Gas-heat network transient model construction and gas-heat dynamic pipe network coupling calculation method

Abstract

The invention relates to the field of integrated energy systems, and provides an electric heat network transient model construction method based on multiple time scales. The method comprises the following steps of: firstly, reviewing a multi-time scale mechanism of a comprehensive energy system, and respectively establishing corresponding mathematical models for natural gas and a heat distribution pipeline; secondly, aiming at the solution of the transient mathematical model, simplifying a time-space two-dimensional pipeline differential equation by utilizing a finite difference method, and reducing the complexity of numerical calculation; on the basis, a pipe network gas and heat grid constraint equation is added to construct a natural gas and hot water pipeline model composed of a plurality of pipelines and a plurality of pipe networks, and a breadth-first traversal method is matched for solving. Finally, in order to verify the effectiveness of the model, a reference grid structure is adopted, and dynamic result solving is conducted on the radiation network. Through comparison with the actual situation, the operation result of the model accords with the actual operation situation of the pipe network, and the dynamic characteristics of the pipe network can be effectively simulated.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated energy systems, and in particular to a method for constructing a gas-heat network transient model and calculating a gas-heat dynamic pipe network coupling. Background Art

[0002] In recent years, the massive emission of greenhouse gases has led to an increasingly severe climate situation, and low-carbon development has gradually become the only way for countries around the world to cope with climate change. The access to renewable resources such as wind power and photovoltaics can effectively reduce the carbon emissions of the power system. However, with the continuous penetration of renewable energy, the inertia of the power system has decreased, and a large amount of wind power and photovoltaic output cannot be absorbed, resulting in serious waste of resources. In addition, the inherent uncertainty and volatility of renewable resources have exacerbated the imbalance between supply and demand and reduced the reliability and stability of the power system. The integrated energy system has the advantages of improving energy utilization efficiency and renewable energy absorption capacity through interconnection, integration and complementary integration of multiple energy types, and is an important solution for the low-carbon transformation of the energy industry.

[0003] The energy media of each subsystem of the integrated energy system are physically highly heterogeneous: the heterogeneity of the energy media leads to inconsistent transmission characteristics of the power system, natural gas system, and thermal system, which leads to the multi-time scale characteristics of the integrated energy system, and different subsystems have different response times to dispatch instructions. This makes the construction of the integrated energy model without considering the time characteristics and the calculation of the gas-heat dynamic pipeline coupling not accurate enough.

[0004] In view of this, a gas-heat network transient model construction and a gas-heat dynamic pipeline network coupling calculation method are needed. Summary of the invention

[0005] In view of the problem that the construction of the comprehensive energy model in the prior art does not consider the time characteristics and the gas-heat dynamic pipe network coupling calculation is not accurate enough, the present invention provides a gas-heat network transient model construction and gas-heat dynamic pipe network coupling calculation method, which can calculate the time delay and dynamic process of the natural gas and thermal pipeline network. The specific technical solution is as follows:

[0006] A method for constructing a transient model of an electrical and thermal network based on multiple time scales, including the construction of a natural gas pipeline model, is as follows:

[0007] Ignoring the effects of gravitational acceleration and inclination, a set of partial differential equations obtained based on the laws of conservation of mass and momentum are as follows:

[0008]

[0009] Where: and are differential operators for distance l and time t respectively; m l,t and p l,tare mass flow and gas pressure respectively; c is the sound velocity of natural gas; A is the cross-sectional area of ​​the pipeline; D is the pipeline diameter; f is the friction coefficient; L is the pipeline length; ρ is the gas density.

[0010] Preferably, the method further comprises the following steps:

[0011] Obtain a natural gas pipeline model and use finite difference approximation to linearize the differential operator and

[0012] The quadratic term "16m l,t 2 / π 2 D 4 ρ" and "-8fc 2 m l,t m l,t | / π 2 D 5 ρ l,t ” is converted into a steady-state point (m l,0 , p l,0 ), the constants at are:

[0013]

[0014] Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; and are the output mass flow and air pressure respectively;

[0015] The "Δτ i =πD 2 ρΔl / 4m l,0 ” Substitute it into the solution and get the following two-port network equation of the differential pipeline Δl:

[0016]

[0017] Preferably, the total gas transmission delay is also calculated as follows:

[0018] By m l,t and The mean of Δτ is re-estimated i for:

[0019]

[0020] Assuming the pipeline length is L, after connecting “L / Δl” two-port networks of formula (4) in series, the total gas transmission delay can be estimated in a rolling manner:

[0021]

[0022] Preferably, it also includes constructing a heating pipeline model, as follows:

[0023]

[0024] In the formula, m l,t and p l,t is the hot water mass flow and pressure of the control body at that time; and is the hot water mass flow and pressure of the next section of the control body at the next moment; m l,0 and p l,0 is the initial steady-state mass flow and initial steady-state pressure of hot water in each section of the control body at each time; c is the speed of sound in hot water; D is the diameter of the hot water pipe; f is the friction coefficient; ρ is the hot water density; Δl is the section length.

