Adaptive Protection Method for Photovoltaic Collector Lines Based on Time-Varying Aging Model

Abstract

This invention provides an adaptive protection method for photovoltaic (PV) collector lines based on a time-varying aging model. The steps include: establishing a full lifecycle performance degradation model for the PV power plant and generating a power degradation lookup table using a Monte Carlo model to describe the relationship between the overall performance ratio (PR) of the PV power plant and the operating year t; for any rated capacity collector line of the PV power plant, calculating the predicted maximum transmission power in year t based on the power degradation lookup table; calculating the maximum load current of the line in year t based on the predicted maximum transmission power and the rated voltage of the collector line, and determining the minimum fault current; setting an adaptive adjustment rule for the protection setting based on the minimum fault current; and adjusting the protection setting based on the adaptive adjustment rule when the triggering condition is met, and sending the adjusted protection setting to the collector line protection device of the PV power plant, thereby improving the reliability and adaptability of the PV power generation system collector line protection throughout its entire lifecycle.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology, and in particular to an adaptive protection method for photovoltaic collector lines based on a time-varying aging model. Background Technology

[0002] Traditional photovoltaic (PV) collector line protection typically employs fixed protection settings, which are primarily based on the rated capacity and short-circuit current level at the initial stage of power plant operation. However, as the PV modules age, they are subjected to long-term environmental factors such as temperature, humidity, and irradiance, causing irreversible degradation in module power. According to relevant standards, the power degradation rate of PV modules over a 25-year lifespan is usually guaranteed to be within 20%, which leads to a gradual decrease in the maximum load current of the collector line. Traditional fixed settings do not take this time-varying characteristic into account.

[0003] The continuous degradation of the output power of a photovoltaic power station directly affects the current-carrying capacity of the collector lines. This leads to the traditional fixed setting values ​​being too high relative to the actual operating current, resulting in decreased protection sensitivity and potential failure to operate or delayed operation in the event of a metallic fault. Secondly, as power degradation intensifies, the load current continuously decreases, while the short-circuit current level remains relatively high. The fixed setting may not be able to effectively avoid the maximum load current during normal operation, posing a risk of erroneous tripping or insufficient disturbance rejection capability. Both of these situations reduce the selectivity, speed, and reliability of the protection, posing potential threats to the safe operation of the photovoltaic power station.

[0004] Existing protection systems lack consideration for the time-varying characteristics of photovoltaic systems and cannot adapt to the slow changes in output power. This mismatch between traditional static protection configurations and dynamic operating systems poses a hidden danger to the long-term safe operation of power plants. Summary of the Invention

[0005] In view of this, the present invention proposes an adaptive protection method for photovoltaic collectors based on a time-varying aging model. The setpoint of the photovoltaic power station can be adjusted according to the attenuation situation, so as to realize adaptive protection of the photovoltaic power station throughout its entire life cycle.

[0006] The technical solution of this invention is implemented as follows: The adaptive protection method for photovoltaic collector lines based on a time-varying aging model includes the following steps: Step S1: Establish a full life cycle performance degradation model for photovoltaic power plants, and use the Monte Carlo model to generate a power degradation lookup table describing the relationship between the overall performance ratio PR of the photovoltaic power plant and the operating year t. Step S2: For any rated capacity collector line of a photovoltaic power station, calculate the predicted maximum transmission power in year t based on the power attenuation lookup table; Step S3: Based on the predicted maximum transmission power and the rated voltage of the collector line in year t, calculate the maximum load current of the line in year t and determine the minimum fault current. Step S4: Set adaptive adjustment rules for protection settings based on minimum fault current; Step S5: When the triggering condition is met, the protection setting is adjusted based on the adaptive adjustment rule of the protection setting, and the adjusted protection setting is sent to the collector protection device of the photovoltaic power station.

