A control method and system for feedwater recirculation under variable load frequency regulation in thermal power units

Abstract

This invention discloses a control method and system for feedwater recirculation under variable load frequency regulation in thermal power units, belonging to the field of intelligent control technology for thermal power units. In the system, a deviation constraint pre-selection subsystem collects flow deviation and valve closing / locking signals, and outputs a pre-selection correction signal; a flow safety calculation subsystem collects the inlet flow of the unit's small turbine, processes it through comparison and constraint operations, and outputs a safety compensation signal; a local manual operation pre-selection subsystem, based on the local control switching state of the bypass valve, obtains a manual compensation signal through a two-choice value selection and rate limiting processing; and an instruction generation and output subsystem sums the safety compensation and manual compensation signals, combines them with the pre-selection correction signal to complete the control logic operation, and generates a control instruction for the feedwater recirculation bypass valve through function conversion. This invention can respond to frequency regulation disturbances in advance, stabilize the flow of the feedwater pump under all operating conditions of variable load frequency regulation, reduce safety risks, and adapt to the needs of deep peak shaving and rapid frequency regulation of the unit.

Description

Technical Field

[0001] This invention belongs to the field of intelligent control technology for thermal power units, specifically relating to a control method and system for feedwater recirculation under variable load frequency regulation in thermal power units. Background Technology

[0002] With the accelerated construction of new power systems and the large-scale grid connection of new energy sources such as wind power and photovoltaics, the contradiction between supply and demand for grid peak shaving and frequency regulation has become prominent. The functional positioning of thermal power units has gradually shifted from traditional base load power generation to the main supporting role of deep peak shaving and rapid primary / secondary frequency regulation. The units are often in a state of large-scale changes in operating conditions over a wide load range and frequent response to grid frequency regulation commands, which puts forward higher requirements for the dynamic adjustment capability, safety stability and economic operation level of auxiliary equipment systems.

[0003] Feedwater pumps are core and critical equipment in the feedwater system of thermal power units. The feedwater recirculation system maintains the feedwater pump outlet flow rate above the minimum safe flow rate by controlling the opening of the recirculation regulating valve. It is a core protective device to prevent cavitation, vibration and shaft damage of the feedwater pump under low flow conditions, and is directly related to the safe and stable operation of the feedwater pump and the entire unit.

[0004] Currently, the feedwater recirculation of existing thermal power units generally adopts a fixed minimum flow setpoint and conventional single-loop PID control mode. The control parameters and protection thresholds are set only based on the rated operating conditions. As a result, the fixed flow setpoint is difficult to adapt to actual operating conditions such as deep load changes, frequency regulation transient disturbances, and feedwater pump speed characteristics drift. Insufficient safety margin during low-load frequency regulation can easily induce cavitation risk, while excessive conservative redundant flow during high-load steady-state stage results in energy waste. Summary of the Invention

[0005] This invention provides a control method and system for feedwater recirculation under variable load frequency regulation in thermal power units. The purpose is to solve the problems in current feedwater recirculation of thermal power units, such as setting control parameters and protection thresholds only based on rated operating conditions, which makes it difficult for fixed flow rate settings to adapt to the actual operating conditions of the unit; insufficient safety margin during low load frequency regulation; and excessive conservative redundant flow during high load steady-state stage, resulting in energy waste.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a control system for feedwater recirculation under variable load frequency regulation in thermal power units, comprising a deviation constraint pre-selection subsystem, a flow safety calculation subsystem, a local manual pre-selection subsystem, and a command generation and output subsystem; wherein: The deviation constraint pre-selection subsystem is used to collect two types of signals: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, it combines the deep adjustment trigger signal to perform parameter optimization and output the pre-selection correction signal. The flow safety accounting subsystem is used to collect the inlet flow of the unit's small unit, and then sequentially performs inertial filtering, multi-path function conversion, nested large and small value logic comparison, and change rate constraint calculation to output a safety compensation signal; The local manual pre-selection subsystem is based on the local control of the switching state of the bypass valve. It selects a value between the given value and a fixed constant and performs rate limiting processing to obtain the manual compensation signal. The instruction generation and output subsystem sums the safety compensation signal and the manual compensation signal, and combines them with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control instruction for the water supply recirculation bypass valve is generated.

