A Distributed Photovoltaic Grid-Connected Coordinated Control Method Based on Converged Terminals

Abstract

This invention proposes a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal. The photovoltaic inverter is connected to the distributed photovoltaic acquisition and monitoring unit via a distributed photovoltaic communication interface adapter. The distributed photovoltaic acquisition and monitoring unit communicates with the intelligent fusion terminal of the distribution area and accepts the control of the intelligent fusion terminal to realize rigid control / flexible adjustment of the grid connection and disconnection of distributed photovoltaic equipment. The intelligent fusion terminal of the distribution area collects data on the operation and grid connection status of each grid connection point in real time, including photovoltaic users, and realizes distributed photovoltaic overvoltage management and / or photovoltaic backfeed management in low-voltage distribution areas based on edge computing.

Description

Technical Field

[0001] This invention relates to the field of distributed photovoltaic power generation grid connection technology, and in particular to a distributed photovoltaic grid connection coordination control method based on a fusion terminal. Background Technology

[0002] Low-voltage distributed photovoltaic (PV) systems are typically connected to the grid via 380V / 220V voltage levels. 380V is a three-phase connection, while 220V is a single-phase connection. Most distributed PV systems are rooftop PV systems, and their grid connection / off-grid status, active power, and reactive power are uncontrollable, resulting in weak "observable-measurable-adjustable-controllable" capabilities. Specifically:

[0003] Observable: Displays the location and status information of photovoltaic power sources in the power grid business system.

[0004] Measurable: The relevant status information of the photovoltaic power source can be uploaded to the intelligent integrated terminal in real time and sent to the distribution automation master station system.

[0005] Adjustable: The power of the photovoltaic inverter can be adjusted locally and remotely.

[0006] Controllable: The distribution automation master station system and intelligent integrated terminal can control the status of photovoltaic inverters.

[0007] Low-voltage distributed photovoltaic (PV) systems suffer from problems such as "decentralization, arbitrariness, and disorder" in grid connection. Distributed PV systems are generally user assets, with diverse inverter communication interfaces and numerous proprietary protocols, making supervision difficult. Due to disordered grid connection, distributed PV grid connection can easily cause problems such as reverse overload in the distribution area, high voltage, and excessive line loss.

[0008] With the large-scale integration of distributed photovoltaic (PV) power into the distribution network, the integration is characterized by disorder, intermittency, randomness, and fluctuation in time and space. This leads to localized and overall random differences in power quality issues across distribution areas, and in the temporal dimension, complex and variable situations such as the same location exceeding upper and lower limits at different times. Traditional control models relying on substation capacitor switching and adjusting transformer tap positions are insufficient to meet the requirements of the new power system. There is an urgent need to deepen the grid-based autonomy of distribution areas, and through reliable, flexible, and intelligent overall management, precisely address dynamically changing voltage quality issues in a categorized manner. Summary of the Invention

[0009] To accelerate the rapid advancement of county-wide photovoltaic (PV) projects while strengthening the safety, orderliness, measurability, and controllability of distributed PV grid connection, this invention aims to achieve safe access management and control of distributed PV by collecting and coordinating grid connection data from distributed PV users, and through "cloud-edge" interaction between the cloud master station and the fusion terminal, as well as "edge-end" interaction between the fusion terminal and the PV inverter. This avoids disorderly grid connection, solves problems such as voltage exceeding limits, harmonic exceedances, low power factor, and reverse overload of equipment, and reduces the impact of distributed PV on the low-voltage distribution network.

[0010] The design objectives of this invention include:

[0011] (1) Realize IoT sensing of key equipment in digital power distribution network through integrated terminal communication interface.

[0012] (2) Distributed photovoltaic monitoring and policy control are realized through edge computing capabilities based on fusion terminals.

[0013] The present invention specifically adopts the following technical solution:

[0014] A distributed photovoltaic grid-connected coordinated control method based on fused terminals:

[0015] The photovoltaic inverter is connected to the distributed photovoltaic acquisition and monitoring unit via a distributed photovoltaic communication interface adapter; the distributed photovoltaic acquisition and monitoring unit communicates with the intelligent integrated terminal of the distribution area and accepts the control of the intelligent integrated terminal of the distribution area to realize the rigid control / flexible adjustment of the grid connection and disconnection of the distributed photovoltaic equipment;

[0016] The intelligent integrated terminal of the distribution area collects data on the operation and grid connection status of each grid-connected point, including photovoltaic users, in real time, and realizes distributed photovoltaic overvoltage management and / or photovoltaic backfeed management in the low-voltage distribution area based on edge computing.

[0017] Furthermore, the distributed photovoltaic overvoltage mitigation specifically includes:

[0018] Based on the PV curve and QV curve, when the voltage exceeds the limit, if the current inverter reactive power support adjustment is available, the inverter reactive power adjustment is executed first. If the voltage still exceeds the limit, then the PV active power adjustment is executed.

[0019] The reactive power regulation specifically refers to:

[0020] When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by referring to the QV curve diagram based on the current over-limit voltage Ui. This is then sent through the smart integration terminal of the distribution area to limit the inverter's reactive power to Qout.

