Optimization analysis method for line loss of distribution area based on photovoltaic propulsion

Abstract

The application discloses a photovoltaic propulsion transformer area line loss optimization analysis method, and belongs to the technical field of line loss optimization analysis, which comprises the following steps: analyzing the working characteristics of a photovoltaic array; constructing a photovoltaic system output model; constructing a line loss calculation model of the photovoltaic access; analyzing the operation efficiency principle of a distribution transformer; and analyzing the influence of the distributed photovoltaic access on the transformer area line loss. The method can realize the analysis of the influence of the distributed photovoltaic power access on the transformer area line loss and the calculation method, and effectively avoids the defects that the prior art does not analyze the influence of the distributed photovoltaic power access on the transformer area line loss and the calculation method.

Description

Technical Field

[0001] This invention belongs to the field of line loss optimization analysis technology, specifically relating to a method for optimizing line loss in photovoltaic power generation areas. Background Technology

[0002] As mentioned in the prior art solution with patent publication number "CN117791632A", the method for optimizing line loss in transformer areas has been applied more and more widely.

[0003] On the other hand, in recent years, with the continuous growth of global energy consumption and the increasing pressure on environmental protection, green sustainability has become a common awareness of development in various countries, and the large-scale development and application of renewable energy sources such as wind, solar, nuclear, and biomass energy has become an inevitable trend. Compared with fossil fuels such as coal and oil, renewable energy is characterized by its dispersed distribution and significant regional differences, making it difficult to achieve efficient utilization of renewable energy through traditional centralized mining and production models. Against this backdrop, distributed generation technology has been vigorously developed and applied.

[0004] Distributed generation (DG) is the application platform for distributed power generation technology. It has a small installed capacity and is widely distributed near the user load. Energy utilization mainly includes renewable energy sources such as wind, solar, biomass, hydro, tidal, and ocean energy, as well as waste heat, waste pressure, and exhaust gas utilization, and combined cooling, heating, and power (CCHP) generation. It has advantages such as low cost, easy installation, high power generation efficiency, flexible control, and clean and environmentally friendly operation. Among the many forms of distributed power generation, distributed photovoltaic (DPV) is particularly widely used.

[0005] Distributed photovoltaic (PV) power generation offers an effective solution to global energy depletion and environmental pollution, but large-scale DPV integration presents new challenges to the safe and stable operation of distribution networks. After large-scale DPV integration, power flow changes from unidirectional to bidirectional, profoundly impacting line voltage, current carrying capacity, and losses. Simultaneously, influenced by variations in solar irradiance, temperature, and wind speed, PV output exhibits significant intermittency and randomness, leading to uncertainties in distribution network operation. Furthermore, the close spatial proximity and similar meteorological conditions among nodes in the distribution network result in significant correlations in PV output within the region, exacerbating the safety risks of distribution network operation.

[0006] Line loss, short for power grid energy loss, refers to the energy loss that occurs in transmission, transformation, and distribution equipment during the process of electricity generation and consumption by users, and is dissipated into the air as heat. Line loss rate is an important comprehensive economic indicator for power supply companies. The distribution network is the tail end of the entire power grid, with low voltage levels, numerous branches, and a large number of distribution transformers. Especially in low-voltage distribution areas, line losses are relatively high. Effective management of distribution area line losses is a key indicator reflecting the company's operational level, making it particularly important to accurately reflect the true level of comprehensive line losses in distribution areas.

[0007] The increasing environmental awareness, the inherent requirements of sustainable development, and the introduction of a series of policies encouraging distributed renewable energy generation have greatly promoted the development of distributed renewable energy generation. The proportion of distributed power sources in the distribution network is gradually increasing, making them an important power source in the distribution network. In-depth analysis of the impact of distributed photovoltaic power generation on transformer substation line losses and its calculation methods is an important basis for improving transformer substation line loss optimization and a crucial way for power companies to achieve energy conservation, loss reduction, and sustainable development.

[0008] Currently, there is no analysis of the impact of distributed photovoltaic power generation on line losses in transformer substations, nor is there a calculation method for this impact. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention proposes a method for optimizing line loss in photovoltaic-driven distribution transformer areas, effectively avoiding the deficiencies in existing technologies that do not analyze the impact of distributed photovoltaic power generation on line loss in distribution transformer areas and their calculation methods.

[0010] The present invention employs the following technical solution.

[0011] A method for optimizing line loss in photovoltaic-driven distribution transformer areas, comprising: Step 1: Analyze the operating characteristics of the photovoltaic array; Step 2: Construct a photovoltaic system output model; Step 3: Construct a line loss calculation model for photovoltaic grid connection; Step 4: Analyze the principle of distribution transformer operating efficiency.

[0012] Furthermore, in step 1, the operating characteristics of the photovoltaic array include: The IV equation for a PN junction solar cell is as follows:

[0013] in, , These are the output current and output voltage of the solar cell during use; , These are the short-circuit current of the solar cell and the reverse saturation current of the PN junction, respectively. It is 1.38×10-23 J / K; For temperature; The temperature is 1.6 × 10⁻¹⁹ C. The operating characteristics of a photovoltaic array also include the solar cell IV characteristic curve, which represents the relationship between the output voltage and output current of the solar cell under a specific temperature and solar irradiance. Several important solar cell parameters can be obtained from the characteristic curve: (1) Short-circuit current; (2) Open-circuit voltage; (3) Maximum power point current; (4) Maximum power point voltage; (5) Maximum power.

[0014] Furthermore, step 2 specifically includes: Step 2-1: Photovoltaic system output calculation model; Step 2-2: Analyze the factors affecting the output of the photovoltaic system.

[0015] Furthermore, in step 2-1, the photovoltaic system output calculation model includes: Defined under reference conditions, I sc V is the short-circuit current of the array. oc V is the open-circuit voltage. m I m The voltage and current at the maximum power point under this condition, and the load current of each photovoltaic cell under the reference condition. It is expressed as follows:

[0016] When considering the effects of radiation intensity and temperature changes, the load current I As shown in the following formula:

[0017] Where: R ref T ref These represent the reference values ​​for solar radiation and photovoltaic cell temperature, respectively; α is the temperature coefficient of current change under reference solar irradiance; β is the temperature coefficient of voltage change (V / ℃) under reference solar irradiance; R S This is the series resistance of the photovoltaic module; Series resistance R of photovoltaic array S The formula for calculation is:

[0018] In the formula: ε represents the material band structure; N p N is the number of photovoltaic array modules connected in parallel; N is the number of photovoltaic array modules connected in series; N sThis represents the number of units connected in series in each module of the photovoltaic array; Power of a photovoltaic array under arbitrary solar radiation intensity and temperature As shown in the following formula:

[0019] From the extremum condition, dP / dV=0, we get:

[0020] The above equation can be solved iteratively using Newton's method to obtain the optimal operating voltage V corresponding to the maximum power point. max :

[0021] When |V k+1 -V k When <ε|, V max =V k+1 In the above formula: V k+1 and V k These are the (k+1)th and kth iteration values ​​of V, respectively; ε is the iteration precision; P'(V k ) and P"(V k These are the first and second derivatives of P with respect to V in the k-th iteration, respectively. The resulting V... max Substituting into the formula, we can obtain I max Thus, the maximum power P max It can be obtained from the following formula: .

