CN113849946A - An integrated energy system modeling and power flow calculation method for electricity-heat interconnection - Google Patents

Abstract

The present invention discloses a method for modeling and calculating power flow of an electric-heat interconnected integrated energy system. The method includes the following steps: (1): constructing a power flow calculation model of a power system with access to distributed power sources, and using an improved forward pushback The generation method performs special processing on the PV node to realize the power flow calculation of the distributed power supply connected to the distribution network. (2): Construct a thermal system model with multiple heat sources radiation type, convert the multiple heat source radiation type heat network into multiple single heat source radiation type heat networks, and use the improved forward-backward substitution method to calculate the decoupled heat network power flow. (3): Based on the modeling of each independent energy system, the coupled parts of the two systems are modeled to realize the energy flow calculation of the entire electric-thermal interconnected integrated energy system. The invention improves the disadvantage that the traditional forward-backward generation method cannot deal with PV nodes, reduces the number of iterations, and lowers the requirements for initial values. The improvement of the thermal system simplifies the model and increases the calculation speed.

Description

An integrated energy system modeling and power flow calculation method for electricity-heat interconnection

technical field

The invention relates to an electric-thermal interconnected integrated energy system, in particular to an electric-thermal interconnected integrated energy system modeling and power flow calculation method with an improved forward-backward substitution method.

Background technique

With the rapid development of today's society, the contradiction between massive energy consumption and ecological protection has become increasingly prominent. Researching an energy system with high efficiency, low pollution and strong controllability has become a hot issue. The development of comprehensive energy is conducive to the rational regulation and optimal utilization of various resources, and is a good way to deal with the problems of huge energy consumption and resource depletion in today's era. In traditional energy systems such as power grids and heat grids, each energy system has an independent operating system, the degree of coupling between them is not tight, and the energy efficiency is low. In the integrated energy system, the coupling between each other is tight, the energy utilization rate is greatly improved, and the ability to absorb renewable energy is also greatly improved.

The energy flow calculation of the integrated energy system is developed on the basis of the power flow calculation of the power system. The back-substitution method includes the following steps: at a node far away from the power supply, use the rated voltage of the line to calculate the power in each line in the opposite direction to the power transmission, and use the required power to calculate each line from the power supply in the direction of power transmission. For the voltage of each node, the above two steps are repeated in the power flow calculation until the accuracy meets the requirements. The described Newton-Raphson method and PQ decomposition method have a strong theoretical system in power systems, and the ideas are relatively mature, but when applied in integrated energy systems, the solution procedures are complex, the number of iterations is large, and the number of iterations is large. Difficult to achieve joint computing and other disadvantages.

Considering that the purpose of energy flow calculation in an integrated energy system is to improve the degree of coupling between systems, achieve optimal energy distribution, reduce energy consumption, and improve the level of comprehensive energy utilization, a simplified integrated energy system model is constructed and a unified energy system is used. The solution method can achieve fast and accurate solution. The forward-backward substitution method in the power flow calculation of the power system has the advantages of simple solution process, high calculation accuracy, concise programming, and does not require too many iterations. In the energy flow calculation, the energy flow solution of the integrated energy system can be realized.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an electric-heat interconnected integrated energy system modeling and power flow calculation method. This method is improved for the inadequacies of the forward-backward generation method in the power system with distributed generation access, and then extended to the radiation thermal system with multiple heat sources, so as to realize the power flow calculation of the integrated energy system.

In order to solve the problems existing in the prior art, the technical scheme adopted in the present invention is as follows:

An electric-heat interconnection integrated energy system modeling and power flow calculation method, comprising the following steps:

Step 1: Construct a power flow calculation model of the power system including distributed power supply access, and use the improved forward push-back method to process the PV nodes to realize the power flow calculation of the distributed power supply access to the distribution network;

Step 2: Build a thermal system model containing multiple heat sources radiation type, the thermal system model is composed of a hydraulic model and a thermal model, convert the multiple heat source radiation type heat network into a plurality of single heat source radiation type heat network, use the improved forward push back The power flow calculation of the decoupled heat network is carried out by using the generation method; the transformation method of converting a multi-heat source radiation heat network into multiple single heat source radiation heat networks is as follows:

(i＝1，…，n，n表示从节点分流的管道数目，j＝1，…，m，m表示热网中热源数目)为转化后所对应的单热源辐射型热网的管道流量，

(i＝1，…，n)为对应热源向节点输入的管道流量，

(i＝1，…，n)为转化前的支路流量即多热源辐射型热网所对应的管道流量；in,

(i=1, .

