Power system energy efficiency analysis and power flow calculation method for distributed power supply connected to power distribution network

Abstract

The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network comprises the following steps: Step 1, collecting the parameters of the distributed power supply connected to the distribution network and establishing a distributed power supply model, and simulating the distributed power supply model as an injected current model; Step 2, processing the distribution network as a few-loop distribution network comprising PV nodes, PI nodes, PQ nodes and PQV nodes, and calculating the injected reactive power correction amount of the PV node at the end of the distribution network; Step 3, according to the loop-breaking point of the distribution network, forward-backward sweep power flow calculation is carried out, and the reactive power, active power of each branch and the voltage of each node are iteratively updated by using the injected current of each node and the injected reactive power correction amount of the PV node; Step 4, when it is determined that the PV node voltage and the PQ node voltage are converged, the power system energy efficiency analysis power flow calculation result of the distributed power supply connected to the distribution network is obtained. The power system energy efficiency analysis power flow calculation method provided by the application improves the calculation speed and calculation accuracy and reduces the memory occupation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power system energy efficiency analysis power flow calculation, and particularly relates to a power system energy efficiency analysis power flow calculation method for distributed power supply connected to a distribution network. BACKGROUND

[0002] The connection of distributed power supply to a distribution network changes the original passive distribution network into an active distribution network, which changes the power transmission, voltage distribution, power quality and short-circuit current of the distribution network, thus having an important influence on the protection, control, operation and planning of the distribution network. Meanwhile, due to the influence of meteorological factors on part of the distributed power supply, the randomness thereof greatly increases the complexity of the distribution network. Since the function of the traditional distribution network is mainly to distribute electric energy, which is a passive system, the planning method for the traditional distribution network cannot be directly used in these problems. After the introduction of distributed power supply into the distribution network system, the influence of the distributed power supply on the original distribution network system must be considered.

[0003] The power flow calculation of the distribution network is an important content of the planning and design of the distribution network. The advantages and disadvantages of each planning scheme are judged through the power loss calculation of the network line. In the prior art, most of the distribution networks are passive distribution networks or active distribution networks with a small amount of distributed power supply connected thereto, and the influence of the distributed power supply on the distribution network system is not considered. The connection of the distributed power supply becomes a trend of upgrading and development of the distribution network. With the grid connection of various forms of distributed power supply, the complexity of the original power flow calculation of the distribution network system is greatly improved. Some traditional calculation methods will no longer be applicable due to the inability to consider the influence of the distributed power supply. Therefore, in the planning of the distribution network, the influence of the addition of the distributed power supply on the system power flow and the new method of power flow calculation must be considered.

[0004] In the prior art 1 (CN102148510A) "Power flow algorithm of distribution network containing distributed power supply", various distributed power supplies are processed as PI nodes in the power flow calculation, photovoltaic and fuel cell power generation types are processed as PQ(V) nodes, micro gas turbine and biomass power station power generation types are processed as PV nodes; then the PI, PQ(V) nodes of various distributed power supply types in the power flow calculation are converted into PQ nodes and PV nodes that can be processed by the traditional power flow calculation method; the power flow calculation of the prior art 1 includes the following steps: 1) determination of admittance matrix; 2) processing of various distributed power supplies in the power flow calculation; 3) conversion of node type; 4) determination of node injection power; 5) power flow calculation; however, the prior art 1 determines the active power and reactive power of each node injected into the distribution network system according to the generator injection power, load power and power of various distributed power supplies connected to the system, in order to avoid the problem of repeated oscillation of PV-PQ in the calculation process and ensure the convergence reliability of the program, the PV node is set to PQ node after the reactive power exceeds the boundary. In the prior art 2 (CN112421617A) "Power flow calculation method and system of distributed power supply", the method includes: identifying the type of distributed power supply of the current power system, matching the type of distributed power supply with the pre-established power flow calculation model, selecting the power flow calculation model with the highest matching degree as the power flow calculation model of the current power system; extracting the power system parameters required for power flow calculation and initializing to obtain the initial value of power flow calculation, calculating the predicted power flow solution according to the power flow calculation model of the current power system and the initial value of power flow calculation, and then correcting the power flow prediction solution by using the fast decoupling method to obtain the accurate power flow solution. Under this method, the special requirements of bidirectional power flow can be met, and the negative impact of distributed power supply on the power system is minimized. Through the above analysis, the prior arts 1 and 2 have the problems of low calculation speed and large memory occupation in the process of power flow calculation, thereby reducing the accuracy of the calculation result.

