Methods, devices, and computer equipment for locating harmonic sources at the grid connection point of a photovoltaic power station

Abstract

In the photovoltaic power plant grid connection point harmonic source localization method provided in this application, the programmed power point time of the photovoltaic power plant is taken as the current time, and the duty cycle and programmed power point current value of the grid-connected inverter are determined. If the programmed power point current value remains unchanged for N consecutive cycles, the distribution network current value is sampled at the last moment of the Nth cycle. If the difference between the programmed power point current value and the distribution network current value does not exceed the difference threshold, the photovoltaic power plant is presumed to be a harmonic source, and the duty cycle of the grid-connected inverter is actively updated to change the programmed power point current value corresponding to the photovoltaic power plant. The changed value is taken as the programmed power point current value. Subsequently, if the programmed power point current value remains unchanged for N consecutive cycles, when the difference between the distribution network current value at the last moment of the Nth cycle and the programmed power point current value does not exceed the difference threshold, the photovoltaic power plant is determined to be a harmonic source. In this way, harmonics generated by the photovoltaic power plant can be effectively identified, avoiding misjudgment.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power plant technology, and in particular to a method, apparatus and computer equipment for locating harmonic sources at the access point of a photovoltaic power plant. Background Technology

[0002] Under the pressure of energy crisis and environmental protection, the cost of traditional fossil fuels has risen sharply, prompting people to seek new solutions. Solar energy, as a new energy source with great development potential, has attracted much attention, with photovoltaic power generation being one of the main utilization methods. Distributed photovoltaic systems are often built on building surfaces, offering advantages such as self-generation and self-consumption, flexible operation, and the ability to compensate for power shortages through grid connection.

[0003] However, when distributed photovoltaic (PV) power stations are connected to the distribution network, the output voltage and current of the photovoltaic cells (PV cells) exhibit nonlinearity due to environmental influences, leading to power output fluctuations. To address these fluctuations, distributed PV power stations employ numerous power electronic devices for tracking and regulation. This may generate harmonics exceeding standards, which are then fed into the public distribution network. Consequently, power quality issues arising from these issues are becoming increasingly prominent, such as harmonic pollution and voltage fluctuations. These problems not only affect the power quality of the distribution network but also adversely impact the stability and reliability of the power system. Harmonic monitoring devices are typically installed at the node where the distributed PV power station connects to the distribution network. However, the distribution network itself contains numerous nonlinear loads, which also generate significant amounts of harmonics and reactive current. Therefore, it is necessary to determine whether the detected harmonics are generated by the distributed PV power station to provide a basis for addressing power quality issues at the point of grid connection. Summary of the Invention

[0004] The purpose of this application is to at least address one of the aforementioned technical deficiencies, particularly the technical deficiency in the prior art that requires clarification on whether the monitored harmonics are generated by the distributed photovoltaic power station, thereby providing a basis for addressing power quality issues at the grid connection point of the distributed photovoltaic power station.

[0005] In a first aspect, this application provides a method for locating harmonic sources at the access point of a photovoltaic power station, the method comprising:

[0006] The current time is taken as the time when the programmed power point of the photovoltaic power station is found, and the current duty cycle and current programmed power point current value of the grid-connected inverter in the photovoltaic power station are determined.

[0007] Starting from the current moment, if the standardized power point current value remains unchanged for N consecutive cycles, then at the last moment of the Nth cycle, the current distribution network current value of the distribution network where the photovoltaic power station is located is sampled, where N is a constant.

[0008] If the difference between the current programmed power point current value and the current distribution network current value does not exceed the preset difference threshold, the photovoltaic power station is predicted to be a harmonic source, and the current duty cycle of the grid-connected inverter is updated, and the new programmed power point current value corresponding to the updated current duty cycle is used as the current programmed power point current value, and the time when the current programmed power point current value is located is used as the current time.

[0009] Starting from the current moment, if the standardized power point current value remains unchanged for N consecutive cycles, then when the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold, the photovoltaic power station is determined to be a harmonic source.

[0010] In one embodiment, the process of searching for the programmed power point of a photovoltaic power plant includes:

[0011] Obtain the current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter;

[0012] The current power tracking value is calculated based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size.

[0013] If the current power tracking value meets the preset standardized power conditions, then the power point corresponding to the current photovoltaic current value is determined as the standardized power point of the photovoltaic power station.

[0014] In one embodiment, the process of searching for the programmed power point of a photovoltaic power plant further includes:

[0015] If the current power tracking value does not meet the preset standardized power conditions, the next photovoltaic current value will be obtained, and the current photovoltaic current value will be used as the previous photovoltaic current value. The next photovoltaic current value will be used as the current current value, the current duty cycle will be updated, and the current power tracking value will continue to be calculated until the standardized power point of the photovoltaic power station is found.

[0016] In one embodiment, the step of updating the current duty cycle includes:

[0017] The current duty cycle is updated using the following formula:

[0018]

[0019] in, Used to indicate the updated current duty cycle Used to indicate the current duty cycle before the update. Used to indicate the current power tracking value that does not meet the preset procedural power conditions. Used to indicate the step size of duty cycle change. This is a sign function used to represent the positive or negative sign of a number.

