Method for calculating line loss of low-voltage transformer area containing distributed photovoltaic

Abstract

The embodiment of the invention discloses a line loss calculation method for a low-voltage transformer area containing distributed photovoltaic. The line loss calculation method comprises the following steps: acquiring typical daily data of the low-voltage transformer area, access phase data and output data of the distributed photovoltaic, electricity consumption and connected phases of users, line impedance of each phase and a network topology structure of the low-voltage transformer area; establishing a line loss theoretical calculation model according to the typical day data of the low-voltage transformer area, the access phase data and output data of the distributed photovoltaic, the electricity consumption and the connected phases of the user, the line impedance of each phase and the network topology structure of the low-voltage transformer area; based on the line loss theoretical calculation model, calculating a user node voltage value of each phase through an improved forward-backward sweep method, taking the voltage value as an initial value of a Newton-Rafson method, and performing load flow calculation on each phase to obtain power loss on each phase line; and adding the total neutral line loss and the loss power consumption of each phase line to obtain the typical daily three-phase bus loss of the transformer area, so that the accuracy and the processing speed of theoretical calculation of the line loss can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-voltage area line loss calculation, and in particular to a method for calculating line loss in a low-voltage area containing distributed photovoltaics. Background Art

[0002] In recent years, household distributed photovoltaics have shown strong growth in the newly added capacity of distributed photovoltaics. Household distributed photovoltaic power sources are composed of photovoltaic modules, inverters, combiner boxes and other components, and are generally installed on roofs or other sites. The inverter converts the direct current generated by the photovoltaic modules into alternating current and transmits it to the public grid or load.

[0003] The low-voltage substation is the end of the power system, generally with a radial structure and serious three-phase load imbalance. According to data, the total line loss of the distribution network accounts for more than 40% of the total network loss. Therefore, accurate calculation of line loss and refined management of line loss have become the primary task of energy saving and consumption reduction in low-voltage substations.

[0004] At present, the commonly used methods for calculating line loss in substations include the equivalent resistance method, equivalent capacity method, forward-backward method, substation loss rate method, improved PQ decoupling method, Newton-Raphson method, etc. Due to the shortcomings of their own algorithms, the improved PQ decoupling method and the Newton-Raphson method have large errors when directly applied to distribution network flow calculations. Moreover, the Newton-Raphson method is prone to situations where the flow iteration does not converge or converges after multiple iterations due to inappropriate initial value selection. The loop impedance method is mainly used in ring network structures, but the numbering of its branches and nodes is relatively complicated and the amount of calculation is large. The forward-backward method is the mainstream algorithm for processing distribution network radiation structures. It has the characteristics of fast calculation speed and good convergence, but it needs to number the network nodes and branches before calculation, which is relatively complicated and prone to errors. For some improved methods, the convergence of the algorithm is significantly reduced for complex multi-node type networks.

[0005] It can be seen that there is an urgent need for a theoretical calculation method for line loss in substations with higher accuracy and faster processing speed. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for calculating line loss in a low-voltage area containing distributed photovoltaics, so as to improve the accuracy and processing speed of theoretical calculation of line loss.

[0007] To achieve the above objectives, the present application provides a method for calculating line loss in a low-voltage area containing distributed photovoltaics, the method comprising:

[0008] Obtain typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area;

[0009] A line loss theoretical calculation model is established based on typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area;

[0010] Based on the line loss theoretical calculation model, the voltage value of each phase user node is calculated by an improved forward-backward method, the voltage value is used as the initial value of the Newton-Raphson method, and the power flow calculation is performed on each phase to obtain the power loss on each phase line;

[0011] The total neutral line loss is added to the power loss on each phase line to obtain the typical daily three-phase bus loss in the platform area.