[0021] Furthermore, the specific adjustment strategies for reactive power regulation include:

[0022] Set the coarse adjustment voltage threshold Ustep1 and adjustment count Cnt1; set the fine adjustment threshold Ustep2, adjustment count Cnt2, and adjustment time interval Tstep;

[0023] Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, look up the QV curve, obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command;

[0024] Based on the current over-limit voltage value - fine adjustment Ustep2 as Ui, look up the QV curve, obtain the adjustable Qout value, issue the current fine adjustment Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the reactive power adjustment process.

[0025] If the voltage at the grid connection point still exceeds the limit, then the PV active power regulation of the adjustable inverter will be executed.

[0026] Furthermore, the active power regulation is as follows:

[0027] When the photovoltaic exceeds the limit, the target voltage Ui is set by decreasing the coarse or fine adjustment threshold at the current over-limit voltage. The active power Pout is calculated by looking up the PV curve diagram and sent through the intelligent integration terminal of the distribution area to limit the active power of the inverter to Pout.

[0028] The target voltage continues to decrease until the set minimum voltage is reached. If the phase voltage value cannot be lowered, a trip command is issued to the photovoltaic switch, causing the photovoltaic circuit breaker at the inverter grid connection point to trip.

[0029] Furthermore, the specific regulation strategy for active power regulation includes:

[0030] Set the coarse adjustment voltage threshold Ustep1 and adjustment count Cnt1; fine adjustment threshold Ustep2 and adjustment count Cnt2; adjustment time interval Tstep;

[0031] Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, look up the PV curve, obtain the expected power generation Pout value, issue the current coarse adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command.

[0032] Based on the current over-limit voltage value - fine adjustment Ustep2 as Ui, look up the PV curve, obtain the expected power generation Pout value, issue the current fine adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the active power regulation process.

[0033] To prevent frequent adjustments, the start adjustment setpoint is set to 236V±1%. Adjustment will be initiated when the currently collected voltage exceeds the limit.

[0034] If the PV curve does not exist, then switch to a coarse-fine adjustment strategy that adjusts by the ratio of coarse and fine adjustment.

[0035] The coarse-tuning and fine-tuning strategies are as follows:

[0036] Set the coarse adjustment threshold Pstep1 and adjustment count CNt1; fine adjustment threshold Pstep2 and adjustment count CNt2; adjustment time interval Tstep.

[0037] Based on the current active power P value - Pstep1, issue the current coarse adjustment command. After a time interval Tstep, repeat the coarse adjustment Cnt1 times, and then switch to the fine adjustment command.

[0038] Based on the current active power P value - Pstep2, issue the current fine-tuning command. After a time interval Tstep, repeat the coarse-tuning Cnt2 times and then end the coarse-tuning and fine-tuning process.

[0039] Furthermore, by recording and analyzing the historical curve relationships of grid connection voltage, current, active power, and reactive power at the grid connection point, the PV curve and QV curve of distributed photovoltaic power generation are formed. By inputting the overvoltage V value to be controlled for distributed photovoltaic power generation, the predicted input P or Q value affected by the grid is calculated.

[0040] Furthermore, for photovoltaic inverters in the transformer substation operating in MPPT mode:

[0041] The intelligent integrated terminal of the distribution area periodically collects the output voltage, current, active power and reactive power data of the photovoltaic inverter, and periodically records the historical curve data every day.

[0042] Based on data from recent days, a curve showing the relationship between photovoltaic voltage access point voltage U and output power P was generated through search and interpolation methods, thus forming a PV relationship curve.

[0043] At the sampling time, the photovoltaic active power Pi is recorded, and the maximum value of the three-phase phase voltage is taken as the voltage Vi;

[0044] Normalization processing is performed, with Pi / PN and Vi / 220 used as the normalized sampled record values ​​for the inverter;

[0045] By discretizing the data, the measurement points are accumulated in different time periods to form and store the PV relationship curve of the same day.

[0046] For the PV curves of the past seven days, the three-day curve with the smallest covariance is selected, and the average value of the V value of the three-day curves is taken as the PV curve trajectory diagram of the inverter operation.

[0047] Furthermore, for inverters with adjustable reactive power in the distribution area, a trigger or fixed interval is set for a specified number of days to collect QV data and conduct impact analysis during peak photovoltaic power generation periods, including the following process:

[0048] Reactive power control commands are issued sequentially from Q=0 to QN, with a reactive power adjustment amount of Q+=0.1×QN;

[0049] The intelligent integrated terminal of the distribution area collects output voltage, current, active power, and reactive power data of the photovoltaic inverter, records the average U value collected at the current reactive power Q level, and generates a QV test curve, which is added to the QV curve library of the corresponding inverter.

[0050] Methods for generating QV curves include:

[0051] At the moment of reactive power adjustment, record the photovoltaic reactive power Qi, and take the maximum value of the three-phase voltage as the voltage Vi;

[0052] After normalization, calculate Qi / QN, where QN is the maximum adjustable reactive power of the photovoltaic system, and Vi / 220 is the normalized sampled record value of the inverter.

[0053] Store the QV test curve for this experiment;

[0054] For the QV curves of the past seven days, the curves with the smallest covariance over the past three days are selected, and the average V value is taken as the QV curve trajectory diagram of the inverter operation.

[0055] Furthermore, the regulation strategy for photovoltaic backflow control includes:

[0056] Using a fixed time interval as the scheduling cycle for the delay strategy, the load rate of the distribution transformer, the total active power, and the active power of the inverters at each grid connection point are repeatedly acquired.

