Modelica-based supercritical carbon dioxide compressor modeling method

Abstract

The invention belongs to the technical field of supercritical carbon dioxide system simulation, and particularly relates to a Modelica-based supercritical carbon dioxide compressor modeling method. Comprising the following steps: decomposing the supercritical carbon dioxide compressor; determining interface attributes of data transmission between the compressor model and the outside; constructing a control body model and a connecting pipe model of the supercritical carbon dioxide compressor; the control volume model corresponds to a mass and energy control equation of the two-fluid six-equation; packaging into a supercritical carbon dioxide compressor model; and connecting the constructed supercritical carbon dioxide compressor model with a pipeline and a boundary. The method has the advantages that based on the Modelica language, only specific physical phenomenon equations of the model need to be given, specific solving principles and solving steps do not need to be given, a simulation platform where the Modelica model is located can automatically compile and solve existing equations during solving, and the modeling threshold is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of supercritical carbon dioxide system simulation, and in particular relates to a supercritical carbon dioxide compressor modeling method based on Modelica. Background Art

[0002] As a new type of power generation technology, supercritical carbon dioxide Brayton cycle power generation technology has the advantages of being environmentally friendly, compact, highly efficient, and economical. It is one of the current international and domestic research hotspots. As the core equipment in the system, the compressor's design and operating parameters, geometric structure, and characteristic curves directly affect the overall power generation efficiency of the system. At present, the engineering research and development design of supercritical carbon dioxide Brayton cycle power generation systems requires system simulation. System simulation requires the construction of a compressor simulation model that meets the requirements of system simulation accuracy and simulation efficiency, and the model is required to cover all compressor design types used in system design. Therefore, it is necessary to build a supercritical carbon dioxide compressor performance simulation model with modular, reusable, and extensible characteristics to improve the modeling efficiency of the compressor simulation model and meet the simulation analysis requirements of the static and dynamic characteristics of the supercritical carbon dioxide Brayton cycle power generation system and compressor. Summary of the invention

[0003] The purpose of the present invention is to provide a supercritical carbon dioxide compressor modeling method based on Modelica, which can effectively improve the compressor modeling efficiency and meet the simulation analysis requirements of the supercritical carbon dioxide Brayton cycle power generation system and the static and dynamic characteristics of the compressor.

[0004] The technical solution of the present invention is as follows: A supercritical carbon dioxide compressor modeling method based on Modelica, comprising the following steps:

[0005] Step 1: Decompose the supercritical carbon dioxide compressor according to the structural composition of the supercritical carbon dioxide compressor model;

[0006] Step 2: According to the working principle of the supercritical carbon dioxide compressor, determine the interface properties for data transmission between the compressor model and the outside world;

[0007] Step 3: Construct the control body model and takeover model of the supercritical carbon dioxide compressor based on the two-fluid six-equation theory;

[0008] In step 3, the control volume model corresponds to the mass and energy control equations of the two-fluid six equations;

[0009] Step 4: Based on the control body model, takeover model, fluid interface and mechanical interface, the above component models are connected according to the physical topology of the supercritical carbon dioxide compressor according to the compressor physical topology, and the data transmission relationship between them is established through the connection, and they are encapsulated into a supercritical carbon dioxide compressor model;

[0010] Step 5: Connect the constructed supercritical carbon dioxide compressor model with the pipeline and boundary, that is, drag-and-drop modeling, drag out the compressor model, pipeline model, boundary model, and then connect them to build a compressor simulation system. The compressor simulation system includes flow boundaries, pressure boundaries, pipelines and compressors to realize compressor system simulation under different working conditions and parameters.

[0011] In the step 1, the supercritical carbon dioxide compressor is decomposed into four models: a control body model, a takeover model, a fluid interface and a mechanical interface.

[0012] The control body model calculates the outlet parameters according to the fluid boundary data such as the compressor inlet temperature, pressure, flow rate and the mechanical boundary data such as the speed and torque, and simulates and calculates the performance of the compressor based on the compressor characteristic curve; the takeover model describes the flow characteristics of the fluid in the inlet pipe section and the outlet pipe section of the compressor; the fluid interface transmits the fluid boundary data such as temperature, pressure and flow rate to the compressor model, and the mechanical interface transmits the mechanical boundary data such as the speed, shaft torque and shaft power to the compressor.

