Distributed photovoltaic grid-connected coordination control method based on fusion terminal

Abstract

The invention provides a distributed photovoltaic grid-connected coordination control method based on a fusion terminal. A photovoltaic inverter is connected to a distributed photovoltaic acquisition monitoring unit through a distributed photovoltaic communication interface adapter; the distributed photovoltaic acquisition monitoring unit communicates with the transformer area intelligent fusion terminal and is regulated and controlled by the transformer area intelligent fusion terminal so as to realize grid-connected and off-grid rigid control / flexible adjustment of distributed photovoltaic equipment; the transformer area intelligent fusion terminal collects data of photovoltaic user operation and grid-connected states of each grid-connected point in real time, and realizes distributed photovoltaic overvoltage treatment and / or photovoltaic reverse transmission treatment of a low-voltage transformer area based on edge calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of distributed photovoltaic power generation grid-connected technology, and in particular to a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal. Background Art

[0002] Low-voltage access distributed photovoltaics are generally connected to the grid through 380 / 220V voltage levels. 380V is three-phase voltage access, and 220V is single-phase voltage access. Most distributed photovoltaics are rooftop photovoltaics, and the information such as grid-connected and off-grid status, active power and reactive power is uncontrollable, and the "observable-measurable-adjustable-controllable" capabilities are relatively weak. Among them: Visible: Display the access location and status information of photovoltaic power sources in the power grid business system.

[0003] Measurable: The relevant status information of photovoltaic power source can be uploaded to the intelligent fusion terminal in real time and sent to the distribution automation master station system.

[0004] Adjustable: Ability to adjust PV inverter power locally and autonomously as well as by remote systems.

[0005] Controllable: The distribution automation master station system and intelligent fusion terminal can control the status of the photovoltaic inverter.

[0006] Low-voltage distributed photovoltaics have problems such as "dispersion, randomness, and disorder" in access. Distributed photovoltaics are generally users' assets, with various inverter communication interfaces and many private protocols, making supervision difficult. Due to disorderly access, distributed photovoltaic grid connection is very likely to cause problems such as reverse overload, high voltage, and excessive line loss in the substation area.

[0007] With the access of a large number of distributed photovoltaics to the distribution network, the access is characterized by disorder, intermittency, randomness, and volatility in time and space, resulting in local and overall random differences in the power quality problems in the substation area. In the time dimension, there are complex and changeable situations such as crossing the upper and lower limits at different times in the same place. The traditional control mode relies on the switching of substation capacitors and the adjustment of the main transformer gear position, which is difficult to adapt to the requirements of the new power system. It is urgent to deepen the autonomy of the substation grid, and through reliable, flexible, and intelligent overall management, accurately solve the dynamically changing voltage quality problems in different categories. Summary of the invention

[0008] In order to accelerate the rapid advancement of photovoltaic power generation in the whole county and strengthen the functional requirements of distributed photovoltaic grid connection such as safety, orderliness, measurability and controllability, the purpose of this invention is to collect and coordinate the grid connection of distributed photovoltaic user data, through the "cloud-edge" interaction between the cloud master station and the fusion terminal, and the "edge" interaction between the fusion terminal and the photovoltaic inverter, to achieve safe access control of distributed photovoltaics, avoid disorderly grid connection, solve the problems of voltage exceeding the limit, harmonic exceeding the standard, low power factor, and equipment reverse overload, and reduce the impact of distributed photovoltaics on the low-voltage distribution network.

[0009] The design objectives of the present invention include: (1) Realize IoT perception of key equipment in digital distribution networks through integrated terminal communication interfaces.

[0010] (2) Distributed photovoltaic monitoring and strategy control can be achieved through edge computing capabilities based on fusion terminals.

[0011] The present invention specifically adopts the following technical solutions: A distributed photovoltaic grid-connected coordinated control method based on fusion terminal: The photovoltaic inverter is connected to the distributed photovoltaic collection and monitoring unit via the distributed photovoltaic communication interface adapter; the distributed photovoltaic collection and monitoring unit communicates with the intelligent fusion terminal in the substation area and accepts the regulation of the intelligent fusion terminal in the substation area to realize the rigid control / flexible regulation of the grid-connected and off-grid distributed photovoltaic equipment; The intelligent fusion terminal in the substation collects data on each grid-connected point, including the operation and grid-connected status of photovoltaic users, in real time, and implements distributed photovoltaic overvoltage control and / or photovoltaic reverse transmission control in the low-voltage substation based on edge computing.

[0012] Furthermore, the distributed photovoltaic overvoltage control is specifically as follows: Based on the PV curve and QV curve, when the voltage exceeds the limit, if the current inverter reactive power supports regulation, the inverter reactive power regulation is performed first. If it still exceeds the limit, the PV active power regulation is performed. The reactive power regulation is specifically as follows: When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by looking up the QV curve diagram according to the current over-limit voltage Ui, and sent through the intelligent fusion terminal in the substation area to limit the reactive power of the inverter to Qout.

