Method for calculating relative increment of line loss of distributed photovoltaic access power distribution network

Abstract

The invention discloses a line loss relative increment calculation method for a distributed photovoltaic access power distribution network, relates to a line loss calculation method in a power system, and aims to solve the problem that the calculation result error is relatively large as the influence of a distributed power supply on current distribution, power injection and load characteristics cannot be accurately considered in the conventional line loss relative increment calculation method. According to the invention, the along-line current of the distribution line is obtained by constructing the along-line current calculation model of the distribution line; calculating the loss function of the three-phase line of the distribution network through the line current when no distributed photovoltaic access exists; calculating a loss function of the three-phase line of the distribution network after the distributed photovoltaic access through the line current; and finally, according to the loss function of the three-phase line of the distribution network when no distributed photovoltaic is accessed and the loss function of the three-phase line of the distribution network after the distributed photovoltaic is accessed, calculating the relative increment of the line loss after the distributed photovoltaic is accessed into the distribution network. The method has the beneficial effect that the calculation precision of the relative increment of the line loss is remarkably improved.

Description

Technical Field

[0001] This invention relates to a method for calculating line losses in a power system. Background Technology

[0002] With the accelerated pace of global energy transition, the proportion of new energy sources in the power system is rapidly increasing. Distributed photovoltaic (PV), as a clean and renewable energy form, is seeing its integration into distribution networks due to its high flexibility, convenient deployment, and local consumption capabilities. However, the large-scale integration of distributed PV has brought many challenges to the operation and management of existing distribution networks, especially in terms of line loss calculation and management.

[0003] Existing distribution network line loss calculations are primarily based on centralized power supply models, where power flow direction is unidirectional and loss calculations are relatively simple. However, with the integration of distributed photovoltaic (PV) systems, the power flow characteristics of the distribution network have changed significantly. Factors such as the location, capacity, power factor, and operating output characteristics of distributed PV systems all affect the current distribution, voltage level, and power flow direction of the distribution network, thereby altering the distribution and magnitude of line losses. Specifically:

[0004] Power flow direction changes: After distributed photovoltaic (PV) systems are integrated, the power flow in the distribution network is no longer a one-way flow from the substation to the load end, but may reverse, meaning power is transmitted from distributed PV systems to the grid. This bidirectional power flow makes line loss calculation more complex, and existing line loss calculation methods cannot accurately reflect actual losses.

[0005] Voltage distribution changes: The integration of distributed photovoltaic power will change the voltage distribution of the distribution network, especially the voltage rise near the connection point is more obvious; the voltage change will affect the impedance characteristics of the line, and thus affect the calculation results of line loss.

[0006] Changes in load characteristics: The output of distributed photovoltaic power is intermittent and fluctuating, and its connection will make the load characteristics of the distribution network more complex; changes in parameters such as the shape factor and power factor of the load curve will also affect line losses.

[0007] Therefore, existing line loss calculation methods are mainly based on static load models and simplified network topologies, failing to accurately account for the dynamic changes after distributed photovoltaic (PV) grid integration. For example, existing methods often neglect the fluctuations in PV output and the time-varying nature of load when calculating the impact of distributed PV on line losses, leading to significant errors in the calculation results. Furthermore, with the continuous increase in distributed PV penetration, the operating conditions of distribution networks are becoming more complex and variable. On the one hand, the integration of distributed PV may reduce line losses, especially when integrated into areas with concentrated loads, reducing the power transmitted from substations and thus lowering line losses. On the other hand, improper integration locations or excessive capacity may also lead to increased line losses and even cause problems such as voltage exceeding limits and power flow overload. Summary of the Invention

[0008] The purpose of this invention is to address the problem that existing methods for calculating the relative increase in line loss cannot accurately account for the impact of distributed generation on current distribution, power injection, and load characteristics, resulting in large errors in the calculation results. This invention proposes a method for calculating the relative increase in line loss when distributed photovoltaic power is connected to the distribution network.