(i=1,...,n) is the pipeline flow input from the corresponding heat source to the node,

(i=1,...,n) is the branch flow before conversion, that is, the pipeline flow corresponding to the multi-heat source radiation heat network;

(i＝1,…，m，m为热网中热源数目)为多热源辐射型热网等效成多个单热源辐射型热网后等效热负荷功率，φ_l为等效前的节点热负荷功率；in,

(i=1,..., m, m is the number of heat sources in the heat network) is the equivalent heat load power after the multi-heat source radiation heat network is equivalent to multiple single heat source radiation heat networks, φ _l is the node before the equivalent heat load power;

Step 3: Based on the power flow calculation model and the thermal system model of the power system, model the coupling parts of the power system and the thermal system to realize the energy flow calculation of the entire power-thermal interconnected integrated energy system.

Further, the step 1 includes the following steps:

S101: Acquire power system network parameters and state variables;

S102: Set the initial value of the voltage, the present invention does not require high initial value of the voltage in the power system, and can be within a reasonable range;

S103: Calculate the power flow of the power system by using the improved forward-backward substitution method, the formula is as follows:

Among them, ΔS is the power loss, ΔP is the active power loss, ΔQ is the reactive power loss, I is the line current, Ri and X _i are the line parameters, _Pi and Qi are the active power and reactive power at node _{i ,} U _N is the rated voltage of the line;

ΔU=Z _i ·ΔS ^* =(R _i +jX _i )(ΔP-jΔQ)=R _i ΔP+X _i ΔQ

Among them, ΔU is the longitudinal component of the voltage drop, Z _i , R _i , X _i are the line parameters, Pi is the active power and reactive power at node _i , ΔP is the active power loss, and ΔQ is the reactive power loss;

For the PV node, ΔP=0, then:

ΔQ=X _i ^-1 ·ΔU

Among them, ΔQ is the reactive power loss, X _i is the line parameter, and ΔU is the longitudinal component of the voltage drop;

S104: Correction of the reactive power of the PV node, that is, the correction of the reactive power injected into the PV node by using the reactive power correction amount in each iteration, so as to ensure the real-time performance of the data. The correction equation is as follows:

Among them, ΔQ is the reactive power correction amount; γ∈(-1, 1) is the calculation step size, generally taking γ=0.1; Q _i is the reactive power calculated by the PV node; Q _ij is all the branches connected to the PV node. Reactive power of the road and node, Pi is the power of the _ith PV node, R and X are the line parameters, ΔU _p is the voltage difference between the PV node and the connected node, and U _i is the input voltage of the ith PV node;

S105: Calculate the values of ΔU, Δδ, and ΔQ;

S106: Determine whether the voltage of each node satisfies the convergence judgment condition of the following formula, if not, return to the power flow calculation to update the voltage amplitude and voltage phase angle, and correct the reactive power of the PV node until the voltage meets the convergence judgment condition Output power flow calculation results. The convergence judgment condition is as follows:

为第k次迭代所得电压值与初始给定电压值之差的绝对值，ε为收敛精度，

为k次迭代所得电压值，U₀为初始给定电压值；in,

is the absolute value of the difference between the voltage value obtained in the k-th iteration and the initial given voltage value, ε is the convergence accuracy,

is the voltage value obtained by k iterations, and U ₀ is the initial given voltage value;

S107: Output the calculation result of the power flow.

Further, in step 2, the water flow in the pipeline and the injected water flow of the heat load node are obtained from the hydraulic model, which is expressed by the following flow continuity equation:

A _l m = m _q

Among them, A _l is the network correlation matrix of the heat load node relative to each pipeline, m is the hot water flow vector in the pipeline, and m _q is the injected water flow vector of the heat load node;

Further, in step 2, the temperature of each node of the thermal network is determined by the thermal model, specifically:

φ=φ _i -φ _Ei =c _p m(T _il -T _ol )

