LNG pump pressure regulating system based on PID control algorithm and control method

Abstract

The invention relates to an LNG (Liquefied Natural Gas) pump pressure regulating system based on a PID (Proportion Integration Differentiation) control algorithm. The LNG pump pressure regulating system comprises a pump rear pressure sensor, a pump front pressure sensor, an immersed pump, a pump liquid level sensor, an LNG storage tank, a storage tank pressure sensor, a storage tank liquid level sensor, a gas dispenser and a PID controller. The invention further relates to a control method of the LNG pump pressure regulating system based on the PID control algorithm. Pressure changes can be responded in real time, and it is guaranteed that after-pumping pressure rapidly returns to a set value; the post-pumping pressure is accurately controlled, and steady-state errors are eliminated; meanwhile, complex working conditions such as flow change and pipeline resistance change can be automatically adapted, and the post-pumping pressure is kept stable; and the rotating speed of the pump can be accurately controlled, so that energy consumption is effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of pressure regulation technology in the transportation and storage of liquefied natural gas (LNG), specifically to an LNG pump pressure regulation system and control method based on a PID control algorithm. Background Technology

[0002] Pumps are one of the key pieces of equipment in the storage and transportation of LNG, and they typically need to operate stably under high pressure. To ensure the safe and efficient transportation of LNG, the pump's output pressure needs to be maintained at a stable value. However, due to factors such as pipeline resistance and changes in external temperature, the pressure after the pump may fluctuate, and traditional pressure regulation methods cannot meet the requirements for precise control. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an LNG pump pressure regulation system and control method based on a PID control algorithm. Its purpose is to respond to pressure changes in real time, ensuring the downstream pressure quickly returns to the set value; to precisely control the downstream pressure and eliminate steady-state errors; to automatically adapt to complex operating conditions such as changes in flow rate and pipeline resistance, maintaining stable downstream pressure; and to precisely control the pump speed, effectively reducing energy consumption.

[0004] To solve the above problems, the technical solution provided by the present invention is as follows: An LNG pump pressure regulating system based on a PID control algorithm includes a downstream pressure sensor, a upstream pressure sensor, a submersible pump, a pump level sensor, an LNG storage tank, a storage tank pressure sensor, a storage tank level sensor, a gas dispenser, and a PID controller, wherein: The submersible pump is equipped with a front-end pressure sensor and a rear-end pressure sensor, respectively; a pump level sensor is installed on the submersible pump; a tank pressure sensor and a tank level sensor are installed on the LNG storage tank; the submersible pump is connected to the gas dispenser and the LNG storage tank via pipelines; the PID controller is electrically coupled to the front-end pressure sensor, the rear-end pressure sensor, the pump level sensor, the tank pressure sensor, the tank level sensor, and the submersible pump speed control system; the PID controller has a built-in single-neuron PID control algorithm for adjusting the submersible pump speed.

[0005] Preferably, the pre-pump pressure sensor, the post-pump pressure sensor, and the storage tank pressure sensor are PDS800H series pressure transmitters.

[0006] A control method for an LNG pump pressure regulating system utilizing the aforementioned PID control algorithm includes the following steps: S100. During the first scan cycle of the system, the system parameters are initialized, expressed as follows: in: The scanning period is used to characterize the system; The control signal used to characterize the submersible pump in the k-th scan cycle; Used to characterize the connection weight coefficients; S200. Determine whether the current pump pool level has reached the manually preset level threshold, and then perform the following operations based on the determination result: If the determination result is that the current liquid level in the pump pool has reached the liquid level threshold, then step S300 is executed; If the determination result is that the current liquid level in the pump pool has not reached the liquid level threshold, then step S800 is executed; S300. Replace the set value of the post-pump pressure in the current scan cycle with the set value of the post-pump pressure in the next scan cycle; the system enters the next scan cycle; the value of the current scan cycle is incremented by 1; S400. Using a step-by-step method, the pressure adjustment process of the current scanning cycle is divided into a preset number of steps, expressed as follows: in: Used to characterize step size; The set value used to characterize the post-pump pressure in the kth scan cycle; n is used to indicate the number of steps; S500. Increase the set value of the post-pump pressure in the current scan cycle by one step, expressed as follows: S600. The set rotational speed of the submersible pump is calculated based on the set value of the post-pump pressure of the current scanning cycle obtained in step S500, and is expressed by the following formula: in: Used to characterize the set rotational speed of the submersible pump; Used to characterize the speed distribution ratio of a submersible pump; Used to characterize the liquid level in the pump pool; Used to characterize stress factors; S700. The actual speed of the submersible pump is adjusted using the single-neuron PID algorithm described above; S800. Determine whether there is a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, and then perform the following operations based on the determination result: If the determination result is that there is a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then step S600 is executed. If the determination result indicates that there is no deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then proceed to step S900; S900. Determine whether the current actual set value of the pump downstream pressure is equal to the actual value of the pump downstream pressure, and then perform the following operation based on the determination result: If the determination result is that the current actual set value of the pump post-pressure is not equal to the actual value of the pump post-pressure, then step S500 is executed. If the determination result is that the current actual set value of the pump post-pressure is equal to the actual value of the pump post-pressure, then step S1000 is executed. S1000. Determine whether the system pressure regulation operation has ended, and then perform the following operations based on the determination result: If the judgment result is that the system pressure regulation operation has not been completed, then proceed to step S200; If the judgment result indicates that the system voltage regulation operation has been completed, the system will exit.