[0025] Preferably, the construction of the hot water temperature calculation method is as follows:

[0026] The hot water in the pipe can be regarded as an incompressible fluid, and the radial temperature distribution of the fluid in the pipe is ignored, and the thermal dynamic model of hot water in the pipe is obtained:

[0027]

[0028] In the formula, c p is the specific heat capacity of water; K s It represents the total heat transfer coefficient between hot water in the pipe network and the external environment, λ is the thermal conductivity of hot water, A is the cross-sectional area of ​​the fluid, T e is the ambient temperature, m is the mass flow rate of the fluid;

[0029] Ignore the heat conduction of hot water along the pipe direction and further simplify the thermal dynamic model of hot water in the pipe to obtain:

[0030]

[0031] The time derivative and space derivative of the hot water temperature in the pipe are replaced by differences and converted into steady-state points, and the numerical calculation format of the first-order implicit upwind difference is obtained as follows:

[0032]

[0033] Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; is the output hot water temperature;

[0034] The "Δτ i =ρAΔl / m l,t Substitute it into the solution and get:

[0035]

[0036] Preferably, it also includes the construction of pipeline network gas and heat flow grid constraint equations, specifically including node flow balance constraints and ring network pressure drop conservation constraints, and the node flow balance constraints are as follows:

[0037]

[0038] In the formula, F i S and F i LD Respectively represent the gas supply and gas consumption at node i; Γ NGN-ND Represents a set of node numbers in a natural gas system; and Represents the set of pipe numbers flowing into and out of node i respectively;

[0039] The specific constraints of ring network voltage drop conservation are as follows:

[0040]

[0041] In the formula, B l,b is the ring network-pipeline joint matrix; S NGN-L It is a collection of ring network numbers in the natural gas network.

[0042] A gas-heat dynamic pipe network coupling calculation method, applied to the method as described above, comprises the following steps:

[0043] At each time step, the steady-state model of the pipe network is used to calculate the mass flow and pressure distribution of the entire network at that time step;

[0044] Combined with the unsteady-state model of the pipeline and the topological relationship of all pipelines in the whole network, the mass flow and pressure distribution of all control bodies of all pipelines in the whole network at this time step are calculated to obtain the mass flow and pressure at the outlet of each pipeline connected to the pipeline network;

[0045] Use the calculated mass flow and pressure at each terminal as well as the network node flow and loop pressure balance equation to recalculate the flow and pressure distribution of the entire network at the next time step;

[0046] And so on, through iterative cycles, the temperature, flow and pressure distribution of the entire network at each time step can be obtained.

[0047] Preferably, the pipe network coupling is numerically calculated by breadth-first traversal.

[0048] A computer-readable storage medium includes a stored program, wherein when the program is run, the device where the computer-readable storage medium is located is controlled to execute the method for constructing an electrical thermal network transient model based on multiple time scales as described above.

[0049] A processor is used to run a program, wherein when the program is run, the gas-heat dynamic pipeline network coupling calculation method as described above is executed.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The present invention models electricity, gas, and heat respectively, and uses the finite difference method to process the model, thereby simplifying its calculation. Compared with the traditional multi-time scale model, the model proposed by the present invention focuses on the transient analysis of integrated energy, and can perform coupling calculations of different energy networks. The present invention can not only simulate the network dynamic characteristics of a single energy source, but also simulate the dynamic response between multiple heterogeneous energy flows. The pipeline dynamic parameters obtained by the simulation calculation are consistent with the actual working conditions, and have reference value for improving the coordination ability and scheduling potential of the integrated energy system. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0053] Figure 1 This is a finite difference schematic diagram of a natural gas pipeline proposed by the present invention;

[0054] Figure 2 A flow chart of numerical calculation of pipe network coupling of breadth-first traversal is proposed for the present invention;

[0055] Figure 3 This is a schematic diagram of energy coupling of the integrated energy system proposed in the present invention;

[0056] Figure 4 This is the IES grid structure diagram proposed by the present invention;

[0057] Figure 5 This is the mass flow pressure variation diagram of the natural gas network node solved by the model;

[0058] Figure 6 This is the temperature variation diagram of the heating network nodes solved by the model;

[0059] Figure 7 This is the time-delay variation diagram of the seven-node six-pipe radial network mass flow solved by the model;

[0060] Figure 8 This is the pressure variation diagram of the seven-node six-pipe radial network solved by the model with time delay;

[0061] Fig. 9The temperature variation with time of the seven-node six-pipe radial network solved by the model;

[0062] Fig.10 This is the temperature variation diagram of the heating network outlet solved by the model;

[0063] Fig.11 This is a graph showing the changes in mass flow at the gas network outlet and voltage at the equilibrium node solved using the model. DETAILED DESCRIPTION

[0064] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0066] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0067] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0068] The specific implementation modes of the present invention are further described below.