[0007] In some embodiments, the deviation constraint pre-selection subsystem includes a large deviation between the feedwater flow rate and the set value, a lockout of the steam pump recirculation bypass valve, a first constant module, a first function module, a second function module, a first switching module, a second switching module, a deep adjustment trigger for the steam pump recirculation bypass valve, and a third switching module. The lockout of the steam pump recirculation bypass valve serves as the selection control signal between the first and second switching modules. The first switching module selects one output from the set value output by the first constant module and the calculation result of the first function module. The second switching module selects one output from the set value output by the first constant module and the calculation result of the second function module. The deep adjustment trigger of the steam pump recirculation bypass valve controls the third switching module to obtain a pre-selected correction signal by selecting the optimal output between the first and second switching modules.

[0008] Furthermore, when the lockout steam pump recirculation bypass control valve outputs a valid signal, both the first switching module and the second switching module select the fixed value output of the first constant module; when the deep adjustment trigger of the steam pump recirculation bypass control valve is validly triggered, the third switching module selects the output of the first switching module, and when there is no trigger signal, it selects the output of the second switching module.

[0009] In some implementations, the traffic safety calculation subsystem includes a small computer inlet traffic, a first-order inertial module, a third function module, a fourth function module, a greater than module, a less than module, and a first rate module; the small computer inlet traffic is filtered by the first-order inertial module and then sent to the third function module and the fourth function module in two paths; the calculation results of the two paths are successively filtered by the greater than module and the less than module, and then sent to the first rate module for rate constraint and output a safety compensation signal.

[0010] In some implementations, the local manual pre-selection subsystem includes a steam pump recirculation bypass regulating valve control, a manual controller module, a second constant module, a fourth switching module, and a second rate module. The steam pump recirculation bypass regulating valve control is the selection condition for the fourth switching module. The fourth switching module selects between the output value of the manual controller module and the set value of the second constant module. The output signal is then speed-limited by the second rate module to form a manual compensation signal.

[0011] Furthermore, when the control of the steam pump recirculation bypass regulating valve is effectively activated, the fourth switching module selects the value output of the handheld controller module; when the control of the steam pump recirculation bypass regulating valve is not activated, the second constant module selects the fixed value output.

[0012] In some implementations, the instruction generation and output subsystem includes an addition module, which receives the security compensation signal and the manual compensation signal and performs a summation operation.

[0013] Furthermore, the instruction generation and output subsystem also includes a control module and a fifth function module; the control module receives the summation signal and pre-selection correction signal output by the addition module to complete the comprehensive control operation; the fifth function module is used to receive the operation result of the control module and perform the final function conversion.

[0014] Furthermore, the instruction generation and output subsystem also includes a feedwater recirculation bypass regulating valve instruction; the feedwater recirculation bypass regulating valve instruction generates the final regulating valve control instruction based on the conversion result of the fifth function module.

[0015] This invention also provides a control method for feedwater recirculation under variable load frequency regulation of thermal power units, which is based on the above-mentioned control system for feedwater recirculation under variable load frequency regulation of thermal power units, and includes the following steps: Two types of signals are collected: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, the parameters are optimized in combination with the deep adjustment trigger signal, and a pre-selected correction signal is output. The inlet flow of the data acquisition unit is sequentially processed through inertial filtering, multi-path function conversion, nested large and small value logic comparison, and change rate constraint calculation, and outputs a safety compensation signal. Based on the local control switching state of the bypass valve, the manual compensation signal is obtained by selecting one of the two values ​​between the manually given value and the fixed constant and performing rate limiting processing. The safety compensation signal and the manual compensation signal are summed and combined with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control command for the water supply recirculation bypass valve is generated.