[0022] Furthermore, in step 2-2, it can be seen from the characteristics of photovoltaic cells and the output calculation model that: (1) The output characteristics of the photovoltaic system change with the change of the light intensity received by the cell surface and the cell temperature. These two factors have a great influence on the photovoltaic output, especially the light intensity, which is the factor with the greatest influence on the photovoltaic output; (2) The electrical parameters of the photovoltaic system, the installation and operation mode, the cleanliness of the cell surface, and whether there are scratches will also affect the output.

[0023] Furthermore, in step 3, the algorithms for calculating line losses in the distribution network after the integration of distributed power sources include the improved equivalent resistance method, the improved equivalent capacity method, and the line loss calculation method based on power flow calculation.

[0024] Furthermore, in step 3, the calculation steps of the improved equivalent resistance algorithm are as follows: A-1: Calculate the required parameters for the headend based on the known parameters of the headend representative day:

[0025] In the formula, The root mean square power at the beginning of the distribution line represents the daily power. The root mean square voltage at the beginning of the distribution line represents the day. , These represent the active and reactive power at the beginning of the line on a given day. Here, α is the equivalent coefficient, and α is the load factor. When only an ammeter is available at the beginning of the distribution line, the current measured by the representative is:

[0026] In the formula, The root mean square current represents the current of the day; A-2: Find the root mean square current of the transformer ( );

[0027] A-3: Request and ;

[0028] A-4: Distribution line represents daily bus power loss ( As shown in the following formula:

[0029] From the above formula, we can obtain:

[0030] Or it can be expressed as:

[0031] When distributed generation is connected to the distribution network and has little impact on the network structure and power flow direction, the total bus power loss for the month can be calculated directly based on the line loss power of the representative day. );

[0032] In the formula, This refers to the actual number of days in the month. For the total monthly electricity supply, then .

[0033] Furthermore, in step 3, the improved equivalent capacity method includes the following steps: B-1: Divide the entire computation time into segments; B-2: Calculation of the first end of the distribution network line.

[0034] Furthermore, in B-2, when the photovoltaic power generation access node is used as the starting point of the distribution line, the equivalent capacity calculation expression for the distribution transformer is:

[0035] In the formula, , These represent the active and reactive power of distributed photovoltaic power generation, respectively. , These are the active and reactive power of the distribution transformer, respectively. When photovoltaic power generation cannot meet load demand, it is treated as a regular load, and the beginning of the distribution line is taken as the main power node. The equivalent capacity of the photovoltaic power generation node at this time is shown below:

[0036] Equivalent capacity of distribution transformer for:

[0037] Line loss is:

[0038] In the formula, t is the wind power generation operation time. When photovoltaic power generation is the first end of a power distribution line, the equivalent resistance of the line is calculated. When photovoltaic power generation is equivalent to ordinary load, its equivalent capacity is expressed as follows: for:

[0039] Line loss is:

[0040] In the formula, The equivalent resistance at the beginning of the circuit; and ; The sum of the power input from photovoltaic power and the power output from the distribution network outlet should meet the power demand of the distribution network, that is:

[0041] Finally, by adding up the line losses under different conditions, the total line loss can be obtained.

[0042] Furthermore, in step 3, the distributed generation distribution network calculation method based on power flow calculation includes: C-1: Assuming the power generation curves of the power sources are identical, the active and reactive power calculation expressions for distributed power sources in each hour are as follows:

[0043] In the formula, , , respectively, are the active and reactive power of the distributed generation in hour t of the representative day; P and Q are the active and reactive energy consumption of the distributed generation in the representative day, respectively. Let be the power allocation factor of the distributed generation at hour t; Voltage representing different times of the day and current It is known that, in the formula The calculation expression is:

[0044] C-2: Calculate the power at the beginning of the distribution line; C-3: Calculate the load power of the distribution transformer node.

[0045] Furthermore, in C-2, assuming that the active and reactive power at the beginning of the distribution network line remains constant per hour, the power at the beginning of the distribution line per hour can be expressed as:

[0046] In the formula, , These represent the active and reactive power of the distributed generation at hour t on the representative day; , These represent the active and reactive power units supplied to the beginning of the distribution line during the day, respectively. Let be the power distribution coefficient at the beginning of the distribution line in hour t. The calculation expression is:

[0047] In the formula, , These represent the voltage and current at the beginning of the power distribution line in the t-th hour of the day.

[0048] Furthermore, in C-2, the total power output from the substation bus s and distributed generation to the distribution network in hour t of the day is... After deducting the power loss of the entire power grid, the total load power of the distribution transformer is the total power of the substation bus and distributed generation minus... ;

[0049] Given that the power loss of the transformer is ,

[0050] In the formula, , These are the active and reactive power of the load on the high-voltage side of distribution transformer i in hour t, respectively. This is the power distribution factor of the distribution transformer.

[0051] Furthermore, step 4 specifically includes: Calculate the operating efficiency of the distribution transformer.

[0052] Furthermore, in step 4, the method for calculating the operating efficiency of the distribution transformer includes: Step 4-1: Calculate the transformer efficiency; Step 4-2: Calculate the transformer operating efficiency.

[0053] Further, in step 4-1, the transformer efficiency is the ratio of its output power to its input power, where: (1) Transformer output power: The transformer output power is: = =

[0054] In the formula The transformer output power is expressed in kW. To calculate the current, in A; Rated voltage, V; Power factor; The load factor is %; The rated capacity of the transformer is kW.

[0055] (2) Transformer input power: The transformer input power is: = + +

[0056] In the formula For transformer no-load loss (i.e., iron loss), kW; The value is kW, representing the transformer load loss (i.e., copper loss).

[0057] because =

[0058] In the formula The load loss of the transformer at its rated current, kW but = + + = + +

[0059] (3) Optimal efficiency and load factor of the transformer: The transformer efficiency is: = =

[0060] To find the extreme value using the above formula, when... When the transformer efficiency reaches its maximum, i.e., the average load factor of the distribution transformer. = At that time, the transformer efficiency reaches its maximum.

[0061] Furthermore, in step 4-2, the formula for calculating the transformer operating efficiency is:

[0062] In the formula For transformers in Load factor (maximum load rate) within the time interval.

[0063] Furthermore, the method for optimizing line loss in photovoltaic power distribution areas also includes: Step 5: Analyze the impact of distributed photovoltaic grid connection on line loss in the transformer area.

[0064] Furthermore, step 5 specifically includes: A theoretical calculation model is constructed to calculate the impact of distributed photovoltaic (PV) grid connection on line loss in transformer substations.

