A power flow calculation method of an electric-thermal integrated energy system considering double-pipe co-encased direct-buried laying mode

Abstract

The application discloses a kind of electric heat comprehensive energy system tidal flow calculation method considering double-pipe co-shell direct-buried laying mode: contain following steps: step 1: initialization power grid, heat network, hydraulic variable;Step 2: according to Newton-Raphson method, carry out hydraulic calculation, update pipe mass flow rate m;Step 3: calculate heat network water supply temperature Ts, backwater temperature Tr;Step 4: whether the error between backwater temperature newTr and Tr satisfies precision, satisfy then next step, not satisfy then return step 3;Step 5: according to Newton-Raphson method, carry out power tidal flow calculation;Step 6: whether electric power deviation ΔF e Satisfy precision, satisfy then output result, not satisfy then return step 2.The temperature drop equation considered in the application fully considers the coupling relationship between water supply temperature and backwater temperature under double-pipe co-shell direct-buried laying mode, so that the water supply temperature and backwater temperature are obviously improved compared with traditional model, and the calculation precision is higher.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy systems, and particularly relates to a power and heat integrated energy system power flow calculation method considering a double-pipe co-shell direct-buried laying mode. BACKGROUND

[0002] The integrated energy system integrates coal, natural gas, oil, electric energy, wind energy, solar energy and various other energies, involves different professional fields of various energies, and aims to coordinate and plan various heterogeneous energies, optimize operation, complement, meet the demand of multiple energies in the system, improve resource utilization, promote sustainable development of energies, break the boundaries between different energy systems, and make various energies connected. In the face of the growing distributed power supply and energy storage technology, the continuous growth of renewable energies such as wind energy and solar energy, and the important trend of low carbonization of energy systems, exploring the connection between different energies, further digging the energy transmission path between various energies, maximizing the utilization of resources, and reducing environmental pollution are the focus of the world. Under the current energy situation and the new situation of power system reform, it is necessary to develop an integrated energy system.

[0003] The integrated energy system research mainly includes the following steps: firstly, modeling the research area, the energy types involved, the relationship between energies, and various devices. On the basis of modeling, the power flow distribution of the integrated energy system is calculated. Finally, the optimal solution of the objective function is achieved through operation scheduling, planning operation, and finally reaching the optimal solution. Modeling is an important part of integrated energy system research, and has an important influence on power flow calculation, optimization scheduling, and optimization operation. Therefore, modeling under the influence of various factors and power flow calculation, scheduling, and operation analysis based on the modeling have more practical significance. In the heat network, the heat medium is mainly transported to the user through the pipeline, and the process often adopts a simple double-pipe direct-buried laying mode. However, the temperature of the heat medium is mostly much higher than the ambient temperature, so that part of the heat in the heat medium is lost to the surrounding environment during the transmission process, resulting in resource waste and even environmental pollution. Therefore, it is of practical significance to study the structure of the pipeline and the heat loss distribution, which is of great significance to subsequent power flow distribution calculation, planning and construction, and scheduling work. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a power and heat integrated energy system power flow calculation method considering a double-pipe co-shell direct-buried laying mode. The method fully considers the temperature coupling between the water supply pipeline and the return water pipeline, and compared with the simple double-pipe direct-buried laying mode, can effectively reduce the heat loss of the water supply pipeline and the return water pipeline, improve the water supply temperature and the return water temperature, and further reduce the CHP unit output, which is of great significance to the economic optimization operation and scheduling strategy of the integrated energy system.

[0005] A kind of electric heat comprehensive energy system power flow calculation method considering double-pipe co-shell direct-buried laying mode, specific steps are as follows:

[0006] First, according to node flow balance, loop pressure balance, head loss equation construction heat network hydraulic model.

[0007] 1) node flow balance equation

[0008]

[0009] In the formula, A is the heat network node branch correlation matrix; For pipe mass flow, unit kg / s; For node mass flow rate, unit kg / s;

[0010] 2) loop pressure balance equation

[0011] B h h f =0

[0012] In the formula B h For loop correlation matrix, h f For each pipe head loss vector.

[0013] 3) head loss equation

[0014]

[0015] In the formula And wherein f is the pipe friction coefficient, D is the inner diameter of pipe, g is the acceleration of gravity, ρ is the density of water, L is the length of pipe.

[0016] Second, according to Newton-Raphson method for hydraulic model calculation, update each pipe mass flow rate.

