Low-voltage out-of-limit regulation and control method and system for distributed photovoltaic power station

Abstract

The invention discloses a low-voltage out-of-limit regulation and control method and system for a distributed photovoltaic power station, and relates to the technical field of photovoltaic power generation, and the method comprises the steps: obtaining the related capacity information of a power grid, determining the capacity of the power grid, obtaining the load data of the power grid, and determining the load degree of the power grid; the grid-connected capacity of the photovoltaic power station is obtained based on the power grid capacity and the power grid load degree, multiple safety margin influence factors are obtained, causal indexes of the multiple safety margin influence factors and the safety margin are calculated, and therefore the safety margin is set; determining an access point according to the grid-connected capacity of the photovoltaic power station with the safety margin and the additional information, and monitoring the change of data near the access point; the voltage state of the power grid is judged according to the change of data near the access point, and multiple means are adopted for corresponding control so as to adjust the voltage level of the power grid. And the accuracy of power grid voltage state judgment, the regulation and control precision and the regulation and control effect are improved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation technology, and more specifically, to a low-voltage over-limit control method and system for a distributed photovoltaic power station. Background Art

[0002] Low voltage over-limit control of distributed photovoltaic power stations is an important technology designed to solve the low voltage problem that may be caused by the grid connection of distributed photovoltaic power stations. In traditional power grids, power transmission is unidirectional, from power plants to users. However, with the rapid development of distributed photovoltaic power stations, more and more photovoltaic power stations are injecting power into the grid, resulting in a two-way flow of power transmission, which poses a challenge to the stability of the grid.

[0003] Low voltage over-limit refers to the voltage in the power grid dropping below the safe operating range. When a distributed photovoltaic power station is connected to the grid, the fluctuation of photovoltaic power generation may cause a significant drop in the grid voltage, especially when the output power of the photovoltaic power station is large or the weather conditions change suddenly. Low voltage over-limit will not only affect the normal operation of the power grid, but may also cause a decline in the quality of electricity used by users and even damage the power grid equipment.

[0004] In the prior art, before low voltage over-limit regulation, it is necessary to first determine the voltage status of the power grid. Voltage data alone cannot reliably describe the voltage status, resulting in inaccurate subsequent regulation and poor regulation effect.

[0005] Therefore, how to improve the accuracy of judging the voltage status of the power grid is a technical problem that needs to be solved. Summary of the invention

[0006] The present invention provides a low voltage over-limit control method for a distributed photovoltaic power station, which is used to solve the technical problem of low accuracy in judging the voltage state of the power grid in the prior art. The method comprises:

[0007] Obtain relevant capacity information of the power grid and determine the capacity of the power grid, obtain power grid load data and determine the degree of power grid load;

[0008] Based on the grid capacity and grid load level, the grid-connected capacity of the photovoltaic power station is obtained, multiple safety margin influencing factors are obtained, and the causal indicators of multiple safety margin influencing factors and safety margin are calculated to set the safety margin;

[0009] Determine the access point based on the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitor the data changes near the access point;

[0010] The grid voltage status is determined based on data changes near the access point, and multiple control methods are used to adjust the grid voltage level.

[0011] In some embodiments of the present application, obtaining grid load data and determining the grid load degree include:

[0012] Grid load data includes daily load curve and peak load;

[0013] Split the daily load curve into multiple sub-load curves according to different time periods within a day;

[0014] Calculate the slope change of each sub-load curve and the peak load of each sub-load curve;

[0015] The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods;

[0016] A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference;

[0017] The grid load level is determined based on the combined difference.

[0018] In some embodiments of the present application, multiple safety margin influencing factors and causal indicators of the safety margin are calculated to set the safety margin, including:

[0019] The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors;

[0020] The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied;

[0021] Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor;

[0022] The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

[0023] In some embodiments of the present application, determining the access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information includes:

[0024] According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected;

[0025] Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability;

[0026] The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

[0027] In some embodiments of the present application, the voltage state of the power grid is determined according to the data changes near the access point, and multiple means are used for corresponding control to adjust the voltage level of the power grid, including:

[0028] Data near the access point include grid voltage, grid frequency, grid load and grid power factor;

[0029] If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low;

[0030] Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships;

[0031] If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower;

[0032] Otherwise, it is judged that the grid voltage state is normal;

[0033] When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

[0034] Correspondingly, the present application also provides a low voltage over-limit control system for a distributed photovoltaic power station, the system comprising:

[0035] The first module is used to obtain the relevant capacity information of the power grid and determine the power grid capacity, obtain the power grid load data and determine the power grid load degree;

[0036] The second module is used to obtain the grid-connected capacity of the photovoltaic power station based on the grid capacity and the grid load level, obtain multiple safety margin influencing factors, and calculate the causal indicators of multiple safety margin influencing factors and the safety margin, so as to set the safety margin;

[0037] The third module is used to determine the access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitor the data changes near the access point;

[0038] The fourth module is used to determine the voltage status of the power grid according to the data changes near the access point, and adopt multiple means of corresponding control to adjust the voltage level of the power grid.

[0039] In some embodiments of the present application, the first module is used to:

[0040] Grid load data includes daily load curve and peak load;

[0041] Split the daily load curve into multiple sub-load curves according to different time periods within a day;

[0042] Calculate the slope change of each sub-load curve and the peak load of each sub-load curve;

[0043] The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods;

[0044] A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference;

[0045] The grid load level is determined based on the combined difference.

[0046] In some embodiments of the present application, the second module is used to:

[0047] The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors;

[0048] The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied;

[0049] Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor;

[0050] The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

[0051] In some embodiments of the present application, the third module is used to:

[0052] According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected;

[0053] Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability;

[0054] The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

[0055] In some embodiments of the present application, the fourth module is used to:

[0056] Data near the access point include grid voltage, grid frequency, grid load and grid power factor;

[0057] If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low;

[0058] Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships;

[0059] If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower;

[0060] Otherwise, it is judged that the grid voltage state is normal;

[0061] When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

[0062] By applying the above technical solutions, the grid-related capacity information is obtained, and the grid capacity is determined, the grid load data is obtained, and the grid load degree is determined; the grid-connected capacity of the photovoltaic power station is obtained based on the grid capacity and the grid load degree, multiple safety margin influencing factors are obtained, and the causal indicators of multiple safety margin influencing factors and safety margin are calculated, so as to set the safety margin; the access point is determined according to the grid-connected capacity of the photovoltaic power station with safety margin and additional information, and the data changes near the access point are monitored; the grid voltage state is judged according to the data changes near the access point, and multiple means are used for corresponding control to adjust the voltage level of the grid. This application improves the accuracy of the grid-connected capacity of the photovoltaic power station and facilitates subsequent state judgment by calculating the causal indicators of multiple safety margin influencing factors and safety margin to set the safety margin. By determining the access point according to the grid-connected capacity of the photovoltaic power station with safety margin and additional information, the accuracy of subsequent state judgment is improved. By judging the grid voltage state according to the data changes near the access point and using multiple means for corresponding control, the accuracy of grid voltage state judgment, regulation accuracy and regulation effect are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0064] Figure 1 A schematic flow chart of a low voltage over-limit control method for a distributed photovoltaic power station proposed in an embodiment of the present invention is shown;

[0065] Figure 2 A schematic structural diagram of a low-voltage over-limit control system for a distributed photovoltaic power station proposed in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0066] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0067] The present application embodiment provides a method for controlling low voltage over-limit of a distributed photovoltaic power station, such as Figure 1 As shown, the method comprises the following steps:

[0068] Step S101, obtaining grid-related capacity information and determining grid capacity, obtaining grid load data and determining grid load degree.

[0069] In this embodiment, the power grid related capacity information includes the power grid's substation capacity, transmission line capacity, and distribution transformer capacity, etc., so as to understand the power supply capacity of the power grid.

[0070] In some embodiments of the present application, obtaining grid load data and determining the grid load degree include:

[0071] Grid load data includes daily load curve and peak load;

[0072] Split the daily load curve into multiple sub-load curves according to different time periods within a day;

[0073] Calculate the slope change of each sub-load curve and the peak load of each sub-load curve;

[0074] The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods;

[0075] A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference;

[0076] The grid load level is determined based on the combined difference.

[0077] In this embodiment, a correction coefficient is determined based on the slope change, so as to correct each difference and obtain a comprehensive difference. Each slope change corresponds to a correction coefficient, and the correction of each difference = correction coefficient * difference.

[0078] Step S102, based on the grid capacity and the grid load level, the grid-connected capacity of the photovoltaic power station is obtained, a plurality of safety margin influencing factors are obtained, and causal indicators of the plurality of safety margin influencing factors and the safety margin are calculated, so as to set the safety margin.