[0012] Optionally, in the improved forward-backward substitution method, the node numbering method includes:

[0013] Classify the nodes, and after traversing the nodes, form a data table, wherein the data table records the type, voltage and load of the nodes, and the branch impedance and current between two nodes;

[0014] A first matrix and a second matrix are generated according to the data table, wherein the first matrix is ​​an a×b matrix, a is the number of leaf nodes, b is the number of nodes passed by the shortest path from the leaf node to the root node, and the first matrix is ​​a sequence of nodes passed by the shortest path from each leaf node to the root node; and the second matrix is ​​a c×d matrix, c is the total number of nodes in the distribution network, d is the number of child nodes of the parent node with the most child nodes in the distribution network, and the second matrix is ​​a sequence of child nodes of each node.

[0015] Optionally, the step of calculating the voltage value of each phase user node by using an improved forward-backward substitution method includes:

[0016] Using the first matrix and the second matrix, in combination with the forward-backward substitution method, a c×d-order matrix is ​​generated during the calculation;

[0017] After computing the i-th node, the i-th row and the d-th column are automatically set to 1, and the node whose value in the d-th column is 1 does not need to be recalculated.

[0018] Optionally, before calculating the voltage value of each phase user node by the improved forward back substitution method, the method further includes:

[0019] Step 1: Assuming that the initial reactive power value of the PV node is 0, convert it into the PQ node;

[0020] Step 2: Obtain the calculated voltage of the parent node of the PV node through power flow calculation;

[0021] Step 3: Calculate the reactive power correction amount of the power supply connected to the PV node based on the calculated voltage of the parent node of the PV node, the impedance of the branch connecting the PV node and its parent node, the constant voltage and active power of the PV node;

[0022] Step 4: Substitute the forward-backward method for calculation. If the calculation converges, the reactive power of the PV node is obtained; if not, step 2 is repeated according to the reactive power correction amount until convergence.

[0023] Optionally, the step 3 uses the following formula:

[0024]

[0025] Where, λ is the step size, P2 and Q2 are the active power and calculated reactive power of the PV node respectively; Q d is the reactive power of all nodes and branches connected to the PV node; U r1 , U r2 are the total components of the node voltages of the PV node and its parent node respectively; U2 is the input voltage of the PV node; R and x are the impedances of the branch connecting the PV node and its parent node.

[0026] Optionally, using the voltage value as an initial value of the Newton-Raphson method to perform power flow calculation on each phase includes:

[0027] The Jacobian matrix J in the Newton-Raphson method iteration is corrected using the gradient descent method to be E is a unit matrix of the same order as J, and the power flow equation of the Newton-Raphson method is expressed as:

[0028]

[0029] Among them, x k , Δx k are the column vectors of the state variables and their corrections at the kth iteration; F(x k ) is the column vector composed of functions at the kth iteration; J k is the Jacobian matrix of iteration k; is the iteration operator;

[0030] The iteration operator Set to 1, and its subsequent iteration value is calculated according to the following formula:

[0031]

[0032] When the iteration operator When it is close to 1, the iteration method is gradient descent;

[0033] When the iteration operator When it is close to 0, the iteration method reverts to the Newton-Raphson method.

[0034] Optionally, the method further comprises calculating the total neutral line loss by the following steps:

[0035] The three-phase current (I A ,I B ,I C ) to obtain the line current in the neutral line:

[0036]

[0037] The amplitude I0 of the current of the neutral line is taken, and the neutral line loss of each section is calculated and summed to obtain the total neutral line loss.

[0038] Another aspect of the present application provides a low voltage area line loss calculation device, comprising:

[0039] An acquisition module is used to acquire typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area;

[0040] Establishing a module for establishing a line loss theoretical calculation model based on typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area;

[0041] A calculation module is used to calculate the voltage value of each phase user node through an improved forward-backward method based on the line loss theoretical calculation model, use the voltage value as the initial value of the Newton-Raphson method, perform power flow calculation on each phase, and obtain the power loss on each phase line;

[0042] The calculation module is also used to add the total neutral line loss and the power loss on each phase line to obtain the typical daily three-phase bus loss of the platform area.