[0017]

[0018]

[0019]

[0020] According to the above Newton-Raphson formula to update pipe mass flow rate, wherein ΔF h Hydraulic deviation vector, J h Hydraulic Jacobian matrix. Wherein Superscript i is the iteration number.

[0021] Third, under the double-pipe co-shell direct-buried laying mode, establish heat network pipe heat model.

[0022] 1) node heat power equation

[0023]

[0024] wherein, is the node thermal power, in W, C ρ is the specific heat capacity of water, in MJ·kg -1 ·℃ -1 , Ts is the supply water temperature of the node, in ℃, To is the return water temperature of the node, in ℃.

[0025] 2) Pipe temperature drop equation

[0026]

[0027]

[0028] wherein, Tg is the average temperature in the supply water pipe, Tge is the end temperature of the supply water pipe, in ℃, Tgs is the start temperature of the supply water pipe, in ℃, Th is the average temperature in a return water pipe, in ℃, The is the end temperature of the return water pipe, in ℃, Ths is the start temperature of the return water pipe, in ℃. Ta is the ambient temperature, in ℃. L is the pipe length, in m. ρ is the specific heat capacity of water, in MJ·kg -1 ·℃ -1 u1, u2 are heat loss coefficients.

[0029] 3) Hydraulic junction model

[0030]

[0031] wherein, T out is the hydraulic junction temperature, T in is the temperature at the end of each pipe flowing into the node, is the mass flow rate of each pipe flowing out of the hydraulic junction, is the mass flow rate of each pipe flowing into the hydraulic junction.

[0032] Fourthly, the hydraulic and thermal models are coupled. First, the node mass flow rate is calculated based on the node thermal power equation, then the hydraulic model is calculated, the pipe mass flow rate is updated, the pipe mass flow rate satisfying the hydraulic model is substituted into the thermal model to calculate the pipe temperature, the supply water temperature and the return water temperature are coupled and iterated until convergence through the pipe temperature drop equation, finally it is judged whether the hydraulic deviation and the temperature deviation between the hydraulic model and the thermal model meet the accuracy requirement, if yes, the next step is performed, if not, the second step is returned.

[0033] The fifth step is to calculate the thermal power and electric power of the CHP unit at the thermal balance node. The thermal balance node can be an extraction condensing steam turbine CHP unit or a gas turbine CHP unit, and the relationship between the electric power and the thermal power is as follows:

[0034]

[0035] In the formula, c is the thermal-electricity ratio of the unit, is the thermal power provided by the unit, P CHP is the electric power provided by the unit.

[0036] The sixth step is to establish a power grid flow model and solve it iteratively using the Newton-Raphson method.

[0037] 1) Power node flow equation

[0038]

[0039]

[0040] In the formula, P i and Q i are the active and reactive power of node i, respectively, with units of kW and kVar; U is the voltage, with subscript being the node number, and unit of kV; G ij and B ij are the node admittance matrix parameters, G representing electric conductance and B representing electric inductance; θ ij is the phase angle difference between two nodes, with subscript indicating node i and node j, and unit of °.

[0041] According to the Newton-Raphson method, the iteration format is:

[0042]

[0043] In which the Jacobian matrix J e is:

[0044]

[0045] The electric power deviation amount ΔF e is:

[0046]

[0047] In the formula, J Sθ and J sU are the partial derivatives of the node complex power deviation amount with respect to θ and U, respectively.

[0048] Seventh step, hydraulic, heat network, power grid model coupling. The CHP unit data of the heat balance node calculated by the heat model and the initialized other unit data are used for iterative calculation of the power grid power flow Newton-Raphson method until convergence, and finally the power flow results of the entire electric-thermal integrated energy system are output.

[0049] Compared with the prior art, the technical highlights and beneficial technical effects of the present application are: the temperature drop equation considered in the present application fully considers the coupling relationship between the supply water temperature and the return water temperature under the double-pipe co-shell direct-buried laying mode, so that the supply water temperature and the return water temperature are obviously improved compared with the traditional model, and the calculation accuracy is higher. The results of the calculation prove that the model provides ideas for subsequent economic dispatching operation for reducing unit output. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a schematic diagram of pipe heat loss;

[0051] Figure 2 is a pipe cross-section view;

[0052] Figure 3 is a pipe cross-section view;

[0053] Figure 4 is a flow chart of power flow calculation;

[0054] Figure 5 is a structure diagram of an electric-thermal integrated energy system;

[0055] Figure 6 is a comparison diagram of supply water temperatures of scene 1 and scene 2;

[0056] Figure 7 is a comparison diagram of return water temperatures of scene 1 and scene 2;

[0057] Figure 8 is a comparison diagram of unit heat power outputs of scene 1 and scene 2. DETAILED DESCRIPTION

[0058] The present application will be specifically described below in combination with the drawings.