[0020] In one embodiment, the formula corresponding to the current power tracking value is:

[0021]

[0022] in, Used to represent the current power tracking value, Used to indicate the current duty cycle. Used to represent the current photovoltaic current value Used to represent the previous photovoltaic current value Used to indicate the step size of duty cycle changes.

[0023] In one embodiment, the method further includes:

[0024] If the difference between the current standardized power point current value and the current distribution network current value exceeds the difference threshold, then the photovoltaic power station is determined not to be a harmonic source.

[0025] Secondly, this application provides a harmonic source locating device for photovoltaic power plant access points, the device comprising:

[0026] The current programmed power point current value determination module is used to take the time when the programmed power point of the photovoltaic power station is found as the current time, and to determine the current duty cycle and current programmed power point current value of the grid-connected inverter in the photovoltaic power station.

[0027] The current distribution network current value sampling module is used to sample the current distribution network current value of the photovoltaic power station at the last moment of the Nth cycle if the standardized power point current value remains unchanged for N consecutive cycles starting from the current moment. N is a constant.

[0028] The harmonic source prediction module is used to predict that the photovoltaic power station is a harmonic source if the difference between the current programmed power point current value and the current distribution network current value does not exceed a preset difference threshold. It also controls and updates the current duty cycle of the grid-connected inverter, and uses the new programmed power point current value corresponding to the updated current duty cycle as the current programmed power point current value, and uses the time when the current programmed power point current value is located as the current time.

[0029] The harmonic source determination module is used to determine the photovoltaic power station as a harmonic source if the standardized power point current value remains unchanged for N consecutive cycles starting from the current moment, and the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold.

[0030] In one embodiment, the current programmed power point current value determination module includes:

[0031] The photovoltaic parameter acquisition unit is used to acquire the current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter.

[0032] The current power tracking value calculation unit is used to calculate the current power tracking value based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size.

[0033] The standardized power point determination unit is used to determine the power point corresponding to the current photovoltaic current value as the standardized power point of the photovoltaic power station if the current power tracking value meets the preset standardized power conditions.

[0034] Thirdly, this application provides a storage medium storing computer-readable instructions, which, when executed by one or more processors, cause the one or more processors to perform the steps of any of the photovoltaic power station access point harmonic source location methods described in the above embodiments.

[0035] Fourthly, this application provides a computer device, including: one or more processors, and a memory;

[0036] The memory stores computer-readable instructions, which, when executed by one or more processors, perform the steps of any of the photovoltaic power station access point harmonic source location methods described in the above embodiments.

[0037] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0038] In the photovoltaic power plant access point harmonic source location method, device, and computer equipment provided in this application, by setting the time of the standardized power point and obtaining the current duty cycle and current value, it can be ensured that the harmonic source location starts from a standardized reference point, reducing measurement deviations caused by environmental factors and thus improving monitoring accuracy; when the standardized power point current value remains unchanged for N consecutive cycles, the distribution network current value is sampled, so that the power output of the photovoltaic power plant can be confirmed through stability testing, reducing the impact of short-term current fluctuations on the judgment, thereby improving the stability and accuracy of the judgment; when the difference between the standardized power point current value and the distribution network current value is not significant... When the threshold is exceeded, the photovoltaic power station is presumed to be a harmonic source. Data verification confirms whether the harmonics originate from the photovoltaic power station, improving the reliability and operability of the judgment. If the photovoltaic power station is presumed to be a harmonic source, the inverter's duty cycle is updated and the standardized power point current value is recalibrated. After N cycles of stable current, the difference between the standardized power point current value and the distribution network current value is verified again. If a significant correlation is found between the changes in the distribution network current value and the changes in the standardized power point current value of the photovoltaic power station, the harmonic source can be further confirmed. This multi-layered verification process improves the reliability and robustness of the results, avoiding misjudgments caused by single sampling. Based on this, this method analyzes current stability and differences over multiple time periods through step-by-step, layer-by-layer verification to accurately distinguish between the harmonic sources of the photovoltaic power station and the distribution network. It can also adapt to dynamically changing environmental conditions, providing a basis for handling power quality issues at the grid connection point of distributed photovoltaic power stations. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A flowchart illustrating the method for locating harmonic sources at the access point of a photovoltaic power station provided in this application embodiment;

[0041] Figure 2 One of the example diagrams is for the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0042] Figure 3 Example diagram two of the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0043] Figure 4 Figure 3 is an example of the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0044] Figure 5 Figure 4 is an example of the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0045] Figure 6 Figure 5 is an example of the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0046] Figure 7 Figure 6 is an example of the photovoltaic power plant access point harmonic source location method provided in the embodiments of this application;

[0047] Figure 8 This is a schematic diagram of the structure of the photovoltaic power station access point harmonic source locating device provided in the embodiments of this application;

[0048] Figure 9 This is a schematic diagram of the internal structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0049] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0050] This application provides a method for locating harmonic sources at the access point of a photovoltaic power station. The following embodiments illustrate this method using a computer device as an example. It is understood that the computer device can be any device with data processing capabilities, including but not limited to a single server, server cluster, personal laptop, desktop computer, etc. Figure 1 As shown, the method may include the following steps:

[0051] S101: Take the time when the programmed power point of the photovoltaic power station is found as the current time, and determine the current duty cycle and current programmed power point current value of the grid-connected inverter in the photovoltaic power station.