[0007] Preferably, step S1 includes the following steps: The factors affecting the degradation rate of photovoltaic modules are identified, including production process, material batch, and installation environment. The dispersion index of annual degradation rate is determined, which includes the degradation rate in the first year and the degradation rate in subsequent years. The Monte Carlo model was used to assess the randomness of the annual decay rate through random sampling, and the probability distribution characteristics of the annual decay rate were obtained. Taking the target photovoltaic power plant as the object, the performance degradation simulation of the whole life cycle is carried out based on the influencing factors, annual degradation rate and probability distribution characteristics, and the power degradation lookup table containing the performance ratio and annual power generation of each operating year is output.

[0008] Preferably, the expression for the performance ratio PR is:

[0009] in Let be the performance ratio in year t. For DC installed capacity, Let be the peak daily sunshine hours of the photovoltaic power station in year t. Let be the grid-connected power generation in year t, and its expression is: , The total efficiency of the photovoltaic power generation system.

[0010] Preferably, the overall efficiency of the photovoltaic power generation system is... The expression is:

[0011] in For fixed losses of photovoltaic power plants, The first-year decay rate, For the subsequent annual decay rate, For inverter efficiency, This refers to the transformer efficiency.

[0012] Preferably, the fixed loss includes cable loss. Component matching loss Shielding loss Temperature loss Dust loss Other losses .

[0013] Preferably, the expression for the predicted maximum transmission power in year t is:

[0014] The Let be the predicted maximum transmission power in year t. The rated capacity of the collector line, The performance ratio for the first year. Let be the performance ratio in year t.

[0015] Preferably, the expression for the maximum line load current in year t is:

[0016] in Let be the maximum load current of the line in year t. Let be the predicted maximum transmission power in year t. The rated voltage of the collector line. The power factor.

[0017] Preferably, in step S3, the minimum fault current that the photovoltaic side can provide in year t is calculated based on the maximum line load current in year t. The expression for the minimum fault current that the photovoltaic side can provide in year t is:

[0018] in Let be the minimum fault current that the photovoltaic side can provide in year t. Let be the maximum load current of the line in year t. This represents the inverter fault overload factor.

[0019] Preferably, the expression for the adaptive adjustment rule of the protection setting is:

[0020] in To protect the set value, This is the minimum sensitivity coefficient.

[0021] Preferably, the specific steps of step S4 are as follows: When the timing or event triggering conditions are met, the protection settings are adjusted based on the adaptive adjustment rules of the protection settings to obtain the adjusted protection settings; The protection settings are sent to the collector protection device of the photovoltaic power station via a standard communication protocol, and the return value is read to confirm whether the modification was successful.

[0022] Compared with the prior art, the beneficial effects of the present invention are: ① Based on the factors affecting the degradation rate of photovoltaic power station components and the dispersion index of annual degradation rate, a full life cycle performance degradation model of photovoltaic power station is constructed to predict and query the evolution trend of performance ratio of photovoltaic power station. Based on the performance ratio of different years, the protection setting value can be adjusted to achieve adaptive setting value protection and ensure the stable operation of photovoltaic power station. ② The performance ratio for the year can be determined from the power attenuation lookup table. Then, for any rated capacity collector line, the maximum transmission power can be calculated. Based on the maximum transmission power, the maximum load current of the line can be calculated, and the minimum fault current can be calculated. Based on the minimum fault current, the protection setting can be adaptively adjusted. Finally, the adjusted protection setting can be sent to the collector line protection device of the photovoltaic power station. When the protection device detects that the current is greater than the protection setting, it can act to protect the collector line of the photovoltaic power station. Through the adaptive adjustment of the protection setting, the sensitivity of the action can be kept stable. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The flowchart shows the adaptive protection method for photovoltaic collector wires based on a time-varying aging model according to the present invention. Figure 2 This is a schematic diagram of the module composition of the photovoltaic collector line adaptive protection method based on the time-varying aging model of the present invention; Figure 3 This is a comparison chart showing the sensitivity of the photovoltaic collector line adaptive protection method based on the time-varying aging model of the present invention with that of traditional protection as a function of years of operation. Figure 4 This is a comparison chart showing the change of current setting value over years between the photovoltaic collector line adaptive protection method based on the time-varying aging model of the present invention and the traditional protection method. Detailed Implementation

[0025] To better understand the technical content of this invention, a specific embodiment is provided below, and the invention will be further described in conjunction with the accompanying drawings.

