Valve cold nitrogen pressure stabilizing system and valve cold leakage detection method

Abstract

The invention discloses a valve cold nitrogen pressure stabilizing system and a valve cold leakage detection method. An aeration device is arranged at the inner bottom of an expansion tank, and an exhaust valve is arranged at the outer top of the expansion tank; the gas supplementing pipeline is connected with a gas supplementing buffer tank and a nitrogen making machine in series, a nitrogen valve is arranged between the gas supplementing buffer tank and the nitrogen making machine, and a gas supplementing valve is arranged between the gas supplementing buffer tank and the expansion tank; the aeration pipeline is connected between the air supply buffer tank and the aeration device and is provided with an aeration valve; the expansion tank and the air supply buffer tank are respectively provided with a pressure transmitter; the expansion tank is also provided with a dissolved oxygen transmitter and a liquid level transmitter; the controller cooperatively controls the start and stop of the nitrogen making machine and the opening and closing time sequence of each valve based on the multi-dimensional detection data; through the integrated design of the nitrogen making machine, multi-parameter cooperative control and dynamic leakage detection, the comprehensive technical problems of long-term voltage stabilization, online oxygen removal, maintenance-free and low false alarm of the offshore converter station valve cooling system are solved, and the reliability and the operation and maintenance economy of the system are remarkably improved.

Description

Technical Field

[0001] This invention relates to a valve-cooled nitrogen pressure stabilization system and a valve-cooled leakage detection method, belonging to the field of cooling technology for offshore flexible DC transmission converter valves. Background Technology

[0002] With the large-scale development of offshore wind power, unmanned operation has become a core requirement for the design of offshore converter stations. Currently, flexible DC transmission systems employ a closed-loop converter valve cooling system (hereinafter referred to as the valve cooling system), and its associated nitrogen pressure stabilization system exhibits significant technical limitations when adapting to the unique offshore operation and maintenance environment. Traditional nitrogen pressure stabilization systems rely on high-pressure cylinders for gas supply, resulting in reliability issues during operation and maintenance. Offshore converter stations are typically located more than 50 kilometers from land, and harsh sea conditions mean that maintenance vessels are available for less than 30% of the year. Existing systems only maintain nitrogen reserves for 2-3 months, leading to frequent cylinder replacements that increase annual maintenance costs by over 40% and fundamentally conflict with the unmanned operation principle. In particular, the system's online nitrogen deoxygenation function requires a continuous gas supply, and the limited storage capacity severely restricts its long-term effectiveness.

[0003] Secondly, the existing valve cooling system's judgment mechanism based on the expansion tank level is affected by changes in the expansion tank level caused by changes in the cooling medium temperature, resulting in a certain false alarm rate and rejection rate, which cannot meet the requirements of unmanned stations for fault self-diagnosis accuracy.

[0004] These technical bottlenecks severely restrict the reliability and maintenance-free operation of valve cooling systems in offshore converter stations, and urgently require optimization and improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a valve-cooled nitrogen pressure stabilization system and a valve-cooled leakage detection method. Through the integrated design of nitrogen generator gas supply, intelligent valve control and dynamic leakage detection, the technical problems of long-term pressure stabilization, online deoxygenation, maintenance-free operation and low false alarm operation of the valve-cooled system of offshore converter stations are solved, significantly improving the system reliability and operation and maintenance economy.

[0006] To achieve the above objectives / to solve the above technical problems, the present invention is implemented using the following technical solution: First aspect: A valve-cooled nitrogen pressure stabilization system, the system comprising: The expansion tank has an aeration device at the bottom and an exhaust valve at the top. The gas supply pipeline is connected in series with a gas supply buffer tank and a nitrogen generator. The nitrogen generator is an online nitrogen generator and serves as the main gas source for the system. A nitrogen valve is installed in the pipeline between the gas supply buffer tank and the nitrogen generator, and a gas supply valve is installed in the pipeline between the gas supply buffer tank and the expansion tank. The aeration pipeline connects the air replenishment buffer tank and the aeration device, and is equipped with an aeration valve; Both the expansion tank and the gas replenishment buffer tank are equipped with pressure transmitters; The expansion tank is also equipped with a dissolved oxygen transmitter and a liquid level transmitter; The controller is used to coordinate the start-up and shutdown of the nitrogen generator and the opening / closing sequence of the nitrogen valve, the nitrogen valve, the gas supply valve, the aeration valve and the exhaust valve based on multi-dimensional data collected from the pressure transmitters of the expansion tank, the dissolved oxygen transmitter, the liquid level transmitter and the pressure transmitter of the gas supply buffer tank.

