CN113849946A - Modeling and load flow calculation method for electric-thermal interconnection comprehensive energy system - Google Patents
Modeling and load flow calculation method for electric-thermal interconnection comprehensive energy system Download PDFInfo
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Abstract
The invention discloses a modeling and load flow calculation method for an electric-thermal interconnection comprehensive energy system, which comprises the following steps: (1): and constructing a power system load flow calculation model containing distributed power supply access, and performing special treatment on the PV nodes by using an improved forward-backward substitution method to realize load flow calculation of the distributed power supply access distribution network. (2): and constructing a model containing a multi-heat-source radiation type thermodynamic system, converting the multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks, and performing decoupled heat supply network load flow calculation by utilizing an improved forward-backward substitution method. (3): on the basis of modeling of each independent energy system, modeling is carried out on the coupling part of the two systems, and energy flow calculation of the whole electricity-heat interconnection comprehensive energy system is realized. The invention improves the defect that the traditional forward-backward substitution method can not process PV nodes, reduces the iteration times, reduces the requirement on initial values, simplifies the model by improving the thermodynamic system and improves the calculation speed.
Description
Technical Field
The invention relates to an electricity-heat interconnection comprehensive energy system, in particular to an electricity-heat interconnection comprehensive energy system modeling and load flow calculation method for improving a forward-backward substitution method.
Background
With the rapid development of the current society, the contradiction between the large energy consumption and ecological protection is increasingly highlighted, and the research of an energy system with high efficiency, small pollution and strong controllability becomes a hot problem. The development of comprehensive energy is beneficial to realizing reasonable regulation and optimal utilization of various resources, and is a good method for solving the problems of huge energy consumption, resource exhaustion and the like in the current times. In traditional energy systems such as power grids and heat supply networks, independent operation systems are arranged among the energy systems, the coupling degree among the energy systems is not tight, and the energy utilization efficiency is low. In the comprehensive energy system, the coupling is tight, the energy utilization rate is greatly improved, and the consumption capacity of renewable energy sources is also greatly improved.
The energy flow calculation of the comprehensive energy system is developed on the basis of the load flow calculation of the power system, the load flow calculation in the power system is mainly represented by a forward-backward substitution method, a Newton-Raphson method and a PQ decomposition method, and the forward-backward substitution method comprises the following steps: and calculating the power in each line according to the direction opposite to the power transmission by using the rated voltage of the line at a node far away from the power supply, calculating the voltage of each node according to the power transmission direction from the power supply end by using the required power, and repeating the two steps until the precision meets the requirement during load flow calculation. The Newton-Raphson method and the PQ decomposition method have stronger theoretical systems and more mature ideas when applied to a power system, but have the defects of complex solving program, more iteration times, difficulty in realizing combined calculation among systems and the like when applied to a comprehensive energy system.
Considering that the purpose of energy flow calculation of the comprehensive energy system is to improve the coupling degree among the systems, realize the optimal distribution of energy, reduce energy loss and improve the comprehensive utilization level of energy, a simplified comprehensive energy system model is constructed and a unified solving method is used, so that quick and accurate calculation can be realized. The forward-backward substitution method in the power system load flow calculation has the advantages of simple solving process, high calculation precision, simple programming, no need of excessive iteration times and the like, and the improvement of the traditional forward-backward substitution method can be applied to the energy flow calculation of the radiation type heat supply network, so that the energy flow solution of the comprehensive energy system is realized.
Disclosure of Invention
The invention aims to provide a modeling and load flow calculation method for an electric-thermal interconnection comprehensive energy system. The method is improved aiming at the defects of a forward-backward substitution method in an electric power system with distributed power supply access, and then is popularized to a radiation type thermodynamic system with multiple heat sources, so that the trend calculation of a comprehensive energy system is realized.
