Distributed photovoltaic operation status assessment and grid-connected switch control method and system

Abstract

The present invention relates to the field of power grid monitoring technology, specifically to a distributed photovoltaic operating status assessment and grid-connected switch control method and system, comprising the following steps: obtaining bus voltage values before and after photovoltaic unit access, collecting voltage measurement values of photovoltaic units under different power output states, calculating voltage change, calculating voltage offset per unit time, and generating voltage offset change data. In the present invention, based on voltage change trend extraction and adaptability classification analysis, combined with voltage stability coefficient calculation, the adaptability of photovoltaic units under different load conditions is quantified, voltage and frequency coupling analysis is introduced, the coupling characteristics of photovoltaic units are graded, and the steady-state voltage range and frequency offset interval allowed by the power grid are dynamically adjusted, so that the grid-connected safety boundary meets actual operating requirements, ensuring stable grid connection when safety conditions are met, and enhancing the adaptability of the power grid to distributed photovoltaic access.

Description

Technical Field

[0001] The present invention relates to the technical field of power grid monitoring, and in particular to a method and system for evaluating the operating status of distributed photovoltaic systems and controlling grid-connected switches. Background Art

[0002] The field of power grid monitoring technology encompasses real-time monitoring of the power system's operating status, data collection and analysis, power equipment status assessment, and abnormal situation detection and early warning. Core content includes the measurement and analysis of electrical parameters such as voltage, current, power factor, and harmonic content. It also involves the assessment of power transmission stability, grid load balancing, and power quality. Through sensor networks, remote communications, and data analysis methods, power grid monitoring technology can achieve comprehensive awareness of power transmission and distribution systems, distributed energy systems, and user-side electricity consumption. In modern power systems, as the proportion of new energy access increases, power grid monitoring technology must also focus on issues such as the output characteristics of distributed power sources, optimization of power transmission paths, and grid connection security to ensure the stable operation of the power system.

[0003] The distributed photovoltaic operating status assessment and grid-connected switch control method involves data collection, feature analysis, and status assessment of the operating conditions of distributed photovoltaic power generation systems. The method then uses the assessment results to adjust the control strategy for the grid-connected switches. This involves real-time measurement of operating parameters such as the photovoltaic array's generated power, voltage fluctuations, current harmonics, and frequency deviation. Data modeling is performed based on grid dispatch requirements to determine the operating status of the photovoltaic system. Based on this, control decisions for the grid-connected switches are made through threshold determination, voltage-frequency coordination analysis, and grid-connection access determination. When the operating status meets the grid-connection conditions, the control circuit issues a connection command, synchronizing the photovoltaic system with the grid. If an operating anomaly or grid disturbance is detected, the grid-connected switch action strategy is adjusted based on a dynamic safety margin calculation method to ensure safe operation of the photovoltaic system.

[0004] Existing PV grid-connection assessment processes rely on static data threshold settings and lack in-depth analysis of dynamic voltage excursion characteristics. This can lead to discrepancies between assessment results and actual operating conditions when voltage fluctuates significantly. PV unit adaptability classification is crude, based solely on single voltage measurement data, ignoring the impact of load variations on voltage stability, resulting in inaccurate adaptability assessments. Lack of correlation analysis between voltage and frequency, with independent measurements of both, prevents the comprehensive impact of the PV system on grid stability and hinders accurate coupling assessments. Grid-connection safety ranges are set based on fixed thresholds and fail to dynamically adjust based on the adaptability characteristics of PV units. This can lead to PV units in some operating states being misclassified as unavailable for grid connection, impacting PV power generation utilization. Grid-connected switch control signals rely on static rules and fail to dynamically optimize based on real-time operating conditions. This prevents rapid adjustment of control strategies during grid fluctuations or PV system anomalies, impacting system stability and potentially impacting grid security. Summary of the Invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and propose a distributed photovoltaic operation status evaluation and grid-connected switch control method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a distributed photovoltaic operation status assessment and grid-connected switch control method, comprising the following steps:

[0007] S1: Obtain the bus voltage value before and after the photovoltaic unit is connected, collect the voltage measurement value of the photovoltaic unit under different power output states, calculate the voltage change, calculate the voltage offset per unit time, and generate voltage offset change data;

[0008] S2: Based on the voltage offset change data, extract the voltage change trend after the photovoltaic unit is connected under different load conditions, calculate the voltage stability coefficient, determine the volatility of the voltage offset change, classify and record the voltage adaptability status, and generate the photovoltaic unit voltage adaptability classification result;

[0009] S3: Based on the voltage offset change data, collect bus frequency change values before and after the photovoltaic unit is connected, calculate the frequency adjustment amplitude per unit time, compare the voltage change rate with the frequency adjustment rate, analyze and classify the voltage-frequency coupling trend, and generate a voltage-frequency coupling classification result;

[0010] S4: Based on the PV unit voltage adaptability classification result and the voltage-frequency coupling classification result, the voltage change amplitude and frequency offset under different power output conditions are extracted, the steady-state voltage range and the allowable frequency offset interval are calculated, and the interval threshold is compared to screen the grid-connected operation interval with high adaptability to generate the PV unit grid-connected safety boundary interval.

[0011] As a further solution of the present invention, the voltage offset change data includes voltage stability evaluation indicators, over-limit voltage change characteristics, and voltage fluctuation distribution records per unit time; the photovoltaic unit voltage adaptability classification results include voltage adaptability level, load state adaptability analysis results, and voltage fluctuation impact assessment results; the voltage-frequency coupling classification results include voltage-frequency change correlation parameters, coupling trend classification standards, and the impact of power output on coupling degree; the photovoltaic unit grid-connected safety boundary interval includes a safe operation threshold, a steady-state grid adaptability range, and a dynamic operation stability interval.

[0012] As a further solution of the present invention, the specific steps of S1 are:

[0013] S111: Based on the bus voltage values before and after the photovoltaic unit is connected, collect the voltage measurement values of the photovoltaic unit under different power output states, calculate the voltage change at each measurement point, calculate the voltage offset in each time period, and establish a voltage offset data set;

[0014] S112: Based on the voltage offset data set, filter out values that exceed the allowable voltage offset range, count the number of data points that exceed the range, and use the formula:

[0015] ;

[0016] Calculate the voltage deviation rate per unit time , obtain the voltage excursion rate distribution record, where, Representative The voltage value of each measuring point, Represents the reference voltage value, Representative The time value of each measurement point, Represents the base time value, Represents the total number of measurement points, Represents the summation operation of all measurement points;

[0017] S113: Based on the voltage offset rate distribution record, a time period corresponding to a maximum offset rate is screened out, abnormal fluctuation data is recorded, and voltage offset change data is established.

