An anti-islanding method and system based on photovoltaic low-voltage grid-connected switch

Abstract

The application discloses a kind of based on photovoltaic low-voltage grid-connected switch's anti-islanding method and system, including the bus grid-connected switch and at least one photovoltaic low-voltage grid-connected switch of mutual communication;The anti-islanding method includes the following processes: photovoltaic low-voltage grid-connected switch real-time detection bus side voltage amplitude, frequency, phase and harmonic content, and respectively establish local model when each parameter above in non-islanding system of table area;Photovoltaic low-voltage grid-connected switch will be acquired the amplitude, frequency, phase and harmonic content data of bus side voltage in real time respectively input to corresponding local model, when certain parameter appears abnormal, report to bus grid-connected switch;So that bus grid-connected switch controls each photovoltaic low-voltage grid-connected switch to carry out tripping action or carry out secondary detection according to the number of reported abnormal data.The application increases the initiative detection of bus grid-connected switch and the method of each expert voting, improves the success rate of detection.

Description

Technical Field

[0001] This invention relates to the field of microgrid system technology, and in particular to an anti-islanding method and system based on a photovoltaic low-voltage grid-connected switch. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] The solar photovoltaic power generation industry is an important means of achieving clean energy substitution at the power generation end. In the future, there will be more and more small photovoltaic power generation and energy storage systems in microgrid systems. The rooftop of a production base or the rooftop of a residential building will become a photovoltaic power generation and energy storage system. How to solve these small isolated systems will become a prominent issue.

[0004] Current research and applications largely focus on active and passive anti-islanding methods based on dedicated anti-islanding equipment configured in large and medium-sized photovoltaic (PV) energy storage systems, or on the islanding protection inherent in the inverter itself. Small-scale PV energy storage systems primarily rely on the inverter's own islanding protection methods. However, this passive detection method often has blind spots due to uncertain detection thresholds, failing to effectively address the islanding problem in small-scale PV energy storage systems. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes an anti-islanding method and system based on photovoltaic low-voltage grid-connected switches. By combining remote communication detection with local active and passive detection, the method solves the problem of blind spots in single detection methods, meets the anti-islanding requirements of miniaturized photovoltaic energy storage systems, and greatly improves the security of microgrid systems.

[0006] In some implementations, the following technical solutions are adopted:

[0007] An anti-islanding method based on a photovoltaic low-voltage grid-connected switch includes interconnected bus grid-connected switches and at least one photovoltaic low-voltage grid-connected switch; the anti-islanding method includes the following process:

[0008] The photovoltaic low-voltage grid-connected switch monitors the amplitude, frequency, phase, and harmonic content of the bus-side voltage in real time, and establishes local models of the above parameters when the distribution area is in a non-islanded system.

[0009] The photovoltaic low-voltage grid-connected switch inputs the amplitude, frequency, phase and harmonic content data of the bus side voltage acquired in real time into the corresponding local model. When a certain parameter is abnormal, it is reported to the bus grid-connected switch, so that the bus grid-connected switch can control each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection according to the number of reported abnormal data.

[0010] As a further embodiment, the bus grid-connected switch controls each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection based on the number of reported abnormal data, specifically including:

[0011] The bus grid-connected switch establishes a decision function based on the amplitude, frequency, phase, and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter.

[0012] The number M of photovoltaic low-voltage grid-connected switches that report abnormal data is determined. When the ratio of the number M to the total number N of photovoltaic low-voltage grid-connected switches is greater than a set threshold, the bus grid-connected switch sends a tripping action command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a characteristic current of a set frequency to the transformer area bus and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters. Based on the detection results, the bus grid-connected switch sends corresponding action commands to each photovoltaic low-voltage grid-connected switch.

[0013] As a further step, considering the weights of each parameter, a decision function is established, specifically including:

[0014] The decision function is the sum of the products of each parameter value and its weight; wherein, the bus grid-connected switch assigns a corresponding weight to each photovoltaic low-voltage grid-connected switch based on the data reported by each photovoltaic low-voltage grid-connected switch.

[0015] As a further embodiment, the busbar grid-connected switch sends a characteristic current of a set frequency to the transformer area busbar and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters, specifically including:

[0016] After the busbar grid-connected switch sends a characteristic current of a set frequency to the transformer area busbar, it sends an islanding detection command to all photovoltaic low-voltage grid-connected switches. The detection content is issued according to the weight value w of the grid-connected switch. Each photovoltaic low-voltage grid-connected switch performs secondary detection of the set parameters based on the issued detection content.

[0017] As a further step, corresponding action commands are sent to each photovoltaic low-voltage grid-connected switch based on the test results, specifically including:

[0018] When the number of photovoltaic low-voltage grid-connected switches that have become islanded exceeds the set threshold, the bus grid-connected switch sends a tripping command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a command to each photovoltaic low-voltage grid-connected switch to maintain the current action.

