A tracking photovoltaic power generation device

Abstract

This invention relates to the field of photovoltaic power generation technology, and particularly to a tracking photovoltaic power generation device, comprising a host computer and a slave computer. The host computer includes a fixed stake and a fixed rod, with a stepper motor mounted on the fixed rod. A photovoltaic panel is fixed to the stepper motor, and an integrated sensor is located in the center of the photovoltaic panel. The slave computer includes a data collection module, a time-period adjustment module, an execution decision module, and a monitoring and recording module. The data collection module collects solar altitude angle, photovoltaic panel tilt angle, and photovoltaic panel geometric dimensions in real time, and stores the stepper motor operating parameters. The time-period adjustment module divides different control strategies and calculation frequencies according to season and time period. The execution decision module calculates the optimal photovoltaic panel tilt angle based on the shaded area range and generates control commands. The monitoring and recording module monitors the system operating status in real time and records historical data.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power generation technology, and in particular to a tracking photovoltaic power generation device. Background Technology

[0002] The efficiency improvement of existing photovoltaic power generation systems mainly relies on the tilt angle adjustment of photovoltaic panels. Traditional tracking systems generally adopt a single control mode, that is, continuously adjusting the photovoltaic panels to make them perpendicular to the sunlight to obtain the maximum radiation.

[0003] However, this strategy has significant drawbacks: First, the excessive pursuit of the theoretically optimal angle leads to frequent mechanical system operations, increasing energy consumption and mechanical wear, and reducing system reliability. It also fails to consider the actual requirements for control precision due to seasonal variations and differences in solar trajectory, maintaining complex tracking even in winter when power generation potential is limited, resulting in resource waste. Furthermore, the lack of a scientific time-segmentation and frequency optimization mechanism between data acquisition and decision-making makes it difficult to achieve a balance between control precision and system load. Therefore, a refined photovoltaic control scheme that can dynamically adjust the control strategy according to seasons and time periods, combining theoretical calculations and sensor verification, is urgently needed to achieve a synergistic improvement in power generation efficiency and system stability. Summary of the Invention

[0004] Technical problems to be solved: Over-pursuing the theoretically optimal angle leads to frequent mechanical system operation, which not only increases energy consumption and mechanical wear, but also reduces system reliability. It also fails to consider the actual requirements for control accuracy due to seasonal changes and differences in solar trajectory, and maintains complex tracking even in winter when power generation potential is limited, resulting in resource waste.

[0005] To address the shortcomings of existing technologies, this invention provides a tracking photovoltaic power generation device, thereby solving the technical problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a tracking photovoltaic power generation device, including an upper computer and a lower computer, wherein the upper computer includes a fixed pile and a fixed rod, a stepper motor is provided on the fixed rod 2, a photovoltaic panel is fixedly connected to the stepper motor, and an integrated sensor 6 is provided in the middle of the photovoltaic panel; The lower-level machine includes: a data collection module, a time period adjustment module, an execution decision module, and a monitoring and recording module; The data collection module collects solar altitude angle, photovoltaic panel tilt angle and photovoltaic panel geometric dimensions in real time, and stores stepper motor operating parameters; The time-segmentation module divides different control strategies and calculation frequencies according to seasons and time periods; The execution decision module calculates the optimal tilt angle of the photovoltaic panel based on the shaded area range and generates control commands. The monitoring and recording module monitors the system's operating status in real time and records historical data.

[0007] In one possible implementation, the time-segmentation adjustment module divides the year into three control seasons: a fixed horizontal mode is used in winter without angle adjustment; a precision tracking mode is used in summer with the target shadow area ranging from 1.2 s min to 1.8 s min; and a moderate tracking mode is used in the transition season with the target shadow area ranging from 1.5 s min to 2.2 s min.

[0008] In one possible implementation, the time-segment adjustment module sets differentiated calculation and adjustment frequencies based on the rate of change of solar altitude angle within each season: during the summer precision tracking period, calculations are performed every 2 minutes and adjustments are made every 10 minutes; during the summer moderate tracking period, calculations are performed every 5 minutes and adjustments are made every 20 minutes; during the transitional season main tracking period, calculations are performed every 5 minutes and adjustments are made every 20 minutes; and during the transitional season secondary tracking period, calculations are performed every 10 minutes and adjustments are made every 30 minutes.

