A method and system for automatic reclosing control of distributed photovoltaic grid connection
By analyzing the difference between the AC signal and current output of the inverter in distributed photovoltaic grid connection and combining it with least squares fitting, the problem of fault judgment under the influence of low voltage ride current was solved, achieving efficient and accurate automatic reclosing control and reducing equipment costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZAOZHUANG POWER SUPPLY COMPANY OF STATE GRID SHANDONG ELECTRIC POWER
- Filing Date
- 2025-02-27
- Publication Date
- 2026-06-02
AI Technical Summary
In existing technologies, when distributed photovoltaic systems are connected to the distribution network, the efficiency of automatic reclosing control is limited by the decay process of low-voltage ride-through current, and a large number of monitoring devices are required, resulting in high costs.
By controlling the secondary use of the AC signal output by the inverter during the initial fluctuation stage of the low-voltage ride-through current, and combining current difference analysis and least squares fitting, a stable and reliable analysis of the trend of low-voltage ride-through current can be achieved, instantaneous faults can be identified, and the inverter output current can be adjusted.
It enables accurate and reliable fault diagnosis at the beginning stage of low-voltage ride-through current decay, reduces the configuration of monitoring equipment, avoids reclosing misoperation, and improves control efficiency.
Smart Images
Figure CN119787245B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of power control technology, and more specifically, to a method and system for automatic reclosing control of distributed photovoltaic grid connection. Background Technology
[0002] Transient faults refer to brief faults in power systems caused by external factors such as lightning strikes and wind damage, or internal factors such as temporary equipment malfunctions. Transient faults generally disappear on their own within a few seconds, and the insulation performance of the line can be restored. In photovoltaic grid-connected systems, transient faults have a high incidence rate, accounting for 80% to 90% of all faults. Automatic reclosing devices (ARDs) are an important means of handling transient faults. When a transient fault occurs on a line, the relay protection device trips the circuit breaker and simultaneously activates the automatic reclosing device, which automatically closes the circuit after a certain time interval, restoring power supply.
[0003] During automatic reclosing of the distribution network, determining whether a transient fault has occurred typically involves injecting an AC signal into the disconnected line, then comparing the real-time current in the line with the theoretical current after the AC signal is injected. If the real-time current is not greater than the theoretical current, the line is generally considered to have a transient fault. For distributed photovoltaic (PV) grid connections, most inverters in PV power supply modules have low-voltage ride-through (LVRT) capability. To reduce the impact of the superimposed LVRT current during automatic reclosing, some existing technologies, when a transient fault is detected, wait for the LVRT current to decay to a negligible level before reclosing. However, the LVRT current decay process generally takes about 3 seconds, which limits the efficiency of automatic reclosing control. Other existing technologies, when a transient fault is detected, monitor the decay of the LVRT current in real time, using this as feedback to provide reference data for adjusting the inverter's output current. However, this method requires monitoring points on the inverter's output side, resulting in a large number of sensors and other equipment needed for distributed PV grid connection, leading to higher costs.
[0004] Therefore, how to research and design an automatic reclosing control method and system for distributed photovoltaic grid access that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the Invention
[0005] To address the shortcomings of existing technologies, the present invention aims to provide an automatic reclosing control method and system for distributed photovoltaic grid connection. This method can achieve instantaneous fault detection while utilizing the low-voltage ride-through current generated by the inverter. Furthermore, it can perform stable and reliable analysis of the changing trend of the low-voltage ride-through current at the beginning of its decay stage, without requiring excessive monitoring equipment.
[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:
[0007] Firstly, a method for automatic reclosing control of distributed photovoltaic power grid connection is provided, including the following steps:
[0008] Determine the target tie line in a de-energized state based on the open position of the circuit breaker after the line trips;
[0009] The first circuit breaker between the control target tie line and the transformer line closes at the first moment;
[0010] The second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line is closed at the second moment to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line.
[0011] The first current generated by the target tie line at the first moment and the second current generated at the second moment are collected, and the current difference between the second current and the first current is compared and analyzed with the setting current difference determined by the injected AC signal to determine whether the target tie line is a transient fault.
[0012] If the target connection line is a momentary fault, the injected AC signal output by the inverter controlling the photovoltaic power supply module will increase within a preset time period.
