Automatic reclosing control method and system for distributed photovoltaic access distribution network

Abstract

The invention discloses an automatic reclosing control method and system for a distributed photovoltaic access distribution network, and relates to the technical field of electric power control, and the key points of the technical scheme are as follows: firstly, a first circuit breaker between a target tie line and a transformation line is controlled to be closed at a first moment; and then a second circuit breaker between an inverter of the photovoltaic power supply module and a transformation line is controlled to be switched on at a second moment, so that transient fault judgment can be realized under the condition that low-voltage ride-through current generated by the inverter is secondarily utilized. Besides, when the target tie line is in a transient fault, an injection alternating current signal output by an inverter of the photovoltaic power supply module is controlled to be in an incremental change state in a preset time period, so that stable and reliable analysis on the change trend of the low-voltage ride-through current can be realized at the decay starting stage of the low-voltage ride-through current when the rated operation condition is approached; and excessive monitoring equipment does not need to be configured.

Description

Technical Field

[0001] The present invention relates to the field of power control technology, and more specifically, to a distributed photovoltaic access distribution network automatic reclosing control method and system. Background Art

[0002] A transient fault refers to a short-term fault in the power system caused by external factors such as lightning strikes and wind damage, or internal factors such as short-term equipment failures. A transient fault generally disappears on its own within a few seconds, and the insulation performance of the line can be restored. In photovoltaic grid-connected systems, the incidence of transient faults is relatively high, accounting for 80% to 90% of the total number of faults. The automatic reclosing device (ARD) is an important means of handling transient faults. When a transient fault occurs in the line, the relay protection device will trip the circuit breaker and start the automatic reclosing device at the same time. After a certain time interval, it will automatically close and restore power supply.

[0003] During the automatic reclosing of the distribution network, the judgment of whether a transient fault occurs in the line is generally to inject an AC signal into the disconnected line, and then collect the real-time current in the line and compare it with the theoretical current after the AC signal is injected into the line. When the real-time current is not greater than the theoretical current, the line is generally judged to be a transient fault. For the case of distributed photovoltaic access to the distribution network, the inverters in most photovoltaic power supply modules have low-voltage ride-through capabilities. In order to reduce the superimposed impact of the low-voltage ride-through current during the automatic reclosing of the distribution network, some existing technologies are to wait for the low-voltage ride-through current to decay to a negligible level before executing the reclosing when the line is judged to be a transient fault. The low-voltage ride-through current decay process generally requires waiting for about 3s, which to a certain extent limits the execution efficiency of the automatic reclosing control of the distribution network; another part of the existing technology is to monitor the decay of the low-voltage ride-through current in real time when the line is judged to be a transient fault, and use this as feedback information to provide reference data for adjusting the output current of the inverter; but this method requires the configuration of monitoring points on the output side of the inverter, resulting in a large number of sensors and other equipment required for distributed photovoltaic grid connection, and a high investment cost.

[0004] Therefore, how to research and design a distributed photovoltaic access distribution network automatic reclosing control method and system that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the purpose of the present invention is to provide a distributed photovoltaic access distribution network automatic reclosing control method and system, which can realize instantaneous fault judgment while making secondary use of the low voltage ride-through current generated by the inverter; and can realize stable and reliable analysis of the changing trend of the low voltage ride-through current at the beginning of the decay of the low voltage ride-through current, without the need to configure too many monitoring equipment.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a method for controlling automatic reclosing of distributed photovoltaic access to a distribution network is provided, comprising the following steps:

[0008] Determine the target interconnection line in a power outage state according to the disconnection position of the circuit breaker after the line trips;

[0009] Controlling the first circuit breaker between the target tie line and the transformer line to close at a first moment;

[0010] Controlling a second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at a second moment, so as to inject the injected AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line;

[0011] Collecting a first current generated by the target tie line at a first moment and a second current generated at a second moment, and comparing and analyzing a current difference between the second current and the first current with a set current difference determined by the injected AC signal, to determine whether the target tie line is an instantaneous fault;

[0012] If the target interconnection line has an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to change in an increasing state within a preset period of time;

[0013] Collect the response change current of the target interconnection line within the preset period, calculate the low voltage ride-through current within the preset period based on the response change current, and estimate the attenuation change current of the low voltage ride-through current after the preset period based on the change trend of the low voltage ride-through current;

[0014] In the process of controlling the target tie line reclosing, the actual current output by the inverter is adjusted according to the attenuated changing current.