[0057] When the total active power of the distribution transformer is less than 0 and the load rate of the distribution area is greater than or equal to 80%, it is determined that photovoltaic backfeed has occurred and reverse heavy overload has occurred. At this time, the intelligent integrated terminal of the distribution area adjusts the active power of photovoltaic power generation of all inverters in sequence by 5% and sends the adjustment command to each inverter.

[0058] After one delay strategy scheduling cycle, it is determined again whether a reverse heavy overload has occurred. If a reverse heavy overload still occurs, the gradient limit active power adjustment process continues.

[0059] If the total active power of the distribution transformer is greater than 0 and the load rate of the distribution area is greater than or equal to 2%, then the photovoltaic reverse overload return is determined. At this time, the integrated terminal adjusts the photovoltaic power generation active power of all inverters in sequence by 5% increment and sends the adjustment command to each inverter.

[0060] Furthermore, the intelligent integrated terminal of the distribution area communicates with the property management platform via 4G / 5G communication to upload data to the IoT cloud master station; so as to realize remote monitoring of the distributed photovoltaic on site by the master station on the distribution cloud master station platform.

[0061] The intelligent converged terminal for the distribution area supports remote adjustment and control functions for the inverters in the power distribution master station.

[0062] The process of achieving cloud-edge collaborative remote control is as follows:

[0063] When the power grid is restored, the intelligent integrated terminal of the distribution area receives the remote grid connection command from the master station and controls the photovoltaic grid connection.

[0064] The main station and the intelligent converged terminal in the distribution area perform cloud-edge collaborative remote adjustment and control functions. The remote adjustment includes one of the following: numerical adjustment, proportional adjustment, or time-based adjustment.

[0065] Numerical adjustment: The main station sends out numerical control commands for the inverter output power through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit sends out control commands according to the values ​​to control the output power of the photovoltaic inverter.

[0066] Proportional adjustment: The main station issues control commands based on the rated power percentage of the inverter through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit issues control commands based on the rated power percentage to control the output of the photovoltaic inverter.

[0067] Time-period adjustment: The main station issues a time-period table containing time values ​​and control values ​​through the converged terminal and the acquisition terminal. The acquisition and monitoring unit receives and stores the table, executes the control instructions according to the time requirements, and automatically restores the table after the control ends.

[0068] Remote control includes controlling photovoltaic inverters in parallel or off-grid mode.

[0069] Compared with existing technologies, this invention and its preferred solution realize photovoltaic data acquisition, overvoltage control, and photovoltaic backfeed control during the grid connection of distributed photovoltaic systems. It can also coordinate with cloud and edge computing to realize remote control of distributed photovoltaic systems, solve the problem of weak sensing and control capabilities of distributed photovoltaic systems, improve the "observable-measurable-adjustable-controllable" capabilities, strengthen the management of distributed photovoltaic systems, and guide the friendly access of distributed photovoltaic systems. Attached Figure Description

[0070] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0071] Figure 1 This is a diagram illustrating the overall architecture of the distributed photovoltaic data acquisition and monitoring system according to an embodiment of the present invention.

[0072] Figure 2 This is a block diagram of the distributed photovoltaic grid-connected coordinated control function according to an embodiment of the present invention;

[0073] Figure 3 This is a block diagram of photovoltaic overvoltage data preprocessing according to an embodiment of the present invention;

[0074] Figure 4 This is a diagram showing the reactive power regulation characteristics of the inverter according to an embodiment of the present invention;

[0075] Figure 5 This is a logic diagram for overvoltage handling in an embodiment of the present invention;

[0076] Figure 6 This is a logic diagram of photovoltaic backfeed processing in an embodiment of the present invention. Detailed Implementation

[0077] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0078] To make the features and advantages of this patent more apparent and understandable, specific embodiments are provided below, along with accompanying drawings, for detailed explanation:

[0079] 1. System Overview

[0080] The overall architecture of the distributed photovoltaic grid-connected coordinated control system provided in this embodiment of the invention is as follows: Figure 1 As shown, its main components include:

[0081] 1. Smart Converged Distribution Terminal (TTU): As the core equipment for low-voltage side management and control, the Smart Converged Distribution Terminal (TTU) is a new generation of distribution network terminal product based on the concept of "software-defined terminal" and an open platform architecture design. It features hardware platformization and software APP-based implementation, employing key technologies such as edge computing, containers, IoT, and cloud-edge collaboration. The converged terminal is a core device on the "edge" side of the power IoT, possessing functions for equipment management, data acquisition and communication, collaborative computing, intelligent analysis, and decision control. It can flexibly expand its functions through software definition, supporting marketing, power distribution, and emerging businesses.

[0082] Distributed Photovoltaic Data Acquisition and Monitoring Unit: The distributed photovoltaic data acquisition and monitoring unit (hereinafter referred to as "data acquisition and monitoring unit") is a device for collecting, processing and monitoring the power generation and consumption information of distributed photovoltaic users in real time. It realizes functions such as automatic collection of photovoltaic user information, monitoring of power quality at the grid connection point, power consumption analysis and management, distributed energy monitoring, flexible regulation of photovoltaic power generation and rigid control of grid connection point switches.