[0013] Furthermore, the specific adjustment strategy of the reactive power regulation includes: Set the coarse adjustment voltage threshold Ustep1, the adjustment times Cnt1; the fine adjustment threshold Ustep2, the adjustment times Cnt2, and the adjustment time interval Tstep; According to the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; According to the current over-limit voltage value - fine-tuning Ustep2 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current fine-tuning Qout adjustment command, and after the time interval Tstep, repeat the coarse-tuning Cnt2 times to end the reactive power adjustment process; If the voltage at the grid connection point still exceeds the limit, the adjustable inverter PV active power regulation is performed.

[0014] Furthermore, the active power regulation is: When the PV exceeds the limit, at the current over-limit voltage, the decreasing coarse adjustment or fine adjustment threshold is used as the target voltage Ui, and the operating active power Pout is calculated by looking up the PV curve diagram, and sent through the intelligent fusion terminal of the substation area, so that the active power of the inverter is limited to Pout; The target voltage continues to decrease until it reaches the set minimum voltage. If the phase voltage value cannot be lowered, a trip command is issued to the photovoltaic switch to trip the photovoltaic circuit breaker at the inverter grid-connected point.

[0015] Furthermore, the specific adjustment strategy of the active power adjustment includes: Set the coarse adjustment voltage threshold Ustep1, the adjustment times Cnt1; the fine adjustment threshold Ustep2, the adjustment times Cnt2; the adjustment time interval Tstep; According to the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the PV curve to obtain the expected power generation Pout value, issue the current coarse adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; According to the current over-limit voltage value - fine-adjust Ustep2 as Ui, search the PV curve, obtain the expected power generation Pout value, issue the current fine-adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt2 times to end the active power regulation process; In order to prevent frequent adjustments, the start adjustment value is set to 236V±1%. When the voltage collected in real time exceeds the limit, the adjustment is started; If the PV curve does not exist, the strategy of coarse adjustment and fine adjustment is switched to according to the coarse adjustment and fine adjustment ratio; The coarse and fine tuning strategies are as follows: Set the coarse adjustment active power threshold Pstep1, adjustment times Cnt1; fine adjustment threshold Pstep2, adjustment times Cnt2; adjustment time interval Tstep; According to the current active power P value - Pstep1, the current coarse adjustment command is issued. After the time interval Tstep, the coarse adjustment is repeated Cnt1 times and then the command is changed to the fine adjustment command. According to the current active power P value - Pstep2, the current fine adjustment command is issued. After the time interval Tstep, the coarse adjustment Cnt2 times are repeated, and the coarse and fine adjustment process ends.

[0016] Furthermore, by recording and analyzing the historical curve relationship of the grid-connected voltage, current, active power and reactive power at the grid-connected point, the PV curve and QV curve of the distributed photovoltaic are formed. By inputting the overvoltage V value to be controlled by the distributed photovoltaic grid-connected, the predicted input P or Q value affected by the power grid is calculated.

[0017] Furthermore, for the PV inverter in MPPT mode: The intelligent fusion terminal in the substation regularly collects the output voltage, current, active power and reactive power data of the photovoltaic inverter, and regularly records the daily historical curve data; Based on the data of recent days, the voltage U and output power P curve of photovoltaic voltage access point are formed through search and interpolation methods, forming the PV relationship curve: At the sampling moment, record the photovoltaic active power Pi, and take the maximum value of the three-phase voltage as the voltage Vi; Normalization processing, using Pi / PN, Vi / 220 as the normalized sampling record values ​​of the inverter; Through discretization processing, the measurement points are accumulated in different time periods to form and store the PV relationship curve of the day; For the PV curves of the past seven days, take the 3-day curves with the smallest covariance, and take the average value of the 3-day curve V as the PV curve trajectory diagram of the inverter operation.

[0018] Furthermore, for inverters with adjustable reactive power in the substation, set a trigger or a fixed interval for a specified number of days, and perform QV data collection and impact analysis during the period of high photovoltaic power generation, including the following processes: From the range of Q=0 to QN, reactive power control instructions are issued with the reactive power adjustment amount of Q+=0.1×QN; The intelligent fusion terminal in the substation collects data of the photovoltaic inverter including output voltage, current, active power and reactive power, and records the average U value currently collected under the gradient reactive power Q; and generates a QV test curve, and adds it to the corresponding inverter QV curve library; The QV curve generation method includes: At the reactive power regulation time, record the PV reactive power Qi, and take the maximum value of the three-phase voltage as the voltage Vi; Normalization processing, calculate Qi / QN, where QN is the maximum reactive power that can be adjusted by photovoltaics, and Vi / 220 is the normalized sampling record value of the inverter; Store the QV test curve of this time; For the QV curves of the past seven days, take the three-day curve with the smallest covariance and take the V average value as the QV curve trajectory diagram of the inverter operation.