[0052] The programmed power point (PPP) refers to the output power of a photovoltaic (PV) power station calculated according to preset rules or standards, while the PPP current value is the current value corresponding to the PPP. The current duty cycle refers to the output state of the PV power station at a specific moment, reflecting the ratio of "on" to "off" states within the current cycle, and is used to control and regulate the output power. The grid-connected inverter is a device in a PV power station used to convert direct current (DC) to alternating current (AC) and synchronize it with the distribution network. The grid-connected inverter not only changes the direction of current but also controls the duty cycle of the output current.

[0053] In this step, the programmed power output records of the photovoltaic power plant can be retrieved from the programmed power database through data logging or real-time monitoring data sources. Timestamp calibration is used to determine the moment that matches the programmed power point, and this moment is set as the "current moment" for current analysis and control. Then, the current duty cycle value is extracted from the real-time data of the grid-connected inverter. Based on the current moment, the programmed preset power point current value is queried or calculated. For example, by combining the inverter's output characteristics and set duty cycle parameters, an output current value matching the current moment can be generated using a formula or preset function; alternatively, the current value at the programmed power point moment can be used as the programmed power point current value.

[0054] It is understandable that by setting the current time to the time of the searched procedural power point, power fluctuations or data misalignments at different time points can be avoided, thereby improving the accuracy of harmonic source location. Using the current value of the current procedural power point as a criterion, it is possible to accurately assess whether the output of the photovoltaic power station meets the stability requirements of the power grid. Automatically comparing the set current value with the measured value can effectively detect abnormal output and provide real-time feedback, reducing misjudgments and improving judgment efficiency.

[0055] S102: Starting from the current moment, if the normalized power point current value remains unchanged for N consecutive cycles, then at the last moment of the Nth cycle, sample the current distribution network current value of the distribution network where the photovoltaic power station is located, where N is a constant.

[0056] Here, N cycles refer to N consecutive complete alternating current cycles, where N is a preset integer constant. The current value of the distribution network refers to the output current of the distribution network measured at the last moment of the Nth cycle. The last moment of the Nth cycle is the time point at which the Nth cycle ends.

[0057] In this step, the standardized power point current value output by the photovoltaic power station can be obtained through timed sampling, and the current value of each cycle can be recorded. If the value remains stable for N consecutive cycles, then at the last moment of the Nth cycle, the current reading can be measured or obtained from a real-time data source of the distribution network.

[0058] It is understandable that by sampling the standardized current value over N consecutive cycles, the characteristics of the photovoltaic power station under stable output conditions can be confirmed, effectively filtering out short-term fluctuations and ensuring that the judgment is based on long-term stable data. Sampling the distribution network current value at the last moment of the Nth cycle allows for a precise comparison with the standardized power point current value of the photovoltaic power station. If the difference between the two is small, it means that the photovoltaic power station may be a harmonic source. This process effectively enhances the accuracy of harmonic source identification and avoids misjudgments caused by instantaneous fluctuations.

[0059] S103: If the difference between the current programmed power point current value and the current distribution network current value does not exceed the preset difference threshold, the photovoltaic power station is predicted to be a harmonic source, and the current duty cycle of the grid-connected inverter is updated, and the new programmed power point current value corresponding to the updated current duty cycle is used as the current programmed power point current value, and the time when the current programmed power point current value is located is used as the current time.

[0060] The difference is the numerical difference between the current value at the current standardized power point and the current value in the current distribution network, used to measure the degree of deviation between the two. The preset difference threshold is a fixed allowable deviation value, which determines the acceptable range of the difference.

[0061] In this step, the current programmed power point current value and the distribution network current value are extracted from the real-time data stream, and then the difference between them is calculated. Next, this difference is compared with a preset difference threshold to determine if the conditions for identifying the photovoltaic power station as a harmonic source are met. If the difference is less than or equal to the preset threshold, the photovoltaic power station is marked as a harmonic source, and the adjustment process begins. This triggers inverter parameter adjustment. A new duty cycle setting is sent to the grid-connected inverter via control commands, such as the inverter interface API or PLC, causing it to adjust its duty cycle. The inverter internally generates a corresponding current waveform based on the new duty cycle. The updated duty cycle results in a new programmed power point current value, which is recorded as the new programmed power point current value. This adjustment time point is simultaneously set as the "current moment".

[0062] It is understandable that by precisely comparing the programmed power point current value with the distribution network current value, harmonic sources can be accurately predicted even with minor deviations. Using a difference threshold ensures that the determination of harmonic sources is not affected by short-term fluctuations, thus obtaining accurate results. Once the photovoltaic power station is predicted to be a harmonic source, the inverter's duty cycle is automatically updated, thereby quickly adjusting the current output characteristics of the photovoltaic power station and reducing harmonic interference. Simultaneously updating the programmed power point current value and the current time allows for further determination of the harmonic source, avoiding errors from a single determination.

[0063] S104: Starting from the current moment, if the standardized power point current value remains unchanged for N consecutive cycles, then when the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold, the photovoltaic power station is determined to be a harmonic source.