[0043] On the other hand, the present application provides an electronic device, including a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the first aspect and any possible implementation method thereof.

[0044] On the other hand, the present application provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes each step of the method described in the first aspect.

[0045] The present application provides a method for calculating line loss in a low-voltage substation containing distributed photovoltaics, by acquiring typical daily data of the low-voltage substation, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage substation; a line loss theoretical calculation model is established according to the typical daily data of the low-voltage substation, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage substation; based on the line loss theoretical calculation model, the voltage value of each phase user node is calculated by an improved forward-backward method, the voltage value is used as the initial value of the Newton-Raphson method, and the power flow calculation is performed on each phase to obtain the power loss on each phase line; the total neutral line loss is added to the power loss on each phase line to obtain the total three-phase bus loss of the substation on a typical day, which can improve the accuracy and processing speed of the line loss theoretical calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] in:

[0048] Figure 1 A schematic flow chart of a method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation provided in an embodiment of the present application;

[0049] Figure 2 A schematic diagram of iterative calculation of reactive power of a PV node provided in an embodiment of the present application;

[0050] Figure 3 A schematic diagram of a line loss theoretical calculation process provided in an embodiment of the present application;

[0051] Figure 4 A schematic diagram of the structure of a low-voltage area line loss calculation device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0052] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0053] The terms "first", "second", etc. in the specification and claims of this application and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0054] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0056] See also Figure 1 , is a flow chart of a method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation provided in an embodiment of the present application. Figure 1 As shown, the method includes:

[0057] 101. Obtain typical daily data of low-voltage areas, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the above low-voltage areas;

[0058] 102. Establish a line loss theoretical calculation model based on the typical daily data of the above low-voltage area, the access phase data and output data of distributed photovoltaics, the power consumption of users and the phases connected, the impedance of each phase line and the network topology of the above low-voltage area;

[0059] 103. Based on the above line loss theoretical calculation model, the voltage value of each phase user node is calculated by the improved forward-backward method, and the above voltage value is used as the initial value of the Newton-Raphson method to calculate the power flow of each phase to obtain the power loss on each phase line;

[0060] 104. Add the total neutral line loss and the power loss on each phase line mentioned above to obtain the typical daily three-phase bus loss in the platform area.

[0061] The method in the embodiment of the present application can be executed by a low-voltage substation line loss calculation device, which can specifically be a terminal device, and mainly performs model establishment and line loss calculation based on the acquired data.

[0062] The topology of the power system mentioned in the embodiments of the present application refers to the connection mode of nodes and branches in the power grid. In the distribution network, it is usually a radial network, that is, radiating outward from one or more power supply points. PV nodes are usually located at the end of the power grid, and they are connected to the upper node through branches.

[0063] In the embodiment of the present application, the voltage value of each phase user node is calculated mainly by an improved forward back substitution method, the voltage value is used as the initial value of the Newton-Raphson method, the power flow calculation is performed on each phase, and the power loss on each phase line is obtained.

[0064] The forward-backward method mentioned in the embodiment of the present application is a method for calculating the power flow of a distribution network, which is particularly suitable for radial distribution networks. The core idea of ​​this method is to divide the nodes of the distribution network into forward-backward nodes and backward-backward nodes, perform power flow calculations on each node, and finally obtain the voltage, current and power distribution of the entire distribution network. The following are the basic principles and steps of the forward-backward method:

[0065] Basic principle:

[0066] The starting voltage and terminal load of the distribution network are known, and the feeder is used as the basic calculation unit.

[0067] Initially, it is assumed that the voltage of the entire network is the rated voltage. The load power is calculated from the end to the beginning step by step. Only the power loss in each component is calculated without calculating the node voltage. The current and power loss on each branch are obtained, and the starting power is obtained based on this. This is the back substitution process.

[0068] Then, based on the given starting voltage and the calculated starting power, the voltage drop is calculated step by step from the starting end to the end to obtain the voltage of each node. This is the forward process.

