A simulation method for electric power-heat steam coupling energy system

Abstract

The present invention discloses a simulation method for an electric-thermal-steam coupled energy system. The method comprises the following steps: S1, establishing a steady-state simulation model of an electric-thermal-steam coupled energy system, including an electric power subsystem, a steam heating subsystem and a thermoelectric coupling device model; S2, determining the solution conditions and solution steps of the steam heating subsystem; S3, determining the solution steps of the electric-thermal-steam coupled energy system according to the type of coupling device; S4, performing solution operations according to the solution steps established in S3. In terms of modeling the steam heating subsystem, the present invention simplifies the model by using piecewise linear fitting, accurately considers the condensation water loss in the hot steam transmission process, and greatly improves the model solution speed while ensuring the accuracy of the solution. The simulation and analysis method for an electric-thermal-steam coupled system provided by the present invention is conducive to promoting the use of thermoelectric coupling complementary characteristics in industrial scenarios with high steam loads to effectively improve energy utilization and new energy consumption capacity.

Description

Technical Field

[0001] The invention relates to the technical field of energy system simulation analysis, and in particular to a simulation method for an electric power-thermal steam coupling energy system. Background Art

[0002] In the integrated energy system, the electric-heat coupled energy network has developed most rapidly. The development of cogeneration units and electrified heating equipment has led to the coupling and interaction between the power grid and the heat network. By using the energy storage characteristics of the heat network to store energy in the power grid, it is possible to adjust the fluctuations of the power grid, which is conducive to the access of new energy and the improvement of energy utilization. The scale of centralized heating and cogeneration is gradually expanding worldwide.

[0003] Central heating systems can be divided into hot water heating systems and steam heating systems according to the type of heat medium. At present, the research on thermoelectric coupling energy systems mainly focuses on the coupling system of urban heating subsystems and power subsystems with hot water as the heat medium, while there is little research on thermoelectric coupling systems with steam as the heat medium. The temperature, pressure, and density of steam change during the flow of the heating pipeline. There is a large heat dissipation loss along the transmission, and phase change may occur and condensed water may be produced, which may even cause the parameters such as the flow rate, pressure, and temperature of the hot steam reaching the final heat user to not meet the user's needs.

[0004] Therefore, in order to promote the development of steam-electricity coupling systems in industrial scenarios with large steam heat loads, it is necessary to establish a fast and accurate coupling simulation system between the power grid and the steam heat network. Summary of the invention

[0005] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a steady-state simulation model of an electricity-heat steam coupled energy system, which is a fast and accurate coupling simulation system of the power grid and the steam heat network, fully realizing the combined utilization and regulation control of thermal energy and electrical energy, improving the energy utilization efficiency of the entire system, optimizing the system operation state, and improving the system safety and stability.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for simulating an electric power-heat steam coupling energy system comprises the following steps:

[0008] S1. Establish a steady-state simulation model of the power-heat steam coupling energy system, including a power subsystem model, a steam heating subsystem model, and a thermoelectric coupling equipment model;

[0009] S2: Based on the steam heating subsystem model established in step S1, by analyzing the total number of equations and unknown quantities to be solved of the equation group and combining with engineering practice, determine the solution conditions and solution steps of the steam heating subsystem model;

[0010] S3: Based on two typical CHP unit types, back pressure unit and extraction condensing unit, determine the coupling degree between the power subsystem and the steam heating subsystem, so as to determine the solution steps;

[0011] S4: Based on the solution steps determined in step S3, the Newton-Raphson method / cplex solver is used to solve the corresponding set of equations and analyze the results.

[0012] Beneficial effects of the present invention:

[0013] The present invention proposes a simulation method for an electric-heat steam coupling energy system taking into account condensate loss, which is beneficial to improving energy utilization efficiency and the consumption of new energy for industrial intensive areas with a large demand for steam heating. The main advantages are: 1) In view of the complex model and inaccurate calculation of condensate loss and heat loss in the traditional steam network, the model is simplified by the piecewise linear fitting method of saturated steam properties, and the heat loss correction coefficient is introduced to correct the heat loss changes caused by weather and other reasons. At the same time, the condensate loss in the steam transmission process is fully considered, and high-precision and high-speed electric-steam coupling simulation is achieved. 2) In view of the operating differences between back pressure and extraction condensing CHP units in the steam network, a modeling and solution method for electric-steam coupling network containing multiple types of CHP units is proposed. 3) The method proposed in this paper is verified by a nine-node tree / ring network case. The relative error of the pipeline flow is within 1.5%, which is slightly better than the traditional simulation method. The simulation time is shortened to 0.479%, and the solution speed is significantly improved. 4) Through this simulation method, its application in the consumption of new energy is expanded. Through simulation, it was found that the introduction of electric boilers can reduce the volatility of grid load, thereby improving the stability of the entire system and facilitating the access of new energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described below in conjunction with the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the pipeline mass flow model in the steam heating subsystem;