[0064] In this step, the programmed power point current value of the photovoltaic power station is continuously sampled, and the current value of each cycle can be recorded using a time window mechanism. If the current value remains constant for N consecutive cycles, then at the last moment of the Nth cycle, the real-time current value of the distribution network is synchronously collected, and the difference between the current programmed power point current value and the distribution network current value is calculated. This difference is compared with a preset difference threshold to determine whether the condition is met. If the difference is within the threshold range, then the photovoltaic power station is marked as a harmonic source.

[0065] Understandably, the purpose of predicting harmonic sources is to use preliminary data to make a quick judgment and detect whether a photovoltaic (PV) power station might be a harmonic source. After the prediction, adjusting the duty cycle and observing the changes in the adjusted programmed power point current and distribution network current is equivalent to a "test adjustment" to confirm whether the harmonics are generated by the PV power station. If the difference in the adjusted current value is still within the threshold, it indicates a significant correlation between the changes in the distribution network current and the programmed power point current of the PV power station, thus allowing for a more accurate identification of the PV power station as a harmonic source.

[0066] In the above embodiments, by setting the time of the programmed power point and obtaining the current duty cycle and current value, it can be ensured that the harmonic source is located from a standardized reference point, reducing measurement deviations caused by environmental factors and thus improving monitoring accuracy. When the programmed power point current value remains unchanged for N consecutive cycles, the distribution network current value is sampled, thereby confirming the power output of the photovoltaic power station through stability testing, reducing the impact of short-term current fluctuations on the judgment, and thus improving the stability and accuracy of the judgment. When the difference between the programmed power point current value and the distribution network current value does not exceed a preset threshold, the photovoltaic power station is predicted to be in operation. The power station is identified as a harmonic source. Data verification confirms whether the harmonics originate from the photovoltaic power station, improving the reliability and operability of the identification. If the photovoltaic power station is presumed to be a harmonic source, the inverter's duty cycle is updated and the standardized power point current value is recalibrated. After N cycles of stable current, the difference between the standardized power point current value and the distribution network current value is verified again. If a significant correlation is found between the changes in the distribution network current value and the changes in the standardized power point current value of the photovoltaic power station, the harmonic source can be further confirmed. This multi-layered verification process improves the reliability and robustness of the results, avoiding misjudgments caused by single sampling. Based on this, this method analyzes current stability and differences over multiple time periods through step-by-step, layer-by-layer verification to accurately distinguish between the harmonic sources of the photovoltaic power station and the distribution network. It can also adapt to dynamically changing environmental conditions, providing a basis for handling power quality issues at the grid connection point of distributed photovoltaic power stations.

[0067] In one embodiment, the process of searching for the programmed power point of a photovoltaic power plant includes:

[0068] Obtain the current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter;

[0069] The current power tracking value is calculated based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size.

[0070] If the current power tracking value meets the preset standardized power conditions, then the power point corresponding to the current photovoltaic current value is determined as the standardized power point of the photovoltaic power station.

[0071] The current photovoltaic (PV) current value is the actual current output of the PV power station at the current time. The previous PV current value is the current output value at the previous time. The duty cycle change step size is the increment or decrement of the inverter's duty cycle adjustment, used to gradually fine-tune the output current and power. The current power point tracking (PPT) value is a value calculated based on the current and previous PV current values, duty cycle, and change step size, used to determine the PPT status. The programmed power condition is a set power standard used to determine whether the current power meets the programmed power output requirements of the PV power station.

[0072] Specifically, the real-time monitored photovoltaic (PV) current value, the PV current value at the previous sampling point, and the current state and step size of the duty cycle can be retrieved from the grid-connected inverter's control system. Using formulas or algorithms, the current power point tracking (PPT) value is calculated based on the acquired current and previous current values ​​and duty cycle step size. The current PPT value is compared with the preset standardized power conditions. If the PPT value meets the standardized power conditions, it is determined that the current PV current value has reached the standardized power point.

[0073] In this embodiment, by acquiring real-time data on current and duty cycle and calculating power point tracking (PPT) values, the output trend of the photovoltaic power station can be accurately tracked, ensuring that the output power approaches the programmed power conditions and optimizing power quality. When the PPT value meets preset conditions, the programmed power point that meets the standard is determined.

[0074] In one embodiment, the process of searching for the programmed power point of a photovoltaic power plant further includes:

[0075] If the current power tracking value does not meet the preset standardized power conditions, the next photovoltaic current value will be obtained, and the current photovoltaic current value will be used as the previous photovoltaic current value. The next photovoltaic current value will be used as the current current value, the current duty cycle will be updated, and the current power tracking value will continue to be calculated until the standardized power point of the photovoltaic power station is found.

[0076] Specifically, if the current power point tracking value does not meet the preset standardized power conditions, the next photovoltaic current value is obtained through the monitoring device of the photovoltaic power station or the inverter data acquisition module. The current photovoltaic current value is assigned to the previous photovoltaic current value, and then the new photovoltaic current value is used as the current photovoltaic current value. The inverter's duty cycle is automatically adjusted. After updating the current current value and duty cycle, the current power point tracking value is recalculated and compared with the preset standardized power conditions to determine whether the standard is met.

[0077] In this embodiment, by obtaining the next photovoltaic current value, it is possible to quickly respond to actual output changes in the photovoltaic power station and perform power tracking in a timely manner. The step of updating the previous and current photovoltaic current values ​​can effectively track the trend of current changes until a photovoltaic current value and power point that meets the preset procedural power conditions are found.