[0026] See Figure 1 The adaptive protection method for photovoltaic current collectors based on a time-varying aging model provided by this invention includes the following steps: Step S1: Establish a full life cycle performance degradation model for photovoltaic power plants, and use the Monte Carlo model to generate a power degradation lookup table describing the relationship between the overall performance ratio PR of the photovoltaic power plant and the operating year t. Step S2: For any rated capacity collector line of a photovoltaic power station, calculate the predicted maximum transmission power in year t based on the power attenuation lookup table; Step S3: Based on the predicted maximum transmission power and the rated voltage of the collector line in year t, calculate the maximum load current of the line in year t and determine the minimum fault current. Step S4: Set adaptive adjustment rules for protection settings based on minimum fault current; Step S5: When the triggering condition is met, the protection setting is adjusted based on the adaptive adjustment rule of the protection setting, and the adjusted protection setting is sent to the collector protection device of the photovoltaic power station.

[0027] This invention discloses an adaptive protection method for photovoltaic collectors based on a time-varying aging model. Compared to the traditional fixed-value method, this invention can adaptively adjust the protection settings of the photovoltaic power station. To achieve this adjustment, it is necessary to analyze the overall performance degradation of the photovoltaic power station, thus requiring the prediction of the performance ratio (PR) of the photovoltaic power station. The PR is defined as follows:

[0028] As a core benchmark for evaluating the power generation performance of photovoltaic (PV) systems, Performance Ratio (PR) encompasses PV array losses as well as inverter and transformer losses, directly reflecting the overall operating status and true performance of the PV power generation system. To determine the relationship between PR and time, this invention introduces a Monte Carlo model as a key probabilistic simulation tool to handle the uncertainty of PV system aging. This model can generate a power degradation lookup table describing the relationship between the PR of a PV power plant and the operating year t. The power degradation lookup table allows for the rapid determination of the specific value of the PR in a future year and the assessment of the PV power plant's performance degradation. This performance degradation directly leads to a continuous decrease in the system's maximum load current. Therefore, based on any rated capacity collector line of the PV power plant, the PR for the future year t can be extracted from the power degradation lookup table, and the corresponding predicted maximum transmission power can be calculated. The predicted maximum transmission power can then be combined with the rated capacity of the collector line. The maximum load current of the line is calculated by considering the inverter's fault-related parameters. This allows for the calculation of the minimum fault current available on the photovoltaic side in year t. Finally, based on the minimum fault current, an adaptive adjustment rule for the protection setting can be set. When the photovoltaic power station meets the corresponding triggering conditions, the protection setting can be adaptively adjusted. The adjusted protection setting can be sent to the collector protection device of the photovoltaic power station, thus updating the setting for year t. When a fault occurs in the photovoltaic system, the protection device can operate when it detects a current greater than the protection setting, thereby ensuring the stable operation of the photovoltaic power station. Because the protection setting can be adaptively adjusted based on performance degradation, it solves the problems of traditional fixed-setting protection, which fails to consider the performance degradation of the photovoltaic power generation system, leading to a decrease in the maximum load current and relatively high protection settings. This optimizes the sensitivity of the protection system and improves the reliability and adaptability of the photovoltaic power generation system's collector line protection throughout its entire lifecycle.

[0029] Preferably, step S1 includes the following steps: The factors affecting the degradation rate of photovoltaic modules are identified, including production process, material batch, and installation environment. The dispersion index of annual degradation rate is determined, which includes the degradation rate in the first year and the degradation rate in subsequent years. The Monte Carlo model was used to assess the randomness of the annual decay rate through random sampling, and the probability distribution characteristics of the annual decay rate were obtained. Taking the target photovoltaic power plant as the object, the performance degradation simulation of the whole life cycle is carried out based on the influencing factors, annual degradation rate and probability distribution characteristics, and the power degradation lookup table containing the performance ratio and annual power generation of each operating year is output.