[0005] Prior art 3 (CN111049144A) "active power distribution network power flow calculation PV node processing method based on constant change rate matrix", the voltage and PV node voltage correction amount of power distribution network are initialized;The linear relationship between the voltage correction amount and the reactive power compensation amount of the PV node is obtained, the elements of the constant change rate matrix D are constants and are independent of the reactive power compensation value, and the constant change rate matrix D is obtained by solving multiple power flow calculation;The reactive power compensation amount of the PV node is calculated by using the constant change rate matrix D and the PV node voltage correction amount;The forward-backward substitution method based on the road matrix T is used to carry out power flow calculation, and the voltage of each node of the power distribution network is obtained;And the voltage correction amount of the PV node is updated;The convergence of the voltage of each node of the power distribution network is judged, if the difference is less than the error, it is judged as convergence;Otherwise, continue to iterate. Prior art 3 overcomes the error caused by directly calculating the transfer reactance, has good convergence and weak sensitivity to the number of PV type DG grid connection and the initial value of reactive power. But the process of obtaining the constant change rate matrix D by using multiple power flow calculation is time-consuming and has large amount of calculation.

[0006] In summary, it is necessary to study a power system energy efficiency analysis power flow calculation method based on distributed power supply access to power distribution network to overcome the shortcomings of the above power flow algorithm. SUMMARY

[0007] In order to solve the problems in the prior art, the purpose of the present application is to provide a power system energy efficiency analysis power flow calculation method based on distributed power supply access to power distribution network.

[0008] The present application adopts the following technical solutions.

[0009] The present application provides a power system energy efficiency analysis power flow calculation method based on distributed power supply access to power distribution network, which comprises:

[0010] Step 1, collecting the parameters of the distributed power supply accessing the power distribution network and establishing various distributed power supply models, the distributed power supply models including: PQ type distributed power supply model, PI type distributed power supply model, PV type distributed power supply model and PQV type distributed power supply model;Simulate various distributed power supply models into injection current model;

[0011] Step 2, processing the power distribution network into a few-loop power distribution network including PV node, PI node, PQ node and PQV node, calculating the injection reactive power correction amount of the PV node at the end of the power distribution network based on the injection current model;

[0012] Step 3, based on the open loop point of the power distribution network, the injection current model is used to calculate the injection current of each node in the power distribution network, and the branch current is corrected to obtain the current compensation value of the open loop port; based on the forward-backward sweep power flow calculation method, the injection current of each node and the injection reactive power correction amount of the PV node are used to iteratively update the branch reactive power, branch active power and node voltage;

[0013] Step 4, the convergence of the PV node voltage and the PQ node voltage in the power distribution network is judged respectively; when it is judged that the PV node voltage and the PQ node voltage in the power distribution network are converged, the obtained branch reactive power, branch active power and node voltage are taken as the power system energy efficiency analysis power flow calculation result of the distributed power source accessing the power distribution network.

[0014] In step 1, the PQ type distributed power source model includes a doubly-fed wind power generator model; the PQ type distributed power source model is simulated as a first injection current model, which satisfies the following relationship:

[0015]

[0016] In the formula,

[0017] is the injection current,

[0018] S is the apparent power of the distributed power source,

[0019] e is the real part of the voltage of the distributed power source, and f is the imaginary part of the voltage of the distributed power source.

[0020] In step 1, the PI type distributed power source model includes a photovoltaic cell model; the PI type distributed power source model is solved to obtain the reactive power, and then the PI type distributed power source model is simulated as a first injection current model.

[0021] In step 1, the PV type distributed power source model includes a micro gas turbine model; the PV type distributed power source model is solved to obtain the reactive power, and the reactive power is corrected; when the corrected reactive power exceeds the rated range, the PV type distributed power source model is simulated as a second injection current model, which satisfies the following relationship:

[0022]

[0023] In the formula,

[0024] Z ii is the self-impedance of the PV type distributed power source, wherein i represents the node number of the PV type distributed power source accessing the power distribution network,

[0025] is the change amount of the voltage amplitude of the node corresponding to the PV type distributed power source,

[0026] Phasor of the compensation current injected by the PV type distributed power supply.

[0027] In step 1, in the first iteration, the PQV type distributed power supply model is simulated as the first injection current model according to the PQ type distributed power supply model; in the second iteration, the voltage of the PQV type distributed power supply is corrected, the reactive power is corrected with the corrected voltage, and the first injection current model obtained in the previous iteration is corrected with the corrected voltage and the corrected reactive power; the iteration is repeated until convergence is achieved, and the first injection current model of the PQV type distributed power supply model is obtained.

[0028] Step 2 includes:

[0029] Step 2.1, the PQ type distributed power supply model, the PI type distributed power supply model and the PQV type distributed power supply model are all processed as PQ nodes, and the PV type distributed power supply model is processed as a PV node; the distribution network adopts a few-ring network structure,

[0030] Step 2.2, for all PV nodes at the end of the distribution network, the network equivalent impedance matrix of the PV node is Z (n×n) =R+jX, the injection current correction of the PV node is ΔI (n×1) =ΔC+jΔD, the voltage increment of the PV node is ΔU (n×1) =ΔE+jΔF, and the following relationship is satisfied:

[0031] ΔU (n×1) =Z (n×n) ΔI (n×1)

[0032] Wherein,

[0033] R is the real part of the network equivalent impedance matrix Z (n×n) of the PV node, and X is the imaginary part of the network equivalent impedance matrix Z (n×n) of the PV node,

[0034] ΔC is the real part of the injection current correction ΔI (n×1) of the PV node, and ΔD is the imaginary part of the injection current correction ΔI (n×1) of the PV node,

[0035] ΔE is the real part of the voltage increment ΔU (n×1) of the PV node, and ΔF is the imaginary part of the voltage increment ΔU (n×1) of the PV node.

