Grid-connected capacity determination system for distribution network distributed photovoltaic mobile power supply equipment

Abstract

The invention relates to the technical field of distributed photovoltaic technology, and discloses a grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment of a distribution network, which comprises a high-irradiation time window determination unit for identifying a time period with stable irradiation and high intensity; the parameter acquisition unit acquires core parameters such as scanning period, phase synchronization, sensitivity and voltage regulation delay; the active fundamental amplitude calculation unit obtains the active fundamental amplitude of group scanning according to the scanning and synchronization parameters; the voltage fundamental wave amplitude processing unit converts and normalizes the voltage fundamental wave amplitude according to the electrical characteristic parameters; the coherence window envelope construction unit generates an envelope weight reflecting a coordination relationship between a scanning period and a phase; the sharp point stress forming unit multiplies the normalization result by the envelope weight to obtain sharp point stress; and the grid-connected capacity output unit outputs the total grid-connected injection power upper limit in the high-irradiation time window by comparing the sharp point stress with a preset threshold value.

Description

Technical Field

[0001] This invention relates to the field of distributed photovoltaic technology, and more specifically, to a system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment in a distribution network. Background Technology

[0002] With the continuous expansion of distributed photovoltaic (PV) grid integration, the issues of voltage control and capacity assessment in distribution networks are becoming increasingly prominent. Traditional grid-connected capacity calculation methods are mostly based on steady-state power flow models, determining the upper limit of connectable capacity by analyzing static constraints such as line impedance, voltage limits, and transformer thermal capacity. In actual engineering projects, the power variations of PV systems are not only affected by the environment but also by equipment control logic, operation and maintenance work, and the cyclical behavior of inverter functions. These dynamic processes can significantly alter the voltage distribution at the grid connection point in a short period, and traditional static models cannot reflect their impact in a timely manner.

[0003] In the operation and maintenance (O&M) of distributed photovoltaic (PV) systems, to improve power generation performance and identify potential problems, O&M personnel frequently conduct system inspections and performance scans during the midday hours when irradiance conditions are stable. For example, inverter manufacturers generally provide multi-peak scanning or global scanning functions to automatically search for the maximum power point. This operation periodically causes the inverter's output power to briefly decrease and then recover. When multiple devices perform this operation on the same power supply line, the line's active power exhibits quasi-periodic fluctuations, leading to periodic fluctuations in the distribution network voltage. Simultaneously, on-load tap-changing transformers and reactive power control devices in the distribution network typically have response delays ranging from seconds to minutes. When the rhythm of external power fluctuations is close to the response time of these devices, the tap changers will frequently tap-change or delay compensation, resulting in repeated voltage changes and short-term flicker, rendering the traditional capacity calculation model based on steady-state voltage limits inaccurate.

[0004] Furthermore, the operation and maintenance of mobile photovoltaic power supply equipment is more complex. When temporarily connected or tested on-site, this type of equipment often migrates between different nodes in the distribution network, and its output control logic typically inherits the scanning strategy of stationary inverters. When multiple mobile devices perform routine checks or self-tests on the same feeder, the resulting periodic power disturbances create a complex time-dependent relationship with the existing voltage regulation system. Because current capacity calculations do not consider the dynamic matching relationship between power changes and voltage regulation device responses during this operation and maintenance period, the calculated grid-connected capacity often differs significantly from the actual measured operating capacity. Summary of the Invention

[0005] This invention provides a system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment in a distribution network, which solves the technical problem of how to identify and calculate the capacity limit changes caused by the combined effects of periodic power disturbances and the dynamic response of voltage regulation in the distribution network within a specific time window of concentrated operation of distributed photovoltaic equipment in the distribution network, so as to obtain the true and effective grid-connected capacity.

[0006] This invention provides a system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment in a distribution network, comprising: The high irradiance time window determination unit is used to determine the high irradiance time window for grid-connected operation of distributed photovoltaic mobile power supply equipment in the distribution network; The parameter acquisition unit is used to acquire scanning-related parameters, synchronization-related parameters, electrical characteristic parameters of the distributed photovoltaic system, and operation-related parameters of the distribution network voltage regulating equipment. The active base amplitude calculation unit is used to calculate the active base amplitude of the group scan based on the scan correlation parameters and the synchronization correlation parameters. The voltage base amplitude processing unit is used to convert the active base amplitude into the voltage base amplitude based on electrical characteristic parameters, and to normalize it according to the action-related parameters. The homology window envelope construction unit is used to construct a homology window envelope based on scan-related parameters. The cusp stress forming unit is used to couple the result of the normalization process with the homology window envelope to form cusp stress; The grid-connected capacity output unit is used to compare the peak stress with a preset threshold and output the upper limit of the total grid-connected injected power of the distributed photovoltaic mobile power supply equipment within the high irradiance time window.