[0013] In the step 2, the supercritical carbon dioxide compressor exchanges data with the outside world through fluid and mechanical rotation, wherein the fluid interface and the mechanical interface are data interfaces, the attributes of the fluid interface define the fluid parameters entering and flowing out of the front and rear pipes of the compressor control body, and the attributes of the mechanical interface define the mechanical parameters entering the compressor control body.

[0014] The fluid interface in step 2 expresses the relationship between the inlet and outlet pressures, temperatures and flows of the compressor inlet and outlet pipes and other connected devices, satisfying the generalized Kirchhoff's law, that is, the pressure and temperature are equal, and the flows and are equal.

[0015] The mechanical interface in step 2 expresses mechanical parameters such as shaft speed and shaft power.

[0016] In step 3, the control body model uses a characteristic curve interpolation algorithm to solve the compressor characteristics, as follows:

[0017] Step 31: According to the speed in the rotor characteristic data, the compressor flow ratio-pressure ratio and flow ratio-efficiency curves at each speed are converted into a corresponding rotor characteristic data table of flow, pressure ratio and efficiency. The control body model receives the fluid data transmitted by the fluid interface, and then interpolates based on the data table to simulate the compressor boost characteristics and calculate the compressor control body outlet data;

[0018] Step 32: According to the input speed N, select the adjacent speed characteristic data in the rotor characteristic data, and use the linear interpolation algorithm to interpolate the flow rate, pressure ratio, and efficiency data at the current speed N to obtain a two-dimensional array, the first column is the flow rate, the second column is the pressure ratio, and the third column is the efficiency;

[0019] Step 33: According to the input flow value W cor , perform linear interpolation in the two-dimensional array obtained in the above steps to obtain the corresponding compression ratio and efficiency.

[0020] In the step 3, the takeover model corresponds to the momentum control equation of the two-fluid six-equation and is cross-connected with the control body model.

[0021] The beneficial effects of the present invention are as follows: the present invention is based on the Modelica language, and only needs to give the specific physical phenomenon equations of the model, without giving the specific solution principles and solution steps. When solving, the simulation platform where the Modelica model is located will automatically compile and solve the existing equations, greatly reducing the modeling threshold; the model has the characteristics of modularization, and the structured components of the model are easy to reuse and integrate, greatly improving the modeling efficiency and model utilization; the model has the characteristics of clear hierarchy, reusability, scalability and complete autonomy, and can quickly update the model based on the latest compressor design scheme and compressor research results. The method of the present invention applies the Modelica language to the modeling and simulation of supercritical carbon dioxide compressors, realizes high-precision simulation of supercritical carbon dioxide compressors, and can be applied to the static and dynamic characteristics analysis of supercritical carbon dioxide compressors of different design types. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the structural diagram of the supercritical carbon dioxide compressor model;

[0023] Figure 2 This is the interpolation process diagram of the rotor characteristic curve;

[0024] Figure 3 It is a schematic diagram of the staggered connection between the takeover model and the control body model;

[0025] Figure 4 This is a schematic diagram of the connection of the supercritical carbon dioxide compressor model;

[0026] Figure 5This is a simulation diagram of the supercritical carbon dioxide compressor system. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the basic implementation principle of the present invention is described below in conjunction with the accompanying drawings. The specific implementation principle described herein is only used to explain the present invention and is not intended to limit the present invention. In the following description, many specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those within the scope of this description, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below. Based on the implementation principle of the present invention, all other implementation cases obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments, as well as the steps in all disclosed methods or processes, except for mutually exclusive features or steps, can be combined, expanded and replaced in any way.

[0028] The present invention provides a modeling method for a supercritical carbon dioxide compressor based on Modelica, wherein Modelica is an object-oriented, multi-domain modeling language specifically used for modeling and simulation of complex physical systems. Its original design intention is to support modeling and simulation between different fields (such as mechanics, electrical, electronics, hydraulics, thermodynamics, control, mechatronics, etc.), thereby simplifying the integration and analysis of multi-domain systems.