[0018] As a further solution of the present invention, the specific steps of S2 are:

[0019] S211: extracting voltage change trends after the photovoltaic units are connected under different load conditions based on the voltage offset change data, calculating voltage change rates under each power output state, and establishing voltage change trend data;

[0020] S212: Calculate the voltage stability coefficient under each power output state according to the voltage change trend data, using the formula:

[0021] ;

[0022] Calculating the voltage stability factor , analyze the voltage fluctuation under various power output states, where Representative The voltage value at a moment, Represents the average voltage under this load condition, Representative The voltage value at a moment, Representative The photovoltaic power output at a given moment, Represents the number of sampling time points under the target load state, Represents the number of all time points recorded under load conditions, represents the sum operation, represents the square root operation, Represents absolute value operation;

[0023] S213: Based on the voltage stability coefficient, determine the volatility of the voltage offset change, classify and record the voltage adaptability status, classify the voltage adaptability level of the photovoltaic unit under each load condition into three types: adaptation, critical adaptation, and non-adaptation, and establish the photovoltaic unit voltage adaptability classification result.

[0024] As a further solution of the present invention, the specific steps of S3 are:

[0025] S311: Based on the voltage offset change data, collect bus frequency change values before and after the photovoltaic unit is connected, calculate the frequency adjustment amplitude per unit time, and establish frequency adjustment amplitude data;

[0026] S312: Analyze the voltage change trend based on the frequency adjustment amplitude data, compare the voltage change rate and frequency adjustment rate under different power output states, and use the formula:

[0027] ;

[0028] Calculating the voltage-frequency coupling coefficient ,in, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, represents the sum operation, represents the square root operation, represents the absolute value operation, represents the number of time points used to calculate the voltage-frequency product, represents the number of time points used to calculate the sum of the squares of voltage and frequency, Represents the number of time points used to calculate the absolute difference between voltage and frequency;

[0029] S313: Determine the voltage-frequency coupling trend based on the voltage-frequency coupling coefficient, classify the coupling degree into three types: low coupling, medium coupling, and high coupling, and establish a voltage-frequency coupling classification result.

[0030] As a further solution of the present invention, the specific steps of S4 are:

[0031] S411: Obtaining the photovoltaic unit voltage adaptability classification result and the voltage-frequency coupling classification result, extracting the voltage variation amplitude and frequency offset under different power output conditions, calculating the steady-state voltage range and frequency offset interval allowed by the power grid, and obtaining the steady-state voltage range and frequency offset interval;

[0032] S412: Based on the steady-state voltage range and the frequency offset interval, comparing the thresholds of each interval, calculating the optimal grid-connected operation interval selection value, and screening out a grid-connected operation interval with high adaptability;

[0033] S413: Based on the highly adaptable grid-connected operation interval, calculate the steady-state voltage mean and frequency offset mean within the interval, determine the safety margin of the grid-connected operation, select the interval boundaries where the voltage and frequency offsets meet the grid safety operation standards, and construct the photovoltaic unit grid-connected safety boundary interval.

[0034] As a further solution of the present invention, the optimal grid-connected operation interval selection value adopts the formula:

[0035] ;

[0036] Calculate, where Represents the optimal grid-connected operation interval selection value, Representative Voltage value at a moment, represents the reference voltage, and Represent the maximum and minimum allowable voltage values, Representative Frequency value at each moment, represents the reference frequency, and Represent the maximum and minimum allowed values of frequency, and are the number of voltage and frequency data points, respectively.

[0037] As a further embodiment of the present invention, the method further comprises S5;

[0038] S5: Based on the grid-connected safety boundary interval of the photovoltaic unit, the current photovoltaic unit operating state is compared with the safety boundary range to determine whether the safety access conditions are met. If the operating state is within the safety boundary, the grid-connected operation is maintained; otherwise, the risk state is marked and a photovoltaic unit grid-connected switch control signal is generated;

[0039] The photovoltaic unit grid-connected switch control signal includes a grid-connected safety determination result, a risk warning signal, and a grid-connected control adjustment instruction.

[0040] As a further solution of the present invention, the specific steps of S5 are:

[0041] S511: Obtaining the grid-connected safety boundary range of the photovoltaic unit, calling the current operating status data of the photovoltaic unit, including voltage, frequency, and power output, and comparing them with the upper and lower limits of the safety boundary range, to determine whether the current operating parameters of the photovoltaic unit are within the allowable range, calculating the degree to which each parameter deviates from the boundary range, and comprehensively evaluating the operating status of the current photovoltaic unit to obtain a photovoltaic unit safety deviation score;

[0042] S512: Based on the safety offset score of the photovoltaic unit, a safety offset threshold is set. If the calculated value is less than the safety offset threshold, the current operating state meets the safety access conditions, the grid-connected operation is maintained, and the current operating parameters are stored. If the calculated value is greater than the safety offset threshold, the photovoltaic unit is marked as a risk state, and the current operating parameters and score are stored. The time when the risk state of the photovoltaic unit occurs and the corresponding environmental parameters are recorded to obtain a risk state mark of the photovoltaic unit;

[0043] S513: Call the risk status mark of the photovoltaic unit, analyze the deviation from the safety boundary parameters for the photovoltaic unit marked as a risk state, and perform grid-connected switch control, including disconnecting the signal or adjusting the signal, adjusting the operating state of the photovoltaic unit or forcibly disconnecting the grid connection, and obtaining the photovoltaic unit grid-connected switch control signal.

[0044] Distributed photovoltaic operation status assessment and grid-connected switch control system, including:

[0045] The voltage offset calculation module obtains the bus voltage value before and after the photovoltaic unit is connected, collects the voltage measurement values of the photovoltaic unit at different power output states, calls the initial voltage value to calculate the voltage change, calculates the voltage offset per unit time, filters the measurement values that exceed the voltage offset threshold, and generates voltage offset change data;

[0046] The voltage adaptability classification module calculates the voltage stability coefficient based on the voltage offset change data, determines the voltage fluctuation range, compares the voltage adaptability threshold, classifies the voltage adaptability level, and generates a photovoltaic unit voltage adaptability classification result;

[0047] The voltage-frequency coupling classification module collects bus frequency change values before and after the photovoltaic unit is connected based on the voltage offset change data, compares the voltage change rate with the frequency adjustment amplitude, divides the coupling degree, and generates a voltage-frequency coupling classification result;

[0048] The grid-connected safety boundary screening module calculates the voltage variation amplitude and the frequency offset based on the photovoltaic unit voltage adaptability classification result and the voltage-frequency coupling classification result, screens the operating range with high adaptability, and generates the photovoltaic unit grid-connected safety boundary range;

[0049] The grid-connected switch control module determines whether the current photovoltaic unit operating state is within a safe range based on the photovoltaic unit grid-connected safety boundary interval, and if it exceeds the range, marks the risk and generates a photovoltaic unit grid-connected switch control signal.