[0007] Optionally, the gas supply line is connected to at least one backup gas supply branch. One end of the backup gas supply branch is connected to the gas supply buffer tank, and the other end is connected to a nitrogen cylinder. The backup gas supply branch serves as an emergency gas source in case of nitrogen generator failure.

[0008] Optionally, the backup gas supply branch is equipped with a gas supply branch valve. When the controller detects a malfunction in the nitrogen generator or nitrogen valve, it opens the gas supply branch valve to activate the backup gas supply branch.

[0009] Optionally, a one-way valve is provided on the pipeline between the aeration valve and the aeration device to prevent the cooling medium in the expansion tank from flowing back into the aeration pipeline.

[0010] Optionally, the output end of the expansion tank, the output end of the gas replenishment pipeline, and the exhaust valve are connected by a tee connector to realize an integrated pipeline for gas replenishment, exhaust, and cooling medium circulation.

[0011] Optionally, the air supply valve, exhaust valve, and aeration valve are all solenoid valves, and the controller controls the solenoid valves through pulse signals, with a switching response time of ≤0.5s.

[0012] Optionally, when the pressure in the gas replenishment buffer tank is lower than the preset gas replenishment value, the controller turns on the nitrogen generator to replenish gas into the gas replenishment buffer tank; when the pressure in the expansion tank is lower than the minimum preset value, the controller opens the gas replenishment valve to replenish gas into the expansion tank; when the pressure in the expansion tank is higher than the maximum preset value, the controller opens the exhaust valve to discharge the gas in the expansion tank. The timing sequence for the controller to start and stop the nitrogen generator is as follows: after the nitrogen generator is turned on, there is a first preset time delay, the nitrogen valve is opened, and when the pressure of the gas replenishment buffer tank reaches the upper limit of the preset gas replenishment value, the nitrogen valve is closed first and then the nitrogen generator is turned off; and during the period when the aeration valve is open, the controller controls the gas replenishment valve to remain in a normally closed state.

[0013] Optionally, when the oxygen content of the cooling medium in the expansion tank is higher than the aeration start preset, the controller opens the aeration valve and the exhaust valve, and charges nitrogen into the bottom aeration device in the expansion tank through the aeration pipeline; The control logic for the aeration operation is as follows: after continuous aeration for a second preset time value, the oxygen content of the cooling medium is detected. If it is still higher than the aeration start preset value, the aeration operation is repeated for a third preset time value until the oxygen content of the cooling medium is lower than the aeration stop preset value. Then, the controller closes the aeration valve and the exhaust valve to stop the aeration operation.

[0014] Optionally, the gas supply line, the backup gas supply branch, and the gas supply buffer tank are connected by a T-junction, and the gas supply branch valve of the backup gas supply branch is interlocked with the start / stop logic of the nitrogen generator. When the nitrogen generator is working normally, the gas supply branch valve remains closed.

[0015] Second aspect: A method for detecting valve cold leakage in a nitrogen pressure stabilization system as described in the first aspect, the method comprising: (a) The level transmitter acquires the liquid level measurement value of the expansion tank in real time. Inlet valve temperature and outlet valve temperature The data is input to the controller, which then establishes a multiple linear regression prediction model for the expansion tank level and the temperature of the medium at the inlet and outlet valves. (b) Based on the dynamic regression model and the multiple linear regression prediction model using a sliding time window, a dynamic leakage detection model is constructed, and the liquid level prediction function of the dynamic leakage detection model is updated in real time using the recursive least squares method: ; in: The predicted liquid level at step k; The constant term of the regression model at step k; : The inlet valve temperature coefficient at step k; : The outlet valve temperature coefficient at step k; The inlet valve temperature measurement value at step k; : The valve outlet temperature measurement value at step k; Regression coefficient Updated using the following recursive formula: ; in: The regression coefficient vector at step k; The Kalman gain matrix at step k; The covariance matrix at step k; The input feature vector at step k is defined as follows: λ: Forgetting factor, with a value range of 0.95 to 0.99; (c) Dynamically correcting the predicted liquid level using a Kalman filter, including: Equations of state: ,in This is the estimated value of the actual liquid level state at step k. This is process noise; Observation equation: ,in To observe noise; Iterative update of the corrected liquid level estimate ; (d) Calculate the liquid level residual And calculate the cumulative liquid level residual over 24 hours. ; (e) When the cumulative liquid level residual Exceeding the preset threshold of liquid level When this occurs, the controller triggers a leakage alarm signal.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: In the multi-functional nitrogen pressure stabilization system for offshore valve cooling of the present invention, a nitrogen generator replaces the previous gas replenishment technology that used nitrogen cylinders as the gas source. This avoids the maintenance operations of frequently replacing nitrogen cylinders and reduces the maintenance costs of nitrogen pressure stabilization when applied at sea. In the multi-functional nitrogen pressure stabilization system for offshore valve cooling of the present invention, since a nitrogen generator is used as the gas source, under the control of the controller on each valve, the medium in the expansion tank can be aerated with nitrogen online an unlimited number of times. This achieves the purpose of replacing oxygen in the medium with nitrogen, ensuring that the oxygen content of the cooling medium meets the operating requirements of the converter valve and improving the operating reliability of the converter valve. Attached Figure Description