[0059] The present application is a kind of electric-thermal integrated energy system power flow calculation method considering double-pipe co-shell direct-buried laying mode, and the specific steps are as follows:

[0060] First step, according to node flow balance, loop pressure balance, head loss equation to build a heat network hydraulic model.

[0061] 1) Node flow balance equation

[0062]

[0063] In the formula, A is the branch associated matrix of the heat network node; is the pipe mass flow rate, unit kg / s; is the node mass flow rate, unit kg / s;

[0064] 2) Loop pressure balance equation

[0065] B h h f = 0

[0066] where B h is the loop incidence matrix, h f is the head loss vector of each pipe section.

[0067] 3) Head loss equation

[0068]

[0069] where and where f is the pipe friction factor, D is the internal diameter of the pipe, g is the acceleration due to gravity, p is the density of water, and L is the length of the pipe.

[0070] Second step, according to Newton-Raphson to update the pipe mass flow rate.

[0071]

[0072]

[0073]

[0074] According to the above Newton-Raphson formula to update the pipe mass flow rate, where AF h is the hydraulic deviation vector, J h is the hydraulic Jacobian matrix. Where the superscript i is the iteration number.

[0075] Third step, under the double-pipe co-shell direct-buried laying mode, the thermal model of the heat network pipe is established.

[0076] 1) Node thermal power equation

[0077]

[0078] where, is the node thermal power, unit W, C ρ is the specific heat capacity of water, unit MJ·kg -1 ·℃ -1 , Ts is the supply water temperature of the node, unit ℃, To is the outlet water temperature of the node, unit ℃.

[0079] 2) Pipe temperature drop equation

[0080] Analysis in the double pipe co-shell buried way, by the attached Figure 1 As shown, the water supply temperature and return water temperature and environmental temperature between the two heat transfer relationship derived formula:

[0081]

[0082]

[0083]

[0084] q g = q1+ q2 (4)

[0085] q h = q3-q2 (5)

[0086] Where R1, R2, R3 are each branch resistance, q1, q2, q3 is each branch heat flow, q z is the total heat loss, q g , q h is the water supply pipe and return pipe heat loss.

[0087] Formula 1, formula 2, formula 3 into formula 4, formula 5 is obtained

[0088]

[0089]

[0090] Let

[0091] Because of the symmetry of the water supply pipe and return pipe distribution (attached Figure 2 ), the heat loss coefficient u1 = u3, so

[0092] q g = u1(T g -T a )-u2(T h -T a ) (6)

[0093] q h = u1(T h -T a )-u2(T g -T a ) (7)

[0094] According to the steady-state heat transfer theorem, the heat medium through the length of L pipe to meet (attached Figure 3 )

[0095]

[0096] Substitute formula 6, formula 7 into formula 8, obtain

[0097]

[0098]

[0099] In the formula, Tg is the average temperature in the water supply pipeline, T ge , T gs , T he , T hs are the temperature at the head of the heating pipeline, the temperature at the tail of the heating pipeline, the temperature at the head of the return pipeline, the temperature at the tail of the return pipeline respectively, all in ℃. Ta is the ambient temperature, in ℃. L is the length of the pipeline, in m. C ρ is the specific heat capacity of water, in MJ·kg -1 ·℃ -1 . u1, u2 are heat loss coefficients. According to the analysis on formula 9, in the calculation of the temperature at the head and tail of the heating pipeline, the temperature at the head and tail of the return pipeline is involved, and for the pipeline with small temperature difference between the head and tail, the heat loss coefficient u2 is a small number, then u2 (T hs -T a ) and u2 (T he -T a ) are almost equal, which will lead to the failure of solving formula 9. Therefore, in the process of substituting formula 6 into formula 8, u2 (T h -T a ) can be regarded as a constant for solving, and considering that the temperature at the head and tail of the pipeline is not equal, u2 (T h -T a ) is regarded as the average temperature in the pipeline u2 (T h -T a ). Therefore, re-substitute formula 6, formula 7 into formula 8, obtain

[0100]

[0101]

[0102] Because the return water temperature and the supply water temperature are involved in the calculation of the return water temperature and the supply water temperature respectively, the temperature needs to be solved by coupling iteration, and the coupling iteration method in the application is to calculate the new supply water temperature according to the initialized return water temperature, calculate the new return water temperature according to the new supply water temperature, judge whether the error between the new return water temperature and the old return water temperature reaches the precision, if yes, output, otherwise replace the new return water temperature with the old return water temperature, re-substitute and calculate, and repeat the above operation until the temperature converges.