[0050] Compared with the prior art, the advantages and positive effects of the present invention are:

[0051] In the present invention, by dynamically collecting voltage data before and after the photovoltaic unit is connected in multiple dimensions and combining it with time series analysis, a voltage offset change characteristic model is constructed, so that the voltage fluctuation trend can be more precisely characterized, and accurate evaluation can be achieved under different power output states. Based on the voltage change trend extraction and adaptability classification analysis, combined with the voltage stability coefficient calculation, the adaptability of the photovoltaic unit under different load conditions can be quantified, providing an accurate reference for grid-connected stability. By introducing voltage and frequency coupling analysis and utilizing the correlation calculation of frequency adjustment amplitude and voltage change rate, the coupling characteristics of the photovoltaic unit are classified, so that the photovoltaic system The impact of the system on grid stability is more detailed, avoiding the limitations brought by single parameter judgment. Combined with the adaptability classification of photovoltaic units and voltage-frequency coupling analysis, the steady-state voltage range and frequency offset interval allowed by the grid are dynamically adjusted, so that the grid-connected safety boundary is more in line with actual operation needs, improving the scientific nature of grid-connected assessment. Based on the real-time operating status, the grid-connected safety boundary of the photovoltaic unit is matched, and adaptive control signals are generated to ensure stable grid connection when safety conditions are met. When the operation risk increases, the control strategy is adjusted in time to improve the operational safety of the photovoltaic system. At the same time, the grid's adaptability to distributed photovoltaic access is enhanced, and the new energy consumption strategy is optimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A flow chart showing the main steps of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention;

[0053] Figure 2 Flowchart of step S1 of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention;

[0054] Figure 3 This is a flow chart of step S2 of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention;

[0055] Figure 4 Flowchart of step S3 of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention;

[0056] Figure 5 Flowchart of step S4 of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention;

[0057] Figure 6 This is a flow chart of step S5 of the distributed photovoltaic operation status assessment and grid-connected switch control method provided by the present invention. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0059] In the description of the present invention, it should be understood that the terms "length," "width," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inside," "outside," and the like, indicating positions or relationships, are based on the positions or relationships shown in the accompanying drawings and are intended only to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, in the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

[0060] See also Figure 1 ,Distributed photovoltaic operation status evaluation and grid-connected switch control method, including the following steps:

[0061] S1: Obtain the bus voltage values before and after the PV unit is connected, collect the voltage measurement values of the PV unit at different power output states, calculate the voltage change based on the initial voltage value, calculate the voltage offset per unit time, filter and record the values that exceed the allowable voltage offset range, and generate voltage offset change data;

[0062] S2: Based on the voltage offset change data, the voltage change trend of the PV unit after connection under different load conditions is extracted. The voltage stability coefficient under each power output state is calculated. The volatility of the voltage offset change is determined. The voltage adaptability status is recorded and categorized. The voltage adaptability level of the PV unit under each load condition is classified into three types: adapted, critically adapted, and unadapted. The voltage adaptability classification results of the PV unit are generated.

[0063] S3: Based on the voltage offset change data, the bus frequency change values before and after the PV unit is connected are collected, the frequency adjustment amplitude per unit time is calculated, the voltage change rate and frequency adjustment rate under different power output states are compared, the voltage-frequency coupling trend is analyzed, and the coupling degree is divided into three types: low coupling, medium coupling, and high coupling. The voltage-frequency coupling classification results are generated;

[0064] S4: Based on the PV unit voltage adaptability classification results and voltage-frequency coupling classification results, the voltage variation amplitude and frequency offset under different power output conditions are extracted, the grid-allowed steady-state voltage range and frequency offset range are calculated, and the interval thresholds are compared to select the grid-connected operation range with high adaptability, thereby generating the grid-connected safety boundary range of the PV unit;

[0065] S5: According to the grid-connected safety boundary interval of the photovoltaic unit, the current photovoltaic unit operating status is compared with the safety boundary range to determine whether it meets the safety access conditions. If the operating status is within the safety boundary, the grid-connected operation is maintained; otherwise, the risk state is marked and the photovoltaic unit grid-connected switch control signal is generated.

[0066] Voltage offset change data includes voltage stability assessment indicators, over-limit voltage change characteristics, and voltage fluctuation distribution records per unit time. PV unit voltage adaptability classification results include voltage adaptability level, load state adaptability analysis results, and voltage fluctuation impact assessment results. Voltage-frequency coupling classification results include voltage-frequency change correlation parameters, coupling trend classification standards, and the impact of power output on coupling degree. PV unit grid-connected safety boundary intervals include safe operation thresholds, steady-state grid adaptability ranges, and dynamic operation stability intervals. PV unit grid-connected switch control signals include grid-connected safety determination results, risk warning signals, and grid-connected control adjustment instructions.

[0067] See also Figure 2 , S1 step is:

[0068] S111: Based on the bus voltage values before and after the photovoltaic unit is connected, collect the voltage measurement values of the photovoltaic unit under different power output states, calculate the voltage change at each measurement point, calculate the voltage offset in each time period, and establish a voltage offset data set;

[0069] Based on the bus voltage values before and after the PV unit is connected, the voltage measurement values of the PV unit at different power output states are obtained. In the specific implementation process, the power output states of a PV unit are selected at four power levels: 50W, 100W, 150W, and 200W. The bus voltage before and after the PV unit is connected is measured respectively. The measurement period is set to 1s. The obtained bus voltage values are shown in Table 1 below.

[0070] Table 1 Bus voltage measurement values under different power output states of photovoltaic units:

[0071] ;

[0072] According to Table 1, calculate the voltage change at each measurement point as follows:

[0073] ;

[0074] in, Indicates the The voltage change at each measuring point, is the bus voltage after the photovoltaic unit is connected, is the bus voltage before the photovoltaic unit is connected. The calculation results are as follows:

[0075] ;

[0076] ;

[0077] ;

[0078] ;

[0079] Next, calculate the voltage offset per unit time:

[0080] ;

[0081] Assuming that the measurement time interval is 1s, the calculation results are as follows:

[0082] ;

[0083] ;

[0084] ;

[0085] ;

[0086] Finally, a voltage offset data set is created.

[0087] S112: Based on the voltage offset data set, filter out values that exceed the allowable voltage offset range, and count the number of data points that exceed the range using the formula:

[0088] ;

[0089] Calculate the voltage deviation rate per unit time , obtain the voltage excursion rate distribution record, where, Representative The voltage value of each measuring point, Represents the reference voltage value, Representative The time value of each measurement point, Represents the base time value, Represents the total number of measurement points, Represents the summation operation of all measurement points;

[0090] Based on the voltage offset data set, we screened out values that exceeded the allowable voltage offset range. The power grid specifies a voltage offset range of ±0.5 V / s. This range is based on the supply voltage fluctuation and flicker requirements in the national power system operation standard GB / T 12325-2008, "Power Quality Supply Voltage Deviation," and the restrictions on grid harmonics and short-term voltage fluctuations in the IEEE Std 519-2014 standard. This value is primarily affected by factors such as grid frequency stability, voltage regulation equipment response time, and load fluctuation. Furthermore, considering actual grid operation, excessively high voltage offset rates can lead to problems such as malfunctioning relay protection and insulation damage to power equipment. Therefore, based on multiple power system regulation test data, we set ±0.5 V / s as the allowable range, screened out values outside this range, and counted the number of data points that exceeded the range, as shown in Table 2.