[0065] Furthermore, the method for constructing a theoretical calculation model of the impact of distributed photovoltaic (PV) grid connection on line losses in transformer substations includes: The revised formula for calculating the comprehensive line loss of a transformer substation is shown below:

[0066] In the formula, The overall line loss rate for the transformer area; This represents the positive active power of the main meter for the transformer area. This is the sum of the positive active power of all users' meters within the distribution area; This represents the sum of the electricity generated by all photovoltaic users within the designated area and fed into the grid. This refers to the reverse active power of the main meter for the transformer area.

[0067] The beneficial effects of the present invention are as follows: Compared with the prior art, the technical effects of the present invention include: This invention analyzes the operating characteristics of photovoltaic arrays; constructs a photovoltaic system output model; constructs a line loss calculation model for photovoltaic grid connection; analyzes the operating efficiency principle of distribution transformers; and analyzes the impact of distributed photovoltaic grid connection on the line loss of distribution areas. This enables the analysis of the impact of distributed photovoltaic power generation on the line loss of distribution areas and its calculation method, effectively avoiding the shortcomings of existing technologies that do not analyze the impact of distributed photovoltaic power generation on the line loss of distribution areas and their calculation methods. Attached Figure Description

[0068] Figure 1 This is a flowchart of the photovoltaic propulsion line loss optimization analysis method described in this invention; Figure 2 This is the IV characteristic curve of the solar cell in this invention; Figure 3 This is a coordinate curve showing the effect of sunlight on solar cells in this invention; Figure 4 This is a coordinate curve showing the effect of temperature on solar cells in this invention; Figure 5 This is a wiring diagram of the photovoltaic system in this invention; Figure 6 This is a schematic diagram of the power flow direction when all photovoltaic power generation is self-consumed in this invention; Figure 7 This is a schematic diagram of the power flow direction when photovoltaic power generation is consumed within the distribution area in this invention; Figure 8 This is a schematic diagram of the power flow direction when the photovoltaic power generation cannot be absorbed within the transformer area in this invention. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, any other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0070] like Figure 1 As shown, the present invention provides a method for optimizing line loss in photovoltaic power generation areas, comprising: Photovoltaic generators are generally in the form of photovoltaic arrays. A single monocrystalline silicon wafer can form a solar cell unit, and several solar cell units together constitute a solar cell module. A photovoltaic array is formed by connecting multiple such solar cell modules. Depending on the load, several modules are connected in parallel or series to create a photovoltaic array. The photovoltaic array converts light energy into electrical energy and outputs voltage and current. After DC / DC or DC / AC conversion, this is converted into a form of electrical energy suitable for the user, thus providing the user with the corresponding electricity.

[0071] In a wind-solar hybrid power generation system, the power generation principle of solar cells is based on the photovoltaic effect, which refers to the phenomenon that a semiconductor generates an electromotive force when it is irradiated by light. This causes sunlight to strike the silicon material and generate current, directly generating electricity. Solar cells convert the radiation of sunlight into electrical energy. Solar cells are connected in series or parallel to form a photovoltaic array to output direct current.

[0072] Currently, the most widely used solar cells are silicon solar cells. A PN junction creates an electric field; the N-region is the surface of the diffusion layer, and the silicon wafer itself is P-type silicon. The junction between these two regions is called the PN junction. To reduce solar energy reflection losses, a reflective film needs to be placed on top of the solar cell. The photovoltaic effect described above occurs under these conditions.

[0073] Light is composed of photons, which are particles with energy determined by their wavelength. When crystalline silicon absorbs photons, paired positive and negative charged particles are generated in the PN junction. Because the positive and negative charges are separated in the PN junction region, an electric field is formed. When a load is connected to both sides of a solar cell, current flows through the load, starting from the bottom of the crystalline silicon cell, passing through the load, and finally reaching the top. The solar cell generates a current of a corresponding magnitude because it absorbs a large number of photons during operation.

[0074] The operating current of a single solar cell is 15–25 mA / cm. 2 Generally, solar cells cannot be used as a standalone power source; their operating voltage is 0.46V to 0.51V. The series and parallel connection of individual solar cells is completed before packaging. The power of solar cells is typically from a few watts to several hundred watts, and they can be used individually as the smallest power unit. Before packaging, the solar cell modules are connected in series and parallel to form a solar cell array, and the array's output power is sufficient to meet load requirements.

[0075] Under normal circumstances, the atomic nucleus and electrons in semiconductor materials are closely linked. However, due to external factors, the ability to bind the nucleus and electrons decreases, allowing electrons to break free of the nucleus and become free electrons. The energy transfer of photons to electrons occurs because sunlight acts on the semiconductor, causing electrons to jump to higher energy states. Among these electrons, those usable in optoelectronic devices include free electrons, valence band electrons, and electrons residing in a certain impurity energy level. In solar cells, valence band electrons are the primary source of light, and in this process, they acquire light.

[0076] Step 1: Analyze the operating characteristics of the photovoltaic array; In a preferred but non-limiting embodiment of the present invention, in step 1, the operating characteristics of the photovoltaic array include: In the use of photovoltaic arrays, it is always desirable for solar cells to output high voltage and relatively large current. The following equation is the IV equation for a PN junction solar cell under ideal conditions:

[0077] in, , These are the output current and output voltage of the solar cell during use; , These are the short-circuit current of the solar cell and the reverse saturation current of the PN junction, respectively. It is 1.38×10-23 J / K; For temperature; The temperature is 1.6 × 10⁻¹⁹ C.

[0078] like Figure 2 As shown, the operating characteristics of a photovoltaic array also include the solar cell IV characteristic curve, which represents the relationship between the output voltage and output current of the solar cell during operation at a specific temperature and solar irradiance. Several important solar cell parameters can be obtained from the characteristic curve: (1) Short-circuit current: The maximum current that can be generated under a given temperature and solar radiation conditions; (2) Open-circuit voltage: The output voltage that can be generated under ideal conditions; (3) Maximum power point current: The current at the maximum power point under certain conditions, such as given temperature and light intensity; (4) Maximum power point voltage: The voltage at the maximum power point under certain conditions, such as given temperature and light intensity; (5) Maximum power: The maximum power that can be produced under given temperature and sunlight conditions.

[0079] The IV characteristic curve shows that solar cells are a non-linear DC power source, neither a constant voltage source nor a constant current source. However, the output current is relatively constant within certain operating voltage ranges, and after reaching a sufficiently high voltage, the current rapidly decreases to zero.

[0080] Changes in solar radiation intensity, while keeping all other conditions constant, are caused by Figure 3 It is evident that solar radiation intensity and short-circuit current are linearly proportional, while the change in open-circuit voltage is less pronounced and exhibits a logarithmic relationship.

[0081] Depend on Figure 4As can be seen, the open-circuit voltage VOC changes linearly with the battery temperature. This is because the internal temperature of the battery changes, while the short-circuit current changes slightly. This refers to the temperature change of the solar cell, not the ambient temperature. The relationship between ambient temperature and battery temperature is closely related to the intensity of sunlight.