[0069] The above process is repeated until the power deviation of each node meets the allowable conditions.

[0070] The following is an improvement on the forward-backward substitution method.

[0071] 1. Improvement of the node numbering method in the forward-backward substitution method

[0072] In an optional implementation, in the above improved push-forward back-substitution method, the node numbering method includes:

[0073] Classify the nodes, and after traversing the nodes, form a data table, which records the type, voltage and load of the node, as well as the branch impedance and current between two nodes;

[0074] The first matrix and the second matrix are generated according to the above data table, wherein the above first matrix is ​​an a×b order matrix, the above a is the number of leaf nodes, the above b is the number of nodes passed by the shortest path from the leaf node to the root node, and the above first matrix is ​​the node sequence passed by the shortest path from each leaf node to the root node; the above second matrix is ​​a c×d order matrix, the above c is the total number of nodes in the distribution network, the above d is the number of child nodes of the parent node with the most child nodes in the distribution network, and the above second matrix is ​​the child node sequence of each node.

[0075] Further optionally, the above-mentioned calculation of the voltage value of each phase user node by the improved forward back substitution method includes:

[0076] The first matrix and the second matrix are used to perform power flow calculation in conjunction with the forward-backward substitution method. During the calculation, a c×d-order matrix is ​​generated.

[0077] After computing the i-th node, the i-th row and the d-th column are automatically set to 1, and the nodes whose d-th column value is 1 do not need to be recalculated.

[0078] Specifically, the improvements to the node numbering method in the forward push-back method are as follows:

[0079] First, the nodes are classified into parent nodes (the root node is also a parent node), child nodes, sibling nodes, and leaf nodes. After traversing the nodes, a data table is formed, which can record the node type, voltage and load, and branch impedance and current between two nodes.

[0080] Secondly, the first matrix and the second matrix are generated according to the data table, which are referred to as A matrix and B matrix respectively. Among them, A is an a×b matrix. a is the number of leaf nodes (i.e. the end nodes), and b is the number of nodes passed by the shortest path from the leaf node to the root node. The A matrix is ​​the node sequence passed by the shortest path from each leaf node to the root node. B is a c×d matrix. c is the total number of nodes in the distribution network, and d is the number of child nodes of the parent node with the most child nodes in the distribution network. The B matrix is ​​the child node sequence of each node.

[0081] Finally, the A and B matrices are used in conjunction with the traditional forward-backward method to perform power flow calculations. In the calculation, a c×d-order matrix is ​​generated. After the calculation of the i node is completed, the B i,d Set to 1. Nodes whose value in column d is 1 do not need to be recalculated.

[0082] In summary, by automatically numbering the nodes, invalid calculations are avoided and the calculation efficiency is significantly improved.

[0083] 2. Improvement of PV node processing method in forward-backward substitution method

[0084] In the power system, nodes are usually divided into PQ nodes, PV nodes and balancing nodes (Slack or Reference nodes). The active power (P) and reactive power (Q) of the PQ nodes are known, while the active power (P) and voltage amplitude (V) of the PV nodes are known, and the reactive power (Q) needs to be calculated. The balancing node is usually used to set the reference voltage and phase angle of the power grid.

[0085] PV nodes have fixed active power and voltage amplitude, while reactive power needs to be calculated through iteration. During the iteration process, the voltage amplitude of the PV node remains unchanged, while the reactive power is adjusted according to the operating status of the power grid.

[0086] The iterative calculation of reactive power of PV nodes is an important part of power system flow calculation, especially in distribution networks with distributed generation. PV nodes have fixed active power and voltage amplitude, and reactive power needs to be calculated iteratively.

[0087] In each iteration, the reactive power correction of the PV node is calculated and the reactive power of the PV node is updated accordingly. This process involves the calculation of the injected current of the PV node and the reactive power adjustment based on the grid operation status.