[0036] Step 2.3, when the distribution network is in normal operation, the amplitude of the voltage of the PV node is constant in the iteration process, and the injection power correction of the PV node is satisfies the following relationship:

[0037]

[0038] wherein U pv is the PV node voltage obtained in the iteration process;

[0039] Step 2.4, the injected active power of the PV node is constant, and the injected reactive power correction amount ΔQ of the PV node satisfies the following relationship:

[0040] ΔQ = X -1 Re{U pv -U sch}·Re{U pv}

[0041] wherein,

[0042] Re{U pv} is the real part of the difference between the PV node voltage U pv obtained in the iteration process and the given PV node voltage amplitude U

[0043] Re{U pv -U sch} is the real part of the difference between the PV node voltage U pv obtained in the iteration process and the given PV node voltage amplitude U sch .

[0044] Preferably, in step 2.2, the network equivalent impedance matrix of the PV node is calculated by using the Thevenin equivalent circuit, and the reactive power of the PV node is calculated by using the network equivalent impedance matrix of the PV node and the PV node voltage.

[0045] Step 3 comprises:

[0046] Step 3.1, obtaining the loop-breaking point of the distribution network; based on the loop-breaking point, forming the incident impedance matrix, the admittance matrix, and the loop-breaking port matrix corresponding to the PV node;

[0047] Step 3.2, the distribution network after loop breaking adopts a radial network structure; the distribution network after loop breaking is initialized to make the superimposed voltage ΔV corresponding to the PV node and the open-circuit voltage V of the loop-breaking port both 0, and at this time, the node voltages in the distribution network are all the root node voltages;

[0048] Step 3.3, respectively solving the injected currents of the PV node, the PI node, the PQ node, and the PQV node in the distribution network;

[0049] Step 3.4, calculating the current compensation value of the loop-breaking port by using the injected currents of the nodes to correct the branch currents;

[0050] Step 3.5, using the calculated injection current of each node and the injection reactive power correction of PV node, based on the forward-backward sweep power flow calculation method, the reactive power of each branch, the active power of each branch and the voltage of each node are updated iteratively according to the following relationship:

[0051]

[0052]

[0053]

[0054] In the formula,

[0055] P k and Q k are the active power and reactive power injected by the node in the kth iteration,

[0056] P k and Q k are the active power and reactive power injected by the node in the (k-1)th iteration,

[0057] R k-1 and X k-1 are the real part and imaginary part of the equivalent impedance of the branch in the (k-1)th iteration,

[0058] U k-1 is the node voltage in the (k-1)th iteration,

[0059] U k is the node voltage in the kth iteration,

[0060] P Lk and Q Lk are the active power and reactive power injected by the load in the kth iteration,

[0061] P DGk and Q DGk are the active power and reactive power injected by the distributed power source in the kth iteration.

[0062] Step 3.3 includes:

[0063] Step 3.3.1, according to the method of Step 1, the PV type distributed power source model is simulated as an injection compensation current model to solve the injection current of the PV node in the distribution network;

[0064] Step 3.3.2, according to the method of Step 1, the PQ type distributed power source model is simulated as an injection current model to solve the injection current of the PQ node in the distribution network;

[0065] Step 3.3.3, first convert the PQV node to PQ node according to the following relationship:

[0066]

[0067] In the formula,

[0068] ΔQ ir is the reactive power variation of node i to node r,

[0069] P rr and Q rr are the active power injection and the reactive power injection of node r, respectively,

[0070] P rm and Q rm are the active power and the reactive power of node r to node m, respectively,

[0071] U r is the voltage of node r,

[0072] m is any node number in the node number set C r , and the node number set C r contains all node numbers except node r,

[0073] X ir is the equivalent reactance value between node i and node r;

[0074] Step 1, the injection current model of the PQ-type distributed power supply model is simulated according to the method in step 1;

[0075] Step 3.3.4, first, the PI-type distributed power supply model is simulated as an injection current model according to the method in step 1, and the PI node in the distribution network is converted into a PQ node; then, the injection current of the PQ node in the distribution network is solved according to the method in step 1.