[0013] The response change current of the target tie line is collected within a preset time period, and the low-voltage ride-through current within the preset time period is calculated based on the response change current. The decay change current of the low-voltage ride-through current after the preset time period is estimated based on the change trend of the low-voltage ride-through current.
[0014] During the reclosing process of the control target tie line, the actual current output by the inverter is adjusted according to the decaying change current.
[0015] Furthermore, both the first and second moments are in the initial fluctuation stage of low-pressure crossing, and the second moment is longer than the first moment.
[0016] Furthermore, the preset time period overlaps with the mid-term continuous decay phase of low-pressure crossing.
[0017] Furthermore, the process of determining whether the target communication line is experiencing a transient fault specifically involves:
[0018] Substitute the first current as the setting result into the setting current equation to calculate the injection current at the first moment;
[0019] The sum of the injected current and the injected AC signal at the first moment is substituted into the setting current equation as the injected signal to calculate the second estimated current at the second moment.
[0020] The current difference is calculated based on the difference between the second current and the first current, and the setting current difference is calculated based on the difference between the second estimated current and the first current.
[0021] If the current difference is less than or equal to the set current difference, the target tie line is determined to have a momentary fault; otherwise, if the current difference is greater than the set current difference, the target tie line is determined to have a fault.
[0022] Furthermore, the process of determining whether the target communication line is experiencing a transient fault specifically involves:
[0023] Substitute the first current as the setting result into the setting current equation to calculate the injection current at the first moment;
[0024] The sum of the injected current, the injected AC signal, and the maximum error value of the initial fluctuation stage of low-voltage ride-through at the first moment is substituted into the setting current equation as the injected signal to calculate the second estimated current at the second moment.
[0025] The current difference is calculated based on the difference between the second current and the first current, and the setting current difference is calculated based on the difference between the second estimated current and the first current.
[0026] If the current difference is less than or equal to the set current difference, the target tie line is determined to have a momentary fault; otherwise, if the current difference is greater than the set current difference, the target tie line is determined to have a fault.
[0027] Furthermore, the setting result in the setting current equation is equal to the product of the setting current and the setting coefficient;
[0028] The setting current is calculated based on the voltage amplitude of the injected signal, the impedance of the target tie line, and the transition resistance of the target tie line.
[0029] Furthermore, the decaying changing current is obtained by curve fitting using the least squares method.
[0030] Furthermore, the actual current output by the inverter is equal to the difference between the preset design current and the decaying change current when the inverter operates at the rated current to meet the target interconnect line.
[0031] Furthermore, the process of controlling the reclosing of the target tie line specifically involves closing the second circuit breaker between the target tie line and the external power supply module.
[0032] Furthermore, the method also includes:
[0033] If there is a fault in the target connection line, the first circuit breaker is controlled to open and lock out.
[0034] Secondly, a distributed photovoltaic grid-connected automatic reclosing control system is provided, comprising:
[0035] The line determination module is used to determine the target tie line in a power outage state based on the open position of the circuit breaker after the line trips.
[0036] The first injection module is used to control the first circuit breaker between the target tie line and the transformer line to close at the first moment.
[0037] The second injection module is used to control the second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at the second moment, so as to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line.
[0038] The fault analysis module is used to collect the first current generated by the target tie line at the first moment and the second current generated at the second moment, and compare the current difference between the second current and the first current with the setting current difference determined by the injected AC signal to determine whether the target tie line is a transient fault.
[0039] The injection regulation module is used to control the injected AC signal output by the inverter of the photovoltaic power supply module to increase within a preset time period when the target tie line is in a transient fault.
[0040] The current analysis module is used to collect the response change current of the target tie line within a preset time period, calculate the low-voltage ride current within the preset time period based on the response change current, and estimate the decay change current of the low-voltage ride current after the preset time period based on the changing trend of the low-voltage ride current.
[0041] The output control module is used to adjust the actual current output by the inverter based on the decaying current during the reclosing process of the control target tie line.
[0042] Compared with the prior art, the present invention has the following beneficial effects:
[0043] 1. The present invention provides an automatic reclosing control method for distributed photovoltaic grid access. It controls the first circuit breaker between the target tie line and the transformer line to close at the first moment, and then controls the second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at the second moment. This allows for the secondary utilization of the low-voltage ride-through current generated by the inverter, enabling instantaneous fault detection. Furthermore, when the target tie line experiences an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to increase within a preset time period. This allows for stable and reliable analysis of the low-voltage ride-through current's changing trend at the beginning of its decay phase, close to rated operating conditions, without requiring excessive monitoring equipment.