[0078] In one embodiment, the step of updating the current duty cycle includes:

[0079] The current duty cycle is updated using the following formula:

[0080]

[0081] in, Used to indicate the updated current duty cycle Used to indicate the current duty cycle before the update. Used to indicate the current power tracking value that does not meet the preset procedural power conditions. Used to indicate the step size of duty cycle change. This is a sign function used to represent the positive or negative sign of a number.

[0082] Specifically, this formula is used to dynamically adjust the duty cycle of a photovoltaic (PV) power plant to make corresponding adjustments when the power output deviates from the target value, thereby gradually reaching the target power output state. If the power tracking value is positive, it indicates that the current power output is insufficient, and the duty cycle needs to be increased to improve the output power of the PV power plant. If the power tracking value is negative, it indicates that the current power output is excessive, and the duty cycle needs to be decreased to reduce the output power of the PV power plant. By adjusting the duty cycle according to the sign of the power tracking value each time, the target power output can be gradually approached.

[0083] In this embodiment, by calculating the power point tracking value in real time and adjusting the duty cycle accordingly, the photovoltaic power station can maintain a relatively stable power output under various environmental conditions. Using a step-by-step adjustment of the duty cycle avoids excessive power fluctuations or oscillations, reduces errors during the adjustment process, and ensures that the output power operates stably near the target value. The sign function in the formula allows for automatic adjustment of the duty cycle based on the positive or negative sign of the power point tracking value, exhibiting good adaptability and effectively responding to different load conditions and environmental changes.

[0084] In one embodiment, the formula corresponding to the current power tracking value is:

[0085]

[0086] in, Used to represent the current power tracking value, Used to indicate the current duty cycle. Used to represent the current photovoltaic current value Used to represent the previous photovoltaic current value Used to indicate the step size of duty cycle changes.

[0087] Specifically, this formula reflects the power changes of a photovoltaic power station by analyzing variations in photovoltaic current and the current duty cycle, allowing for timely adjustments to the power output. This calculation method dynamically tracks the actual power output of the photovoltaic power station, ensuring more precise power regulation. It utilizes the duty cycle variation step size... The power tracking value is calculated to ensure that the duty cycle adjustment is neither too large nor too small, avoiding drastic fluctuations in output power. Through gradual adjustments, the output power can be more smoothly approached, reducing overshoot or oscillations. The formula reflects the dynamic response of the photovoltaic power station's output power to environmental changes through variations in the photovoltaic current. If the photovoltaic current fluctuates significantly, the formula can quickly adjust the duty cycle using the power tracking value, helping the photovoltaic power station adapt rapidly to environmental changes.

[0088] Furthermore, in the example, the formula corresponding to the power tracking value of the next sampled current value is also:

[0089]

[0090] in, Used to represent the power tracking value corresponding to the next sampled current value.

[0091] In one embodiment, the method further includes:

[0092] If the difference between the current standardized power point current value and the current distribution network current value exceeds the difference threshold, then the photovoltaic power station is determined not to be a harmonic source.

[0093] Specifically, the difference between the current standardized power point current value and the current distribution network current value is calculated to determine whether it exceeds a preset difference threshold. If the difference is greater than the threshold, this information is recorded, the status is updated, and the photovoltaic power station is marked as a non-harmonic source.

[0094] In this embodiment, by calculating and determining the difference between the current value at the current standardization power point and the current value in the distribution network, it is possible to effectively identify whether a photovoltaic power station has a significant impact on harmonic generation. This clarity helps reduce interference from photovoltaic power stations and provides a basis for subsequent power quality management.

[0095] To facilitate understanding of the scheme in this application, specific examples are provided below.

[0096] like Figures 2 to 7 As shown, a method for locating harmonic sources at the access point of a photovoltaic power station includes the following steps:

[0097] Step 1, the PU curve of the photovoltaic cell is as follows Figure 2 As shown in the figure, when tracing the standardized power point M from the PV short-circuit point (origin), the slope of each point on the curve is positive and gets smaller and smaller; while when tracing point M from the open-circuit point, the slope is negative and gets larger and larger, but the absolute value gets smaller and smaller, and the slope of the curve at point M is zero.

[0098] Based on the PU curve of photovoltaic cells, the slope at a certain point in the PU curve is calculated using the ratio of the coordinate increments from the previous time point to the current working point. The solution to formula (1) is:

[0099]

[0100] In the formula Sampling points in the PU curve Slope at point; Sampling points in the PU curve At the previous sampling point The change in power at the location; Sampling points in the PU curve At the previous sampling point The voltage variation at the location; Sampling points in the PU curve At the previous sampling point The change in current at the location; and These are the sampling points in the PU curve. At the previous sampling point The sampled voltage value at the location; and These are the sampling points in the PU curve. At the previous sampling point The sampling current value at that location.

[0101] Step 2: Define the input voltage of the photovoltaic cells in a distributed photovoltaic power station as the PV voltage. The output voltage is the DC voltage from the back end. Circuit input and output voltages and circuit duty cycle The relation (2) is:

[0102]

[0103] In the formula, This is the DC component of the inductor current. The equivalent resistance of an inductor; and These are the forward voltage drop and equivalent resistance of diode D, respectively; The on-resistance of the switching transistor S; This represents the duty cycle.

