Three-phase unbalance optimization method and system for distributed photovoltaic access

Abstract

The present invention discloses a method and system for optimizing the three-phase imbalance of a substation using distributed photovoltaic access. The method comprises the following steps: the intelligent fusion terminal periodically sends a request instruction to the intelligent plastic shell switch and the photovoltaic grid-connected switch; the intelligent plastic shell switch sends the apparent power of the shunt node, and the photovoltaic grid-connected switch reads the real-time power of the photovoltaic inverter and sends it up; the intelligent fusion terminal uses an intelligent optimization algorithm to analyze and process the received apparent power of the shunt node and the real-time power of the photovoltaic inverter, obtains the optimal value of the adjustable photovoltaic three-phase inverter power, and sends a three-phase inverter adjustment request instruction to the photovoltaic grid-connected switch; the photovoltaic grid-connected switch receives the three-phase inverter adjustment request instruction and sets the associated photovoltaic inverter, and the photovoltaic inverter performs inverter output power adjustment. The present invention can ensure the three-phase balance of the substation side area and the line between the substation side and the user terminal, and has the advantages of systematicity, globality and economy.

Description

Technical Field

[0001] The present invention relates to the field of intelligent power distribution technology, and in particular to a method and system for optimizing three-phase imbalance in a distribution area using distributed photovoltaic access. Background Art

[0002] At present, low-voltage photovoltaic access only provides distributed power at the end of the substation. In fact, photovoltaic access can regulate the energy of the line through the inverter to achieve power quality management at the end of the substation, such as power factor, three-phase imbalance, etc.

[0003] The low-voltage substation usually supplies power to users in a three-phase four-wire system after being stepped down by a 10kV / 400V transformer. It is a power supply network that uses a mixture of three-phase production power and single-phase loads. Due to the unpredictability of the growth of single-phase loads in the substation, the random phase access of new user loads, the differences in the use time of power equipment and the instability of seasonal power consumption, the three-phase power load deviates from the early power planning, resulting in three-phase imbalance in the substation. The manifestation of three-phase imbalance is that the amplitudes of the three-phase current (or voltage) in the power system are inconsistent, and the amplitude difference exceeds the specified range. The three-phase imbalance in the substation will cause transformer and line losses, increase neutral line losses, and significantly reduce the efficiency of the motor in the line. It will also increase the temperature of the motor and generate reactive power losses. If the motor runs in a three-phase imbalance state for a long time, it will have an adverse effect on the life of the motor and other related linkage equipment.

[0004] Power supply companies take various measures to solve the three-phase imbalance problem in distribution stations. Common methods include installing static capacitors or SVG devices on the transformer side and installing three-phase phase-changing switches at user load nodes. Installing capacitors on the transformer side cannot cope with the change of single-phase load access, while installing SVG devices can cope with the rapid change of load access. However, the three-phase imbalance control range of both is limited to the distribution station transformer side area (see Figure 1 The area I is very small and has great limitations. Install a phase-changing switch at the user's end load to quickly switch the phase of the single-phase load to ensure the area between the user's end and the transformer side (see Figure 1 The three-phase load balance of area II) is achieved through the method, which has the advantages of being systematic and global, but the cost of the phase-changing switch is relatively high. If each user load is equipped with a phase-changing switch, the construction cost of the substation will be very high, which is not economical. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method and system for optimizing the three-phase imbalance of the substation area using distributed photovoltaic access. In the method and system, the real-time power of the substation side area is automatically monitored by the SVG device installed on the substation transformer side, and the power switching transfer of the area is performed through the IGBT power electronic device to ensure the three-phase balance of the substation side area; on the other hand, combined with the measured apparent power of the shunt node and the real-time power generation power of the photovoltaic inverter at the household terminal in the lower area of ​​the shunt node, the intelligent fusion terminal on the substation transformer side calculates the power parameters of the household terminal photovoltaic required for three-phase inversion, and sends the photovoltaic inversion instruction to the relevant grid-connected switch, and finally the photovoltaic inverter executes the instruction to perform the inversion output, offsetting the three-phase unbalanced power demand of the load in the area, thereby ensuring the three-phase balance of the large-scale line between the substation side and the user terminal. The system and method have the advantages of systematicity and globality. In addition, the photovoltaic inverter adopts a three-phase independently adjustable photovoltaic inverter, and the other equipment involved are all existing equipment in the low-voltage substation area, and no additional investment is required. The system and method also have the advantages of economy.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] The method for optimizing three-phase imbalance in a distribution area using distributed photovoltaic access is characterized by comprising the following steps:

[0008] The intelligent fusion terminal periodically sends request instructions to the intelligent molded case switch and photovoltaic grid-connected switch;

[0009] The intelligent molded case switch sends the apparent power of the branch node according to the received request instruction, and the photovoltaic grid-connected switch reads the associated photovoltaic inverter real-time power according to the received request instruction and sends it up;

[0010] The intelligent fusion terminal uses an intelligent optimization algorithm to analyze and process the received branch node apparent power and photovoltaic inverter real-time power, obtains the optimal value of the adjustable photovoltaic three-phase inverter power, and sends a three-phase inverter adjustment request instruction to the photovoltaic grid-connected switch;

[0011] The photovoltaic grid-connected switch receives the three-phase inverter regulation request instruction and sets the associated photovoltaic inverter, and the photovoltaic inverter performs inverter output power regulation to ensure the three-phase balance of the line between the transformer side area of ​​the main grid station and the user terminal.

[0012] The intelligent optimization algorithm specifically includes the following steps:

[0013] Design the objective function, the objective function form is as follows:

[0014]

[0015] st

[0016]

[0017]

[0018] (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3

[0019]

[0020] 1≥r>0

[0021] Where S is the three-phase inverter regulation power parameter of the household terminal photovoltaic inverter, s pt_max Indicates the total power generated by the photovoltaic access at this moment, which can be directly read from the photovoltaic inverter; mon_k Indicates the apparent power from the branch node of the intelligent molded case switch; Represents the real-time photovoltaic power from the photovoltaic grid-connected switch; s dmd_k Indicates the apparent power demand of the load in the lower-level area of ​​the branch; k = 1, 2, 3 represent the load connected to phases A, B, and C respectively, and r represents the single-phase regulation inversion factor of the photovoltaic inverter;

[0022] The objective function is converted into the normal vector projection of a point in three-dimensional space onto a plane by using the method of spatial analytic geometry, wherein the point in three-dimensional space is the apparent power demand of the load of phases A, B, and C, and the plane is the inverter regulation power parameter plane of the photovoltaic inverter without the single-phase regulation inverter factor constraint;

[0023] Determine whether the normal vector projection point satisfies the plane single-phase regulation inverter factor constraint condition (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3, if it is satisfied, the current projection point is the optimal value of the adjustable photovoltaic three-phase inverter power; otherwise, the minimum value of the projection point to the single-phase regulation inverter factor constraint area Π is the optimal value of the adjustable photovoltaic three-phase inverter power.

[0024] Preferably, the periodicity is 8 to 15 seconds.

[0025] Preferably, the intelligent fusion terminal communicates with the intelligent molded case switch and the photovoltaic grid-connected switch respectively via HPLC.

[0026] Preferably, the photovoltaic grid-connected switch and the photovoltaic inverter communicate via RS485.

[0027] Preferably, the method further comprises the following step: using an SVG device to automatically adjust the three-phase balance of the transformer-side area of ​​the main power grid.

[0028] A three-phase unbalanced optimization system using low-voltage distributed photovoltaic access includes an intelligent fusion terminal arranged in a transformer-side area, an intelligent molded case switch arranged on a low-voltage branch node, and a photovoltaic grid-connected switch and a photovoltaic inverter arranged at household terminals in a lower area of ​​the low-voltage branch node. The intelligent fusion terminal is respectively connected to the intelligent molded case switch and the photovoltaic grid-connected switch through HPLC communication; the photovoltaic grid-connected switch and the photovoltaic inverter are connected through RS485 communication.

[0029] Preferably, the intelligent fusion terminal is integrated with an HPLC head-end module, and the photovoltaic grid-connected switch and the intelligent molded case switch are both integrated with an HPLC tail-end module compatible with the HPLC head-end module.

[0030] Preferably, the photovoltaic inverter is a three-phase independently adjustable photovoltaic inverter.

[0031] Preferably, it also includes an SVG device installed in the transformer-side area, which is used to automatically adjust the three-phase balance of the transformer-side area of ​​the main power grid.