[0016] Figure 2 It is a schematic diagram of the principle of the back pressure unit;

[0017] Figure 3 This is the electric and thermal characteristic diagram of the back pressure unit;

[0018] Figure 4 This is a schematic diagram of the principle of the extraction condensing unit;

[0019] Figure 5 This is the electric and thermal characteristic diagram of the extraction condensing unit;

[0020] Figure 6The solution flow chart of the power-heat steam coupled energy system containing only back pressure units;

[0021] Figure 7 It is a solution flow chart for the electric power-heat steam coupled energy system containing extraction condensing units;

[0022] Figure 8 The network structure of the electric power-heat steam coupling energy system in the embodiment;

[0023] Fig. 9 This is a graph showing the relationship between the active power of the grid balancing node and the steam load. DETAILED DESCRIPTION

[0024] 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 only 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.

[0025] The system structure in the embodiment of the present invention is as follows Figure 8 As shown, the network part marked with “·”-shaped nodes is the power grid subsystem, which uses the IEEE five-machine 14-node network, among which the balancing unit is connected to node 1; The node network part is the steam heating subsystem. The network structure of this part has a certain correspondence with the power grid subsystem. It is an 11-node double-ring network, in which a steam boiler with a capacity of 50t / h is connected at node 1. The power subsystem and the hot steam subsystem are coupled through the CHP unit at their respective nodes 2. Referring to the product data of Qingdao Jieneng Steam Turbine Group Co., Ltd., the CHP unit uses 4 9MW back-pressure thermal power units with a maximum steam output of 90t / h. When the CHP unit still cannot meet the thermal load at the maximum thermal power, the steam boiler at node 1 provides the insufficient thermal power. Other parameters of the coupled system are detailed in Table 1.

[0026] Table 1 Steam heating subsystem pipeline parameters

[0027]

[0028] An embodiment of the present invention provides a method for simulating an electric power-heat steam coupling energy system taking into account condensed water loss, comprising the following steps:

[0029] Step 1): Establish a steady-state simulation model of the power-heat steam coupling energy system, which mainly includes three aspects: 1. Power subsystem model, 2. Steam heating subsystem model, 3. Thermoelectric coupling equipment model. The steam heating subsystem model mainly includes four aspects: pipeline momentum balance equation, node mass flow balance equation, pipeline mass flow balance equation and pipeline energy balance equation. The thermoelectric coupling equipment model selects two typical thermoelectric coupling equipment CHP units and electric boilers for steady-state mathematical modeling;

[0030] Step 2): Based on the steam heating subsystem model established in step 1), by analyzing the total number of equations and unknown quantities to be solved in the equation group and combining with engineering practice, determine the solution conditions and solution steps of the steam heating subsystem model;

[0031] Step 3): Based on two typical CHP unit types (back pressure unit and extraction condensing unit), determine the coupling degree between the power subsystem and the steam heating subsystem under different CHP unit types, thereby determining two different solution steps;

[0032] Step 4): Based on the solution steps determined in step 3), the Newton-Raphson method / cplex solver is used to solve the corresponding set of equations and analyze the results.

[0033] The steady-state simulation model of the electric-thermal steam coupling energy system described in step 1) is established, including the electric power subsystem model, the steam heating subsystem model and the thermoelectric coupling equipment model. The steam heating subsystem model mainly includes four aspects: the pipeline momentum balance equation, the node mass flow balance equation, the pipeline mass flow balance equation and the pipeline energy balance equation. The thermoelectric coupling equipment model selects two typical thermoelectric coupling equipment CHP units and electric boilers for steady-state mathematical modeling. The process is:

[0034] Step 101) Power subsystem model:

[0035] At present, the research on steady-state mathematical models and power flow calculations of power systems has been very mature and widely used in the planning and scheduling of actual power grids. It is still applicable in integrated energy networks containing CHP units, photovoltaics, and wind power. Therefore, based on the traditional AC power flow equation, a mathematical model of the power subsystem can be established and subsequent power flow calculations can be performed.

