Multi-stage centrifugal heat pump steam unit PID regulation and control method based on priority

Abstract

The invention belongs to the technical field of heat pumps, and particularly relates to a priority-based PID regulation and control method for a multistage centrifugal heat pump steam unit. The method comprises the following steps: acquiring basic data of each container, wherein the basic data comprises instant liquid level data and rated capacity data; calculating a relative capacity based on the acquired basic data; performing priority ranking based on the relative capacity and a preset priority evaluation standard; according to the method, the priority regulation output increment is calculated, and the container inlet and outlet regulation valve with high priority is regulated according to the calculated priority regulation output increment, so that the quicker and more accurate response to the unit is realized, and the problems of time delay and out-of-control possibly occurring in the traditional PID regulation and control method are avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of heat pumps, and in particular relates to a priority-based PID control method for a multi-stage centrifugal heat pump steam unit. Background Art

[0002] As an important equipment in the field of energy utilization, multi-stage centrifugal heat pump steam units have attracted much attention due to their high efficiency and wide application scenarios, especially under conditions of large temperature rise (such as 100℃+). However, the multi-stage compression cycle structure centrifugal heat pump steam units also face a series of challenges during operation. Among them, the control of the container liquid level during the refrigerant circulation process is particularly important. When the container liquid level is too high, the separation effect will be significantly reduced, and the refrigerant in the droplet state may enter the compressor, posing a serious threat to the safety and stable operation of the centrifugal heat pump steam unit.

[0003] To solve this problem, conventional units reduce structural complexity and use a PID control system to keep the container liquid level within a safe range. Specifically, multiple PID liquid level sensors need to be set to monitor the liquid level parameters of the evaporator, condenser, and flash evaporator respectively. The PID controller collects these parameters in real time and calculates the control signal by setting the liquid level parameters of the flash evaporator. The control signal is then transmitted to the actuators of the evaporator and condenser to adjust their working status and ensure the overall operating efficiency of the unit. However, the complex internal structure of the multi-stage centrifugal heat pump steam unit also increases the difficulty of liquid level control.

[0004] Reference Figure 1 , a centrifugal heat pump steam unit contains at least five containers, including an evaporator, a condenser, and three flash evaporators. The liquid levels of these containers are interrelated. When the water flow in and out of the evaporator fluctuates, the liquid levels of other containers will also be affected. When the centrifugal heat pump steam unit performs multi-stage air replenishment operation, the PID regulation condition will change significantly. This change makes parallel regulation of the multi-stage PID control system possible, but it also brings new problems. An actuator may receive liquid level parameter signals from multiple flash evaporators at the same time. Since the actuator cannot execute multiple commands at the same time, these signals will interfere with each other, resulting in an extension of the regulation cycle or even loss of control. The liquid level of the flash evaporator cannot be adjusted in time, further exacerbating the risk of liquid refrigerant entering the compressor, thereby shortening the service life of the unit. Summary of the invention

[0005] In order to overcome the problems in the prior art, the present invention proposes a priority-based PID control method for a multi-stage centrifugal heat pump steam unit.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The present invention provides a priority-based PID control method for a multi-stage centrifugal heat pump steam unit, comprising the following steps:

[0008] Obtaining basic data of each container, the basic data including instant liquid level data and rated capacity data;

[0009] Based on the basic data obtained, the relative capacity is calculated;

[0010] Prioritizing based on the relative capacity and preset priority assessment criteria;

[0011] The priority adjustment output increment is calculated, and the inlet and outlet regulating valves of the container with high priority are adjusted according to the calculated priority adjustment output increment.

[0012] Furthermore, the relative capacity is calculated based on the acquired basic data, and the calculation formula is:

[0013] C relative =(C rated -C current ) / C rated ;

[0014] In the above formula, C relative Relative capacity, C rated Indicates rated capacity data, C current Indicates real-time liquid level data.

[0015] Furthermore, the preset priority assessment criteria include: the capacity scale characteristics of the container itself;

[0016] Priority sorting based on the capacity scale characteristics of the container itself includes: traversing all containers to find containers with liquid levels higher than a preset first threshold; sorting the found containers from low to high according to relative capacity to determine a priority adjustment order.

[0017] Furthermore, the preset priority assessment criteria include: characteristics of the upper and lower level containers; and priority sorting based on the characteristics of the upper and lower level containers includes:

[0018] For each container that needs to be adjusted, calculate the relative capacity of the container at the previous level and the relative capacity of the container at the next level;

[0019] According to the relative capacity of the upper-level container and the relative capacity of the lower-level container, as well as the preset second threshold and third threshold, it is determined to adjust the opening of the inlet and outlet regulating valves of the container to be adjusted;

[0020] If the relative capacity of the upper-level container is higher than the preset second threshold, reducing the opening of the inlet regulating valve of the container that needs to be regulated;

[0021] If the relative capacity of the next-stage container is higher than the preset third threshold, the opening of the outlet regulating valve of the container that needs to be adjusted is increased.