[0009] The method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network, as described in this invention, includes the following steps:

[0010] Construct a model for calculating the current along the power distribution line to obtain the current along the power distribution line;

[0011] Based on the current along the line, the loss function of the three-phase distribution network along the line is calculated when there is no distributed photovoltaic access;

[0012] Based on the current along the line, the loss function of the three phases along the distribution network after the distributed photovoltaic system is connected is calculated.

[0013] By using the calculated loss function along the three phases of the distribution network without distributed photovoltaic (PV) access and the calculated loss function along the three phases of the distribution network after distributed PV access, the relative increase in line loss after distributed PV access to the distribution network is calculated.

[0014] Furthermore, the constructed power distribution line current calculation model is expressed as follows:

[0015]

[0016] In the formula, This is the load curve shape factor; It is a function of the active power of the load and the distance; This is the rated line voltage of the line; The load power factor; This refers to the actual running time of the line; Indicates the distance to the beginning of the feeder; This refers to the current along the power distribution line.

[0017] Furthermore, the loss function along the three-phase distribution network without distributed photovoltaic access is expressed as:

[0018]

[0019] In the formula, This represents the loss value along the three-phase distribution network when there is no distributed photovoltaic access. This refers to the feeder start current. This refers to the current at the end of the feeder. The resistance per unit length of the feeder.

[0020] Furthermore, the loss function along the three-phase distribution network after distributed photovoltaic (PV) grid integration is expressed as:

[0021]

[0022] In the formula, This represents the loss value along the three-phase distribution network after the distributed photovoltaic system is connected. For single-phase current of distributed photovoltaic power connected to the distribution network; This refers to the distance from the first section of the feeder to the distributed photovoltaic grid connection. This represents the power factor of distributed photovoltaic systems.

[0023] Furthermore, the specific formula for calculating the relative increase in line loss after distributed photovoltaic power is connected to the distribution network is as follows:

[0024]

[0025] in, This refers to the relative increase in line loss after distributed photovoltaic power is connected to the distribution network. Load power factor The difference in power factor between distributed photovoltaic power and other photovoltaic power. feeder end current With feeder start current The ratio; Single-phase current for distributed photovoltaic power grid connection With feeder start current The ratio of .

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The method for calculating the relative increase in line loss when distributed photovoltaic (PV) is connected to a distribution network, as described in this invention, uses current as the data source and employs methods such as the shape factor of the load curve to correct the calculated line loss, accurately considering the impact of distributed power sources on current distribution, power injection, and load characteristics. By accurately calculating the changes in line loss before and after PV access, the accuracy of the calculation of the relative increase in line loss is significantly improved.

[0028] This invention clarifies the factors influencing line losses caused by distributed photovoltaic (PV) grid connection, including power supply radius, load power factor and PV power factor, PV connection location, and the ratio of distributed PV connection capacity to total load. By quantitatively analyzing the relationship between these factors and line losses, it provides a scientific basis for selecting the connection location and capacity of distributed PV. It provides theoretical support for the orderly connection of distributed PV in distribution networks, helping grid operators optimize distributed PV connection schemes and avoid problems such as increased line losses and voltage exceeding limits caused by unreasonable connection locations or excessive connection capacity. Attached Figure Description

[0029] Figure 1 The flowchart below shows a method for calculating the relative increase in line loss when a distributed photovoltaic power grid is connected to a distribution network, as described in Specific Implementation Method 1.

[0030] Figure 2 This is a schematic diagram showing the variation of feeder current in a uniformly distributed load in Implementation Method 2.

[0031] Figure 3 This is a schematic diagram showing the change in distribution network current after a single distributed photovoltaic (PV) ... Detailed Implementation

[0032] Specific Implementation Method 1: Combination Figure 1 This embodiment describes a method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network, which includes the following steps:

[0033] Construct a model for calculating the current along the power distribution line to obtain the current along the power distribution line;

[0034] Based on the current along the line, the loss function of the three-phase distribution network along the line is calculated when there is no distributed photovoltaic access;

[0035] Based on the current along the line, the loss function of the three phases along the distribution network after the distributed photovoltaic system is connected is calculated.