[0017] Figure 1 The diagram shown is a schematic diagram of the pipeline layout of the valve-cooled multifunctional nitrogen pressure stabilizing system according to an embodiment of the present invention. Figure 2 The diagram shows a flowchart of the valve cold leakage detection method provided in an embodiment of the present invention.

[0018] In the diagram: 1—Expansion tank, 2—Maintenance gas pipeline, 3—Aeration pipeline, 4—Backup replenishment gas branch, 5—Maintenance gas buffer tank, 6—Nitrogen generator, 7—Nitrogen cylinder, 8—Maintenance gas valve, 9—Aeration valve, 10—Nitrogen valve, 11—Exhaust valve, 12—Maintenance gas branch valve, 13—Check valve, 14—Aeration device, 15—Dissolved oxygen transmitter, 16—Level transmitter, 17—Pressure transmitter. Detailed Implementation

[0019] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0020] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Example 1, such as Figure 1 As shown, a valve-cooled nitrogen pressure stabilizing system is disclosed, comprising: The expansion tank 1 has an aeration device 14 at the bottom of the tank for nitrogen aeration treatment and an exhaust valve 11 at the top of the tank. The gas supply line 2 is connected in series with the gas supply buffer tank 5 and the nitrogen generator 6. A nitrogen valve 10 is connected in series in the pipeline between the gas supply buffer tank 5 and the nitrogen generator 6. A gas supply valve 8 is connected in series in the pipeline between the gas supply buffer tank 5 and the expansion tank 1. The expansion tank 1, the gas supply line 2 and the exhaust valve 11 are connected by a tee.

[0023] Aeration pipeline 3 is connected between the aeration device 14 in the air replenishment buffer tank 5 and the expansion tank 1, and an aeration valve 9 is connected in series on it. Both the expansion tank 1 and the gas replenishment buffer tank 5 are equipped with pressure transmitters 17; The expansion tank is also equipped with a dissolved oxygen transmitter 15 and a level transmitter 16. The controller can control the opening and closing of various valves and the nitrogen generator; When the pressure in the gas replenishment buffer tank is lower than the preset gas replenishment value, the controller turns on the nitrogen generator to replenish gas into the gas replenishment buffer tank; when the pressure in the expansion tank is lower than the minimum preset value, the controller opens the gas replenishment valve to replenish gas into the expansion tank; when the pressure in the expansion tank is higher than the maximum preset value, the controller opens the exhaust valve to discharge the gas in the expansion tank.

[0024] The expansion tank 1 is used to introduce nitrogen gas and the cooling medium in the converter valve. The valve cooling multi-functional nitrogen pressure stabilization system of the present invention mainly changes the amount of nitrogen gas in the expansion tank 1 to keep the pressure in the expansion tank 1 within a certain range, thereby keeping the pressure of the cooling medium in the converter valve cooling system within a certain range.

[0025] In this embodiment, as Figure 1 As shown, at least one backup gas supply branch 4 is connected to the gas supply line 2 via a tee. The backup gas supply branch 4 is connected in series between the nitrogen cylinder 7 and the gas supply buffer tank 5. A gas supply branch valve 12 is installed in the backup gas supply branch 4. When the nitrogen generator 6 or the nitrogen valve 10 fails to supply gas, gas is supplied to the gas supply buffer tank 5 through the backup gas supply branch 4 to ensure the normal operation of the valve-cooled multi-functional nitrogen pressure stabilizing system, while also allowing time for the maintenance of the nitrogen generator 6.