[0022] Further, the preset priority assessment criteria include: container relevance order;

[0023] Prioritization based on the order of container dependencies, including:

[0024] According to the hierarchical relationship between containers, determine the upper-level container that needs to be adjusted;

[0025] According to the liquid level of the upper level container, adjust the opening of its inlet and outlet regulating valves;

[0026] Sort the containers directly under the previous level or related next level containers, and gradually adjust the liquid level of the next level containers according to the sorting.

[0027] Further, the calculating priority adjustment output increment includes:

[0028] Calculate the refrigerant mass flow rate Qm at the inlet and outlet of the container:

[0029] Qm=CV*rou / (1.17*(rou / 1000*detar_P) 0.5 );

[0030] Get the instant liquid level C based on the container liquid level sensor current With rated liquid level C rated :

[0031]

[0032] S 2 (t)=(C current -C rated )*rou*A / deter_Q m ;

[0033] S 3 (t) = RANK(P / 1000);

[0034] Calculate the final priority adjustment output increment:

[0035] X(t)=aS 1 (t)+bS 2 (t)+cS 3 (t)+δθ(t);

[0036] Where A represents the cross-sectional area of ​​the container; d(C current) represents the instantaneous liquid level change speed; in represents the inlet state; out represents the outlet state; deter_Qm represents the change of refrigerant mass flow rate; Qm_in represents the refrigerant mass flow rate when entering; Qm_out represents the refrigerant mass flow rate when leaving; CV represents the flow coefficient; rou represents the density; detar_P represents the valve inlet and outlet pressure difference; RANK represents the order of pressure from large to small; P represents the pressure of different containers, that is, the refrigerant pressure; X(t) is the priority adjustment output increment, a, b, c are weighting coefficients; S 1 (t), S 2 (t), S 3 (t) is the output increment; δθ(t) is the correction parameter; t represents time, t 1 -t 2 Refers to a specified length of time.

[0037] Compared with the prior art, the present invention has the following technical effects:

[0038] The present invention can more accurately control the operation of multi-stage centrifugal heat pump steam units under different working conditions through a priority-based PID control method. By calculating the basic data of each container, such as the instantaneous liquid level and rated capacity, and determining the relative capacity and priority ranking accordingly, a faster and more accurate response to the centrifugal heat pump steam unit is achieved, avoiding the delay and loss of control problems that may occur in traditional PID control methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is a schematic diagram of the structure of a centrifugal heat pump steam unit;

[0041] Figure 2 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0042] In order to further explain the technical means and effects taken by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the technical solutions proposed by the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments. The specific features, structures or characteristics in one or more embodiments may be combined in any suitable form. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of the present invention.

[0043] After multi-level PID control is implemented in parallel, since the actuators of the evaporator and the condenser cannot execute multiple commands at the same time, these signals will interfere with each other, resulting in delays in the control cycle or even loss of control. The liquid level of the flash evaporator cannot be adjusted in time, which will cause the problem of liquid refrigerant entering the compressor, thereby damaging the service life of the unit.

[0044] This embodiment introduces the concept of relative capacity and relevant priority standards. When the liquid level of a container is high, the liquid level signals of other containers are called, and the relative capacities of other containers are calculated based on the size characteristics of the containers themselves. With reference to the priority standards, the inlet and outlet regulating valves of the containers with higher priorities are adjusted preferentially, thereby indirectly or directly adjusting the liquid level of the container with the higher liquid level without interfering with the liquid levels of other containers.

[0045] In one embodiment of the present invention, referring to Figure 2 , provides a priority-based PID control method for a multi-stage centrifugal heat pump steam unit, comprising the following steps:

[0046] Obtaining basic data of each container, the basic data including instant liquid level data and rated capacity data;

[0047] Based on the basic data obtained, the relative capacity is calculated;

[0048] Prioritizing based on the relative capacity and preset priority assessment criteria;

[0049] The priority adjustment output increment is calculated, and the inlet and outlet regulating valves of the container with high priority are adjusted according to the calculated priority adjustment output increment.

[0050] The following is a detailed explanation of each of the above steps:

[0051] Step 100: Obtain basic data of each container, wherein the basic data includes real-time liquid level data and rated capacity data.

[0052] Real-time collection of instantaneous liquid level data and rated capacity data of evaporators, condensers, flash evaporators and other containers, which provide the basis for subsequent calculation of relative capacity and priority sorting.

[0053] Step 200: Calculate the relative capacity based on the acquired basic data.