[0016] Compared with the prior art, the control method and system for feedwater recirculation under variable load frequency regulation of thermal power units of the present invention has the following beneficial effects: This invention discloses an intelligent control system for feedwater recirculation in thermal power units under variable load frequency regulation. It collects parameters such as feedwater pump speed, inlet pressure, outlet temperature, feedwater header pressure, real-time unit load, grid AGC commands, primary frequency regulation commands, load change rate, and effective and required net positive suction head (NPSH) of the feedwater pump. The collected parameters undergo noise filtering, outlier removal, and standardization to generate a real-time operating condition data set for control decisions, avoiding interference from data affecting control accuracy. By receiving grid AGC commands and primary frequency regulation commands in real time, it extracts the load change amplitude and rate, and based on a pre-stored valve opening mapping matrix, it outputs the pre-adjusted opening of the recirculation valve relatively quickly, responding to frequency regulation disturbances in advance and shortening the regulation lag time. Through dynamic minimum flow adaptive calculation and multi-level safety constraints, this invention can achieve a certain degree of feedwater pump flow stability under all operating conditions of variable load frequency regulation, reducing safety risks and adapting to the needs of deep peak shaving and rapid frequency regulation of the unit. Attached Figure Description

[0017] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 This is a schematic diagram of the architecture of a control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to the present invention. Figure 2 This is a schematic diagram of the dynamic change curve of the power grid frequency in an embodiment of the control method for feedwater recirculation under variable load frequency regulation of a thermal power unit according to the present invention.

[0019] Among them, 1. Large deviation between feedwater flow rate and set value; 2. Locking the steam pump recirculation bypass regulating valve closed; 3. Locking the steam pump recirculation bypass regulating valve open; 4. Deep adjustment trigger of steam pump recirculation bypass regulating valve; 5. Small turbine inlet flow rate; 6. Steam pump recirculation bypass regulating valve control; 7. First function module; 8. First constant module; 9. Second function module; 10. First switching module; 11. Second switching module; 12. Third switching module; 13. First inertia module; 14. Handheld device module; 15. Second constant module; 16. Third function module; 17. Fourth function module; 18. Greater than module; 19. Less than module; 20. Fourth switching module; 21. First rate module; 22. Second rate module; 23. Addition module; 24. Control module; 25. Fifth function module; 26. Feedwater recirculation bypass regulating valve command. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0022] It should be noted that, in this document, the terms include, encompass, or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "including one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0023] It should be noted that the apparatus and methods disclosed in the embodiments herein can also be implemented in other ways. The apparatus embodiments described above are merely illustrative; for example, the flowcharts and block diagrams in the accompanying drawings show the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments herein. In this regard, each block in a flowchart or block diagram may represent a module, program, or part of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system to perform the specified function or action, or can be implemented using a combination of dedicated hardware and computer instructions.

[0024] In addition, the functional modules in the various embodiments of this article can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0025] like Figure 1 As shown, this invention provides a control system for feedwater recirculation under variable load frequency regulation in thermal power units, including a deviation constraint pre-selection subsystem, a flow safety calculation subsystem, a local manual pre-selection subsystem, and a command generation and output subsystem; wherein: The deviation constraint pre-selection subsystem is used to collect two types of signals: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, it combines the deep adjustment trigger signal to perform parameter optimization and output the pre-selection correction signal. The flow safety accounting subsystem is used to collect the inlet flow of the unit's small unit, and then sequentially performs inertial filtering, multi-path function conversion, nested large and small value logic comparison, and change rate constraint calculation to output a safety compensation signal; The local manual pre-selection subsystem is based on the local control of the switching state of the bypass valve. It selects a value between the given value and a fixed constant and performs rate limiting processing to obtain the manual compensation signal. The instruction generation and output subsystem sums the safety compensation signal and the manual compensation signal, and combines them with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control instruction for the water supply recirculation bypass valve is generated.