[0104] Step 3: Simplify formula (2) to obtain the equivalent formula (3):

[0105] Within the normal operating range of the circuit, , , All remain stable and at a very small level in small-capacity distributed photovoltaic power sources. The value is much smaller than The numerical value, therefore in equation (2) " "Ignoreable" It is a constant; in the photovoltaic cells of distributed photovoltaic power stations To remain stable, we simplify equation (2) to obtain equation (3):

[0106]

[0107] In the formula, for and The sum of numbers; It is a constant; equal .

[0108] Step 4: Substitute equation (3) into equation (1) above, and implement step changes such as duty cycle, with a step size of . ,set up >0, simplifying to obtain formula (4):

[0109]

[0110] Recorded as,

[0111] In the formula Sampling points in the PU curve Slope at point; To implement step sizes for duty cycle and other step size changes; Sampling points The duty cycle value in the system; and These are the system sampling points. At the previous sampling point The sampled current value at the location; To simplify the notation, the term on the right side of formula (4) is the numerator.

[0112] This allows for a standardized tracking and output of the photovoltaic cells in a distributed photovoltaic power station, from small to large.

[0113] In step 4, the process of implementing output power programmable tracking for photovoltaic cells in a distributed photovoltaic power station is as follows:

[0114] Step 4.1, Steady-state time Set the initial duty cycle in the controller to be [value]. Measure the output current of the corresponding photovoltaic cell ;

[0115] Step 4.2, the duty cycle becomes And at steady state time Measure the corresponding ;

[0116] Step 4.3, calculate the criterion numerator according to formula (4). And perform the following judgments and actions:

[0117] Step 4.3.1, if ,but A negative value indicates that the photovoltaic cell Since the circuit is currently positioned to the right of the normalized power point M, the next step should be to reduce the voltage and control the increase in the duty cycle. ;

[0118] Step 4.3.2, if ,but A positive value indicates that the photovoltaic cell is to the left of the programmed power point M. The next step is to increase the voltage and control the duty cycle to decrease. ;

[0119] Step 4.3.3, if If it is zero, then =0 indicates that the photovoltaic cell is exactly at the standardized power point M, and the next step is to maintain the duty cycle. constant.

[0120] In step 4.3.3, finding a curve with a slope K of zero in finite sampling is impossible. Considering that the absolute value of the slope K in the PU curve decreases closer to point M, therefore, when Or slope If the value is sufficiently small, it is considered to be at the normalized power point, and tracking stops. That is, step 4.3.3 in the above judgment and execution is changed to:

[0121] Step 4.3.3', if ( , Either one can be chosen (ε is a very small constant), then the normalized power point is found, and the duty cycle is maintained thereafter. constant.

[0122] Because the output current of PV is affected by light. The changes are significant, therefore, it is set to occur during operation. Compared to the stored programmed power point current Only after the change exceeds the limit will the programmed tracking output of the power point be restarted from small to large. The program algorithm flowchart is as follows. Figure 3 As shown.

[0123] The specific practical experiments and verifications of the method for locating harmonic sources at the grid connection point of a photovoltaic power station are as follows:

[0124] A distributed photovoltaic power station photovoltaic cell was built in Matlab. The output of the distributed photovoltaic power station photovoltaic cell's volt-ampere characteristic is referenced. Figure 2 This paper analyzes the relationship between PV voltage and duty cycle in photovoltaic cells of distributed photovoltaic power stations, and examines the correctness and feasibility of the proposed power procedural output method. The circuit parameters are as follows: , and its equivalent resistance , The inductors are set to 470uF and 470uF, and 5mΩ and 5mΩ respectively; the inductor L and its equivalent resistance are 0.2mH and 100mΩ respectively; the forward voltage drop of the diode D is... It is 0.5V. The impedance is 10mΩ; the DC output voltage reference value is 640V; the switching frequency is 20kHz; and the simulation step size is 1e-6(s). Initial duty cycle of the Boost circuit. Set to 0.65, startup time is 0.1s (i.e., maintain). (Constant time), duty cycle variation step size The threshold value is 0.01, and it remains unchanged for 20ms after each change. Set to 0.5A, and the termination search constant ε to 0.05 (using...). termination).

[0125] A distributed photovoltaic (PV) power station was constructed, comprising photovoltaic cells, lead-acid batteries, various conversion circuits, a DC bus, and local loads. The DC output voltage is stabilized at a reference value of 360V by the lead-acid battery through a controller and a bidirectional half-bridge converter circuit. The PV cell output PU curve and other relevant parameter settings are as follows: Figure 4 As shown.

[0126] The experiment used the shared output current sampling value of the programmable DC power supply and the duty cycle of the circuit controlled by the controller. The initial value is 0.15. The value is 0.02, and it remains unchanged for 100ms after each change. Terminate tracking, implement power procedural output according to the method proposed in this paper, and the tracked procedural power point is as follows: Figure 4 The waveform at the top dot indicates the DC output voltage during tracking. Photovoltaic cell current and output power The test waveform is as follows Figure 5 As shown.

[0127] When the duty cycle is actively changed, the output voltage PV current ,Voltage like Figure 6 As shown in the figure. Under stable conditions: the controller controls the duty cycle. The corresponding change , It also changes, but quickly reaches an equilibrium state, and the waveform becomes stable.

