Distributed photovoltaic grid-connected and off-grid coordination control method

Abstract

The invention discloses a distributed photovoltaic grid-connected and off-grid coordination control method. The method comprises the following steps: a photovoltaic data acquisition terminal acquires an operation state data set of a photovoltaic array, an inverter and the like through each node sensor and intelligent equipment; the photovoltaic data preprocessing terminal performs denoising, normalization and the like on the original data to form a standardized data set; the data analysis terminal calculates a power balance equal coefficient, inputs the power balance equal coefficient into the decision model and outputs a grid-connected and off-grid coordination index; the coordination control terminal judges a grid-connected operation mode or an off-grid operation mode according to the index; the energy management terminal coordinates the power output of each unit during grid connection, and optimizes an energy storage charging and discharging strategy during off-grid; the state monitoring terminal performs real-time monitoring, discovers abnormal early warning and triggers fault processing; according to the method, the operation stability and the energy utilization efficiency of the photovoltaic system are improved.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation technology, and in particular to a method for coordinated control of distributed photovoltaic power generation between the grid and off-grid. Background Technology

[0002] With the acceleration of the global energy transition and the continuous advancement of dual-carbon goals, distributed photovoltaic (PV) power generation has seen a significant increase in its penetration rate in the power system due to its advantages such as clean and low-carbon operation, flexible deployment, and local consumption. Distributed PV systems typically need to dynamically switch between grid-connected and off-grid operation modes to adapt to grid stability requirements, user-side electricity consumption characteristics, and the volatility of renewable energy output. Therefore, higher demands are placed on power balance, voltage and frequency stability, and coordinated control of energy storage devices during the grid connection and off-grid processes.

[0003] Currently, distributed photovoltaic (PV) grid-connected and off-grid control technology has evolved from single-mode independent control to multi-mode collaborative control. Traditional control methods mainly achieve power regulation through droop control and PQ control, and frequency and voltage stability through dual closed-loop voltage and current control. However, in complex scenarios, such as weak grid environments and high-proportion renewable energy integration, problems exist, including uneven power distribution among multiple nodes, transient response lag during grid-connected / off-grid switching, and a single charging and discharging strategy for energy storage devices. Although existing technologies have introduced data acquisition and monitoring systems for operational status monitoring, they lack in-depth analysis and fusion of multi-source data, making it difficult to construct a comprehensive evaluation system that reflects the system's operational status. This results in a lack of comprehensiveness and dynamic adaptability in the formulation of control strategies.

[0004] The main bottlenecks of existing technologies are concentrated in the following aspects: First, power balance control relies only on local node data and does not consider the global characteristics of distributed photovoltaic systems, which can easily lead to an aggravation of power imbalance between regions; Second, voltage stability regulation does not fully utilize the reactive power compensation capability and line impedance characteristics of photovoltaic inverters, resulting in large voltage fluctuations at the grid connection point; Third, frequency regulation is insufficient in its dynamic response to the state of charge of energy storage devices, which may lead to the risk of frequency collapse due to limited energy storage capacity or unreasonable charging and discharging strategies; Fourth, the switching between grid-connected and off-grid modes lacks quantitative evaluation indicators and dynamic weight adjustment mechanisms, and the mode switching logic is rigid, making it unable to adapt to real-time operating conditions such as grid frequency change rate and load mutations; Fifth, fault monitoring and handling rely on threshold judgment and lack multi-parameter joint early warning and active fault tolerance capabilities, which may lead to the spread of abnormal states.