[0036] In the steady-state mathematical model of the power system, the variables that can represent the node or bus state are the node or bus voltage vector and the node injection power. The power flow equation of the power network is:

[0037]

[0038] Where U i and θ iis the voltage amplitude and phase angle of node i, E is the set of all nodes in the power network, P i and Q i is the active power and reactive power injected into node i, G ij and B ij It is the real and imaginary parts of the mutual admittance between nodes i and j (the self-admittance of node i when i=j).

[0039] In the process of power flow solution, the four state variables U of node i i ,θ i , P i , Q i In the process, there are two known quantities and two unknown quantities, and according to the different known quantities, the nodes can be classified into PV nodes, PQ nodes and balance nodes.

[0040] Step 102) Steam heating subsystem model:

[0041] Step 1021) Model Assumptions:

[0042] For the modeling of the hot steam network, the following assumptions were made:

[0043] 1) Convert curves into straight lines: Most of the actual steam pipes are laid in a curved manner. In order to simplify the calculation of the model, straight pipes of the same length are used to replace curved pipes during the modeling process.

[0044] 2) Treat the steam in the pipe as a one-dimensional steady-state flow: Since the parameters of the steam at the same cross-section of the pipe do not change much, in order to simplify the model, it can be considered that the steam parameters are uniformly distributed on the same cross-section and only change in one dimension, which is the pipe direction.

[0045] 3) Treat the steam in the pipe as a single-phase compressible fluid: During the transmission of steam in the pipeline, condensed water will be produced during the process of pressure loss and temperature reduction. In the modeling process, it is believed that the condensed water can be completely discharged along the way by the steam trap, so the steam in the pipe can be modeled as a unidirectional compressible fluid.

[0046] Step 1022) Pipe segment momentum balance equation:

[0047] Since the hot steam is assumed to be a one-dimensional steady-state flow in the modeling, the cross-sectional area of ​​the pipe section is A (m 2 ), establish the x-axis along the pipeline direction (take the steam flow direction as the positive direction of the x-axis, unit: m), then the volume of the steam element can be expressed as A·dx, and the steam pressure at the coordinate x is P=P(x,t) (unit: Pa), t represents time (s).

[0048] The connotation of the momentum balance equation is that the momentum change of the steam element is equal to the sum of the impulses of all external forces acting on the element. From the model assumption, it can be seen that the steam is in a stable flow state. Based on the actual situation, we can ignore the inertia term, gravity term, and convection term of the momentum equation, and we can get the momentum balance equation of stable steam flow:

[0049]

[0050] Where ρ is the density of the steam element (kg / m 3 ), u is the flow velocity of the steam element (m / s), λ is the friction coefficient of the pipe section (dimensionless), and d is the inner diameter of the pipe (m).

[0051] By using the relationship between the steam mass flow rate Q (kg / s) and the steam parameters to eliminate the steam flow rate u, the momentum differential equation of the steam in the pipeline at steady state can be obtained:

[0052]

[0053] When the steam is saturated steam, the steam density ρ can be regarded as a function of the pressure P only. This method uses the piecewise linear fitting relationship between the saturated steam density and the pressure. Within each pressure range, the relative error of the fitting formula is within ±2%. Its expression is:

[0054] ρ=c1P+c2 (4)

[0055] In the formula, c1 and c2 are fitting coefficients, and their values ​​are shown in Table 2:

[0056] Table 2 Calculation of fitting coefficients for saturated steam density

[0057]

[0058] And integrating the differential equation, we get:

[0059]

[0060] Where, L is the length of the pipeline (m), P in and P out are the steam pressures at the steam inlet and outlet ends of the pipe respectively.

[0061] Finally, the influence of local resistance loss in the pipeline is considered and the flow efficiency factor e is introduced. The steady-state momentum balance equation of the pipeline after considering the local resistance loss is:

[0062]

[0063] Therefore, the pipeline momentum balance equation can be written for the entire hot steam network:

[0064]

[0065] Where W is the set of all pipes in the steam network, Q i is the steam flow rate in pipe i, which can be substituted with the average steam flow rate at the beginning and end of the pipe, that is:

[0066]

[0067] Among them, Q in,i and Q out,i are the steam flow rates flowing into and out of pipe i, respectively.