[0029] A supercritical carbon dioxide compressor modeling method based on Modelica comprises the following steps:

[0030] Step 1: According to the structural composition of the supercritical carbon dioxide compressor model, the supercritical carbon dioxide compressor is decomposed into four models: the control body model, the takeover model, the fluid interface and the mechanical interface. These four models are the components of the compressor model. Specifically, the control body model calculates the outlet parameters based on the fluid boundary data such as the compressor inlet temperature, pressure, flow rate and the mechanical boundary data such as speed and torque, and simulates the performance of the compressor based on the compressor characteristic curve; the takeover model is to describe the flow characteristics of the fluid in the inlet pipe section and the outlet pipe section of the compressor; the fluid interface is to transmit the fluid boundary data such as temperature, pressure, flow rate to the compressor model, and the mechanical interface is to transmit the mechanical boundary data such as speed, shaft torque and shaft power to the compressor.

[0031] Step 2: According to the working principle of the supercritical carbon dioxide compressor, determine the interface properties for data transmission between the compressor model and the outside world;

[0032] In step 2, the supercritical carbon dioxide compressor exchanges data with the outside world through fluid and mechanical rotation, where the fluid interface and mechanical interface are data interfaces. The attributes of the fluid interface define the fluid parameters entering and outflowing from the front and rear pipes of the compressor control body, and the attributes of the mechanical interface define the mechanical parameters entering the compressor control body.

[0033] The fluid interface expresses the relationship between the inlet and outlet pressure, temperature, flow rate and other parameters of the compressor inlet and outlet pipes and other connected devices, satisfying the generalized Kirchhoff's law, that is, the pressure and temperature at the connection point of the connected equipment are equal, and the flow rate is equal;

[0034] The mechanical interface expresses mechanical parameters such as shaft speed and shaft power.

[0035] Step 3: Construct the control body model and takeover model of the supercritical carbon dioxide compressor based on the two-fluid six-equation theory;

[0036] In step 3, the control volume model corresponds to the mass and energy control equations of the two-fluid six equations;

[0037] The control body model uses the characteristic curve interpolation algorithm to solve the compressor characteristics, as follows:

[0038] Step 31: According to the speed in the rotor characteristic data, the compressor flow ratio-pressure ratio and flow ratio-efficiency curves at each speed are converted into the corresponding rotor characteristic data table of flow, pressure ratio and efficiency. The control body model receives the fluid data transmitted by the fluid interface, and then interpolates based on the data table to simulate the compressor boost characteristics and calculate the compressor control body outlet data;

[0039] Step 32: According to the input speed N, select the adjacent speed characteristic data in the rotor characteristic data, and use the linear interpolation algorithm to interpolate the flow rate, pressure ratio, and efficiency data at the current speed N to obtain a two-dimensional array, the first column is the flow rate, the second column is the pressure ratio, and the third column is the efficiency;

[0040] Step 33: According to the input flow value W cor , perform linear interpolation in the two-dimensional array obtained in the above steps to obtain the corresponding compression ratio and efficiency.

[0041] In step 3, the takeover model corresponds to the momentum control equations of the two-fluid six-equation system and is cross-connected with the control body model.

[0042] The main calculation of the momentum equation in the takeover model includes three source items: takeover parameter calculation, wall friction calculation and phase friction calculation. All three source items need to be calculated with fluid velocity as input. At time 0, the fluid velocity is filled in the parameter panel as input, and at other times, the fluid velocity calculation result obtained by the solver is used as input for calculation.

[0043] Step 4: Based on the control body model, takeover model, fluid interface and mechanical interface, the above component models are connected according to the physical topology of the supercritical carbon dioxide compressor according to the physical topology of the compressor, and the data transmission relationship between them is established through the connection. The model is encapsulated into a supercritical carbon dioxide compressor model to simulate the behavioral characteristics of the compressor.

