameters are within the allowable adjustment range. The second loop has an adjustment margin to match the flow rate increase of the first loop.

4. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 1, characterized in that: The grouping process of the DC steam generator in step S3 is as follows: S31. Calculate the pressure risk coefficient of the i-th DC steam generator. The formula for calculating the pressure risk coefficient is: in For the first Pressure risk factor of a DC steam generator For the first The pressure of a DC steam generator The corresponding pressure setting value, To allow for pressure deviation, The rate of change of pressure, To allow for the rate of pressure change, and These are the weighting coefficients; The feedwater response deviation of the second loop corresponding to the i-th DC steam generator is calculated using the following formula: in For the first The feedwater response deviation of the two loops corresponding to each DC steam generator Set the water supply flow rate. This refers to the actual water supply flow rate; S32. When the pressure risk coefficient of the i-th DC steam generator is greater than or equal to the first risk threshold, or the pressure change rate is greater than or equal to the preset pressure change rate threshold, it is classified into the pressure rise limit group. S33. When the pressure risk coefficient of the i-th DC steam generator is less than the first risk threshold, the pressure change rate is less than the preset pressure change rate threshold, and the feedwater response deviation is less than the preset feedwater response deviation threshold, it is classified into the normal matching group. S34. When the feedwater response deviation corresponding to the i-th DC steam generator is greater than or equal to the preset feedwater response deviation threshold, or when the corresponding second-loop feedwater regulation or load regulation reaches the preset regulation boundary, it is classified as a response lag group.

5. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 1, characterized in that: The control process of the circulating pump in step S4 is as follows: S41. Calculate the inlet pressure margin of the circulating pump based on the inlet pressure of the circulating pump and the preset lower limit of the inlet pressure, and calculate the rate of change of the circulating pump flow rate in real time. S42. When the conversion conditions are met and the inlet pressure margin of the circulating pump is greater than the minimum inlet pressure margin threshold, control the circulating pump to start at a low speed according to the preset low speed start value to establish the initial forced circulation flow. S43. When the inlet pressure margin of the circulating pump is greater than the rapid speed-up pressure margin threshold, the flow rate change rate of the circulating pump is less than the preset flow rate change rate threshold, and the DC steam generator is in the normal matching group, control the circulating pump to execute the rapid speed-up mode. S44. When the inlet pressure margin of the circulating pump is between the minimum inlet pressure margin threshold and the rapid speed-up pressure margin threshold, or when the DC steam generator is in the pressure rise limit group, control the circulating pump to execute the slow speed-up mode. S45. When the rate of change of the circulating pump flow is greater than or equal to the preset rate of change of the flow, or when the DC steam generator is in the response lag group, control the circulating pump to execute the speed holding mode. S46. When the inlet pressure margin of the circulating pump is less than or equal to the minimum inlet pressure margin threshold, or the pressure risk coefficient of the DC steam generator is greater than or equal to the second risk threshold, control the circulating pump to execute the reversal speed reduction mode.

6. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 1, characterized in that: Step S5 includes the following steps: S51. Feedforward correction is made to the setpoint of the secondary circuit water supply flow rate based on the change in the speed of the circulating pump. The setpoint of the secondary circuit water supply flow rate is determined based on the water supply flow rate during the low-load natural circulation stage, the water supply adjustment coefficient, the change in the speed of the circulating pump, and the advance adjustment time. S52. When the DC steam generator is in the pressure rise limit group, the speed increase of the circulating pump is limited, and the corresponding secondary loop load parameters are corrected so that the pressure change rate of the corresponding DC steam generator is lower than the preset pressure change rate threshold. S53. When the DC steam generator is in the normal matching group, the corresponding secondary circuit water supply flow rate set value is synchronously corrected according to the change in the circulating pump speed, and the secondary circuit matching control is maintained according to the adjustment direction of the current load parameters. S54. When the DC steam generator is in the response lag group, the corresponding secondary circuit feedwater flow rate setting value is corrected in advance; when the feedwater response deviation is still greater than or equal to the preset feedwater response deviation threshold, the circulating pump is controlled to switch to the slow-up mode or the speed-maintaining mode.

7. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 6, characterized in that: The correction formula for feedforward correction of the secondary circuit feedwater flow rate setpoint based on the change in circulating pump speed is as follows: in, This is the setpoint for the feedwater flow rate of the second loop corresponding to the i-th DC steam generator. The corresponding secondary circuit water supply flow rate during the low-load natural circulation phase is... This is the water supply regulation coefficient. Adjust the timing of the second circuit in advance.

8. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 6, characterized in that: When the circulation pump flow rate reaches the preset forced circulation flow rate range, the DC steam generator pressure change rate is lower than the preset pressure change rate threshold, and the feedwater response deviation is less than the preset feedwater response deviation threshold, the transition from natural circulation to forced circulation is determined to be complete.

9. The method for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control according to claim 5, characterized in that: After the circulating pump executes the reversal speed reduction mode, the natural circulation to forced circulation conversion condition judgment step and the DC steam generator grouping criterion step are re-executed to determine whether the conversion condition is met and update the grouping results.

10. A system for converting natural circulation to forced circulation based on OTSG group coordination and circulating pump control, characterized in that: The conversion system uses the conversion method according to any one of claims 1-9, including a data acquisition module, a conversion condition judgment module, a DC steam generator grouping criterion module, a circulating pump control module, and a two-loop matching control module; The data acquisition module is used to acquire the operating parameters of the circulating pump, the operating parameters of the DC steam generator, and the operating parameters of the secondary loop in real time under low-load natural circulation conditions, and output them to the conversion condition judgment module. The conversion condition judgment module is used to determine whether the conversion condition from natural cycle to forced cycle is met based on the received parameters. If the condition is met, it outputs a conversion permission signal to the DC steam generator grouping criterion module. If the condition is not met, it outputs a signal to maintain the natural cycle state. The DC steam generator grouping criterion module is used to receive the allowable conversion signal, divide the DC steam generator into a pressure rise limit group, a normal matching group, and a response lag group, and output the grouping results to the circulating pump control module and the second loop matching control module in parallel, as a common control criterion for the two modules. The circulating pump control module is used to control the circulating pump to enter at low speed and dynamically select the speed-up mode based on the circulating pump inlet pressure margin, the circulating pump flow rate change rate and the received grouping results, and at the same time output the circulating pump speed change to the second loop matching control module. The dual-loop matching control module is used to correct the feedwater flow rate setpoint and load parameters of the corresponding dual loop according to the received grouping results and the change in the speed of the circulating pump, and at the same time, it feeds back the feedwater response status of the dual loop to the circulating pump control module to realize the dynamic update of the circulating pump speed-up mode.

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