In order to solve the problems in the prior art, the technical scheme adopted by the invention is as follows:
a modeling and load flow calculation method for an electric-thermal interconnection comprehensive energy system comprises the following steps:
step 1: a power system load flow calculation model containing distributed power supply access is constructed, PV nodes are processed by an improved forward-backward substitution method, and load flow calculation of the distributed power supply access to a power distribution network is achieved;
step 2: constructing a model containing a multi-heat-source radiation type thermodynamic system, wherein the thermodynamic system model consists of a hydraulic model and a thermodynamic model, converting a multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks, and performing decoupled heat supply network load flow calculation by utilizing an improved forward-backward substitution method; the conversion mode of converting the multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks is as follows:
wherein the content of the first and second substances,
(i is 1, …, n, n represents the number of pipelines branched from the node, j is 1, …, m, m represents the number of heat sources in the heat supply network) is the pipeline flow of the corresponding single heat source radiation type heat supply network after conversion,
(i is 1, …, n) is the pipe flow rate corresponding to the heat source input to the node,
(i is 1, …, n) is branch flow before conversion, namely pipeline flow corresponding to the multi-heat-source radiation type heat supply network;
wherein the content of the first and second substances,
(i is 1, …, m is the number of heat sources in the heat supply network) is equivalent to the equivalent heat load power after a multi-heat-source radiation type heat supply network is equivalent to a plurality of single-heat-source radiation type heat supply networks, philThe node thermal load power before equivalence;
and step 3: on the basis of a power flow calculation model and a thermodynamic system model of the power system, a model is established for the coupling part of the power system and the thermodynamic system, and the energy flow calculation of the whole electricity-heat interconnection comprehensive energy system is realized.
Further, the step 1 comprises the following steps:
s101: acquiring network parameters and state variables of the power system;
s102: setting an initial voltage value, wherein the requirement on the initial voltage value in the power system is not high and only within a reasonable range;
s103: calculating the power flow of the power system by using an improved forward-backward substitution method, wherein the formula is as follows:
where Δ S is power loss, Δ P is active loss, Δ Q is reactive loss, I is line current, R is power loss, Δ P is active loss, Δ Q is reactive loss, and Δ Q is line currenti、XiAs a line parameter, Pi、QiFor active and reactive power at node i, UNIs the rated voltage of the line;
ΔU＝Zi·ΔS*＝(Ri+jXi)(ΔP-jΔQ)＝RiΔP+XiΔQ
wherein, Δ U is the longitudinal component of voltage drop, Zi、Ri、XiAs a line parameter, PiActive power and reactive power at a node i are shown, delta P is active loss, and delta Q is reactive loss;
for a PV node, if Δ P is 0, then:
ΔQ＝Xi -1·ΔU
wherein, Delta Q is reactive loss, XiIs a line parameter, and delta U is a voltage drop longitudinal component;
s104: correcting the reactive power of the PV node, namely correcting the reactive power injected into the PV node by using a reactive correction value in each iteration so as to ensure the real-time performance of data, wherein a correction equation is as follows:
wherein, the delta Q is a reactive correction quantity; gamma belongs to (-1, 1) as the calculation step length, and is generally equal to 0.1; qiCalculating the obtained reactive power for the PV node; qijFor all branches and nodes connected to the PV node, PiPower of the ith PV node, R, X is the line parameter, Δ UpIs the voltage difference between the PV node and the connected node, UiThe input voltage of the ith PV node;
s105: calculating values of delta U, delta and delta Q;
s106: and judging whether the voltage of each node meets the convergence judgment condition of the following formula, if not, returning to the step of updating the voltage amplitude and the voltage phase angle before the load flow calculation, and correcting the reactive power of the PV node until the voltage meets the convergence judgment condition to output a load flow calculation result. The convergence determination condition is as follows:
wherein the content of the first and second substances,
is the absolute value of the difference between the voltage value obtained in the kth iteration and the initial given voltage value, epsilon is the convergence accuracy,
for the voltage values obtained for k iterations, U0Is an initial given voltage value;
s107: and outputting a load flow calculation result.
Further, in step 2, the water flow in the pipeline and the injection water flow of the heat load node are obtained from the hydraulic model, and the flow continuity equation is used for representing the following flow continuity equation:
Alm＝mq
wherein A islIs a network incidence matrix of heat load nodes relative to each pipeline, m is a hot water flow vector in the pipeline, m isqThe flow vector of the injected water for the heat load node;
further, in step 2, the temperature of each node of the heat supply network is determined by the thermodynamic model, specifically:
φ＝φi-φEi＝cpm(Til-Tol)
wherein phi is a thermal power vector injected into the node, phiiIs a node thermal load power vector, phiEiInjecting a thermal power vector, c, into the nodal electric boilerpIs the specific heat capacity of water, m is the mass flow, TilSupply water temperature vector, T, to the nodeolIs a node loopWater temperature vector;
wherein T isendFor the temperature of the hot water flowing out of the pipe, TstartFor the temperature of the hot water flowing into the pipe, TeIs the external natural temperature, lambda is the heat conduction coefficient per unit length in the pipeline, d is the pipeline transmission distance, CpIs the specific heat capacity of water, m is the mass flow, mu is the temperature compensation parameter;
wherein m isout,aFor branch flow of the a-th branch out of the pipe, ToutReturn the mixing temperature, m, for the nodein,bBranch flow, T, for the b-th branch into the pipein,bAnd (4) flowing the terminal pipe temperature of the node for the b branch.