[0015] Furthermore, the first moment and the second moment are both in the initial fluctuation stage of low pressure crossing, and the second moment is greater than the first moment;

[0016] Furthermore, the preset time period intersects with the mid-term continuous attenuation stage of the low pressure crossing.

[0017] Furthermore, the process of determining whether the target tie line is a transient fault is specifically as follows:

[0018] Substituting the first current as the setting result into the setting current equation, the injection current at the first moment is calculated;

[0019] Substituting the sum of the injected current and the injected AC signal at the first moment into the setting current equation as the injected signal, and calculating a second estimated current at the second moment;

[0020] Calculating a current difference value by the difference between the second current and the first current, and calculating a set current difference by 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 interconnection line is judged to be an instantaneous fault; conversely, if the current difference is greater than the set current difference, the target interconnection line is judged to be a fault.

[0022] Furthermore, the process of determining whether the target tie line is a transient fault is specifically as follows:

[0023] Substituting the first current as the setting result into the setting current equation, the injection current at the first moment is calculated;

[0024] Substituting the sum of the injected current, injected AC signal and the maximum error value of the initial fluctuation stage of low voltage ride-through at the first moment into the setting current equation as the injected signal, the second estimated current at the second moment is calculated;

[0025] Calculating a current difference value by the difference between the second current and the first current, and calculating a set current difference by 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 interconnection line is judged to be an instantaneous fault; conversely, if the current difference is greater than the set current difference, the target interconnection line is judged to be 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 set current is calculated based on the voltage amplitude of the injected signal, the impedance of the target interconnection line, and the transition resistance of the target interconnection line.

[0029] Furthermore, the attenuated variation current is obtained by curve fitting using the least square method.

[0030] Furthermore, the actual current output by the inverter is equal to the difference between the preset design current output by the inverter to meet the target tie line operation at the rated current and the attenuated change current.

[0031] Furthermore, the process of controlling the target tie line to reclose is specifically: controlling the second circuit breaker between the target tie line and the external power supply module to close.

[0032] Furthermore, the method also includes:

[0033] If there is a fault in the target tie line, the first circuit breaker is controlled to be opened and locked.

[0034] In the second aspect, a distributed photovoltaic access distribution network automatic reclosing control system is provided, comprising:

[0035] A line determination module, used to determine a target interconnection line in a power outage state according to the disconnection position of the circuit breaker after the line trips;

[0036] A first injection module, used for controlling a first circuit breaker between a target tie line and a transformer line to close at a first moment;

[0037] A second injection module, used for controlling a second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at a second moment, so as to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target interconnection line through the transformer line;

[0038] A fault analysis module is used to collect a first current generated by the target tie line at a first moment and a second current generated at a second moment, and compare and analyze the current difference between the second current and the first current with a set 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 injection AC signal output by the inverter of the photovoltaic power supply module to change in an incremental manner within a preset period of time when the target interconnection line is in an instantaneous fault;

[0040] The current analysis module is used to collect the response change current of the target interconnection line within a preset period of time, calculate the low voltage ride-through current within the preset period of time based on the response change current, and estimate the attenuation change current of the low voltage ride-through current after the preset period of time based on the change trend of the low voltage ride-through current;