[0079] In this embodiment, when determining the grid-connected capacity of the photovoltaic power station, it is generally necessary to set a certain safety margin. The safety margin is to ensure the stable operation of the power grid and the safe operation of the photovoltaic power station, and to make appropriate conservative settings for the grid-connected capacity in consideration of unforeseen factors and changes. Multiple safety margin influencing factors include weather and climate, sunshine intensity, inverter capacity, etc.

[0080] In this embodiment, the causal index here is a nonlinear interdependence index, which is a method based on state space reconstruction and neighbor distance, and is used to determine the direction and size of the causal relationship. For two independent systems or factors X and Y, the state space of the two systems is established according to the state space reconstruction theory.

[0081] For a sample point x in the state space X n , x rn，1 , ..., x rn，k . represents x n k nearest neighbors in the state space X, calculate x n The average Euclidean distance to k nearest neighbors;

[0082]

[0083] For a sample point y in the state space Y n ,y sn，1 , ..., y sn，k Represents y n The k nearest points in the state space Y are mapped to the state space X and x is calculated. n and k nearest neighbor points x sn，1 , ..., x sn，k The average Euclidean distance of

[0084]

[0085] In order to simplify the calculation, we can use x n The average distance to all N sample points;

[0086]

[0087] The nonlinear interdependence indicator is the state space method, which determines the causal relationship between systems based on the mapping relationship of the state space and is defined as:

[0088]

[0089] According to the definition, 0<S X→Y ≤1, when S X→Y When S approaches 0, systems X and Y are independent of each other. X→Y When it is significantly greater than 0, there is a causal relationship from system X to Y, and the closer it is to 1, the stronger the causality.

[0090] In some embodiments of the present application, multiple safety margin influencing factors and causal indicators of the safety margin are calculated to set the safety margin, including:

[0091] The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors;

[0092] The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied;

[0093] Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor;

[0094] The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

[0095] Step S103, determining an access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitoring data changes near the access point.

[0096] In this embodiment, the nearby data include voltage, frequency, load, etc. Just looking at the voltage cannot accurately indicate the voltage state of the power grid, and it needs to be judged in combination with other relevant parameters.

[0097] When the power grid is in a low voltage or high voltage state, the following parameters may change:

[0098] Grid voltage: In the low voltage state, the grid voltage will decrease and be lower than the rated voltage range; in the high voltage state, the grid voltage will increase and exceed the rated voltage range.

[0099] Grid frequency: Grid frequency is usually stable, but it may be affected under low or high voltage conditions. For example, when the grid voltage is low, the grid frequency may decrease; when the grid voltage is high, the grid frequency may increase.

[0100] Grid load: In a low-voltage state, the grid load may be large because the grid voltage drops and more electricity is needed to meet the load demand; in a high-voltage state, the grid load may be small because the grid voltage rises and less electricity is needed to meet the load demand.

[0101] Grid power factor: Under low voltage conditions, due to voltage drop, the power factor may be low, resulting in a mismatch between active power and reactive power; under high voltage conditions, the power factor may be high, resulting in a mismatch between active power and reactive power.

[0102] In some embodiments of the present application, determining the access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information includes:

[0103] According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected;

[0104] Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability;

[0105] The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

[0106] In this embodiment, the priorities of the distance to the substation, the grid load and the grid stability are set according to the specific situation, so as to select the optimal access point.

[0107] Step S104, judging the voltage status of the power grid according to the data changes near the access point, and adopting multiple means to control accordingly to adjust the voltage level of the power grid.

[0108] In some embodiments of the present application, the voltage state of the power grid is determined according to the data changes near the access point, and multiple means are used for corresponding control to adjust the voltage level of the power grid, including:

[0109] Data near the access point include grid voltage, grid frequency, grid load and grid power factor;

[0110] If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low;

[0111] Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships;

[0112] If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower;

[0113] Otherwise, it is judged that the grid voltage state is normal;

[0114] When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

[0115] In this embodiment, active power control: the control system of the distributed photovoltaic power station adjusts the active power of the photovoltaic power station according to the information provided by the voltage monitoring device. When the grid voltage is too low, the active power output of the photovoltaic power station is reduced to reduce the power injected into the grid. Reactive power control: In addition to active power control, the voltage level of the grid can also be affected by adjusting the reactive power output of the photovoltaic power station. Increase or decrease the reactive power output of the photovoltaic power station to adjust the voltage to an appropriate range. Energy storage system assists in regulation: If the distributed photovoltaic power station is equipped with an energy storage system, the energy storage system can be used to adjust the voltage. In low-voltage conditions, the energy storage system can inject stored power into the grid to increase the grid voltage.