[0044] 2. In this invention, both the first and second moments are in the initial fluctuation stage of low-voltage ride-through, so the changes in low-voltage ride-through current at the first and second moments can be ignored, effectively ensuring the accuracy of instantaneous fault judgment.
[0045] 3. When judging instantaneous faults, this invention takes into account the maximum error value caused by fluctuations in the initial fluctuation stage, which can effectively avoid the occurrence of reclosing misoperation. Attached Figure Description
[0046] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:
[0047] Figure 1 This is a flowchart from Embodiment 1 of the present invention;
[0048] Figure 2 This is a system block diagram in Embodiment 2 of the present invention. Detailed Implementation
[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.
[0050] Example 1: A method for automatic reclosing control of distributed photovoltaic power grid connection, such as... Figure 1 As shown, it includes the following steps:
[0051] S1: Determine the target tie line in a de-energized state based on the open position of the circuit breaker after the line trips;
[0052] S2: The first circuit breaker between the control target tie line and the transformer line closes at the first moment;
[0053] S3: The second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line is closed at the second moment to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line.
[0054] S4: Collect the first current generated by the target tie line at the first moment and the second current generated at the second moment, and compare and analyze the current difference between the second current and the first current with the setting current difference determined by the injected AC signal to determine whether the target tie line is a transient fault.
[0055] S5: If the target connection line is a momentary fault, the injected AC signal output by the inverter controlling the photovoltaic power supply module will increase within a preset time period.
[0056] S6: Collect the response change current of the target tie line within a preset time period, calculate the low-voltage ride-through current within the preset time period based on the response change current, and estimate the decay change current of the low-voltage ride-through current after the preset time period based on the change trend of the low-voltage ride-through current.
[0057] S7: During the reclosing process of the control target tie line, adjust the actual current output by the inverter according to the decaying change current.
[0058] Distributed photovoltaic (PV) systems typically consist of multiple PV power supply modules. Each PV power supply module is equipped with an inverter on its output side. The inverter converts the direct current (DC) output from the PV power supply module into alternating current (AC). The AC output from the inverter is then stepped up or down through one or more transformers. All the transformers are connected to the transformer lines. The lines between the transformer lines and other external power supply modules, such as power plants, are called interconnection lines.
[0059] In step S1, after a line fault occurs, the circuit breakers on both sides of the line where the fault is located will disconnect. Therefore, the target tie line in a power outage state can be determined based on the disconnection position of the circuit breaker after the line trips.
[0060] In steps S2 and S3, both the first and second moments occur during the initial fluctuation phase of low-voltage ride-through, with the second moment being longer than the first moment. It should be noted that the first moment is generally spaced 0.1 seconds apart from the disconnection time of the first circuit breaker to avoid drastic changes at the beginning of the low-voltage ride-through phase.
[0061] Furthermore, the preset time period overlaps with the mid-term continuous decay phase of low-voltage ride-through. Therefore, the present invention does not require the preset time period to completely cover the mid-term continuous decay phase, thus enabling instantaneous fault reclosing within 1.2s-1.5s, effectively shortening the reclosing operation time.
[0062] In step S4, as an optional implementation, the process of determining whether the target tie line is a transient fault specifically involves: substituting the first current as the setting result into the setting current equation to calculate the injection current at the first moment; substituting the sum of the injection current at the first moment and the injection AC signal as the injection signal into the setting current equation to calculate the second estimated current at the second moment; calculating the current difference between the second current and the first current, and calculating the setting current difference between the second estimated current and the first current; if the current difference is less than or equal to the setting current difference, the target tie line is determined to be a transient fault; otherwise, if the current difference is greater than the setting current difference, the target tie line is determined to have a fault.