[0076] Step 4 includes:

[0077] Step 4.1, whether the voltage of all PV nodes in the distribution network meets the convergence accuracy is judged by the following relationship:

[0078]

[0079] In the formula,

[0080] is the voltage of the i-th PV node calculated in the k-th iteration,

[0081] U schi is the given amplitude of the voltage of the i-th PV node,

[0082] ε pv is the convergence precision of the PV node voltage;

[0083] Step 4.2, judging whether all the PQ node voltages in the distribution network satisfy the convergence precision by the following relationship, if yes, entering step 4.5, otherwise entering step 4.3:

[0084]

[0085] in the formula,

[0086] represents the real part of the change amount of the voltage of the i-th PQ node calculated in the k-th iteration and the voltage of the i-th PQ node calculated in the k-1-th iteration,

[0087] represents the imaginary part of the change amount of the voltage of the i-th PQ node calculated in the k-th iteration and the voltage of the i-th PQ node calculated in the k-1-th iteration,

[0088] ε pq is the convergence precision of the PQ node voltage;

[0089] Step 4.3, correcting the reactive power injection amount of the PV node by using the PV node voltage;

[0090] Step 4.4, using the node voltage calculated in the k-th iteration to replace the node voltage calculated in the k-1-th iteration, and returning to step 4.2;

[0091] Step 4.5, judging whether the PV node voltage and the PQ node voltage in the distribution network converge, so as to obtain the reactive power of each branch, the active power of each branch and the node voltage as the power system energy efficiency analysis power flow calculation result of the distributed power supply connected to the distribution network.

[0092] The power system energy efficiency analysis power flow calculation method provided by the application can improve the calculation speed, reduce the memory occupation, and significantly improve the accuracy of the calculation result compared with the prior art.

[0093] The application considers the influence of the connection of the distributed power supply on the power flow of the distribution network system, studies the reactive power correction method of the PV node in the forward-backward substitution power flow calculation, obtains the network equivalent reactance matrix of the PV node by using the Thevenin equivalent circuit, and further obtains the reactive power correction amount of the PV node, and accordingly designs the forward-backward substitution power flow algorithm suitable for the PV type distributed power supply, effectively overcomes the limitation that the forward-backward substitution method is only applicable to the PQ constant type node, and expands the application range of the forward-backward substitution power flow algorithm.

[0094] The power flow calculation method for power system energy efficiency analysis proposed in this invention is applicable to distribution network parameter calculation and risk assessment, improving the accuracy and speed of distribution network power flow calculation. Choosing different load models does not significantly affect the speed of power flow calculation. Attached Figure Description

[0095] Figure 1 This is a flowchart of the power system energy efficiency analysis and power flow calculation method for distributed generation access to the distribution network proposed in this invention. Detailed Implementation

[0096] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0097] like Figure 1 As shown, this invention proposes a power system energy efficiency analysis and power flow calculation method for distributed generation connected to the distribution network. The calculation method includes steps 1 to 4.

[0098] Step 1: Collect parameters of distributed generation sources connected to the distribution network and establish various distributed generation source models, including: PQ type distributed generation source model, PI type distributed generation source model, PV type distributed generation source model and PQV type distributed generation source model; simulate various distributed generation source models as injection current models.

[0099] If the operating parameters of a distributed generation (DG) do not exceed their rated range when connected to the distribution network, then the DG can be treated as a PQ node when performing power flow calculations for a distribution network containing DG. When a DG is used as a PQ node, the values ​​of its output active and reactive power tend to stabilize. Based on this characteristic, wind turbines, the most common type of distributed green energy source, can be analyzed as a PQ node.

[0100] In step 1, the PQ-type distributed generation model includes a doubly-fed wind turbine model. The doubly-fed wind turbine model is treated as a load with opposite power direction but the same power magnitude, and the PQ constant-type distributed generation is analyzed. The PQ-type distributed generation model is simulated as the first injection current model, satisfying the following relationship:

[0101]

[0102] In the formula,

[0103] To inject current,

[0104] S is the apparent power of the distributed power source, S = P + jQ, where P is the active power of the distributed power source and Q is the reactive power of the distributed power source.

[0105] e is the real part of the distributed power supply voltage, and f is the imaginary part of the distributed power supply voltage.

[0106] After the photovoltaic power generation system introduces the inverter, the active power and the injected current are constant, so in step 1, the PI type distributed power supply model includes the photovoltaic cell model; the PI type distributed power supply model is solved to obtain the reactive power, and then the The PI type distributed power supply model is processed into the PQ type distributed power supply model, and then simulated into the first injected current model.

[0107] When the PV constant type distributed power supply, such as a micro gas turbine, appears in the case where the corrected reactive power exceeds the required range, the processing method is changed to inject a compensation current into the PV node.

[0108] In step 1, the PV type distributed power supply model includes the micro gas turbine model; the PV type distributed power supply model is solved to obtain the reactive power, and the reactive power is corrected; when the corrected reactive power exceeds the rated range, the PV type distributed power supply model is simulated into the second injected current model, satisfying the following relationship:

[0109]

[0110] In the formula, V is the voltage amplitude of the PV type distributed power supply,

[0111] Z ii is the self-impedance of the PV type distributed power supply, where i represents the node number of the PV type distributed power supply connected to the distribution network,

[0112] is the change of the voltage amplitude of the node corresponding to the PV type distributed power supply,

[0113] is the phasor of the compensation current injected by the PV type distributed power supply.