[0083] Distributed Photovoltaic Communication Interface Adapter: The distributed photovoltaic communication interface adapter (hereinafter referred to as "adapter") is an accessory for connecting the distributed photovoltaic data acquisition and monitoring unit to the photovoltaic inverter. Each data acquisition and monitoring unit can be used with one adapter to realize the hardware wiring connection of the photovoltaic inverter. It is used to realize the communication switching between a single inverter and the power distribution automation system and the manufacturer's cloud platform as dual master stations. It expands the inverter's original one 485 communication channel into two channels. While ensuring that the communication with the manufacturer's cloud platform is not affected, the other 485 channel is connected to the data acquisition and monitoring unit, so that both master stations can normally acquire data and issue control commands.

[0084] Architecture Description:

[0085] In the architecture provided in this embodiment of the invention, the photovoltaic inverter is connected to the "adapter" via RS485 communication; one RS485 channel of the "adapter" is connected to the communication rod for accessing the inverter manufacturer's cloud platform, and the other RS485 channel is connected to the "acquisition and monitoring unit" to realize the multiplexing of the inverter's communication interface; the "acquisition and monitoring unit" communicates with the intelligent integrated terminal of the distribution area via HPLC / RF / LORA communication (embedded with a pluggable communication module, which can select the communication method according to the on-site communication situation), and receives the control of the intelligent integrated terminal of the distribution area, which can realize the rigid control / flexible adjustment of the grid connection and disconnection of distributed photovoltaic equipment; the intelligent integrated terminal of the distribution area communicates with the property management platform via 4G / 5G communication to upload data to the IoT cloud master station; on the distribution cloud master station platform side, the master station can remotely monitor the distributed photovoltaic on site through user information registration and graphic drawing.

[0086] 2. Technical Solution

[0087] Based on the above architecture, this invention, through edge computing on a smart integrated terminal for distribution substations, implements distributed photovoltaic (PV) grid-connected protocol control in the form of a software app. It mainly includes four functions: data acquisition and processing, overvoltage management, backfeed management, and cloud-edge collaborative remote control. The smart integrated terminal collects real-time data on the operation and grid connection status of PV users at each grid-connected point, and performs distributed PV overvoltage management and backfeed management locally in low-voltage distribution substations based on edge computing. It also supports remote control functions for inverters at the distribution master station, such as... Figure 2 As shown.

[0088] (1) Data acquisition and processing

[0089] The fusion terminal communicates with the acquisition and monitoring unit via HPLC / RF / LORA communication to acquire distributed photovoltaic data.

[0090] This is achieved through a data acquisition and monitoring unit:

[0091] 1) Grid connection point sampling function: Enables sampling of grid connection point voltage and current, with a voltage and current measurement accuracy of 0.5 class.

[0092] 2) Power Quality Analysis: By monitoring electrical parameters such as voltage, current, frequency, and harmonics at the grid connection point, power quality analysis can be performed. Through interaction with the integrated terminal, power supply quality and reliability can be improved. This mainly includes harmonic analysis: voltage 2nd to 25th harmonics, harmonic distortion rate; voltage deviation, frequency deviation; voltage fluctuation and flicker; three-phase voltage imbalance; and DC component.

[0093] 3) Data Acquisition and Control Functions: The acquisition and monitoring unit supports data acquisition and control of the downstream photovoltaic inverters. It has photovoltaic inverter communication link monitoring functions, which can monitor the downlink communication link status, and has proxy functions, which can forward commands or parameters that need to be transmitted by the acquisition terminal through the corresponding communication ports.

[0094] 4) Protocol conversion function: The acquisition and monitoring unit supports the automatic identification function of downlink Modbus protocol, which can automatically identify the protocol of all connected inverters and automatically convert uplink protocols such as DL / T698.45 and DL / T645 into the corresponding identified Modbus protocol for communication.

[0095] 5) Grid connection point control function: The data acquisition and monitoring unit has one remote control interface and one remote signaling interface. It controls the opening and closing of external circuit breakers by outputting relay signals and provides feedback on the circuit breaker's opening / closing status signals via remote signaling.

[0096] 6) Flexible adjustment function: The data acquisition and monitoring unit supports the following flexible adjustment methods:

[0097] Numerical adjustment: The main station and acquisition terminal send out numerical control commands for the inverter output power (active power, reactive power, power factor). After receiving the commands, the acquisition and monitoring unit sends out control commands according to the values ​​to control the output of the photovoltaic inverter.

[0098] Proportional adjustment: The main station and acquisition terminal send control commands based on the rated power (active power and reactive power) percentage of the inverter. After receiving the commands, the acquisition and monitoring unit sends control commands based on the rated power percentage to control the output of the photovoltaic inverter.

[0099] Time period adjustment: The main station and the acquisition terminal issue a time period table containing time values ​​and control values ​​(the indicators support percentages or numerical values). After receiving and storing the table, the acquisition and monitoring unit executes the control instructions according to the time requirements and automatically restores the table after the control ends.

[0100] 7) Event logging function: The data acquisition and monitoring unit has the following event logging function:

[0101] Record the total number of overvoltage events (6 threshold parameters can be set), the time of occurrence and voltage data of the last 50 events;

[0102] Record the total number of undervoltage events and the times of the last 50 control events;

[0103] Record control events, including the timing and information of the last 50 control events;

[0104] Record the communication anomalies of the photovoltaic inverter, including the times of the 10 most recent communication anomalies;

[0105] Record the power-on and power-off events of the distributed power supply access unit equipment, including the times of the last 10 power outages and power-on events.