[0041] The output control module is used to adjust the actual current output by the inverter according to the attenuated changing current during the process of controlling the target tie line reclosing.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention provides a distributed photovoltaic access distribution network automatic reclosing control method, which controls the first circuit breaker between the target interconnection line and the transformer line to close at a 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 a second moment, which can realize instantaneous fault judgment under the condition of secondary utilization of the low voltage ride-through current generated by the inverter; in addition, when the target interconnection line is an instantaneous fault, the injection AC signal output by the inverter of the photovoltaic power supply module is controlled to be in an increasing change state within a preset time period, so that when approaching the rated operating condition, the change trend of the low voltage ride-through current can be stably and reliably analyzed at the beginning stage of decay of the low voltage ride-through current, without the need to configure too many monitoring devices;

[0044] 2. The first moment and the second moment in the present invention are both in the initial fluctuation stage of low voltage ride-through, so the change of low voltage ride-through current at the first moment and the second moment can be ignored, which effectively ensures the accuracy of instantaneous fault judgment;

[0045] 3. When judging instantaneous faults, the present invention takes into account the maximum error value caused by fluctuations in the initial fluctuation stage, which can effectively avoid the occurrence of erroneous operation of the reclosing switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0047] Figure 1 is a flow chart of Embodiment 1 of the present invention;

[0048] Figure 2 It is a system block diagram in Example 2 of the present invention. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0050] Embodiment 1: A distributed photovoltaic access distribution network automatic reclosing control method, such as Figure 1 As shown, the following steps are included:

[0051] S1: Determine the target interconnection line in a power outage state according to the disconnection position of the circuit breaker after the line trips;

[0052] S2: Control the first circuit breaker between the target tie line and the transformer line to close at the first moment;

[0053] S3: 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 injected AC signal output by the inverter of the photovoltaic power supply module into the target interconnection line through the transformer line;

[0054] S4: collecting a first current generated by the target tie line at a first moment and a second current generated at a second moment, and comparing and analyzing a current difference between the second current and the first current and a set current difference determined by the injected AC signal to determine whether the target tie line is an instantaneous fault;

[0055] S5: If the target interconnection line has an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to be in an increasing state within a preset period of time;

[0056] S6: collecting the response change current of the target tie line within the preset period, calculating the low voltage ride through current within the preset period according to the response change current, and estimating the attenuation change current of the low voltage ride through current after the preset period according to the change trend of the low voltage ride through current;

[0057] S7: In the process of controlling the target tie line reclosing, the actual current output by the inverter is adjusted according to the attenuated changing current.

[0058] Distributed photovoltaics generally include multiple photovoltaic power supply modules. Each photovoltaic power supply module is equipped with an inverter on the output side. The inverter can convert the direct current output of the photovoltaic power supply module into alternating current. The alternating current output by the inverter is then stepped up or down through one or more transformers. The lines where all transformers are located are transformer lines. The lines between the transformer lines and other external power supply modules are interconnecting lines, such as power plants.

[0059] In step S1, after a line fault occurs, the circuit breakers on both sides of the line where the fault location is located will be disconnected, so the target interconnection 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, the first moment and the second moment are both in the initial fluctuation stage of low voltage ride-through, and the second moment is greater than the first moment. It should be noted that the first moment and the disconnection time of the first circuit breaker are generally separated by 0.1s to avoid drastic changes in the initial stage of low voltage ride-through.

[0061] In addition, the preset time period intersects with the mid-term continuous decay stage of the low voltage ride-through. The present invention does not require the preset time period to completely cover the mid-term continuous decay stage, so instantaneous fault reclosing can be achieved 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 interconnection line is a transient fault is specifically as follows: substituting the first current as a setting result into the setting current equation to calculate the injected current at the first moment; substituting the sum of the injected current at the first moment and the injected AC signal as the injected signal into the setting current equation to calculate the second estimated current at the second moment; calculating the current difference as the difference between the second current and the first current, and calculating the set current difference as 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, determining that the target interconnection line is a transient fault; conversely, if the current difference is greater than the set current difference, determining that there is a fault in the target interconnection line.