[0007] Preferably, the single-neuron PID algorithm in step S700 is expressed by the following formula: in: The proportionality coefficient used to characterize neurons, and >0; Used to characterize the differential learning rate; Used to characterize the proportional learning rate; Used to characterize the integral learning rate; Signal error used to characterize submersible pumps; The minimum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range. The maximum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range. The signal error of the submersible pump is expressed by the following formula: in: Used to characterize the set rotational speed of the submersible pump; Used to characterize the actual rotational speed of the submersible pump.

[0008] Preferably, the differential learning rate is obtained by self-tuning, specifically within the range of 1.2 to 1.9.

[0009] Preferably, the proportional learning rate is obtained by self-tuning adjustment, specifically in the range of 0.8 to 1.0.

[0010] Preferably, the integral learning rate is obtained by self-tuning adjustment, specifically within the range of 0.03 to 0.5.

[0011] Preferably, the set value of the pump post-pressure is 1.4 MPa.

[0012] Preferably, the number of steps in step S400 is 10.

[0013] Compared with the prior art, the present invention has the following advantages: This invention utilizes a high-precision pressure sensor and a PID controller with a built-in PID control algorithm to respond to pressure changes in real time and ensure that the pressure after the pump quickly returns to the set value.

[0014] This invention enables the system to precisely control the pump post-pump pressure and eliminate steady-state errors through PID control.

[0015] The system of the present invention can automatically adapt to complex operating conditions such as changes in flow rate and changes in pipeline resistance, and maintain stable pressure after the pump.

[0016] This invention achieves precise control of pump speed through a PID control algorithm, thereby effectively reducing energy consumption. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an LNG pump pressure regulating system based on a PID control algorithm, according to a specific embodiment of the present invention.

[0018] The components include: 1. Post-pump pressure sensor, 2. Pre-pump pressure sensor, 3. Submersible pump, 4. Pump level sensor, 5. LNG storage tank, 6. Tank pressure sensor, 7. Tank level sensor, 8. Gas dispenser, and 9. PID controller. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0020] This invention application claims protection for an LNG pump pressure regulating system based on a PID control algorithm, such as... Figure 1 As shown, the system includes a downstream pressure sensor 1, a upstream pressure sensor 2, a submersible pump 3, a pump level sensor 4, an LNG storage tank 5, a storage tank pressure sensor 6, a storage tank level sensor 7, a gas dispenser 8, and a PID controller 9, wherein: The submersible pump 3 is equipped with a front-end pressure sensor 2 and a rear-end pressure sensor 1, respectively; a pump level sensor 4 is installed on the submersible pump 3; a tank pressure sensor 6 and a tank level sensor 7 are installed on the LNG storage tank 5; the submersible pump 3 is connected to the gas dispenser 8 and the LNG storage tank 5 through pipelines; the PID controller 9 is electrically coupled to the front-end pressure sensor 2, the rear-end pressure sensor 1, the pump level sensor 4, the tank pressure sensor 6, the tank level sensor 7, and the speed control system of the submersible pump 3; the PID controller 9 has a built-in single-neuron PID control algorithm for adjusting the speed of the submersible pump 3.