[0026] In this embodiment, as Figure 1 As shown, the aeration pipeline 3 is connected between the aeration device 14 in the air replenishment buffer tank 5 and the expansion tank 1. An aeration valve 9 and a one-way valve 13 are connected in series in the aeration pipeline 3. The one-way valve 13 is used to prevent the medium in the expansion tank 1 from flowing back into the air path and causing damage to the related components in the air path.

[0027] In this embodiment, when the pressure of the gas replenishment buffer tank is lower than the preset gas replenishment value, the controller turns on the nitrogen generator to replenish gas into the gas replenishment buffer tank; when the pressure of the expansion tank is lower than the minimum preset value, the controller opens the gas replenishment valve to replenish gas into the expansion tank; when the pressure of the expansion tank is higher than the maximum preset value, the controller opens the exhaust valve to discharge the gas in the expansion tank. The controller controls the nitrogen generator's start-up and shutdown sequence as follows: after starting the nitrogen generator, there is a first preset time delay, approximately 30 seconds, then the nitrogen valve is opened. When the pressure in the gas replenishment buffer tank reaches the upper limit of the preset gas replenishment value, the nitrogen valve is closed first, followed by the nitrogen generator. Furthermore, during the opening of the aeration valve, the controller keeps the gas replenishment valve normally closed. When the oxygen content of the cooling medium in the expansion tank is higher than the preset aeration start value, the controller opens the aeration valve and the exhaust valve, injecting nitrogen into the bottom aeration device in the expansion tank through the aeration pipeline. The control logic for the aeration operation is as follows: continuous aeration for a second preset time value, approximately 2 minutes, then detecting the oxygen content of the cooling medium. If it is still higher than the aeration start preset value, then delay for a third preset time value, approximately 1 minute, and repeat the aeration operation until the oxygen content of the cooling medium is lower than the aeration stop preset value. At this point, the controller closes the aeration valve and the exhaust valve to stop the aeration operation.

[0028] Optionally, the gas supply line, the backup gas supply branch, and the gas supply buffer tank are connected by a T-junction, and the gas supply branch valve of the backup gas supply branch is interlocked with the start / stop logic of the nitrogen generator. When the nitrogen generator is working normally, the gas supply branch valve remains closed.

[0029] In the specific working process of the valve-cooled multi-functional nitrogen pressure stabilizing system, such as... Figure 1 As shown, when the pressure of the gas replenishment buffer tank 5 is lower than the preset value A+0.13MPa, the controller turns on the nitrogen generator 6, and after a delay of 30s, opens the nitrogen valve 10 to replenish gas into the gas replenishment buffer tank 5 until the pressure of the gas replenishment buffer tank 5 reaches the preset value A+0.33MPa. Then, the nitrogen valve 10 is closed first, and then the nitrogen generator 6 is turned off.

[0030] In this embodiment, as Figure 1 As shown, when the pressure of expansion tank 1 is lower than the preset value A-0.03MPa, the controller opens the gas supply valve 8 to supply gas into expansion tank 1 until the pressure of expansion tank 1 reaches the preset value A-0.02MPa, and then closes the gas supply valve 8 to stop supplying gas; when the pressure of expansion tank 1 is higher than the preset value A+0.03MPa, the controller opens the exhaust valve 11 to discharge the gas in expansion tank 1 until the pressure of expansion tank 1 reaches the preset value A+0.02MPa, and then closes the exhaust valve 11 to stop venting.

[0031] In this embodiment, as Figure 1 As shown, expansion tank 1 is equipped with dissolved oxygen transmitter 15. When the oxygen content of the cooling medium in expansion tank 1 is higher than the preset value B, the controller opens aeration valve 9 and exhaust valve 11, and nitrogen is introduced into the bottom aeration device 14 in expansion tank 1 through aeration pipeline 3 for 2 minutes. If the oxygen content of the cooling medium is still higher than the preset value B, the above operation is repeated after a delay of 1 minute until the oxygen content is lower than the preset value C. Then the controller closes aeration valve 9 and exhaust valve 11 to stop the aeration operation. During the aeration process, the replenishment valve 8 is always in the normally closed state.