[0063] As another optional implementation, the process of determining whether the target interconnection line is a transient fault is specifically as follows: substituting the first current as a setting result into the setting current equation to calculate the injected current at the first moment; substituting 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 the low voltage ride-through as the injection signal into the setting current equation to calculate the second estimated current at the second moment; calculating the current difference as the difference between the second current and the first current, and calculating the set current difference as 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, determining that the target interconnection line is a transient fault; conversely, if the current difference is greater than the set current difference, determining that there is a fault in the target interconnection line.

[0064] When judging instantaneous faults, the present invention takes into account the maximum error value caused by fluctuations in the initial fluctuation stage, which can effectively avoid the occurrence of erroneous operation of the reclosing switch.

[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; wherein the setting current is calculated based on the voltage amplitude of the injected signal, the impedance of the target interconnection line and the transition resistance of the target interconnection line, and the specific expression of the setting current equation is the prior art and will not be described in detail here.

[0066] In step S5, the value of the injected AC signal at the start time, ie, the second time, is generally 80% of the normal output value of the inverter, and the value of the injected AC signal at the final time 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 set current equation, and the injection value can be obtained by inverse solution. Then, the injection value output by the inverter is subtracted from the total injection value to obtain the low voltage ride-through current within the preset time period. Then, the least squares method is used to perform curve fitting on the obtained low voltage ride-through current to predict subsequent current changes.

[0068] In step S7, the actual current output by the inverter is equal to the difference between the preset design current output by the inverter to meet the target tie line operation at the rated current and the attenuated change current.

[0069] In addition, by controlling the closing of the second circuit breaker between the target tie line and the external power supply module, the target tie line can be controlled to be reclosed.

[0070] In addition, if there is a fault in the target tie line, the first circuit breaker can be controlled to be disconnected and locked.

[0071] Embodiment 2: A distributed photovoltaic access distribution network automatic reclosing control system, 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] Among them, the line determination module is used to determine the target interconnection line in the power outage state according to the disconnection position of the circuit breaker after the line trips; the first injection module is used to control the first circuit breaker between the target interconnection 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 interconnection line through the transformer line; the fault analysis module is used to collect the first current generated by the target interconnection 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 current determined by the injected AC signal The target interconnection line is compared and analyzed with the set current difference to determine whether the target interconnection line is a transient fault; the injection regulation module is used to control the injection AC signal output by the inverter of the photovoltaic power supply module to be in an increasing state within a preset period of time when the target interconnection line is a transient fault; the current analysis module is used to collect the response change current of the target interconnection line within the preset period of time, and calculate the low voltage ride-through current within the preset period of time based on the response change current, and estimate the attenuation change current of the low voltage ride-through current after the preset period of time based on the change trend of the low voltage ride-through current; the output control module is used to adjust the actual current output by the inverter according to the attenuation change current during the process of controlling the target interconnection line reclosing.

[0073] Working principle: The present invention first controls the first circuit breaker between the target interconnection line and the transformer line to close at a 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 a second moment, which can realize instantaneous fault judgment under the condition of secondary utilization of the low-voltage ride-through current generated by the inverter; in addition, when the target interconnection line is an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to be in an increasing state within a preset time period, so that when approaching the rated operating conditions, the changing trend of the low-voltage ride-through current can be stably and reliably analyzed at the beginning stage of decay of the low-voltage ride-through current, without the need to configure too many monitoring equipment.

[0074] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method 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 in the scope of protection of the present invention.