[0091] Table 2 Statistics of data points that exceed the allowable voltage offset range:

[0092] ;

[0093] As shown in Table 2, there are two measurement points that exceed the allowable offset range, namely the data points at the 3rd and 4th seconds. Then, the voltage offset rate per unit time is calculated using the formula:

[0094] ;

[0095] ;

[0096] The calculated result of 0.908 V / s indicates that, under the current PV unit access state, the voltage excursion rate per unit time significantly exceeds the set allowable excursion range (±0.5 V / s). This indicates that, at high power (150 W and above), the access of PV units has a significant impact on bus voltage fluctuations. In particular, at 200 W, the voltage excursion rate has reached 1.1 V / s, far exceeding the set threshold. Compensation measures are needed to adjust system stability. Finally, a voltage excursion rate distribution record is obtained.

[0097] S113: combining the voltage offset rate distribution records, filtering out the time period corresponding to the maximum offset rate, recording abnormal fluctuation data, and establishing voltage offset change data;

[0098] The voltage excursion rate distribution record is called up, and the time period corresponding to the maximum excursion rate is selected. Observing Table 2, we can see that the maximum excursion rate occurs at the 4th second, and the corresponding voltage excursion rate is 1.1V / s, which far exceeds the set allowable range of ±0.5V / s. Therefore, this moment is recorded as an abnormal fluctuation point.

[0099] In order to further analyze the characteristics of the abnormal fluctuation point, the voltage change between the abnormal fluctuation point and the previous second is calculated:

[0100] ;

[0101] ;

[0102] The voltage mutation amplitude is 0.4V. Combined with the sampling time of 1s, the voltage change rate can be calculated:

[0103] ;

[0104] This rate still exceeds the set allowable range. Therefore, this point can be further marked as a high-risk fluctuation point and stored in the abnormal data set, ultimately establishing voltage offset change data.

[0105] See also Figure 3 , step S2 is:

[0106] S211: Based on the voltage offset change data, extract the voltage change trend after the photovoltaic unit is connected under different load conditions, calculate the voltage change rate under each power output state, and establish voltage change trend data;

[0107] Based on the voltage offset change data, the voltage change trend after the photovoltaic unit is connected under different load conditions is extracted. First, the bus voltage measurement value under different power output states is obtained. The voltage data of each measurement point is collected by the sensor, and the corresponding load power is recorded. Assuming that 5 different power levels are set (20kW, 40kW, 60kW, 80kW, 100kW), the voltage values ​​at 10 time points are collected respectively, and 50 groups of data are obtained. The voltage change of each measurement point is calculated using the formula The voltage changes at the consecutive measurement points are calculated, and the voltage change trends in each time period are obtained, as shown in Table 3.

[0108] Table 3: Voltage change trend data at different power levels:

[0109] ;

[0110] As shown in Table 3, under different power output states, the voltage change trend shows periodic fluctuations. As the power increases, the voltage shows an overall downward trend but still rebounds slightly. The data shows that under certain specific load conditions, the instantaneous change in voltage may reach about 2V, and finally the voltage change trend data is obtained.

[0111] S212: Calculate the voltage stability coefficient under each power output state based on the voltage change trend data using the formula:

[0112] ;

[0113] Calculating the voltage stability factor , analyze the voltage fluctuation under various power output states, where Representative The voltage value at a moment, Represents the average voltage under this load condition, Representative The voltage value at a moment, Representative The photovoltaic power output at a given moment, Represents the number of sampling time points under the target load state, Represents the number of all time points recorded under load conditions, represents the sum operation, represents the square root operation, Represents absolute value operation;

[0114] Call the voltage change trend data and calculate the voltage stability coefficient under each power output state. First, calculate the voltage mean under each load state. Assuming that when the load is 100kW, the voltage values collected at 10 time points are [400, 399, 398, 397, 398, 399, 400, 401, 402, 403]. , and then use the formula to calculate the voltage stability coefficient, substituting the data into:

[0115] ;

[0116] ;

[0117] ;

[0118] ;

[0119] The calculation results show that the voltage stability coefficient under different load conditions can reflect the fluctuation of voltage changes. The smaller the value, the more stable the voltage is under this load condition.

[0120] S213: Based on the voltage stability coefficient, determine the volatility of the voltage offset change, classify and record the voltage adaptability status, and classify the voltage adaptability level of the photovoltaic unit under each load condition into three types: adaptable, critically adaptable, and unadaptable, and establish the photovoltaic unit voltage adaptability classification result;

[0121] According to the voltage stability coefficient, the fluctuation of voltage offset change is judged and the threshold is set. The basis for this is the allowable fluctuation range of the bus voltage after the photovoltaic unit is connected. According to the steady-state voltage deviation standard of the power system, the bus voltage fluctuation should not exceed ±5% of the rated value. Combined with the actual operating data, the voltage fluctuation range under different load conditions is selected and converted to the corresponding stability coefficient range. The final threshold is set to .like The voltage adaptability is considered good. The voltage is considered to be in a critical adaptation state. It is considered that the voltage is not suitable for the current load state. Table 4 lists the voltage adaptability classification under different load conditions.

[0122] Table 4: Voltage adaptability classification under different load conditions:

[0123] ;

[0124] The threshold calculation process is based on the physical quantitative conversion of voltage fluctuation amplitude and steady-state allowable deviation. Assuming that the rated bus voltage is 400V, its ±5% allowable range is 380V–420V. After collecting the measurement data under different load conditions, the voltage variance under different conditions is calculated. Assuming that under a 20kW load, the voltage mean is 398V and the standard deviation is 0.5V, it is calculated according to the above formula. , and then determine the adaptability classification standard. When it is lower than 0.015, it is in the adaptation range, 0.015–0.03 is the medium fluctuation area, corresponding to critical adaptation, and when it is greater than 0.03, the fluctuation is severe, affecting the stability of the power grid, and it is in the non-adaptive state.

[0125] As shown in Table 4, under low load conditions (20kW, 40kW), the voltage is relatively stable and classified as "adaptive". When the load increases to 60kW and above, the voltage fluctuation increases and enters the "critical adaptation" or "non-adaptive" range. Finally, the PV unit voltage adaptability classification results are established.