Further, the step 3 comprises the following steps:
step 301: modeling the coupling part of the electric-thermal combined system:
when the backpressure unit is used as a main heat source of a thermodynamic system and the electric boiler is used as a peak regulation heat source, the thermal power and the electric power generated by the backpressure unit satisfy the following relations:
ζ-1·φBY＝PBY
where ζ is the ratio of heat generation to electricity generation, and is generally a constant value, φBYFor heat power, P, from backpressure unitsBYElectric power generated for the backpressure unit;
the thermal power and the electric power generated by the peak-shaving electric boiler satisfy the following formula:
δ-1·φEB＝PEB
wherein delta is the ratio of heat production to electricity production, and is generally a constant value phiEBFor the thermal power, P, generated by peak-shaving electric boilersEBElectric power generated for the peak shaving electric boiler;
step 302: and converting the sum of the thermal powers of all the balance nodes in the thermodynamic system into the power of the electrical load by utilizing the coupling part modeling in the step 301, so as to realize the conversion process from the thermodynamic system to the power flow solution of the power system.
The invention has the advantages and beneficial effects that:
the method comprises the steps of firstly carrying out PV node reactive power correction on a power system with distributed power access by utilizing an improved forward-backward substitution method, then equivalently changing a multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks, then carrying out energy flow calculation, and finally converting thermal power into electric power through a coupling element to realize load flow calculation of the comprehensive energy system. The invention improves the defect that the traditional forward-backward substitution method can not process PV nodes, reduces the iteration times, reduces the requirement on initial values, simplifies the model by improving the thermodynamic system and improves the calculation speed.
Drawings
FIG. 1 is a flow chart of a power system flow solving method based on an improved forward-backward substitution method;
FIG. 2 is a decoupling diagram of a radiative thermodynamic system with multiple heat sources;
FIG. 3 is a schematic diagram of an integrated energy testing system;
fig. 4 is a comparison graph of power flow calculation results of the power system.
Detailed Description
The invention is described in detail below with reference to the following figures and examples:
the invention relates to a modeling and load flow calculation method for an electric-thermal interconnection comprehensive energy system, which is improved aiming at the defects of a forward-backward substitution method in an electric power system with distributed power supply access and then popularized to a radiation-type thermodynamic system with multiple heat sources, so that the load flow calculation of the comprehensive energy system is realized, and the modeling and load flow calculation method comprises the following steps:
step 1: and constructing a power system load flow calculation model containing distributed power supply access, and performing special treatment on the PV nodes by using an improved forward-backward substitution method to realize load flow calculation of the distributed power supply access distribution network.
As shown in fig. 1, the step 1 includes the following steps:
s101: acquiring network parameters and state variables of the power system;
s102: setting an initial voltage value, wherein the requirement on the initial voltage value in the power system is not high and only within a reasonable range;
s103: calculating the power flow of the power system by utilizing an improved push-back substitution method, wherein the improved push-back substitution method is used for calculating the voltage and power distribution in two steps, for a radiation type power grid, the power loss and the node power of each branch are calculated from a position far away from a power supply in the opposite direction of power transmission, and the formula is as follows:
where Δ S is power loss, Δ P is active loss, Δ Q is reactive loss, I is line current, R is power loss, Δ P is active loss, Δ Q is reactive loss, and Δ Q is line currenti、XiAs a line parameter, Pi、QiFor active and reactive power at node i, UNIs the nominal voltage of the line.