[0005] Therefore, it is essential to invent a distributed photovoltaic grid-connected and off-grid coordinated control method to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a distributed photovoltaic grid-connected and off-grid coordinated control method to solve the problems mentioned in the background art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a distributed photovoltaic grid-connected and off-grid coordinated control method, comprising the following steps: Step 1: The photovoltaic data acquisition terminal collects photovoltaic operation status datasets from the photovoltaic array, inverter, grid connection point and energy storage device through sensors and smart devices deployed at each node of the distributed photovoltaic power station. Step 2: The photovoltaic data preprocessing terminal performs noise reduction, normalization and format unification processing on the raw data in the photovoltaic operation status dataset, removes abnormal data points, fills in missing data, and forms a standardized dataset in a standard format. Step 3: The data analysis terminal analyzes and calculates the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient of the standardized dataset, and inputs the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient into the grid connection and off-grid coordination decision model, and outputs the grid connection and off-grid coordination index. Step 4: The coordination control terminal divides the current operation mode of the distributed photovoltaic system into grid-connected operation mode and off-grid operation mode according to the grid-connected and off-grid coordination index. Step 5: When the energy management terminal is in grid-connected operation mode, it coordinates and controls the active and reactive power output of each distributed photovoltaic unit according to the load demand of the grid, the output power of the photovoltaic system and the regulation capability of the energy storage device; when it is in off-grid operation mode, it optimizes the charging and discharging strategy of the energy storage device according to the remaining capacity of the energy storage device, the load demand, the real-time output of the photovoltaic system and the frequency regulation demand. Step 6: The status monitoring terminal monitors the operating status of each device in the distributed photovoltaic system and the key parameters in the grid-connected and off-grid coordinated control process in real time. If an abnormality is detected, an early warning signal is issued immediately, and the corresponding fault handling mechanism is automatically triggered, including adjusting control parameters, switching operating modes, and starting backup equipment.

[0008] Preferably, the photovoltaic operating status dataset in step 1 includes the real-time active power of the photovoltaic array, the real-time active power of the energy storage device, the active power of the node AC load, the rated active power of the photovoltaic unit, the real-time efficiency of the inverter, the grid frequency, the real-time bus voltage at the grid connection point, the rated voltage at the grid connection point, the real-time reactive power compensation of the photovoltaic unit, the maximum reactive power output capacity of the photovoltaic unit, the equivalent reactance from the grid connection point to the system power supply, the equivalent resistance from the grid connection point to the system power supply, the active power regulation of the energy storage device based on droop control, the rated active power of the energy storage device, the real-time state of charge of the energy storage device, the minimum allowable state of charge of the energy storage device, and the maximum allowable state of charge of the energy storage device.

[0009] Preferably, in step 3, the power balance coefficient is specifically: ; Where, α iThe weight coefficient for the i-th node is, specifically... N is the total number of distributed photovoltaic nodes, P pv，i Let P be the real-time active power of the i-th photovoltaic array. ess，i Let P be the real-time active power of the i-th energy storage device, with negative values ​​for charging and positive values ​​for discharging. load，i Let P be the active power of the AC load at the i-th node. rated，i η is the rated active power of the i-th photovoltaic unit. inv，i Let f be the real-time efficiency of the i-th inverter. rated Let T be the rated frequency of the power grid, T be the dynamic monitoring period, and Δf(t) be the frequency deviation of the power grid at time t, specifically Δf(t) = f(t) - f rated , where f(t) is the real-time frequency of the power grid at time t.

[0010] Preferably, in step 3, the voltage stability coefficient is specifically: ; in, M represents the number of grid connection points, and V represents... bus，j V is the real-time bus voltage at the j-th grid connection point. nom，j Q is the rated voltage of the j-th grid connection point. c，j Let Q be the real-time reactive power compensation of the j-th photovoltaic unit. c，max，j X represents the maximum reactive power output capacity of the j-th photovoltaic unit. j R is the equivalent reactance from the j-th grid connection point to the system power supply. j Let be the equivalent resistance from the j-th grid connection point to the system power supply.

[0011] Preferably, in step 3, the frequency adjustment coefficient is specifically: ; in, T represents the dynamic monitoring period, and L represents the total number of energy storage devices. Let P be the rate of change of the power grid frequency at time t. ess，k Let P be the active power regulation power of the k-th energy storage device based on droop control. ess，max，k For the rated active power of the k-th energy storage device, SOC k For the k-th energy storage device, the real-time state of charge (SOC) is... min，k For the k-th energy storage device, the minimum permissible state of charge (SOC) is... max，k This represents the maximum permissible state of charge of the k-th energy storage device.

[0012] Preferably, in step 3, the on-grid / off-grid coordination decision model specifically comprises: , in, ωp ω is the power weighting coefficient. v ω is the voltage weighting coefficient. f ω is the frequency weighting coefficient. p +ω v +ω f =1 and ω p ω v and ω f ∈[0,1],ω p ′ represents the dynamic weighting coefficient. Let K be the rate of change of the power grid frequency at time t. p K is the power balance factor. v K is the voltage stability coefficient. f This is the frequency adjustment coefficient.