[0030] The degradation rate of photovoltaic modules is not a fixed value, but is affected by many factors such as production process, material batch, and installation environment, and exhibits significant dispersion. For example, the degradation rate in the first year is 2.5%±0.3%, and the degradation rate in subsequent years is 0.7%±0.1%. Traditional deterministic models cannot quantify the risks brought about by the randomness of degradation, while Monte Carlo simulation, through tens of thousands of random samplings, can scientifically assess the probability distribution of degradation parameters and ultimately establish a full life cycle performance degradation model to predict the performance ratio in year t at any time.

[0031] Preferably, the expression for the performance ratio PR is:

[0032] in Let be the performance ratio in year t. For DC installed capacity, Let be the peak daily sunshine hours of the photovoltaic power station in year t. Let be the grid-connected power generation in year t, and its expression is: , The total efficiency of the photovoltaic power generation system is expressed as:

[0033] in The fixed losses of a photovoltaic power plant are represented by numbers 1-6, indicating losses in different parts. The first-year decay rate, For the subsequent annual decay rate, For inverter efficiency, This refers to the transformer efficiency.

[0034] In the expression for performance ratio PR That is to say ,and Then it means , It is used to integrate fixed losses and time-varying decay losses of components to quantify the system's energy conversion efficiency.

[0035] Preferably, the fixed loss includes cable loss. Component matching loss Shielding loss Temperature loss Dust loss Other losses .

[0036] The degradation of the performance ratio is related to multiple losses, which include fixed losses, annual degradation rate, inverter efficiency, and transformer efficiency. Different losses have corresponding default values, which are taken into account when calculating the performance ratio. The default values ​​and explanations of the multiple losses are shown in Table 1. Table 1. Default values ​​and corresponding explanations for multi-party losses.

[0037] Preferably, the expression for the predicted maximum transmission power in year t is:

[0038] The Let be the predicted maximum transmission power in year t. The rated capacity of the collector line, The performance ratio for the first year. Let be the performance ratio in year t.

[0039] and The power attenuation value can be directly obtained from a power attenuation lookup table, while the rated capacity of the collector line can be obtained from the design standards of the collector line. The maximum power that the line can safely transmit in year t can be determined.

[0040] Preferably, the expression for the maximum line load current in year t is:

[0041] in Let be the maximum load current of the line in year t. Let be the predicted maximum transmission power in year t. The rated voltage of the collector line. The power factor.

[0042] After obtaining the predicted maximum transmission power for year t, the maximum line load current for year t can be calculated accordingly. Based on the relationship between power and current, the rated voltage of the collector line also needs to be determined. Then, the maximum load current of the line in year t is calculated using the formula, where the power factor is... It can be set according to actual needs, and the value is usually between 0.95 and 1.0. Used to define the maximum current boundary for normal operation of the line in year t, distinguishing between normal operation and fault conditions.

[0043] Preferably, in step S3, the minimum fault current that the photovoltaic side can provide in year t is calculated based on the maximum line load current in year t. The expression for the minimum fault current that the photovoltaic side can provide in year t is:

[0044] in Let be the minimum fault current that the photovoltaic side can provide in year t. Let be the maximum load current of the line in year t. This represents the inverter fault overload factor.

[0045] After determining the maximum line load current in year t, the minimum fault current that the system can provide during a fault in year t can be calculated and determined based on the inverter fault overload coefficient. This is a key reference for ensuring the reliable operation of the protection device.

[0046] Preferably, the expression for the adaptive adjustment rule of the protection setting is:

[0047] in To protect the set value, This is the minimum sensitivity coefficient.