Secondly, starting from the power supply, calculating the voltage drop of each line and the voltage of each node along the power transmission direction, wherein the formula is as follows:
ΔU＝Zi·ΔS*＝(Ri+jXi)(ΔP-jΔQ)＝RiΔP+XiΔQ
wherein, Δ U is the longitudinal component of voltage drop, Zi、Ri、XiAs a line parameter, PiActive power and reactive power at a node i are shown, delta P is active loss, and delta Q is reactive loss;
for a PV node, if Δ P is 0, then:
ΔQ＝Xi -1·ΔU
wherein, Delta Q is reactive loss, XiIs a line parameter, and delta U is a voltage drop longitudinal component;
s104: the reactive power at the PV node is modified using an improved push-back substitution:
for a power distribution network injected by a distributed power supply, the number of PV nodes in a power system is increased, calculation of a large number of PV nodes cannot be realized when a forward-backward substitution method is used, and if the initial reactive power output value of the PV node is recorded as 0, the PV node can be equivalent to a PQ node to facilitate subsequent solution. The correction of the reactive power of the PV node can be realized by using an improved forward-backward substitution method, namely, the correction of the reactive power injected into the PV node is carried out by using the reactive correction value during each iteration, so that the real-time property of data is ensured, and a correction equation is as follows:
wherein, the delta Q is a reactive correction quantity; gamma belongs to (-1, 1) as the calculation step length, and is generally equal to 0.1; qiCalculating the obtained reactive power for the PV node; qijFor all branches and nodes connected to the PV node, PiPower of the ith PV node, R, X is the line parameter, Δ UpIs the voltage difference between the PV node and the connected node, UiThe input voltage of the ith PV node.
S105: calculating values of delta U, delta and delta Q;
s106: and judging whether the voltage of each node meets the convergence judgment condition of the following formula, if not, returning to the step of updating the voltage amplitude and the voltage phase angle before the load flow calculation, and correcting the reactive power of the PV node until the voltage meets the convergence judgment condition to output a load flow calculation result. The convergence determination condition is as follows:
wherein the content of the first and second substances,
is the absolute value of the difference between the voltage value obtained in the kth iteration and the initial given voltage value, epsilon is the convergence accuracy,
for the voltage values obtained for k iterations, U0Is initially given a voltage value.
S107: outputting a load flow calculation result;
Step 2: and constructing a radiation type thermodynamic system model containing multiple heat sources, wherein the thermodynamic system model consists of a hydraulic model and a thermodynamic model. And converting the multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks, and performing decoupled heat supply network load flow calculation by adopting an improved forward-backward substitution method.
S201: the thermodynamic system model consists of a hydraulic model and a thermodynamic model, the hydraulic model is used for obtaining water flow in a pipeline and injection water flow of a heat load node, and the flow continuous equation is used for representing the following flow continuous equation:
Alm＝mq
wherein A islIs a network incidence matrix of heat load nodes relative to each pipeline, m is a hot water flow vector in the pipeline, m isqThe injection water flow vector for the heat load node.
Pressure loop equation:
Bhf＝0
wherein B is a branch incidence matrix of the pipeline in the heating loop, hfIs the pressure variation vector of the hot water in the pipeline.
Determining the temperature of each node of the heat supply network by the thermal model, and determining the relationship between the node injection thermal power and the mass flow and the node temperature:
φ＝φi-φEi＝cpm(Til-Tol)
wherein phi is a thermal power vector injected into the node, phiiIs a node thermal load power vector, phiEiInjecting a thermal power vector, c, into the nodal electric boilerpIs the specific heat capacity of water, m is the mass flow, TilTemperature vector of water supply for node，TolAnd the vector is the return water temperature of the node.
The temperature variation relationship of the head end and the tail end of the pipeline is as follows:
wherein T isendFor the temperature of the hot water flowing out of the pipe, TstartFor the temperature of the hot water flowing into the pipe, TeIs the external natural temperature, lambda is the heat conduction coefficient per unit length in the pipeline, d is the pipeline transmission distance, CpIs the specific heat capacity of water, m is the mass flow, and μ is the temperature compensation parameter.
The hot water flowing from the heat source through the different heat supply networks and finally mixing at the heat load can be expressed by the following formula:
wherein m isout,aFor branch flow of the a-th branch out of the pipe, ToutReturn the mixing temperature, m, for the nodein,bBranch flow, T, for the b-th branch into the pipein,bAnd (4) flowing the terminal pipe temperature of the node for the b branch.