[0013] Preferably, in step 4, when the grid connection coordination index is greater than or equal to the preset grid connection threshold, a grid connection control command is issued to switch to the grid connection operation mode; when the grid connection coordination index is less than the grid connection threshold but greater than or equal to the preset grid disconnection threshold, a grid disconnection control command is issued to switch to the grid disconnection operation mode.

[0014] Preferably, the charging and discharging strategy in step 5 includes: When the output power of the distributed photovoltaic system is greater than the sum of the load demand and the energy storage charging power, the energy storage device is controlled to charge at maximum power until the maximum allowable state of charge is reached.

[0015] Preferably, the charging and discharging strategy in step 5 further includes: when the output power of the distributed photovoltaic system is less than the load demand, controlling the energy storage device to discharge power to meet the frequency regulation requirements, supplementing the insufficient energy, and ensuring that the state of charge is not lower than the minimum allowable value.

[0016] Preferably, the abnormal conditions include: a sudden drop in the output power of the photovoltaic array; the inverter temperature continuously exceeding the rated operating temperature; the grid voltage deviation exceeding the rated voltage threshold; the frequency change rate continuously exceeding the preset change rate threshold; and abnormal state of charge of the energy storage device, including being below the minimum permissible state of charge and exceeding the maximum permissible state of charge.

[0017] Beneficial effects of this invention: 1. This invention calculates the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient through a data analysis terminal, and outputs the grid connection and disconnection coordination index using a grid connection and disconnection coordination decision model, providing a scientific and quantitative decision basis for switching system operation modes and improving the scientific nature of grid connection and disconnection coordination control. 2. This invention uses a coordinated control terminal to divide the grid-connected and off-grid operation modes according to the grid-connected and off-grid coordination index, thereby realizing intelligent switching of the operation mode of the distributed photovoltaic system. This enables the system to select the optimal mode according to the actual operating status, improving the adaptability and stability of the system operation. 3. This invention coordinates and controls power output and optimizes energy storage charging and discharging strategies under different operating modes through an energy management terminal. When connected to the grid, it meets the grid load demand, and when disconnected from the grid, it makes reasonable use of energy storage, improves energy utilization efficiency, and ensures the balance of energy supply and demand in the system. 4. This invention monitors the operating status and key parameters of equipment in real time through a status monitoring terminal, promptly detects anomalies and triggers a fault handling mechanism, realizes dynamic monitoring and fault self-healing of the system, ensures the safe and stable operation of the distributed photovoltaic system, and reduces fault risks and maintenance costs. Attached Figure Description

[0018] Figure 1 A flowchart of a distributed photovoltaic grid-connected and off-grid coordinated control method; Figure 2 This is a schematic diagram of the device connection involved in the method of the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: The present invention provides, as follows Figure 1 The distributed photovoltaic grid-connected and off-grid coordinated control method shown includes the following steps: S1. The photovoltaic data acquisition terminal collects photovoltaic operation status datasets from the photovoltaic array, inverter, grid connection point and energy storage device through sensors and intelligent devices deployed at each node of the distributed photovoltaic power station. Furthermore, in the above technical solution, the photovoltaic operating status dataset includes the real-time active power of the photovoltaic array, the real-time active power of the energy storage device, the active power of the node AC load, the rated active power of the photovoltaic unit, the real-time efficiency of the inverter, the grid frequency, the real-time bus voltage at the grid connection point, the rated voltage at the grid connection point, the real-time reactive power compensation of the photovoltaic unit, the maximum reactive power output capacity of the photovoltaic unit, the equivalent reactance from the grid connection point to the system power supply, the equivalent resistance from the grid connection point to the system power supply, the active power regulation of the energy storage device based on droop control, the rated active power of the energy storage device, the real-time state of charge of the energy storage device, the minimum allowable state of charge of the energy storage device, and the maximum allowable state of charge of the energy storage device.