[0048] The minimum sensitivity coefficient serves as the operating threshold for the protection device, ensuring that sensitivity requirements are met during faults. This prevents both failure to operate during faults and erroneous operation during normal operation. The value is 1.37. In the adaptive strategy of this invention, as... decline, Decrease, through automatic adjustment This ensures the reliable sensitivity of the photovoltaic power generation system throughout its entire life cycle.

[0049] Preferably, the specific steps of step S4 are as follows: When the timing or event triggering conditions are met, the protection settings are adjusted based on the adaptive adjustment rules of the protection settings to obtain the adjusted protection settings; The protection settings are sent to the collector protection device of the photovoltaic power station via a standard communication protocol, and the return value is read to confirm whether the modification was successful.

[0050] Triggering conditions include timed triggers or event triggers. Timed triggers include once a year, while event triggers include viscosity checks, etc. When the triggering conditions are met, the protection settings can be adjusted based on preset adaptive adjustment rules, and then... The message is sent via a standard communication protocol (such as IEC 61850), and the return value is used to confirm whether the modification was successful.

[0051] After the above-mentioned protection setting adjustment, the protection device's setting for the current year t has been updated to... When a system fault occurs (fault flag = 1), the protection device detects the current. That is, the action, because It is based on the current aging state of the system (reflected in) The result is obtained through dynamic calculation, thus ensuring that the motion sensitivity remains stable at a constant level. .

[0052] A protection system is built based on the adaptive protection method of the present invention, and the system modules are as follows: Figure 2 As shown, the system's operating logic is as follows: input the operating year t, match the system's power attenuation lookup table according to the operating year, and calculate the predicted maximum transmission power, maximum load current, minimum fault current, and protection setting value for the system in the t-th year of operation. The protection will only operate when the system is in a fault state and the fault current exceeds the protection setting value, that is, when (fault current > protection setting value) AND (fault flag = 1), the protection will operate.

[0053] To verify the effectiveness of the present invention, the following embodiments are provided for verification: To quantify the PR value, a photovoltaic project is used as an example. The configuration parameters of a 100MW photovoltaic project are shown in Table 2.

[0054] Table 2 A 100MW photovoltaic power generation project

[0055] The Monte Carlo model was used to simulate and analyze the performance degradation of the 100MW photovoltaic power generation system over its 25-year life cycle. The simulation results are shown in Table 3. The PR value decreased linearly from 90.01% in the first year to 70.72% in the 25th year, and the annual power generation decreased from 177.0GWh to 139.1GWh, with a degradation of 21.4%.

[0056] Table 3 Monte Carlo simulation results of power degradation of photovoltaic power generation system over 25 years

[0057] The adaptive setting protection of the collector wire of the above 1000MW photovoltaic power plant is compared with the traditional fixed setting protection. The specific data comparison is shown in Table 4.

[0058] Table 4. Comparison of the full life cycle performance of traditional fixed protection and adaptive protection

[0059] Traditional fixed-set protection has certain technical defects under this background. For example, in the first year, when the fixed protection setting is set to 215A, the initial fault current of the system is 322.85A, the action sensitivity is 1.5, and the protection operates reliably. However, by the 10th year, the fault current drops to 296.90A, and the action sensitivity drops to 1.38, which is close to the reliable operation threshold of relay 1.37, and is in a critical risk state. By the 25th year, the fault current further drops to 253.40A, and the action sensitivity is only 1.19, which already has an extremely high risk of failure to operate.

[0060] As the service life increases, the actual sensitivity of the protection system continuously declines, falling significantly below the reliable operating threshold in the later stages of power plant operation (e.g., starting from the 15th year), creating a serious "hidden" risk of failure to operate. In other words, the traditional approach sacrifices later-stage safety for initial reliability. Its sensitivity degradation trend is as follows... Figure 3 As shown.

[0061] This invention introduces a time-varying aging model, enabling the protection settings to be dynamically adjusted according to the actual system state. The trend of the setting changes is as follows: Figure 4 As shown. In the initial stage, a relatively high setpoint (235.65A) is set to prevent malfunction and ensure operating margin; in the later stage, the setpoint is adjusted down synchronously with the fault current (to 184.97A) to always maintain the sensitivity at the optimal value of 1.37, thereby achieving the stability of the photovoltaic power generation system sensitivity throughout its entire life cycle and ensuring the initial reliability and later safety of the system protection device.