S202: a multi-heat-source radiation type heat supply network is converted into a plurality of single-heat-source radiation type heat supply networks, for example, a model containing a multi-heat-source radiation type thermodynamic system shown in fig. 2, two heat sources in the model supply heat to a heat load at the same time, and then the two heat sources are converted into two equivalent heat sources to supply heat to the heat load, so that the multi-heat-source radiation type heat supply network is converted into the plurality of single-heat-source radiation type heat supply networks and then subjected to load flow calculation, wherein the conversion mode is as follows:
rewritten in matrix form as:
wherein the content of the first and second substances,
(i is 1, …, n, n represents the number of pipelines branched from the node, j is 1, …, m, m represents the number of heat sources in the heat supply network) is the pipeline flow of the corresponding single heat source radiation type heat supply network after conversion,
(i is 1, …, n) is the pipe flow rate corresponding to the heat source input to the node,
(i is 1, …, n) is branch flow before conversion, namely pipeline flow corresponding to the multi-heat-source radiation type heat supply network;
wherein the content of the first and second substances,
(i is 1, …, m is the number of heat sources in the heat supply network) is equivalent to the equivalent heat load power after a multi-heat-source radiation type heat supply network is equivalent to a plurality of single-heat-source radiation type heat supply networks, philIs the node thermal load power before the equivalence.
S203: adopting an improved forward-backward substitution method to calculate the flow of the decoupled heat supply network, and carrying out the following analogy after decoupling the heat supply network:
the temperature in the thermodynamic system is analogized to the voltage in the power system, the heat flow, namely the mass flow rate, is analogized to the current in the power system, the heat load node is analogized to the PQ node in the power system, the heat source node is analogized to the PV node in the power system, for the node with known heat supply temperature, the node is analogized to the balance node in the power system, the thermodynamic system can be equivalently converted into the power system to solve the power flow by utilizing the above analogism, and the improved forward-backward substitution method in the step 1 is used in the solving method.
And 2, a model containing a multi-heat-source radiation type thermal system is constructed, the multi-heat-source radiation type heat supply network is converted into a plurality of single-heat-source radiation type heat supply networks, and the flow calculation of the multi-heat-source radiation type heat supply network is realized by analogy with the improved forward-backward substitution method provided in the step 1.
And step 3: on the basis of a power flow calculation model and a thermodynamic system model of the power system, a model is established for the coupling part of the power system and the thermodynamic system, and the energy flow calculation of the whole electricity-heat interconnection comprehensive energy system is realized.
The step 3 comprises the following steps:
step 301: modeling the coupling part of the electric-thermal combined system:
as a widely used thermoelectric unit, the back pressure unit does not comprise a condenser, exhaust heat in the back pressure unit is fully utilized, and the heat efficiency is high. The method has the defects that the generated energy of the back pressure unit is based on the generated heat quantity, and the regulation sensitivity is not strong. Therefore, a backpressure unit is generally selected as a main heat source of the thermal system in the thermal system, and an electric boiler is used as a peak shaving heat source.
The thermal power and the electric power generated by the backpressure unit satisfy the following relations:
ζ-1·φBY＝PBY
where ζ is the ratio of heat generation to electricity generation, and is generally a constant value, φBYFor heat power, P, from backpressure unitsBYElectric power generated for the backpressure unit;
the thermal power and the electric power generated by the peak-shaving electric boiler satisfy the following formula:
δ-1·φEB＝PEB
wherein delta is the ratio of heat production to electricity production, and is generally a constant value phiEBFor the thermal power, P, generated by peak-shaving electric boilersEBThe peak shaving electric boiler generates electric power.
Step 302: and converting the sum of the thermal powers of all the balance nodes in the thermodynamic system into the power of the electrical load by utilizing the coupling part modeling in the step 301, so as to realize the conversion process from the thermodynamic system to the power flow solution of the power system.
Taking the integrated energy testing system shown in fig. 3 as an example, the thermodynamic system and the electrical system are coupled together by a cogeneration unit. The heat supply network part comprises two heat Source nodes (Source 1 and Source 2) using a backpressure unit, a peak regulation electric boiler positioned at the No. 5 node and 14 heat load nodes, the peak regulation ratio is 0.45, the heat supply temperature of the combined heat and power generation unit is set to be 120 ℃, the heat-electricity ratio is 1.4, the heat loads are all set to be 0.5MW, the natural environment temperature is 2 ℃, the length of each pipeline is set to be 1.58km, and the heat conduction coefficient of the unit length in the pipeline is set to be 0.289Wm-1·K-1And taking the diameter of the pipeline as 100mm, converting the multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks according to the step 2, calculating the power flow of the thermodynamic system by using an improved forward-backward substitution method, wherein the table 1 is the pipeline flow of the thermodynamic system, and the table 2 is the node supply temperature and the node return temperature of the thermodynamic system.