[0007] The beneficial effects of this invention are as follows: By introducing a cusp stress calculation mechanism based on dynamic time behavior, accurate identification of the actual grid-connected capacity of distributed photovoltaic mobile power supply equipment in distribution networks during high-irradiance periods is achieved. This invention not only considers dynamic scanning characteristics such as the photovoltaic inverter scanning cycle, synchronization phase, duty cycle, and relative power dip, but also combines electrical and voltage regulation characteristic parameters such as the voltage reactive power smoothing time constant, the first-order sensitivity of the grid connection point voltage and active power, and the voltage dead zone of the voltage regulating equipment to construct a unified model of the homogeneity window envelope and normalized voltage response. Through cusp stress and threshold comparison, quantitative calculation of capacity limits is achieved, transforming grid-connected capacity assessment from traditional steady-state static judgment to accurate prediction under dynamic response constraints. This effectively avoids voltage flicker and frequent voltage regulation problems induced by group scanning during concentrated high-irradiance operations, thereby significantly improving the safety, stability, and capacity utilization of the distribution network. Attached Figure Description

[0008] Figure 1 This is a block diagram of a distribution network distributed photovoltaic mobile power supply equipment grid connection capacity determination system according to the present invention. Detailed Implementation

[0009] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, features described in some examples may be combined in other examples.

[0010] like Figure 1 As shown, a system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment in a distribution network includes: The high irradiance time window determination unit is used to determine the high irradiance time window for grid-connected operation of distributed photovoltaic mobile power supply equipment in the distribution network; The parameter acquisition unit is used to acquire scanning-related parameters, synchronization-related parameters, electrical characteristic parameters of the distributed photovoltaic system, and operation-related parameters of the distribution network voltage regulating equipment. The active base amplitude calculation unit is used to calculate the active base amplitude of the group scan based on the scan correlation parameters and the synchronization correlation parameters. The voltage base amplitude processing unit is used to convert the active base amplitude into the voltage base amplitude based on electrical characteristic parameters, and to normalize it according to the action-related parameters. The homology window envelope construction unit is used to construct a homology window envelope based on scan-related parameters. The cusp stress forming unit is used to couple the result of the normalization process with the homology window envelope to form cusp stress; The grid-connected capacity output unit is used to compare the peak stress with a preset threshold and output the upper limit of the total grid-connected injected power of the distributed photovoltaic mobile power supply equipment within the high irradiance time window.

[0011] In one embodiment of the present invention, determining the high-irradiance time window for grid-connected operation of distributed photovoltaic mobile power supply equipment in the distribution network includes: Obtain the time series of irradiance; For the acquired irradiance time series, according to the preset smoothing time length, the irradiance time series within the time interval corresponding to the smoothing time length is integrated and then divided by the smoothing time length to obtain the smoothed irradiance. The rate of change of smooth irradiance is obtained by taking the absolute value of the derivative of the smoothed irradiance. Set an irradiance threshold and a rate of change threshold, and filter out all times when the smooth irradiance is not lower than the irradiance threshold and the smooth irradiance rate of change is not higher than the rate of change threshold to form a candidate time set; Set a minimum duration, filter out all possible time intervals in the candidate time set whose time intervals are not less than the minimum duration, perform integral calculation on the smooth irradiance in each time interval to obtain the irradiance integral value, and select the start and end times corresponding to the time interval with the largest irradiance integral value. The high-irradiation time window is formed based on the selected start and end times.

[0012] Irradiance time series is a numerical sequence of solar irradiance intensity at different times at a certain location, collected continuously at fixed time intervals (e.g., 1 minute / time). To obtain irradiance time series, it is necessary to collect data through an irradiance sensor (e.g., a silicon-based radiometer), and the collection time must cover at least one full day (e.g., 6:00-18:00).

[0013] The preset smoothing time is a fixed time interval set to eliminate short-term irradiance fluctuations (such as instantaneous changes in cloud cover). The preset smoothing time needs to be set in combination with the characteristics of irradiance fluctuations. Its value range is usually 5-15 minutes (10-15 minutes in areas with many clouds, and 5-8 minutes in sunny days, to adapt to the intensity of irradiance fluctuations under different weather conditions).

[0014] Smoothed irradiance is the average irradiance intensity after eliminating short-term fluctuations. Smoothed irradiance can more accurately reflect the overall trend of irradiance. Specifically, the first step is to determine the current calculation time and, using the current calculation time as the endpoint, extract the time interval corresponding to the preset smoothing time length. The second step is to calculate the integral of all irradiance data within this time interval (i.e., add the irradiance values ​​at each time point within this time interval and then multiply by the collection time interval of the irradiance time series to obtain the integral result). The third step is to divide the integral result by the preset smoothing time length to obtain the smoothed irradiance at the current time.

[0015] The smoothed irradiance change rate is an indicator reflecting how quickly smoothed irradiance intensity changes over time. It is used to determine whether irradiance is stable. Specifically, the process involves four steps: First, selecting smoothed irradiance values ​​at two adjacent calculation times (e.g., smoothed irradiance E1 at time t1, smoothed irradiance E2 at time t2, with the time interval between t2 and t1 equal to the time interval of the irradiance time series acquisition). Second, calculating the change (E2 minus E1). Third, dividing the change by the time interval (t2 minus t1) to obtain the change rate. Fourth, taking the absolute value of the change rate to obtain the smoothed irradiance change rate.