[0088] In an optional implementation, before the above step 103, the above method further includes:

[0089] Step 1: Assume that the initial reactive power value of the above PV node is 0 and convert it into the above PQ node;

[0090] Step 2: Obtain the calculated voltage of the parent node of the above PV node through power flow calculation;

[0091] Step 3: Calculate the reactive power correction amount of the power supply connected to the PV node based on the calculated voltage of the parent node of the PV node, the impedance of the branch connecting the PV node and its parent node, the constant voltage and active power of the PV node;

[0092] Step 4: Substitute the forward-backward method into the above calculation. If the calculation converges, the reactive power of the above PV node is obtained. If it does not converge, repeat the above step 2 according to the above reactive power correction amount until convergence.

[0093] Specifically, the active power P of the current-controlled distributed photovoltaic power source is constant with the injected current I, and the reactive power Q can be obtained by the formula, which is the PI node in the power flow calculation, and can also be converted into a PQ node during the power flow calculation iteration. Therefore, it will not be discussed in the embodiments of this application.

[0094] The active power P and node voltage U of the voltage-controlled distributed photovoltaic power source are constant values, which are PV nodes in the power flow calculation. Since the forward-backward method cannot process PV nodes, the PV type photovoltaic node is specially processed in the embodiment of the present application to calculate the reactive power output thereof, thereby converting the PV node into a PQ node.

[0095] ① Assume that the initial reactive power value of the PV node is 0 and convert it into a PQ node;

[0096] ② The calculated voltage of the parent node of the PV node can be obtained through power flow calculation;

[0097] ③ Figure 2 A schematic diagram of iterative calculation of reactive power of a PV node provided in an embodiment of the present application. Figure 2 , the reactive power correction amount of the PV node connected to the power supply can be calculated based on the calculated voltage of the PV node's parent node, the impedance of the branch connecting the PV node and its parent node, the constant voltage and active power of the PV node.

[0098] Optionally, the above step 3 can use the following formula:

[0099]

[0100] Among them, λ is the step size, P2 and Q2 are the active power and calculated reactive power of the above PV nodes respectively; Q d is the reactive power of all nodes and branches connected to the above PV node; U r1 , U r2 are the total components of the node voltages of the above PV node and its parent node respectively; U2 is the input voltage of the above PV node; R, x are the impedances of the branch connecting the above PV node and its parent node;

[0101] ④ Substitute the forward-backward method for calculation. If the calculation converges, the reactive power of the PV node can be obtained. If it does not converge, according to the reactive correction amount obtained in the above formula, go to step 2 for iterative calculation until convergence.

[0102] The Newton-Raphson method, also known as the Newton-Raphson method, is a numerical method for solving nonlinear equations. The core idea of ​​this method is to approximate the root of the equation through iteration.

[0103] The following is an improvement on the Newton-Raphson method.

[0104] The Newton-Raphson method is prone to the situation where the power flow iteration does not converge or converges only after multiple iterations due to inappropriate initial value selection. In the embodiment of the present application, an improved forward-backward method is used to first calculate the voltage of each node in the platform area, and then the voltage of each node is substituted as the initial value into the Newton-Raphson method for iterative calculation.

[0105] The Jacobian matrix is ​​the key to power flow calculation. Therefore, the correction of the Jacobian matrix is ​​the key to solving the convergence problem of the Newton-Raphson method. Under the condition that the initial value is greatly different from the true value, the Newton-Raphson method is difficult to iterate and converge in the process of linearizing the nonlinear equation one by one. In the embodiment of the present application, in order to avoid the occurrence of this problem, the Jacobian matrix in the Newton-Raphson method iteration is corrected by using the gradient descent method.

[0106] Specifically, in the above step 103, the above voltage value is used as the initial value of the Newton-Raphson method to perform power flow calculation on each phase, including:

[0107] Using the gradient descent method, the Jacobian matrix J in the Newton-Raphson method iteration is corrected to E is a unit matrix of the same order as J, then the Newton-Raphson method power flow equation can be expressed as:

[0108]

[0109] Where: x k , Δx k are the column vectors of the state variables and their corrections at the kth iteration; F(x k ) is the column vector composed of functions at the kth iteration; J k is the Jacobian matrix of iteration k; is the iteration operator.