[0106] Record the total number of faults in the distributed power access unit equipment, the type of the most recent 10 fault events in the distributed power access unit equipment, and the time of the fault occurrence.

[0107] Record the total number of times the distributed power supply access unit event is cleared, and the times when the most recent 10 distributed power supply access unit event clears occurred;

[0108] Record the total number of times the distributed power supply access unit is initialized, and the times when the most recent 10 distributed power supply access unit initializations occurred;

[0109] Record the total number of online software upgrades for the distributed power supply access unit, as well as the version information before and after the last 10 upgrades;

[0110] Record the total number of time synchronizations for the distributed power supply access unit and the times before and after the last 10 time synchronizations.

[0111] 7) Local Maintenance Function: The data acquisition and monitoring unit features local status indication and a local Bluetooth maintenance interface. Handheld devices can read information such as the supplier, model, and software version of the data acquisition and monitoring unit via Bluetooth and RS-485 interfaces, set parameters, and read inverter data on-site. Upgrades are supported remotely and locally (Bluetooth, RS485 maintenance), and breakpoint resume functionality is also supported. Upgrades and other operations do not affect historical data.

[0112] 8) Functional configuration: The data items collected by the monitoring unit are shown in Table 1.

[0113] Table 1 Data Items Collected by the Monitoring Unit

[0114]

[0115] Data processing:

[0116] Low-voltage distribution substations are affected by numerous factors, including grid parameters, capacity, wire diameter / line impedance, and load, at the inverter's grid connection point. The mechanisms are complex, making theoretical analysis and calculations difficult to apply in engineering. This embodiment analyzes historical data, recording and analyzing the historical curves of grid connection voltage, current, active power, and reactive power at the grid connection point to generate PV and QV curves for distributed photovoltaic systems. By inputting the overvoltage V value to be controlled for distributed photovoltaic grid connection, the predicted input P or Q value affected by the grid is calculated. Specifically... Figure 3 As shown:

[0117] The implementation process of data preprocessing:

[0118] 1) Enable the photovoltaic inverter to operate in MPPT mode

[0119] The integrated terminal periodically collects data such as output voltage, current, active power, and reactive power of the photovoltaic inverter, and periodically (default 5 minutes) records historical curve data every day (default stores the curves of the most recent 7 days).

[0120] Every day at 00:00, based on data from the past few days, a curve of photovoltaic voltage access point voltage U versus output power P is generated through search and interpolation methods, thus forming a PV relationship curve.

[0121] PV curve generation algorithm:

[0122] ① At the sampling time, record the photovoltaic active power Pi and the voltage Vi (take the maximum value of the three-phase phase voltage).

[0123] ② Normalization processing: Calculate Pi / PN,Vi / 220 as the normalized sampled record value of the inverter;

[0124] ③ Discretization process: Divide the sample into 32 equal parts and accumulate the measurement points in the range of Pi = 0 to 1 / 32. For example, take the average voltage Avg(Vi) as the first voltage sampling point. Other measurement points are similar, thus forming the PV relationship curve of the same day and storing the PV curve.

[0125] ④ For the PV curves of the past seven days, take the 3-day curve with the smallest covariance, and take the average value of V of the 3-day curves as the PV curve trajectory diagram of the inverter operation.

[0126] 2) Enable the photovoltaic inverter to operate in reactive power regulation mode.

[0127] According to GBT-37408-2019 Technical Requirements for Grid-Connected Inverters for Photovoltaic Power Generation, 380V inverters in low-voltage distribution areas belong to Class B inverters, which generally require flexible and adjustable reactive power output.

[0128] The inverter's steady-state reactive power output range should meet the following requirements: Figure 4The requirements are as follows: Class A inverters should be dynamically adjustable within the solid-line rectangle shown, and Class B inverters should be dynamically adjustable within the shaded rectangle shown. For Class A inverters with grid reactive power support capabilities, the reactive power output range should preferably be dynamically adjustable within the dashed-line rectangle.

[0129] For inverters with adjustable reactive power in the distribution area, manual triggering or a fixed interval of a specified number of days (e.g., 7 days) can be set to collect QV data and perform impact analysis during periods of high photovoltaic power generation. The main process is as follows:

[0130] ① Reactive power is sequentially distributed from Q=0 to QN, and reactive power control commands are issued with a reactive power adjustment amount of Q+=0.1×QN (QN can be taken as 0.3PN).

[0131] ② The integrated terminal collects data such as output voltage, current, active power, and reactive power of the photovoltaic inverter, and records the average U value collected at the current reactive power Q gradient.

[0132] ③ Generate the QV test curve and add it to the inverter's QV curve library.

[0133] QV curve generation algorithm:

[0134] ① At the moment of reactive power adjustment, record the photovoltaic reactive power Qi and the voltage Vi (take the maximum value of the three-phase phase voltage).

[0135] ② Normalization processing, calculate Qi / QN (QN is the maximum adjustable reactive power of the photovoltaic system), and use Vi / 220 as the normalized sampling record value of the inverter;

[0136] ③ Store the QV test curve for this experiment;

[0137] ④ For the QV curves of the past seven days, take the curves with the smallest covariance over the past three days, and take the average V value as the QV curve trajectory diagram of the inverter operation.