[0019] Furthermore, the regulation strategy for photovoltaic reverse power management includes: A fixed time is used as the delay strategy scheduling cycle to repeatedly obtain the distribution transformer load rate, total active power and active power of inverters at each grid connection point: When the total active power of the distribution transformer is less than 0 and the load rate of the substation is ≥80%, it is judged that photovoltaic reverse transmission occurs and a reverse heavy overload occurs; at this time, the substation intelligent fusion terminal reduces the active power of photovoltaic power generation for all inverters in turn by a gradient of 5%, and sends the adjustment command to each inverter; After a delay strategy scheduling cycle, it is determined again whether a reverse heavy overload occurs. If it is still a reverse heavy overload, the gradient limited active power regulation process continues; If the total active power of the distribution transformer is > 0 and the load factor of the substation is ≥ 2%, it is judged that the photovoltaic reverse overload has returned. At this time, the fusion terminal increases the active power of photovoltaic power generation for all inverters in turn by a gradient of 5%, and sends the adjustment instructions to each inverter.

[0020] Furthermore, the intelligent fusion terminal in the substation area communicates with the property management platform through 4G / 5G communication mode, and uploads the data to the IoT cloud master station; so as to realize the remote monitoring of the on-site distributed photovoltaic by the master station on the distribution cloud master station platform side; The intelligent fusion terminal in the substation supports the remote adjustment and remote control functions of the inverters in the distribution master station: The process of implementing cloud-edge collaborative remote control is as follows: When the power grid is restored, the intelligent fusion terminal in the substation controls the photovoltaic grid connection when receiving the remote control grid connection command from the master station; The master station and the intelligent fusion terminal of the substation area perform cloud-edge collaborative remote adjustment and remote control functions. Remote adjustment includes one of numerical adjustment, proportional adjustment, and time period adjustment: Numerical adjustment: The master station sends the inverter output power numerical control instructions through the fusion terminal and the acquisition terminal. After receiving the instructions, the acquisition monitoring unit sends the control command according to the numerical value to control the output of the photovoltaic inverter; Proportional regulation: The master station sends the inverter rated power percentage control instruction through the fusion terminal and the acquisition terminal. After receiving it, the acquisition monitoring unit sends the control command according to the rated power percentage to control the output of the photovoltaic inverter; Time period adjustment: The master station sends a control period table containing time values ​​and control values ​​through the fusion terminal and the acquisition terminal. The acquisition monitoring unit receives and stores the control instructions according to the time requirements and automatically recovers after the control ends. Remote control includes controlling the photovoltaic inverter on / off the grid.

[0021] Compared with the existing technology, the present invention and its preferred solution realize photovoltaic data collection, overvoltage control, and photovoltaic reverse transmission control during the distributed photovoltaic grid-connected process, and can collaborate with the cloud edge to realize remote adjustment and control of distributed photovoltaics, solve the problem of weak distributed photovoltaic perception and control capabilities, improve the "observable-measurable-adjustable-controllable" capabilities, strengthen distributed photovoltaic management, and guide distributed photovoltaic friendly access. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a general architecture diagram of a distributed photovoltaic collection and monitoring system according to an embodiment of the present invention; Figure 2 This is a functional block diagram of the coordinated control of distributed photovoltaic grid connection according to an embodiment of the present invention; Figure 3 This is a block diagram of photovoltaic overvoltage data preprocessing according to an embodiment of the present invention; Figure 4 This is a reactive power regulation characteristic diagram of the inverter according to an embodiment of the present invention; Figure 5 This is an overvoltage processing logic diagram of an embodiment of the present invention; Figure 6 This is a logic diagram of photovoltaic reverse transmission processing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] Hereinafter, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings. According to these detailed descriptions, those skilled in the art can clearly understand the present application and can implement the present application. Without violating the principles of the present application, the features in the various embodiments can be combined to obtain new implementations, or certain features in certain embodiments can be replaced to obtain other preferred implementations.

[0024] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail with the accompanying drawings as follows: 1. System Overview The overall architecture of the distributed photovoltaic grid-connected coordinated control system provided by the embodiment of the present invention is as follows: Figure 1 As shown, its main components include: 1. Intelligent fusion terminal in the substation: The intelligent fusion terminal TTU in the substation (referred to as "fusion terminal") is the core equipment for low-voltage side control. It is based on the concept of "software-defined terminal" and open platform architecture design, with hardware platformization and software APPization. It is a new generation of distribution network terminal products designed with key technologies such as edge computing, containers, Internet of Things, and cloud-edge collaboration. The fusion terminal is the core equipment on the "edge" side of the power Internet of Things. It also has the functions of equipment management, collection and communication, collaborative computing, intelligent analysis, and decision-making control. It can realize flexible functional expansion in a software-defined way to support marketing, power distribution and emerging businesses.

[0025] Distributed photovoltaic collection and monitoring unit: The distributed photovoltaic collection and monitoring unit (referred to as "collection and monitoring unit") is a device for collecting, processing and real-time monitoring of the power generation and power consumption information of distributed photovoltaic users, realizing functions such as automatic collection of photovoltaic user information, grid-connected point power quality monitoring, power consumption analysis and management, distributed energy monitoring, flexible regulation of photovoltaic power generation and rigid control of grid-connected point switches.