[0021] The real-time active power of the photovoltaic array is collected by the inverter's built-in power sensor at its DC input or AC output, and the power is calculated using current and voltage sensors before being uploaded via a communication interface. The real-time active power of the energy storage device is calculated by measuring voltage, current, and power factor at its AC output using sensors built into the energy storage converter or an external transmitter, and is collected and transmitted by the controller. The active power of the node AC load is measured and calculated using a power meter or combined sensor installed in the distribution cabinet at the load's inlet, and the sum of the three-phase active power is calculated via current and voltage transformers. The real-time efficiency of the inverter is calculated in real-time using the ratio of AC output power to DC input power by its internal DC and AC power sensors. The grid frequency is obtained by measuring the AC voltage period or phase change using a power quality monitoring device or phasor measurement unit at the grid connection point. The real-time bus voltage at the grid connection point is obtained using a voltage transformer and a data acquisition module. The data is collected at the AC bus of the grid connection point, converted, and digitized before transmission. The real-time reactive power compensation of the photovoltaic unit is generated by the inverter supporting reactive power regulation at the AC output terminal, which outputs reactive power according to instructions and calculates and uploads it through the internal controller. The active power regulation of the energy storage device based on droop control is automatically adjusted and calculated in real time by the droop control module of the energy storage converter according to the grid deviation through algorithms. The real-time state of charge of the energy storage device is updated in real time in the energy storage battery pack controller by the battery management system through algorithms such as ampere-hour integration. The rated active power, maximum reactive power output capacity of the photovoltaic unit, and rated active power of the energy storage device are obtained from the equipment nameplate parameters. The rated voltage of the grid connection point, the equivalent reactance from the grid connection point to the system power supply, and the equivalent resistance from the grid connection point to the system power supply are provided by the power company. The minimum allowable state of charge and the maximum allowable state of charge of the energy storage device are safety operating parameters provided by the battery manufacturer.

[0022] S2. The photovoltaic data preprocessing terminal performs noise reduction, normalization and format unification processing on the raw data in the photovoltaic operation status dataset, removes abnormal data points, fills in missing data, and forms a standardized dataset in a standard format. The execution process of the photovoltaic data preprocessing terminal is as follows: First, noise reduction is performed. Random noise introduced into the original data due to factors such as sensor accuracy and environmental interference is addressed using algorithms such as median filtering, Gaussian filtering, or wavelet denoising to filter time-series data such as the real-time active power of the photovoltaic array and the real-time active power of the energy storage device collected by each node. This eliminates high-frequency noise and glitches, preserving the true trend of the data. Next, outlier data point removal is performed. Statistical analysis methods, such as IQR, are used to identify and mark outlier data points that exceed the normal operating range, such as a sudden drop in photovoltaic array output power to below 20% of the rated power. These outliers are removed from the dataset to avoid misleading subsequent analysis. Then, missing data is filled in. For missing data caused by communication failures, equipment failures, etc., an appropriate filling strategy is selected based on the data characteristics: for short-term continuous missing data, linear interpolation is used; for long-term missing data or data with periodic patterns, such as grid frequency and load power, time-series models, such as ARIMA and LSTM, are used for predictive filling to ensure the integrity of the dataset. Further normalization is performed to eliminate the impact of different physical dimensions, such as voltage, power, and frequency, on data analysis. The data is uniformly quantified: for static parameters such as the rated active power of photovoltaic units and the rated active power of energy storage devices, minimum-maximum normalization is used to map the data to the [0,1] interval; for dynamic parameters such as grid frequency deviation and the state of charge of energy storage devices, Z-score standardization is used. Finally, format unification is achieved. Data from each node is structured according to preset standard data formats, such as CSV, JSON, or a custom binary format: a unified timestamp format is used to ensure data time synchronization; parameter naming, units, and data types are standardized to form a standardized two-dimensional data table, where each row represents a sampling time and each column corresponds to a physical parameter, facilitating direct access and calculation by the data analysis terminal.

[0023] S3. The data analysis terminal analyzes and calculates the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient of the standardized dataset, and inputs the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient into the grid-connected and off-grid coordination decision model, and outputs the grid-connected and off-grid coordination index.

[0024] In step 3, the power balance coefficient is specifically as follows: ; Where, α i The weight coefficient for the i-th node is, specifically... N is the total number of distributed photovoltaic nodes, P pv，i Let P be the real-time active power of the i-th photovoltaic array. ess，i Let P be the real-time active power of the i-th energy storage device, with negative values ​​for charging and positive values ​​for discharging. load，iLet P be the active power of the AC load at the i-th node. rated，i η is the rated active power of the i-th photovoltaic unit. inv，i Let f be the real-time efficiency of the i-th inverter. rated Let T be the rated frequency of the power grid, T be the dynamic monitoring period, and Δf(t) be the frequency deviation of the power grid at time t, specifically Δf(t) = f(t) - f rated , where f(t) is the real-time frequency of the power grid at time t.