[0069] In the following, we first review the multi-time scale mechanism of the integrated energy system and establish corresponding mathematical models for natural gas and thermal pipelines respectively. Then, we set up corresponding grid constraints for solving transient mathematical models and propose a breadth-first traversal method to perform numerical calculations on pipeline network coupling. Finally, we verify the effectiveness of the model by comparing the calculation results of the model with the actual situation.

[0070] 1. Modeling of comprehensive energy models for electricity, gas and heat

[0071] 1.1 Multi-time scale characteristics of integrated energy

[0072] The integrated energy system includes the power system, the natural gas system, and the thermal system. The power in the power system is balanced in real time, and the dynamic process is in seconds; the dynamic process of the natural gas system varies from minutes to hours; and the dynamic process of the thermal system is in hours. As a result, heterogeneous energy systems exhibit different time scale characteristics when responding to dispatch instructions: the thermal system responds to load changes slowly, the natural gas system responds to load changes slowly, and the generator in the power system can respond quickly to load changes.

[0073] The power system transmits electric energy, which propagates at the speed of light in the power grid in the form of electromagnetic waves. It is a typical fast dynamic time scale system with a short transient response time. It is generally believed that the time scale is in the microsecond level. On the minute-level time scale of the present invention, the dynamic processes of the power system at the second and millisecond levels can be ignored. Therefore, the steady-state AC power flow model of the power system can be used to describe the power flow distribution in the power network.

[0074] The transmission medium of the natural gas system is gas, and the time scale is minutes and hours. It is a typical slow time scale system. Due to the compressibility of natural gas, as the gas source intake increases or decreases, it takes a certain amount of time for the natural gas to be transmitted from the source node to the load node, which will lead to inconsistent mass flow rates at both ends of the pipeline. In the dynamic transmission process of natural gas, after a disturbance or fault is triggered, the pressure level and mass flow rate distribution of the natural gas pipeline network require a certain transition process time to reach a new operating state. At this time, the steady-state transmission model of natural gas is not applicable. In order to characterize the above dynamic process, the present invention is based on the dynamic transmission model of the natural gas pipeline network.

[0075] The transmission medium of the thermal system is hot water, and the time scale is in the hour level, which is a typical slower time scale system. The thermal characteristics of the heating network are generally divided into steady-state thermal characteristics and dynamic thermal characteristics. Steady-state thermal characteristics refer to the transition time of the temperature at a certain point in the heating network from one steady state to another is much shorter than the scheduling time of the entire energy supply system. At this time, since the heating network is faster than the energy supply system scheduling reaction, the heating network at this time can be regarded as reaching a stable state instantaneously during modeling, that is, steady-state thermal characteristics; on the contrary, transient thermal characteristics refer to the time scale required for the transition when the temperature at a certain point in the heating network changes from one steady state to another, which is equivalent to the scheduling time scale of the entire energy supply system. The characteristics of the heating network have an unignorable impact on the scheduling of the energy system, and should be fully considered when modeling the entire system. At this time, the thermal characteristics obtained by considering the transition process of the heating network reaching a steady state are the dynamic thermal characteristics of the heating network. On the minute-level time scale studied in this invention, complex partial differential equations are needed to describe the transient hydraulic and thermal characteristics of the thermal system.

[0076] Table 1 Transmission rules and models of electricity, gas and heat systems

[0077]

[0078] 1.2 Mathematical model of power system

[0079] The power system is a typical fast dynamic time scale system with a short transient response time. It is generally believed that the time scale is in the microsecond to minute level. Therefore, the steady-state AC power flow model of the power system can be used to describe the power flow distribution in the power network:

[0080]

[0081] Where: P i , Q i are the active power and reactive power injected into node i respectively; e i 、e j and f i 、f j are the real and imaginary parts of the voltage at nodes i and j respectively; G ij and B ij are the real and imaginary parts of the node admittance matrix elements, respectively.

[0082] Since there are PV nodes with given voltage magnitude in the system, a set of equations should be added:

[0083]

[0084] Where U i is the voltage of the PV node.

[0085] 1.3 Mathematical model of natural gas pipeline

[0086] The natural gas system is mainly composed of a gas source, a natural gas pipeline and a natural gas load. A compressor is also provided in a long-distance gas transmission system. The radial gas distribution network considered in the present invention does not have a compressor.

[0087] The flow of natural gas is driven by the pressure difference between the beginning and the end of the pipeline, and is affected by many factors such as pipeline length, inner diameter, roughness, transmission path height and boundary conditions; therefore, correctly describing the relationship between the change of gas flow and pressure in the gas distribution network pipeline with time and space is the key to the state space modeling of the gas distribution network.