[0021] In this specific embodiment, the pre-pump pressure sensor 2, post-pump pressure sensor 1, and storage tank pressure sensor 6 are all PDS800H series pressure transmitters.

[0022] It should be noted that this invention uses a high-precision pressure sensor to monitor the pressure of the submersible pump 3 in real time and transmits the real-time pressure data to the PID controller 9. The PID controller 9 is connected to the speed control system of the submersible pump 3 and adjusts the speed of the submersible pump 3 based on the pressure data.

[0023] A control method for an LNG pump pressure regulating system utilizing a PID control algorithm includes the following steps: S100. During the first scan cycle of the system, the system parameters are initialized as shown in Equation 1: (1) in: Used to characterize the scanning cycle of the system; The control signal used to characterize the submersible pump in the k-th scan cycle; Used to characterize the connection weight coefficients.

[0024] S200. Determine whether the current pump pool level has reached the manually preset level threshold, and then perform the following operations based on the determination result: If the determination result is that the current pump pool liquid level has reached the liquid level threshold, then proceed to step S300.

[0025] If the judgment result is that the current pump pool liquid level has not reached the liquid level threshold, then step S800 is executed.

[0026] S300. Replace the set value of the pump post-pressure in the current scan cycle with the set value of the pump post-pressure in the next scan cycle; the system enters the next scan cycle; the value of the current scan cycle is incremented by 1.

[0027] S400. Using a step-by-step method, the pressure adjustment process of the current scanning cycle is divided into a preset number of steps, expressed as follows: (2) in: Used to characterize step size; The set value used to characterize the post-pump pressure in the k-th scan cycle; n is used to indicate the number of steps.

[0028] S500. Increase the set value of the post-pump pressure for the current scan cycle by one step, expressed as follows: (3) S600. The set rotational speed of the submersible pump is calculated based on the set value of the post-pump pressure of the current scanning cycle obtained in step S500, and is expressed by the following formula 4: (4) in: Used to characterize the set speed of the submersible pump; Used to characterize the speed distribution ratio of a submersible pump; Used to characterize the liquid level in the pump pool; Used to characterize stress factors.

[0029] The S700 uses a single-neuron PID algorithm to adjust the actual speed of the submersible pump.

[0030] S800. Determine if there is a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, and then perform the following operations based on the determination result: If the judgment result indicates a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then proceed to step S600.

[0031] If the determination result indicates that there is no deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then proceed to step S900; S900. Determine whether the current actual downstream pressure setpoint is equal to the actual downstream pressure value, and then perform the following operations based on the determination result: If the judgment result is that the current actual pump post-pressure setting value is not equal to the actual pump post-pressure value, then execute step S500.

[0032] If the judgment result is that the current actual pump post-pressure setting value is equal to the actual pump post-pressure value, then proceed to step S1000.

[0033] S1000. Determine whether the system pressure regulation operation has ended, and then perform the following operations based on the determination result: If the judgment result is that the system pressure regulation operation has not been completed, then proceed to step S200.

[0034] If the judgment result indicates that the system voltage regulation operation has been completed, the system will exit.

[0035] It should be noted that the single-neuron PID algorithm in step S700 is expressed by equations 5, 6, and 7: (5) (6) (7) in: The proportionality coefficient used to characterize neurons, and >0; Used to characterize the differential learning rate; Used to characterize the proportional learning rate; Used to characterize the integral learning rate; Signal error used to characterize submersible pumps; The minimum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range. The maximum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range.

[0036] The signal error of the submersible pump is expressed by the following formula 8: (8) in: Used to characterize the set speed of the submersible pump; Used to characterize the actual rotational speed of a submersible pump.

[0037] In this specific embodiment, the set value of the downstream pressure is 1.4 MPa.

[0038] It should be noted that the single-neuron PID control algorithm directly affects the rotational speed of submersible pump 3. By adjusting the rotational speed of submersible pump 3, the flow rate and output pressure can be controlled. When the downstream pressure approaches the set value, the PID controller 9 reduces the control input, thereby maintaining the downstream pressure near the set value of 1.4 MPa. The control objective of the LNG pressure regulating PID control algorithm is the submersible pump rotational speed; when the submersible pump rotational speed reaches the set value from the actual value, the downstream pressure also reaches the set value from the actual value.