[0082] Under suitable temperature, climatic conditions, and sufficient sunlight, solar cells achieve their maximum output power. During photovoltaic (PV) power generation, solar radiation intensity not only affects ambient temperature and load but also influences the performance of the solar cells. Only by adjusting the load impedance to achieve an optimal match can maximum power be obtained during PV power generation, thereby improving system efficiency. The load operating point, determined by the intersection of the volt-ampere characteristic curves of the PV array and the load, is also called the quiescent operating point. Different types of loads have different volt-ampere characteristics, resulting in varying output power for the PV array.

[0083] Step 2: Construct a photovoltaic system output model; In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes: Because grid-connected photovoltaic (PV) power generation systems are connected to the power grid, their unstable output power can affect the grid's operation. Therefore, PV output forecasting mainly focuses on grid-connected PV systems. The following is an introduction to the components of a grid-connected PV power generation system. A grid-connected power generation system converts the direct current (DC) generated by the solar cell array into alternating current (AC) through an inverter, directly transmitting it to the grid. This system includes components such as a solar cell array, a DC / DC converter, a DC / AC inverter, AC loads, a transformer, and batteries. Figure 5 As shown.

[0084] Grid-connected photovoltaic (PV) power generation often requires a certain installed capacity; therefore, grid-connected solar cell arrays are generally composed of multiple solar cell modules connected in series and parallel. In practical applications, combiner boxes are often used to reduce the wiring between the solar PV array and the inverter. Several PV series are connected in parallel and input into the combiner box. After being combined within the combiner box, the power is then connected to the grid via a controller, DC distribution cabinet, PV inverter, AC distribution cabinet, and other supporting devices to form a complete PV power generation system, achieving grid connection.

[0085] Inverters are essential components of photovoltaic (PV) power generation systems, converting direct current (DC) to alternating current (AC). A PV system must have an inverter to supply power to AC loads. Inverters also feature automatic frequency and voltage stabilization to ensure the quality of power supply to the PV system. The efficiency of the inverter significantly impacts the effective power generation of the PV system. Generally, inverters have low power losses (including conduction and switching losses), resulting in high conversion efficiency; for example, a 10kW inverter typically has an efficiency of over 90%.

[0086] In recent years, grid-connected power generation systems have developed rapidly, especially distributed small-scale photovoltaic (PV) power generation systems connected to residential grids, which are becoming increasingly widely used. These distributed power generation systems are often equipped with battery banks, which draw power from the grid during off-peak hours and store it. During peak hours, they use the electricity generated by the PV system or feed the stored energy back into the grid, thus playing a role in peak shaving and valley filling. Besides peak shaving and valley filling, the most important function of batteries is to improve the reliability of the power supply system. Due to the uncertainty of PV power generation, battery banks, as energy storage devices in PV power plants, can store excess electricity generated by the array during sunny periods and supply it to the load at night or on cloudy days.

[0087] The function of the blocking diode is to prevent the battery from discharging through the solar array. When the array is operating, there is a certain voltage drop across the blocking diode, but it does not exceed 1V. The requirements for the blocking diode are that its operating current must be greater than the maximum output current of the array, and its reverse withstand voltage must be higher than the voltage of the battery pack. This ensures that current does not flow through the photovoltaic array when the battery is discharging.

[0088] Step 2-1: Photovoltaic system output calculation model; In a preferred but non-limiting embodiment of the present invention, in step 2-1, the photovoltaic system output calculation model includes: Defined under reference conditions (G) STC =1000W / m 2 T STC =25℃), I sc V is the short-circuit current of the array. oc V is the open-circuit voltage. m I m The voltage and current at the maximum power point under this condition, and the load current of each photovoltaic cell under the reference condition. It can be expressed as follows:

[0089] When considering the effects of radiation intensity and temperature changes, the load current I As shown in the following formula:

[0090] Where: R ref T ref These are reference values ​​for solar radiation and photovoltaic cell temperature, respectively, typically taken as 1000 W / m². 2 , 25℃; α is the temperature coefficient of current change (A / ℃) under reference solar irradiance; β is the temperature coefficient of voltage change (V / ℃) under reference solar irradiance; R S This is the series resistance of the photovoltaic module; Series resistance R of photovoltaic array S The formula for calculation is:

[0091] In the formula: ε is the energy band of the material, and is taken as 1.12 eV for silicon; N p N is the number of photovoltaic array modules connected in parallel; N is the number of photovoltaic array modules connected in series; N s This represents the number of units connected in series in each module of the photovoltaic array; Because the voltage of photovoltaic cells varies with light intensity and temperature, photovoltaic power plants are generally equipped with maximum power point tracking (MPPT) devices to maximize solar energy utilization. MPPT devices correct the load current and voltage of the photovoltaic panels, ensuring they operate at their maximum power output point. The power output of a photovoltaic array under arbitrary solar radiation intensity and temperature... As shown in the following formula:

[0092] From the extremum condition, dP / dV=0, we get:

[0093] The above equation can be solved iteratively using Newton's method to obtain the optimal operating voltage V corresponding to the maximum power point. max :

[0094] When |V k+1 -V k When <ε|, V max =V k+1 In the above formula: V k+1 and V k These are the (k+1)th and kth iteration values ​​of V, respectively; ε is the iteration precision; P'(V k ) and P"(V k These are the first and second derivatives of P with respect to V in the k-th iteration, respectively. The resulting V... max Substituting into the formula, we can obtain I max Thus, the maximum power P max It can be obtained from the following formula: .

[0095] Step 2-2: Analyze the factors affecting the output of the photovoltaic system.

[0096] In a preferred but non-limiting embodiment of the present invention, in step 2-2, based on the characteristics of the photovoltaic cell and the output calculation model, it can be seen that: (1) the output characteristics of the photovoltaic system change with the change in the light intensity received by the cell surface and the cell temperature. These two factors have a significant impact on the photovoltaic output, especially the light intensity, which has the greatest impact on the photovoltaic output; (2) the electrical parameters of the photovoltaic system, the installation and operation mode, and the cleanliness and presence of scratches on the cell panel surface also affect the output. The first factor is mainly affected by environmental conditions and is relatively complex and variable, while the second factor is generally determined during system design or will not change in the short term and is relatively fixed, and can be represented by fixed parameters. Therefore, when performing photovoltaic output prediction calculations, the first factor, namely the influence of the light intensity received by the cell and the cell temperature on the output, is mainly considered.

[0097] Step 3: Construct a line loss calculation model for photovoltaic grid connection; In a preferred but non-limiting embodiment of the present invention, in step 3, traditional theoretical line loss calculation methods do not consider the changes in the power supply direction and the influence of known parameters of the distributed power source on the line losses of the distribution network after the distributed power source is connected to the distribution network. Currently, the main algorithms for calculating line losses in distribution networks containing distributed power sources include the improved equivalent resistance method, the improved equivalent capacity method, and line loss calculation methods based on power flow calculation.