[0114] When the distributed power supply is analyzed, the active power emitted is a fixed value, and the change of the reactive power depends on the change of the terminal voltage, that is, a kind of constant, and the Q is a node limited by P and V, which is called a PQV type node. Therefore, each iteration, the voltage is corrected and the PQV node is processed, and the system absorbed reactive power is calculated.

[0115] In step 1, in the first iteration, the PQV distributed power supply model is simulated into the first injection current model according to the PQ type distributed power supply model; in the second iteration, the voltage of the PQV distributed power supply is corrected, the reactive power is corrected with the corrected voltage, and the first injection current model obtained in the previous iteration is corrected with the corrected voltage and the corrected reactive power; the iteration is repeated until convergence is obtained, and the first injection current model of the PQV distributed power supply model is obtained.

[0116] In step 2, the distribution network is processed into a few-loop distribution network including PV nodes, PI nodes, PQ nodes and PQV nodes, and the injection reactive power correction amount of the PV node at the end of the distribution network is calculated based on the injection current model.

[0117] Step 2 includes:

[0118] Step 2.1, the PQ type distributed power supply model, the PI type distributed power supply model and the PQV type distributed power supply model are all processed into PQ nodes, and the PV type distributed power supply model is processed into a PV node; the distribution network adopts a few-loop network structure,

[0119] Step 2.2, for all PV nodes at the end of the distribution network, the network equivalent impedance matrix of the PV node is set as Z (n×n) =R+jX, the injection current correction amount of the PV node is ΔI (n×1) =ΔC+jΔD, the voltage increment of the PV node is ΔU (n×1) =ΔE+jΔF, and the following relationship is satisfied:

[0120] ΔU (n×1) =Z (n×n) ΔI (n×1)

[0121] Wherein,

[0122] R is the real part of the network equivalent impedance matrix Z (n×n) of the PV node, and X is the imaginary part of the network equivalent impedance matrix Z (n×n) of the PV node,

[0123] ΔC is the real part of the injection current correction amount ΔI (n×1) of the PV node, and ΔD is the imaginary part of the injection current correction amount ΔI (n×1) of the PV node,

[0124] ΔE is the real part of the voltage increment ΔU (n×1) of the PV node, and ΔF is the imaginary part of the voltage increment ΔU (n×1) of the PV node.

[0125] In the preferred embodiment, U pvi , I pvi and Spvi respectively, the voltage, the injected current and the injected power at the i-th PV node, satisfy the following relations:

[0126]

[0127] wherein,

[0128] U pv is the voltage matrix,

[0129] I pv is the injected current matrix,

[0130] is the injected power matrix;

[0131] Step 2.3, when the power distribution network is in normal operation, the amplitude of the voltage at each node is small, and the amplitude of the voltage at the PV node is constant in the iteration process, then the correction amount of the injected power of the PV node satisfies the following relation:

[0132]

[0133] wherein, U pv is the voltage at the PV node obtained in the iteration process;

[0134] Step 2.4, when the active power injected by the PV node is constant, the correction amount of the reactive power injected by the PV node ΔQ satisfies the following relation:

[0135] ΔQ = X -1 Re{U pv -U sch}·Re{U pv}

[0136] wherein,

[0137] Re{U pv} is the real part of the difference between the voltage U pv at the PV node obtained in the iteration process and the given amplitude of the voltage U pv at the PV node.

[0138] Re{U sch -U pv} is the real part of the difference between the voltage U sch at the PV node obtained in the iteration process and the given amplitude of the voltage U pv at the PV node.

[0139] Preferably, in step 2.2, the network equivalent impedance matrix of the PV node is calculated by using Thevenin equivalent circuit, which satisfies the following relation:

[0140] U (n×n) = Z pv I = (R + jX)Ipv

[0141] The reactive power of the PV node is calculated by using the network equivalent impedance matrix of the PV node and the voltage of the PV node.

[0142] Step 3, based on the loop-breaking point of the distribution network, the injection current of each node in the distribution network is calculated by using the injection current model, and then the branch current is corrected to obtain the current compensation value of the loop-breaking port; based on the forward-backward sweep power flow calculation method, the injection current of each node and the injection reactive power correction amount of the PV node are used to iteratively update the branch reactive power, the branch active power and the node voltage.