[0039] It should be noted that the derivative control section considers the rate of error change and can predict the trend of error change, thereby adjusting the pump speed to prevent over-adjustment or system oscillation. Through derivative gain, the PID controller 9 can accurately control the pump's response speed, avoiding overshoot or oscillation.

[0040] In this specific embodiment, the differential learning rate is obtained by self-tuning adjustment, and the specific range is 1.2~1.9.

[0041] It should be noted that the proportional control section determines the adjustment amount of the pump speed based on the magnitude of the error. When there is a large error between the pump outlet pressure and the set value, the PID controller 9 will quickly adjust the pump speed to ensure that the pressure rapidly approaches the set value of 1.4 MPa.

[0042] In this specific embodiment, the proportional learning rate is obtained by self-tuning adjustment, and the specific range is 0.8~1.0.

[0043] It should be noted that integral control is used to eliminate steady-state errors in the system. Even if the pressure deviates from the set value for a long period, the integral component will accumulate errors and gradually correct the pump speed. By using an appropriate integral gain, steady-state errors can be eliminated, ensuring long-term stability of the downstream pressure.

[0044] In this specific embodiment, the integral learning rate is obtained by self-tuning adjustment, and the specific range is 0.03~0.5.

[0045] In this specific embodiment, the number of steps in step S400 is 10.

[0046] In this specific embodiment, the scan period is set to 300ms.

[0047] It should be noted that, in order to improve the system's stability and response speed, the three parameters of the PID controller 9—derivative learning rate, integral learning rate, and proportional learning rate—need to be optimized according to specific operating conditions. This can be achieved through experimental or algorithmic tuning methods, such as the Ziegler-Nichols method or genetic algorithms, to obtain the best control performance.

[0048] It should be noted that this system is not limited to regulating a single pump; it can also work in conjunction with other equipment (such as valves and coolers) in LNG storage and transportation systems to form a complete automated control network. The PID control algorithm, combined with other control strategies (such as feedforward control and adaptive control), can maintain stable pressure regulation in complex fluid dynamic environments.

[0049] It should be noted that, taking the LNG pump system as an example, the downstream pressure needs to be precisely controlled at 1.4 MPa during the transportation of liquefied natural gas. The system uses a PID controller to dynamically adjust the pump speed based on real-time pressure feedback signals. For example, when the flow rate of liquefied natural gas changes or pipeline resistance increases, the PID control system will automatically increase the pump speed to compensate for the pressure drop, ensuring that the downstream pressure remains at the set value of 1.4 MPa.

[0050] In the detailed description above, various features are combined together in a single embodiment to simplify this disclosure. This approach to disclosure should not be construed as reflecting an intention that embodiments of the claimed subject matter require more features than are explicitly stated in each claim. Rather, as reflected in the appended claims, the invention is presented with fewer features than all of the features in a single disclosed embodiment. Therefore, the appended claims are hereby explicitly incorporated into the detailed description, with each claim representing a separate preferred embodiment of the invention.

[0051] The disclosed embodiments have been described above to enable any person skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the spirit and scope of this disclosure. Therefore, this disclosure is not limited to the embodiments given herein, but is consistent with the broadest scope of the principles and novel features disclosed in this application.

[0052] The foregoing description includes examples of one or more embodiments. It is certainly impossible to describe all possible combinations of components or methods in order to describe the above embodiments, but those skilled in the art will recognize that further combinations and arrangements of the various embodiments are possible. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

[0053] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An LNG pump pressure regulating system based on a PID control algorithm, characterized in that: Includes a post-pump pressure sensor (1), a pre-pump pressure sensor (2), a submersible pump (3), a pump level sensor (4), an LNG storage tank (5), a storage tank pressure sensor (6), a storage tank level sensor (7), a gas dispenser (8), and a PID controller (9), wherein: The front and rear ends of the submersible pump (3) are respectively equipped with the pump front pressure sensor (2) and the pump rear pressure sensor (1); the submersible pump (3) is equipped with the pump level sensor (4); the LNG storage tank (5) is equipped with the storage tank pressure sensor (6) and the storage tank level sensor (7); the submersible pump (3) is connected to the gas dispenser (8) and the LNG storage tank (5) through pipelines; the PID controller (9) is electrically coupled to the pump front pressure sensor (2), the pump rear pressure sensor (1), the pump level sensor (4), the storage tank pressure sensor (6), the storage tank level sensor (7), and the speed control system of the submersible pump (3); the PID controller (9) has a built-in single-neuron PID control algorithm for adjusting the speed of the submersible pump (3).