[0032] Based on the above technical solution, the beneficial effects of the present invention are:

[0033] 1. The present invention automatically monitors the real-time power of the transformer side area through the SVG device on the transformer side of the station area, and performs power switching transfer in the area through the IGBT power electronic device, ensuring the transformer side area (see Figure 1 On the other hand, combined with the measured apparent power of the branch node and the real-time power generation of the photovoltaic inverter at the household terminal in the lower area of ​​the branch node, the intelligent fusion terminal on the transformer side of the station area calculates the power parameters of the three-phase inverter required for the household terminal photovoltaic, and sends the photovoltaic inverter command to the relevant grid-connected switch. Finally, the photovoltaic inverter executes the command to perform the inverter output, offsetting the unbalanced three-phase power demand of the load in the area, thereby ensuring the large-scale line between the station transformer side and the user terminal (see Figure 1 The three-phase balance of region II) has the advantages of systematicity and globality;

[0034] 2. The photovoltaic inverter of the present invention adopts a three-phase independently adjustable photovoltaic inverter, and other equipment involved are existing equipment in the low-voltage area, and no additional equipment investment is required, which has the advantage of economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a structural block diagram of a three-phase unbalanced optimization system for a substation using distributed photovoltaic access in an embodiment;

[0036] Figure 2 is a flow chart of a method for optimizing three-phase imbalance in a substation using distributed photovoltaic access in an embodiment;

[0037] Figure 3 is a collaborative control flow chart of a platform-side intelligent fusion terminal in an embodiment;

[0038] Figure 4 is a collaborative control flow chart of a photovoltaic grid-connected switch in an embodiment;

[0039] Figure 5 is a collaborative control flow chart of a low-voltage branch intelligent molded case switch in a substation area in an embodiment;

[0040] Figure 6 is a schematic diagram of a projection I of a regional load on a photovoltaic inverter plane in an embodiment;

[0041] Figure 7 is a schematic diagram of a projection II of a regional load on a photovoltaic inverter plane in an embodiment;

[0042] Figure 8 is a schematic diagram of selecting a regional optimal photovoltaic inverter vector in an embodiment;

[0043] Fig. 9 It is a schematic diagram of the projection of the projection point in the photovoltaic inverter plane to the edge projection of the single-phase regulation inverter factor constraint triangle area. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0045] like Figure 1 As shown, this embodiment provides a three-phase imbalance optimization system for a substation area using distributed photovoltaic access, including an SVG device, an intelligent fusion terminal, an intelligent molded case switch, a photovoltaic grid-connected switch, a photovoltaic inverter, an HPLC head-end module, and an HPLC tail-end module. On the one hand, the SVG device on the substation transformer side automatically monitors the real-time power of the substation side area, and performs power switching and transfer in the area through IGBT power electronic devices to ensure the three-phase balance of the substation side area (see Figure 1 On the other hand, by combining the measured apparent power of the branch node and the real-time power generation of the photovoltaic inverter at the household end in the lower area of ​​the branch node, the intelligent fusion terminal on the transformer side of the substation calculates the power parameters of the three-phase inverter required for the household end photovoltaic, and sends the photovoltaic inverter command to the relevant grid-connected switch. Finally, the photovoltaic inverter executes the command to perform the inverter output to offset the unbalanced three-phase power demand of the load in the area, thereby ensuring the large-scale line between the transformer side and the user end (see Figure 1 The three-phase balance of region II) is referenced Figure 2The photovoltaic inverter in this system is a three-phase independent adjustable photovoltaic inverter. Other equipment involved are existing equipment in the low-voltage area and do not require additional investment. The detailed description is as follows:

[0046] The SVG device is a mature integrated equipment for harmonic control, reactive power compensation, and three-phase unbalance optimization. It is installed inside the transformer cabinet near the transformer in the substation area. It measures the electrical operating conditions of the transformer in real time, and uses IGBT power electronic devices to transfer and compensate power near the measurement point to achieve three-phase balance of the line on the transformer side.

[0047] The HPLC head-end module is installed on the intelligent fusion terminal. There is only one HPLC head-end module in the HPLC communication network of a substation to realize the communication message aggregation, forwarding and communication scheduling of the entire substation. If the HPLC head-end module does not work, the HPLC communication network of the substation will not be able to communicate. The HPLC tail-end module is installed on each intelligent molded case switch and photovoltaic grid-connected switch to realize the communication between them and the intelligent fusion terminal. The HPLC tail terminal modules between the intelligent molded case switch and the photovoltaic grid-connected switch cannot communicate directly and need to be forwarded through the HPLC head-end module. The two types of modules, the HPLC head-end module and the HPLC tail-end module, work together to communicate with each other based on the existing power lines inside the substation, without the need for additional engineering construction.