[0016] The irradiance threshold is the minimum standard for judging high irradiance. The irradiance threshold needs to be set in conjunction with the power generation efficiency of photovoltaic equipment. Its value is usually 800-1000 watts per square meter (specifically set at 80%-100% of the rated irradiance of photovoltaic modules (1000 watts per square meter). If it is below this range, the photovoltaic power output is low and there is no need to focus on evaluating the grid-connected capacity).

[0017] The rate of change threshold is the highest standard for judging the stability of irradiance. Exceeding the rate of change threshold indicates that the irradiance fluctuates greatly and is not suitable for grid-connected capacity assessment. The range of the rate of change threshold is usually 50-100 watts per square meter per minute (80-100 watts per square meter per minute for areas with large fluctuations, and 50-70 watts per square meter per minute for stable areas, specifically determined by reverse calculation based on the standard that the photovoltaic power fluctuation does not exceed 5%).

[0018] The candidate time set is the set of all times that simultaneously satisfy high irradiance and stable irradiance. The candidate time set is represented by multiple discrete times (such as 10:05, 10:06, ..., 13:58). The candidate time set is the basis for subsequent selection of time intervals.

[0019] The minimum duration is the shortest time length to ensure that the high irradiance window has practical operation and maintenance significance. The minimum duration needs to be set in conjunction with the duration of photovoltaic operation and maintenance work. Its value range is usually 2-4 hours (specifically set according to the operation time of 1-3 hours for a single grid connection commissioning plus 1 hour of redundancy to avoid the window being too short to complete the operation and maintenance work).

[0020] A possible time interval is a continuous time segment extracted from the candidate time set, with a duration not less than the minimum duration (e.g., 10:00-12:30, duration 2.5 hours). The possible time interval must ensure that all times within the interval are in the candidate time set. If multiple possible time intervals have the same irradiance integral value, the possible time interval with the earliest starting time is selected.

[0021] Irradiance integral is an indicator that measures the total irradiance energy within a certain time interval. The larger the irradiance integral value, the richer the irradiance resources within the interval. Specifically, the first step is to determine the start and end times of the possible time interval (e.g., tstart to tend); the second step is to extract the smoothed irradiance for all times within the possible time interval; the third step is to calculate the integral (by adding the smoothed irradiance values ​​for each time moment within the possible time interval and multiplying them by the time interval of the irradiance time series acquisition, the integral result is the irradiance integral value).

[0022] The start and end times are the beginning and end times of the possible time intervals (e.g., 10:00 is the start time and 12:30 is the end time). The final selected start and end times are the start and end times of the possible time interval with the largest irradiance integral value. If multiple possible time intervals have the same irradiance integral value, the final selected start and end times are the start and end times of the possible time interval with the earliest start time.

[0023] The high irradiance time window is a continuous time interval (such as 10:00-12:30) determined by the final selected start and end times. The irradiance intensity is high and stable within the high irradiance time window, which is the optimal time period for grid-connected operation and maintenance of distributed photovoltaic mobile power supply equipment.

[0024] In one embodiment of the present invention, the scanning-related parameters, synchronization-related parameters, electrical characteristic parameters of the distributed photovoltaic system, and the operation-related parameters of the distribution network voltage regulating equipment include: The scanning parameters include: scanning period, single scan duration, duty cycle, and relative power dip. The scanning period is the time interval between the start times of two adjacent scans, the single scan duration is the length of time from the start to the end of a scan, the duty cycle is obtained by dividing the single scan duration by the scanning period, and the relative power dip is obtained by subtracting the ratio of the average active power during the scan to the average active power at the stable maximum power point before the scan from 1. Synchronization-related parameters include: the number of inverters participating in the scan, the scan start phase, and the phase synchronization sequence parameter. The number of inverters participating in the scan is the number of inverters performing the scan within the high irradiance time window. The scan start phase is the phase within a scan cycle mapped from the scan start time of the i-th inverter. The phase synchronization sequence parameter is obtained by first calculating the sum of the complex exponents corresponding to the scan start phase of each inverter, then dividing the sum by the number of inverters participating in the scan, and finally taking the absolute value of the result. Electrical characteristic parameters include: first-order sensitivity of grid connection point voltage and active power and voltage-reactive power smoothing time constant. The first-order sensitivity of grid connection point voltage and active power is obtained by dividing the change in grid connection point voltage between two steady states by the change in active power over the same period. The voltage-reactive power smoothing time constant is a parameter describing the time scale of voltage-reactive power regulation smoothing response. The relevant parameters for the operation of distribution network voltage regulating equipment include: the initial operation delay of the on-load tap-changing transformer and the voltage dead zone. The initial operation delay of the on-load tap-changing transformer is the delay before the voltage regulation starts to respond, and the voltage dead zone is the allowable voltage deviation range that prevents the voltage regulation from triggering.

[0025] The scan period is the time interval between the start times of two consecutive scan operations in a distributed photovoltaic system. The value of the scan period is generally 10-60 minutes. It needs to be set in conjunction with the irradiance stability. In scenarios with large irradiance fluctuations, a smaller value should be used to track power changes in a timely manner, while a larger value should be used in stable scenarios to reduce energy consumption.