[0098] In a preferred but non-limiting embodiment of the present invention, in step 3, the improved equivalent resistance method can obtain real-time data of the distribution transformer load by actual measurement when calculating the variable losses of the line, and then use the actual data to perform equivalent calculations of the line. This calculation method is labor-intensive, difficult to implement, and wastes manpower, but it has high calculation accuracy. Alternatively, the real-time data of the distribution transformer load can be omitted, and the equivalent resistance method can be used directly for equivalence. This method is simple to calculate and easy to implement, but it has a large deviation from the actual value. Combining the advantages of both methods and avoiding the shortcomings of previous algorithms, the traditional equivalent resistance method is improved.

[0099] The calculation steps of the improved equivalent resistance algorithm are as follows: A-1: Calculate the required parameters for the headend based on the known parameters of the headend representative day:

[0100] In the formula, The root mean square power at the beginning of the distribution line represents the daily power. The root mean square voltage at the beginning of the distribution line represents the day. , These represent the active and reactive power at the beginning of the line on a given day. Here, α is the equivalent coefficient, and α is the load factor. When only an ammeter is available at the beginning of the distribution line, the current measured by the representative is:

[0101] In the formula, The root mean square current represents the current of the day; A-2: Find the root mean square current of the transformer ( );

[0102] A-3: Request and ;

[0103] A-4: Distribution line represents daily bus power loss ( As shown in the following formula:

[0104] From the above formula, we can obtain:

[0105] Or it can be expressed as:

[0106] When distributed generation is connected to the distribution network and has little impact on the network structure and power flow direction, the total bus power loss for the month can be calculated directly based on the line loss power of the representative day. );

[0107] In the formula, This refers to the actual number of days in the month. For the total monthly electricity supply, then .

[0108] In a preferred but non-limiting embodiment of the present invention, step 3 of the improved equivalent capacity method includes the following steps: The traditional equivalent capacity method is as follows: the ratio of the power supply of the distributed generation source to the load consumption of the distribution transformer is the equivalent capacity. The current value at the head-end is allocated based on the injected capacity and the proportion of the total power consumption accounted for by the distribution transformer. Thus, the current of the distributed generation source can be obtained using the equivalent capacity based on the known parameters at the head-end. The equivalent capacity of the distributed generation source is also added to the equivalent capacity of each of the remaining distribution transformers, making the allocated current value more consistent with reality. The equivalent capacity allocation of the distributed generation source is shown in the following formula:

[0109] In the formula, , These are the root mean square current at the beginning of the distribution line and the injection current of the distributed generation, respectively. , These are the active power and reactive power at the beginning of the power distribution line, respectively. , These refer to the active power and reactive power injected by the distributed generation, respectively. , These are the voltage at the beginning of the distribution transformer and the voltage injected by the distributed power source, respectively. t represents the rated capacity of the distribution transformer; t represents the operating time.

[0110] The formula for calculating the equivalent resistance is as follows:

[0111] In the formula, R is the equivalent resistance of the entire distribution network; The equivalent resistance of the power distribution line; This is the equivalent resistance of the distribution transformer. The daily line loss A is:

[0112] In the formula, Let be the no-load loss of the distribution transformer at node i.

[0113] The above algorithms do not consider the impact of load curves and power factors differing from those at the headend on line loss calculations, neglect the instability of distributed generation and the real-time changing characteristics of generation curves, and do not consider the direction of power supply from distributed generation to the distribution network. Therefore, it is necessary to improve the shortcomings of the original algorithms and research and analyze a calculation method suitable for new network structures after distributed generation is connected to the distribution network.

[0114] The improved equivalent capacity method is as follows: B-1: Divide the entire computation time into segments; Because photovoltaic power generation is unstable and greatly affected by environmental factors, its power generation curve fluctuates greatly. Dividing the daily power generation curve into several time periods, with the flow direction in each time period being the same as the beginning, and ignoring the changes in the power supply direction in each time period, will result in a more realistic photovoltaic power generation curve.

[0115] B-2: Calculation of the first end of the distribution network line.

[0116] In a preferred but non-limiting embodiment of the present invention, in B-2, photovoltaic power generation is constantly changing due to environmental factors. When its power supply is used to supply power to the entire distribution network load, the photovoltaic power generation node is used as the starting point of the distribution line; if photovoltaic power generation is insufficient, then photovoltaic power generation is equivalent to ordinary load, and in this case, the starting point of the distribution line is used as the total power source. When the photovoltaic power generation access node is used as the starting point of the distribution line, the equivalent capacity calculation expression of the distribution transformer is:

[0117] In the formula, , These represent the active and reactive power of distributed photovoltaic power generation, respectively. , These are the active and reactive power of the distribution transformer, respectively. When photovoltaic power generation cannot meet load demand, it is treated as a regular load, and the beginning of the distribution line is taken as the main power node. The equivalent capacity of the photovoltaic power generation node at this time is shown below:

[0118] Equivalent capacity of distribution transformer for:

[0119] Line loss is:

[0120] In the formula, t is the wind power generation operation time. When photovoltaic power generation is the first end of a power distribution line, the equivalent resistance of the line is calculated. When photovoltaic power generation is equivalent to ordinary load, its equivalent capacity is expressed as follows: for:

[0121] Line loss is:

[0122] In the formula, The equivalent resistance at the beginning of the circuit; and ; The sum of the power input from photovoltaic power and the power output from the distribution network outlet should meet the power demand of the distribution network, that is:

[0123] Finally, by adding up the line losses under different conditions, the total line loss can be obtained.

[0124] In a preferred but non-limiting embodiment of the present invention, step 3, the distributed generation distribution network calculation method based on power flow calculation, includes: Traditional theoretical line loss calculation methods are based on certain assumptions and are prone to significant errors. With the large-scale grid connection of distributed generation, reducing these assumptions and simplifying data that is difficult to measure in the distribution network significantly improves the calculation of distribution network line losses.

[0125] Since real-time load data is difficult to obtain, the power factor and load curve of each load node are considered to be the same as those at the headend, avoiding a large amount of work in statistically analyzing load data. This section introduces an improved line loss calculation method based on power flow calculation for distributed generation. Compared with conventional calculation methods, this method does not ignore the voltage drop generated when current flows through the line and the impact of the voltage drop on line losses, weakens the assumptions, improves the accuracy of line loss calculation, and flexibly changes the load curves of each node based on power flow analysis, rather than solely utilizing the load curve at the headend.

[0126] This method is based on the forward-backward substitution method.

[0127] C-1: Assuming the power generation curves of the power sources are identical, the active and reactive power calculation expressions for distributed power sources in each hour are as follows:

[0128] In the formula, , , respectively, are the active and reactive power of the distributed generation in hour t of the representative day; P and Q are the active and reactive energy consumption of the distributed generation in the representative day, respectively. Let be the power allocation factor of the distributed generation at hour t; Voltage representing different times of the day and current It is known that, in the formula The calculation expression is:

[0129] C-2: Calculate the power at the beginning of the distribution line; In a preferred but non-limiting embodiment of the present invention, in C-2, assuming that the active and reactive power at the beginning of the distribution network line is constant per hour, the power at the beginning of the distribution line per hour can be expressed as:

[0130] In the formula, , These represent the active and reactive power of the distributed generation at hour t on the representative day; , These represent the active and reactive power units supplied to the beginning of the distribution line during the day, respectively. Let be the power distribution coefficient at the beginning of the distribution line in hour t. The calculation expression is:

[0131] In the formula, , These represent the voltage and current at the beginning of the power distribution line in hour t of the representative day; C-3: Calculate the load power of the distribution transformer node.