[0110] The iteration operator Set to 1, and its subsequent iteration value can be calculated by the following formula:

[0111]

[0112] When the iteration operator When it is close to 1, the iteration method is gradient descent; when the iteration operator When it is close to 0, the iteration method reverts to the Newton-Raphson method.

[0113] The gradient descent method converges faster during iteration, but when iterating to the vicinity of the optimal solution, the gradient tends to zero and the convergence speed slows down, while the Newton-Raphson method converges faster near the optimal solution. Therefore, the above steps combine the advantages of the gradient descent method and the Newton-Raphson method, which can effectively avoid the pathological condition of the Jacobian matrix J and significantly improve the convergence speed.

[0114] Typical calculation process:

[0115] Specifically, in the embodiment of the present application, based on the typical daily data of the low-voltage area (current data collected daily), the access phase data and output data of distributed photovoltaics, the user's power consumption and the connected phase, the impedance of each phase line and the area topology structure and other information, a line loss theoretical calculation model is established with a period of 0.5h to calculate the three-phase current imbalance δ%. The calculation formula can be:

[0116]

[0117] Among them, I max is the maximum phase load current; I p is the average value of the three-phase load current.

[0118] The voltage value of each phase user node is calculated by the improved forward-backward method, and the voltage value is used as the initial value of the Newton-Raphson method to calculate the power flow of each phase and obtain the power loss on each phase line.

[0119] The line current of the neutral line is the three-phase current (I A ,I B ,I C ), the current in the neutral line can be calculated by the following formula:

[0120]

[0121] The neutral line parameters are the same as other three-phase lines, so the neutral line resistance R0 is equal to the resistance value of each phase line, and the amplitude of the neutral line current I0 is taken. By calculating the neutral line loss of each section, the sum of the losses is the total neutral line loss. Finally, the total neutral line loss is added to the loss of each phase line to obtain the typical daily three-phase bus loss in the Taiwan area.

[0122] Figure 3 A schematic diagram of a line loss theoretical calculation process provided in an embodiment of the present application. Figure 3 As shown, the method for calculating line loss in a low-voltage area containing distributed photovoltaics in the embodiment of the present application mainly includes the following main steps:

[0123] ① Collect relevant data of the substation area and determine the load power of 48 sections of each phase and each user in one day;

[0124] ② Establish a calculation model for distributed photovoltaic power sources and determine the photovoltaic output power;

[0125] ③ Calculate the voltage of each node in the substation area by using the improved forward-backward method and set it as the initial value of the Newton-Raphson method;

[0126] ④ Calculate the power distribution of each phase in the low-voltage area by using the improved Newton-Raphson method, and calculate the losses of the three-phase lines respectively;

[0127] ⑤Calculate the neutral line loss;

[0128] ⑥Calculate the bus loss in the substation area.

[0129] The specific steps involved can be found in Figure 1 The description in the illustrated embodiment will not be repeated here.

[0130] At present, the commonly used methods for calculating line loss in substations include the equivalent resistance method, equivalent capacity method, forward-backward method, substation loss rate method, improved PQ decoupling method, Newton-Raphson method, etc. Due to the shortcomings of their own algorithms, the improved PQ decoupling method and the Newton-Raphson method have large errors when directly applied to distribution network flow calculations. Moreover, the Newton-Raphson method is prone to situations where the flow iteration does not converge or converges after multiple iterations due to inappropriate initial value selection. The loop impedance method is mainly used in ring network structures, but the numbering of its branches and nodes is relatively complicated and the amount of calculation is large. The forward-backward method is the mainstream algorithm for processing distribution network radiation structures, with the characteristics of fast calculation speed and good convergence. However, it is necessary to number the network nodes and branches before calculation, which is relatively complicated and prone to errors.