[0088] Under the condition of horizontal pipeline, without considering the influence of gravity acceleration and inclination angle, the transient change process inside the pipeline can be described by the one-dimensional isothermal transmission dynamic equation along the axis of the natural gas pipeline, that is, a set of partial differential equations obtained according to the law of conservation of mass and momentum, specifically:

[0089]

[0090] Where: and are the differential operators for distance l and time t respectively; m l,t and p l,t are mass flow and gas pressure respectively; c is the sound velocity of natural gas; A is the cross-sectional area of ​​the pipeline; D is the pipeline diameter; f is the friction coefficient; L is the pipeline length; ρ is the gas density.

[0091] Formula (3) contains two-dimensional time and space differentials, which makes it difficult to quickly estimate the time delay. Finite difference approximation is used to linearize the differential operator and At the same time, the quadratic term "16m l,t 2 / π 2 D 4 ρ" and "-8fc 2 m l,t |m l,t | / π 2 D 5 p l,t ” is converted into a steady-state point (m l,0 ,p l,0 ), there is

[0092]

[0093] Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; and are the output mass flow and air pressure respectively.

[0094] The "Δτ i =πD 2 ρΔl / 4m l,0 Substituting into equation (4) and solving, we get the following two-port network equation of the differential pipeline Δl:

[0095]

[0096] By m l,t and The mean of Δτ is re-estimated i for:

[0097]

[0098] Assuming the pipeline length is L, after connecting “L / Δl” two-port networks of formula (6) in series, the total gas transmission delay can be estimated in a rolling manner:

[0099]

[0100] 1.3 Heating pipeline model

[0101] According to the theory of fluid mechanics and thermodynamics, the heat network can be divided into two parts: hydraulic model and thermal model. The main purpose of the steady-state analysis of the heat network is to calculate the water temperature at each node of the water supply network and the return network, the pipeline flow, and the heat source output at the balance node. The flow calculation of the heat network and the gas network both require the calculation of the operating state of the fluid in the pipeline. The difference is that the state of hot water (or steam) in the heat network is divided into two contents: hydraulic and thermal: the hydraulic working conditions are usually the working fluid flow rate and pressure; while the thermal working conditions are temperature and thermal energy (heat source / load). Therefore, the heat network is slightly more complicated than the gas network.

[0102] In the current research on district heating systems (DHS), the transmission speed of fluid pressure wave changes in the heating pipeline is about 400 to 1200 times that of temperature changes. The difference in time scale between hydraulic parameters and thermal parameters is ignored, that is, it is assumed that the hydraulic conditions remain stable in a thermal calculation cycle. However, based on the time scale of the instantaneous response of the power system, the hydraulic conditions of the heating network will undergo a series of complex non-steady-state processes. In the non-steady-state process, the pressure and flow of each part of the network continue to change with time. Since the dynamic model of the hydraulic pipeline of the heating system is similar to the dynamic model of the natural gas pipeline, except that the transmission medium is different, the continuity equation and momentum equation of a single heating pipeline in this chapter are derived by analogy with the establishment of the dynamic model of the natural gas pipeline above:

[0103]

[0104] In the formula, m l,t 、p l,t is the hot water mass flow and pressure of the control body at that time; is the hot water mass flow and pressure of the next section of the control body at the next moment; m l,0 、p l,0 is the initial steady-state mass flow and initial steady-state pressure of hot water in each section of the control body at each time; c is the speed of sound in hot water; D is the diameter of the hot water pipe; f is the friction coefficient; ρ is the hot water density; Δl is the section length.

[0105] Since the hot water in the pipe can be regarded as a one-dimensional incompressible fluid, the flow rate into the control body is equal to the flow rate out of the control body, there is no internal heat source in the pipe, and the diameter of the pipe is small compared to the length of the pipe, the radial temperature distribution of the fluid in the pipe can be ignored:

[0106]

[0107] In the formula, c p is the specific heat capacity of water; K s It represents the total heat transfer coefficient between hot water in the pipe network and the external environment, λ is the thermal conductivity of hot water, A is the cross-sectional area of ​​the fluid, T eis the ambient temperature, and m is the mass flow rate of the fluid.

[0108] The heat conduction of hot water in the heat network along the pipe length is weaker than the convection heat transfer, so the heat conduction of hot water along the pipe direction is ignored here. Further simplifying the thermal dynamic model of hot water in the pipe, the following equation can be obtained:

[0109]

[0110] By replacing the time derivative and space derivative of the hot water temperature in the pipe with differences and converting them into steady-state points, the numerical calculation format of the first-order implicit upwind difference can be obtained as follows:

[0111]

[0112] Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; Output hot water temperature.

[0113] The "Δτ i =ρAΔl / m l,t Substitute into the above formula and solve:

[0114]

[0115] The temperature of each control body of the pipeline at the nth moment can be calculated from the temperature of the control body of the adjacent pipeline.

[0116] For natural gas systems and thermal systems composed of multiple pipelines, the external constraints of the pipelines need to satisfy node flow balance constraints, ring network pressure drop conservation constraints, etc.