[0026] Distributed photovoltaic communication interface adapter: Distributed photovoltaic communication interface adapter (referred to as "adapter") is an accessory for connecting distributed photovoltaic collection and monitoring units to photovoltaic inverters. Each collection and monitoring unit can be used with an adapter to achieve hardware line connection of photovoltaic inverters. It is used to achieve communication switching between a single inverter and the distribution automation system and the manufacturer's cloud platform dual master station. The original 485 communication channel of the inverter is expanded into two channels. While one channel ensures that the communication with the manufacturer's cloud platform is not affected, the other 485 channel is connected to the collection and monitoring unit, so that both master stations can collect and issue control instructions normally.

[0027] Architecture Description: In the architecture provided by the embodiment of the present invention, the photovoltaic inverter is connected to the "adapter" via 485 communication; one RS485 channel of the "adapter" is connected to the communication stick 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 communication interface; the "acquisition and monitoring unit" communicates with the substation intelligent fusion terminal via HPLC / RF / LORA communication (with an embedded pluggable communication module, and the communication method can be selected according to the on-site communication situation), accepts the regulation of the substation intelligent fusion terminal, and can realize the rigid control / flexible adjustment of the grid-connected and off-grid distributed photovoltaic equipment; the substation intelligent fusion terminal communicates with the property management platform via 4G / 5G communication, and uploads the data to the Internet of Things cloud master station; on the distribution cloud master station platform side, the master station remotely monitors the on-site distributed photovoltaics through user information registration and graphics drawing.

[0028] 2. Technical solution Based on the above architecture, the embodiment of the present invention realizes distributed photovoltaic grid-connected protocol control in the form of software APP based on the edge computing of the intelligent fusion terminal in the substation, which mainly includes four functions: data collection and processing, overvoltage control, reverse transmission control and cloud-edge collaborative remote control. The intelligent fusion terminal in the substation collects data such as the operation and grid-connected status of photovoltaic users at each grid-connected point in real time, and carries out distributed photovoltaic overvoltage control and photovoltaic reverse transmission control in the low-voltage substation based on edge computing, and supports the remote control function of the inverter of the distribution master station, such as Figure 2 shown.

[0029] (1) Data collection and processing The fusion terminal communicates with the acquisition monitoring unit through HPLC / RF / LORA communication to collect distributed photovoltaic data.

[0030] The acquisition monitoring unit is used to achieve: 1) Grid-connected point sampling function: realize the grid-connected point voltage and current sampling function, and the measurement accuracy of voltage and current is 0.5 level.

[0031] 2) Power quality analysis: By monitoring the voltage, current, frequency, harmonics and other electrical parameters at the grid connection point and analyzing the quality of the power, the power supply quality and power reliability can be improved through interaction with the fusion terminal. It mainly includes harmonic analysis: voltage 2~25 harmonics, harmonic distortion rate; voltage deviation, frequency deviation; voltage fluctuation and flicker; three-phase voltage imbalance; DC component.

[0032] 3) Data collection and control function: The data collection and monitoring unit can support the data collection and control of the photovoltaic inverter. It has the function of monitoring the communication link of the photovoltaic inverter, which can monitor the status of the downlink communication link, and has the proxy function, which can forward the commands or parameters and other data that the collection terminal needs to transmit through the corresponding communication port.

[0033] 4) Protocol conversion function: The acquisition and monitoring unit supports the automatic identification function of the downstream Modbus protocol, which can automatically identify all the inverter protocols hanging down, and can automatically convert the upstream DL / T698.45, DL / T645 and other protocols into the corresponding Modbus protocol that has been identified for communication.

[0034] 5) Grid connection point control function: The data acquisition monitoring unit has 1 remote control interface and 1 remote signal interface. It controls the opening and closing of external circuit breakers by outputting signals through the output relay, and feedbacks the circuit breaker opening / closing status signals through remote signaling.

[0035] 6) Flexible adjustment function: The acquisition monitoring unit supports the following flexible adjustment methods: Numerical adjustment: The master station and the acquisition terminal send numerical control instructions for the inverter output power (active power, reactive power, power factor). After receiving the numerical control instructions, the acquisition monitoring unit sends control commands according to the numerical values ​​to control the output of the photovoltaic inverter. Proportional regulation: The master station and the acquisition terminal send the inverter rated power (active power, reactive power) percentage control instruction. After receiving it, the acquisition monitoring unit sends the control command according to the rated power percentage to control the output of the photovoltaic inverter; Time period adjustment: The master station and the acquisition terminal send a control period table containing time values ​​and control values ​​(indicators support percentages or numerical values). After receiving and storing, the acquisition and monitoring unit executes the control instructions according to the time requirements and automatically recovers after the control ends.

[0036] 7) Event recording function: The acquisition monitoring unit has the following event recording functions: Record the total number of overvoltage events (6 levels of threshold parameters can be set), the time and voltage data of the latest 50 occurrences; Record the total number of undervoltage events and the time when the latest 50 control events occurred; Record control events, the time and information of the latest 50 control events; Record abnormal communication events of photovoltaic inverters and the time when the last 10 abnormal communication events occurred; Record the power-on events of the distributed power supply access unit equipment and the time when the last 10 power-offs and power-on occurred; Record the total number of distributed power access unit equipment failures, the types of the most recent 10 distributed power access unit equipment failure events and the time when the failures occurred; Record the total number of times the distributed power access unit event is cleared, and the time when the latest 10 distributed power access unit events are cleared; Record the total number of distributed power access unit initializations and the time when the last 10 distributed power access unit initializations occurred; Record the total number of online software upgrades of the distributed power access unit and the version information before and after the last 10 upgrades; Record the total number of time calibrations of the distributed generation access unit and the times before and after the most recent 10 time calibrations.