[0026] The deviation constraint pre-selection subsystem of this invention generates a pre-selection correction signal based on multi-dimensional conditions such as flow deviation, valve interlocking, and deep adjustment triggering. It can correct control parameters in advance under extreme conditions such as abnormal feedwater interlocking and deep peak shaving. The flow safety calculation subsystem generates a safety compensation signal by combining the actual flow of the turbine with filtering, function conversion, limit screening, and rate constraint. It dynamically compensates the control quantity according to the real-time feedwater conditions of the unit, improving the rationality of recirculation valve opening and closing. The local manual operation pre-selection subsystem flexibly switches between manual input and fixed constant according to the local control switching status and performs speed limiting. The instruction generation and output subsystem integrates multi-path compensation signals to comprehensively calculate and output the final valve instruction. Under the conditions of unit load change and grid primary frequency regulation disturbance, it adaptively optimizes the recirculation bypass opening, controls the stability of feedwater flow, improves the reliability of the unit's primary frequency regulation response, and reduces equipment losses caused by frequent reciprocating actions of the bypass valve.

[0027] Specifically, the principle of the system of the present invention is as follows: The deviation between the water supply flow rate and the set value is large 1, which is connected to the first function module 7. The lockout steam pump recirculation bypass regulating valve 2, the first constant module 8, and the output terminal of the first function module 7 are respectively connected to the enable trigger terminal, Y terminal, and N terminal of the first switching module 10. The deviation between the water supply flow rate and the set value is large 1, which is connected to the second function module 9. The lockout steam pump recirculation bypass regulating valve 2, the first constant module 8, and the output terminal of the second function module 9 are respectively connected to the enable trigger terminal, Y terminal, and N terminal of the second switching module 11. The steam pump recirculation bypass regulating valve deep adjustment trigger 4, the output terminal of the first switching module 10, and the output terminal of the second switching module 11 are respectively connected to the enable trigger terminal, Y terminal, and N terminal of the third switching module 12. The inlet flow rate of the small turbine is connected to the first-order inertia module 13, and the output terminal of the first-order inertia module 13 is respectively connected to the third function module 16 and the fourth function module 17. The output terminals of the third function module 16 and the less than module 19 are both connected to the greater than module 18. The output terminals of the fourth function module 17 and the greater than module 18 are both connected to the less than module 19. The output terminal of the less than module 19 is connected to the first rate module 21. The steam pump recirculation bypass regulating valve control 6, the hand controller module 14, and the second constant module 15 are respectively connected to the enable trigger terminal, the Y terminal, and the N terminal of the fourth switching module 20. The output terminal of the fourth switching module 20 is connected to the second rate module 22. The output terminals of the first rate module 21 and the second rate module 22 are both connected to the summing module 23. The output terminals of the third switching module 12 and the summing module 23 are both connected to the control module 24. The output terminal of the control module 24 is connected to the fifth function module 25. The output terminal of the fifth function module 25 is connected to the feedwater recirculation bypass regulating valve command 26.

[0028] Specifically, the control method of the system of the present invention is as follows: The error message "The deviation between the water flow rate and the set value is greater than 1" is input to the first function module 7. After calculation by the function module, the output value is obtained.

[0029] The outputs of the lockout steam pump recirculation bypass control valve 2, the first constant module 8, and the first function module 7 are respectively input to the enable trigger terminal, the Y terminal, and the N terminal of the first switching module 10. When the lockout steam pump recirculation bypass control valve 2 is 1, the output of the first switching module 10 is the first constant module 8. When the lockout steam pump recirculation bypass control valve 2 is 0, the output of the first switching module 10 is the output value of the first function module 7.

[0030] The error message "The deviation between the water flow rate and the set value is greater than 1" is input to the second function module 9. After calculation by the function module, the output value is obtained.