[0068] Step 1023) Node mass flow balance equation:

[0069] Based on Kirchhoff's first law (or continuity theorem), the mass flow rate flowing into any node is equal to the sum of the mass flow rates flowing out of it. Therefore, the mass flow balance equation of the node can be written as shown below:

[0070]

[0071] In the formula, Q n,i is the injected steam flow rate at node i, W in,i is the set of all pipes flowing into node i, W out,i is the set of all pipes flowing out of node i. For a hot steam network with N nodes, a total of N node mass flow balance equations can be listed.

[0072] Step 1024) Pipe section mass flow balance equation:

[0073] Since the steam temperature in the pipeline is higher than 100°C and there is a temperature difference with the external environment, there must be heat dissipation loss during steam transmission, which reduces the steam temperature in the pipeline and causes part of the steam to undergo phase change and condense into condensed water. In the model assumptions, it is assumed that the condensed water in the pipeline can be discharged along the way through the steam trap. Assume that for pipeline i, the total mass flow rate of condensed water generated along the way is Q c,i (kg / s), established as Figure 1 Pipe mass flow model shown.

[0074] The mass flow balance equation of the pipeline can be established based on the law of mass conservation, as shown below:

[0075] Q in,i =Q out,i +Q c,i ,i∈W (10)

[0076] Among them, Q in,i and Q out,iare the steam flow rates (kg / s) flowing into and out of pipe i respectively.

[0077] Step 1025) Pipe section energy balance equation:

[0078] Based on the principle of energy conservation, the change in enthalpy of steam at the beginning and end of the pipeline should be consistent with the heat loss of steam in the pipeline. Therefore, the energy balance equation of the steam pipeline can be established, as shown in the following formula:

[0079] Q in,i h in,i =Q out,i h out,i +Q c,i h c,i +H i ,i∈W (11)

[0080] In the formula, h in,i 、h out,i 、h c,i are the specific enthalpy of the beginning and end of pipe i and the condensed water (kJ / kg), H i is the heat loss power (kW) during the steam flow in pipe i.

[0081] The specific enthalpy of saturated steam or saturated water can be obtained by looking up the table based on the known pressure P. However, for the convenience of model solution, this model uses a fitting relationship to calculate the specific enthalpy. For the specific enthalpy of steam at the beginning and end of the pipeline h in,i 、h out,i , and its calculation formula is:

[0082]

[0083] In the formula, the unit of pressure P needs to be converted into MPa, and a0-a6 is a constant coefficient. The applicable range of this calculation formula is 0.40Mpa≤P≤2.50MPa, and the relative error is ±8.7×10 -6 Within.

[0084] For the specific enthalpy of condensed water h c,i , calculated using the following formula:

[0085]

[0086] Where P i It still needs to be converted to MPa, the applicable range is 0.40Mpa≤P≤2.50MPa, and the relative error is ±2.4×10 -5 Within.

[0087] The heat loss power H of the pipeline is proportional to the length of the pipeline and the temperature difference between the inside and outside of the pipe. The calculation formula commonly used in existing literature is:

[0088] H i =K i L i (T i -T a ),i∈W (14)

[0089] In the formula, K i is the total heat transfer coefficient of pipe i (kW / (m·K)), that is, the amount of heat dissipated per unit length of pipe per unit time when the temperature difference between the inside and outside of the pipe is 1°C. i is the length of pipe i (m), T i is the average steam temperature in pipe i, T a is the ambient temperature outside the pipe.

[0090] The fitting formula of the relationship between temperature and pressure of saturated steam:

[0091] T=202.7651P 0.2148 -22.907 (15)

[0092] Take the average steam temperature at the beginning and end of pipe i as the average steam temperature T of pipe i i (℃), then its expression is:

[0093]

[0094] For the total heat transfer coefficient of the pipeline K i The calculation method is different according to the pipeline laying method, mainly including overhead laying, direct burial laying, trench laying and underground semi-trench laying. However, empirical calculations have found that the heat dissipation loss calculated by the formula is quite different from the data provided. The formula is derived from pure theory and has a certain deviation from the actual project. This model introduces the correction coefficient C based on the formula. t , in order to correct the influence of weather and other factors on heat dissipation loss, so that the calculated value is closer to reality. t After that, the heat dissipation loss power H is calculated as:

[0095] H i =C t K i L i (T i -T a ),i∈W (17)

[0096] On sunny days, considering the additional losses in various aspects, C is recommended. t =1.3; on cloudy days, different correction factors should be selected according to specific weather conditions, and should be reasonably selected in combination with the specific conditions and empirical data of the locations of each system.