[0037] 7) Local maintenance function: The acquisition monitoring unit has local status indication and local Bluetooth maintenance interface. It supports handheld devices to read the acquisition monitoring unit supplier, model, software version and other information through the Bluetooth communication interface and maintenance RS-485 interface, set parameters, read inverter data on site, and support remote and local methods (Bluetooth, RS485 maintenance) for upgrades, and supports breakpoint resume. Upgrades and other operations do not affect historical data.

[0038] 8) Functional configuration: The data items collected by the acquisition monitoring unit are shown in Table 1.

[0039] Table 1 Data items collected by the monitoring unit

[0040] Data processing: In low-voltage distribution substations, the grid connection point where the inverter is located is affected by grid parameters, capacity, line diameter / line impedance, load, etc. There are many influencing factors and complex mechanisms. It is difficult to apply engineering based on theoretical analysis and calculation. This embodiment forms the PV curve and QV curve of distributed photovoltaics through historical data analysis, by recording and analyzing the historical curve relationship of grid connection voltage, current, active power and reactive power at the grid connection point, and calculates the predicted input P or Q value affected by the grid by inputting the overvoltage V value to be controlled by the distributed photovoltaic grid connection. Specifically, Figure 3 As shown: Implementation process of data preprocessing: 1) Make the photovoltaic inverter work in MPPT mode The fusion terminal collects the output voltage, current, active power, reactive power and other data of the photovoltaic inverter at regular intervals, and records the daily historical curve data at regular intervals (5 minutes by default) (the curves of the last 7 days are stored by default); At 00:00 every day, based on the data of the most recent days, the photovoltaic voltage access point voltage U and output power P curve are formed through search and interpolation methods to form the PV relationship curve.

[0041] PV curve generation algorithm: ① At the sampling moment, record the photovoltaic active power Pi and voltage Vi (take the maximum value of the three-phase voltage); ② Normalization processing, calculate Pi / PN, Vi / 220 as the normalized sampling record value of the inverter; ③ Discretization processing, taking 32 equal parts, and accumulating the measurement points in the range of Pi = 0 ~ 1 / 32, for example, taking the voltage average value Avg (Vi) as the first voltage sampling point, and other measurement points are similar, so as to form an equal PV relationship curve for the day, and store the PV curve; ④ For the PV curves of the past seven days, take the 3-day curves with the smallest covariance, and take the average value of the 3-day curve V as the PV curve trajectory diagram of the inverter operation.

[0042] 2) Make the photovoltaic inverter work in reactive power regulation mode According to GBT-37408-2019 Technical Requirements for Photovoltaic Grid-connected Inverters, the 380V inverter in the low-voltage area belongs to Class B inverter, which generally requires flexible and adjustable reactive power output.

[0043] The inverter steady-state reactive power output range should meet the following requirements: Figure 4The requirements shown are: Class A inverters should be dynamically adjustable within the solid rectangular frame, and Class B inverters should be dynamically adjustable within the shaded frame. The reactive power output range of Class A inverters with grid reactive support capability should be dynamically adjustable within the dotted rectangular frame.

[0044] For inverters with adjustable reactive power in the substation, manual triggering or fixed intervals of specified days (e.g. 7 days) can be set to collect QV data and conduct impact analysis during the period of high photovoltaic power generation. The main process is: ① The reactive power ranges from Q=0 to QN, and the reactive power control command is issued with the reactive power adjustment amount of Q+=0.1×QN (QN can be taken as 0.3PN); ② The fusion terminal collects data such as the output voltage, current, active power, and reactive power of the photovoltaic inverter, and records the average U value currently collected under the gradient reactive power Q; ③ Form a QV test curve and add it to the inverter QV curve library.

[0045] QV curve generation algorithm: ① At the moment of reactive power regulation, record the PV reactive power Qi and voltage Vi (take the maximum value of the three-phase voltage); ② Normalization processing, calculate Qi / QN (QN is the maximum reactive power that can be adjusted by the photovoltaic power plant), Vi / 220 as the normalized sampling record value of the inverter; ③ Store the QV test curve of this time; ④ For the QV curves of the past seven days, take the 3-day curve with the smallest covariance and take the V average value as the QV curve trajectory diagram of the inverter operation.

[0046] (2) Overvoltage control The embodiment of the present invention adopts a PQ comprehensive overvoltage control method based on the PV curve and the QV curve. When the voltage exceeds the limit, if the current inverter reactive power supports adjustment, the inverter reactive power adjustment is performed first. If it still exceeds the limit, the PV active power adjustment process is continued. Figure 5 shown.