[0048] The intelligent fusion terminal is installed inside the transformer cabinet near the transformer in the substation area. It integrates telemetry, telesignaling, centralized meter reading, substation area topology, statistics, wireless communication, and HPLC communication functions. It is the core brain of the low-voltage distribution substation area as an autonomous unit. The intelligent fusion terminal interacts with the intelligent molded case switch and photovoltaic grid-connected switch in the substation area through the HPLC head-end module. On the one hand, it broadcasts requests to send instructions for the measured power of the branch node and the real-time photovoltaic power. After receiving the apparent power of the branch measurement point from the intelligent molded case switch and the real-time photovoltaic power generation forwarded from the photovoltaic grid-connected switch, the intelligent fusion terminal will calculate the total apparent power consumed by the load in the lower-level area of ​​the branch node where the intelligent molded case switch is located according to the substation area topology. On the other hand, according to the three-phase unbalanced intelligent optimization algorithm, the optimal adjustable photovoltaic three-phase inverter power of the household terminal in the lower-level area is calculated, and the corresponding photovoltaic inverter inverter output power is achieved through HPLC communication and photovoltaic grid-connected switch coordinated control to compensate for the load imbalance in the area. The working control process of the intelligent fusion terminal is as follows: Figure 3 As shown:

[0049] 1) The intelligent fusion terminal will start the three-phase unbalance optimization task in the substation every 10 seconds, and broadcast the instructions of measuring the apparent power of the branch nodes and the real-time power generation of the household photovoltaic power in the entire substation through the HPLC head-end module;

[0050] 2) When receiving the branch node from the intelligent molded case switch, the apparent power s is measured in real time mon_k and real-time photovoltaic power generation from photovoltaic grid-connected switches After that, the intelligent fusion terminal will calculate the total apparent power consumed by the load in each low-voltage branch area of ​​the substation in real time according to the substation topology.

[0051] 3) According to the three-phase unbalanced intelligent optimization algorithm, the intelligent fusion terminal calculates the optimal value of the adjustable photovoltaic three-phase inverter power at the household terminal in the lower-level area of ​​the low-voltage branch, and then sends it to the corresponding photovoltaic grid-connected switch through the HPLC head-end module. Finally, the photovoltaic inverter associated with the photovoltaic grid-connected switch adjusts the inverter output power.

[0052] Among them, the three-phase unbalanced intelligent optimization algorithm uses the method of three-dimensional space analytical geometry to solve the nonlinear optimization problem of distributed photovoltaic three-phase inverter adjustment power vector based on the three-phase unbalanced management of the substation. The mathematical function of the optimization problem is as follows:

[0053]

[0054] st

[0055]

[0056]

[0057] (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3

[0058]

[0059] 1≥r>0

[0060] Where S is the three-phase inverter regulation power parameter of the household terminal photovoltaic inverter, s pt_max Indicates the total power generated by the photovoltaic access at this moment, which can be directly read from the photovoltaic inverter; mon_k Indicates the apparent power from the branch node of the intelligent molded case switch; Represents the real-time photovoltaic power from the photovoltaic grid-connected switch; s dmd_k It represents the apparent power demand of the load in the lower-level area of ​​the branch; k=1, 2, 3 represent the load connected to phases A, B, and C respectively.

[0061] r represents the single-phase regulation inversion factor of the three-phase independent adjustable photovoltaic inverter, which indicates the maximum ratio of the inter-phase switching power to the average power generation of the three-phase independent adjustable photovoltaic inverter, and is an inherent property of the three-phase independent adjustable photovoltaic inverter. For example: the power generation of the photovoltaic inverter is 6kW at this moment, r is 0.8, then the default inverter power of each phase is 2kW, and the maximum power that can be switched between phases is 1.6kW, so the minimum power generation of a phase is 0.4kW and the maximum is 5.2kW.

[0062] The above nonlinear constrained optimization problem is difficult to solve. Since the vector S involved is three-dimensional, the objective function can be transformed into the normal vector projection of the midpoint (the apparent power demand of the load of phases A, B, and C) in the three-dimensional space to the plane (the inverter adjustment power parameter plane of the photovoltaic inverter without the single-phase adjustment inverter factor constraint) through the method of spatial analytic geometry.