[0063] As another optional implementation, the process of determining whether the target tie line is a transient fault is as follows: Substitute the first current as the setting result into the setting current equation to calculate the injected current at the first moment; substitute the sum of the injected current at the first moment, the injected AC signal, and the maximum error value of the initial fluctuation stage of low-voltage ride-through as the injected signal into the setting current equation to calculate the second estimated current at the second moment; calculate the current difference between the second current and the first current, and calculate the setting current difference between the second estimated current and the first current; if the current difference is less than or equal to the setting current difference, the target tie line is determined to be a transient fault; otherwise, if the current difference is greater than the setting current difference, the target tie line is determined to have a fault.
[0064] When judging instantaneous faults, this invention takes into account the maximum error value caused by fluctuations in the initial fluctuation stage, which can effectively avoid the occurrence of reclosing misoperation.
[0065] It should be noted that the setting result in the setting current equation is equal to the product of the setting current and the setting coefficient. The setting current is calculated based on the voltage amplitude of the injected signal, the impedance of the target tie line, and the transition resistance of the target tie line. The specific expression of the setting current equation is existing technology and will not be described in detail here.
[0066] In step S5, the value of the injected AC signal at the initial moment, i.e., the second moment, is generally 80% of the normal output value of the inverter, while the value of the injected AC signal at the final moment of the incremental change is generally 90% of the normal output value of the inverter.
[0067] In step S6, the response change current is first input into the setting current equation, and the injection value can be obtained by inverse solution. Then, the low-voltage ride-through current within the preset time period is obtained by subtracting the injection value output by the inverter from the total injection value. Then, the curve of the obtained low-voltage ride-through current is fitted by the least squares method, and the subsequent current change can be predicted.
[0068] In step S7, the actual current output by the inverter is equal to the difference between the preset design current and the decaying change current when the inverter operates at the rated current to meet the target interconnection.
[0069] In addition, the reclosing of the target tie line can be achieved by closing the second circuit breaker between the target tie line and the external power supply module.
[0070] In addition, if there is a fault in the target connection line, the first circuit breaker can be controlled to open and be locked.
[0071] Example 2: An automatic reclosing control system for distributed photovoltaic grid connection, such as... Figure 2As shown, it includes a line determination module, a first injection module, a second injection module, a fault analysis module, an injection adjustment module, a current analysis module, and an output control module.
[0072] The system includes the following modules: a line determination module for identifying the target tie line in a de-energized state based on the open position of the circuit breaker after a line trip; a first injection module for controlling the first circuit breaker between the target tie line and the transformer line to close at the first moment; a second injection module for controlling the second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at the second moment, so as to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line via the transformer line; and a fault analysis module for collecting the first current generated by the target tie line at the first moment and the second current generated at the second moment, and comparing the current difference between the second current and the first current with the injected AC signal. The system compares and analyzes the set current difference to determine whether the target tie line is experiencing a transient fault. The injection adjustment module, when the target tie line experiences a transient fault, controls the inverter output of the photovoltaic power supply module to increase the injected AC signal within a preset time period. The current analysis module collects the response current changes of the target tie line within the preset time period, calculates the low-voltage ride-through current based on the response current changes, and estimates the decaying current changes of the low-voltage ride-through current after the preset time period based on the trend of the low-voltage ride-through current changes. The output control module adjusts the actual current output by the inverter based on the decaying current changes during the reclosing process of the target tie line.
[0073] Working principle: This invention first controls the first circuit breaker between the target tie line and the transformer line to close at the first moment, and then controls the second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at the second moment. This allows for instantaneous fault detection while making secondary use of the low-voltage ride-through current generated by the inverter. In addition, when the target tie line is experiencing an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to increase within a preset time period. This allows for stable and reliable analysis of the trend of low-voltage ride-through current at the beginning of its decay stage, close to the rated operating conditions, without the need for excessive monitoring equipment.
[0074] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for automatic reclosing control of distributed photovoltaic power grid connection, characterized in that, Includes the following steps: Determine the target tie line in a de-energized state based on the open position of the circuit breaker after the line trips; The first circuit breaker between the control target tie line and the transformer line closes at the first moment; The second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line is closed at the second moment to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line. The first current generated by the target tie line at the first moment and the second current generated at the second moment are collected, and the current difference between the second current and the first current is compared and analyzed with the setting current difference determined by the injected AC signal to determine whether the target tie line is a transient fault. If the target connection line is a momentary fault, the injected AC signal output by the inverter controlling the photovoltaic power supply module will increase within a preset time period. The response change current of the target tie line is collected within a preset time period, and the low-voltage ride-through current within the preset time period is calculated based on the response change current. The decay change current of the low-voltage ride-through current after the preset time period is estimated based on the change trend of the low-voltage ride-through current. During the reclosing process of the control target tie line, the actual current output by the inverter is adjusted according to the decaying change current; The attenuation variation current is obtained by curve fitting of the low-voltage ride-through current using the least squares method. The actual current output by the inverter is equal to the difference between the preset design current and the decaying change current when the inverter operates at the rated current to meet the target interconnection.