[0117] Assuming that there is no gas leakage problem inside the pipe network, the sum of the airflow entering any node should be equal to the sum of the airflow leaving the node. The flow continuity constraint of this node is expressed by the following formula:

[0118]

[0119] In the formula, F i S and F i LD Respectively represent the gas supply and gas consumption at node i; Γ NGN-ND Represents a set of node numbers in a natural gas system; and Represents the set of pipe numbers flowing into and out of node i respectively.

[0120] Similar to Kirchhoff's voltage law in circuits, when the network contains a ring network structure, when starting from a point and going around the pipes of the ring network and returning to the same point, the algebraic sum of the squares of the pressure drop in each section of the pipeline is always zero. Assuming that the gas flow direction in each section of the pipeline in the ring network is known, the constraint can be expressed as:

[0121]

[0122] In the formula, B l,b is the ring network-pipeline joint matrix; S NGN-L It is a collection of ring network numbers in the natural gas network.

[0123] The basic principle of gas-heat dynamic network coupling calculation is as follows: at each time step, the steady-state model of the pipeline network is used to calculate the mass flow and pressure distribution of the entire network at that time step. Combined with the unsteady-state model of the pipeline and the topological relationship of all pipelines in the entire network, the mass flow and pressure distribution of all control bodies of all pipelines in the entire network at that time step are calculated to obtain the mass flow and pressure at the outlet of each pipeline connected to the pipeline network. The calculated mass flow and pressure at each terminal and the flow and loop pressure balance equation of the pipeline network node are used to recalculate the flow and pressure distribution of the entire network at the next time step. This process is repeated and repeated to obtain the temperature, flow and pressure distribution of the entire network at each time step.

[0124] The steady-state condition of the pipe network can be solved based on the iterative algorithm, and the unsteady-state process of the pipeline can be solved using the second-order implicit difference method proposed above. The inlet and outlet boundary conditions of each pipeline in the entire pipe network system should be determined based on the topological connection relationship between the pipelines and the flow direction of the fluid in the pipeline.

[0125] Nodes and pipe sections are the basic units in the pipeline network of the integrated energy system, and the calculation of the pipeline network conditions is also based on the parameters of nodes and pipe sections. For large and complex gas and heat networks, the flow direction of the fluid in each pipe section is determined by the pressure conditions of the entire network, and the calculation of the unsteady process of the pipe section depends on its upstream inlet boundary conditions and the initial steady-state mass flow distribution and initial steady-state pressure distribution at the previous moment. The flow direction of the fluid in each pipe section of a large and complex gas and heat network may change during actual operation, so its upstream inlet boundary and downstream outlet boundary may be converted. When calculating the mass flow, pressure, and temperature distribution of each pipe section at each time step, it is necessary to ensure that the upstream boundary conditions have been calculated. This requires that the dynamic characteristics simulation process of the gas and heat network should be implemented in a certain pipe section sequence.

[0126] The breadth-first traversal algorithm is a graph search algorithm widely used in computer science, which can traverse the nodes and edges of a network graph. This section traverses the nodes and pipelines of the natural gas pipeline network and the heating pipeline network based on the breadth-first traversal method to determine the solution order of the non-steady-state process of each pipeline.

[0127] Based on the principles of graph theory, the natural gas pipeline network and the heating pipeline network can be regarded as a directed graph. The pipe sections and nodes are interrelated, and the premise of traversing the pipe sections is to traverse the nodes. As an efficient graph search strategy, the basic principle of breadth-first traversal is: starting from a node, radially traverse the surrounding area first. This method is simple and can effectively realize the traversal of nodes and pipe sections. The calculation order of the non-steady-state process of the pipe section obtained based on this can ensure that the upstream inlet boundary conditions of each pipe section precede the mass flow, pressure, and temperature distribution calculation of the pipe section. The specific calculation process is as follows Figure 2 shown.

[0128] In addition, when the external system is disturbed (such as a 10% reduction in heat supply at 10 minutes in the calculation example), there is no time delay in the power system, and it responds instantaneously, resulting in a power shortage. At this time, it is necessary to calculate the reduction in thermal power and temperature changes at the outlet of the heating system based on the heat-to-electricity ratio of the CHP unit in the "heat-to-electricity" mode. This process has a time delay. Then, based on the electric power shortage and the thermal power shortage, the gas transmission volume that needs to be increased in the gas transmission network is calculated to supplement the electric thermal power. This process has a time delay. Eventually, the system reaches a steady state, the voltage at the balance node of the power system rises, the mass flow rate at the outlet of the natural gas system increases, and the outlet temperature of the heating system decreases.

[0129] In the integrated energy system, each energy supply system is connected by coupling elements to realize the flow of energy, such as Figure 3 As shown:

[0130] The combined heat and power (CHP) unit consists of a gas unit, a waste heat boiler, an internal combustion engine and an external combustion engine. It is a production method that combines heat supply and power generation to produce both electricity and heat. Compared with the separate production of heat and power, it has many advantages, such as reducing energy consumption, improving air quality, reducing CO2 emissions, and facilitating comprehensive utilization.