[0143] Step 3 includes:

[0144] Step 3.1, obtaining the loop-breaking point of the distribution network; based on the loop-breaking point, forming the entry impedance matrix, the admittance matrix and the loop-breaking port matrix corresponding to the PV node;

[0145] Step 3.2, the distribution network after loop-breaking adopts a radial network structure; the distribution network after loop-breaking is initialized to make the superimposed voltage ΔV corresponding to the PV node and the open-circuit voltage V of the loop-breaking port both 0, at this time, the node voltage in the distribution network is the root node voltage;

[0146] Step 3.3, respectively solving the injection current of the PV node, the PI node, the PQ node and the PQV node in the distribution network;

[0147] Step 3.4, correcting the branch current by using the injection current of each node, and calculating the current compensation value of the loop-breaking port;

[0148] Step 3.5, based on the forward-backward sweep power flow calculation method, the injection current of each node and the injection reactive power correction amount of the PV node are used to iteratively update the branch reactive power, the branch active power and the node voltage according to the following relationship:

[0149]

[0150]

[0151]

[0152] In the formula,

[0153] P k and Q k are the active power and the reactive power injected by the node in the kth iteration,

[0154] P k and Q kP and Q are the active power and reactive power injected by the load in the kth iteration, respectively,

[0155] P k-1 and X k-1 are the real and imaginary parts of the branch equivalent impedance in the k-1th iteration, respectively,

[0156] U k-1 is the node voltage in the k-1th iteration,

[0157] U k is the node voltage in the kth iteration,

[0158] P and Q are the active power and reactive power injected by the load in the kth iteration, respectively, Lk and Q Lk are the active power and reactive power injected by the distributed generator in the kth iteration, respectively.

[0159] P and Q are the active power and reactive power injected by the load in the kth iteration, respectively, DGk and Q DGk are the active power and reactive power injected by the distributed generator in the kth iteration, respectively.

[0160] Step 3.3 comprises:

[0161] Step 3.3.1, solving the injected current of the PV node in the distribution network according to the method of simulating the PV type distributed generator model as the injected current model in step 1;

[0162] Step 3.3.2, solving the injected current of the PQ node in the distribution network according to the method of simulating the PQ type distributed generator model as the injected current model in step 1;

[0163] Step 3.3.3, converting the PQV node into a PQ node according to the following relationship:

[0164]

[0165] In the formula,

[0166] ΔQ ir is the change of the reactive power flowing from the node i to the node r,

[0167] P and Q are the active power and reactive power injected by the load in the kth iteration, respectively, rr and Q rr are the active power and reactive power injected by the load in the kth iteration, respectively,

[0168] P and Q are the active power and reactive power injected by the load in the kth iteration, respectively, rm and Q rm are the active power and reactive power injected by the load in the kth iteration, respectively,

[0169] U r is the node voltage,

[0170] m is the node number set Cr any of the node numbers in the set C r comprises all node numbers except node r,

[0171] X ir is an equivalent reactance value between node i and node r;

[0172] Step 3.3.4, first, according to the method of Step 1, the PI type distributed power supply model simulation for injection current model, the PI node in the distribution network is converted into a PQ node; then, according to the method of Step 1, the PQ type distributed power supply model simulation for injection current model, the injection current of the PQ node in the distribution network is solved.

[0173] Step 3.3.4, first, according to the method of Step 1, the PI type distributed power supply model simulation for injection current model, the PI node in the distribution network is converted into a PQ node; then, according to the method of Step 1, the PQ type distributed power supply model simulation for injection current model, the injection current of the PQ node in the distribution network is solved.

[0174] Step 4, respectively, the convergence of the voltage of the PV node and the voltage of the PQ node in the distribution network is determined; when it is determined that the voltage of the PV node and the voltage of the PQ node in the distribution network are converged, the obtained reactive power of each branch, active power of each branch and node voltage are taken as the power system energy efficiency analysis power flow calculation results of the distributed power supply connected to the distribution network.

[0175] Step 4 includes:

[0176] Step 4.1, whether all the PV node voltages in the distribution network satisfy the convergence accuracy is judged by the following relationship, if yes, go to Step 4.2, otherwise go to Step 4.3:

[0177]

[0178] In the formula,

[0179] is the voltage of the i-th PV node calculated in the k-th iteration,

[0180] U schi is the given amplitude of the voltage of the i-th PV node,

[0181] ε pv is the convergence accuracy of the PV node voltage;

[0182] Step 4.2, whether all the PQ node voltages in the distribution network satisfy the convergence accuracy is judged by the following relationship, if yes, go to Step 4.5, otherwise go to Step 4.3:

[0183]

[0184] In the formula,

[0185] represents the real part of the voltage variation of the i-th PQ node calculated by the k-th iteration and the voltage of the i-th PQ node calculated by the k-1-th iteration,

[0186] represents the imaginary part of the voltage variation of the i-th PQ node calculated by the k-th iteration and the voltage of the i-th PQ node calculated by the k-1-th iteration,

[0187] ε pq is the convergence accuracy of the PQ node voltage;

[0188] Step 4.3, the reactive power injection of the PV node is corrected by the PV node voltage;

[0189] Step 4.4, the node voltage calculated by the k-th iteration is used to replace the node voltage calculated by the k-1-th iteration, and returns to step 4.2;

[0190] Step 4.5, the power system energy efficiency analysis power flow calculation result of the distributed power supply accessing the distribution network is obtained by judging that the PV node voltage and the PQ node voltage in the distribution network are converged, and the obtained branch reactive power, branch active power and node voltage.