[0019] As a further step, local models of the above parameters are established separately when the transformer area is in a non-islanded system, specifically including:

[0020] The local model for the voltage amplitude is a first-order Gaussian function, and the standard deviation of the function is the maximum voltage amplitude obtained by statistically analyzing the voltage amplitude fluctuation within a set time period collected in real time by the photovoltaic low-voltage grid-connected switch.

[0021] The local model of the voltage frequency is a first-order Gaussian function, and the standard deviation of the function is the maximum value of the voltage frequency obtained by statistically analyzing the voltage frequency fluctuations within a set time period collected in real time by the photovoltaic low-voltage grid-connected switch.

[0022] The local model of the voltage phase is a phase angle with time interval T. The difference function; where, It was acquired at time T1. It was acquired at time T2; the standard voltage phase angle change was calculated based on the time interval T. according to Calculate the voltage phase change value;

[0023] The local model of voltage harmonics compares the data of each harmonic content with the standard data of each harmonic content to obtain the voltage waveform distortion rate.

[0024] As a further measure, when a certain parameter becomes abnormal, it is reported to the bus grid connection switch, specifically including:

[0025] When the probability of a voltage amplitude / frequency appearing in its local model is 0, it is reported to the bus grid connection switch; when the probability density of voltage amplitude / frequency appearing in the set range is greater than the set normal value, it is reported to the bus grid connection switch.

[0026] When the voltage phase change value / harmonic distortion rate is greater than the set threshold, it is reported to the bus grid connection switch.

[0027] In other embodiments, the following technical solutions are adopted:

[0028] An anti-islanding photovoltaic low-voltage grid-connected switch, comprising:

[0029] The local modeling module is used to create local models of the above parameters when the transformer area is in a non-islanded system.

[0030] The islanding detection module is used to input the amplitude, frequency, phase and harmonic content data of the bus side voltage acquired in real time into the corresponding local model. When a certain parameter is abnormal, it is reported to the bus grid-connected switch, so that the bus grid-connected switch can control each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection according to the number of reported abnormal data.

[0031] In other embodiments, the following technical solutions are adopted:

[0032] An anti-islanding busbar grid-connected switch includes:

[0033] The decision function module is used to establish a decision function based on the amplitude, frequency, phase and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter.

[0034] The anti-islanding control module is used to determine the number M of photovoltaic low-voltage grid-connected switches that report abnormal data. When the ratio of the number M to the total number N of photovoltaic low-voltage grid-connected switches is greater than a set threshold, the bus grid-connected switch sends a tripping action command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a characteristic current of a set frequency to the transformer area bus and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters, and sends corresponding action commands to each photovoltaic low-voltage grid-connected switch according to the detection results.

[0035] In other embodiments, the following technical solutions are adopted:

[0036] An anti-islanding system based on a photovoltaic low-voltage grid-connected switch includes:

[0037] The photovoltaic low-voltage grid-connected switch and the bus grid-connected switch mentioned above; the photovoltaic low-voltage grid-connected switch and the bus grid-connected switch communicate with each other.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] (1) This invention utilizes the communication between the photovoltaic low-voltage grid-connected switch and the bus grid-connected switch to achieve anti-islanding. In cases where the single passive detection method has blind spots or is not very accurate, the invention adds active detection of the bus grid-connected switch and voting by various experts, thereby improving the success rate of detection.

[0040] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the photovoltaic low-voltage grid-connected switch functional unit in an embodiment of the present invention;

[0042] Figure 2 This is a schematic diagram illustrating the communication between the photovoltaic low-voltage grid-connected switch and the bus grid-connected switch in an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of an anti-islanding method based on a photovoltaic low-voltage grid-connected switch in an embodiment of the present invention. Detailed Implementation

[0044] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] Example 1

[0047] In one or more embodiments, an anti-islanding method based on a photovoltaic low-voltage grid-connected switch is disclosed, comprising mutually communicating bus grid-connected switches and at least one photovoltaic low-voltage grid-connected switch; wherein, combined with Figure 1 The photovoltaic low-voltage grid-connected switch mainly consists of a power supply unit, a metering unit, an MCU1 protection unit, an execution unit, an MCU2 data processing unit, an HPLC carrier communication unit, and a topology analysis unit.

[0048] The three-phase four-wire connection is to the power supply unit. The main functions of the power supply unit include AD to DC conversion to power the grid-connected switch, and providing voltage sampling points for the metering module by performing AC voltage division. The metering unit, through the voltage sampling points of the power supply unit and the current transformers on the three-phase four-wire connection, performs voltage acquisition, current acquisition, and metering functions. The MCU1 protection unit, based on data from the metering unit, implements overvoltage, overcurrent, and short-circuit protection functions, as well as power quality analysis functions. The execution unit, part of the drive section, allows MCU1 to perform actions such as disconnection, tripping, and closing. The power supply unit, metering unit, MCU1 protection unit, and execution unit can form a traditional grid-connected protection switch. The HPLC carrier communication unit uses broadband power line carrier technology to transmit data over low-voltage power lines (L and N). The network uses power lines as the communication medium to realize the aggregation, transmission, and interaction of electricity consumption information for low-voltage power users. The topology analysis unit can analyze the power topology. The MCU2 data processing unit mainly processes data from the metering unit, protection unit, HPLC carrier communication unit, and topology analysis unit, and is responsible for data processing and external communication functions.