[0044] Step 5: Connect the constructed supercritical carbon dioxide compressor model with other components such as pipelines and boundaries. The other components are adjusted according to the actual design of the compressor system. For example, if there is a valve, add a valve; if there is a flow meter, add a flow meter; if there is a pipeline, build a pipeline. This depends entirely on the composition of the compressor system. By dragging - on the Modelica modeling platform, drag out all the above model components and connect them), drag out the compressor model, pipeline model, boundary model, and then connect them to build a compressor simulation system. The compressor simulation system includes flow boundaries, pressure boundaries, pipelines and compressors to realize compressor system simulation under different working conditions and parameters.

[0045] Example

[0046] A supercritical carbon dioxide compressor modeling method based on Modelica comprises the following steps:

[0047] Step 1: Decompose according to the actual physical structure of the supercritical carbon dioxide compressor;

[0048] The structure of the supercritical carbon dioxide compressor model is as follows Figure 1 According to the composition of the supercritical carbon dioxide compressor model, it is decomposed into a control body model, a takeover model, a fluid interface and a mechanical interface.

[0049] Step 2: Determine the interface properties of the supercritical CO2 compressor

[0050] The supercritical carbon dioxide compressor takes over the data exchange with the control body in the form of fluid, and exchanges data with the outside world in the form of fluid and mechanical rotation. Therefore, the supercritical carbon dioxide compressor should also include a fluid interface and a mechanical interface, where the fluid interface expresses the relationship between the pipeline inlet and outlet pressure, temperature, flow medium components and other parameters and other connected equipment, satisfying the generalized Kirchhoff's law, that is, the pressure and temperature are equal, and the flow and are equal; the mechanical interface expresses the mechanical parameters such as shaft speed, shaft power, shaft torque, shaft moment of inertia. The exchange parameter data of the fluid interface and the mechanical interface are shown in Table 1.

[0051] Table 1 Interface exchange data

[0052]

[0053] Step 3: Construct the control body model and takeover model of the supercritical carbon dioxide compressor based on the two-fluid six equations.

[0054] The control volume model is mainly described by the mass and energy control equations of the two-fluid six equations, in which the compressor characteristics are solved by the characteristic curve interpolation algorithm. The rotor characteristic curve interpolation operation process is as follows: Figure 2 As shown, the following process is included:

[0055] 1) According to the speed in the rotor characteristic data, create a data table in the order of flow rate, pressure ratio, and efficiency for the corresponding input at each speed, and input it into the interpolation algorithm model;

[0056] 2) According to the input speed N, the adjacent speed characteristic data is selected from the rotor characteristic data through an algorithm, and the flow rate, pressure ratio, and efficiency data at the current speed N are interpolated using a linear interpolation algorithm to obtain a two-dimensional array, where the first column is the flow rate, the second column is the pressure ratio, and the third column is the efficiency;

[0057] 3) According to the input flow value W cor , substitute into the flow rate, pressure ratio, and efficiency table, perform linear interpolation, and obtain the corresponding pressure ratio and efficiency.

[0058] The takeover model corresponds to the momentum control equation of the two-fluid six-equation, and is interlaced with the control body model. The interlaced connection between the takeover model and the control body model is as follows: Figure 3 shown.

[0059] Step 4: Build a supercritical carbon dioxide compressor model based on the component model.

[0060] A supercritical carbon dioxide compressor model is built based on the physical topology of the supercritical carbon dioxide compressor. The supercritical carbon dioxide compressor model consists of Figure 4 shown.

[0061] Step 5: Connect the constructed supercritical carbon dioxide compressor model with the pipeline model and boundary model to build a compressor simulation system to realize compressor system simulation under different working conditions and parameters.

[0062] According to the actual operating conditions of the supercritical carbon dioxide compressor, a supercritical carbon dioxide compressor simulation system is built. Figure 5As shown. The simulation system model includes a flow inlet component, a pipeline model component, a supercritical carbon dioxide compressor model component, and a pressure outlet component. The simulation starts at time T = 0 seconds using the Euler method and ends at time T = 150 seconds. The output step is 0.01 and the calculation accuracy is 0.0001. Among them, the speed of the supercritical carbon dioxide compressor is 2300 / 6900 / 11500 / 16100 / 18400 / 20700 / 23000 / 25300. On each speed curve, the flow rate takes 5 test points, a total of 40 test points. The calculation results are compared in Table 2.