[0032] Example 2, the present invention also discloses a valve cold leakage detection method based on the nitrogen pressure stabilization system described in Example 1, the method comprising: as follows Figure 1 As shown, expansion tank 1 is equipped with a level transmitter 16. When the level transmitter 16 on expansion tank 1 detects the liquid level in the tank in real time, it sends the data to the controller. The controller establishes a relationship between the liquid level of expansion tank 1 and the temperature of the medium at the inlet and outlet valves (…). Figure 1A multiple linear regression prediction model (not shown) is used, combined with a sliding time window and Kalman filtering algorithm, to construct a dynamic leakage detection model, providing a highly reliable leakage monitoring method for offshore valve cooling systems. The specific prediction function and steps are as follows: (a) Real-time acquisition of liquid level measurement values ​​in expansion tank 1 Inlet valve temperature and outlet valve temperature And input it to the controller; (b) Based on a dynamic regression model with a sliding time window of 15–30 min, the liquid level prediction function is updated in real time using the recursive least squares method: ; Among them, regression coefficients Updated using the following recursive formula: ; in For the input feature vector, Let λ be the Kalman gain matrix, and λ be the forgetting factor (usually taken as 0.95~0.99). Let be the covariance matrix.

[0033] (c) Dynamically correcting the predicted liquid level using a Kalman filter, including: State equations (also describing dynamic changes): ,in This refers to process noise (such as mechanical vibration). Observation equation (regression model predicted value): ,in For observation noise (such as sensor error); Iterative update of the corrected liquid level estimate ; (d) Calculate the liquid level residual And calculate the cumulative liquid level residual over 24 hours. ; (e) When the cumulative liquid level residual Exceeding the preset threshold of liquid level When this occurs, the controller triggers a leakage alarm signal.

[0034] Using the liquid level prediction curve of expansion tank 1, the liquid level residual is calculated at a frequency of once every 3 minutes. If the cumulative liquid level residual of 480 data points in 24 hours exceeds the preset value, a leakage alarm message of the valve cooling system is issued to remind the operation and maintenance personnel.

[0035] In the above-mentioned valve-cooled multifunctional nitrogen pressure stabilizing system, it should be noted that all valves except the one-way valve 13 in the aeration pipeline 3 are solenoid valves, so as to facilitate the controller to control the solenoid valves and realize the automatic control of the valve-cooled multifunctional nitrogen pressure stabilizing system.

[0036] The valve-cooled multifunctional nitrogen pressure stabilization system in this embodiment uses a nitrogen generator 6 as the pressure stabilization and aeration gas source. Under the control of the controller, it realizes nitrogen pressure stabilization and online aeration deoxygenation functions. This not only meets the requirements of long-term stable operation of the valve-cooled system for system pressure stabilization and dissolved oxygen in the medium, but also avoids frequent operation and maintenance of the pressure stabilization system, reducing the operation and maintenance costs of nitrogen pressure stabilization when applied at sea. At the same time, the controller effectively separates the actual liquid level change from measurement noise through the synergy of dynamic regression model and Kalman filtering, improving the leakage detection sensitivity. The sliding window mechanism and recursive least squares method enable real-time updating of model parameters, adapting to temperature fluctuations and equipment aging, significantly reducing the false alarm rate and rejection rate, and providing a highly reliable leakage monitoring solution for offshore valve-cooled systems.

[0037] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A valve-cooled nitrogen pressure stabilization system, characterized in that, The system includes: The expansion tank has an aeration device at the bottom and an exhaust valve at the top. The gas supply pipeline is connected in series with a gas supply buffer tank and a nitrogen generator. The nitrogen generator is an online nitrogen generator and serves as the main gas source for the system. A nitrogen valve is installed in the pipeline between the gas supply buffer tank and the nitrogen generator, and a gas supply valve is installed in the pipeline between the gas supply buffer tank and the expansion tank. The aeration pipeline connects the air replenishment buffer tank and the aeration device, and is equipped with an aeration valve; Both the expansion tank and the gas replenishment buffer tank are equipped with pressure transmitters; The expansion tank is also equipped with a dissolved oxygen transmitter and a liquid level transmitter; The controller is used to coordinate the start-up and shutdown of the nitrogen generator and the opening / closing sequence of the nitrogen valve, the nitrogen valve, the gas supply valve, the aeration valve and the exhaust valve based on multi-dimensional data collected from the pressure transmitters of the expansion tank, the dissolved oxygen transmitter, the liquid level transmitter and the pressure transmitter of the gas supply buffer tank.

2. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, The gas supply line is connected to at least one backup gas supply branch. One end of the backup gas supply branch is connected to the gas supply buffer tank, and the other end is connected to a nitrogen cylinder. The backup gas supply branch serves as an emergency gas source in case of nitrogen generator failure.