[0131] The relationship between the thermal power and electrical power of a CHP unit can be expressed as:

[0132]

[0133] In the formula, k CHP is the heat-to-electricity ratio of the CHP unit; is the thermal power of the CHP unit at time τ; is the electric power of CHP at time τ.

[0134] The gas consumption of the CHP unit is:

[0135]

[0136] In the formula, is the gas consumption of the CHP unit; η CHPis the efficiency of the CHP unit; H GV It is the high calorific value of natural gas.

[0137] The CHP unit outputs heat to the heating system, and its heat output and water temperature meet the following requirements:

[0138]

[0139] In the formula, c p is the specific heat capacity of water; is the working fluid flow rate; is the water supply temperature at time τ; is the return water temperature at time τ.

[0140] Finally, in order to verify the proposed method, the IES with electricity, gas and heat coupling is taken as the research object, and the dynamic characteristics of gas, heat and other energy transmission are focused on. The dynamic response of different energy flows when the IES load changes is simulated and analyzed. Figure 4 The IES shown in the figure is used for case study. The integrated energy system mainly includes energy subsystems such as electricity, gas, and heat, and coupled equipment such as CHP. Among them, the power system is an IEEE 9-node power system, which is coupled with a 7-node natural gas system and a 7-node heating system through CHP units. The grid structure of the IEEE 9-node system: nodes 1, 2, and 3 are generator nodes, and nodes 5, 7, and 9 are load nodes. Both the natural gas system and the heating system are seven-node six-pipeline radial networks, and the power flow is as follows Figure 4 As shown, the natural gas network node 1 is used as the input of the CHP unit, and the heating network node 1 and the power network node 7 are used as the output of the CHP unit.

[0141] The mass flow, pressure and other data involved in the simulation are all from real data. The parameters of the natural gas pipeline and hot water pipeline are shown in Tables 2 and 3.

[0142] Table 2 Natural gas pipeline parameters

[0143]

[0144] Table 3 Hot water pipeline parameters

[0145]

[0146] Simulation results analysis:

[0147] 1. Verification of dynamic results of radiation network

[0148] Using the mathematical model of the natural gas pipeline in formula (3) above, the outlet mass flow and pressure of each section are calculated recursively for each section according to the initial steady-state mass flow and initial steady-state pressure of each section. The initial steady-state mass flow, initial steady-state pressure and initial steady-state temperature of each section of the heating network are known. The outlet mass flow, pressure and temperature of each section are calculated for each section according to formulas (8) and (12).

[0149] Figure 5 The left figure shows the change of the outlet mass flow rate of each section in the natural gas network with the number of sections. As shown in the figure, the mass flow of pipeline 1 drops from 453 (kg / s) to 431 (kg / s), and the mass flow of pipeline 1 outlet, that is, the mass flow of node 2, is 431 (kg / s). The inlet mass flow of pipeline 2 is 211 (kg / s), the inlet mass flow of pipeline 3 is 100 (kg / s), and the inlet mass flow of pipeline 4 is 120 (kg / s). The sum of the three is equal to the mass flow value of node 2, which verifies that the input mass flow at node 2 is equal to the output mass flow. The mass flow of pipeline 2 drops from 211 (kg / s) to 200 (kg / s), that is, the mass flow of node 3 is 200 (kg / s), while the inlet mass flow of pipeline 5 is 110 (kg / s), and the inlet mass flow of pipeline 6 is 90 (kg / s). The sum of the two is equal to the mass flow value of node 3. It meets the connection relationship of the pipeline network.

[0150] Figure 5 The right figure shows the change of outlet pressure of each section in the natural gas network with the number of sections. As shown in the figure, the pressure of pipeline 1 rises from 50 (bar) to 50.03 (bar), while the inlet pressures of pipelines 2, 3, and 4 are equal to the outlet pressure of pipeline 1, which is 50.03 (bar). The pressure of pipeline 2 rises from 50.03 (bar) to 50.06 (bar), and the inlet pressures of pipelines 5 and 6 are equal to the outlet pressure of pipeline 3, which is 50.06 (bar). Similarly, it conforms to the connection relationship of the pipeline network. Even if the initial pressures of pipelines 2, 3, and pipeline 4 are equal, and the pipeline parameters are also equal, but due to the different mass flows passing through each pipeline, the pressure rise trends of pipelines 2, 3, and 4 are also different. The mass flow of pipeline 2 is large, and the pressure rises slowly. The mass flow of pipeline 3 is small, and the pressure rises faster. The mass flow of pipeline 4 is smaller, and the pressure rises fastest. The dynamic mathematical model of the natural gas pipeline is consistent with the actual situation.