[0132] In a preferred but non-limiting embodiment of the present invention, in C-2, the total power output from the substation bus s and distributed generation to the distribution network in the t-th hour of the day is... After deducting the power loss of the entire power grid, the total load power of the distribution transformer is the total power of the substation bus and distributed generation minus... ;

[0133] Given that the power loss of the transformer is ,

[0134] In the formula, , These are the active and reactive power of the load on the high-voltage side of distribution transformer i in hour t, respectively. This is the power distribution factor of the distribution transformer.

[0135] Step 4: Analyze the principle of distribution transformer operating efficiency.

[0136] The economic operation theory of distribution transformers is as follows: Transformer losses primarily originate from internal iron and copper losses. When the transformer output is zero, its efficiency is also zero; as the output increases, efficiency initially rises until it reaches its maximum value, at which point it begins to decline again. Furthermore, under heavy load, the internal temperature rise of the transformer increases the coil resistance, leading to increased copper losses. This can cause the insulation material to lose its original performance, significantly impacting its safety and potentially burning out the transformer. Therefore, controlling the transformer's load rate is crucial for its safe and efficient operation.

[0137] Because the load on a transformer fluctuates over time during actual operation, the optimal load factor is not a constant value. It is impossible to keep a transformer operating at its most economical level under real-world conditions. The principle of economical transformer operation is to ensure both maximum efficiency and minimum losses, thereby minimizing energy consumption, maximizing efficiency, and ultimately maximizing economic benefits.

[0138] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes: Calculate the operating efficiency of the distribution transformer.

[0139] In a preferred but non-limiting embodiment of the present invention, in step 4, the operating efficiency of the distribution transformer reflects the overall efficiency of the transformer. In engineering design, the selection of the transformer has a significant impact on the economic and energy-saving operation of the power distribution system. Therefore, determining the optimal load factor of the transformer by calculating its operating efficiency and optimal operating efficiency should be an important step in selecting the transformer capacity. The operating efficiency of a distribution transformer is the ratio of its output power to its input power. The method for calculating the operating efficiency of a distribution transformer includes: Step 4-1: Calculate the transformer efficiency; In a preferred but non-limiting embodiment of the present invention, in step 4-1, the transformer efficiency is the ratio of its output power to its input power, wherein: (1) Transformer output power: The transformer output power is: = =

[0140] In the formula The transformer output power is expressed in kW. To calculate the current, in A; Rated voltage, V; Power factor; The load factor is %; The rated capacity of the transformer is kW.

[0141] (2) Transformer input power: The transformer input power is: = + +

[0142] In the formula For transformer no-load loss (i.e., iron loss), kW; The value is kW, representing the transformer load loss (i.e., copper loss).

[0143] because =

[0144] In the formula The load loss of the transformer at its rated current, kW but = + + = + +

[0145] (3) Optimal efficiency and load factor of the transformer: The transformer efficiency is: = =

[0146] To find the extreme value using the above formula, when... When the transformer efficiency reaches its maximum, i.e., the average load factor of the distribution transformer. = At that time, the transformer efficiency reaches its maximum.

[0147] According to the formula = Taking a common 10kV transformer of a certain manufacturer as an example, the theoretical optimal load factor is shown in Table 1 below (the parameters of transformers from different manufacturers may vary, the same below).

[0148] Table 1 Theoretical Optimal Load Rate of Commonly Used 10kV Transformers

[0149] As can be seen from the table above, the lower the transformer loss, the lower the theoretical optimal load rate. This is because the load rate is calculated under continuous constant load conditions. Obviously, the theoretical optimal load rate is not the final or best choice for determining the transformer capacity. Furthermore, Article 4.3.2 of JGJ16-2008 "Code for Electrical Design of Civil Buildings" stipulates that the long-term operating load rate of distribution transformers should not exceed 85%. Therefore, this provision should be understood as the annual operating load rate of the distribution transformer, not the load rate determined by calculated load under continuous constant load operation.

[0150] Step 4-2: Calculate the transformer operating efficiency.

[0151] In a preferred but non-limiting embodiment of the present invention, in step 4-2, the transformer operating efficiency refers to the overall efficiency of the transformer within a certain time interval. Since the load rate of the transformer changes continuously during operation, it is more convenient to calculate the transformer operating efficiency as the ratio of output to input electrical energy. Therefore, the transformer operating efficiency is the ratio of the output electrical energy to the input electrical energy of the transformer within that time interval. Introducing a time factor, the formula for calculating the transformer operating efficiency is:

[0152] In the formula For transformers in Load factor (maximum load rate) within the time interval.

[0153] Because transformers are not always operating at the calculated load. The optimal efficiency of a transformer varies depending on the object it supplies power to.

[0154] In a preferred but non-limiting embodiment of the present invention, the method for optimizing line loss in photovoltaic-driven distribution areas further includes: Step 5: Analyze the impact of distributed photovoltaic grid connection on line loss in the transformer area.

[0155] In a preferred but non-limiting embodiment of the present invention, step 5 specifically includes: A theoretical calculation model is constructed to calculate the impact of distributed photovoltaic (PV) grid connection on line loss in transformer substations.

[0156] In a preferred but non-limiting embodiment of the present invention, the method for constructing a theoretical calculation model of the impact of distributed photovoltaic (PV) grid connection on line losses in transformer substations includes: In traditional passive distribution networks, the formula for calculating line losses in transformer substations is as follows: Comprehensive line loss rate of the transformer area = (Electricity supplied to the transformer area - Electricity sold to the transformer area) / Electricity supplied to the transformer area × 100% The power supply of the transformer substation is obtained from the positive active power of the main meter of the substation, and the power sales of the substation are obtained by accumulating the positive active power of the user meters. Therefore, the above formula can also be expressed as:

[0157] In the formula, The overall line loss rate for the transformer area; This refers to the total electricity consumption of the transformer substation. This represents the sum of electricity consumption measured by all users within the designated area.

[0158] If a distribution area contains distributed photovoltaic users in addition to general users, the power flow direction in the distribution area may change due to the addition of photovoltaic power sources. Specifically, there are three situations.

[0159] (1) All photovoltaic power generation is for self-consumption, with no surplus power fed into the grid, such as Figure 6 As shown. In this case, the power flow direction within the transformer area remains unchanged, the composition of the power supply and sales volume in the transformer area remains unchanged, and the distributed power source has no impact on the calculation of the line loss rate of the transformer area.