[0062] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An adaptive protection method for photovoltaic current collectors based on a time-varying aging model, characterized in that, Includes the following steps: Step S1: Establish a full life cycle performance degradation model for photovoltaic power plants, and use the Monte Carlo model to generate a power degradation lookup table describing the relationship between the overall performance ratio PR of the photovoltaic power plant and the operating year t. Step S2: For any rated capacity collector line of a photovoltaic power station, calculate the predicted maximum transmission power in year t based on the power attenuation lookup table; Step S3: Based on the predicted maximum transmission power and the rated voltage of the collector line in year t, calculate the maximum load current of the line in year t and determine the minimum fault current. Step S4: Set adaptive adjustment rules for protection settings based on minimum fault current; Step S5: When the triggering conditions are met, the protection setting is adjusted based on the adaptive adjustment rule of the protection setting, and the adjusted protection setting is sent to the collector protection device of the photovoltaic power station.

2. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 1, characterized in that, The specific steps of step S1 include: The factors affecting the degradation rate of photovoltaic modules are identified, including production process, material batch, and installation environment. The dispersion index of annual degradation rate is determined, which includes the degradation rate in the first year and the degradation rate in subsequent years. The Monte Carlo model was used to assess the randomness of the annual decay rate through random sampling, and the probability distribution characteristics of the annual decay rate were obtained. Taking the target photovoltaic power plant as the object, the performance degradation simulation of the whole life cycle is carried out based on the influencing factors, annual degradation rate and probability distribution characteristics, and the power degradation lookup table containing the performance ratio and annual power generation of each operating year is output.

3. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 1, characterized in that, The expression for the performance ratio PR is: in Let be the performance ratio in year t. For DC installed capacity, Let be the peak daily sunshine hours of the photovoltaic power station in year t. Let be the grid-connected power generation in year t, and its expression is: , The total efficiency of the photovoltaic power generation system.

4. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 3, characterized in that, The overall efficiency of the photovoltaic power generation system The expression is: in For fixed losses of photovoltaic power plants, The first-year decay rate, For the subsequent annual decay rate, For inverter efficiency, This refers to the transformer efficiency.

5. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 4, characterized in that, The fixed losses include cable losses. Component matching loss shading loss Temperature loss Dust loss Other losses .

6. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 1, characterized in that, The expression for the predicted maximum transmission power in year t is: The Let be the predicted maximum transmission power in year t. The rated capacity of the collector line, The performance ratio for the first year. Let be the performance ratio in year t.

7. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 1, characterized in that, The expression for the maximum line load current in year t is: in Let t be the maximum load current of the line in year t. Let be the predicted maximum transmission power in year t. The rated voltage of the collector line. The power factor.

8. The adaptive protection method for photovoltaic current collectors based on a time-varying aging model according to claim 1, characterized in that, In step S3, the minimum fault current that the photovoltaic side can provide in year t is calculated based on the maximum line load current in year t. The expression for the minimum fault current that the photovoltaic side can provide in year t is: in Let be the minimum fault current that the photovoltaic side can provide in year t. Let t be the maximum load current of the line in year t. This represents the inverter fault overload factor.

9. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 8, characterized in that, The expression for the adaptive adjustment rule of the protection setting is: in To protect the set value, This is the minimum sensitivity coefficient.

10. The photovoltaic current collector adaptive protection method based on a time-varying aging model according to claim 1, characterized in that, The specific steps of step S4 are as follows: When the timing or event triggering conditions are met, the protection settings are adjusted based on the adaptive adjustment rules of the protection settings to obtain the adjusted protection settings; The protection settings are sent to the collector protection device of the photovoltaic power station via a standard communication protocol, and the return value is read to confirm whether the modification was successful.

Images