[0026] The duration of a single scan is the time required for a distributed photovoltaic system to complete one full scan operation. The value of the duration of a single scan is generally in the range of 10-60 seconds. It needs to be matched with the inverter response speed. For devices with fast response, a smaller value should be used to avoid excessive scanning affecting power output.

[0027] Duty cycle is the proportion of a single scan duration to the scan cycle, with a value ranging from 0.003 to 0.1. The duty cycle reflects the degree of impact of the scan operation on the normal operation of the system. The smaller the duty cycle, the less interference to normal power generation. Specifically, the first step is to obtain the set single scan duration and scan cycle; the second step is to divide the single scan duration by the scan cycle to obtain the duty cycle.

[0028] Relative power dip is a quantitative indicator of the degree of active power reduction during a scan, typically ranging from 0.05 to 0.2. It is used to assess the impact of scanning on power generation efficiency; the smaller the value, the smaller the power loss caused by the scan. Specifically, the steps are as follows: First, calculate the average active power at all times during the scan period to obtain the average active power during the scan period. Second, calculate the average active power over a period of time when the system was at its stable maximum power point before the scan begins to obtain the average active power at the stable maximum power point before the scan. Third, divide the average active power during the scan period by the average active power at the stable maximum power point before the scan to obtain the ratio. Fourth, subtract this ratio from 1 to obtain the relative power dip.

[0029] The number of inverters participating in the scan is the number of inverters that actually perform the scan operation during the high irradiation time window. Its value needs to be set in combination with the total number of inverters in the system and the grid-connected capacity assessment requirements. It is usually 30%-100% of the total number, and a larger value is taken when the assessment accuracy requirement is high.

[0030] The scan start phase is the angle value corresponding to the scan start time of the i-th inverter in a single scan cycle. The mapping method is to divide the time difference between the scan start time and the scan cycle start time by the scan cycle, and then multiply by 360 degrees. The value range of the scan start phase is 0-360 degrees, which is used to characterize the time position of a single inverter scan.

[0031] The phase synchronization sequence parameter is an indicator that measures the degree of synchronization of the starting phases of multiple inverters during scanning. Its value ranges from 0 to 1; the closer the value is to 1, the better the synchronization. Generally, a value greater than 0.9 is considered acceptable to reduce power fluctuation interference during scanning. Specifically, the process involves: first, determining the starting phase of scanning for each inverter and calculating the complex exponent (i.e., a complex number with a base of the natural constant and an imaginary unit multiplied by the starting phase); second, summing the complex exponents of all inverters; third, dividing the sum of complex exponents by the number of inverters participating in the scan to obtain the quotient; and fourth, taking the absolute value of the quotient to obtain the phase synchronization sequence parameter.

[0032] The first-order sensitivity of grid connection point voltage to active power is an indicator reflecting the sensitivity of grid connection point voltage to changes in active power. Its value needs to be set in conjunction with the distribution network impedance characteristics; areas with higher distribution network impedance have higher sensitivity values. It is used to assess the impact of active power changes on grid connection point voltage. Specifically, the steps are as follows: First, select two different steady-state operating conditions of the system, and record the grid connection point voltage and active power of the first steady-state condition, as well as the grid connection point voltage and active power of the second steady-state condition. Second, subtract the grid connection point voltage of the first steady-state condition from the grid connection point voltage of the second steady-state condition to obtain the change in grid connection point voltage between the two steady states. Third, subtract the active power of the first steady-state condition from the active power of the second steady-state condition to obtain the change in active power over the same period. Fourth, divide the change in grid connection point voltage by the change in active power to obtain the first-order sensitivity of grid connection point voltage to active power.

[0033] The voltage reactive power smoothing time constant is a time-scale parameter that characterizes the smoothness of the voltage reactive power regulation process in a distributed photovoltaic system. Its value range is generally 1-10 seconds. It needs to be set in conjunction with the response speed of the reactive power compensation equipment. Smaller values ​​are used for equipment with fast response to enable rapid adjustment, while larger values ​​are used for equipment with slow response to avoid oscillation.

[0034] The on-load tap-changing transformer's first action delay is the time interval between when the on-load tap-changing transformer detects a voltage deviation and before it begins to perform the tap-changing action. The value range is generally 30-300 seconds, and it needs to be set in conjunction with the scan cycle. It is usually longer than the duration of a single scan to avoid the tap-changing action interfering with the scan results.

[0035] The voltage dead zone is the allowable fluctuation range of the grid connection point voltage when the on-load tap-changing transformer does not start tap-changing action. The value range is generally ±2% to ±5% of the rated voltage. It needs to be set in combination with the grid connection point voltage stability and scanning accuracy requirements. A larger value can be taken during scanning to reduce voltage regulation interference.

[0036] In one embodiment of the present invention, the active base amplitude of the group scan is calculated based on scan correlation parameters and synchronization correlation parameters, including: The sum of the grid-connected active power of all inverters participating in the scan at the stable maximum power point before the scan is obtained as the total grid-connected injected power; Multiplying 2 by pi yields the first product; dividing the first product by the scanning period yields the scanning angular frequency. Dividing 2 by pi yields the second product; multiplying the second product by the phase synchronization sequence parameter yields the third product; multiplying the third product by the relative power dip yields the fourth product; multiplying the fourth product by the total grid-injected power yields the fifth product. Multiplying pi by the duty cycle yields the first calculated value; taking the sine of the first calculated value and then taking its absolute value yields the sixth product. Multiplying the fifth product by the sixth product yields the active base amplitude of the group scan.