[0160] (2) If there is surplus photovoltaic power generation connected to the grid and the excess power is only consumed by other users within the same distribution area, then in addition to the power flow from the grid to the users, there is also a power flow from the photovoltaic users to other nearby users within the distribution area, such as... Figure 7 As shown, the power supply composition of this distribution area has changed. It now includes not only the electricity measured by the main meter of the distribution area, but also the electricity generated by photovoltaic power generation. This portion of electricity is purchased by the grid at the benchmark price for desulfurized coal-fired power.

[0161] For ease of analysis, the amount of electricity transmitted from the power grid to users is denoted as... This refers to the positive active power of the total meter in the distribution area; the on-grid power of photovoltaic users (the reverse active power of photovoltaic user meters) is recorded as... Furthermore, the transmission loss of this portion of the grid-connected electricity within the distribution area is not considered; the positive active power transmitted from the grid to the user within the distribution area and measured by the user's meter is recorded as... Then, without considering losses, the total amount of electricity transmitted from photovoltaic users to other users within the distribution area and measured by user meters is: .

[0162] According to the traditional formula for calculating the comprehensive line loss of a transformer area,

[0163] Obviously, in 0 < < At that time, the power supply of the distribution area did not include the power generated by photovoltaic power generation connected to the grid. Comprehensive line loss rate of the transformer area Obviously too small; > hour, <0 indicates a negative line loss.

[0164] (3) At a certain moment, there is surplus photovoltaic power generation that can not be fully absorbed within the distribution area, and some of the power is still fed into the grid. The active power is transmitted in reverse from the main meter of the transformer substation to other transformer substations for consumption, meaning that the main meter of the transformer substation will show reverse active power. Figure 8 As shown in the diagram, at this time, the power flow direction within the distribution area is as follows: part of the power flow from photovoltaic users to the grid flows to other users within the area to meet their load demands, and the remaining part flows to the public grid after being boosted in reverse through the distribution area's main meter and distribution transformer. When the photovoltaic power generation capacity is insufficient to meet all the loads within the distribution area, the power grid still supplies power to the users.

[0165] According to the traditional formula for calculating the comprehensive line loss of a transformer area,

[0166] In 0< < At that time, the power supply of the transformer substation did not include the amount of photovoltaic power generated and fed into the grid within the substation. Comprehensive line loss rate of the transformer area Too small; > hour, <0 indicates a negative line loss.

[0167] Analysis of these three scenarios shows that in areas with distributed photovoltaic power generation users, the comprehensive line loss rate of the area obtained by the traditional line loss rate calculation formula often fails to accurately reflect the actual comprehensive line loss rate of the area, and may even be too low or result in unreasonable negative line losses.

[0168] In transformer substations containing distributed power sources such as photovoltaic (PV) generators, when calculating the substation's overall line loss based on power supply and sales, it is essential to consider the PV generators' grid-connected electricity and the reverse active power from the substation's main meter. These two components are also part of the substation's power supply. The corrected formula for calculating the substation's overall line loss is shown below (considering the transmission loss of PV generators' grid-connected electricity within the substation):

[0169] In the formula, The overall line loss rate for the transformer area; This represents the positive active power of the main meter for the transformer area. This is the sum of the positive active power of all users' meters within the distribution area; It is the sum of the on-grid electricity (reverse active power of photovoltaic user meters) of all photovoltaic users in the distribution area; This refers to the reverse active power of the main meter for the transformer area.

[0170] The beneficial effects of the present invention are as follows: Compared with the prior art, the technical effects of the present invention include: This invention analyzes the operating characteristics of photovoltaic arrays; constructs a photovoltaic system output model; constructs a line loss calculation model for photovoltaic grid connection; analyzes the operating efficiency principle of distribution transformers; and analyzes the impact of distributed photovoltaic grid connection on the line loss of distribution areas. This enables the analysis of the impact of distributed photovoltaic power generation on the line loss of distribution areas and its calculation method, effectively avoiding the shortcomings of existing technologies that do not analyze the impact of distributed photovoltaic power generation on the line loss of distribution areas and their calculation methods.

[0171] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention without departing from the spirit and scope of the present invention. Any modifications or equivalent substitutions should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for optimizing line loss in photovoltaic-driven distribution areas, characterized in that, include: Step 1: Analyze the operating characteristics of the photovoltaic array; Step 2: Construct a photovoltaic system output model; Step 3: Construct a line loss calculation model for photovoltaic grid connection; Step 4: Analyze the principle of distribution transformer operating efficiency.

2. The method for optimizing line loss in photovoltaic power generation according to claim 1, characterized in that, In step 1, the operating characteristics of the photovoltaic array include: The IV equation for a PN junction solar cell is as follows: in, , These are the output current and output voltage of the solar cell during use; , These are the short-circuit current of the solar cell and the reverse saturation current of the PN junction, respectively. It is 1.38×10-23 J / K; For temperature; The temperature is 1.6 × 10⁻¹⁹ C. The operating characteristics of a photovoltaic array also include the solar cell IV characteristic curve, which represents the relationship between the output voltage and output current of the solar cell under a specific temperature and solar irradiance. Several important solar cell parameters can be obtained from the characteristic curve: (1) Short-circuit current; (2) Open-circuit voltage; (3) Maximum power point current; (4) Maximum power point voltage; (5) Maximum power.

3. The method for optimizing line loss in photovoltaic power generation according to claim 2, characterized in that, Step 2 specifically includes: Step 2-1: Photovoltaic system output calculation model; Step 2-2: Analyze the factors affecting the output of the photovoltaic system.

4. The method for optimizing line loss in photovoltaic power generation according to claim 3, characterized in that, In step 2-1, the photovoltaic system output calculation model includes: Defined under reference conditions, I sc V is the short-circuit current of the array. oc V is the open-circuit voltage. m I m The voltage and current at the maximum power point under this condition, and the load current of each photovoltaic cell under the reference condition. It is expressed as follows: When considering the effects of radiation intensity and temperature changes, the load current I As shown in the following formula: Where: R ref T ref These represent the reference values ​​for solar radiation and photovoltaic cell temperature, respectively; α is the temperature coefficient of current change under reference solar irradiance; β is the temperature coefficient of voltage change (V / ℃) under reference solar irradiance; R S This is the series resistance of the photovoltaic module; Series resistance R of photovoltaic array S The formula for calculation is: In the formula: ε represents the material band structure; N p N is the number of photovoltaic array modules connected in parallel; N is the number of photovoltaic array modules connected in series; N s This represents the number of units connected in series in each module of the photovoltaic array; Power of a photovoltaic array under arbitrary solar radiation intensity and temperature As shown in the following formula: From the extremum condition, dP / dV=0, we get: The above equation can be solved iteratively using Newton's method to obtain the optimal operating voltage V corresponding to the maximum power point. max : When |V k+1 -V k <ε|, V max =V k+1 In the above formula: V k+1 and V k These are the (k+1)th and kth iteration values ​​of V, respectively; ε is the iteration precision; P'(V k ) and P"(V k These are the first and second derivatives of P with respect to V in the k-th iteration, respectively. The resulting V... max Substituting into the formula, we can obtain I max Thus, the maximum power P max It can be obtained from the following formula: ； In step 2-2, based on the characteristics of photovoltaic cells and the output calculation model, it can be seen that: (1) The output characteristics of the photovoltaic system change with the change of the light intensity received by the cell surface and the cell temperature. These two factors have a great influence on the photovoltaic output, especially the light intensity, which is the factor with the greatest influence on the photovoltaic output; (2) The electrical parameters of the photovoltaic system, the installation and operation mode, the cleanliness of the cell panel surface, and whether there are scratches will also affect the output.