[0047] When the photovoltaic inverter absorbs or outputs reactive power from the grid within its own capacity regulation range, it has almost no effect on the active power of the grid connection point; and most photovoltaic inverters currently have reactive power regulation capabilities. The design of this embodiment can fully utilize the regulation effect of reactive power regulation on voltage and reduce the limit on the user's photovoltaic active power.

[0048] Reactive power regulation: When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by looking up the QV curve diagram according to the current over-limit voltage Ui, and then the fusion terminal sends the inverter reactive power limit to Qout; Specific adjustment strategies: a. The coarse adjustment voltage threshold Ustep1 (default 4V), adjustment times Cnt1 (default 2 times) can be set; the fine adjustment threshold Ustep2 (default 2V), adjustment times Cnt2 (default 4 times); adjustment time interval Tstep (default 10 minutes); b. Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; c. Based on the current over-limit voltage value - fine-tuning Ustep2 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current fine-tuning Qout adjustment command, and after the time interval Tstep, repeat the coarse-tuning Cnt2 times to end the reactive power adjustment process.

[0049] d. If the voltage at the grid connection point still exceeds the limit, the adjustable inverter PV active power regulation is performed.

[0050] Active power regulation: When the PV exceeds the limit, 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 fusion terminal sends the inverter reactive power limit to Pout; The target voltage continues to decrease until it reaches the set minimum voltage (default 200V). If the phase voltage value cannot be lowered, a trip command is issued to the photovoltaic switch to trip the intelligent photovoltaic circuit breaker at the inverter grid-connected point.

[0051] To avoid frequent tripping and closing of the switch, the closing recovery process can be judged only after the tripping lasts for more than 30 minutes. If the voltage value of the grid connection point still does not change, the switch will be controlled to close after 1 hour.

[0052] The smart photovoltaic circuit breaker is set to trip a certain number of times per day (5 times by default). If the number of trips is exceeded, it will be locked to prevent it from tripping.

[0053] Specific adjustment strategies: a. The coarse adjustment voltage threshold Ustep1 (default 4V), adjustment times Cnt1 (default 2 times) can be set; the fine adjustment threshold Ustep2 (default 2V), adjustment times Cnt2 (default 4 times); adjustment time interval Tstep (default 10 minutes); b. Based on the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the PV curve to obtain the expected power generation Pout value, issue the current coarse adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; c. According to the current over-limit voltage value - fine-adjust Ustep2 as Ui, search the PV curve to obtain the expected power generation Pout value, issue the current fine-adjustment command, repeat the coarse adjustment Cnt2 times after the time interval Tstep, and end the active power regulation process; d. In order to prevent frequent adjustments, the start adjustment value is set to 236V±1%. When the voltage collected in real time exceeds the limit, the adjustment is started; e. If the PV curve does not exist, switch to the coarse adjustment strategy based on the coarse adjustment and fine adjustment ratio.

[0054] The coarse and fine tuning strategies are as follows: a. The coarse adjustment threshold Pstep1 (default 5%Pn) and the number of adjustments Cnt1 (for example, 3 times) can be set; the fine adjustment threshold Pstep2 (default 2%Pn) and the number of adjustments Cnt2 (for example, 3 times); the adjustment time interval Tstep (default 10 minutes) can be set.

[0055] b. According to the current active power P value - Pstep1, the current coarse adjustment command is issued. After the time interval Tstep, the coarse adjustment is repeated Cnt1 times and then the fine adjustment command is switched; c. According to the current active power P value - Pstep2, the current fine adjustment command is issued. After the time interval Tstep, the coarse adjustment Cnt2 times are repeated to end the coarse and fine adjustment process.

[0056] (3) Backflow management Specific adjustment strategies such as Figure 6 As shown: a. Obtain the load rate of the distribution transformer, the total active power and the active power of the inverter at each grid connection point; b. When the total active power of the distribution transformer is <0 and the load rate of the substation is ≥80%, photovoltaic reverse transmission occurs and reverse heavy overload occurs; c. The fusion terminal adjusts down the active power of photovoltaic power generation for all inverters by 5% in sequence, and sends the adjustment instructions to each inverter; d. Delay the strategy scheduling cycle (default 15 minutes) and determine again whether a reverse heavy overload occurs. If a reverse heavy overload still occurs, continue the gradient limited active power adjustment process; e. If the total active power of the distribution transformer is greater than 0 and the load rate of the substation is greater than or equal to 2%, the photovoltaic reverse overload returns, and the fusion terminal increases the photovoltaic power generation active power of all inverters in turn by a gradient of 5%, and sends the adjustment command to each inverter; f. Delay the policy scheduling period (15 minutes by default) and repeat the above adjustment policy logic.

[0057] (4) Cloud-edge collaborative remote control When the power grid is restored and the fusion terminal receives the remote control grid connection command from the master station, it controls the photovoltaic grid connection.

[0058] The master station and the fusion terminal can perform cloud-edge collaborative remote adjustment and remote control functions. The remote adjustment can support three functions: numerical adjustment, proportional adjustment, and time period adjustment. The remote control can support the grid-connected and off-grid functions of photovoltaic inverters.