[0103] 3) Hydraulic junction point model

[0104]

[0105] where T out is the temperature of the hydraulic junction, T in is the temperature of the end of each pipe flowing into the junction, is the mass flow rate of each pipe flowing out of the hydraulic junction, is the mass flow rate of each pipe flowing into the hydraulic junction.

[0106] Fourthly, the hydraulic and thermal model coupling is carried out. Firstly, the node mass flow rate is calculated based on the node thermal power equation, then the hydraulic model is calculated, the pipe mass flow rate is updated, the pipe mass flow rate meeting the hydraulic model is substituted into the thermal model to calculate the pipe temperature, the coupling iteration between the supply water temperature and the return water temperature is carried out through the pipe temperature drop equation until convergence, finally it is judged whether the hydraulic deviation and the temperature deviation between the hydraulic model and the thermal model meet the accuracy requirement, if yes, the fifth step is carried out, if not, the second step is returned.

[0107] Fifthly, the thermal power and electric power of the CHP unit at the thermal balance node are calculated. The thermal balance node can adopt the extraction condensing steam turbine CHP unit or the gas turbine CHP unit, and the relationship between the electric power and the thermal power is as follows:

[0108]

[0109] where c is the thermal-electric ratio of the unit, is the thermal power provided by the unit, P CHP is the electric power provided by the unit.

[0110] Sixthly, the power grid flow model is established, and the Newton-Raphson method is used for iterative solution.

[0111] 1) Power node flow equation

[0112]

[0113]

[0114] where P i and Q i are the active and reactive power of node i, respectively, with the unit of kW and kVar; U is the voltage with the subscript of node number, with the unit of kV; G ij and B ij are the node admittance matrix parameters, G represents the conductance and B represents the susceptance; θ ij is the phase angle difference between two nodes, with the subscript indicating node i and node j, with the unit of °.

[0115] According to the Newton-Raphson method, the iteration format is as follows:

[0116]

[0117] Where the Jacobian matrix J e for:

[0118]

[0119] Power deviation ΔF e for

[0120]

[0121] In the formula, J Sθ J SU Take the partial derivatives of the nodal complex power deviation with respect to θ and U, respectively.

[0122] Step 7: Couple the hydraulic, heating network, and power grid models. Using the CHP unit data from the thermal equilibrium node calculated by the thermal model and the initialized data from other units, perform iterative calculations of the power flow using the Newton-Raphson method until convergence. Finally, output the power flow results for the entire integrated electric and thermal energy system. The above steps are illustrated in the attached diagram. Figure 4 As shown.

[0123] This example uses a 32-node thermal system and a 5-node electrical system in Bali. The electric heating system is shown in the attached diagram. Figure 5 As shown, the water supply temperature is set to 95℃, the return water temperature is set to 70℃, and the ambient temperature is set to -5℃. To fully demonstrate the effectiveness of the model of this invention, scenario one is set as the power flow calculation considering the direct burial method of dual-pipe shared shell, and scenario two is the power flow calculation under the traditional model.

[0124] From the appendix Figure 6 and attached Figure 7 As shown, after considering the direct-buried dual-pipe common-shell installation method, the temperature at each node of the supply water pipeline in most heating networks is higher than that under the traditional model. Furthermore, except for the nodes with a given outlet water temperature, the return water temperature at other nodes is also higher than that under the traditional model. This is because, compared to the traditional model, in the direct-buried dual-pipe common-shell installation method, the supply and return water temperatures not only transfer heat with the ambient temperature but also transfer heat with each other, limiting the heat dissipated from the supply and return water temperatures to the external environment. Correspondingly, after performing power flow calculations, the unit output also decreases, as shown in the attached figure. Figure 8 As shown.

[0125] Finally, it should be noted that the above description is only for specific embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. Equivalent modifications and substitutions made to the present invention by those skilled in the art are also within the scope of the present invention. Therefore, all equivalent changes and modifications made without departing from the spirit and scope of the present invention are covered within the scope of the present invention.