[0138] (2) Overpressure control

[0139] This invention employs a PQ integrated overvoltage control method based on PV and QV curves. When the voltage exceeds the limit, if the current inverter reactive power support adjustment is available, inverter reactive power adjustment is prioritized. If the voltage still exceeds the limit, then the PV active power adjustment process continues. Figure 5 As shown.

[0140] Since photovoltaic inverters absorb or output reactive power from the grid within their own capacity regulation range, they have almost no impact on the active power at the grid connection point; and most photovoltaic inverters currently have reactive power regulation capabilities. This embodiment can fully utilize the voltage regulation effect of reactive power regulation to reduce the amount of restriction on the active power of photovoltaic power for users.

[0141] Reactive power regulation:

[0142] When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by referring to the QV curve diagram based on the current over-limit voltage Ui, and then the reactive power of the inverter is limited to Qout by the terminal.

[0143] Specific adjustment strategies:

[0144] a. The coarse adjustment voltage threshold Ustep1 (default 4V) and adjustment count Cnt1 (default 2 times) can be set; the fine adjustment threshold Ustep2 (default 2V) and adjustment count Cnt2 (default 4 times) can be set; the adjustment time interval Tstep (default 10 minutes) can be set.

[0145] b. Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the QV curve, obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command;

[0146] c. Based on the current over-limit voltage value - fine-tuning Ustep2 as Ui, search the QV curve, obtain the adjustable Qout value, issue the current fine-tuning Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the reactive power adjustment process.

[0147] d. If the voltage at the grid connection point still exceeds the limit, then the adjustable inverter PV active power regulation is executed.

[0148] Active power regulation:

[0149] When the photovoltaic limit is exceeded, the current over-limit voltage is used as the target voltage Ui by decreasing the coarse or fine adjustment threshold. The active power Pout of the operation is calculated by looking up the PV curve diagram, and then the reactive power of the inverter is limited to Pout by the terminal.

[0150] The target voltage continues to decrease until the set minimum voltage (default 200V). If the phase voltage value cannot be lowered, a trip command is sent to the photovoltaic switch, causing the intelligent photovoltaic circuit breaker at the inverter grid connection point to trip.

[0151] To avoid frequent tripping and closing of the switch, the closing and restoration process can only be initiated after a tripping period of more than 30 minutes. If the voltage value at the grid connection point still does not change, the switch will be closed after 1 hour.

[0152] The intelligent photovoltaic circuit breaker is set to trip a certain number of times per day (default 5 times). If the number of trips is exceeded, it will be locked to prevent tripping.

[0153] Specific adjustment strategies:

[0154] a. The coarse adjustment voltage threshold Ustep1 (default 4V) and adjustment count Cnt1 (default 2 times) can be set; the fine adjustment threshold Ustep2 (default 2V) and adjustment count Cnt2 (default 4 times) can be set; the adjustment time interval Tstep (default 10 minutes) can be set.

[0155] b. Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the PV curve, obtain the expected power generation Pout value, issue the current coarse adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command.

[0156] c. Based on the current over-limit voltage value - fine adjustment Ustep2 as Ui, search the PV curve, obtain the expected power generation Pout value, issue the current fine adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the active power regulation process.

[0157] d. To prevent frequent adjustments, the start-up adjustment setpoint is set to 236V±1%. Adjustment will be initiated when the currently collected voltage exceeds the limit.

[0158] e. If the PV curve does not exist, switch to a coarse adjustment strategy that adjusts by the ratio of coarse to fine adjustment.

[0159] The coarse-to-fine adjustment strategy is as follows:

[0160] a. The coarse adjustment threshold Pstep1 (default 5%Pn) and adjustment number Cnt1 (e.g. 3 times) can be set; the fine adjustment threshold Pstep2 (default 2%Pn) and adjustment number Cnt2 (e.g. 3 times) can be set; the adjustment time interval Tstep (default 10 minutes) can be set.

[0161] b. Based on the current active power P value - Pstep1, issue the current coarse adjustment command. After a time interval Tstep, repeat the coarse adjustment Cnt1 times, and then switch to the fine adjustment command.

[0162] c. Based on the current active power P value - Pstep2, issue the current fine-tuning command. After a time interval Tstep, repeat the coarse-tuning Cnt2 times and then end the coarse-tuning and fine-tuning process.

[0163] (3) Backflow treatment

[0164] Specific adjustment strategies include: Figure 6 As shown:

[0165] a. Obtain the distribution transformer load rate, total active power, and active power of inverters at each grid connection point;

[0166] b. When the total active power of the distribution transformer is less than 0 and the load rate of the distribution area is greater than or equal to 80%, photovoltaic reverse transmission occurs, resulting in reverse heavy overload;

[0167] c. The integrated terminal reduces the photovoltaic power generation active power of all inverters in a 5% gradient and sends the adjustment command to each inverter.

[0168] d. Delay the policy scheduling period (default 15 minutes), then check again whether a reverse overload occurs. If a reverse overload still occurs, continue with the gradient limit active power adjustment process.