[0009] In one possible implementation, the execution decision module employs a dual verification mechanism: four miniature light intensity sensors are pre-embedded at the edge of the ground shadow area below the photovoltaic array; the tilt adjustment action is triggered if and only if the calculated shadow area S exceeds the target range and the light intensity of any sensor is less than 200 lx.

[0010] In one possible implementation, the tilt angle back-calculation algorithm of the execution decision module includes the following steps: S1: Determine the target shadow area range [Smin×k1,Smin×k2], and calculate the deviation ΔS between the current shadow area and the median of the target range, where k1 and k2 are seasonal coefficients; S2: Use a fixed step size iterative method to perform gradient search based on the current tilt angle with a step size of 1° until the new shadow area falls into the target range; S3: Calculate the number of steps required by the stepper motor N = Δθ / 0.018 based on the difference Δθ between the target tilt angle and the current tilt angle.

[0011] In one possible implementation, the data collection module has a tilt sensor and an elevation angle sensor at the center of the photovoltaic panel, which are used to collect the tilt angle θ of the photovoltaic panel and the solar elevation angle α in real time, respectively.

[0012] In one possible implementation, the monitoring and recording module employs a hierarchical storage strategy: high-frequency data is retained in seconds for the most recent 24 hours; medium-frequency data is retained in minutes for the most recent 30 days; and low-frequency statistical data is permanently stored.

[0013] One possible implementation includes the following steps: S1: Obtain real-time solar altitude angle α, photovoltaic panel tilt angle θ, and photovoltaic panel width W through the data collection module; S2: Determine the control strategy and calculation frequency corresponding to the current season and time period through the time period adjustment module; S3: Calculate the current shadow area S through the execution decision module and determine whether it is within the target range; S4: When the shadow area exceeds the target range and the light intensity sensor passes the verification, execute the tilt angle back calculation algorithm to calculate the optimal tilt angle; S5: Drive the photovoltaic panel to rotate to the target tilt angle via a stepper motor.

[0014] Beneficial effects compared to existing technologies: 1. By employing a seasonal and time-of-day variable frequency control strategy, a fixed horizontal mode is used in winter to avoid ineffective adjustments. In summer and transitional seasons, the calculation and adjustment frequency is set differently based on the rate of change of solar altitude angle, ensuring that the shadow area is always maintained within the optimal range (1.2-1.8 times the minimum shadow area in summer, and 1.5-2.2 times in transitional seasons). This significantly reduces the frequency of mechanical movement while ensuring power generation efficiency, significantly reduces motor energy consumption and mechanical wear, improves system reliability and service life, and enhances environmental anti-interference capabilities and control precision. Through a shadow area calculation model based on geometric optics principles and a dual verification mechanism using a pre-embedded light intensity sensor, adjustment is only triggered when both conditions are met: the calculated shadow area exceeds the target range and the sensor light intensity is below 200 lx. This effectively avoids malfunctions caused by environmental factors such as cloud drift and weed obstruction, ensuring that the photovoltaic panels can receive direct sunlight to the maximum extent. Attached Figure Description

[0015] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0017] Figure 2 This is a schematic diagram of the overall top structure of the present invention.

[0018] Figure 3 This is a schematic diagram of the overall system structure of the present invention.

[0019] Figure 4 This is a schematic diagram of the method flow structure of the present invention. Attached Figure

[0020] 1. Fixed stake; 2. Fixed pole; 3. Stepper motor; 4. Photovoltaic panel; 6. Integrated sensor. Detailed Implementation