[0131] With the popularization and use of power grid line loss management systems, PLC (power carrier) technology and smart meters, the conditions for using the power flow method to calculate the line loss of distributed photovoltaic areas have gradually been met. Based on the summary of the existing power flow method to calculate the line loss of the area. Optimization algorithms have been proposed, including improved iteration method, matching power flow method, loop analysis method, etc. However, these methods basically do not consider the impact of three-phase imbalance on line loss, and simplify some calculations. Although the calculation speed is improved, the convergence of the algorithm is significantly reduced for complex multi-node type networks.

[0132] In this application, the mathematical model of distributed photovoltaic power sources is used as the basis, and the three-phase imbalance is taken into consideration. The user load curve is first drawn through the measured current data of the substation, and then the power consumption of each user in each time period is determined. The improved forward back substitution method and the improved Newton-Raphson method are combined to calculate the line loss of each phase in the substation, which can improve the accuracy and processing speed of the theoretical calculation of line loss.

[0133] Based on the description of the aforementioned method embodiment, the embodiment of the present application also provides a low-voltage area line loss calculation device.

[0134] Figure 4 A schematic diagram of a low voltage area line loss calculation device provided in an embodiment of the present application is shown in FIG. Figure 4 As shown, the device 400 includes:

[0135] The acquisition module 410 is used to acquire typical daily data of the low-voltage area, the access phase data and output data of the distributed photovoltaic, the power consumption of the user and the phases connected, the impedance of each phase line and the network topology of the low-voltage area;

[0136] Establishing module 420, for establishing a line loss theoretical calculation model according to typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaic, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area;

[0137] A calculation module 430 is used to calculate the voltage value of each phase user node by an improved forward-backward method based on the line loss theoretical calculation model, use the voltage value as the initial value of the Newton-Raphson method, perform power flow calculation on each phase, and obtain the power loss on each phase line;

[0138] The calculation module 430 is further used to add the total neutral line loss and the power loss on each phase line to obtain the typical daily three-phase bus loss of the platform area.

[0139] It can be understood that the relevant contents of each module in the above device have been described in detail in the aforementioned method embodiment, and the specific contents can be referred to the method embodiment; that is, a low-voltage area line loss calculation device provided in this application can be executed as follows Figure 1 , Figure 2 or Figure 3 Any steps in the illustrated embodiment will not be described in detail here.

[0140] In one embodiment of the present application, an electronic device is also provided. The electronic device may include a processor and a memory, wherein the memory stores a computer program, and when the computer program is executed by the processor, the execution Figure 1 , Figure 2 or Figure 3 Any step in the method embodiment shown. The electronic device may also include an input / output device, etc. In a specific implementation, the electronic device may be a terminal device, etc.

[0141] In one embodiment, a computer-readable storage medium is further provided. The computer-readable storage medium stores a computer program. When the computer program is executed by a processor, the processor executes any step in the above method embodiment.

[0142] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the program can be stored in a non-volatile computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0143] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0144] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for calculating line loss in a low-voltage area containing distributed photovoltaics, characterized in that: The method comprises: Obtain typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area; A line loss theoretical calculation model is established based on typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area; Based on the line loss theoretical calculation model, the voltage value of each phase user node is calculated by an improved forward-backward method, the voltage value is used as the initial value of the Newton-Raphson method, and the power flow calculation is performed on each phase to obtain the power loss on each phase line; The total neutral line loss is added to the power loss on each phase line to obtain the typical daily three-phase bus loss in the platform area.

2. The method for calculating line loss in a low-voltage area containing distributed photovoltaics according to claim 1 is characterized in that: In the improved forward push-back method, the node numbering method includes: Classify the nodes, and after traversing the nodes, form a data table, wherein the data table records the type, voltage and load of the nodes, and the branch impedance and current between two nodes; A first matrix and a second matrix are generated according to the data table, wherein the first matrix is ​​an a×b matrix, a is the number of leaf nodes, b is the number of nodes passed by the shortest path from the leaf node to the root node, and the first matrix is ​​a sequence of nodes passed by the shortest path from each leaf node to the root node; and the second matrix is ​​a c×d matrix, c is the total number of nodes in the distribution network, d is the number of child nodes of the parent node with the most child nodes in the distribution network, and the second matrix is ​​a sequence of child nodes of each node.