[0037] The total grid-connected injected power is the sum of the grid-connected active power outputs of all participating inverters when the system is in a stable maximum power point operating state before the scanning operation begins. The time range for stabilizing the maximum power point before scanning should be set to 5-10 minutes before the start of scanning (to ensure no power fluctuations) to avoid errors caused by taking instantaneous values.

[0038] The first product is the result of multiplying 2 by pi. The first product is an intermediate variable for calculating the scanning angular frequency.

[0039] The scan period is the time interval between the start times of two consecutive scans.

[0040] The second product is the result obtained by dividing the number 2 by pi. It is a core component of the fundamental coefficient in the calculation of the active fundamental amplitude of the group scan and is used to extract the fundamental component of the active fluctuation.

[0041] The scanning angular frequency is an angular frequency parameter that reflects the periodicity of the scanning operation time. It is used to quantify the angular rate corresponding to the scanning period. This parameter directly affects the frequency matching of the subsequent fundamental amplitude calculation. Specifically, the first step is to determine the set scanning period; the second step is to multiply 2 by pi to obtain the first product; the third step is to divide the first product by the scanning period, and the result is the scanning angular frequency.

[0042] The third product is obtained by multiplying the second product (2 divided by pi) by the phase synchronization sequence parameter. This product reflects the correction effect of the synchronization degree on the fundamental frequency coefficient (the better the synchronization, the closer the third product is to the second product).

[0043] The fourth product is the result of multiplying the third product by the relative power dip. The fourth product combines the fundamental frequency coefficient-synchronization correction with the degree of power drop, quantifying the correlation between the fundamental frequency amplitude and the power dip.

[0044] The fifth product is obtained by multiplying the fourth product by the total grid-connected injected power. The fifth product reflects the active power fluctuation amplitude after the fundamental coefficient, synchronization correction, and power dip correction under the total power scale.

[0045] The first calculated value is the result obtained by multiplying pi by the duty cycle. The first calculated value is the basic variable for calculating the fundamental attenuation coefficient corresponding to the duty cycle.

[0046] The sine value is the result of performing a sine function operation on the first calculated value (pi × duty cycle). The value ranges from -1 to 1. It quantifies the attenuation effect of the duty cycle on the fundamental component of active power fluctuation (the closer the duty cycle is to 0.5, the closer the sine value is to 1, and the smaller the attenuation).

[0047] The sixth product is the result of taking the absolute value of the sine of the first calculated value. It is the fundamental attenuation coefficient corresponding to the duty cycle and is used to correct the fundamental component in the total power fluctuation (the more the duty cycle deviates from 0.5, the smaller the sixth product and the weaker the fundamental component).

[0048] The active power fundamental amplitude of a group scan reflects the amplitude of the fundamental component in the active power fluctuation when multiple inverters scan synchronously. Its calculation requires ensuring that all intermediate variables are in the same unit (e.g., the scan period is uniformly in minutes). If the scan period is in seconds, it needs to be converted to minutes before calculation.

[0049] In one embodiment of the present invention, the conversion of the active base amplitude to the voltage base amplitude based on electrical characteristic parameters includes: Calculate the seventh product of the scanning angular frequency and the voltage reactive smoothing time constant. Square the seventh product to obtain the first squared value. Add the first squared value to 1 to obtain the first sum. Take the square root of the first sum to obtain the first square root. Divide 1 by the first square root to obtain the voltage reactive smoothing amplitude-frequency gain. Multiply the grid connection point voltage by the first-order sensitivity of active power, the active base amplitude of the group scan, and the voltage reactive smoothing amplitude-frequency gain in sequence to obtain the voltage base amplitude.

[0050] The seventh product is obtained by multiplying the scanning angular frequency by the voltage reactive smoothing time constant converted to minutes. The seventh product is the core intermediate variable for calculating the voltage reactive smoothing amplitude-frequency gain.

[0051] The first squared value is the result obtained by squaring the seventh product. The first squared value is used to construct the denominator of the amplitude-frequency gain, reflecting the coupling strength between the scanning frequency and the reactive power regulation time scale.

[0052] The first sum is the result obtained by adding the first square value to the number 1, and it is the basis for calculating the denominator (first square root) of the voltage reactive power smoothing amplitude-frequency gain.

[0053] The first square root is the result of taking the square root of the first sum, and its value is greater than or equal to 1 (because the first sum is greater than or equal to 1). It is the direct denominator of the amplitude-frequency gain.

[0054] The voltage reactive power smoothing amplitude-frequency gain is an indicator reflecting the attenuation capability of a voltage reactive power regulation system to voltage fluctuations at a scanning frequency. Its value ranges from 0 to 1; the closer the value is to 1, the weaker the attenuation capability (the scanning frequency is close to the reactive power regulation resonant frequency), and the closer the value is to 0, the stronger the attenuation capability. Specifically, the steps are as follows: First, convert the voltage reactive power smoothing time constant from seconds to minutes (by dividing the voltage reactive power smoothing time constant by 60); second, calculate the seventh product of the scanning angular frequency and the converted voltage reactive power smoothing time constant; third, square the seventh product to obtain the first square value; fourth, add the first square value to 1 to obtain the first sum; fifth, take the square root of the first sum to obtain the first square root; sixth, divide 1 by the first square root to obtain the voltage reactive power smoothing amplitude-frequency gain.