Claims

1. A distributed photovoltaic access distribution network automatic reclosing control method, characterized in that: The following steps are involved: Determine the target interconnection line in a power outage state according to the disconnection position of the circuit breaker after the line trips; Controlling the first circuit breaker between the target tie line and the transformer line to close at a first moment; Controlling a second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at a second moment, so as to inject the injected AC signal output by the inverter of the photovoltaic power supply module into the target tie line through the transformer line; Collecting a first current generated by the target tie line at a first moment and a second current generated at a second moment, and comparing and analyzing a current difference between the second current and the first current with a set current difference determined by the injected AC signal, to determine whether the target tie line is an instantaneous fault; If the target interconnection line is in an instantaneous fault, the injected AC signal output by the inverter of the photovoltaic power supply module is controlled to be in an increasing change state within a preset period of time; Collect the response change current of the target interconnection line within the preset period, calculate the low voltage ride-through current within the preset period based on the response change current, and estimate the attenuation change current of the low voltage ride-through current after the preset period based on the change trend of the low voltage ride-through current; In the process of controlling the target tie line reclosing, the actual current output by the inverter is adjusted according to the attenuated changing current.

2. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The first moment and the second moment are both in the initial fluctuation stage of low pressure crossing, and the second moment is greater than the first moment; Furthermore, the preset time period intersects with the mid-term continuous attenuation stage of the low pressure crossing.

3. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The process of determining whether the target tie line is a transient fault is specifically as follows: Substituting the first current as the setting result into the setting current equation, the injection current at the first moment is calculated; Substituting the sum of the injected current and the injected AC signal at the first moment into the setting current equation as the injected signal, and calculating a second estimated current at the second moment; Calculating a current difference value by the difference between the second current and the first current, and calculating a set current difference by 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 judged to be an instantaneous fault; On the contrary, if the current difference is greater than the set current difference, it is determined that there is a fault in the target interconnection line.

4. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The process of determining whether the target tie line is a transient fault is specifically as follows: Substituting the first current as the setting result into the setting current equation, the injection current at the first moment is calculated; Substituting the sum of the injected current, injected AC signal and the maximum error value of the initial fluctuation stage of low voltage ride-through at the first moment into the setting current equation as the injected signal, and calculating the second estimated current at the second moment; Calculating a current difference value by the difference between the second current and the first current, and calculating a set current difference by 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 judged to be an instantaneous fault; On the contrary, if the current difference is greater than the set current difference, it is determined that there is a fault in the target interconnection line.

5. A distributed photovoltaic access distribution network automatic reclosing control method 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 set current is calculated based on the voltage amplitude of the injected signal, the impedance of the target interconnection line, and the transition resistance of the target interconnection line.

6. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The attenuated variation current is obtained by curve fitting using the least square method.

7. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The actual current output by the inverter is equal to the difference between the preset design current output by the inverter to meet the target tie line operation at the rated current and the attenuated change current.

8. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The process of controlling the target tie line to reclose is specifically: controlling the second circuit breaker between the target tie line and the external power supply module to close.

9. A distributed photovoltaic access distribution network automatic reclosing control method according to claim 1, characterized in that: The method further includes: If there is a fault in the target tie line, the first circuit breaker is controlled to be opened and locked.

10. A distributed photovoltaic access distribution network automatic reclosing control system, characterized in that: include: A line determination module, used to determine a target interconnection line in a power outage state according to the disconnection position of the circuit breaker after the line trips; A first injection module, used for controlling a first circuit breaker between a target tie line and a transformer line to close at a first moment; A second injection module, used for controlling a second circuit breaker between the inverter of the photovoltaic power supply module and the transformer line to close at a second moment, so as to inject the injection AC signal output by the inverter of the photovoltaic power supply module into the target interconnection line through the transformer line; A fault analysis module is used to collect a first current generated by the target tie line at a first moment and a second current generated at a second moment, and compare and analyze the current difference between the second current and the first current with a set 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 injection AC signal output by the inverter of the photovoltaic power supply module to change in an incremental manner within a preset period of time when the target interconnection line is in an instantaneous fault; The current analysis module is used to collect the response change current of the target interconnection line within a preset period of time, calculate the low voltage ride-through current within the preset period of time based on the response change current, and estimate the attenuation change current of the low voltage ride-through current after the preset period of time based on the change trend of the low voltage ride-through current; The output control module is used to adjust the actual current output by the inverter according to the attenuated changing current during the process of controlling the target tie line reclosing.

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