Among them, φ is the injected heat power vector of the node, φ _i is the node heat load power vector, φ _Ei is the injected heat power vector of the electric boiler at the node, _cp is the specific heat capacity of water, m is the mass flow rate, and T _il is the node water supply temperature vector, T _ol is the node return water temperature vector;

where T _end is the temperature at which the hot water flows out of the pipe, T _start is the temperature at which the hot water flows into the pipe, T _e is the outside natural temperature, λ is the heat transfer coefficient per unit length in the pipe, d is the transmission distance of the pipe, and C _p is the temperature of the water. Specific heat capacity, m is mass flow, μ is temperature compensation parameter;

Among them, m _out,a is the branch flow of the a-th branch out of the pipeline, T _out is the node return mixing temperature, min _,b is the branch flow of the b-th branch into the pipeline, and T _in,b is the branch flow of the b-th branch. The pipe temperature at the end of the b branch into the node.

Further, the step 3 includes the following steps:

Step 301: Model the coupling part of the combined electric-thermal system:

When the back pressure unit is used as the main heat source of the thermal system and the electric boiler is used as the peak-shaving heat source, the thermal power and electric power generated by the back pressure unit satisfy the following relationship:

ζ ^-1 ·φ _BY =P _BY

Among them, ζ is the ratio of heat and electricity generation, which is generally a fixed value, φ _BY is the thermal power generated by the back pressure unit, and P _BY is the electrical power generated by the back pressure unit;

The thermal power and electric power emitted by the peak-shaving electric boiler satisfy the following formula:

δ ^-1 ·φ _EB =P _EB

Among them, δ is the ratio of heat generation and electricity generation, which is generally a fixed value, φ _EB is the thermal power emitted by the peak-shaving electric boiler, and P _EB is the electric power emitted by the peak-shaving electric boiler;

Step 302: Using the coupling part modeling described in Step 301 to convert the sum of the thermal power of all the balance nodes in the thermal system into the power of the electrical load, so as to realize the transformation process from the thermal system to the power flow solution of the power system.

The advantages and beneficial effects that the present invention has are:

The present invention firstly uses the improved forward push-back substitution method to correct the reactive power of the PV nodes in the power system connected to the distributed power source, and then converts the multi-heat source radiation type heat network into a plurality of single heat source radiation type heat networks. Energy flow calculation, and finally, the power flow calculation of the integrated energy system is realized by converting the thermal power into electric power through the coupling element. The invention improves the disadvantage that the traditional forward-backward generation method cannot deal with PV nodes, reduces the number of iterations, and lowers the requirements for initial values. The improvement of the thermal system simplifies the model and increases the calculation speed.

Description of drawings

Fig. 1 is the flow chart of the power flow solution based on the improved forward push-back substitution method in the power system;

Figure 2 is a decoupling diagram of a radiant thermal system with multiple heat sources;

Figure 3 is a schematic diagram of a comprehensive energy testing system;

Figure 4 is a comparison diagram of the power flow calculation results of the power system.

Detailed ways

The present invention is described in detail below in conjunction with accompanying drawing and embodiment:

The present invention is a method for modeling and calculating power flow of an electric-heat interconnected integrated energy system. The method is improved for the inadequacies of the forward push-back substitution method in a power system with distributed power supply access, and is extended to a power system with multiple heat sources. In the radiant thermal system, the power flow solution of the integrated energy system is realized, which includes the following steps:

Step 1: Construct the power flow calculation model of the power system including the access of the distributed power source, and use the improved forward-backward substitution method to perform special processing on the PV nodes to realize the power flow calculation of the distributed power source access to the distribution network.

As shown in Figure 1, the step 1 includes the following steps:

S101: Acquire power system network parameters and state variables;

S102: Set the initial value of the voltage, the present invention does not require high initial value of the voltage in the power system, and can be within a reasonable range;

S103: Calculate the power flow of the power system by using the improved forward push-back method. The improved forward push-back method is used to calculate the voltage and power distribution in two steps. The far position starts to calculate the power loss of each branch and the node power against the direction of power transmission, the formula is as follows:

Among them, ΔS is the power loss, ΔP is the active power loss, ΔQ is the reactive power loss, I is the line current, Ri and X _i are the line parameters, _Pi and Qi are the active power and reactive power at node _{i ,} U _N is the rated voltage of the line.