[0116] By applying the above technical solutions, the grid-related capacity information is obtained, and the grid capacity is determined, the grid load data is obtained, and the grid load degree is determined; the grid-connected capacity of the photovoltaic power station is obtained based on the grid capacity and the grid load degree, multiple safety margin influencing factors are obtained, and the causal indicators of multiple safety margin influencing factors and safety margin are calculated, so as to set the safety margin; the access point is determined according to the grid-connected capacity of the photovoltaic power station with safety margin and additional information, and the data changes near the access point are monitored; the grid voltage state is judged according to the data changes near the access point, and multiple means are used for corresponding control to adjust the voltage level of the grid. This application improves the accuracy of the grid-connected capacity of the photovoltaic power station and facilitates subsequent state judgment by calculating the causal indicators of multiple safety margin influencing factors and safety margin to set the safety margin. By determining the access point according to the grid-connected capacity of the photovoltaic power station with safety margin and additional information, the accuracy of subsequent state judgment is improved. By judging the grid voltage state according to the data changes near the access point and using multiple means for corresponding control, the accuracy of grid voltage state judgment, regulation accuracy and regulation effect are improved.

[0117] Through the description of the above implementation methods, those skilled in the art can clearly understand that the present invention can be implemented by hardware, or by means of software plus a necessary general hardware platform. Based on such an understanding, the technical solution of the present invention can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.), including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each implementation scenario of the present invention.

[0118] Correspondingly, the present application also provides a low voltage over-limit control system for a distributed photovoltaic power station, such as Figure 2 As shown, the system comprises:

[0119] The first module 201 is used to obtain grid-related capacity information and determine grid capacity, obtain grid load data and determine grid load level;

[0120] The second module 202 is used to obtain the grid-connected capacity of the photovoltaic power station based on the grid capacity and the grid load degree, obtain multiple safety margin influencing factors, and calculate the causal indicators of the multiple safety margin influencing factors and the safety margin, so as to set the safety margin;

[0121] The third module 203 is used to determine the access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitor the data changes near the access point;

[0122] The fourth module 204 is used to determine the voltage status of the power grid according to the data changes near the access point, and adopt multiple means to control accordingly to adjust the voltage level of the power grid.

[0123] In some embodiments of the present application, the first module 201 is used to:

[0124] Grid load data includes daily load curve and peak load;

[0125] Split the daily load curve into multiple sub-load curves according to different time periods within a day;

[0126] Calculate the slope change of each sub-load curve and the peak load of each sub-load curve;

[0127] The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods;

[0128] A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference;

[0129] The grid load level is determined based on the combined difference.

[0130] In some embodiments of the present application, the second module 202 is used to:

[0131] The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors;

[0132] The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied;

[0133] Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor;

[0134] The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

[0135] In some embodiments of the present application, the third module 203 is used to:

[0136] According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected;

[0137] Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability;

[0138] The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

[0139] In some embodiments of the present application, the fourth module 204 is used to:

[0140] Data near the access point include grid voltage, grid frequency, grid load and grid power factor;

[0141] If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low;

[0142] Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships;

[0143] If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower;

[0144] Otherwise, it is judged that the grid voltage state is normal;

[0145] When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

[0146] Those skilled in the art will appreciate that the modules in the system in the implementation scenario can be distributed in the system of the implementation scenario according to the implementation scenario description, or can be changed accordingly and located in one or more systems different from the implementation scenario. The modules in the above implementation scenario can be combined into one module, or can be further split into multiple sub-modules.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A low voltage over-limit control method for a distributed photovoltaic power station, characterized in that: The method comprises: Obtain relevant capacity information of the power grid and determine the capacity of the power grid, obtain power grid load data and determine the degree of power grid load; Based on the grid capacity and grid load level, the grid-connected capacity of the photovoltaic power station is obtained, multiple safety margin influencing factors are obtained, and the causal indicators of multiple safety margin influencing factors and safety margin are calculated to set the safety margin; Determine the access point based on the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitor the data changes near the access point; The grid voltage status is determined based on data changes near the access point, and multiple control methods are used to adjust the grid voltage level.