[0055] The voltage fundamental amplitude is the amplitude of the fundamental component of the voltage fluctuation at the grid connection point, which is obtained by converting the active fundamental amplitude of the group scan through electrical characteristic parameters.

[0056] In one embodiment of the present invention, normalization processing based on action-related parameters includes: The normalized voltage base amplitude is obtained by dividing the voltage dead zone by the voltage base amplitude.

[0057] Normalized voltage base amplitude is a parameter obtained by dividing the voltage base amplitude by the voltage dead zone. It is used to quantify the size of the voltage base amplitude relative to the voltage dead zone (a value greater than 1 indicates that the voltage base amplitude exceeds the voltage dead zone, which may trigger the operation of the distribution network voltage regulating equipment; a value less than or equal to 1 indicates that the voltage base amplitude is within the voltage dead zone and will not trigger voltage regulation). Specifically, the first step is to unify the units of voltage base amplitude and voltage dead zone (if the voltage dead zone is a percentage of the rated voltage, it needs to be converted first according to voltage dead zone = system rated voltage × voltage dead zone percentage); the second step is to divide the voltage base amplitude by the voltage dead zone, and the result is the normalized voltage base amplitude.

[0058] In one embodiment of the present invention, constructing a homology window envelope based on scan-related parameters includes: Calculate the eighth product of pi and duty cycle, take the sine of the eighth product and then take its absolute value to obtain the first calculation result; multiply the phase synchronization sequence parameter with the first calculation result to obtain the homology window envelope weight.

[0059] The eighth product is the result of multiplying pi by the duty cycle. The eighth product is an intermediate variable that quantifies the relationship between the duty cycle and periodicity.

[0060] The sine value of the eighth product is the result of performing a sine function operation on the eighth product, and its value ranges from 0 to 1 (because the eighth product is pi × duty cycle, the duty cycle ≤ 0.1, the eighth product ≤ 0.31416, and the sine value is non-negative). It is the attenuation effect of the quantization duty cycle on the homology window envelope (the closer the duty cycle is to 0.5, the closer the sine value is to 1, and the smaller the attenuation).

[0061] The absolute value is obtained by taking the sine of the eighth product and then taking its absolute value. The absolute value is the non-negative result of the sine of the eighth product, and the value ranges from 0 to 1. This avoids errors in subsequent weight calculations caused by extreme duty cycles (such as a duty cycle close to 0.6, the eighth product close to 1.885, and the sine value may be negative), and ensures that the result is non-negative.

[0062] The first calculation result is a parameter obtained by taking the absolute value of the sine of the eighth product, with a value ranging from 0 to 1. This result is the attenuation coefficient of the coherence window corresponding to the duty cycle, which is used to correct the influence of the phase synchronization sequence parameter on the envelope of the coherence window (the more reasonable the duty cycle, the closer the first calculation result is to 1, and the closer the corrected weight is to the phase synchronization sequence parameter). Specifically, the first step is to obtain the duty cycle; the second step is to multiply the duty cycle by pi (3.1416) to obtain the eighth product; the third step is to perform a sine function operation on the eighth product to obtain the sine value; the fourth step is to take the absolute value of the sine value to obtain the first calculation result.

[0063] The synchronization window envelope weight is a parameter reflecting the degree of matching between the scanning cycle and the action time scale of the distribution network voltage regulating equipment under the combined effect of inverter group scanning synchronization and duty cycle rationality. The value ranges from 0 to 1. The closer the value is to 1, the higher the matching degree (the easier it is to trigger the limit loop of the voltage regulating equipment), and the closer the value is to 0, the lower the matching degree (the smaller the impact on the voltage regulating equipment). Specifically, the first step is to obtain the phase synchronization sequence parameter; the second step is to obtain the first calculation result; the third step is to multiply the phase synchronization sequence parameter by the first calculation result, and the result is the synchronization window envelope weight.

[0064] In one embodiment of the present invention, the result of the normalization process is coupled with the homogeneity window envelope to form a cusp stress, including: The cusp stress is obtained by multiplying the normalized voltage base amplitude by the weight of the homogeneous window envelope.

[0065] Cusp stress is a parameter obtained by multiplying the normalized voltage base amplitude with the coherence window envelope weight. It is used to comprehensively quantify the grid-connected capacity constraint risk under the combined effect of the degree to which voltage fluctuations exceed the dead zone and the matching degree of the scan-regulation time scale (the larger the value, the higher the risk of abnormal operation of the voltage regulation equipment due to scan disturbance, resulting in capacity limitation). Specifically, the first step is to obtain the normalized voltage base amplitude; the second step is to obtain the coherence window envelope weight; the third step is to multiply the normalized voltage base amplitude by the coherence window envelope weight, and the result is the cusp stress.