5. The method for optimizing line loss in photovoltaic-driven distribution areas according to claim 4, characterized in that, In step 3, the algorithms for calculating line losses in the distribution network after the integration of distributed power sources include the improved equivalent resistance method, the improved equivalent capacity method, and the line loss calculation method based on power flow calculation.

6. The method for optimizing line loss in photovoltaic power generation according to claim 5, characterized in that, In step 3, the calculation steps of the improved equivalent resistance algorithm are as follows: A-1: Calculate the required parameters for the headend based on the known parameters of the headend representative day: In the formula, The root mean square power at the beginning of the distribution line represents the daily power. The root mean square voltage at the beginning of the distribution line represents the day. , These represent the active and reactive power at the beginning of the line on a given day. Here, α is the equivalent coefficient, and α is the load factor. When only an ammeter is available at the beginning of the distribution line, the current measured by the representative is: In the formula, The root mean square current represents the current of the day; A-2: Find the root mean square current of the transformer ( ); A-3: Request and ; A-4: Distribution line represents daily bus power loss ( As shown in the following formula: From the above formula, we can obtain: Or it can be expressed as: When distributed generation is connected to the distribution network and has little impact on the network structure and power flow direction, the total bus power loss for the month can be calculated directly based on the line loss power of the representative day. ); In the formula, This refers to the actual number of days in the month. For the total monthly electricity supply, then 。 7. The method for optimizing line loss in photovoltaic-driven distribution areas according to claim 6, characterized in that, In step 3, the improved equivalent capacity method includes the following steps: B-1: Divide the entire computation time into segments; B-2: Calculation of the first end of the distribution network line; In B-2, when the photovoltaic power generation access node is used as the starting point of the distribution line, the equivalent capacity calculation expression for the distribution transformer is: In the formula, , These represent the active and reactive power of distributed photovoltaic power generation, respectively. , These are the active and reactive power of the distribution transformer, respectively. When photovoltaic power generation cannot meet load demand, it is treated as a regular load, and the beginning of the distribution line is taken as the main power node. The equivalent capacity of the photovoltaic power generation node at this time is shown below: Equivalent capacity of distribution transformer for: Line loss is: In the formula, t is the wind power generation operation time. When photovoltaic power generation is the first end of a power distribution line, the equivalent resistance of the line is calculated. When photovoltaic power generation is equivalent to ordinary load, its equivalent capacity is expressed as follows: for: Line loss is: In the formula, The equivalent resistance at the beginning of the circuit; and ; The sum of the power input from photovoltaic power and the power output from the distribution network outlet should meet the power demand of the distribution network, that is: Finally, by adding up the line losses under different conditions, the total line loss can be obtained. In step 3, the distributed generation distribution network calculation method based on power flow calculation includes: C-1: Assuming the power generation curves of the power sources are identical, the active and reactive power calculation expressions for distributed power sources in each hour are as follows: In the formula, , , respectively, are the active and reactive power of the distributed generation in hour t of the representative day; P and Q are the active and reactive energy consumption of the distributed generation in the representative day, respectively. Let be the power allocation factor of the distributed generation at hour t; Voltage representing different times of the day and current It is known that, in the formula The calculation expression is: C-2: Calculate the power at the beginning of the distribution line; C-3: Calculation of distribution transformer node load power; In C-2, assuming that the active and reactive power at the beginning of the distribution network line remains constant per hour, the power at the beginning of the distribution line per hour can be expressed as: In the formula, , These represent the active and reactive power of the distributed generation at hour t on the representative day; , These represent the active and reactive power units supplied to the beginning of the distribution line during the day, respectively. Let be the power distribution coefficient at the beginning of the distribution line in hour t. The calculation expression is: In the formula, , These represent the voltage and current at the beginning of the power distribution line in hour t of the representative day; In C-2, the total power output from the substation bus s and distributed generation to the distribution network in hour t of the day is represented by... After deducting the power loss of the entire power grid, the total load power of the distribution transformer is the total power of the substation bus and distributed generation minus... ; Given that the power loss of the transformer is , In the formula, , These are the active and reactive power of the load on the high-voltage side of distribution transformer i in hour t, respectively. This is the power distribution factor of the distribution transformer.

8. The method for optimizing line loss in photovoltaic power generation according to claim 7, characterized in that, Step 4 specifically includes: Calculate the operating efficiency of the distribution transformer. Furthermore, in step 4, the method for calculating the operating efficiency of the distribution transformer includes: Step 4-1: Calculate the transformer efficiency; Step 4-2: Calculate the transformer operating efficiency.

9. The method for optimizing line loss in photovoltaic power generation according to claim 8, characterized in that, In step 4-1, the transformer efficiency is the ratio of its output power to its input power, where: (1) Transformer output power: The transformer output power is: = = In the formula The transformer output power is expressed in kW. To calculate the current, in A; Rated voltage, V; Power factor; The load factor is %; The rated capacity of the transformer is kW. (2) Transformer input power: The transformer input power is: = + + In the formula For transformer no-load loss (i.e., iron loss), kW; The value is kW, representing the transformer load loss (i.e., copper loss). because = In the formula The load loss of the transformer at its rated current, kW but = + + = + + (3) Optimal efficiency and load factor of the transformer: The transformer efficiency is: = = To find the extreme value using the above formula, when... When the transformer efficiency reaches its maximum, i.e., the average load factor of the distribution transformer. = At that time, the transformer efficiency reaches its maximum; In step 4-2, the formula for calculating the transformer operating efficiency is: In the formula For transformers in Load factor (maximum load rate) within the time interval.

10. The method for optimizing line loss in photovoltaic-driven distribution areas according to claim 9, characterized in that, The method for optimizing line loss in photovoltaic power distribution areas also includes: Step 5: Analyze the impact of distributed photovoltaic (PV) grid connection on line losses in the distribution area; Step 5 specifically includes: Construct a theoretical calculation model for the impact of distributed photovoltaic grid connection on line losses in transformer substations; Methods for constructing theoretical calculation models of the impact of distributed photovoltaic (PV) grid connection on line losses in transformer substations include: The revised formula for calculating the comprehensive line loss of a transformer substation is shown below: In the formula, The overall line loss rate for the transformer area; This represents the positive active power of the main meter for the transformer area. This is the sum of the positive active power of all users' meters within the distribution area; This represents the sum of the electricity generated by all photovoltaic users within the designated area and fed into the grid. This refers to the reverse active power of the main meter for the transformer area.

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