[0097] Substituting the formula into the formula, we can get the final expression of the steam pipeline energy balance equation:

[0098] Q in,i h in,i =Q out,i h out,i +Q c,i h c,i +C t K i L i (T i -T a ),i∈W (18)

[0099] Step 1026) Summary of hot steam network control equations:

[0100] Through the analysis of the control equations of the hot steam network in the previous article, for a hot steam network with N nodes and M branches, we can list M pipe segment momentum balance equations, N node mass balance equations, M pipe segment mass balance equations, and M pipe segment energy balance equations, totaling (3M+N) network equations. The control equations of the hot steam network are summarized as follows:

[0101]

[0102] Step 103) Thermoelectric coupling device model:

[0103] Thermoelectric coupling devices are the link between the power system and the thermal system. They are the hubs for connection, conversion, and restriction between different energy forms, which creates a coupling relationship between the originally independent power system and thermal system. They are a vital component of the thermoelectric coupling energy system. Typical thermoelectric coupling devices include CHP units, electric boilers, heat pumps, etc. In the power-thermal steam coupling energy system, the key ones are CHP units and electric boilers. The steady-state models of these two coupling devices will be established below.

[0104] Step 1031) CHP unit model:

[0105] CHP units (combined heat and power units) can supply both electricity and heat by burning coal or natural gas. Based on the different uses of the new steam, CHP units can be divided into back pressure units and extraction condensing units. Extraction condensing units can be divided into single extraction units and double extraction units according to different heating principles. Since different types of CHP units have different principles, their models also have certain differences.

[0106] 1) Back pressure unit

[0107] The principle diagram of the back pressure unit is as follows Figure 2As shown, since there is no condenser, the new steam generated will expand and do work in the turbine, and the exhaust steam will be completely used for heating, so the exhaust steam heat will be fully utilized and the thermal efficiency is high.

[0108] Since the exhaust steam of the back pressure unit is all used for heating, it can be considered that the electrical power P and thermal power Φ supplied by it are basically in a linear relationship:

[0109] P=K CHP Φ (20)

[0110] Or it can be expressed in the form of a constant heat-to-electricity ratio, that is, the ratio of the thermal power generated by the CHP unit to the electrical power is a certain value K CHP , as shown below:

[0111]

[0112] The electrothermal characteristics of the back pressure unit are shown in the figure below: Figure 3 shown.

[0113] 2) Extraction condensing unit

[0114] The difference between the extraction condensing unit and the back pressure unit is that part of the steam entering the turbine will be extracted to provide heat to the heat load users, while the remaining part will continue to expand in the turbine to do work and be used for power generation, and finally condense into water through the condenser and return to the boiler for recycling. Figure 4 shown.

[0115] Because the steam extraction volume and steam extraction pressure used for heating are adjustable, the active power output and steam supply of the extraction condensing unit have greater adjustment space than the back pressure unit. For the extraction condensing unit, part of its fresh steam is extracted for heating, and the rest is continued to be used for power generation, so there is a certain coupling relationship between its power supply and heating power. The electric and thermal characteristics of the extraction condensing unit are shown in the figure below. Figure 5 shown.

[0116] Based on the electric and thermal characteristics of the extraction condensing unit, the coupling relationship between the power supply power P and the heating power Φ of the extraction condensing unit can be written as:

[0117]

[0118] In the formula, (P i ,Φ i )correspond Figure 5 Obviously, for the extraction condensing unit, its thermal-electric ratio is variable within a certain range.

[0119] Step 1032) Electric boiler model:

[0120] In the thermoelectric coupling energy system, electric boilers are also very important thermoelectric coupling devices. Peak-shaving electric boilers can be used as a supplementary heat source in the entire coupling system. They are often used at night in winter when the heat load is high and the electricity load is low. Electric boilers can use excess electricity to produce heat energy, which plays a role in reducing the peak of heat load and filling the valley of electricity load, thereby improving the operating efficiency, safety and stability of the system, and also creating more possibilities for the access of new energy such as photovoltaic and wind power.