[0059] Numerical adjustment: The master station sends numerical control instructions for the inverter output power (active power, reactive power, power factor) through the fusion terminal and the acquisition terminal. After receiving the numerical control instructions, the acquisition monitoring unit sends control commands according to the numerical values ​​to control the output of the photovoltaic inverter. Proportional regulation: The master station sends the inverter rated power (active power, reactive power) percentage control instruction through the fusion terminal and the acquisition terminal. After receiving it, the acquisition monitoring unit sends the control command according to the rated power percentage to control the output of the photovoltaic inverter; Time period adjustment: The master station sends a control period table containing time values ​​and control values ​​(indicators support percentages or numerical values) through the fusion terminal and the collection terminal. The collection and monitoring unit receives and stores the control instructions according to the time requirements and automatically recovers after the control ends.

[0060] The above is a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

[0061] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by 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 collection and monitoring unit via the distributed photovoltaic communication interface adapter; the distributed photovoltaic collection and monitoring unit communicates with the intelligent fusion terminal in the substation area and accepts the regulation of the intelligent fusion terminal in the substation area to realize the rigid control / flexible regulation of the grid-connected and off-grid distributed photovoltaic equipment; The intelligent fusion terminal in the substation collects data on each grid-connected point, including the operation and grid-connected status of photovoltaic users, in real time, and implements distributed photovoltaic overvoltage control and / or photovoltaic reverse transmission control in the low-voltage substation based on edge computing.

2. According to claim 1, a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal is characterized in that: The distributed photovoltaic overvoltage control is specifically as follows: Based on the PV curve and QV curve, when the voltage exceeds the limit, if the current inverter reactive power supports regulation, the inverter reactive power regulation is performed first. If it still exceeds the limit, the PV active power regulation is performed. The reactive power regulation is specifically as follows: When the photovoltaic voltage exceeds the limit, the adjustable reactive power Qout is calculated by looking up the QV curve diagram according to the current over-limit voltage Ui, and sent through the intelligent fusion terminal in the substation area to limit the reactive power of the inverter to Qout.

3. According to claim 3, a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal is characterized in that: The specific regulation strategy of reactive power regulation includes: Set the coarse adjustment voltage threshold Ustep1, the adjustment times Cnt1; the fine adjustment threshold Ustep2, the adjustment times Cnt2, and the adjustment time interval Tstep; According to the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current coarse adjustment Qout adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; According to the current over-limit voltage value - fine-tuning Ustep2 as Ui, search the QV curve to obtain the adjustable Qout value, issue the current fine-tuning Qout adjustment command, and after the time interval Tstep, repeat the coarse-tuning Cnt2 times to end the reactive power adjustment process; If the voltage at the grid connection point still exceeds the limit, the adjustable inverter PV active power regulation is performed.

4. According to claim 2, a distributed photovoltaic grid-connected coordinated control method based on a fusion terminal is characterized in that: The active power regulation is: When the PV exceeds the limit, at the current over-limit voltage, the decreasing coarse adjustment or fine adjustment threshold is used as the target voltage Ui, and the operating active power Pout is calculated by looking up the PV curve diagram, and sent through the intelligent fusion terminal of the substation area, so that the active power of the inverter is limited to Pout; The target voltage continues to decrease until it reaches the set minimum voltage. If the phase voltage value cannot be lowered, a trip command is issued to the photovoltaic switch to trip the photovoltaic circuit breaker at the inverter grid-connected point.

5. A distributed photovoltaic grid-connected coordinated control method based on fusion terminal according to claim 4, characterized in that: The specific regulation strategy of the active power regulation includes: Set the coarse adjustment voltage threshold Ustep1, the adjustment times Cnt1; the fine adjustment threshold Ustep2, the adjustment times Cnt2; the adjustment time interval Tstep; According to the current over-limit voltage value - coarse adjustment Ustep1 as Ui, search the PV curve to obtain the expected power generation Pout value, issue the current coarse adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt1 times and then switch to the fine adjustment command; According to the current over-limit voltage value - fine-adjust Ustep2 as Ui, search the PV curve to obtain the expected power generation Pout value, issue the current fine-adjustment command, and after the time interval Tstep, repeat the coarse adjustment Cnt2 times to end the active power regulation process; In order to prevent frequent adjustments, the start adjustment value is set to 236V±1%. When the voltage collected in real time exceeds the limit, the adjustment is started; If the PV curve does not exist, the strategy of coarse and fine adjustment is switched to the coarse and fine adjustment ratio; The coarse and fine tuning strategies are as follows: Set the coarse adjustment active power threshold Pstep1, adjustment times Cnt1; fine adjustment threshold Pstep2, adjustment times Cnt2; adjustment time interval Tstep; According to the current active power P value - Pstep1, the current coarse adjustment command is issued. After the time interval Tstep, the coarse adjustment is repeated Cnt1 times and then the command is changed to the fine adjustment command. According to the current active power P value - Pstep2, the current fine adjustment command is issued. After the time interval Tstep, the coarse adjustment Cnt2 times are repeated, and the coarse and fine adjustment process ends.