Secondly, starting from the power supply, calculate the voltage drop of each line and the voltage of each node along the direction of power transmission. The formula is as follows:

ΔU=Z _i ·ΔS ^* =(R _i +jX _i )(ΔP-jΔQ)=R _i ΔP+X _i ΔQ

Among them, ΔU is the longitudinal component of the voltage drop, Z _i , R _i , X _i are the line parameters, Pi is the active power and reactive power at node _i , ΔP is the active power loss, and ΔQ is the reactive power loss;

For the PV node, ΔP=0, then:

ΔQ=X _i ^-1 ·ΔU

Among them, ΔQ is the reactive power loss, X _i is the line parameter, and ΔU is the longitudinal component of the voltage drop;

S104: Correct the reactive power at the PV node by using the improved forward push-back substitution method:

For the distribution network injected by distributed power sources, the number of PV nodes in the power system will increase, and the calculation of a large number of PV nodes cannot be realized when the forward push-back method is used. If the initial value of the reactive power output of the PV nodes is recorded as 0, The PV node can be equivalent to the PQ node first to facilitate the subsequent solution. Using the improved forward push-back substitution method can realize the correction of the reactive power of the PV node, that is, by using the reactive power correction amount to correct the reactive power injected into the PV node in each iteration, so as to ensure the real-time performance of the data, the correction equation is as follows :

Among them, ΔQ is the reactive power correction amount; γ∈(-1, 1) is the calculation step size, generally taking γ=0.1; Q _i is the reactive power calculated by the PV node; Q _ij is all the branches connected to the PV node. The reactive power of the road and the node, Pi is the power of the _ith PV node, R and X are the line parameters, ΔU _p is the voltage difference between the PV node and the connected node, and U _i is the input voltage of the ith PV node.

S105: Calculate the values of ΔU, Δδ, and ΔQ;

S106: Determine whether the voltage of each node satisfies the convergence judgment condition of the following formula, if not, return to the power flow calculation to update the voltage amplitude and voltage phase angle, and correct the reactive power of the PV node until the voltage meets the convergence judgment condition Output power flow calculation results. Convergence judgment conditions are as follows:

为第k次迭代所得电压值与初始给定电压值之差的绝对值，ε为收敛精度，

为k次迭代所得电压值，U₀为初始给定电压值。in,

is the absolute value of the difference between the voltage value obtained in the k-th iteration and the initial given voltage value, ε is the convergence accuracy,

is the voltage value obtained by k iterations, and U ₀ is the initial given voltage value.

S107: output the calculation result of power flow;

Step 1 realizes the power flow calculation of the distributed power supply connected to the distribution network, and improves the disadvantage that the traditional forward push-back method cannot handle the PV node, so that the reactive power of the PV node can be corrected in each iteration. .

Step 2: constructing a multi-heat source radiation type thermodynamic system model, the thermodynamic system model is composed of a hydraulic model and a thermodynamic model. The multi-heat source radiation heat network is converted into multiple single heat source radiation heat networks, and the decoupled heat flow calculation is carried out by using the improved forward push-back method.

S201: The thermal system model is composed of a hydraulic model and a thermal model, and the hydraulic model is used to obtain the water flow in the pipeline and the injected water flow of the heat load node, which is expressed by the following flow continuity equation:

A _l m = m _q

Among them, A _l is the network correlation matrix of the heat load node relative to each pipeline, m is the hot water flow vector in the pipeline, and m _q is the injected water flow vector of the heat load node.

Pressure loop equation:

Bh _f = 0

Among them, B is the branch correlation matrix of the pipeline in the heating loop, and h _f is the pressure change vector of the hot water in the pipeline.

The temperature of each node of the thermal network, the relationship between the injected thermal power and the mass flow rate and the node temperature are determined from the thermal model:

φ=φ _i -φ _Ei =c _p m(T _il -T _ol )

Among them, φ is the injected heat power vector of the node, φ _i is the node heat load power vector, φ _Ei is the injected heat power vector of the electric boiler at the node, _cp is the specific heat capacity of water, m is the mass flow rate, and T _il is the node water supply temperature vector, T _ol is the node return water temperature vector.

The relationship between the temperature changes at the beginning and end of the pipe:

where T _end is the temperature at which the hot water flows out of the pipe, T _start is the temperature at which the hot water flows into the pipe, T _e is the outside natural temperature, λ is the heat transfer coefficient per unit length in the pipe, d is the transmission distance of the pipe, and C _p is the temperature of the water. Specific heat capacity, m is mass flow, μ is temperature compensation parameter.