[0151] Figure 6 The graph of the outlet temperature of each section in the heating network changes with the number of sections. The mass flow pressure change trend of the heating network is Figure 5As shown in the figure, the temperature of pipe 1 drops from 98 (℃) to 97.8 (℃), and the starting values ​​of the temperatures of pipes 2, 3, and 4 are all 97.78 (℃), which is equal to the end temperature of pipe 1; the temperature of pipe 2 drops from 97.78 (℃) to 97.35 (℃), and the starting values ​​of the temperatures of pipes 5 and 6 are all 97.35 (℃), which is consistent with the end temperature of pipe 2, which is consistent with the pipe network connection relationship. It can be seen that as the fluid flows, the trend of pipe temperature decreases faster and faster, which is consistent with the actual temperature transmission law of the heating pipe.

[0152] After the mass flow, pressure and temperature are calculated section by section, the time delay of each section is calculated according to formula (6), and the time delay is accumulated section by section.

[0153] Depend on Figure 7 , 8 As shown in Figure 9, the mass flow, pressure, and temperature change in the time delay when flowing in the seven-node six-pipeline radial network. The mass flow flows from 453 (kg / s) at the beginning of the network to 81.91 (kg / s) at the end of the network, and the pressure rises from 50 (bar) at the beginning of the network to 50.12 (bar) at the end of the network in 2.049 (s), which reflects the delay characteristics of natural gas transmission in the pipeline. Figure 7 , 8 It can be seen that with the passage of time, the mass flow and pressure changes of natural gas in the pipeline are becoming slower and slower.

[0154] Depend on Fig. 9 It can be seen that it takes 2202 (s) for the temperature to drop from 98 (℃) at the beginning of the network to 95.65 (℃) at the end of the network. The time difference between the response of the first pipe and the response of the sixth pipe is about 30 minutes, which reflects the delay characteristics of heat transmission in the pipe.

[0155] Verify the changes of mass flow and pressure with time delay in the seven-node six-pipeline radial network. Compared with the changes of mass flow and pressure with the number of segments, the horizontal axis is time delay, which can more clearly show the connection relationship of the pipeline network and the changing trends of mass flow, pressure and temperature during the pipeline flow.

[0156] 2. Simulation results and analysis of load change conditions

[0157] Electricity, gas, and heat are coupled through cogeneration units, consuming gas to generate electricity and heat. When external disturbances occur, the electricity reaction is completed transiently, resulting in a power shortage, which requires gas turbines to consume gas to make up for the shortage. The entire natural gas network increases the gas transmission volume, and the gas flow through the pipeline will inevitably change the pipeline flow and pressure state quantity, and will also produce time delays. The cogeneration unit will then cause changes in the temperature, flow, and pressure state quantity of the heating pipeline, resulting in time delays.

[0158] Assume that the heating system gradually decreases by 10% after running for 10 minutes, and other conditions remain unchanged. The CHP unit is in the "heat-to-electricity" mode. Since the CHP unit is in the "heat-to-electricity" mode, when the heating supply drops by 10%, its heat and electricity output also decreases accordingly. At this time, the power load demand of the power system is borne by the balancing node. Solve the changes in the electric power and gas consumption of the balancing node.

[0159] like Fig.10 As shown, at the 10th minute, the outlet temperature of the heating system began to drop from 98 (℃), and after 32.61 minutes, at the 42.61th minute, the outlet temperature reached a steady state of 88 (℃), and the temperature drop trend became slower and slower.

[0160] like Fig.11 As shown in the figure, at 2556.5 seconds (42.61 minutes), the voltage of the balancing node increased from 0.52pu to 0.71pu, and the mass flow rate at the outlet of the natural gas system began to increase from 91 (kg / s). At 2558.26 seconds, the mass flow rate at the outlet reached a steady state of 100 (kg / s), and the rising trend became slower and slower. In order to meet the demand for electrical load, the voltage of the balancing node increased from 0.52pu to 0.71pu.

[0161] The mutual coupling between the power system and the heating system causes the internal disturbance of the heating system to act on the source side of the power system, causing the redistribution of power output. The state changes of the power system and the heating system also cause the response of the natural gas system, first affecting the load side of the gas system, causing rapid changes in gas load, and then causing the redistribution of pressure and transmission flow of each branch pipe.

[0162] The above research shows that the dynamic simulation analysis method of the integrated energy system can not only simulate the network dynamic characteristics of a single energy source, but also simulate the dynamic response between multiple heterogeneous energy flows, and the simulation effect is good. This method can provide theoretical support for research such as IES operation optimization and multi-agent online energy flow analysis.

[0163] Those of ordinary skill in the art will appreciate that the units of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition of each example has been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0164] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical function division, and there may be other division methods in actual implementation, for example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.

[0165] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0166] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-0nlyMemory), random access memory (RAM, RandomAccessMemory), mobile hard disk, magnetic disk or optical disk, etc., which can store program code.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention 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 replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A method for constructing a transient model of an electrical thermal network based on multiple time scales, characterized in that: Including the construction of a natural gas pipeline model, as follows: Ignoring the effects of gravitational acceleration and inclination, a set of partial differential equations obtained based on the laws of conservation of mass and momentum are as follows: Where: and are differential operators for distance l and time t respectively; m l,t and p l,t are mass flow and gas pressure respectively; c is the sound velocity of natural gas; A is the cross-sectional area of ​​the pipeline; D is the pipeline diameter; f is the friction coefficient; L is the pipeline length; ρ is the gas density.