[0121] This paper adopts an electric boiler model with a fixed peak load ratio. The peak load ratio refers to the ratio of the peak load borne by the electric boiler to the total heat load at the node, and its expression is:

[0122]

[0123] In the formula, K p That is, the peak regulation ratio, Φ EB It represents the peak thermal power provided by the electric boiler, and Φ represents the total thermal load of the node.

[0124] In step 2), based on the steam heating subsystem model established in step 1), by analyzing the total number of equations and unknown quantities to be solved in the equation group and combining with engineering practice, the process of determining the solution conditions and solution steps of the steam heating subsystem model is as follows:

[0125] Step 201) Establish and solve the steam heating subsystem equation:

[0126] Based on the hot steam system simulation model established in step 102), if you want to solve the steam network flow, you also need to know some known conditions under the stable operation of the entire system:

[0127] 1) For any node in the system, one of the two variables, node pressure and node injection flow, is a known variable and the other is an unknown variable.

[0128] 2) The pressure of at least one node in the whole system is known, and this node is usually at the heat source. When the output steam flow of the heat source does not reach the maximum limit, it is usually set to a constant outlet steam pressure and a variable output flow; when it is fully operational, the output flow is constant and the outlet steam pressure is unknown.

[0129] 3) Usually at heat users and intermediate nodes, the flow rate is a known quantity and the pressure is an unknown quantity.

[0130] 4) The topological structure of the steam pipe network system and the parameters of each pipeline are known quantities.

[0131] 5) The external ambient temperature of the steam pipe is known, and the actual measured value of the outdoor temperature can be taken.

[0132] Step 202) Steam heating subsystem solution conditions:

[0133] In the hot steam network simulation model established in step 102), for a hot steam pipe network system with N nodes and M branches, (3M+N) network control equations can be listed, as shown in Table 3:

[0134] Table 3 Network control equations of N-node and M-branch hot steam network

[0135]

[0136] In this pipe network, the quantity to be determined is the flow rate Q at the beginning of M pipes. in , terminal flow Q out , Pipeline condensate water volume Q c , and the pressure P of N nodes or the node injection flow Q i So there is a total of (3M+N) terminal flow Q out For these (3M+N) unknown quantities, by combining (3M+N) network control equations, all unknown quantities can be uniquely solved. The network control equation is a set of nonlinear equations. According to engineering practice, the network topology of the steam heat network is generally relatively simple, and the number of nodes and pipelines is relatively small, so the Newton-Raphson method can be used to solve the nonlinear equations.

[0137] In step 3), based on two typical CHP unit types (back pressure unit and extraction condensing unit), the coupling degree between the power subsystem and the steam heating subsystem under different CHP unit types is determined, thereby determining two different solution steps, and the process is as follows;

[0138] When different thermoelectric coupling device models are selected in the power-heat steam coupled energy system, the coupling degree between the power subsystem and the steam heating subsystem is also different, so the best simulation solution method for the power-heat steam coupled energy system is different. The following will analyze the solution ideas and process of the steady-state simulation of the power-heat steam coupled energy system from the two cases of using a back pressure unit and an extraction condensing unit for the CHP unit.

[0139] Step 301) only includes back pressure units:

[0140] For back-pressure thermal power units, their power supply is proportional to the heating power, that is, the heat-to-power ratio is fixed. Usually, because the topology of the thermal steam network is relatively simple and has fewer heat sources, and the power system is usually larger and has stronger adjustable performance, the "heat-to-power" operation mode is usually adopted, that is, the heating power of the back-pressure unit is determined according to the heat load demand of the steam heating network, and then the active power output is determined by the coupling relationship between the unit's heating power and power supply power.

[0141] In the "heat-to-electricity" operation mode, the decoupling between the steam heating subsystem and the power subsystem can be fully realized: that is, when the thermal load of the hot steam system is known, the power flow calculation of the hot steam network can be performed first to calculate the heating power of each heat source (including the CHP unit); then the power supply power of the back-pressure unit can be calculated based on the thermal-electric coupling relationship; finally, the power flow calculation of the power network can be performed. It is precisely because of the decoupling between the heating subsystem and the power subsystem that the power flow solution of the electric-thermal steam coupling energy system with the CHP unit as a back-pressure unit is simplified. The solution process is as follows: Figure 6 shown.