[0021] Preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can also be implemented in various different forms, and therefore the present invention is not limited to the embodiments described below. The technical solution in this application embodiment is to solve the problems mentioned in the background art, and the overall idea is as follows: Please refer to Figures 1 to 4 As shown in the figure, this embodiment introduces a tracking photovoltaic power generation device, including a host computer and a slave computer; The lower-level machine includes a fixed pile 1. During the installation process, the location to be installed is excavated, and the fixed pile 1 is buried deep in the foundation pit after excavation. Concrete is poured, and a fixed rod 2 is fixedly connected to the top of the fixed pile 1. The fixed pile 1 is fixed to the fixed rod 1 with bolts, so that a good fixation is formed between the fixed pile 1 and the fixed rod 2. A stepper motor 3 is fixedly installed at the top of the fixed rod 2. A connecting plate is fixedly installed on the output shaft of the stepper motor 3. A photovoltaic panel 4 is set on the connecting plate. The stepper motor 3 will drive the photovoltaic panel 4 to rotate through the drive shaft. The rotation range of the photovoltaic panel 4 of the stepper motor 3 is 0° to 90°, so as to ensure that the photovoltaic panel can receive direct sunlight to the maximum extent and meet the power generation needs of the photovoltaic panel. The lower-level machine includes a data collection module, a time period adjustment module, an execution decision module, and a monitoring and recording module. Through the cooperation between these modules, precise control of the photovoltaic power generation device is achieved, thereby improving the power generation efficiency of the photovoltaic panel. When sunlight shines on a photovoltaic panel, it creates a projected area on the ground behind it, known as the shadow area. The size of the shadow area is determined by three key factors: the angle between the sunlight and the horizontal plane (solar altitude angle), the angle between the photovoltaic panel plane and the horizontal plane (photovoltaic panel tilt angle), and the geometric dimensions of the photovoltaic panel itself.

[0022] To obtain the angle between sunlight and the horizontal plane in real time (solar altitude angle α), and with the photovoltaic panel tilt angle θ, an integrated sensor 6 is set in the center of 4. The integrated sensor 6 contains a tilt sensor and an altitude sensor. The tilt angle θ of the photovoltaic panel is obtained through the tilt sensor, and the acquired data will be stored in the data collection module at all times. At the same time, the size of the photovoltaic panel itself, the width of the photovoltaic panel is W (for rectangular panels, the shorter side length is taken), is also stored in the data collection module. The data collection module also includes the corresponding data of the stepper motor 3, with a stepper motor angle of 0.018° (1.8° / step).

[0023] By using data from the data collection module and starting from the principles of geometric optics, a precise formula for calculating the shadow area can be derived. Given a photovoltaic panel width of W (taking the shorter side for rectangular panels), a solar altitude angle of α, and a photovoltaic panel tilt angle of θ, the shadow area S can be expressed as: This formula clearly reveals the inherent laws governing how the shaded area changes with the solar altitude angle and the tilt angle of the photovoltaic panel.

[0024] When the tilt angle θ of the photovoltaic panel is equal to the solar altitude angle α, the plane of the photovoltaic panel is exactly perpendicular to the sunlight, and the shadow area reaches its theoretical minimum. Value Smin = W² × sinα This minimum state corresponds to the angle at which the photovoltaic panel receives the strongest solar radiation, which is the optimal power generation angle sought by traditional photovoltaic tracking systems.

[0025] Time-of-day adjustment module: The sun's trajectory across the sky changes regularly with the seasons, primarily due to the Earth's revolution around the sun and the tilt of its axial tilt. Significant differences exist in the sun's noon altitude angle, daylight hours, and sunrise and sunset positions across different seasons, directly impacting shadow formation and control strategies. The year is divided into three control seasons: summer, winter, and transition season. The division criteria are based on two core considerations: the actual changes in the solar altitude angle and the operating characteristics of the photovoltaic system.

[0026] In winter, the simplest horizontal fixed mode is adopted. This decision is based on several rational considerations: First, the solar altitude angle is low in winter. Although the amount of solar radiation received per unit area when the photovoltaic panels are placed horizontally is lower than the optimal tilt angle, the absolute increase in power generation is limited considering the weak solar intensity in winter. Second, horizontal placement facilitates snow sliding off, preventing snow cover from affecting power generation. Third, there are more windy days in winter, and the horizontal orientation minimizes the wind-receiving area and provides the most structural stability. Finally, the fixed mode completely eliminates mechanical movement, significantly improving system reliability and reducing maintenance requirements.