[0063]

[0064] If the normal vector projection point satisfies the single-phase regulation inverter factor constraint condition of the plane (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3Then the projection point is the optimal solution, that is, the target parameter S of the adjustable three-phase inverter power opt =S, such as Figure 6 shown.

[0065] If the projection point S does not satisfy the single-phase regulation inverter factor constraint of the plane (refer to Figure 7 ), then the minimum value of the projection point to the single-phase regulation inverter factor constraint region Π is the optimal solution, that is, the adjustable three-phase inverter power target parameter (reference Figure 8 ). Since the single-phase regulation inverter factor constraint region Π is a triangular region, the shortest distance connection point from the projection point to the region must be in the set of perpendicular mapping points to the edge of the triangle {D i |i=1,2,3}(reference Fig. 9 ). Then select three vertical mapping points that satisfy the mapping point in the single-phase regulation inverter factor constraint area Λ and have the shortest distance {h i |h i =h opt ,D i ∈Λ} is the optimal solution, which is the target parameter of the adjustable three-phase inverter power. The specific formula is:

[0066]

[0067]

[0068]

[0069] Λ={D i |D i ∈Π, i=1,2,3}

[0070] h opt =min{h i |h i =|SD i |, D i ∈Λ}

[0071] S opt ={D i |h i =h opt ,h i =|SD i |, D i ∈Λ}

[0072] The intelligent molded case switch is installed in each branch box in the substation to realize the functions of monitoring the electrical working conditions (voltage, current, frequency, apparent power, etc.) of the branch node and switch control. After receiving the request from the intelligent fusion terminal to send the node measurement power instruction, the intelligent molded case switch will send the real-time apparent power of the branch node to the intelligent fusion terminal through the HPLC tail module. The working control process of the intelligent molded case switch is as follows: Figure 5 shown.

[0073] 1) The HPLC tail module of the intelligent molded case switch will monitor in real time whether there is an instruction from the intelligent fusion terminal. When receiving an instruction, it will trigger task processing in time;

[0074] 2) If the received instruction is a request to send the real-time apparent power of the branch node, the intelligent molded case switch will measure the apparent power of the branch node at that moment and send it to the intelligent fusion terminal on the station transformer side through the HPLC tail module;

[0075] 3) If other instructions are received, the smart molded case switch will ignore them or perform other business operation processes (not within the scope of this patent).

[0076] The photovoltaic grid-connected switch is installed inside the photovoltaic grid-connected box, etc. It communicates with the intelligent fusion terminal through the HPLC tail module on the one hand, and communicates with the nearby photovoltaic inverter through RS485 on the other hand. The photovoltaic grid-connected switch has the functions of electrical monitoring of the photovoltaic grid-connected point, switch control and interaction with related photovoltaic inverters. The working control process of the photovoltaic grid-connected switch is as follows: Figure 4 As shown:

[0077] 1) The HPLC tail module of the photovoltaic grid-connected switch will monitor in real time whether there is an instruction from the intelligent fusion terminal. When receiving an instruction, it will trigger task processing in time;

[0078] 2) If the received instruction is a request to upload the real-time photovoltaic power, the photovoltaic grid-connected switch obtains the real-time photovoltaic power generation at that moment from the associated photovoltaic inverter through RS485, and sends it to the intelligent fusion terminal on the transformer side through the HPLC tail module;

[0079] 3) If the received instruction is a request to adjust the photovoltaic three-phase inverter output power, the photovoltaic grid-connected switch sets the three-phase inverter power of the associated photovoltaic inverter through RS485, and finally the photovoltaic inverter performs three-phase inverter output adjustment to compensate for the load imbalance in the lower-level area, thereby ensuring the balance of the large-scale line from the transformer side to its upper branch node;

[0080] 4) If other instructions are received, the photovoltaic grid-connected switch will ignore them, or perform other business operation processes (not within the scope of this patent).

[0081] The above description is only a preferred implementation of the method and system for optimizing the three-phase imbalance of the substation area using distributed photovoltaic access disclosed by the present invention, and is not intended to limit the protection scope of the embodiments of this specification. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the embodiments of this specification shall be included in the protection scope of the embodiments of this specification.