[0142] In step 4), based on the solution steps determined in step 3), the Newton-Raphson method is used to solve the steam heating sub-network and the power sub-network in turn, and the results are analyzed.

[0143] 1) Result analysis

[0144] Since the analyzed network only contains back-pressure thermal power units, the coupled system simulation is solved by the "heat-to-power" calculation method: first solve the thermal steam network, then calculate the active output of the CHP from the back-pressure unit model, and finally solve the power grid flow calculation. Therefore, when the heating power of the CHP unit changes, its power supply power will also change. If the electrical load remains unchanged, the change in the CHP power supply power will directly affect the output of the balancing unit. Fig. 9 The figure shows the change of active power of the grid balancing node when the heat load of the steam network gradually increases from 200t / h to 400t / h. As can be seen from the figure, with the increase of heat load, the heating power of the CHP unit will also increase, so its power supply power will also increase accordingly, so that the active power of the grid balancing node will continue to decrease under the premise of unchanged power load; the heat power and electric power of the CHP unit will continue to increase to the maximum output and will no longer change, and the active power of the grid balancing node will also remain unchanged. At this time, the insufficient heat power will be supplied by the steam boiler of the No. 1 node of the hot steam network.

[0145] 2) Impact of electric boilers on new energy consumption

[0146] Uncontrollability and randomness are one of the main factors restricting the consumption of new energy. When the power system operates alone, there is often an excess of new energy generation, far exceeding the load demand, resulting in a large amount of new energy generation being abandoned. In the power-heat steam coupled energy network, the power grid is no longer an independent entity. At this time, electric boilers can be used to convert excess electricity into heat energy to provide heat to heat users. This control method is very suitable for areas with abundant wind resources and large heat loads.

[0147] Normally, the power generation of wind power at night is higher than that during the day, but the power load at night is much lower than that during the day. At this time, the power generation does not match the power consumption, and wind power is difficult to absorb. However, for the heating network, the thermal load at night is not necessarily lower than that during the day, and sometimes it is even much higher than that during the day. At this time, for the power-heat steam coupling system, if the electric boiler is put into use at night, it can play a role in reducing the peak of the thermal load and filling the valley of the electric load. The electric boiler consumes excess electricity for steam supply, which can be used as a supplementary heat source. At the same time, it can consume excess electricity in the power grid and fill a certain valley load, thereby reducing the amount of abandoned wind to a certain extent. Next, the simulation model is used to discuss the peak-shaving function and impact of the electric boiler.

[0148] The conditions at 12:00 noon and 0:00 at night are selected for calculation and comparison. Assuming that the nighttime electric load drops to 50% of the daytime load, the thermal load drops to 83% of the daytime load, and the load of each node is reduced in equal proportion, the thermal load during the day and at night is shown in Table 4:

[0149] Table 4 Thermal power load of electricity-heat steam coupling system

[0150]

[0151] Considering that the electric boiler is not enabled during the day and is enabled at the node with higher heat load at night, the peak load regulation ratio of the electric boiler Kp=0.4 is taken. For the convenience of analysis, it is assumed that the output of the generators of the power grid except the balancing units is consistent at night and during the day, and the load fluctuation of the power grid is all borne by the balancing units. Therefore, the change of the active power of the balancing node can represent the change of the load of the power subsystem. Through simulation solution, the active power of the balancing node of the power grid during the day and at night can be calculated, and the peak-to-valley difference of the balancing node power can be calculated. Table 5 shows the simulation calculation results:

[0152] Table 5 Simulation results after putting electric boiler into use

[0153]

[0154] From the data in Table 5, we can see that as the number of nodes that put electric boilers into use at night increases, the active power of the grid balancing nodes at night also increases, so the peak-to-valley difference of the balancing nodes decreases, thereby reducing the volatility of the active output of the balancing units. In essence, the use of peak-shaving electric boilers reduces the volatility of the grid load, which improves the operating efficiency and economy of the network on the one hand, and improves the safety and stability of the system and its ability to bear load changes on the other. Since the valley load in the power system is partially filled by electric boilers, it provides an effective solution to the problem of new energy consumption, especially the consumption of wind power.