The hot water flows from the heat source through different heat networks and finally mixes at the heat load, which can be expressed by the following formula:

Among them, m _out,a is the branch flow of the a-th branch out of the pipeline, T _out is the node return mixing temperature, min _,b is the branch flow of the b-th branch into the pipeline, and T _in,b is the branch flow of the b-th branch. The pipe temperature at the end of the b branch into the node.

S202: Convert the multi-heat source radiation type heat network into multiple single heat source radiation type heat networks, as shown in Figure 2, which contains a multi-heat source radiation type thermal system model. In this model, there are two heat sources that simultaneously supply heat to the heat load , then the two heat sources should be converted into two equivalent heat sources to supply heat to the heat load, so that the multi-heat source radiation type heat network is converted into multiple single heat source radiation type heat networks and then the power flow calculation is performed. The conversion method is as follows:

Rewritten in matrix form as:

θ∈(1，m)

θ∈(1, m)

(i＝1，…，n，n表示从节点分流的管道数目，j＝1，…，m，m表示热网中热源数目)为转化后所对应的单热源辐射型热网的管道流量，

(i＝1，…，n)为对应热源向节点输入的管道流量，

(i＝1，…，n)为转化前的支路流量即多热源辐射型热网所对应的管道流量；in,

(i=1, .

(i=1,...,n) is the pipeline flow input from the corresponding heat source to the node,

(i=1,...,n) is the branch flow before conversion, that is, the pipeline flow corresponding to the multi-heat source radiation heat network;

(i＝1,…，m，m为热网中热源数目)为多热源辐射型热网等效成多个单热源辐射型热网后等效热负荷功率，φ_l为等效前的节点热负荷功率。in,

(i=1,..., m, m is the number of heat sources in the heat network) is the equivalent heat load power after the multi-heat source radiation heat network is equivalent to multiple single heat source radiation heat networks, φ _l is the node before the equivalent Thermal load power.

S203: Use the improved forward push-back method to calculate the thermal network power flow after decoupling, and perform the following analogy after decoupling the thermal network:

The temperature in the thermal system is analogous to the voltage in the power system, the heat flow or mass flow is analogous to the current in the power system, the heat load node is analogous to the PQ node in the power system, and the heat source node is analogous to the PV node in the power system. The node with known heating temperature is analogous to the balance node in the power system. Using the above analogy idea, the thermal system can be equivalent to the power system to solve the power flow. Law.

In step 2, by constructing a multi-heat source radiation thermal system model, the multi-heat source radiation heat network is converted into multiple single heat source radiation heat networks, and the multi-heat source radiation is realized by analogy to the improved forward-backward substitution method proposed in step 1. Power flow solution for type heat network.

Step 3: Based on the power flow calculation model and the thermal system model of the power system, model the coupling parts of the power system and the thermal system to realize the energy flow calculation of the entire power-thermal interconnected integrated energy system.

The step 3 includes the following steps:

Step 301: Model the coupling part of the combined electric-thermal system:

As a widely used thermal power unit, the back pressure unit does not contain a condenser, and the exhaust heat will be fully utilized in the back pressure unit, which has a high thermal efficiency. The disadvantage is that the power generation of the back pressure unit is based on the heat production, and the control sensitivity is not strong. Therefore, in the thermal system, the back pressure unit is generally selected as the main heat source of the thermal system, and the electric boiler is used as the peak-shaving heat source.

The thermal power and electric power emitted by the back pressure unit satisfy the following relationship:

ζ ^-1 ·φ _BY =P _BY

Among them, ζ is the ratio of heat and electricity generation, which is generally a fixed value, φ _BY is the thermal power generated by the back pressure unit, and P _BY is the electrical power generated by the back pressure unit;

The thermal power and electric power emitted by the peak-shaving electric boiler satisfy the following formula:

δ ^-1 ·φ _EB =P _EB

Among them, δ is the ratio of heat generation and electricity generation, which is generally a fixed value, φ _EB is the thermal power emitted by the peak-shaving electric boiler, and P _EB is the electric power emitted by the peak-shaving electric boiler.

Step 302: Using the coupling part modeling described in Step 301 to convert the sum of the thermal power of all the balance nodes in the thermal system into the power of the electrical load, so as to realize the transformation process from the thermal system to the power flow solution of the power system.