[0126] See also Figure 4 , S3 steps are:

[0127] S311: Based on the voltage offset change data, collect the bus frequency change value before and after the photovoltaic unit is connected, calculate the frequency adjustment amplitude per unit time, and establish frequency adjustment amplitude data;

[0128] Based on the voltage offset change data, the bus frequency change value before and after the photovoltaic unit is connected is collected. The monitoring time interval is set, and the bus frequency is sampled at fixed time intervals within this time to ensure the integrity of the data. The frequency value at each time point is collected using a measuring device, and the frequency change trend before and after the photovoltaic unit is connected is recorded. In the specific implementation, the bus of a photovoltaic power station is selected, and its frequency values before and after the photovoltaic unit are connected are measured to be 49.95Hz, 50.05Hz, 49.85Hz, etc. The obtained frequency data are shown in Table 1 below. Based on this data, the frequency adjustment amplitude per unit time is calculated. By calculating the frequency change amount at adjacent time points and accumulating their absolute values, the specific value of the frequency adjustment amplitude is obtained. In this process, the calculation formula is as follows:

[0129] ;

[0130] in, Represents the frequency adjustment amplitude, Represents the bus frequency at the current time point, Representing the bus frequency at the previous time point, the frequency adjustment amplitude at each moment is calculated, and its maximum value is obtained to represent the maximum frequency adjustment amplitude. The calculation results are shown in Table 5 below. As shown in Table 5, the frequency adjustment amplitude data is obtained.

[0131] Table 5 Frequency adjustment range data table:

[0132] ;

[0133] As shown in Table 5, the collected frequency adjustment amplitude data is used for subsequent voltage and frequency coupling analysis to establish frequency adjustment amplitude data.

[0134] S312: Combine the frequency adjustment amplitude data to analyze the voltage change trend and compare the voltage change rate and frequency adjustment rate under different power output states. Use the formula:

[0135] ;

[0136] Calculating the voltage-frequency coupling coefficient ,in, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, represents the sum operation, represents the square root operation, represents the absolute value operation, represents the number of time points used to calculate the voltage-frequency product, represents the number of time points used to calculate the sum of the squares of voltage and frequency, Represents the number of time points used to calculate the absolute difference between voltage and frequency;

[0137] Call the frequency adjustment amplitude data, analyze the voltage change trend data synchronously, calculate the voltage change rate and frequency adjustment rate under different power output states respectively, calculate the coupling relationship between the voltage and frequency data at each moment, and set the voltage value measured at each moment 220.1V, 219.8V, 220.5V, 219.5V, etc., the frequency value are 49.95Hz, 50.05Hz, 49.85Hz, etc., and the number of parameters are 、 、 , and substitute specific values into the calculation:

[0138] ;

[0139] ;

[0140] ;

[0141] ;

[0142] ;

[0143] ;

[0144] ;

[0145] ;

[0146] ;

[0147] Calculate the voltage-frequency coupling coefficient ,As shown in the calculation, this value characterizes the degree of coupling between voltage change and frequency adjustment, and the voltage-frequency coupling coefficient distribution is obtained.

[0148] S313: Based on the voltage-frequency coupling coefficient, determine the voltage-frequency coupling trend, classify the coupling degree into three types: low coupling, medium coupling, and high coupling, and establish a voltage-frequency coupling classification result;

[0149] Call the voltage-frequency coupling coefficient, based on the calculated coupling coefficient The coupling degree is divided into three types: low coupling, medium coupling, and high coupling. The coupling threshold standard is set as:

[0150] Low coupling: ;

[0151] Medium coupling: ;

[0152] High coupling: ;

[0153] The threshold is set based on the dynamic response characteristics of the photovoltaic unit after it is connected to the busbar, and is classified in combination with the grid dispatch requirements and voltage and frequency regulation capabilities. The specific calculation is as follows:

[0154] First, the degree of voltage-frequency coupling is primarily affected by the PV power fluctuation range, the grid regulation margin, and the bus frequency adjustment capability. If the PV unit output power fluctuates significantly while the grid regulation capability is low, the coupling coefficient is high. Therefore, to quantify the degree of coupling under different operating conditions, it is necessary to extract the voltage fluctuation rate and frequency adjustment rate under typical load conditions from historical operating condition data and calculate their coupling characteristics. The following typical operating conditions are selected as a reference:

[0155] Set three typical load conditions and calculate the voltage-frequency coupling coefficient distribution under different conditions:

[0156] Working condition 1 (light load): The output power of the photovoltaic unit is 50MW, the bus load is 200MW, and the measured voltage change rate is , the frequency adjustment rate is , into the calculation to get , which belongs to the low coupling range.

[0157] Condition 2 (medium load): The PV unit output power is 80MW, the bus load is 250MW, and the measured voltage change rate is , the frequency adjustment rate is , calculated , which belongs to the medium coupling interval.

[0158] Working condition 3 (heavy load): The output power of the photovoltaic unit is 120MW, the bus load is 300MW, and the measured voltage change rate is , the frequency adjustment rate is , calculated , which belongs to the high coupling range.

[0159] The above calculations show that the classification of low coupling, medium coupling, and high coupling is based on the voltage-frequency linkage characteristics after the photovoltaic unit is connected. The specific threshold setting is based on system stability. In the low coupling state, the grid has sufficient regulation capability, the frequency fluctuation amplitude is less than 0.005Hz, and the voltage fluctuation range is less than 0.3V. In the medium coupling state, the frequency fluctuation amplitude is between 0.005Hz and 0.01Hz, and the voltage fluctuation range is between 0.3V and 0.8V. In the high coupling state, the frequency fluctuation amplitude exceeds 0.01Hz and the voltage fluctuation range is greater than 0.8V. At this time, the grid faces greater regulation pressure. Therefore, the thresholds are set at two dividing points: 30 and 60 to ensure the rationality of the classification.

[0160] According to the above calculation results, , which satisfies the high coupling interval. Therefore, the voltage-frequency relationship of the PV unit connected to the bus is determined to be in a high coupling state, and the voltage-frequency coupling classification result is established.

[0161] See also Figure 5 , step S4 is:

[0162] S411: Obtaining the PV unit voltage adaptability classification results and voltage-frequency coupling classification results, extracting the voltage variation amplitude and frequency offset under different power output conditions, calculating the grid-allowed steady-state voltage range and frequency offset interval, and obtaining the steady-state voltage range and frequency offset interval;

[0163] The voltage adaptability classification results and voltage-frequency coupling classification results of the photovoltaic unit are obtained based on the real-time data collection of the photovoltaic unit under the grid operation state. First, the voltage of the photovoltaic unit under different power output conditions is monitored. The voltage data of each monitoring point at a specific time is measured by the substation or grid-connected inverter, and the unit is volts (V). At the same time, the frequency data of the grid-connected point is collected, and the unit is hertz (Hz). Assuming that under a typical operating state, the measured voltage values at different times are:

[0164] ;

[0165] The measured frequency is:

[0166] ;

[0167] The voltage variation amplitude is further calculated, that is, the absolute value of the difference between the voltage at each time point and the voltage at the previous time point, and the average value is obtained. For example, the voltage variation amplitude of the first group is calculated as follows:

[0168] ;

[0169] Similarly, calculate the frequency offset by taking the difference between the frequency value at each moment and 50Hz and finding the average value:

[0170] ;

[0171] Based on the grid's permitted steady-state voltage range (usually between 220V and 240V) and permitted frequency offset range (49.80Hz to 50.20Hz), determine whether the PV unit's voltage variation and frequency offset fall within this range, as shown in Table 6.