[0027] In summer, a precision tracking mode is employed. Summer brings high solar altitude angles and intense sunlight, meaning even a small improvement in power generation efficiency can lead to a significant increase in electricity output. Simultaneously, effective shading and cooling are crucial in the high-temperature summer environment, making precise shadow area control particularly important. Therefore, the summer mode prioritizes high-precision shadow area control, aiming to stabilize the shadow area within 1.2-1.8 times the minimum value. A moderate tracking mode is adopted during the transitional season. Solar conditions during this season fall between winter and summer, exhibiting neither the limited power generation potential of winter nor the stringent accuracy requirements of summer. Therefore, a compromise strategy is employed: the target range is 1.5-2.2 times the minimum shadow area. Minimum shaded area formula (This is the moment when the photovoltaic panel is perpendicular to the sunlight).

[0028] Within each season, based on the different rates of change of the solar altitude angle throughout the day, it is further divided into multiple control periods, and differentiated calculation frequencies are set: Summer daytime is divided into three control periods: the precision tracking period (8:00 AM to 4:00 PM), during which the solar altitude angle changes relatively steadily, using a high-frequency mode of calculation every 2 minutes and adjustment every 10 minutes; the moderate tracking period (6:00 AM to 8:00 AM and 4:00 PM to 6:00 PM), during which the solar altitude angle changes more rapidly, using a medium-frequency mode of calculation every 5 minutes and adjustment every 20 minutes; the remaining time is the dormancy period, during which only basic monitoring is performed and the angle of the photovoltaic panels is not actively adjusted.

[0029] The daytime during the transition season is divided into four control periods: the main tracking period (9:00 AM to 3:00 PM) is calculated every 5 minutes and adjusted every 20 minutes; the secondary tracking period (7:00 AM to 9:00 AM and 3:00 PM to 5:00 PM) is calculated every 10 minutes and adjusted every 30 minutes; the monitoring period (5:00 AM to 7:00 AM and 5:00 PM) is monitored but not adjusted; and the nighttime is the dormancy period.

[0030] During winter, the system remains in a fixed horizontal mode throughout the day, without any calculations or adjustments.

[0031] This time-segmented frequency variation fully considers the physical laws of solar motion: during periods when the solar altitude angle changes rapidly, the calculation frequency is appropriately increased to ensure control accuracy; during periods when the solar altitude angle changes slowly, the frequency is appropriately reduced to save system resources; and during periods when the solar altitude angle is too low or too high, it enters a low-power monitoring state.

[0032] This moderate control ensures basic power generation efficiency and functionality while avoiding resource consumption caused by overly complex control.

[0033] The execution decision module is responsible for calculating the optimal photovoltaic panel tilt angle adjustment scheme based on the real-time data provided by the data collection module and the control strategy determined by the time period adjustment module, and generating specific control commands.

[0034] When the time period adjustment module determines that the time period is winter, the execution module adopts the fixed mode of winter and does not perform calculations or adjustments. When the time period adjustment module determines that the time period is summer, the execution decision module obtains the necessary calculation data from the data collection module, including the solar altitude angle α, the photovoltaic panel tilt angle θ, and the dimensions of the photovoltaic panel itself, specifically the width W of the photovoltaic panel. The formula for the area of ​​the resulting shadow is: Where S: the projected area of ​​the photovoltaic panel on the ground (m²), W: the characteristic width of the photovoltaic panel (m), θ: the angle between the plane of the photovoltaic panel and the horizontal plane (0°-90°), α: the solar altitude angle (0°-90°). This formula is applicable to square photovoltaic panels or rectangular panels with an aspect ratio close to 1. For rectangular plates with side lengths significantly greater than their shorter sides, the following should be adopted: Where L is the length of the photovoltaic panel, and to simplify the calculation, this system assumes a square panel. To ensure that the photovoltaic panels receive maximum direct sunlight, during the summer, the area of ​​shade on the photovoltaic panels should be maintained at a certain level. （ 1.2 Smin- 1.8 Smin), Smin=W²×sinα; As the solar altitude angle changes continuously, S will change, the shadow area will increase, and eventually it will no longer be within the range of the summer shadow area. Meanwhile, at the edge of the ground shadow area below the photovoltaic panel array 4, four miniature light intensity sensors are pre-embedded at equal intervals around the array to form a rectangular monitoring frame. The installation depth of the miniature sensors is flush with the ground, and the surface is covered with a transparent protective cover. When the shadow area expands to cover the sensor, the light intensity at that point drops sharply from natural light intensity (typically >1000 lx) to below 200 lx. The system helps verify the consistency between the calculated shadow area and the actual shadow by determining the number and location of the covered sensors. For example, if all three sensors detect <200 lx, but the calculated shadow area does not exceed the limit, it is determined to be a sensor error or weed obstruction; if only one sensor detects <200 lx and the calculated value exceeds the limit, it is determined to be a momentary cloud interference. The light intensity sensor does not participate in real-time control, but only serves as a boundary verification mechanism. Execution decisions are triggered only when both conditions are met simultaneously: "the calculated shadow area S exceeds the range, and the light intensity of any sensor is <200 lx". This avoids erroneous actions caused by cloud drift.