TABLE 1 thermodynamic system pipe flow
TABLE 2 thermodynamic system node supply and node return temperatures
The thermal power system is coupled with the electric power system through a node 14, and the thermal power of the node 14 is 7.32725MW and is converted into 5.23375 MW.
The power grid part selects a 14-node power distribution network, a node 1 is connected with an external power grid, the voltage amplitude is 1.00pu, a node 2 is a PV node, the voltage amplitude is 0.993pu, a node 6 is a PV node, the voltage amplitude is 0.964pu, and the other nodes are PQ nodes. Programming is carried out according to a flow chart of the power system in the figure 1 based on the improved forward-backward substitution method, firstly, taking the nodes 1 and 2 as PQ nodes, carrying out first iterative calculation, then returning to a program to carry out calculation of reactive power correction, carrying out next iterative calculation after substituting the reactive power correction, and outputting a power flow calculation result of the power system after three iterations and meeting convergence judgment conditions. Compared with the traditional Newton-Raphson method for load flow calculation, the maximum error of the node voltage is 0.00028%, and the accuracy of the method is verified, wherein the load flow calculation result obtained by the method is shown in figure 4.
Claims (5)
1. A modeling and load flow calculation method for an electric-thermal interconnection comprehensive energy system is characterized by comprising the following steps:
step 1: a power system load flow calculation model containing distributed power supply access is constructed, PV nodes are processed by an improved forward-backward substitution method, and load flow calculation of the distributed power supply access to a power distribution network is achieved;
step 2: constructing a model containing a multi-heat-source radiation type thermodynamic system, wherein the thermodynamic system model consists of a hydraulic model and a thermodynamic model, converting a multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks, and performing decoupled heat supply network load flow calculation by utilizing an improved forward-backward substitution method; the conversion mode of converting the multi-heat-source radiation type heat supply network into a plurality of single-heat-source radiation type heat supply networks is as follows:
wherein the content of the first and second substances,
(i is 1, …, n, n represents the number of pipelines branched from the node, j is 1, …, m, m represents the number of heat sources in the heat supply network) is the pipeline flow of the corresponding single heat source radiation type heat supply network after conversion,
(i is 1, …, n) is the pipe flow rate corresponding to the heat source input to the node,
(i is 1, …, n) is branch flow before conversion, namely pipeline flow corresponding to the multi-heat-source radiation type heat supply network;
wherein the content of the first and second substances,
(i is 1, …, m is the number of heat sources in the heat supply network) is equivalent to the equivalent heat load power after a multi-heat-source radiation type heat supply network is equivalent to a plurality of single-heat-source radiation type heat supply networks, philThe node thermal load power before equivalence;
and step 3: on the basis of a power flow calculation model and a thermodynamic system model of the power system, a model is established for the coupling part of the power system and the thermodynamic system, and the energy flow calculation of the whole electricity-heat interconnection comprehensive energy system is realized.