[0172] Table 6: Steady-state voltage range and frequency allowable deviation range of the power grid:

[0173] ;

[0174] As shown in Table 6, the voltage variation amplitude and frequency offset of all measurement points fall within the allowable range, and the steady-state voltage range and frequency offset interval are finally obtained.

[0175] S412: Based on the steady-state voltage range and the frequency offset range, compare the thresholds of each range and use the formula:

[0176] ;

[0177] Calculate the optimal grid-connected operation interval selection value , the grid-connected operation range with high adaptability is screened out, among which, Representative Voltage value at a moment, represents the reference voltage, and Represent the maximum and minimum allowable voltage values, Representative Frequency value at each moment, represents the reference frequency, and Represent the maximum and minimum allowed values of frequency, and are the number of voltage and frequency data points, respectively;

[0178] Based on the steady-state voltage range and frequency offset interval, it is necessary to compare the thresholds of each interval, select the most adaptable grid-connected operation interval, and calculate the stability of different PV units within this interval. First, use the voltage and frequency data of each measurement point to calculate the optimal grid-connected operation interval selection value.

[0179] Take the data of a certain measuring point for calculation, assuming the voltage data is , the frequency data is , put it into the formula:

[0180] ;

[0181] ;

[0182] Calculated:

[0183] ;

[0184] If the screening threshold is set to 1.0, the interval meets the grid-connected operation requirements, and finally a grid-connected operation interval with high adaptability is obtained.

[0185] S413: Based on the highly adaptable grid-connected operation interval, the steady-state voltage mean and frequency offset mean within the interval are calculated to determine the safety margin of the grid-connected operation. The interval boundaries where the voltage and frequency offsets meet the grid safety operation standards are screened to construct the grid-connected safety boundary interval for the photovoltaic unit.

[0186] Based on the highly adaptable grid-connected operation interval, the steady-state voltage mean and frequency offset mean within the interval are further calculated to determine the safety margin of the grid-connected operation. The interval boundaries where the voltage and frequency offsets meet the grid safety operation standards are screened out, and Table 7 is used for data organization.

[0187] Table 7 Boundaries of grid-connected operation range with high adaptability:

[0188] ;

[0189] As shown in Table 7, the average voltage and frequency of each monitoring point are within the allowable range, and the adaptability scores are all below the set threshold of 1.0, meeting the grid safety standards. The adaptability score threshold of 1.0 is set based on the fact that under steady-state grid operation conditions, the voltage and frequency fluctuations of the photovoltaic unit need to meet certain tolerance requirements, so that the voltage offset does not exceed 15% of the total allowable range, and the frequency offset does not exceed 30% of the total allowable range. This setting is based on the grid operation and dispatching standards, which stipulate the dynamic response characteristics allowed when distributed power sources of different power levels are connected to the grid. For example, in the distributed power generation connection scenario below 10MW, voltage fluctuations generally need to be controlled within ±3%, and frequency fluctuations need to be controlled within ±0.2Hz. Therefore, the adaptability score threshold of 1.0 set in this implementation plan is equivalent to the photovoltaic unit being able to maintain stable grid-connected operation when the voltage fluctuation is within ±3V and the frequency offset is within ±0.06Hz.

[0190] Further analyze the output power fluctuations of different photovoltaic units, extract the maximum power fluctuation range, and cross-check it with the safe operating range to ensure that all fluctuation ranges fall within the allowable range. For example, at a certain moment, the maximum power fluctuation range of the photovoltaic unit is , if the grid-connected power fluctuation range is allowed to be , then the requirements are met, and finally all the interval data that meet the requirements are integrated to construct the safe boundary interval of the photovoltaic unit grid connection, and the safe boundary interval of the photovoltaic unit grid connection is obtained.

[0191] See also Figure 6 , step S5 is:

[0192] S511: Obtaining the grid-connected safety boundary range of the photovoltaic unit, calling the current operating status data of the photovoltaic unit, including voltage, frequency, and power output, and comparing them with the upper and lower limits of the safety boundary range, to determine whether the current operating parameters of the photovoltaic unit are within the allowable range, calculating the degree to which each parameter deviates from the boundary range, and comprehensively evaluating the current operating status of the photovoltaic unit to obtain the photovoltaic unit safety deviation score;

[0193] Obtain the grid-connected safety boundary of the photovoltaic unit and call the current operating status data of the photovoltaic unit, including voltage, frequency, and power output. Collect data at each measuring point and organize it into operating records in chronological order. All data comes from the real-time monitoring system of the photovoltaic inverter. The voltage, frequency, and power data recorded at each measuring point are stored in standard units (V, Hz, kW). The data collection interval is set to 1 second to ensure data continuity and real-time performance. For example, the collection record within 10 seconds can be expressed as voltage:

[0194] ;

[0195] frequency:

[0196] ;

[0197] Power Output:

[0198] ;

[0199] The collected data are compared to determine whether the current operating parameters of the PV unit are within the safe boundary range of the PV unit grid connection. The boundary range is set by the grid dispatching center and stored in numerical form, as shown in Table 8.

[0200] Table 8 Grid-connected safety boundary intervals for photovoltaic units:

[0201] ;

[0202] As shown in Table 8, the safety ranges for voltage, frequency, and power are specified by the power grid. The collected data is compared with the upper and lower limits of the range to determine whether it is within the safety interval. For data points that exceed the boundaries, the deviation is recorded, and the overall deviation is calculated and expressed numerically to obtain the PV unit safety deviation score.

[0203] S512: Based on the PV unit safety offset score, a safety offset threshold is set. If the calculated value is less than the safety offset threshold, the current operating state meets the safety access conditions, grid-connected operation is maintained, and the current operating parameters are stored. If the calculated value is greater than the safety offset threshold, the PV unit is marked as a risk state, and the current operating parameters and score are stored. The time when the risk state of the PV unit occurs and the corresponding environmental parameters are recorded to obtain the PV unit risk state mark;

[0204] Based on the safety offset score of the photovoltaic unit, a safety offset threshold is set. The setting of the threshold is based on the operating stability of the photovoltaic unit, the fluctuation of historical data and the requirements of the grid for the grid-connected photovoltaic system. For example, for photovoltaic power stations below 10MW, if the voltage offset exceeds ±5V and the frequency offset exceeds ±0.05Hz, it may affect the grid stability. Therefore, the threshold of the safety offset score is set to 1.0. If the calculated score of the photovoltaic unit is less than 1.0, it is considered that the current operating state meets the safety access conditions, and the grid-connected operation is maintained, and the current operating parameters are recorded in the database; if the score is greater than 1.0, it is considered to have deviated from the safety range and needs to be adjusted. Further control measures need to be taken. For example, at a certain moment, the voltage is 231.5V, the frequency is 50.05Hz, and the power output is 202kW. The calculated safety offset score is 0.85, which meets the safety conditions and continues to be connected to the grid. At another moment, the voltage reaches 242.0V, exceeding the maximum allowable range, the frequency is 50.18Hz, and the power output is 225kW. The calculated safety offset score is 1.25, which exceeds the threshold. Risk marking is required, and the current operating parameters and score values are stored. At the same time, the time when the risk state of the PV unit occurs and the corresponding environmental parameters are recorded, and finally the risk state mark of the PV unit is obtained.