[0169] e. If the total active power of the distribution transformer is greater than 0 and the load rate of the distribution area is greater than or equal to 2%, the photovoltaic reverse overload return will be initiated. The integrated terminal will sequentially increase the photovoltaic power generation active power of all inverters by 5% and send the adjustment command to each inverter.

[0170] f. Delay strategy scheduling period (default 15 minutes): Repeat the above adjustment strategy logic.

[0171] (4) Cloud-edge collaborative remote control

[0172] When the power grid is restored, the integrated terminal receives the remote grid connection command from the master station and controls the photovoltaic grid connection.

[0173] The main station and the converged terminal can perform cloud-edge collaborative remote adjustment and control functions. Remote adjustment supports three functions: numerical adjustment, proportional adjustment, and time-based adjustment. Remote control supports the grid-connected and off-grid functions of photovoltaic inverters.

[0174] Numerical regulation: The main station sends out numerical control commands on the inverter output power (active power, reactive power, power factor) through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit sends out control commands according to the values ​​to control the output of the photovoltaic inverter.

[0175] Proportional adjustment: The main station sends control commands on the rated power (active power and reactive power) percentage of the inverter through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit sends control commands on the rated power percentage to control the output of the photovoltaic inverter.

[0176] Time period adjustment: The main station issues a time period table containing time values ​​and control values ​​(indicators support percentages or numerical values) through the converged terminal and the acquisition terminal. After receiving and storing the table, the acquisition and monitoring unit executes the control instructions according to the time requirements and automatically restores the table after the control ends.

[0177] The above description is a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

[0178] This patent is not limited to the above-described preferred embodiment. Anyone can derive other forms of distributed photovoltaic grid-connected coordinated control method based on fusion terminals under the guidance of this patent. All equivalent changes and modifications made within the scope of this patent application shall fall within the scope of this patent.

Claims

1. A distributed photovoltaic grid-connected coordinated control method based on a fusion terminal, characterized in that: The photovoltaic inverter is connected to the distributed photovoltaic acquisition and monitoring unit via a distributed photovoltaic communication interface adapter; the distributed photovoltaic acquisition and monitoring unit communicates with the intelligent integrated terminal of the distribution area and accepts the control of the intelligent integrated terminal of the distribution area to realize the rigid control / flexible adjustment of the grid connection and disconnection of the distributed photovoltaic equipment; The intelligent integrated terminal of the distribution area collects data on the operation and grid connection status of each grid-connected point, including photovoltaic users, in real time, and realizes distributed photovoltaic overvoltage management and / or photovoltaic backfeed management in the low-voltage distribution area based on edge computing; The specific measures for managing overvoltage in distributed photovoltaic systems are as follows: Based on the PV curve and QV curve, when the voltage exceeds the limit, if the current inverter reactive power support adjustment is available, the inverter reactive power adjustment is executed first. If the voltage still exceeds the limit, then the PV active power adjustment is executed. The reactive power regulation specifically refers to: When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by referring to the QV curve diagram based on the current over-limit voltage Ui, and then sent through the intelligent integration terminal of the distribution area to limit the reactive power of the inverter to Qout. The regulation strategies for controlling photovoltaic backflow include: Using a fixed time interval as the scheduling cycle for the delay strategy, the load rate of the distribution transformer, the total active power, and the active power of the inverters at each grid connection point are repeatedly acquired. When the total active power of the distribution transformer is less than 0 and the load rate of the distribution area is greater than or equal to 80%, it is determined that photovoltaic backfeed has occurred and reverse heavy overload has occurred. At this time, the intelligent integrated terminal of the distribution area adjusts the active power of photovoltaic power generation of all inverters in sequence by 5% and sends the adjustment command to each inverter. After one delay strategy scheduling cycle, it is determined again whether a reverse heavy overload has occurred. If a reverse heavy overload still occurs, the gradient limit active power adjustment process continues. If the total active power of the distribution transformer is greater than 0 and the load rate of the distribution area is greater than or equal to 2%, then the photovoltaic reverse overload return is determined. At this time, the integrated terminal adjusts the photovoltaic power generation active power of all inverters in sequence by 5% increment and sends the adjustment command to each inverter. The intelligent integrated terminal of the distribution area communicates with the property management platform via 4G / 5G communication and uploads data to the IoT cloud master station; so as to realize remote monitoring of the distributed photovoltaic on site by the master station on the power distribution cloud master station platform. The intelligent converged terminal for the distribution area supports remote adjustment and control functions for the inverters in the power distribution master station. The process of achieving cloud-edge collaborative remote control is as follows: When the power grid is restored, the intelligent integrated terminal of the distribution area receives the remote grid connection command from the master station and controls the photovoltaic grid connection. The main station and the intelligent converged terminal in the distribution area perform cloud-edge collaborative remote adjustment and control functions. The remote adjustment includes one of the following: numerical adjustment, proportional adjustment, or time-based adjustment. Numerical adjustment: The main station sends out numerical control commands for the inverter output power through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit sends out control commands according to the values ​​to control the output power of the photovoltaic inverter. Proportional adjustment: The main station issues control commands based on the rated power percentage of the inverter through the converged terminal and the acquisition terminal. After receiving the commands, the acquisition and monitoring unit issues control commands based on the rated power percentage to control the output of the photovoltaic inverter. Time-period adjustment: The main station issues a time-period table containing time values ​​and control values ​​through the converged terminal and the acquisition terminal. The acquisition and monitoring unit receives and stores the table, executes the control instructions according to the time requirements, and automatically restores the table after the control ends. Remote control includes controlling photovoltaic inverters in parallel or off-grid mode.

2. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 1, characterized in that: The specific adjustment strategies for reactive power regulation include: Set the coarse adjustment voltage threshold Ustep1 and adjustment count Cnt1; set the fine adjustment threshold Ustep2, adjustment count Cnt2, and adjustment time interval Tstep; Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, look up the QV curve, obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command; Based on the current over-limit voltage value - fine adjustment Ustep2 as Ui, look up the QV curve, obtain the adjustable Qout value, issue the current fine adjustment Qout adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the reactive power adjustment process. If the voltage at the grid connection point still exceeds the limit, then the adjustable inverter PV active power regulation will be executed.

3. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 1, characterized in that: The active power regulation is as follows: When the photovoltaic power exceeds the limit, the target voltage Ui is set by decreasing the coarse or fine adjustment threshold at the current over-limit voltage. The active power Pout is calculated by looking up the PV curve diagram and then sent through the smart integration terminal of the distribution area to limit the active power of the inverter to Pout. The target voltage continues to decrease until the set minimum voltage is reached. If the phase voltage value cannot be lowered, a trip command is issued to the photovoltaic switch, causing the photovoltaic circuit breaker at the inverter grid connection point to trip.

4. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 3, characterized in that: The specific regulation strategies for active power regulation include: Set the coarse adjustment voltage threshold Ustep1 and adjustment count Cnt1; fine adjustment threshold Ustep2 and adjustment count Cnt2; adjustment time interval Tstep; Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, look up the PV curve, obtain the expected power generation Pout value, issue the current coarse adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt1 times before switching to the fine adjustment command. Based on the current over-limit voltage value - fine adjustment Ustep2 as Ui, look up the PV curve, obtain the expected power generation Pout value, issue the current fine adjustment command, and after a time interval Tstep, repeat the coarse adjustment Cnt2 times to end the active power regulation process. To prevent frequent adjustments, the start adjustment setpoint is set to 236V±1%. Adjustment will be initiated when the currently collected voltage exceeds the limit. If the PV curve does not exist, then switch to a coarse-fine adjustment strategy that adjusts by the ratio of coarse and fine adjustment. The coarse-tuning and fine-tuning strategies are as follows: Set the coarse adjustment threshold Pstep1 and adjustment count CNt1; fine adjustment threshold Pstep2 and adjustment count CNt2; adjustment time interval Tstep. Based on the current active power P value - Pstep1, issue the current coarse adjustment command. After a time interval Tstep, repeat the coarse adjustment Cnt1 times, and then switch to the fine adjustment command. Based on the current active power P value - Pstep2, issue the current fine-tuning command. After a time interval Tstep, repeat the coarse-tuning Cnt2 times and then end the coarse-tuning and fine-tuning process.

5. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 1, characterized in that: By recording and analyzing the historical curves of grid connection voltage, current, active power, and reactive power at the grid connection point, the PV curve and QV curve of distributed photovoltaic power generation are formed. By inputting the overvoltage V value to be controlled for distributed photovoltaic power generation, the predicted input P or Q value affected by the grid is calculated.

6. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 5, characterized in that: For photovoltaic inverters in MPPT mode in the distribution area: The intelligent integrated terminal of the distribution area periodically collects the output voltage, current, active power and reactive power data of the photovoltaic inverter, and periodically records the historical curve data every day. Based on data from recent days, a curve showing the relationship between photovoltaic voltage access point voltage U and output power P was generated through search and interpolation methods, thus forming a PV relationship curve. At the sampling time, the photovoltaic active power Pi is recorded, and the maximum value of the three-phase phase voltage is taken as the voltage Vi; Normalization processing was performed, and Pi / PN, Vi / 220 were used as the normalized sampled record values ​​of the photovoltaic inverter. By discretizing the data, the measurement points are accumulated in different time periods to form and store the PV relationship curve of the same day. For the PV curves of the past seven days, the three-day curve with the smallest covariance is selected, and the average value of the V value of the three-day curves is taken as the PV curve trajectory diagram of the photovoltaic inverter operation.

7. The distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 5, characterized in that: For inverters with adjustable reactive power in the distribution area, a trigger or fixed interval is set to specify the number of days. During periods of high photovoltaic power generation, QV data collection and impact analysis are performed, including the following process: Reactive power control commands are issued sequentially from Q=0 to QN, with a reactive power adjustment amount of Q+=0.1×QN; The intelligent integrated terminal of the distribution area collects output voltage, current, active power, and reactive power data of the photovoltaic inverter, and records the average U value collected at the current reactive power Q level. And generate the QV test curve and add it to the corresponding inverter QV curve library; Methods for generating QV curves include: At the moment of reactive power adjustment, record the photovoltaic reactive power Qi, and take the maximum value of the three-phase voltage as the voltage Vi; After normalization, calculate Qi / QN, where QN is the maximum adjustable reactive power of the photovoltaic system, and Vi / 220 is the normalized sampled record value of the inverter. Store the QV test curve for this experiment; For the QV curves of the past seven days, the curves with the smallest covariance over the past three days are selected, and the average V value is taken as the QV curve trajectory diagram of the inverter operation.

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