[0031] The outputs of the lockout steam pump recirculation bypass control valve 2, the first constant module 8, and the second function module 9 are respectively input to the enable trigger terminal, Y terminal, and N terminal of the second switching module 11. When the lockout steam pump recirculation bypass control valve 2 is 1, the output of the second switching module 11 is the first constant module 8. When the lockout steam pump recirculation bypass control valve 2 is 0, the output of the second switching module 11 is the output value of the second function module 9.

[0032] The output terminals of the steam pump recirculation bypass valve deep adjustment trigger 4, the first switching module 10, and the second switching module 11 are respectively input to the enable trigger terminal, Y terminal, and N terminal of the third switching module 12. When the steam pump recirculation bypass valve deep adjustment trigger 4 is 1, the output of the third switching module 12 is the output value of the first switching module 10. When the steam pump recirculation bypass valve deep adjustment trigger 4 is 0, the output of the third switching module 12 is the output value of the second switching module 11.

[0033] The small machine's inlet flow rate 5 is input to the first-order inertial module 13, and the small machine's inlet flow rate 5 is calculated by the first-order inertial time module to obtain the output value.

[0034] The output value of the first-order inertial module 13 is input to the third function module 16 and the fourth function module 17 respectively. The output value of the first-order inertial module 13 is calculated by different function modules to obtain their respective output values.

[0035] The output of the third function module 16 and the output of the less than module 19 are both input to the greater than module 18. The output value of the third function module 16 and the output value of the less than module 19 are used as two input values ​​by the less than module, and the smaller value is selected and output.

[0036] The output of the fourth function module 17 and the output of the greater than module 18 are both connected to the less than module 19.

[0037] The output of module 19 is input to the first rate module 21. The output value of module 19 is calculated by the rate module to obtain the output value.

[0038] The steam pump recirculation bypass regulating valve control 6, the handheld device module 14, and the second constant module 15 are respectively input to the enable trigger terminal, Y terminal, and N terminal of the fourth switching module 20. When the steam pump recirculation bypass regulating valve control 6 is 1, the output of the fourth switching module 20 is the output value of the handheld device module 14. When the steam pump recirculation bypass regulating valve control 6 is 0, the output of the fourth switching module 20 is the second constant module 15.

[0039] The output of the fourth switching module 20 is input to the second rate module 22, and the output value of the fourth switching module 20 is calculated by the rate module to obtain the output value.

[0040] The outputs of the first rate module 21 and the second rate module 22 are both input to the summing module 23. The output values ​​of the first rate module 21 and the second rate module 22 are summed by the summing module to obtain the output value.

[0041] The output of the third switching module 12 and the output of the summing module 23 are both input to the control module 24, and the output value is obtained after calculation by the control module.

[0042] The output of the control module 24 is input to the fifth function module 25, and the output value of the control module 24 is calculated by the function module to obtain the output value.

[0043] The output of the fifth function module 25 is input to the water supply recirculation bypass regulating valve instruction 26.

[0044] The present invention also provides a control method for feedwater recirculation under variable load frequency regulation of thermal power units, comprising the following steps: Two types of signals are collected: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, the parameters are optimized in combination with the deep adjustment trigger signal, and a pre-selected correction signal is output. The inlet flow of the data acquisition unit is sequentially processed through inertial filtering, multi-path function conversion, nested large and small value logic comparison, and change rate constraint calculation, and outputs a safety compensation signal. Based on the local control switching state of the bypass valve, the manual compensation signal is obtained by selecting one of the two values ​​between the manually given value and the fixed constant and performing rate limiting processing. The safety compensation signal and the manual compensation signal are summed and combined with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control command for the water supply recirculation bypass valve is generated.

[0045] The present invention will be further described in detail below through specific embodiments.

[0046] like Figure 2 As shown, the present invention is applied to the unit operation control process.