2. The LNG pump pressure regulating system based on PID control algorithm according to claim 1, characterized in that: The pressure sensor (2) before the pump, the pressure sensor (1) after the pump, and the pressure sensor (6) of the storage tank adopt the PDS800H series pressure transmitter.

3. A control method for an LNG pump pressure regulating system based on the PID control algorithm as described in claim 1, characterized in that: Includes the following steps: S100. During the first scan cycle of the system, the system parameters are initialized, expressed as follows: in: The scanning period is used to characterize the system; The control signal used to characterize the submersible pump in the k-th scan cycle; Used to characterize the connection weight coefficients; S200. Determine whether the current pump pool level has reached the manually preset level threshold, and then perform the following operations based on the determination result: If the determination result is that the current liquid level in the pump pool has reached the liquid level threshold, then step S300 is executed; If the determination result is that the current liquid level in the pump pool has not reached the liquid level threshold, then step S800 is executed; S300. Replace the set value of the post-pump pressure in the current scan cycle with the set value of the post-pump pressure in the next scan cycle; the system enters the next scan cycle; the value of the current scan cycle is incremented by 1; S400. Using a step-by-step method, the pressure adjustment process of the current scanning cycle is divided into a preset number of steps, expressed as follows: in: Used to characterize step size; The set value used to characterize the post-pump pressure in the kth scan cycle; n is used to indicate the number of steps; S500. Increase the set value of the post-pump pressure in the current scan cycle by one step, expressed as follows: S600. The set rotational speed of the submersible pump is calculated based on the set value of the post-pump pressure of the current scanning cycle obtained in step S500, and is expressed by the following formula: in: Used to characterize the set rotational speed of the submersible pump; Used to characterize the speed distribution ratio of a submersible pump; Used to characterize the liquid level in the pump pool; Used to characterize stress factors; S700. The actual speed of the submersible pump is adjusted using the single-neuron PID algorithm described above; S800. Determine whether there is a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, and then perform the following operations based on the determination result: If the determination result is that there is a deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then step S600 is executed. If the determination result indicates that there is no deviation between the set speed of the submersible pump and the actual speed of the submersible pump, then proceed to step S900; S900. Determine whether the current actual set value of the pump downstream pressure is equal to the actual value of the pump downstream pressure, and then perform the following operation based on the determination result: If the determination result is that the current actual set value of the pump post-pressure is not equal to the actual value of the pump post-pressure, then step S500 is executed. If the determination result is that the current actual set value of the pump post-pressure is equal to the actual value of the pump post-pressure, then step S1000 is executed. S1000. Determine whether the system pressure regulation operation has ended, and then perform the following operations based on the determination result: If the judgment result is that the system pressure regulation operation has not been completed, then proceed to step S200; If the judgment result indicates that the system voltage regulation operation has been completed, the system will exit.

4. The control method according to claim 3, characterized in that: The single-neuron PID algorithm described in step S700 is expressed by the following formula: in: The proportionality coefficient used to characterize neurons, and >0; Used to characterize the differential learning rate; Used to characterize the proportional learning rate; Used to characterize the integral learning rate; Signal error used to characterize submersible pumps; The minimum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range. The maximum value of the control signal used to characterize the submersible pump is obtained based on the actual operating parameters and the sensor range. The signal error of the submersible pump is expressed by the following formula: in: Used to characterize the set rotational speed of the submersible pump; Used to characterize the actual rotational speed of the submersible pump.

5. The LNG pump pressure regulating system based on PID control algorithm according to claim 4, characterized in that: The differential learning rate is obtained by self-tuning, and its specific range is 1.2~1.

9.

6. The LNG pump pressure regulating system based on PID control algorithm according to claim 5, characterized in that: The proportional learning rate is obtained by self-tuning, and its specific range is 0.8~1.

0.

7. The LNG pump pressure regulating system based on PID control algorithm according to claim 6, characterized in that: The integral learning rate is obtained by self-tuning, and its specific range is 0.03~0.

5.

8. The LNG pump pressure regulating system based on PID control algorithm according to claim 7, characterized in that: The set value for the pump post-pressure is 1.4 MPa.

9. The LNG pump pressure regulating system based on PID control algorithm according to claim 8, characterized in that: The number of steps in step S400 is 10.

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