[0063] Table 2 Comparison of calculation results

[0064]

[0065]

Claims

1. A supercritical carbon dioxide compressor modeling method based on Modelica, characterized in that: The following steps are involved: Step 1: Decompose the supercritical carbon dioxide compressor according to the structural composition of the supercritical carbon dioxide compressor model; Step 2: According to the working principle of the supercritical carbon dioxide compressor, determine the interface properties for data transmission between the compressor model and the outside world; Step 3: Construct the control body model and takeover model of the supercritical carbon dioxide compressor based on the two-fluid six-equation theory; In step 3, the control volume model corresponds to the mass and energy control equations of the two-fluid six equations; Step 4: Based on the control body model, takeover model, fluid interface and mechanical interface, the above component models are connected according to the physical topology of the supercritical carbon dioxide compressor according to the compressor physical topology, and the data transmission relationship between them is established through the connection, and they are encapsulated into a supercritical carbon dioxide compressor model; Step 5: Connect the constructed supercritical carbon dioxide compressor model with the pipeline and boundary, that is, drag-and-drop modeling, drag out the compressor model, pipeline model, boundary model, and then connect them to build a compressor simulation system. The compressor simulation system includes flow boundaries, pressure boundaries, pipelines and compressors to realize compressor system simulation under different working conditions and parameters.

2. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 1, characterized in that: In the step 1, the supercritical carbon dioxide compressor is decomposed into four models: a control body model, a takeover model, a fluid interface and a mechanical interface.

3. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 2, characterized in that: The control body model calculates the outlet parameters according to the fluid boundary data such as the compressor inlet temperature, pressure, flow rate and the mechanical boundary data such as the speed and torque, and simulates and calculates the performance of the compressor based on the compressor characteristic curve; the takeover model describes the flow characteristics of the fluid in the inlet pipe section and the outlet pipe section of the compressor; the fluid interface transmits the fluid boundary data such as temperature, pressure and flow rate to the compressor model, and the mechanical interface transmits the mechanical boundary data such as the speed, shaft torque and shaft power to the compressor.

4. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 1, characterized in that: In the step 2, the supercritical carbon dioxide compressor exchanges data with the outside world through fluid and mechanical rotation, wherein the fluid interface and the mechanical interface are data interfaces, the attributes of the fluid interface define the fluid parameters entering and flowing out of the front and rear pipes of the compressor control body, and the attributes of the mechanical interface define the mechanical parameters entering the compressor control body.

5. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 4, characterized in that: The fluid interface in step 2 expresses the relationship between the inlet and outlet pressures, temperatures and flows of the compressor inlet and outlet pipes and other connected devices, satisfying the generalized Kirchhoff's law, that is, the pressure and temperature are equal, and the flows and are equal.

6. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 4, characterized in that: The mechanical interface in step 2 expresses mechanical parameters such as shaft speed and shaft power.

7. A supercritical carbon dioxide compressor modeling method based on Modelica as claimed in claim 1, characterized in that: In step 3, the control body model uses a characteristic curve interpolation algorithm to solve the compressor characteristics, as follows: Step 31: According to the speed in the rotor characteristic data, the compressor flow ratio-pressure ratio and flow ratio-efficiency curves at each speed are converted into a corresponding rotor characteristic data table of flow, pressure ratio and efficiency. The control body model receives the fluid data transmitted by the fluid interface, and then interpolates based on the data table to simulate the compressor boost characteristics and calculate the compressor control body outlet data; Step 32: According to the input speed N, select the adjacent speed characteristic data in the rotor characteristic data, and use the linear interpolation algorithm to interpolate the flow rate, pressure ratio, and efficiency data at the current speed N to obtain a two-dimensional array, the first column is the flow rate, the second column is the pressure ratio, and the third column is the efficiency; Step 33: According to the input flow value W cor , perform linear interpolation in the two-dimensional array obtained in the above steps to obtain the corresponding compression ratio and efficiency.

8. The supercritical carbon dioxide compressor modeling method based on Modelica according to claim 1, characterized in that: In the step 3, the takeover model corresponds to the momentum control equation of the two-fluid six-equation and is cross-connected with the control body model.

Images