[0047] Initial steady-state stage (approximately 0~50s): The unit is in rated operating condition, the grid frequency is stable at the rated value of 50.00Hz, the water supply system is operating normally according to the main water supply flow, the recirculation valve is in the closed state, and the water supply pump flow and outlet pressure are stable at the design value without any additional adjustment action.

[0048] Frequency regulation disturbance triggering stage (approximately 50-55 seconds): The grid frequency experiences a momentary step increase, reaching a peak of approximately 50.20 Hz, triggering the unit's primary frequency regulation response. At this time, the unit responds quickly to the grid frequency deviation, the turbine control valves operate rapidly, the main steam flow and boiler load change rapidly, and the feedwater flow fluctuates briefly. To prevent the feedwater pump flow from falling below the protection threshold, the feedwater recirculation valve opens rapidly, forming flow recirculation, resulting in a short-term spike in the corresponding frequency curve.

[0049] Steady-state maintenance phase after frequency regulation (approximately 55-180 seconds): After the recirculation valve opens, the feedwater pump flow stabilizes within the safe operating range, avoiding the risk of pump cavitation at low flow rates. The unit's primary frequency regulation becomes smoother, and the grid frequency drops and stabilizes in the 50.17-50.18Hz range, forming a plateau. During this phase, the feedwater recirculation valve maintains a certain opening to maintain the minimum safe flow of the feedwater pump. This, combined with the differential regulation process of the unit's primary frequency regulation, achieves flow balance between the boiler and turbine sides, preventing sudden changes in feedwater flow from impacting the boiler drum water level and main steam parameters.

[0050] Adjustment and recovery phase (approximately 180-220 seconds): As the grid frequency deviation gradually disappears, the unit's primary frequency regulation process ends, the main feedwater flow returns to normal levels, the feedwater recirculation valve gradually closes, and the feedwater pump flow and pressure return to rated operating conditions. The corresponding frequency curve shows a slow upward trend and tends to stabilize. Finally, the grid frequency returns to a stable range close to the rated value, the unit's feedwater system resumes normal operation, the recirculation valve is completely closed, and a complete feedwater recirculation regulation process under variable load frequency regulation conditions is completed.

[0051] In summary, this invention can relatively ensure the safe and stable operation of feedwater pumps in thermal power units under wide load variations and rapid frequency regulation, reduce energy consumption to a certain extent, improve frequency regulation performance, and meet the needs of thermal power units under the power system, thus having certain practical engineering significance.

[0052] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Anyone skilled in the art can readily implement the present invention according to the description and above. Any modifications, alterations, or equivalent variations made using the technical content disclosed above are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A control system for feedwater recirculation under variable load frequency regulation in a thermal power unit, characterized in that, It includes a deviation constraint pre-selection subsystem, a flow safety accounting subsystem, a local manual operation pre-selection subsystem, and an instruction generation and output subsystem; among which: The deviation constraint pre-selection subsystem is used to collect two types of signals: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, it combines the deep adjustment trigger signal to perform parameter optimization and output the pre-selection correction signal. The flow safety accounting subsystem is used to collect the inlet flow of the unit's small unit, and then sequentially performs inertial filtering, multi-path function conversion, nested large and small value logic comparison, and change rate constraint calculation to output a safety compensation signal; The local manual pre-selection subsystem is based on the local control of the switching state of the bypass valve. It selects a value between the given value and a fixed constant and performs rate limiting processing to obtain the manual compensation signal. The instruction generation and output subsystem sums the safety compensation signal and the manual compensation signal, and combines them with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control instruction for the water supply recirculation bypass valve is generated.

2. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 1, characterized in that, The deviation constraint pre-selection subsystem includes a large deviation between the feedwater flow rate and the set value (1), a lockout of the steam pump recirculation bypass valve (2), a first constant module (8), a first function module (7), a second function module (9), a first switching module (10), a second switching module (11), a deep adjustment trigger for the steam pump recirculation bypass valve (4), and a third switching module (12). The lockout of the steam pump recirculation bypass valve (2) serves as the selection control signal for the first switching module (10) and the second switching module (11). The first switching module (10) selects one output from the set value output by the first constant module (8) and the calculation result of the first function module (7). The second switching module (11) selects one output from the set value output by the first constant module (8) and the calculation result of the second function module (9). The deep adjustment trigger for the steam pump recirculation bypass valve (4) controls the third switching module (12) to obtain the pre-selected correction signal by selecting the best output between the first switching module (10) and the second switching module (11).

3. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 2, characterized in that, When the lockout steam pump recirculation bypass valve (2) outputs a valid signal, the first switching module (10) and the second switching module (11) both select the fixed value output of the first constant module (8); when the steam pump recirculation bypass valve deep adjustment trigger (4) is effectively triggered, the third switching module (12) selects the output of the first switching module (10), and when there is no trigger signal, the second switching module (11) is selected to output.

4. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 1, characterized in that, The flow safety calculation subsystem includes the small computer inlet flow (5), the first-order inertial module (13), the third function module (16), the fourth function module (17), the greater than module (18), the less than module (19), and the first rate module (21). The small computer inlet flow (5) is filtered by the first-order inertial module (13) and then sent to the third function module (16) and the fourth function module (17) in two paths. The two calculation results are successively filtered by the greater than module (18) and the less than module (19) and then sent to the first rate module (21) for rate constraint and output safety compensation signal.

5. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 1, characterized in that, The local manual pre-selection subsystem includes a steam pump recirculation bypass regulating valve control (6), a manual controller module (14), a second constant module (15), a fourth switching module (20), and a second rate module (22). The steam pump recirculation bypass regulating valve control (6) is the selection condition for the fourth switching module (20). The fourth switching module (20) selects between the output value of the manual controller module (14) and the set value of the second constant module (15). The output signal is limited by the second rate module (22) to form a manual compensation signal.

6. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 5, characterized in that, When the steam pump recirculation bypass regulating valve control (6) is effectively activated, the fourth switching module (20) selects the numerical output of the handheld device module (14); when the steam pump recirculation bypass regulating valve control (6) is not activated, the second constant module (15) selects the fixed numerical output.

7. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 1, characterized in that, The instruction generation and output subsystem includes an addition module (23), which is used to receive the security compensation signal and the manual compensation signal and perform the summation operation.

8. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 7, characterized in that, The instruction generation and output subsystem also includes a control module (24) and a fifth function module (25); the control module (24) receives the summation signal and the pre-selection correction signal output by the addition module (23) and completes the comprehensive control operation; the fifth function module (25) is used to receive the operation result of the control module (24) and perform the final function conversion.

9. The control system for feedwater recirculation under variable load frequency regulation of a thermal power unit according to claim 8, characterized in that, The instruction generation and output subsystem also includes a water recirculation bypass regulating valve instruction (26); the water recirculation bypass regulating valve instruction (26) generates the final regulating valve control instruction based on the conversion result of the fifth function module (25).

10. A control method for feedwater recirculation under variable load frequency regulation of a thermal power unit, implemented based on the control system for feedwater recirculation under variable load frequency regulation of a thermal power unit as described in any one of claims 1-9, characterized in that, Includes the following steps: Two types of signals are collected: flow deviation and regulating valve closing and interlocking. After two independent function operations and two-level channel switching selection, the parameters are optimized in combination with the deep adjustment trigger signal, and a pre-selected correction signal is output. The inlet flow of the data acquisition unit is sequentially processed through inertial filtering, multi-channel function conversion, nested large and small value logic comparison, and change rate constraint calculation, and outputs a safety compensation signal. Based on the local control switching state of the bypass valve, the manual compensation signal is obtained by selecting one of the two values ​​between the manually given value and the fixed constant and performing rate limiting processing. The safety compensation signal and the manual compensation signal are summed and combined with the pre-selected correction signal to complete the control logic operation. After final function conversion, the control command for the water supply recirculation bypass valve is generated.

Images