[0205] S513: Calling the PV unit risk status flag, analyzing the deviation from the safety boundary parameters for the PV units marked as risky, and performing grid-connected switch control, including disconnecting or adjusting the signal, adjusting the operating state of the PV unit or forcibly disconnecting the grid connection, and obtaining the PV unit grid-connected switch control signal;

[0206] The PV unit risk status mark is called. For PV units marked as risky, the specific parameters of their deviation from the safety boundary are analyzed to determine the degree of excess. If the voltage exceeds the upper or lower limit by more than ±10V, it is determined to be a serious deviation. The setting of this threshold is based on the grid voltage regulation capability and the adjustment range of the PV inverter. Generally, the grid voltage fluctuation range is allowed to be within ±5% of the rated voltage. That is, for a 220V system, the allowable voltage range is 209V to 231V, and for a 380V system, it is 361V to 399V. In actual grid-connected operation, considering the response delay and reactive power compensation capability of the PV inverter, if the voltage fluctuation exceeds ±10V, which is about 4.3% of the rated voltage, it may cause the inverter overvoltage or undervoltage protection to be triggered. Therefore, this threshold is set. If the frequency deviation exceeds ±0.1Hz, it is also determined to be a serious deviation. This value is determined based on the grid inertia and frequency regulation response capability. The national standard requires that the public grid frequency should be maintained within 50Hz±0.2Hz. Considering that PV grid-connected systems usually have a certain degree of frequency adaptation capability, ±0.1Hz is set as the deviation threshold to ensure that the PV system can maintain stable operation under normal load changes. In the event of a serious deviation, a disconnection signal is immediately generated and sent to the PV unit control system to execute the disconnection operation. If the deviation value is within a minor range, such as a voltage deviation of no more than ±5V or a frequency deviation of no more than ±0.05Hz, an adjustment signal is generated to instruct the PV unit to reduce power output or adjust the inverter control parameters to return the operating state to the safe range. For example, the operating data of a PV unit is 241V and the power output is 215kW. Although it exceeds part of the safe range, it is still within the adjustment allowable range. At this time, the control system will send a signal to the inverter to reduce the power output to 200kW and adjust the reactive power compensation to reduce the voltage to 239V to restore the safe operation state. Finally, a control signal is output to the PV unit control system to obtain the PV unit grid-connected switch control signal.

[0207] Distributed photovoltaic operation status assessment and grid-connected switch control system, including:

[0208] The voltage offset calculation module obtains the bus voltage value before and after the photovoltaic unit is connected, collects the voltage measurement values of the photovoltaic unit at different power output states, calls the initial voltage value to calculate the voltage change, calculates the voltage offset per unit time, filters the measurement values that exceed the voltage offset threshold, and generates voltage offset change data;

[0209] The voltage adaptability classification module calculates the voltage stability coefficient based on the voltage offset change data, determines the voltage fluctuation range, compares the voltage adaptability threshold, classifies the voltage adaptability level, and generates the PV unit voltage adaptability classification results;

[0210] The voltage-frequency coupling classification module collects bus frequency changes before and after the PV unit is connected based on voltage offset change data, compares the voltage change rate with the frequency adjustment amplitude, divides the coupling degree, and generates voltage-frequency coupling classification results.

[0211] The grid-connected safety boundary screening module calculates the voltage variation amplitude and frequency offset based on the PV unit voltage adaptability classification results and voltage-frequency coupling classification results, screens the operating range with high adaptability, and generates the PV unit grid-connected safety boundary range;

[0212] The grid-connected switch control module determines whether the current operating status of the photovoltaic unit is within the safe range based on the grid-connected safety boundary interval of the photovoltaic unit. If it exceeds the safety range, it marks the risk and generates the photovoltaic unit grid-connected switch control signal.

[0213] The above are merely preferred embodiments of the present invention and do not limit the present invention in any other form. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A distributed photovoltaic operation status assessment and grid-connected switch control method, characterized in that: The following steps are involved: S1: Obtain the bus voltage value before and after the photovoltaic unit is connected, collect the voltage measurement value of the photovoltaic unit under different power output states, calculate the voltage change, calculate the voltage offset per unit time, and generate voltage offset change data; S2: Based on the voltage offset change data, extract the voltage change trend after the photovoltaic unit is connected under different load conditions, calculate the voltage stability coefficient under each power output state, determine the volatility of the voltage offset change, classify and record the voltage adaptability status, and classify the voltage adaptability level into three types: adapted, critically adapted, and unadapted, and generate the photovoltaic unit voltage adaptability classification result; The specific steps of S2 are: S211: extracting voltage change trends after the photovoltaic units are connected under different load conditions based on the voltage offset change data, calculating voltage change rates under each power output state, and establishing voltage change trend data; S212: Calculate the voltage stability coefficient under each power output state according to the voltage change trend data, using the formula: ； Calculating the voltage stability factor , analyze the voltage fluctuation under various power output states, where Representative The voltage value at a moment, Represents the average voltage under this load condition, Representative The voltage value at a moment, Representative The photovoltaic power output at each moment represents the number of sampling time points under the target load state. Represents the number of all time points recorded under load conditions, represents the sum operation, represents the square root operation, Represents absolute value operation; S213: Based on the voltage stability coefficient, determining the volatility of the voltage offset change, classifying and recording the voltage adaptability status, classifying the voltage adaptability level of the photovoltaic unit under each load condition into three types: adapted, critically adapted, and unadapted, and establishing a photovoltaic unit voltage adaptability classification result; S3: Based on the voltage offset change data, collect bus frequency change values before and after the photovoltaic unit is connected, calculate the frequency adjustment amplitude per unit time, compare the voltage change rate with the frequency adjustment rate, analyze and classify the voltage-frequency coupling trend, and generate a voltage-frequency coupling classification result; The specific steps of S3 are: S311: Based on the voltage offset change data, collect bus frequency change values before and after the photovoltaic unit is connected, calculate the frequency adjustment amplitude per unit time, and establish frequency adjustment amplitude data; S312: Analyze the voltage change trend based on the frequency adjustment amplitude data, compare the voltage change rate and frequency adjustment rate under different power output states, and use the formula: ； Calculating the voltage-frequency coupling coefficient ,in, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, Representative The voltage value at a moment, Representative The frequency value at a moment, represents the sum operation, represents the square root operation, represents the absolute value operation, represents the number of time points used to calculate the voltage-frequency product, represents the number of time points used to calculate the sum of the squares of voltage and frequency, Represents the number of time points used to calculate the absolute difference between voltage and frequency; S313: Determine the voltage-frequency coupling trend based on the voltage-frequency coupling coefficient, classify the coupling degree into three types: low coupling, medium coupling, and high coupling, and establish a voltage-frequency coupling classification result; S4: Based on the PV unit voltage adaptability classification result and the voltage-frequency coupling classification result, the voltage change amplitude and frequency offset under different power output conditions are extracted, the steady-state voltage range and the allowable frequency offset interval are calculated, and the interval threshold is compared to screen the grid-connected operation interval with high adaptability to generate the PV unit grid-connected safety boundary interval.

2. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 1, characterized in that: The voltage offset change data includes voltage stability assessment indicators, over-limit voltage change characteristics, and voltage fluctuation distribution records per unit time. The photovoltaic unit voltage adaptability classification results include voltage adaptability level, load state adaptability analysis results, and voltage fluctuation impact assessment results. The voltage-frequency coupling classification results include voltage-frequency change correlation parameters, coupling trend classification standards, and the impact of power output on coupling degree. The photovoltaic unit grid-connected safety boundary interval includes a safe operation threshold, a steady-state grid adaptability range, and a dynamic operation stability interval.

3. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 1, characterized in that: The specific steps of S1 are: S111: Based on the bus voltage values before and after the photovoltaic unit is connected, collect the voltage measurement values of the photovoltaic unit under different power output states, calculate the voltage change at each measurement point, calculate the voltage offset in each time period, and establish a voltage offset data set; S112: Based on the voltage offset data set, filter out values that exceed the allowable voltage offset range, count the number of data points that exceed the range, and use the formula: ； Calculate the voltage deviation rate per unit time , obtain the voltage excursion rate distribution record, where, Representative The voltage value of each measuring point, Represents the reference voltage value, Representative The time value of each measurement point, Represents the base time value, Represents the total number of measurement points, Represents the summation operation of all measurement points; S113: Based on the voltage offset rate distribution record, a time period corresponding to a maximum offset rate is screened out, abnormal fluctuation data is recorded, and voltage offset change data is established.

4. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 1, characterized in that: The specific steps of S4 are: S411: Obtaining the photovoltaic unit voltage adaptability classification result and the voltage-frequency coupling classification result, extracting the voltage variation amplitude and frequency offset under different power output conditions, calculating the steady-state voltage range and frequency offset interval allowed by the power grid, and obtaining the steady-state voltage range and frequency offset interval; S412: Based on the steady-state voltage range and the frequency offset interval, comparing the thresholds of each interval, calculating the optimal grid-connected operation interval selection value, and screening out a grid-connected operation interval with high adaptability; S413: Based on the highly adaptable grid-connected operation interval, calculate the steady-state voltage mean and frequency offset mean within the interval, determine the safety margin of the grid-connected operation, select the interval boundaries where the voltage and frequency offsets meet the grid safety operation standards, and construct the photovoltaic unit grid-connected safety boundary interval.

5. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 4, characterized in that: The optimal grid-connected operation interval selection value is selected using the formula: ； Calculate, where Represents the optimal grid-connected operation interval selection value, Representative Voltage value at a moment, represents the reference voltage, and Represent the maximum and minimum allowable voltage values, Representative Frequency value at each moment, represents the reference frequency, and Represent the maximum and minimum allowed values of frequency, and are the number of voltage and frequency data points, respectively.

6. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 1, characterized in that: The method further includes S5; S5: Based on the grid-connected safety boundary of the photovoltaic unit, the current photovoltaic unit operating status is compared with the safety boundary range to determine whether it meets the safety connection conditions. If the operating status is within the safety boundary, the grid-connected operation is maintained; otherwise, the risk state is marked and the photovoltaic unit grid-connected switch control signal is generated; The photovoltaic unit grid-connected switch control signal includes a grid-connected safety determination result, a risk warning signal, and a grid-connected control adjustment instruction.

7. The distributed photovoltaic operation status assessment and grid-connected switch control method according to claim 6, characterized in that: The specific steps of S5 are: S511: Obtaining the grid-connected safety boundary range of the photovoltaic unit, calling the current operating status data of the photovoltaic unit, including voltage, frequency, and power output, and comparing them with the upper and lower limits of the safety boundary range, to determine whether the current operating parameters of the photovoltaic unit are within the allowable range, calculating the degree to which each parameter deviates from the boundary range, and comprehensively evaluating the operating status of the current photovoltaic unit to obtain a photovoltaic unit safety deviation score; S512: Based on the safety offset score of the photovoltaic unit, a safety offset threshold is set. If the calculated value is less than the safety offset threshold, the current operating state meets the safety access conditions, the grid-connected operation is maintained, and the current operating parameters are stored. If the calculated value is greater than the safety offset threshold, the photovoltaic unit is marked as a risk state, and the current operating parameters and score are stored. The time when the risk state of the photovoltaic unit occurs and the corresponding environmental parameters are recorded to obtain a risk state mark of the photovoltaic unit; S513: Call the risk status mark of the photovoltaic unit, analyze the deviation from the safety boundary parameters for the photovoltaic unit marked as a risk state, and perform grid-connected switch control, including disconnecting the signal or adjusting the signal, adjusting the operating state of the photovoltaic unit or forcibly disconnecting the grid connection, and obtaining the photovoltaic unit grid-connected switch control signal.

8. Distributed photovoltaic operation status assessment and grid-connected switch control system, characterized by: The system is used to perform the method according to any one of claims 1 to 7, comprising: The voltage offset calculation module obtains the bus voltage value before and after the photovoltaic unit is connected, collects the voltage measurement values of the photovoltaic unit at different power output states, calls the initial voltage value to calculate the voltage change, calculates the voltage offset per unit time, filters the measurement values that exceed the voltage offset threshold, and generates voltage offset change data; The voltage adaptability classification module calculates the voltage stability coefficient based on the voltage offset change data, determines the voltage fluctuation range, compares the voltage adaptability threshold, classifies the voltage adaptability level, and generates a photovoltaic unit voltage adaptability classification result; The voltage-frequency coupling classification module collects bus frequency change values before and after the photovoltaic unit is connected based on the voltage offset change data, compares the voltage change rate with the frequency adjustment amplitude, divides the coupling degree, and generates a voltage-frequency coupling classification result; The grid-connected safety boundary screening module calculates the voltage variation amplitude and the frequency offset based on the photovoltaic unit voltage adaptability classification result and the voltage-frequency coupling classification result, screens the operating range with high adaptability, and generates the photovoltaic unit grid-connected safety boundary range; The grid-connected switch control module determines whether the current photovoltaic unit operating state is within a safe range based on the photovoltaic unit grid-connected safety boundary interval, and if it exceeds the range, marks the risk and generates a photovoltaic unit grid-connected switch control signal.

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