3. The valve-cooled nitrogen pressure stabilizing system according to claim 2, characterized in that, The backup gas supply branch is equipped with a gas supply branch valve. When the controller detects a malfunction in the nitrogen generator or nitrogen valve, it opens the gas supply branch valve to activate the backup gas supply branch.

4. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, A one-way valve is installed on the pipeline between the aeration valve and the aeration device to prevent the cooling medium in the expansion tank from flowing back into the aeration pipeline.

5. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, The output end of the expansion tank, the output end of the gas replenishment pipeline, and the exhaust valve are connected by a tee connector to realize an integrated pipeline for gas replenishment, exhaust, and cooling medium circulation.

6. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, The air supply valve, air exhaust valve, and aeration valve are all solenoid valves. The controller controls the solenoid valves via pulse signals, and the switching response time is ≤0.5s.

7. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, When the pressure in the gas replenishment buffer tank is lower than the preset gas replenishment value, the controller turns on the nitrogen generator to replenish gas into the gas replenishment buffer tank; when the pressure in the expansion tank is lower than the minimum preset value, the controller opens the gas replenishment valve to replenish gas into the expansion tank; when the pressure in the expansion tank is higher than the maximum preset value, the controller opens the exhaust valve to discharge the gas in the expansion tank. The timing sequence for the controller to start and stop the nitrogen generator is as follows: after the nitrogen generator is turned on, there is a first preset time delay, the nitrogen valve is opened, and when the pressure of the gas replenishment buffer tank reaches the upper limit of the preset gas replenishment value, the nitrogen valve is closed first and then the nitrogen generator is turned off; and during the period when the aeration valve is open, the controller controls the gas replenishment valve to remain in a normally closed state.

8. The valve-cooled nitrogen pressure stabilizing system according to claim 1, characterized in that, When the oxygen content of the cooling medium in the expansion tank is higher than the aeration start preset, the controller opens the aeration valve and the exhaust valve, and charges nitrogen into the bottom aeration device in the expansion tank through the aeration pipeline. The control logic for the aeration operation is as follows: after continuous aeration for a second preset time value, the oxygen content of the cooling medium is detected. If it is still higher than the aeration start preset value, the aeration operation is repeated for a third preset time value until the oxygen content of the cooling medium is lower than the aeration stop preset value. Then, the controller closes the aeration valve and the exhaust valve to stop the aeration operation.

9. The valve-cooled nitrogen pressure stabilizing system according to claim 2, characterized in that, The gas supply line, the backup gas supply branch, and the gas supply buffer tank are connected by a T-junction, and the gas supply branch valve of the backup gas supply branch is interlocked with the start / stop logic of the nitrogen generator. When the nitrogen generator is working normally, the gas supply branch valve remains closed.

10. A method for detecting valve cold leakage in a nitrogen pressure stabilizing system according to any one of claims 1-9, characterized in that, The method includes: (a) The level transmitter acquires the liquid level measurement value of the expansion tank in real time. Inlet valve temperature and outlet valve temperature The data is input to the controller, which then establishes a multiple linear regression prediction model for the expansion tank level and the temperature of the medium at the inlet and outlet valves. (b) Based on the dynamic regression model and the multiple linear regression prediction model using a sliding time window, a dynamic leakage detection model is constructed, and the liquid level prediction function of the dynamic leakage detection model is updated in real time using the recursive least squares method: ; in: The predicted liquid level at step k; The constant term of the regression model at step k; : The inlet valve temperature coefficient at step k; : The outlet valve temperature coefficient at step k; The inlet valve temperature measurement value at step k; : The valve outlet temperature measurement value at step k; Regression coefficient Updated using the following recursive formula: ； in: The regression coefficient vector at step k; The Kalman gain matrix at step k; The covariance matrix at step k; The input feature vector at step k is defined as follows: ; λ: Forgetting factor, with a value range of 0.95 to 0.99; (c) Dynamically correcting the predicted liquid level using a Kalman filter, including: Equations of state: ,in This is the estimated value of the actual liquid level state at step k. This refers to process noise (such as mechanical vibration). Observation equation: ,in To observe noise; Iterative update of the corrected liquid level estimate ; (d) Calculate the liquid level residual And calculate the cumulative liquid level residual over 24 hours. ; (e) When the cumulative liquid level residual Exceeding the preset threshold of liquid level When this occurs, the controller triggers a leakage alarm signal.

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