[0036] By using the calculated loss function along the three phases of the distribution network without distributed photovoltaic (PV) access and the calculated loss function along the three phases of the distribution network after distributed PV access, the relative increase in line loss after distributed PV access to the distribution network is calculated.

[0037] In this embodiment, by establishing an accurate model for calculating the current along the distribution line and using readily available current data as the data source, the accuracy and practicality of line loss calculation are improved. Dynamic analysis of line loss changes after distributed photovoltaic (PV) grid connection and evaluation through quantitative indicators provide data support for optimizing grid connection schemes. This provides a scientific basis for distributed PV grid connection decisions and distribution network operation strategy optimization, helping to reduce line losses and improve operational efficiency. The method is applicable to different types of distribution network topologies and operating conditions, and has broad applicability and promotional value.

[0038] Specific Implementation Method Two: Combination Figure 2 This embodiment further defines the method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network as described in Specific Embodiment 1. In this embodiment, the constructed distribution line current calculation model is expressed as follows:

[0039]

[0040] In the formula, This is the load curve shape factor; It is a function of the active power of the load and the distance; This is the rated line voltage of the line; The load power factor; This refers to the actual running time of the line; Indicates the distance to the beginning of the feeder; This refers to the current along the power distribution line.

[0041] In this embodiment, a 10kV distribution line is used as an example, assuming the load is evenly distributed along the line. Figure 2 This diagram simplifies the radial distribution network with uniform load power distribution along the feeders when there is no distributed photovoltaic (PV) grid connection, and shows the feeder current variation. The feeder current at the beginning of the diagram is... The current at the end of the feeder is The load power factor of the power distribution line is The current in a power distribution line decreases linearly with increasing distance. Based on the current distribution, the current along the line is:

[0042]

[0043] In the formula: This represents the distance to the beginning of the feeder. Assuming the total length of the feeder between the centralized load end and the centralized power supply end is 1 unit, then... ∈(0,1).

[0044] Specific Implementation Method Three: This implementation method further defines the method for calculating the relative increase in line loss when distributed photovoltaic (PV) grids are connected to a distribution network as described in Specific Implementation Method Two. In this implementation method, the loss function along the three-phase distribution network when there is no distributed PV grid connection is expressed as follows:

[0045]

[0046] In the formula, This represents the loss value along the three-phase distribution network when there is no distributed photovoltaic access. This refers to the feeder start current. This refers to the current at the end of the feeder. The resistance per unit length of the feeder.

[0047] In this embodiment, the loss function value along the three-phase distribution network when there is no distributed photovoltaic access is... This system provides baseline line loss data for subsequent analysis, offering a reliable benchmark for line loss changes after distributed photovoltaic (PV) integration. It simplifies the calculation process by establishing a loss function, improving computational efficiency. Furthermore, it adapts to various load distribution scenarios, demonstrating broad applicability and flexibility, and can accommodate different types of distribution networks. It provides data support for subsequent steps, offering a crucial data foundation for line loss analysis and optimization schemes after distributed PV integration. It improves the reliability of line loss calculations by accurately calculating line losses without distributed PV integration, reducing sources of error in subsequent analyses. Finally, it supports distribution network planning and operation management, providing important reference data and contributing to the optimization of distribution network operation strategies.

[0048] Detailed Implementation Method Four: Combination Figure 3 This embodiment further defines the method for calculating the relative increase in line loss when distributed photovoltaic (PV) power is integrated into a distribution network, as described in Specific Embodiment Three. In this embodiment, the loss function along the three-phase distribution network after distributed PV integration is expressed as follows:

[0049]

[0050] In the formula, This represents the loss value along the three-phase distribution network after the distributed photovoltaic system is connected. For single-phase current of distributed photovoltaic power connected to the distribution network; This refers to the distance from the first section of the feeder to the distributed photovoltaic grid connection. This represents the power factor of distributed photovoltaic systems.