2. The modeling and load flow calculation method for electric-thermal interconnection integrated energy system according to claim 1, characterized in that the step 1 comprises the following steps:
s101: acquiring network parameters and state variables of the power system;
s102: setting an initial voltage value, wherein the requirement on the initial voltage value in the power system is not high and only within a reasonable range;
s103: calculating the power flow of the power system by using an improved forward-backward substitution method, wherein the formula is as follows:
where Δ S is power loss, Δ P is active loss, Δ Q is reactive loss, I is line current, R is power loss, Δ P is active loss, Δ Q is reactive loss, and Δ Q is line currenti、XiAs a line parameter, Pi、QiFor active and reactive power at node i, UNIs the rated voltage of the line;
ΔU＝Zi·ΔS*＝(Ri+jXi)(ΔP-jΔQ)＝RiΔP+XiΔQ
wherein, Δ U is the longitudinal component of voltage drop, Zi、Ri、XiAs a line parameter, PiActive power and reactive power at a node i are shown, delta P is active loss, and delta Q is reactive loss;
for a PV node, if Δ P is 0, then:
ΔQ＝Xi -1·ΔU
wherein, Delta Q is reactive loss, XiIs a line parameter, and delta U is a voltage drop longitudinal component;
s104: correcting the reactive power of the PV node, namely correcting the reactive power injected into the PV node by using a reactive correction value in each iteration so as to ensure the real-time performance of data, wherein a correction equation is as follows:
wherein, the delta Q is a reactive correction quantity; gamma belongs to (-1, 1) as the calculation step length, and is generally equal to 0.1; qiCalculating the obtained reactive power for the PV node; qijFor all branches and nodes connected to the PV node, PiPower of the ith PV node, R, X is the line parameter, Δ UpIs the voltage difference between the PV node and the connected node, UiThe input voltage of the ith PV node;
s105: calculating values of delta U, delta and delta Q;
s106: and judging whether the voltage of each node meets the convergence judgment condition of the following formula, if not, returning to the step of updating the voltage amplitude and the voltage phase angle before the load flow calculation, and correcting the reactive power of the PV node until the voltage meets the convergence judgment condition to output a load flow calculation result. The convergence determination condition is as follows:
wherein the content of the first and second substances,
is the absolute value of the difference between the voltage value obtained in the kth iteration and the initial given voltage value, epsilon is the convergence accuracy,
for the voltage values obtained for k iterations, U0Is an initial given voltage value;
s107: and outputting a load flow calculation result.
3. The modeling and load flow calculation method for electric-thermal interconnection comprehensive energy system according to claim 1, wherein the water flow in the pipeline and the injection water flow of the thermal load node are obtained from the hydraulic model in step 2, and are expressed by using the following flow continuity equation:
Alm＝mq
wherein A islIs a network incidence matrix of heat load nodes relative to each pipeline, m is a hot water flow vector in the pipeline, m isqThe injection water flow vector for the heat load node.
4. The method for modeling and load flow calculation of an electric-thermal interconnected integrated energy system according to claim 1, wherein the temperature of each node of the heat supply network is determined by the thermodynamic model in step 2, specifically:
φ＝φi-φEi＝cpm(Til-Tol)
wherein phi is a thermal power vector injected into the node, phiiIs a node thermal load power vector, phiEiInjecting a thermal power vector, c, into the nodal electric boilerpIs the specific heat capacity of water, m is the mass flow, TilSupply water temperature vector, T, to the nodeolTo the node return water temperatureAn amount;
wherein T isendFor the temperature of the hot water flowing out of the pipe, TstartFor the temperature of the hot water flowing into the pipe, TeIs the external natural temperature, lambda is the heat conduction coefficient per unit length in the pipeline, d is the pipeline transmission distance, CpIs the specific heat capacity of water, m is the mass flow, mu is the temperature compensation parameter;
wherein m isout,aFor branch flow of the a-th branch out of the pipe, ToutReturn the mixing temperature, m, for the nodein,bBranch flow, T, for the b-th branch into the pipein,bAnd (4) flowing the terminal pipe temperature of the node for the b branch.
5. The modeling and load flow calculation method for electric-thermal interconnection integrated energy system according to claim 1, wherein the step 3 comprises the steps of:
step 301: modeling the coupling part of the electric-thermal combined system:
when the backpressure unit is used as a main heat source of a thermodynamic system and the electric boiler is used as a peak regulation heat source, the thermal power and the electric power generated by the backpressure unit satisfy the following relations:
ζ-1·φBY＝PBY
where ζ is the ratio of heat generation to electricity generation, and is generally a constant value, φBYFor heat power, P, from backpressure unitsBYElectric power generated for the backpressure unit;
the thermal power and the electric power generated by the peak-shaving electric boiler satisfy the following formula:
δ-1·φEB＝PEB
wherein delta is the ratio of heat production to electricity production, and is generally a constant value phiEBFor the thermal power, P, generated by peak-shaving electric boilersEBElectric power generated for the peak shaving electric boiler;
step 302: and converting the sum of the thermal powers of all the balance nodes in the thermodynamic system into the power of the electrical load by utilizing the coupling part modeling in the step 301, so as to realize the conversion process from the thermodynamic system to the power flow solution of the power system.
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