[0025] In step 3, the voltage stability coefficient is specifically: ; in, M represents the number of grid connection points, and V represents... bus，j V is the real-time bus voltage at the j-th grid connection point. nom，j Q is the rated voltage of the j-th grid connection point. c，j Let Q be the real-time reactive power compensation of the j-th photovoltaic unit. c，max，j X represents the maximum reactive power output capacity of the j-th photovoltaic unit. j R is the equivalent reactance from the j-th grid connection point to the system power supply. j Let be the equivalent resistance from the j-th grid connection point to the system power supply.

[0026] In step 3, the frequency adjustment coefficient is specifically as follows: ; in, T represents the dynamic monitoring period, and L represents the total number of energy storage devices. Let P be the rate of change of the power grid frequency at time t. ess，k Let P be the active power regulation power of the k-th energy storage device based on droop control. ess，max，k For the rated active power of the k-th energy storage device, SOC k For the k-th energy storage device, the real-time state of charge (SOC) is... min，k For the k-th energy storage device, the minimum permissible state of charge (SOC) is... max，k This represents the maximum permissible state of charge of the k-th energy storage device.

[0027] In step 3, the on-grid and off-grid coordination decision model is specifically as follows: , in, ω p ω is the power weighting coefficient. v ω is the voltage weighting coefficient. f ω is the frequency weighting coefficient. p +ω v +ω f =1 and ω p ωv and ω f ∈[0,1],ω p ′ represents the dynamic weighting coefficient. Let K be the rate of change of the power grid frequency at time t. p K is the power balance factor. v K is the voltage stability coefficient. f This is the frequency adjustment coefficient.

[0028] S4. The coordination control terminal divides the current operation mode of the distributed photovoltaic system into grid-connected operation mode and off-grid operation mode according to the grid-connected and off-grid coordination index. Furthermore, in the above technical solution, the grid-connected operation mode is to issue a grid-connected control command and switch to the grid-connected operation mode when the grid-connected / off-grid coordination index is greater than or equal to a preset grid-connected threshold; the off-grid operation mode is to issue an off-grid control command and switch to the off-grid operation mode when the grid-connected / off-grid coordination index is less than the grid-connected threshold but greater than or equal to a preset off-grid threshold.

[0029] The preset grid connection threshold is typically set to 0.7 to 0.9, and needs to be adjusted according to the grid stability requirements. It can be appropriately lowered for strong grids and raised for weak grids. The preset off-grid threshold is typically set to 0.4 to 0.6 to ensure that energy storage and photovoltaic synergy can maintain a basic balance and avoid frequent switching.

[0030] S5. In grid-connected operation mode, the energy management terminal coordinates and controls the active and reactive power output of each distributed photovoltaic unit according to the grid load demand, the output power of the photovoltaic system and the regulation capability of the energy storage device; in off-grid operation mode, it optimizes the charging and discharging strategy of the energy storage device according to the remaining capacity of the energy storage device, load demand, real-time output of the photovoltaic system and frequency regulation requirements. The distributed photovoltaic (PV) unit refers to a basic unit in a distributed PV power station that has independent power generation and control functions. It typically consists of a PV array and an inverter, and may also include energy storage devices associated with that node. Each unit corresponds to a node in the distributed PV system and can independently regulate active and reactive power. It collects operational data through sensors and smart devices and participates in the power balance, voltage stability, and frequency regulation control of the entire system. Active power regulation includes dynamically allocating the active power output of each PV unit according to local load demand. If the PV output power exceeds the load demand, excess energy is preferentially stored in the energy storage device or fed into the grid through the inverter. If the PV output power is less than the load demand, the energy storage device discharges to fill the gap, or power is drawn from the grid. Reactive power regulation includes utilizing the reactive power capacity of the PV inverter to provide reactive power support to the grid; and dynamically adjusting reactive power output according to the voltage stability coefficient: when the voltage stability coefficient is low, the reactive power compensation of the inverter is increased.