[0066] In one embodiment of the present invention, comparing the cusp stress with a preset threshold and outputting the upper limit of the total grid-connected injected power of the distributed photovoltaic mobile power supply equipment within the high irradiance time window includes: Multiply the preset threshold by the voltage dead zone to obtain the molecular result; Multiply the grid connection point voltage by the first-order sensitivity of active power and the voltage-reactive power smoothing amplitude-frequency gain to obtain the first denominator factor; Multiply 2 by the relative power concavity to obtain the second denominator factor; The phase synchronization sequence parameter is squared to obtain the third denominator factor; Multiply pi by the duty cycle, take the sine of the product, and then square it to obtain the fourth denominator factor. Multiply the first denominator factor, the second denominator factor, the third denominator factor, and the fourth denominator factor in sequence to obtain the total denominator result; Divide the numerator by the total denominator to obtain the upper limit of the total grid-connected injected power.

[0067] The preset threshold is a critical value used to determine whether the apex stress exceeds the safe range. The value of the preset threshold needs to be set in combination with the withstand capability of the distribution network voltage regulating equipment (such as on-load tap-changing transformer) and the grid connection safety standard. The usual value range is 1 to 2 (1.2 for low-risk scenarios, 1.5 for medium-risk scenarios, and 2.0 for high-risk scenarios). When the apex stress is greater than the preset threshold, the upper limit of the total grid-connected injected power needs to be calculated to limit the risk.

[0068] The numerator result is obtained by multiplying a preset threshold by the voltage dead zone. The unit of the numerator result is 1 / 2 Ω. This result is the numerator of the calculation of the upper limit of the total grid-connected injected power, reflecting the coupling between the safe voltage deviation range and the risk threshold.

[0069] The first denominator factor is obtained by multiplying the grid connection point voltage by the first-order sensitivity of active power and the voltage-reactive power smoothing amplitude-frequency gain, reflecting the constraint of voltage-active power sensitivity and reactive power attenuation capability on the upper limit of power.

[0070] The second denominator factor is the result of multiplying 2 by the relative power concavity, reflecting the constraint of the scan power reduction on the upper limit of power.

[0071] The third denominator factor is the result obtained by squaring the phase synchronization sequence parameter, which reflects the constraint of scanning synchronization on the upper limit of power (the higher the synchronization, the larger the third denominator factor, and the lower the upper limit of power).

[0072] The fourth denominator factor is a parameter obtained by squaring the sine of pi × duty cycle. It reflects the constraint of the scan duty cycle on the upper limit of power (the closer the duty cycle is to 0.5, the larger the fourth denominator factor, and the lower the upper limit of power).

[0073] The total denominator result is obtained by multiplying the first to fourth denominator factors in sequence. The total denominator result is the denominator term used to calculate the upper limit of the total grid-connected injected power, which comprehensively reflects the constraints of multiple factors on the upper limit of power.

[0074] The upper limit of total grid-connected injected power is the maximum total power that distributed photovoltaic mobile power supply equipment in the distribution network is allowed to inject within a high irradiance time window. The unit of the upper limit of total grid-connected injected power is kilowatts.

[0075] The embodiments of this example have been described above. However, this example is not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms based on the guidance of this example, and all of them are within the protection scope of this example.

Claims

1. A system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment in a distribution network, characterized in that, include: The high irradiance time window determination unit is used to determine the high irradiance time window for grid-connected operation of distributed photovoltaic mobile power supply equipment in the distribution network; The parameter acquisition unit is used to acquire scanning-related parameters, synchronization-related parameters, electrical characteristic parameters of the distributed photovoltaic system, and operation-related parameters of the distribution network voltage regulating equipment. The active base amplitude calculation unit is used to calculate the active base amplitude of the group scan based on the scan correlation parameters and the synchronization correlation parameters. The voltage base amplitude processing unit is used to convert the active base amplitude into the voltage base amplitude based on electrical characteristic parameters, and to normalize it according to the action-related parameters. The homology window envelope construction unit is used to construct a homology window envelope based on scan-related parameters. The cusp stress forming unit is used to couple the result of the normalization process with the homology window envelope to form cusp stress; The grid-connected capacity output unit is used to compare the peak stress with a preset threshold and output the upper limit of the total grid-connected injected power of the distributed photovoltaic mobile power supply equipment within the high irradiance time window.

2. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 1, characterized in that, Determine the high-irradiance time window for grid-connected operation of distributed photovoltaic mobile power supply equipment in the distribution network, including: Obtain the time series of irradiance; For the acquired irradiance time series, according to the preset smoothing time length, the irradiance time series within the time interval corresponding to the smoothing time length is integrated and then divided by the smoothing time length to obtain the smoothed irradiance. The rate of change of smooth irradiance is obtained by taking the absolute value of the derivative of the smoothed irradiance. Set an irradiance threshold and a rate of change threshold, and filter out all times when the smooth irradiance is not lower than the irradiance threshold and the smooth irradiance rate of change is not higher than the rate of change threshold to form a candidate time set; Set a minimum duration, filter out all possible time intervals in the candidate time set whose time intervals are not less than the minimum duration, perform integral calculation on the smooth irradiance in each time interval to obtain the irradiance integral value, and select the start and end times corresponding to the time interval with the largest irradiance integral value. The high-irradiation time window is formed based on the selected start and end times.

3. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 2, characterized in that, The scanning-related parameters, synchronization-related parameters, electrical characteristic parameters of the distributed photovoltaic system, and the operation-related parameters of the distribution network voltage regulating equipment include: The scanning parameters include: scanning period, single scan duration, duty cycle, and relative power dip. The scanning period is the time interval between the start times of two adjacent scans, the single scan duration is the length of time from the start to the end of a scan, the duty cycle is obtained by dividing the single scan duration by the scanning period, and the relative power dip is obtained by subtracting the ratio of the average active power during the scan to the average active power at the stable maximum power point before the scan from 1. Synchronization-related parameters include: the number of inverters participating in the scan, the scan start phase, and the phase synchronization sequence parameter. The number of inverters participating in the scan is the number of inverters performing the scan within the high irradiance time window. The scan start phase is the phase within a scan cycle mapped from the scan start time of the i-th inverter. The phase synchronization sequence parameter is obtained by first calculating the sum of the complex exponents corresponding to the scan start phase of each inverter, then dividing the sum by the number of inverters participating in the scan, and finally taking the absolute value of the result. Electrical characteristic parameters include: first-order sensitivity of grid connection point voltage and active power and voltage-reactive power smoothing time constant. The first-order sensitivity of grid connection point voltage and active power is obtained by dividing the change in grid connection point voltage between two steady states by the change in active power over the same period. The voltage-reactive power smoothing time constant is a parameter describing the time scale of voltage-reactive power regulation smoothing response. The relevant parameters for the operation of distribution network voltage regulating equipment include: the initial operation delay of the on-load tap-changing transformer and the voltage dead zone. The initial operation delay of the on-load tap-changing transformer is the delay before the voltage regulation starts to respond, and the voltage dead zone is the allowable voltage deviation range that prevents the voltage regulation from triggering.

4. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 3, characterized in that, Based on scan correlation parameters and synchronization correlation parameters, the active base amplitude of the population scan is calculated, including: The sum of the grid-connected active power of all inverters participating in the scan at the stable maximum power point before the scan is obtained as the total grid-connected injected power; Multiplying 2 by pi yields the first product; dividing the first product by the scanning period yields the scanning angular frequency. Dividing 2 by pi yields the second product; multiplying the second product by the phase synchronization sequence parameter yields the third product; multiplying the third product by the relative power dip yields the fourth product; multiplying the fourth product by the total grid-injected power yields the fifth product. Multiplying pi by the duty cycle yields the first calculated value; taking the sine of the first calculated value and then taking its absolute value yields the sixth product. Multiplying the fifth product by the sixth product yields the active base amplitude of the group scan.

5. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 4, characterized in that, Based on electrical characteristic parameters, the active power base amplitude is converted into the voltage base amplitude, including: Calculate the seventh product of the scanning angular frequency and the voltage reactive smoothing time constant. Square the seventh product to obtain the first squared value. Add the first squared value to 1 to obtain the first sum. Take the square root of the first sum to obtain the first square root. Divide 1 by the first square root to obtain the voltage reactive smoothing amplitude-frequency gain. Multiply the grid connection point voltage by the first-order sensitivity of active power, the active base amplitude of the group scan, and the voltage reactive smoothing amplitude-frequency gain in sequence to obtain the voltage base amplitude.

6. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 5, characterized in that, Normalization is performed based on action-related parameters, including: The normalized voltage base amplitude is obtained by dividing the voltage dead zone by the voltage base amplitude.

7. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 6, characterized in that, Constructing a homology window envelope based on scan-related parameters includes: Calculate the eighth product of pi and duty cycle, take the sine of the eighth product and then take its absolute value to obtain the first calculation result; multiply the phase synchronization sequence parameter with the first calculation result to obtain the homology window envelope weight.

8. The grid-connected capacity determination system for distributed photovoltaic mobile power supply equipment according to claim 7, characterized in that, The result of the normalization process is coupled with the homology window envelope to form cusp stresses, including: The cusp stress is obtained by multiplying the normalized voltage base amplitude by the weight of the homogeneous window envelope.

9. A system for determining the grid-connected capacity of distributed photovoltaic mobile power supply equipment according to claim 8, characterized in that, The peak stress is compared with a preset threshold to output the upper limit of the total grid-connected injected power of distributed photovoltaic mobile power supply equipment within the high irradiance time window, including: Multiply the preset threshold by the voltage dead zone to obtain the molecular result; Multiply the grid connection point voltage by the first-order sensitivity of active power and the voltage-reactive power smoothing amplitude-frequency gain to obtain the first denominator factor; Multiply 2 by the relative power concavity to obtain the second denominator factor; The phase synchronization sequence parameter is squared to obtain the third denominator factor; Multiply pi by the duty cycle, take the sine of the product, and then square it to obtain the fourth denominator factor. Multiply the first denominator factor, the second denominator factor, the third denominator factor, and the fourth denominator factor in sequence to obtain the total denominator result; Divide the numerator by the total denominator to obtain the upper limit of the total grid-connected injected power.

Images