2. The method for constructing a transient model of an electrical thermal network based on multiple time scales according to claim 1, characterized in that: The following steps are also included: Obtain a natural gas pipeline model and use finite difference approximation to linearize the differential operator and The quadratic term "16m l,t 2 / π 2 D 4 ρ" and "-8fc 2 m l,t m l,t | / π 2 D 5 ρ l,t ” is converted into a steady-state point (m l,0 , p l,0 ), the constants at are: Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; and are the output mass flow and air pressure respectively; "Δτ i =πD 2 ρΔl / 4m l,0 Substitute it into the solution and get the following two-port network equation of the differential pipeline Δl:

3. The method for constructing a transient model of an electrical thermal network based on multiple time scales according to claim 2, characterized in that: It also includes the calculation of the total gas transmission delay, as follows: By m l,t and The mean of Δτ is re-estimated i for: Assuming the pipeline length is L, after connecting "L / Δl" two-port networks of formula (4) in series, the total gas transmission delay can be estimated in a rolling manner:

4. The method for constructing a transient model of an electrical thermal network based on multiple time scales according to claim 2, characterized in that: It also includes building a heating pipeline model, as follows: In the formula, m l,t and p l,t is the hot water mass flow and pressure of the control body at that time; and is the hot water mass flow and pressure of the next section of the control body at the next moment; m l,0 and p l,0 is the initial steady-state mass flow and initial steady-state pressure of hot water in each section of the control body at each time; c is the speed of sound in hot water; D is the diameter of the hot water pipe; f is the friction coefficient; ρ is the hot water density; Δl is the section length.

5. The method for constructing a transient model of an electrical thermal network based on multiple time scales according to claim 4, characterized in that: Including the construction of hot water temperature calculation method, as follows: The hot water in the pipe can be regarded as an incompressible fluid, and the radial temperature distribution of the fluid in the pipe is ignored, and the thermal dynamic model of hot water in the pipe is obtained: In the formula, c p is the specific heat capacity of water; K s It represents the total heat transfer coefficient between hot water in the pipe network and the external environment, λ is the thermal conductivity of hot water, A is the cross-sectional area of ​​the fluid, T e is the ambient temperature, m is the mass flow rate of the fluid; Ignore the heat conduction of hot water along the pipe direction and further simplify the thermal dynamic model of hot water in the pipe to obtain: The time derivative and space derivative of the hot water temperature in the pipe are replaced by differences and converted into steady-state points, and the numerical calculation format of the first-order implicit upwind difference is obtained as follows: Where: Δτ i is the transmission delay of the i-th differential pipeline Δl; is the output hot water temperature; "Δτ i =ρAΔl / m l,t Substitute it into the solution and get:

6. The method for constructing a transient model of an electrical thermal network based on multiple time scales according to claim 1, characterized in that: It also includes the construction of network gas and heat flow grid constraint equations, including node flow balance constraints and ring network pressure drop conservation constraints. The node flow balance constraints are as follows: In the formula, F i S and F i LD Respectively represent the gas supply and gas consumption at node i; Γ NGN-ND Represents a set of node numbers in a natural gas system; and Represents the set of pipe numbers flowing into and out of node i respectively; The specific constraints of ring network voltage drop conservation are as follows: In the formula, B l,b is the ring network-pipeline joint matrix; S NGN-L It is a collection of ring network numbers in the natural gas network.

7. A gas-heat dynamic pipe network coupling calculation method, characterized in that: The method applied to any one of claims 1 to 6 comprises the following steps: At each time step, the steady-state model of the pipe network is used to calculate the mass flow and pressure distribution of the entire network at that time step; Combined with the unsteady-state model of the pipeline and the topological relationship of all pipelines in the whole network, the mass flow and pressure distribution of all control bodies of all pipelines in the whole network at this time step are calculated to obtain the mass flow and pressure at the outlet of each pipeline connected to the pipeline network; Use the calculated mass flow and pressure at each terminal as well as the network node flow and loop pressure balance equation to recalculate the flow and pressure distribution of the entire network at the next time step; And so on, through iterative cycles, the temperature, flow and pressure distribution of the entire network at each time step can be obtained.

8. A gas-heat dynamic network coupling calculation method according to claim 7, characterized in that: The pipe network coupling is numerically calculated through breadth-first traversal.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium includes a stored program, wherein when the program is running, the device where the computer-readable storage medium is located is controlled to execute the method for constructing an electrical thermal network transient model based on multiple time scales as described in any one of claims 1 to 6.

10. A processor, characterized in that: The processor is used to run a program, wherein when the program is run, the gas-heat dynamic pipeline network coupling calculation method described in any one of claims 7 to 8 is executed.

Images