[0031] S6. The status monitoring terminal monitors the operating status of each device in the distributed photovoltaic system and the key parameters in the grid-connected and off-grid coordinated control process in real time. If an abnormality is detected, it will immediately issue an early warning signal and automatically trigger the corresponding fault handling mechanism, including adjusting control parameters, switching operating modes, and starting backup equipment.

[0032] Furthermore, in the above technical solution, the abnormal conditions include: a sudden drop in the output power of the photovoltaic array; the inverter temperature continuously exceeding the rated operating temperature; the grid voltage deviation exceeding the rated voltage threshold; the frequency change rate continuously exceeding the preset change rate threshold; and abnormal state of charge of the energy storage device, including being below the minimum allowable state of charge and exceeding the maximum allowable state of charge.

[0033] The sudden drop in photovoltaic array output power refers to a short period of time, such as within minutes, where the output power drops to below 20% of the rated power. Causes of this abnormality may include sudden weather changes, such as cloud cover or heavy rain; photovoltaic module malfunctions, such as damaged cells or loose wiring; inverter malfunctions; or communication interruptions. The reason the inverter temperature consistently exceeds the rated operating temperature may be due to a malfunctioning cooling fan, blocked vents, prolonged full-load operation, excessively high ambient temperature, or aging of internal inverter components. The rated operating temperature range is between 70℃ and 85℃, depending on the equipment model. A grid voltage deviation exceeding the rated voltage threshold refers to a deviation of the real-time bus voltage at the grid connection point from the rated voltage at the grid connection point by a factor exceeding a preset threshold, typically ±5% to ±10% of the rated voltage, specifically determined according to grid standards. The cause of the abnormal situation may be a grid-side fault, such as a short circuit or open circuit, insufficient or excessive reactive power compensation of the distributed photovoltaic system, or voltage fluctuations caused by sudden load changes. A frequency change rate continuously exceeding the preset change rate threshold refers to a frequency fluctuation amplitude continuously exceeding a preset value per unit time, such as 0.1Hz / s to 0.2Hz / s, specifically set according to grid stability requirements.

[0034] Example 2: The present invention provides, as follows Figure 2 The method for coordinated control of distributed photovoltaic grid connection and off-grid operation, as shown, includes a photovoltaic data acquisition terminal, a photovoltaic data preprocessing terminal, a data analysis terminal, a coordinated control terminal, an energy management terminal, and a status monitoring terminal.

[0035] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for coordinated control of distributed photovoltaic grid connection and off-grid operation, characterized in that, Includes the following steps: Step 1: The photovoltaic data acquisition terminal collects photovoltaic operation status datasets from the photovoltaic array, inverter, grid connection point and energy storage device through sensors and smart devices deployed at each node of the distributed photovoltaic power station. Step 2: The photovoltaic data preprocessing terminal performs noise reduction, normalization and format unification processing on the raw data in the photovoltaic operation status dataset, removes abnormal data points, fills in missing data, and forms a standardized dataset in a standard format. Step 3: The data analysis terminal analyzes and calculates the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient of the standardized dataset, and inputs the power balance coefficient, voltage stability coefficient, and frequency regulation coefficient into the grid connection and off-grid coordination decision model, and outputs the grid connection and off-grid coordination index. Step 4: The coordination control terminal divides the current operation mode of the distributed photovoltaic system into grid-connected operation mode and off-grid operation mode according to the grid-connected and off-grid coordination index. Step 5: When the energy management terminal is in grid-connected operation mode, it coordinates and controls the active and reactive power output of each distributed photovoltaic unit according to the load demand of the grid, the output power of the photovoltaic system and the regulation capability of the energy storage device; when it is in off-grid operation mode, it optimizes the charging and discharging strategy of the energy storage device according to the remaining capacity of the energy storage device, the load demand, the real-time output of the photovoltaic system and the frequency regulation demand. Step 6: The status monitoring terminal monitors the operating status of each device in the distributed photovoltaic system and the key parameters in the grid-connected and off-grid coordinated control process in real time. If an abnormality is detected, an early warning signal is issued immediately, and the corresponding fault handling mechanism is automatically triggered, including adjusting control parameters, switching operating modes, and starting backup equipment.

2. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, The photovoltaic operating status dataset in step 1 includes the real-time active power of the photovoltaic array, the real-time active power of the energy storage device, the active power of the node AC load, the rated active power of the photovoltaic unit, the real-time efficiency of the inverter, the grid frequency, the real-time bus voltage at the grid connection point, the rated voltage at the grid connection point, the real-time reactive power compensation of the photovoltaic unit, the maximum reactive power output capacity of the photovoltaic unit, the equivalent reactance from the grid connection point to the system power supply, the equivalent resistance from the grid connection point to the system power supply, the active power regulation of the energy storage device based on droop control, the rated active power of the energy storage device, the real-time state of charge of the energy storage device, the minimum allowable state of charge of the energy storage device, and the maximum allowable state of charge of the energy storage device.

3. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, In step 3, the power balance coefficient is specifically as follows: ； Where, α i The weight coefficient for the i-th node is, specifically... N is the total number of distributed photovoltaic nodes, P pv，i Let P be the real-time active power of the i-th photovoltaic array. ess，i Let P be the real-time active power of the i-th energy storage device, with negative values ​​for charging and positive values ​​for discharging. load，i Let P be the active power of the AC load at the i-th node. rated，i η is the rated active power of the i-th photovoltaic unit. inv，i Let f be the real-time efficiency of the i-th inverter. rated Let T be the rated frequency of the power grid, T be the dynamic monitoring period, and Δf(t) be the frequency deviation of the power grid at time t, specifically Δf(t) = f(t) - f rated , where f(t) is the real-time frequency of the power grid at time t.

4. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, In step 3, the voltage stability coefficient is specifically: ； in, M represents the number of grid connection points, and V represents... bus，j V is the real-time bus voltage at the j-th grid connection point. nom，j Q is the rated voltage of the j-th grid connection point. c，j Let Q be the real-time reactive power compensation of the j-th photovoltaic unit. c，max，j X represents the maximum reactive power output capacity of the j-th photovoltaic unit. j R is the equivalent reactance from the j-th grid connection point to the system power supply. j Let be the equivalent resistance from the j-th grid connection point to the system power supply.

5. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, In step 3, the frequency adjustment coefficient is specifically as follows: ； in, T represents the dynamic monitoring period, and L represents the total number of energy storage devices. Let P be the rate of change of the power grid frequency at time t. ess，k Let P be the active power regulation power of the k-th energy storage device based on droop control. ess，max，k For the rated active power of the k-th energy storage device, SOC k For the k-th energy storage device, the real-time state of charge (SOC) is... min，k For the k-th energy storage device, the minimum permissible state of charge (SOC) is... max，k This represents the maximum permissible state of charge of the k-th energy storage device.

6. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, In step 3, the on-grid and off-grid coordination decision model is specifically as follows: ， in, ω p ω is the power weighting coefficient. v ω is the voltage weighting coefficient. f ω is the frequency weighting coefficient. p +ω v +ω f =1 and ω p ω v and ω f ∈[0,1],ω p ′ represents the dynamic weighting coefficient. Let K be the rate of change of the power grid frequency at time t. p K is the power balance factor. v K is the voltage stability coefficient. f This is the frequency adjustment coefficient.

7. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, In step 4, when the grid connection coordination index is greater than or equal to the preset grid connection threshold, a grid connection control command is issued to switch to the grid connection operation mode; when the grid connection coordination index is less than the grid connection threshold but greater than or equal to the preset grid disconnection threshold, a grid disconnection control command is issued to switch to the grid disconnection operation mode.

8. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, The charging and discharging strategy in step 5 includes: When the output power of the distributed photovoltaic system is greater than the sum of the load demand and the energy storage charging power, the energy storage device is controlled to charge at maximum power until the maximum allowable state of charge is reached.

9. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, The charging and discharging strategy in step 5 also includes: when the output power of the distributed photovoltaic system is less than the load demand, controlling the energy storage device to discharge power to meet the frequency regulation requirements, supplementing the insufficient energy, and ensuring that the state of charge is not lower than the minimum allowable value.

10. The distributed photovoltaic grid-connected and off-grid coordinated control method according to claim 1, characterized in that, The abnormal conditions include: a sudden drop in the output power of the photovoltaic array; the inverter temperature continuously exceeding the rated operating temperature; the grid voltage deviation exceeding the rated voltage threshold; the frequency change rate continuously exceeding the preset change rate threshold; and abnormal state of charge of the energy storage device, including being below the minimum permissible state of charge and exceeding the maximum permissible state of charge.

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