[0128] Figure 7 To sample only PV current The power output is programmed using the steps proposed in this method. The PV output power curve shows that the system finds its maximum power (12kW) after 0.3s after startup; the light intensity S increases from 1kW / m² after 0.545s. 2 The change was 0.8 kW / m 2 It returned to normal at 0.705s, due to the S mutation. A sudden change occurs, exceeding the limit and triggering power programming output. Since the programmed power point voltage remains essentially constant for the same PV array at the same temperature, in... Under stable conditions, the duty cycle changes one step and then returns to the original duty cycle. As can be seen from the waveform, the power tracking quickly locates and stabilizes at the programmed power point.

[0129] The following describes the photovoltaic power plant access point harmonic source location device provided in the embodiments of this application. The photovoltaic power plant access point harmonic source location device described below can be referred to in correspondence with the photovoltaic power plant access point harmonic source location method described above. Figure 8 As shown, this application provides a harmonic source locating device for a photovoltaic power station access point, the device comprising:

[0130] The current programmed power point current value determination module 201 is used to take the time when the programmed power point of the photovoltaic power station is found as the current time, and determine the current duty cycle and current programmed power point current value of the grid-connected inverter in the photovoltaic power station.

[0131] The current distribution network current value sampling module 202 is used to sample the current distribution network current value of the distribution network where the photovoltaic power station is located at the last moment of the Nth cycle if the standardized power point current value of N consecutive cycles remains unchanged starting from the current moment. N is a constant.

[0132] The harmonic source prediction module 203 is used to predict that the photovoltaic power station is a harmonic source if the difference between the current programmed power point current value and the current distribution network current value does not exceed a preset difference threshold, and to control the update of the current duty cycle of the grid-connected inverter, and to take the new programmed power point current value corresponding to the updated current duty cycle as the current programmed power point current value, and to take the time when the current programmed power point current value is located as the current time.

[0133] The harmonic source determination module 204 is used to determine the photovoltaic power station as a harmonic source if the standardized power point current value of the distribution network remains unchanged for N consecutive cycles starting from the current moment, and the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold.

[0134] In one embodiment, the current programmed power point current value determination module 201 includes:

[0135] The photovoltaic parameter acquisition unit is used to acquire the current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter.

[0136] The current power tracking value calculation unit is used to calculate the current power tracking value based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size.

[0137] The standardized power point determination unit is used to determine the power point corresponding to the current photovoltaic current value as the standardized power point of the photovoltaic power station if the current power tracking value meets the preset standardized power conditions.

[0138] In one embodiment, the current programmed power point current value determination module 201 further includes:

[0139] The photovoltaic parameter update unit is used to obtain the next photovoltaic current value if the current power tracking value does not meet the preset standardized power conditions. The current photovoltaic current value is used as the previous photovoltaic current value, and the next photovoltaic current value is used as the current current value. The current duty cycle is updated, and the current power tracking value is calculated until the standardized power point of the photovoltaic power station is found.

[0140] In one embodiment, the photovoltaic parameter updating unit includes:

[0141] The duty cycle update subcell is used to update the current duty cycle using the following formula:

[0142]

[0143] in, Used to indicate the updated current duty cycle Used to indicate the current duty cycle before the update. Used to indicate the current power tracking value that does not meet the preset procedural power conditions. Used to indicate the step size of duty cycle change. This is a sign function used to represent the positive or negative sign of a number.

[0144] In one embodiment, the formula corresponding to the current power tracking value is:

[0145]

[0146] in, Used to represent the current power tracking value, Used to indicate the current duty cycle. Used to represent the current photovoltaic current value Used to represent the previous photovoltaic current value Used to indicate the step size of duty cycle changes.

[0147] In one embodiment, the apparatus further includes:

[0148] The difference judgment module is used to determine that the photovoltaic power station is not a harmonic source if the difference between the current standardized power point current value and the current distribution network current value exceeds the difference threshold.

[0149] In one embodiment, this application also provides a storage medium storing computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the photovoltaic power station access point harmonic source localization method as described in any of the above embodiments.

[0150] In one embodiment, this application also provides a computer device storing computer-readable instructions that, when executed by one or more processors, cause the one or more processors to perform the steps of the photovoltaic power station access point harmonic source localization method as described in any of the above embodiments.

[0151] Indicatively, such as Figure 9 As shown, Figure 9This is a schematic diagram of the internal structure of a computer device 300 provided in an embodiment of this application. The computer device 300 can be provided as a server. (Refer to...) Figure 9 The computer device 300 includes a processing component 302, which further includes one or more processors, and memory resources represented by memory 301 for storing instructions, such as application programs, that can be executed by the processing component 302. The application programs stored in memory 301 may include one or more modules, each corresponding to a set of instructions. Furthermore, the processing component 302 is configured to execute instructions to perform the photovoltaic power plant access point harmonic source localization method of any of the above embodiments.

[0152] The computer device 300 may also include a power supply component 303 configured to perform power management of the computer device 300, a wired or wireless network interface 304 configured to connect the computer device 300 to a network, and an input / output (I / O) interface 305. The computer device 300 may operate on an operating system stored in memory 301, such as Windows Server™, Mac OS X™, Unix™, Linux™, Free BSD™, or similar.