Claims

1. A method for power flow calculation of an integrated energy system with electric heating, considering the double-pipe co-encased direct-buried laying mode, characterized in that, The specific steps are as follows: Step 1, according to the node flow balance, loop pressure balance, head loss equation to build the heat network hydraulic model; Step 2, according to Newton-Raphson method for hydraulic model calculation, update the mass flow rate of each pipeline; Step 3, in the double-pipe co-shell direct-buried laying mode, the heat network pipeline thermal model is established, and the heat network pipeline thermal model is: 1) Node thermal power equation ； wherein, is the node thermal power, is the specific heat capacity of water, is the supply water temperature for the node, is the outlet water temperature for the node; 2) Pipeline temperature drop equation ； ； wherein Tsup is the supply pipe end temperature, Tsup is the supply pipe end temperature, Tret is the return pipe average temperature, Tret is the return pipe end temperature, Tret is the return pipe end temperature, Tret is the return pipe end temperature, L is the pipe length, Cp is the specific heat capacity of water, , K is the thermal loss coefficient; 3) Hydraulic junction point model ； wherein Tj is the temperature of the hydraulic junction, Tj is the temperature of the hydraulic junction, is the mass flow rate of each pipe out of the hydraulic junction, is the mass flow rate of each pipe into the hydraulic junction; Step 4, the hydraulic and thermal model coupling is carried out, and the steps are as follows: Firstly, the node mass flow rate is calculated based on the node thermal power equation; then the hydraulic model is calculated, and the pipeline mass flow rate is updated; the pipeline mass flow rate meeting the hydraulic model is substituted into the thermal model to calculate the pipeline temperature, and the coupling iteration between the supply water temperature and the return water temperature is carried out through the pipeline temperature drop equation until convergence; finally, it is judged whether the hydraulic model and the thermal model temperature deviation meet the accuracy requirement, if yes, the next step is carried out, if not, it is returned to step 2; Step 5, the thermal power and electric power of CHP unit at the thermal balance node are calculated; Step 6, the power grid power flow model is established, and Newton-Raphson method is used for iterative solution; Step 7, the hydraulic, heat network and power grid model coupling is carried out, the CHP unit data at the thermal balance node calculated by the thermal model and the initialized other unit data are used for power grid power flow Newton-Raphson method iterative calculation until convergence, and finally the power flow result is output.

2. The power flow calculation method of an electric-thermal integrated energy system considering the double-pipe common-enclosure direct-buried laying mode according to claim 1, characterized in that, Step 1 includes: 1) Node flow balance equation ； wherein is the heat network node branch incidence matrix, is the pipe mass flow, is the node mass flow rate; 2) Loop pressure balance equation ； wherein is the loop incidence matrix, is the head loss vector for each pipe segment; 3) Head loss equation ； In the formula wherein is the pipe friction factor, D is the internal diameter of the pipe, g is the acceleration of gravity, is the density of water, L is the pipe length.

3. The power flow calculation method of an electric-thermal integrated energy system considering the double-pipe common-enclosure direct-buried laying mode according to claim 2, characterized in that, Step 2 includes: = ； ； ； The pipe mass flow rate is updated according to the Newton-Raphson formula above, where is the hydraulic bias vector, is the hydraulic Jacobian matrix, where the superscript i is the iteration number.

4. The power flow calculation method of an electric-thermal integrated energy system considering the double-pipe common-enclosure direct-buried laying mode according to claim 1, characterized in that, Step 5 includes: The thermal balance node adopts extraction condensing steam turbine CHP unit or gas turbine CHP unit, and the relationship between electric power and thermal power is as follows: ； wherein is the heat to power ratio of the unit, is the heat power provided by the unit, is the electric power provided by the unit.

5. The power flow calculation method of an electric-thermal integrated energy system considering the double-pipe common-enclosure direct-buried laying mode according to claim 1, characterized in that, Step 6 includes: 1) Power node power flow equation ； ； wherein, , are the active and reactive power of node i, respectively, U is the voltage, and the subscript is the node number; , is the node admittance matrix parameter, represents conductance, represents susceptance; is the phase angle difference between two nodes, and the subscript indicates node i and node j; 2) According to Newton-Raphson method, the iteration format is: ； where the Jacobian matrix is: ； Electric power power deviation amount To ； wherein , are partial derivatives of the node complex power deviation with respect to , are partial derivatives of the node complex power deviation with respect to

Images