[0035] The 200lx threshold is determined by on-site calibration: on a sunny noon, manually adjust the photovoltaic panel to the target shadow boundary, and record 80% of the sensor reading at this time as the trigger threshold to ensure reliability.

[0036] The tilt angle of the photovoltaic panel needs to be deduced if and only if both conditions are met simultaneously: "the calculated shadow area S is out of range and the light intensity of any sensor is <200lx". Specific steps for tilt angle reverse calculation: S1: Let the range of the target's shadow area be... Current tilt angle , solar altitude angle α.

[0037] Determine the target area value: Take the deviation between the current shadow area Scurrent and the midpoint of the target range. ΔS = Scurrent - Smin × 1.5 S2 gradient search for optimal tilt angle Since the relationship between θ and S in the formula S=W2×(cosθ / tanα+sinθ) is nonlinear, a fixed step-size iteration method is adopted: Preset adjustment step size Δθ=1° Based on θcurrent, calculate the new shadow areas S+1 and S-1 at ±1° respectively. Select the direction that makes |Starget-Snew| smaller as the adjustment direction and repeat the iteration until Snew falls into the target range.

[0038] S3: Stepper motor step count calculation After determining the target tilt angle θtarget, calculate the required rotation angle: Δθ = |θtarget - θcurrent| Motor parameters: Stepper motor speed is 0.018° / step (i.e., 0.018 degrees per step, approximately 2000 steps / revolution). Step count calculation formula: After rounding to the nearest integer, the photovoltaic panel is adjusted by stepper motor 3 so that the entire photovoltaic panel can receive direct sunlight at the most suitable tilt angle.

[0039] During the transitional seasons (spring and autumn), daytime is divided into four control periods, during which the shaded area needs to be maintained at a certain level. Through the above-described tilt angle reverse calculation steps, the tilt angle of the photovoltaic panel that the stepper motor 3 needs to adjust is then calculated. .

[0040] Monitoring and Recording Module: Responsible for comprehensively recording the system's operating status, monitoring system performance in real time, and providing data support for long-term optimization.

[0041] The module monitors key operating indicators in real time, including photovoltaic panel tilt angle, solar altitude angle, and shadow area. These data are displayed in a visual form on a local display screen or remote monitoring interface, allowing operators to understand the system status in real time.

[0042] The monitoring function is not limited to displaying normal indicators, but also includes the detection and alarm of abnormal states. The module has a built-in intelligent diagnostic algorithm that can identify various abnormal patterns, such as sensor failure (data exceeding the reasonable range or remaining unchanged for a long time), communication abnormalities (data transmission interruption), and mechanical failures (motor stall or excessive positional deviation). Once an abnormality is detected, the alarm mechanism is immediately triggered, notifying relevant personnel through various means such as audible and visual alarms, SMS notifications, and remote push notifications.

[0043] The module has comprehensive data logging capabilities, enabling long-term storage of historical system data. Data logging employs a tiered storage strategy: high-frequency data (seconds, tilt angle) is retained for the most recent 24 hours; mid-frequency data is retained for the most recent 30 days; and low-frequency data (such as daily statistical indicators) is permanently stored.