Claims

1. A three-phase unbalanced optimization method for distributed photovoltaic access, characterized in that: The steps include: The intelligent fusion terminal periodically sends request instructions to the intelligent molded case switch and photovoltaic grid-connected switch; The intelligent molded case switch sends the apparent power of the branch node according to the received request instruction, and the photovoltaic grid-connected switch reads the photovoltaic real-time power of the associated photovoltaic inverter according to the received request instruction and sends it up; The intelligent fusion terminal uses an intelligent optimization algorithm to analyze and process the received branch node apparent power and photovoltaic inverter real-time power, obtains the optimal value of the adjustable photovoltaic three-phase inverter power, and sends a three-phase inverter adjustment request instruction to the photovoltaic grid-connected switch; The photovoltaic grid-connected switch receives the three-phase inverter adjustment request instruction and sets the associated photovoltaic inverter, and the photovoltaic inverter performs inverter output power adjustment to ensure the three-phase balance of the line between the transformer side area of ​​the main grid station and the user terminal, wherein the intelligent optimization algorithm specifically includes the following steps: Design the objective function, the objective function form is as follows: (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3 1≥r>0 Where S is the three-phase inverter regulation power parameter of the household terminal photovoltaic inverter, s pt_max Indicates the total power generated by the photovoltaic access at this moment, which can be directly read from the photovoltaic inverter; mon_k Indicates the apparent power from the branch node of the intelligent molded case switch; Represents the real-time photovoltaic power from the photovoltaic grid-connected switch; s dmd_k Indicates the apparent power demand of the load in the lower-level area of ​​the branch; k = 1, 2, 3 represent the load connected to phases A, B, and C respectively, and r represents the single-phase regulation inversion factor of the photovoltaic inverter; The objective function is converted into the normal vector projection of a point in three-dimensional space onto a plane by using the method of spatial analytic geometry, wherein the point in three-dimensional space is the apparent power demand of the load of phases A, B, and C, and the plane is the inverter regulation power parameter plane of the photovoltaic inverter without the single-phase regulation inverter factor constraint; Determine whether the normal vector projection point satisfies the plane single-phase regulation inverter factor constraint condition (1-r)*s pt_max / 3≤s k ≤(1+2r)*s pt_max / 3, if it is satisfied, the current projection point is the optimal value of the adjustable photovoltaic three-phase inverter power; otherwise, the minimum value of the projection point to the single-phase regulation inverter factor constraint area Π is the optimal value of the adjustable photovoltaic three-phase inverter power.

2. The method for optimizing three-phase imbalance in a distributed photovoltaic access area according to claim 1 is characterized in that: The periodicity is 8 to 15 seconds.

3. The method for optimizing three-phase imbalance in a distributed photovoltaic access area according to claim 1 is characterized in that: The intelligent fusion terminal communicates with the intelligent molded case switch and the photovoltaic grid-connected switch respectively through HPLC.

4. The method for optimizing three-phase imbalance in a distribution area using distributed photovoltaic access according to claim 1, characterized in that: The photovoltaic grid-connected switch and the photovoltaic inverter communicate via RS485.

5. The method for optimizing three-phase imbalance in a distribution area using distributed photovoltaic access according to claim 1, characterized in that: The method also includes the following steps: using an SVG device to automatically adjust the three-phase balance of the transformer side area of ​​the main power grid.

6. A system using the method for optimizing the three-phase imbalance in a distributed photovoltaic access area in claim 1, characterized in that: It includes an intelligent fusion terminal installed in the transformer side area, an intelligent molded case switch installed on the low-voltage branch node, and a photovoltaic grid-connected switch and a photovoltaic inverter installed at the household terminal in the lower area of ​​the low-voltage branch node. The intelligent fusion terminal is connected to the intelligent molded case switch and the photovoltaic grid-connected switch through HPLC communication; the photovoltaic grid-connected switch and the photovoltaic inverter are connected through RS485 communication.

7. The system according to claim 6, characterized in that The intelligent fusion terminal is integrated with an HPLC head-end module, and the photovoltaic grid-connected switch and the intelligent molded case switch are both integrated with an HPLC tail-end module that is compatible with the HPLC head-end module.

8. The system according to claim 6, characterized in that The photovoltaic inverter adopts a three-phase independently adjustable photovoltaic inverter.

9. The system according to claim 6, characterized in that It also includes an SVG device installed in the transformer-side area, which is used to automatically adjust the three-phase balance in the transformer-side area of ​​the main power grid.

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