Taking the integrated energy test system shown in Figure 3 as an example, the thermal system and the power system are coupled together through a cogeneration unit. The heat network part includes two heat source nodes Source 1 and Source 2 using back pressure units, a peak-shaving electric boiler located at node 5, and 14 heat load nodes. The peak-shaving ratio is taken as 0.45, and the cogeneration unit provides heat. The temperature is set to 120°C, the thermoelectric ratio is set to 1.4, the heat load is set to 0.5MW, the natural environment temperature is set to 2°C, the length of each pipeline section is set to 1.58km, and the thermal conductivity per unit length of the pipeline is set to 0.289Wm ^-1 ·K ^-1 , the diameter of the pipeline is taken as 100mm, according to step 2, the multi-heat source radiation type heat network is converted into multiple single heat source radiation type heat network, and the improved forward push-back substitution method is used to calculate the power flow of the thermal system, Table 1 is the pipeline flow of the thermal system, and Table 2 is the supply temperature of the thermal system node and the node return temperature.

Table 1 Pipe flow of thermal system

Table 2 Node supply temperature and node return temperature of thermal system

The thermal system and the power system are coupled through the node 14, and the thermal power of the node 14 is 7.32725MW, which is converted into electric power of 5.23375MW.

The power grid part selects a 14-node power distribution network, node 1 is connected to the external power grid, the voltage amplitude is 1.00pu, node 2 is the PV node, the voltage amplitude is 0.993pu, node 6 is the PV node, the voltage amplitude is 0.964pu, and the remaining nodes are is the PQ node. According to Figure 1, the power system is programmed based on the power flow solution flow chart of the improved forward push-back substitution method. First, nodes 1 and 2 are regarded as PQ nodes, and the first iterative calculation is performed, and then the program is returned to the calculation of the reactive power correction amount. After the power correction amount is substituted, the next iterative calculation is performed. After three iterations, the convergence judgment condition is satisfied and the power flow calculation result of the power system is output. The power flow calculation results obtained using this method are compared with the traditional Newton-Raphson method for power flow calculation as shown in Figure 4. The maximum error of the node voltage is 0.00028%, which verifies the accuracy of the method.

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,

(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,

(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, phi_lThe 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 current_i、X_iAs a line parameter, P_i、Q_iFor active and reactive power at node i, U_NIs the rated voltage of the line;

ΔU＝Z_i·ΔS^*＝(R_i+jX_i)(ΔP-jΔQ)＝R_iΔP+X_iΔQ

wherein, Δ U is the longitudinal component of voltage drop, Z_i、R_i、X_iAs a line parameter, P_iActive 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＝X_i ^-1·ΔU

wherein, Delta Q is reactive loss, X_iIs 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; q_iCalculating the obtained reactive power for the PV node; q_ijFor all branches and nodes connected to the PV node, P_iPower of the ith PV node, R, X is the line parameter, Δ U_pIs the voltage difference between the PV node and the connected node, U_iThe 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,

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:

A_lm＝m_q

wherein A is_lIs a network incidence matrix of heat load nodes relative to each pipeline, m is a hot water flow vector in the pipeline, m is_qThe 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＝φ_i-φ_Ei＝c_pm(T_il-T_ol)

wherein phi is a thermal power vector injected into the node, phi_iIs a node thermal load power vector, phi_EiInjecting a thermal power vector, c, into the nodal electric boiler_pIs the specific heat capacity of water, m is the mass flow, T_ilSupply water temperature vector, T, to the node_olTo the node return water temperatureAn amount;

wherein T is_endFor the temperature of the hot water flowing out of the pipe, T_startFor the temperature of the hot water flowing into the pipe, T_eIs the external natural temperature, lambda is the heat conduction coefficient per unit length in the pipeline, d is the pipeline transmission distance, C_pIs the specific heat capacity of water, m is the mass flow, mu is the temperature compensation parameter;

wherein m is_out,aFor branch flow of the a-th branch out of the pipe, T_outReturn the mixing temperature, m, for the node_in,bBranch flow, T, for the b-th branch into the pipe_in,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·φ_BY＝P_BY

where ζ is the ratio of heat generation to electricity generation, and is generally a constant value, φ_BYFor heat power, P, from backpressure units_BYElectric 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·φ_EB＝P_EB

wherein delta is the ratio of heat production to electricity production, and is generally a constant value phi_EBFor the thermal power, P, generated by peak-shaving electric boilers_EBElectric 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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