[0044] The recorded data includes: timestamps, photovoltaic panel tilt angles, solar altitude angles, calculated shadow area, target shadow area, control commands, and execution results. All data is fully time-stamped to ensure accurate tracking of the system's historical state.

[0045] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A tracking photovoltaic power generation device, characterized in that, It includes a host computer and a slave computer. The host computer includes a fixed pile 1 and a fixed rod 2. A stepper motor 3 is provided on the fixed rod 2. A photovoltaic panel 4 is fixedly connected to the stepper motor 3. An integrated sensor 6 is provided in the middle of the photovoltaic panel 4. The lower-level machine includes: a data collection module, a time period adjustment module, an execution decision module, and a monitoring and recording module; The data collection module collects solar altitude angle, photovoltaic panel tilt angle and photovoltaic panel geometric dimensions in real time, and stores stepper motor operating parameters; The time-segmentation module divides different control strategies and calculation frequencies according to seasons and time periods; The execution decision module calculates the optimal tilt angle of the photovoltaic panel based on the shaded area range and generates control commands. The monitoring and recording module monitors the system's operating status in real time and records historical data.

2. The tracking photovoltaic power generation device as described in claim 1, characterized in that, The time-segmentation adjustment module divides the year into three control seasons: winter uses a fixed horizontal mode without angle adjustment; summer uses a precision tracking mode with a target shadow area ranging from 1.2 s min to 1.8 s min; and the transition season uses a moderate tracking mode with a target shadow area ranging from 1.5 s min to 2.2 s min.

3. A tracking photovoltaic power generation device as described in claim 1, characterized in that, The time-segment adjustment module sets differentiated calculation and adjustment frequencies based on the rate of change of solar altitude angle within each season: during the summer precision tracking period, calculations are performed every 2 minutes and adjustments are made every 10 minutes; during the summer moderate tracking period, calculations are performed every 5 minutes and adjustments are made every 20 minutes; during the transitional season main tracking period, calculations are performed every 5 minutes and adjustments are made every 20 minutes; and during the transitional season secondary tracking period, calculations are performed every 10 minutes and adjustments are made every 30 minutes.

4. A tracking photovoltaic power generation device as described in claim 1, characterized in that, The execution decision module adopts a dual verification mechanism: four miniature light intensity sensors are pre-embedded at the edge of the ground shadow area below the photovoltaic array; the tilt angle adjustment action is triggered only when the calculated shadow area S exceeds the target range and the light intensity of any sensor is less than 200 lx.

5. A tracking photovoltaic power generation device as described in claim 1, characterized in that, The tilt angle back-calculation algorithm of the execution decision module includes the following steps: S1: Determine the target shadow area range and calculate the deviation ΔS between the current shadow area and the median of the target range; S2: Use a fixed step size iterative method to perform gradient search based on the current tilt angle with a step size of 1° until the new shadow area falls into the target range; S3: Calculate the number of steps required by the stepper motor N = Δθ / 0.018 based on the difference Δθ between the target tilt angle and the current tilt angle.

6. A tracking photovoltaic power generation device as described in claim 1, characterized in that, The data collection module has a tilt sensor and an elevation angle sensor installed in the center of the photovoltaic panel, which are used to collect the tilt angle θ of the photovoltaic panel and the solar elevation angle α in real time, respectively.

7. A tracking photovoltaic power generation device as described in claim 1, characterized in that, The monitoring and recording module adopts a hierarchical storage strategy: high-frequency data is retained in seconds for the most recent 24 hours; Mid-frequency data is retained in minutes for the most recent 30 days; low-frequency statistics are stored permanently.

8. The method according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Obtain real-time solar altitude angle α, photovoltaic panel tilt angle θ, and photovoltaic panel width W through the data collection module; S2 determines the control strategy and calculation frequency corresponding to the current season and time period through the time period adjustment module; S3 calculates the current shadow area S through the execution decision module and determines whether it is within the target range; S4 When the shadow area exceeds the target range and the light intensity sensor passes the verification, execute the tilt angle back calculation algorithm to calculate the optimal tilt angle; S5 drives the photovoltaic panel to rotate to the target tilt angle via a stepper motor.

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