[0191] The applicant of the present application has made a detailed description and explanation of the embodiment of the present application in combination with the drawings of the specification, but the skilled in the art should understand that the above embodiment is only the preferred embodiment of the present application, and the detailed description is only to help the reader better understand the spirit of the present application, and is not a limitation on the protection scope of the present application, on the contrary, any improvement or modification based on the spirit of the present application should fall within the protection scope of the present application.

Claims

1. A power system energy efficiency analysis power flow calculation method for distributed power access to a power distribution network, characterized in that, The power system energy efficiency analysis power flow calculation method comprises the following steps: Step 1, collecting parameters of the distributed power supply connected to the distribution network and establishing various distributed power supply models, wherein the distributed power supply models comprise a PQ-type distributed power supply model, a PI-type distributed power supply model, a PV-type distributed power supply model and a PQV-type distributed power supply model; and the various distributed power supply models are simulated as injection current models; The PV-type distributed power supply model comprises a micro gas turbine model; the PV-type distributed power supply model is solved to obtain a reactive power, and the reactive power is corrected; when the corrected reactive power exceeds a rated range, the PV-type distributed power supply model is simulated as a second injection current model, and the following relationship is satisfied: In the formula, is the self-impedance of the PV-type distributed power supply, wherein represents the node number of the PV-type distributed power supply connected to the distribution network, is the change amount of the voltage amplitude of the node corresponding to the PV-type distributed power supply, is the phasor of the compensation current injected by the PV-type distributed power supply. In the first iteration, the PQV-type distributed power supply model is simulated as a first injection current model according to the PQ-type distributed power supply model; in the second iteration, the voltage of the PQV-type distributed power supply is corrected, the first injection current model obtained in the previous iteration is corrected with the corrected voltage and the corrected reactive power, and the iteration is repeated until convergence is achieved to obtain the first injection current model of the PQV-type distributed power supply model; Step 2, processing the distribution network into a few-loop distribution network comprising PV nodes, PI nodes, PQ nodes and PQV nodes, and calculating an injection reactive power correction amount of the PV node at the end of the distribution network based on the injection current model; Step 3, converting the distribution network into a radial network based on a loop-breaking point of the distribution network, correcting branch currents after calculating injection currents of the nodes in the distribution network to obtain current compensation values of the loop-breaking ports, and iteratively updating branch reactive powers, branch active powers and node voltages based on the forward-backward sweep power flow calculation method and the calculated injection currents of the nodes and the injection reactive power correction amount of the PV node; Step 4, respectively judging convergence of the PV node voltage and the PQ node voltage in the distribution network; when it is judged that the PV node voltage and the PQ node voltage in the distribution network both converge, taking the obtained branch reactive powers, branch active powers and node voltages as power system energy efficiency analysis power flow calculation results of the distributed power supply connected to the distribution network.

2. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 1, wherein in step 1, the PQ-type distributed power supply model comprises a doubly-fed wind power generator model; and the PQ-type distributed power supply model is simulated as a first injection current model, and the following relationship is satisfied: wherein, 3. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 2, wherein in step 1, the PI-type distributed power supply model comprises a photovoltaic cell model; the PI-type distributed power supply model is solved to obtain a reactive power, and then the PI-type distributed power supply model is simulated as a first injection current model. To inject current, for the apparent power of the distributed power source, is a real part of the distributed power supply voltage, is an imaginary part of the distributed power supply voltage.

4. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to any one of claims 1 to 3, wherein step 2 comprises: ​ ​ ​ Step 2.1, the PQ type distributed power supply model, the PI type distributed power supply model and the PQV type distributed power supply model are all treated as PQ nodes, and the PV type distributed power supply model is treated as a PV node; the distribution network adopts a few ring network structure, Step 2.2, for all PV nodes at the end of the distribution network, let the network equivalent impedance matrix of the PV node be , the injection current correction of the PV node be , the voltage increment of the PV node be , and the following relationship be satisfied: wherein, the real part of the network equivalent impedance matrix of the PV node, the imaginary part of the network equivalent impedance matrix of the PV node, the imaginary part of the network equivalent impedance matrix of the PV node,​ the real part of the injection current correction quantity for the PV node the real part of the injection current correction quantity for the PV node the real part of the injection current correction quantity for the PV node the imaginary part of the injection current correction quantity for the PV node the real part of the voltage increment for the PV node is the imaginary part of the voltage increment for the PV node is the imaginary part of the voltage increment for the PV node is​ Step 2.3, when the power distribution network is in normal operation, the amplitude of the voltage of the PV node is constant in the iteration process, then the injection power correction amount of the PV node satisfies the following relationship: In the formula, is the PV node voltage obtained in the iteration process; Step 2.4, the injected active power of the PV node is constant, then the injected reactive power correction amount of the PV node satisfies the following relationship: In the formula, To obtain the PV node voltage Take the real part, The real part of the difference between the PV node voltage and the given PV node voltage magnitude is taken.

5. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 4, characterized in that, In step 2.2, the network equivalent impedance matrix of the PV node is calculated by using the Thevenin equivalent circuit, and the reactive power of the PV node is calculated by using the network equivalent impedance matrix of the PV node and the voltage of the PV node.

6. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 4, characterized in that, Step 3 includes: Step 3.1, obtaining the loop-breaking point of the distribution network; based on the loop-breaking point, forming the input end impedance matrix, the admittance matrix and the loop-breaking port matrix corresponding to the PV node; Step 3.2, the distribution network after loop breaking adopts a radial network structure; the distribution network after loop breaking is initialized to make the superimposed voltage ΔV of the PV node and the open circuit voltage V of the loop-breaking port both 0, at which time the voltages of all nodes in the distribution network are the root node voltage; Step 3.3, the injection currents of the PV node, the PI node, the PQ node and the PQV node in the distribution network are solved respectively; Step 3.4, the branch current is corrected by using the injection currents of all nodes, and the current compensation value of the loop-breaking port is calculated; Step 3.5, based on the forward-backward substitution power flow calculation method, the reactive power of each branch, the active power of each branch and the voltage of each node are iteratively updated by using the injection currents of all nodes and the injection reactive power correction amount of the PV node according to the following relationship: In the formula, and are the first active power and reactive power injected by the node in the first iteration, respectively, and are the first active power and reactive power injected by the node in the first iteration, respectively, and are the real and imaginary parts of the branch impedance in the th iteration, respectively, for the first time in the iteration of the node voltage, for the first iteration, the node voltage, and are the first active power and reactive power injected in the load in the n-th iteration, respectively, and are the reactive power and active power of the distributed power injection in the n-th iteration, respectively. th iteration.

7. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 6, characterized in that, Step 3.3 includes: Step 3.3.1, the injection current of the PV node in the distribution network is solved according to the method of simulating the PV type distributed power supply model as the injection compensation current model in step 1; Step 3.3.2, the injection current of the PQ node in the distribution network is solved according to the method of simulating the PQ type distributed power supply model as the injection current model in step 1; Step 3.3.3, the PQV node is converted into a PQ node according to the following relationship: In the formula, for the node flow to the node of reactive power, and are the active power injection and the reactive power injection of the node respectively, and are the nodes active power and reactive power flowing to the nodes , respectively, for the node voltage, for any node number in the set of node numbers the set of node numbers contains all node numbers except the node ​ for the node with the node between the node and the node; and then the injection current of the PQ node in the distribution network is solved according to the method of simulating the PQ type distributed power supply model as the injection current model in step 1; Step 3.3.4, the PI node in the distribution network is converted into a PQ node according to the method of simulating the PI type distributed power supply model as the injection current model in step 1; and then the injection current of the PQ node in the distribution network is solved according to the method of simulating the PQ type distributed power supply model as the injection current model in step 1.

8. The power system energy efficiency analysis power flow calculation method for the distributed power supply connected to the distribution network according to claim 4, characterized in that, Step 4 includes: Step 4.1, judge whether the voltage of all PV nodes in the distribution network meets the convergence accuracy by the following relationship, if yes, go to step 4.2, otherwise go to step 4.3: In the formula, For the first The calculation obtained in the nth iteration The voltage of each PV node, The voltage of the first PV node is given a magnitude, the second PV node. Convergence accuracy for PV node voltage; Step 4.2, judge whether the voltage of all PQ nodes in the distribution network meets the convergence accuracy by the following relationship, if yes, go to step 4.5, otherwise go to step 4.3: In the formula, represents a real part of a voltage of the PQ node obtained by the first iteration calculation the change amount of the voltage of the PQ node obtained by the second iteration calculation​​​ represents a change amount of the voltage of the PQ node obtained by the first the imaginary part is calculated​​​ is the convergence accuracy for the PQ node voltage; Step 4.3, correct the reactive power injection of the PV node by the voltage of the PV node; Step 4.4, using the node voltages calculated in the previous iteration instead of the node voltages calculated in the first iteration, and returning to Step 4.

2. Step 4.4, using the node voltages calculated in the previous iteration instead of the node voltages calculated in the first iteration, and returning to Step 4.

2. Step 4.4, using the node voltages calculated in the previous iteration instead of the node voltages calculated in the first iteration, Step 4.5, judge whether the voltage of the PV node and the voltage of the PQ node in the distribution network are converged, and take the obtained reactive power of each branch, the active power of each branch and the voltage of each node as the power system energy efficiency analysis power flow calculation result of the distributed power supply connected to the distribution network.

Images