3. The method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation according to claim 2 is characterized in that: The method of calculating the voltage value of each phase user node by using the improved forward-backward substitution method includes: Using the first matrix and the second matrix, in combination with the forward-backward substitution method, a c×d-order matrix is ​​generated during the calculation; After computing the i-th node, the i-th row and the d-th column are automatically set to 1, and the node whose value in the d-th column is 1 does not need to be recalculated.

4. The method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation according to claim 3 is characterized in that: Before calculating the voltage value of each phase user node by the improved forward back substitution method, the method further includes: Step 1: Assuming that the initial reactive power value of the PV node is 0, convert it into the PQ node; Step 2: Obtain the calculated voltage of the parent node of the PV node through power flow calculation; Step 3: Calculate the reactive power correction amount of the power supply connected to the PV node based on the calculated voltage of the parent node of the PV node, the impedance of the branch connecting the PV node and its parent node, the constant voltage and active power of the PV node; Step 4: Substitute the forward-backward method for calculation. If the calculation converges, the reactive power of the PV node is obtained; if not, step 2 is repeated according to the reactive power correction amount until convergence.

5. The method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation according to claim 4 is characterized in that: Step 3 uses the following formula: Where, λ is the step size, P2 and Q2 are the active power and calculated reactive power of the PV node respectively; Q d is the reactive power of all nodes and branches connected to the PV node; U r1 , U r2 are the total components of the node voltages of the PV node and its parent node respectively; U2 is the input voltage of the PV node; R and x are the impedances of the branch connecting the PV node and its parent node.

6. The method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation according to any one of claims 1 to 5, characterized in that: The voltage value is used as the initial value of the Newton-Raphson method to perform power flow calculation on each phase, including: The Jacobian matrix J in the Newton-Raphson method iteration is corrected using the gradient descent method to be E is a unit matrix of the same order as J, and the power flow equation of the Newton-Raphson method is expressed as: Among them, x k , Δx k are the column vectors of the state variables and their corrections at the kth iteration; F(x k ) is the column vector composed of functions at the kth iteration; J k is the Jacobian matrix of iteration k; is the iteration operator; The iteration operator Set to 1, and its subsequent iteration value is calculated according to the following formula: When the iteration operator When it is close to 1, the iteration method is gradient descent; When the iteration operator When it is close to 0, the iteration method reverts to the Newton-Raphson method.

7. The method for calculating line loss in a low-voltage area containing distributed photovoltaic power generation according to claim 6, characterized in that: The method further comprises calculating the total neutral line loss by the following steps: The three-phase current (I A ,I B ,I C ) to obtain the line current in the neutral line: The amplitude I0 of the current of the neutral line is taken, and the neutral line loss of each section is calculated and summed to obtain the total neutral line loss.

8. A low voltage area line loss calculation device, characterized in that: include: An acquisition module is used to acquire typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area; Establishing a module for establishing a line loss theoretical calculation model based on typical daily data of the low-voltage area, access phase data and output data of distributed photovoltaics, power consumption of users and connected phases, impedance of each phase line and network topology of the low-voltage area; A calculation module is used to calculate the voltage value of each phase user node through an improved forward-backward method based on the line loss theoretical calculation model, use the voltage value as the initial value of the Newton-Raphson method, perform power flow calculation on each phase, and obtain the power loss on each phase line; The calculation module is also used to add the total neutral line loss and the power loss on each phase line to obtain the typical daily three-phase bus loss of the platform area.

9. An electronic device, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method according to any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the processor is caused to perform the steps of the method according to any one of claims 1 to 7.

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