2. The method for automatic reclosing control of distributed photovoltaic power grid access according to claim 1, characterized in that, Both the first and second moments are in the initial fluctuation stage of low-pressure crossing, and the second moment is longer than the first moment; Furthermore, the preset time period overlaps with the mid-term continuous decay phase of low-pressure crossing.
3. The automatic reclosing control method for distributed photovoltaic grid connection according to claim 1, characterized in that, The process of determining whether the target communication line is experiencing a transient fault is as follows: Substitute the first current as the setting result into the setting current equation to calculate the injection current at the first moment; The sum of the injected current and the injected AC signal at the first moment is substituted into the setting current equation as the injected signal to calculate the second estimated current at the second moment. The current difference is calculated based on the difference between the second current and the first current, and the setting current difference is calculated based on the difference between the second estimated current and the first current. If the current difference is less than or equal to the set current difference, the target tie line is determined to be a transient fault. Conversely, if the current difference is greater than the set current difference, the target tie line is determined to be faulty.
4. The automatic reclosing control method for distributed photovoltaic grid connection according to claim 1, characterized in that, The process of determining whether the target communication line is experiencing a transient fault is as follows: Substitute the first current as the setting result into the setting current equation to calculate the injection current at the first moment; The sum of the injected current, the injected AC signal, and the maximum error value of the initial fluctuation stage of low-voltage ride-through at the first moment is substituted into the setting current equation as the injected signal to calculate the second estimated current at the second moment. The current difference is calculated based on the difference between the second current and the first current, and the setting current difference is calculated based on the difference between the second estimated current and the first current. If the current difference is less than or equal to the set current difference, the target tie line is determined to be a transient fault. Conversely, if the current difference is greater than the set current difference, the target tie line is determined to be faulty.
5. A method for automatic reclosing control of distributed photovoltaic power grid access according to claim 3 or 4, characterized in that, The setting result in the setting current equation is equal to the product of the setting current and the setting coefficient; The setting current is calculated based on the voltage amplitude of the injected signal, the impedance of the target tie line, and the transition resistance of the target tie line.
6. The automatic reclosing control method for distributed photovoltaic grid connection according to claim 1, characterized in that, The process of controlling the reclosing of the target tie line is as follows: the second circuit breaker between the target tie line and the external power supply module is closed.
7. The automatic reclosing control method for distributed photovoltaic grid connection according to claim 1, characterized in that, The method also includes: If there is a fault in the target connection line, the first circuit breaker is controlled to open and lock out.
8. An automatic reclosing control system for distributed photovoltaic grid connection, characterized in that, include: The line determination module is used to determine the target tie line in a power outage state based on the open position of the circuit breaker after the line trips. The first injection module is used to control the first circuit breaker between the target tie line and the transformer line to close at the first moment. The second injection module is used to control the second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at the second moment, so as to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line. The fault analysis module is used to collect the first current generated by the target tie line at the first moment and the second current generated at the second moment, and compare the current difference between the second current and the first current with the setting current difference determined by the injected AC signal to determine whether the target tie line is a transient fault. The injection regulation module is used to control the injected AC signal output by the inverter of the photovoltaic power supply module to increase within a preset time period when the target tie line is in a transient fault. The current analysis module is used to collect the response change current of the target tie line within a preset time period, calculate the low-voltage ride current within the preset time period based on the response change current, and estimate the decay change current of the low-voltage ride current after the preset time period based on the change trend of the low-voltage ride current; the decay change current is obtained by curve fitting of the low-voltage ride current using the least squares method. The output control module is used to adjust the actual current output by the inverter according to the decaying current during the reclosing process of the control target tie line; The actual current output by the inverter is equal to the difference between the preset design current and the decaying change current when the inverter operates at the rated current to meet the target interconnection.