[0153] Those skilled in the art will understand that Figure 9 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0154] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this document, "a," "an," "the," "the," and "its" may also include plural forms unless the context clearly indicates otherwise. "Multiple" refers to at least two, such as 2, 3, 5, or 8, etc. "And / or" includes any and all combinations of the related listed items.

[0155] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0156] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for locating harmonic sources at the access point of a photovoltaic power station, characterized in that, The method includes: The current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter in the photovoltaic power station are obtained. Based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size, the current power tracking value is calculated. If the current power tracking value meets the preset standardized power conditions, the power point corresponding to the current photovoltaic current value is determined as the standardized power point of the photovoltaic power station. The time when the standardized power point of the photovoltaic power station is located is taken as the current time, and the current duty cycle and the current standardized power point current value of the grid-connected inverter in the photovoltaic power station are determined. Starting from the current moment, if the normalized power point current value remains unchanged for N consecutive cycles, then at the last moment of the Nth cycle, the current distribution network current value of the distribution network where the photovoltaic power station is located is sampled, where N is a constant. If the difference between the current programmed power point current value and the current distribution network current value does not exceed the preset difference threshold, the photovoltaic power station is predicted to be a harmonic source, and the current duty cycle of the grid-connected inverter is updated, and the new programmed power point current value corresponding to the updated current duty cycle is used as the current programmed power point current value, and the time when the current programmed power point current value is located is used as the current time. Starting from the current moment, if the standardized power point current value remains unchanged for N consecutive cycles, then when the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold, the photovoltaic power station is determined to be a harmonic source.

2. The method for locating harmonic sources at the photovoltaic power station access point according to claim 1, characterized in that, The method further includes: If the current power tracking value does not meet the preset standardized power conditions, the next photovoltaic current value will be obtained, and the current photovoltaic current value will be used as the previous photovoltaic current value. The next photovoltaic current value will be used as the current current value, the current duty cycle will be updated, and the current power tracking value will continue to be calculated until the standardized power point of the photovoltaic power station is found.

3. The method for locating harmonic sources at the photovoltaic power station access point according to claim 2, characterized in that, The step of updating the current duty cycle includes: The current duty cycle is updated using the following formula: ； in, Used to indicate the updated current duty cycle Used to indicate the current duty cycle before the update. Used to indicate the current power tracking value that does not meet the preset procedural power conditions. Used to indicate the step size of duty cycle change. This is a sign function used to represent the positive or negative sign of a number.

4. The method for locating harmonic sources at the access point of a photovoltaic power station according to any one of claims 1 to 3, characterized in that, The formula corresponding to the current power tracking value is: ； in, Used to represent the current power tracking value, Used to indicate the current duty cycle. Used to represent the current photovoltaic current value Used to represent the previous photovoltaic current value. Used to indicate the step size of the duty cycle change.

5. The method for locating harmonic sources at the access point of a photovoltaic power station according to any one of claims 1 to 3, characterized in that, The method further includes: If the difference between the current standardized power point current value and the current distribution network current value exceeds the difference threshold, then the photovoltaic power station is determined not to be a harmonic source.

6. A harmonic source locating device for a photovoltaic power station access point, characterized in that, The device includes: The current programmed power point current value determination module is used to obtain the current photovoltaic current value, the previous photovoltaic current value, and the duty cycle change step size of the grid-connected inverter in the photovoltaic power station. Based on the current photovoltaic current value, the previous photovoltaic current value, the current duty cycle, and the duty cycle change step size, the current power tracking value is calculated. If the current power tracking value meets the preset programmed power conditions, the power point corresponding to the current photovoltaic current value is determined as the programmed power point of the photovoltaic power station. The time when the programmed power point of the photovoltaic power station is located is taken as the current time, and the current duty cycle and the current programmed power point current value of the grid-connected inverter in the photovoltaic power station are determined. The current distribution network current value sampling module is used to sample the current distribution network current value of the photovoltaic power station at the last moment of the Nth cycle if the standardized power point current value remains unchanged for N consecutive cycles starting from the current moment. N is a constant. The harmonic source prediction module is used to predict that the photovoltaic power station is a harmonic source if the difference between the current programmed power point current value and the current distribution network current value does not exceed a preset difference threshold. The module then controls the update of the current duty cycle of the grid-connected inverter, and uses the new programmed power point current value corresponding to the updated current duty cycle as the current programmed power point current value, and uses the time when the current programmed power point current value is located as the current time. The harmonic source determination module is used to determine the photovoltaic power station as a harmonic source if, starting from the current moment, the standardized power point current value remains unchanged for N consecutive cycles, and the difference between the distribution network current value at the last moment of the Nth cycle and the current standardized power point current value does not exceed the difference threshold.

7. A storage medium, characterized in that: The storage medium stores computer-readable instructions, which, when executed by one or more processors, cause the one or more processors to perform the steps of the photovoltaic power station access point harmonic source location method as described in any one of claims 1 to 5.

8. A computer device, characterized in that, include: One or more processors, and memory; The memory stores computer-readable instructions, which, when executed by the one or more processors, perform the steps of the photovoltaic power station access point harmonic source location method as described in any one of claims 1 to 5.

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