[0054] For each container, calculate the relative capacity based on the instantaneous level and the rated capacity:

[0055] C relative =(C rated -C current ) / C rated ;

[0056] In the above formula, C relative Relative capacity, C rated Indicates rated capacity data, C current Indicates real-time liquid level data.

[0057] The relative capacity is set to avoid the situation where the liquid level in a small container is low but it cannot accommodate excess refrigerant.

[0058] Step 300: Prioritize based on the relative capacity and priority assessment criteria, wherein the priority assessment criteria include the capacity scale characteristics of the container itself, the characteristics of the upper and lower level containers, and the order of container relevance.

[0059] As an example, this step may include:

[0060] Step 310: Prioritization based on the capacity scale characteristics of the container itself;

[0061] Traverse all containers and find out the containers whose liquid level is higher than the preset first threshold; sort the found containers from low to high according to their relative capacity, and determine the priority adjustment order, that is, give priority to adjusting the containers with lower relative capacity and delay the processing of the containers with higher relative capacity.

[0062] Containers with smaller capacity have relatively lower capacity and poorer anti-interference ability to liquid level signals, that is, the container itself requires fast processing of liquid level adjustment commands, otherwise it will affect the safe operation of the unit.

[0063] Step 320: Prioritize based on the characteristics of the upper and lower level containers:

[0064] For each container that needs to be adjusted, calculate the relative capacity of the container at the previous level and the relative capacity of the container at the next level;

[0065] According to the relative capacity of the upper-level container and the lower-level container, as well as the preset second threshold and third threshold, it is decided to adjust the opening of the inlet and outlet regulating valves of the container to achieve that the liquid level of the container is kept within the normal operating range;

[0066] If the relative capacity of the container is low, and the relative capacity of the upper-level container is higher than the preset second threshold, then the opening of the inlet regulating valve of the container is reduced to reduce the inflow;

[0067] If the relative capacity of the container is low and the relative capacity of the next-stage container is higher than the preset third threshold, the opening of the outlet regulating valve of the container is increased to promote the outflow.

[0068] Step 330: Prioritization based on container relevance order;

[0069] Due to the correlation of the liquid levels of multiple containers, the complexity of liquid level regulation increases rapidly as the number of liquid level adjustments increases. In the liquid level adjustment process of the upper-level container, the inlet and outlet valves interfere with each other, that is, the liquid level is sometimes high and sometimes low; when this happens in the upper-level container, the liquid level of the lower-level container will definitely be similar, especially the three flash evaporators, because they are directly connected in series. That is, when the liquid level of the upper-level container is unstable, the liquid level of the lower-level container will also fluctuate, which is not conducive to the stable operation of the unit.

[0070] According to the hierarchical relationship between containers, determine the upper-level container of the container with unstable liquid level; according to the liquid level of the upper-level container, adjust the opening of its inlet and outlet regulating valves to stabilize the liquid level; after the adjustment, continuously monitor the liquid level of the upper-level container to ensure that it is stable within the preset range; according to the hierarchical relationship, sort the upper-level container's direct lower-level or related lower-level containers; on the basis of ensuring the stability of the liquid level of the upper-level container, gradually adjust the liquid level of the lower-level container according to the sorting to ensure safe operation.

[0071] Step 400: Calculate the priority adjustment output increment.

[0072] Calculate the refrigerant mass flow rate Qm at the inlet and outlet of the container:

[0073] Qm=CV*rou / 1.17*(rou / 1000*detar_P) 0.5 );

[0074] Get the instant liquid level C based on the container liquid level sensor current With rated liquid level C rated :

[0075]

[0076] S 2 (t)=(C current -C rated )*rou*A / deter_Q m ;

[0077] S 3 (t) = RANK(P / 1000);

[0078] Calculate the final priority adjustment output increment:

[0079] X(t)=aS 1 (t)+bS 2 (t)+cS 3 (t)+δθ(t);

[0080] Where A represents the cross-sectional area of ​​the container; d(C current) represents the instantaneous liquid level change speed; in represents the inlet state; out represents the outlet state; deter_Qm represents the change of refrigerant mass flow rate; Qm_in represents the refrigerant mass flow rate when entering; Qm_out represents the refrigerant mass flow rate when leaving; CV represents the flow coefficient; rou represents the density; detar_P represents the valve inlet and outlet pressure difference; RANK represents the order of pressure from large to small; P represents the pressure of different containers, that is, the refrigerant pressure; X(t) is the priority adjustment output increment, a, b, c are weighting coefficients; S 1 (t), S 2 (t), S 3 (t) is the output increment; δθ(t) is the correction parameter; t represents time, t 1 -t 2 Refers to a specified length of time.

[0081] Step 500: Implement multi-level PID priority control.