[0051] In this embodiment, the distance between the distributed photovoltaic access point and the first section of the feeder is set. At this location, the single-phase current of the distributed photovoltaic injection system is The power factor of distributed photovoltaic power is The reductions in active and reactive current between the distributed photovoltaic system and the feeder start-up point are respectively and ;Depend on Figure 2 It can be seen that after a single distributed photovoltaic (PV) ...

[0052] Specific Implementation Method Five: This implementation method further defines the method for calculating the relative increase in line loss after distributed photovoltaic (PV) grid connection as described in Specific Implementation Method Four. In this implementation method, the specific formula for calculating the relative increase in line loss after distributed PV grid connection is as follows:

[0053]

[0054] in, This refers to the relative increase in line loss after distributed photovoltaic power is connected to the distribution network. Load power factor The difference in power factor between distributed photovoltaic power and other photovoltaic power. feeder end current With feeder start current The ratio; Single-phase current for distributed photovoltaic power grid connection With feeder start current The ratio of .

[0055] In this embodiment, as shown in the above formula, there are four factors affecting the system line loss when photovoltaic (PV) grid connection to a medium-voltage distribution network: power supply radius, load power factor and PV power factor (operating mode), PV grid connection location, and the ratio of distributed PV grid connection capacity to total load. Quantitative analysis of the relationship between these factors and line loss provides a scientific basis for selecting the grid connection location and capacity of distributed PV. This provides theoretical support for the orderly grid connection of distributed PV in the distribution network, helping grid operators optimize distributed PV grid connection schemes and avoid problems such as increased line loss and voltage exceeding limits caused by unreasonable grid connection locations or excessive grid connection capacity.

[0056] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network, characterized in that, Includes the following steps: Construct a model for calculating the current along the power distribution line to obtain the current along the power distribution line; Based on the current along the line, the loss function of the three-phase distribution network along the line is calculated when there is no distributed photovoltaic access; Based on the current along the line, the loss function of the three phases along the distribution network after the distributed photovoltaic system is connected is calculated. By using the calculated loss function along the three phases of the distribution network without distributed photovoltaic (PV) access and the calculated loss function along the three phases of the distribution network after distributed PV access, the relative increase in line loss after distributed PV access to the distribution network is calculated.

2. The method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network according to claim 1, characterized in that, The constructed power distribution line current calculation model is represented as follows: In the formula, This is the load curve shape factor; It is a function of the active power of the load and the distance; This is the rated line voltage of the line; The load power factor; This refers to the actual running time of the line; Indicates the distance to the beginning of the feeder; This refers to the current along the power distribution line.

3. The method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network according to claim 2, characterized in that, The loss function along the three-phase distribution network without distributed photovoltaic (PV) grid connection is expressed as: In the formula, This represents the loss value along the three-phase distribution network when there is no distributed photovoltaic access. This refers to the feeder start current. This refers to the current at the end of the feeder. The resistance per unit length of the feeder.

4. The method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network according to claim 3, characterized in that, The loss function along the three-phase distribution network after distributed photovoltaic (PV) grid integration is expressed as: In the formula, This represents the loss value along the three-phase distribution network after the distributed photovoltaic system is connected. For single-phase current of distributed photovoltaic power connected to the distribution network; This refers to the distance from the first section of the feeder to the distributed photovoltaic grid connection. This represents the power factor of distributed photovoltaic systems.

5. The method for calculating the relative increase in line loss when distributed photovoltaic power is connected to a distribution network according to claim 4, characterized in that, The specific formula for calculating the relative increase in line loss after distributed photovoltaic power is connected to the distribution network is as follows: in, This refers to the relative increase in line loss after distributed photovoltaic power is connected to the distribution network. Load power factor The difference in power factor between distributed photovoltaic power and other photovoltaic power. feeder end current With feeder start current The ratio; Single-phase current for distributed photovoltaic power grid connection With feeder start current The ratio of .

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