2. The low voltage over-limit control method of a distributed photovoltaic power station according to claim 1, characterized in that: Obtain grid load data and determine the grid load level, including: Grid load data includes daily load curve and peak load; Split the daily load curve into multiple sub-load curves according to different time periods within a day; Calculate the slope change of each sub-load curve and the peak load of each sub-load curve; The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods; A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference; The grid load level is determined based on the combined difference.

3. The low voltage over-limit control method of a distributed photovoltaic power station according to claim 1, characterized in that: And calculate multiple safety margin influencing factors and safety margin causal indicators to set the safety margin, including: The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors; The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied; Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor; The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

4. The low voltage over-limit control method of a distributed photovoltaic power station according to claim 1, characterized in that: Determine the access point based on the grid-connected capacity of the PV power plant with a safety margin and additional information, including: According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected; Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability; The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

5. The low voltage over-limit control method of a distributed photovoltaic power station as claimed in claim 4, characterized in that: The grid voltage status is determined based on the data changes near the access point, and multiple control methods are used to adjust the grid voltage level, including: Data near the access point include grid voltage, grid frequency, grid load and grid power factor; If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low; Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships; If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower; Otherwise, it is judged that the grid voltage state is normal; When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

6. A low voltage over-limit control system for a distributed photovoltaic power station, characterized in that: The system comprises: The first module is used to obtain the relevant capacity information of the power grid and determine the power grid capacity, obtain the power grid load data and determine the power grid load degree; The second module is used to obtain the grid-connected capacity of the photovoltaic power station based on the grid capacity and the grid load level, obtain multiple safety margin influencing factors, and calculate the causal indicators of multiple safety margin influencing factors and the safety margin, so as to set the safety margin; The third module is used to determine the access point according to the grid-connected capacity of the photovoltaic power station with a safety margin and additional information, and monitor the data changes near the access point; The fourth module is used to determine the voltage status of the power grid according to the data changes near the access point, and adopt multiple means of corresponding control to adjust the voltage level of the power grid.

7. The low voltage over-limit control system of a distributed photovoltaic power station according to claim 6, characterized in that: The first module is used to: Grid load data includes daily load curve and peak load; Split the daily load curve into multiple sub-load curves according to different time periods within a day; Calculate the slope change of each sub-load curve and the peak load of each sub-load curve; The difference between the peak load of each sub-load curve and the grid capacity is calculated according to the time impact weight corresponding to different time periods; A correction coefficient is determined based on the slope change, thereby correcting each difference to obtain a comprehensive difference; The grid load level is determined based on the combined difference.

8. The low voltage over-limit control system of a distributed photovoltaic power station as claimed in claim 6, characterized in that: The second module is used to: The safety margin influencing factors whose causal indicators exceed the threshold of the first indicator are regarded as the main influencing factors; The safety margin influencing factors whose causal indicators exceed the second indicator threshold and do not exceed the first indicator threshold are taken as the influencing factors to be studied; Calculate the causal index between the influencing factor to be investigated and the main influencing factor, and take the influencing factor to be investigated whose causal index exceeds the third indicator threshold as the auxiliary influencing factor; The corresponding influence weights are assigned to the main influencing factors and the auxiliary influencing factors respectively, so as to set the safety margin.

9. The low voltage over-limit control system of a distributed photovoltaic power station according to claim 6, characterized in that: The third module is used to: According to the grid-connected capacity of the photovoltaic power station with a safety margin, multiple voltages matching its capacity are determined, thereby determining multiple access points to be selected; Additional information includes the distance from the access point to the substation, grid load conditions, and grid stability; The priorities of the distance to the substation, the grid load and the grid stability are determined respectively, and an optimal access point is selected from multiple candidate access points according to the priority comparison.

10. The low voltage over-limit control system of a distributed photovoltaic power station according to claim 9, characterized in that: The fourth module is used to: Data near the access point include grid voltage, grid frequency, grid load and grid power factor; If the grid voltage is not within the preset reasonable range, the grid voltage state is judged to be high or low; Otherwise, the grid voltage state is determined according to the degree of matching between the grid frequency, grid load and grid power factor and their respective preset change relationships; If the comprehensive matching degree exceeds the preset matching degree, it is judged that the grid voltage state is higher or lower; Otherwise, it is judged that the grid voltage state is normal; When the grid voltage is high or low, active power control, reactive power control and energy storage system control are performed.

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