6. A distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 2, characterized in that: By recording and analyzing the historical curve relationship of the grid-connected voltage, current, active power and reactive power at the grid-connected point, the PV curve and QV curve of the distributed photovoltaic are formed. By inputting the overvoltage V value to be controlled by the distributed photovoltaic grid-connected, the predicted input P or Q value affected by the power grid is calculated.

7. A distributed photovoltaic grid-connected coordinated control method based on fusion terminal according to claim 6, characterized in that: For PV inverters in MPPT mode: The intelligent fusion terminal in the substation regularly collects the output voltage, current, active power and reactive power data of the photovoltaic inverter, and regularly records the daily historical curve data; Based on the data of recent days, the voltage U and output power P curve of photovoltaic voltage access point are formed through search and interpolation methods, forming the PV relationship curve: At the sampling moment, record the photovoltaic active power Pi, and take the maximum value of the three-phase voltage as the voltage Vi; Normalization processing, using Pi / PN, Vi / 220 as the normalized sampling record values ​​of the inverter; Through discretization processing, the measurement points are accumulated in different time periods to form and store the PV relationship curve of the day; For the PV curves of the past seven days, take the 3-day curves with the smallest covariance, and take the average value of the 3-day curve V as the PV curve trajectory diagram of the inverter operation.

8. A distributed photovoltaic grid-connected coordinated control method based on a fusion terminal according to claim 6, characterized in that: For inverters with adjustable reactive power in the area, set a trigger or a fixed interval for a specified number of days, and collect QV data and analyze the impact during the period of high photovoltaic power generation, including the following processes: From the range of Q=0 to QN, reactive power control instructions are issued with reactive power control amount Q+=0.1×QN; The intelligent fusion terminal in the substation collects data of the photovoltaic inverter including output voltage, current, active power and reactive power, and records the average U value currently collected under the gradient reactive power Q; And generate QV test curve and add it to the corresponding inverter QV curve library; The QV curve generation method includes: At the reactive power regulation time, record the PV reactive power Qi, and take the maximum value of the three-phase voltage as the voltage Vi; Normalization processing, calculate Qi / QN, where QN is the maximum reactive power that can be adjusted by photovoltaics, and Vi / 220 is the normalized sampling record value of the inverter; Store the QV test curve of this time; For the QV curves of the past seven days, take the three-day curve with the smallest covariance and take the V average value as the QV curve trajectory diagram of the inverter operation.

9. The method for coordinated control of distributed photovoltaic grid connection based on fusion terminal according to claim 1, characterized in that: The regulation strategy of photovoltaic reverse transmission management includes: A fixed time is used as the delay strategy scheduling cycle to repeatedly obtain the distribution transformer load rate, total active power and active power of inverters at each grid connection point: When the total active power of the distribution transformer is less than 0 and the load rate of the substation is ≥80%, it is judged that photovoltaic reverse transmission occurs and a reverse heavy overload occurs; at this time, the substation intelligent fusion terminal reduces the active power of photovoltaic power generation for all inverters in turn by a gradient of 5%, and sends the adjustment command to each inverter; After a delay strategy scheduling cycle, it is determined again whether a reverse heavy overload occurs. If it is still a reverse heavy overload, the gradient limited active power regulation process continues; If the total active power of the distribution transformer is > 0 and the load factor of the substation is ≥ 2%, it is judged that the photovoltaic reverse overload has returned. At this time, the fusion terminal increases the active power of photovoltaic power generation for all inverters in turn by a gradient of 5%, and sends the adjustment instructions to each inverter.

10. A distributed photovoltaic grid-connected coordinated control method based on fusion terminal according to claim 1, characterized in that: The intelligent fusion terminal in the substation area communicates with the property management platform through 4G / 5G communication mode, and uploads the data to the IoT cloud master station; so as to realize the remote monitoring of the on-site distributed photovoltaic by the master station on the distribution cloud master station platform side; The intelligent fusion terminal in the substation supports the remote control function of the inverter of the distribution master station: The process of implementing cloud-edge collaborative remote control is as follows: When the power grid is restored, the intelligent fusion terminal in the substation controls the photovoltaic grid connection when receiving the remote control grid connection command from the master station; The master station and the intelligent fusion terminal of the substation area perform cloud-edge collaborative remote adjustment and remote control functions. Remote adjustment includes one of numerical adjustment, proportional adjustment, and time period adjustment: Numerical adjustment: The master station sends the inverter output power numerical control instructions through the fusion terminal and the acquisition terminal. After receiving the instructions, the acquisition monitoring unit sends the control command according to the numerical value to control the output of the photovoltaic inverter; Proportional regulation: The master station sends the inverter rated power percentage control instruction through the fusion terminal and the acquisition terminal. After receiving it, the acquisition monitoring unit sends the control command according to the rated power percentage to control the output of the photovoltaic inverter; Time period adjustment: The master station sends a control period table containing time values ​​and control values ​​through the fusion terminal and the acquisition terminal. The acquisition monitoring unit receives and stores the control instructions according to the time requirements and automatically recovers after the control ends. Remote control includes controlling the photovoltaic inverter on / off the grid.

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