[0155] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0156] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for simulating an electric power-heat steam coupling energy system, characterized in that: The following steps are involved: S1. Establish a steady-state simulation model of the power-heat steam coupling energy system, including a power subsystem model, a steam heating subsystem model, and a thermoelectric coupling equipment model; S2: Based on the steam heating subsystem model established in step S1, by analyzing the total number of equations and unknown quantities to be solved of the equation group and combining with engineering practice, determine the solution conditions and solution steps of the steam heating subsystem model; S3: Based on two typical CHP unit types, back pressure unit and extraction condensing unit, determine the degree of coupling between the power subsystem and the steam heating subsystem, so as to determine the solution steps; S4: Based on the solution steps determined in step S3, the Newton-Raphson method / cplex solver is used to solve the corresponding set of equations and analyze the results; The power subsystem model is established based on the traditional AC power flow equation, and subsequent power flow calculation is performed as follows: The power flow equation for the power network is: In formula (1), U i and θ i is the voltage amplitude and phase angle of node i, E is the set of all nodes in the power network, P i and Q i is the active power and reactive power injected into node i, G ij and B ij is the real and imaginary part of the mutual admittance between node i and node j, and is the self-admittance of node i when i=j; In the process of power flow solution, the four state variables U of node i i ,θ i , P i , Q i In the process, there are two known quantities and two unknown quantities, and according to the different known quantities, the nodes can be classified into PV nodes, PQ nodes and balance nodes; The steam heating subsystem model includes the pipe segment momentum balance equation, the node mass flow balance equation, the pipe segment mass flow balance equation and the pipe segment energy balance equation, which are as follows: (1) Momentum balance equation of pipe section: Where: λ is the friction coefficient of the pipe section; d is the inner diameter of the pipe, P in and P out are the steam pressures at the steam inlet and outlet ends of the pipeline, c1 and c2 are fitting coefficients, L is the length of the pipeline, W is the set of all pipelines in the steam network, Q i is the steam flow rate in pipe i; Among them, Q in,i and Q out,i are the steam flow rates flowing into and out of pipe i respectively; (2) Node mass flow balance equation: In the formula, Q n,i is the injected steam flow rate at node i, W in,i is the set of all pipes flowing into node i, W out,i is the set of all pipes that flow out of node i; (3) Pipe section mass flow balance equation: Q in,i =Q out,i +Q c,i ,i∈W (10) Among them, Q in,i and Q out,i are the steam flow rates flowing into and out of pipe i respectively; (4) Pipe section energy balance equation: Q in,i h in,i =Q out,i h out,i +Q c,i h c,i +C t K i L i (T i -T a ),i∈W (11) In the formula, h in,i 、h out,i 、h c,i are the specific enthalpy of the beginning and end of pipe i and the condensed water, H i is the heat loss power of steam during the flow of pipe i, K i is the total heat transfer coefficient of pipe i; The thermoelectric coupling equipment model selects two typical thermoelectric coupling equipment CHP units and electric boilers for steady-state mathematical modeling, as follows: (1) CHP unit model: Based on the different uses of fresh steam, CHP units are divided into back-pressure units and extraction-condensing units. The electric power P supplied by the back-pressure unit is basically linearly related to the thermal power Φ: P=K CHP F (20) The ratio of thermal power to electrical power of a back pressure unit is a certain value K CHP : The coupling relationship between the power supply power P and the heating power Φ of the extraction condensing unit is: The ratio of thermal power to electrical power of an extraction condensing unit is variable within a certain range; (2) Electric boiler model: Using the electric boiler model with a fixed peak load ratio, the ratio of the peak load borne by the electric boiler to the total heat load at node i is as follows: In the formula, K p That is, the peak regulation ratio, Φ EB It represents the peak thermal power provided by the electric boiler, and Φ represents the total thermal load of the node.

2. The method for simulating an electric power-heat steam coupling energy system according to claim 1, characterized in that: In step S2, for a hot steam pipe network system with N nodes and M branches, 3M+N network control equations can be listed. In this pipe network, the quantity to be determined is the flow rate Q at the beginning of M pipes. in , terminal flow Q out , Pipeline condensate water volume Q c , and the pressure P of N nodes or the node injection flow Q i So there is a total of 3M + N-terminal flow Q out For these 3M+N unknown quantities, all unknown quantities can be uniquely solved by combining 3M+N network control equations. The network control equation is a set of nonlinear equations. According to engineering practice, the network topology of the steam heating network is generally relatively simple, and the number of nodes and pipelines is relatively small. The Newton-Raphson method can be used to solve the nonlinear equations.

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