[0082] The output increment is adjusted according to the priority calculated in step 400, and multi-level PID priority control is implemented to ensure that control interference caused by the traditional PID parallelization characteristics is avoided during the control process.

[0083] Step 600: Monitoring and feedback.

[0084] Monitor the changes in the liquid level of each container and provide feedback and adjust the control strategy based on actual conditions.

[0085] A systematic and intelligent container level control strategy is implemented by obtaining basic data, calculating relative capacity, prioritizing based on multiple characteristics, calculating priority adjustment output increments, implementing multi-level PID priority control, and monitoring and feedback. This strategy not only improves the accuracy and stability of level control, but also avoids the control interference problem caused by the traditional PID parallelization characteristics.

[0086] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A PID control method for a multi-stage centrifugal heat pump steam unit based on priority, characterized in that: The following steps are involved: Obtaining basic data of each container, the basic data including instant liquid level data and rated capacity data; Based on the basic data obtained, the relative capacity is calculated; Prioritizing based on the relative capacity and preset priority assessment criteria; The priority adjustment output increment is calculated, and the inlet and outlet regulating valves of the container with high priority are adjusted according to the calculated priority adjustment output increment.

2. The priority-based PID control method for a multi-stage centrifugal heat pump steam unit according to claim 1 is characterized in that: The relative capacity is calculated based on the basic data obtained, and the calculation formula is: C relative =(C rated -C current ) / C rated ; In the above formula, C relative Relative capacity, C rated Indicates rated capacity data, C current Indicates real-time liquid level data.

3. The priority-based PID control method for a multi-stage centrifugal heat pump steam unit according to claim 1 is characterized in that: The preset priority assessment criteria include: the capacity scale characteristics of the container itself; Priority sorting based on the capacity scale characteristics of the container itself includes: traversing all containers to find containers with liquid levels higher than a preset first threshold; sorting the found containers from low to high according to relative capacity to determine a priority adjustment order.

4. The priority-based PID control method for a multi-stage centrifugal heat pump steam unit according to claim 3 is characterized in that: The preset priority assessment criteria include: characteristics of the upper and lower level containers; The priority order based on the characteristics of the upper and lower level containers includes: For each container that needs to be adjusted, calculate the relative capacity of the container at the previous level and the relative capacity of the container at the next level; According to the relative capacity of the upper-level container and the relative capacity of the lower-level container, as well as the preset second threshold and third threshold, it is determined to adjust the opening of the inlet and outlet regulating valves of the container to be adjusted; If the relative capacity of the upper-level container is higher than the preset second threshold, reducing the opening of the inlet regulating valve of the container that needs to be regulated; If the relative capacity of the next-stage container is higher than the preset third threshold, the opening of the outlet regulating valve of the container that needs to be adjusted is increased.

5. The priority-based PID control method for a multi-stage centrifugal heat pump steam unit according to claim 4 is characterized in that: The preset priority assessment criteria include: container relevance order; Prioritization based on the order of container dependencies, including: According to the hierarchical relationship between containers, determine the upper-level container that needs to be adjusted; According to the liquid level of the upper level container, adjust the opening of its inlet and outlet regulating valves; The next level or related next level containers of the previous level container are sorted, and the liquid level of the next level container is gradually adjusted according to the sorting.

6. A priority-based PID control method for a multi-stage centrifugal heat pump steam unit according to claim 5, characterized in that: The calculating priority adjustment output increment comprises: Calculate the refrigerant mass flow rate Qm flowing through the container inlet and outlet regulating valves: Qm=CV*rou / (1.17*(rou / 1000*detar_P) 0.5 ); Based on the refrigerant mass flow rate at the outlet of the previous container and the inlet of the next container, calculate the net refrigerant flow rate of the regulating container: deter_Qm=Qm_in-Qm_out; Get the instant liquid level C based on the container liquid level sensor current With rated liquid level C rated : S2(t)=(C current -C rated )*rou*A / deter_Q m ; S3(t)=RANK(P / 1000); Calculate the final priority adjustment output increment: X(t)=aS1(t)+bS2(t)+cS3(t)+δθ(t); Where A represents the cross-sectional area of ​​the container; d(C current ) represents the instantaneous liquid level change speed; in represents the inlet state; out represents the outlet state; deter_Qm represents the refrigerant mass flow change; Qm_in represents the refrigerant mass flow when entering; Qm_out represents the refrigerant mass flow when leaving; CV represents the flow coefficient; rou represents the density; detar_P represents the valve inlet and outlet pressure difference; RANK represents the pressure sorting from large to small; P represents the pressure of different containers, that is, the refrigerant pressure; X(t) is the priority adjustment output increment, a, b, c are weighting coefficients; S1(t), S2(t), S3(t) are output increments; δθ(t) is the correction parameter; t represents time, t1-t2 refers to the specified time length.

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