[0049] Combination Figure 2 Within a transformer substation, there is a busbar grid connection switch located on the transformer side. When the busbar switch is closed, electrical energy from the main power grid is supplied to the loads within the substation via the busbar switch.

[0050] Within a transformer substation, there are N photovoltaic low-voltage grid-connected switches, located on the photovoltaic energy storage side. When the photovoltaic low-voltage grid-connected switch is closed, the main power grid and the photovoltaic energy storage system jointly supply power to the loads within the substation.

[0051] When the main power grid system loses power or the bus switch is disconnected, and one or more grid-connected switches are closed, the photovoltaic energy storage system will supply power to the load in the distribution area, forming an uncontrolled island system. If it operates for a long time, the power supply voltage and frequency in the island system will deviate significantly, causing serious damage to the energy storage equipment and load electrical equipment in the distribution area.

[0052] The busbar grid-connected switch and the photovoltaic low-voltage grid-connected switch are interconnected via HPLC, a communication method unique to power systems. HPLC utilizes existing power lines to transmit analog or digital signals at high speed via carrier waves. Its biggest advantage is that it eliminates the need for re-establishing a network; data transmission can be achieved as long as there are power lines.

[0053] This invention relies on the interaction between the busbar grid-connected switch and the photovoltaic low-voltage grid-connected switch to jointly protect against islanding within the transformer area. In this anti-islanding method based on the photovoltaic low-voltage grid-connected switch, after passive detection, the photovoltaic low-voltage grid-connected switch reports to the busbar grid-connected switch, which then performs active detection. Once an islanding system is confirmed, the busbar grid-connected switch sends a command to all grid-connected switches via HPLC to disconnect the photovoltaic low-voltage grid-connected switches. Furthermore, all N photovoltaic low-voltage grid-connected switches in this system perform anti-islanding detection in real time. If even one photovoltaic low-voltage grid-connected switch detects an islanding system, all photovoltaic low-voltage grid-connected switches receive a command to disconnect their grid connections, thus effectively preventing islanding hazards.

[0054] Specifically, in combination Figure 3 This embodiment is based on an anti-islanding method for photovoltaic low-voltage grid-connected switches, which specifically includes the following process:

[0055] (1) Passive detection process of photovoltaic low-voltage grid-connected switch

[0056] 1) Real-time monitoring of the amplitude, frequency, phase, and harmonic content of the photovoltaic low-voltage grid-connected switch on the bus side, and establishment of a local model of the voltage amplitude, frequency, phase, and harmonics when the distribution area is in a non-islanded system; specifically including:

[0057] a) The local model for voltage amplitude is established by creating a first-order Gaussian function with an expected value μ = 220 and a standard deviation σ = m. The m-value is the maximum value statistically derived from the voltage amplitude fluctuations over a certain period of time collected in real time by the grid-connected switch. This function can be used to calculate the probability of a specific voltage amplitude point occurring, and also to statistically determine the probability of a range of voltage amplitude values ​​occurring within that range.

[0058] b) The local model for voltage frequency is established by creating a first-order Gaussian function with an expected value μ = 50 and a standard deviation σ = n. The n-value is the maximum value obtained by statistically analyzing the voltage frequency fluctuations over a certain period of time, collected in real time by the grid-connected switch. This function can be used to calculate the probability of a specific frequency point occurring, or to statistically determine the probability of a range of voltage frequencies occurring within that range.

[0059] c) A local model of the voltage phase is established by setting a phase angle at time intervals T. The difference function, where, It was acquired at time T1. It was acquired at time T2; the standard voltage phase angle change can be calculated based on time T. Therefore, according to Calculate the value of the voltage phase change.

[0060] d) The local model of voltage harmonics is f(t)=∑(k=1,n)cos(kwt+ak), and the component f(t)=cos(wt+a)c when k=1 is called the fundamental component; the component f(t)=cos(3wt+a3) when k=3 is called the third harmonic component.

[0061] The waveform data acquired by the ADC is stored in an array, and the data in the array is then substituted into the function sequentially. We obtain Dn = Ren + Imn, where Re is the real part and Im is the imaginary part; then we calculate the fundamental frequency as follows: The nth harmonic is The harmonic content is Yin = K * Yn / Y0, where K is a constant coefficient. The voltage waveform distortion rate is obtained by comparing the data of each harmonic content with the standard harmonic content data.

[0062] 2) The photovoltaic low-voltage grid-connected switch inputs the collected voltage amplitude, frequency, phase, and harmonic data into the established local model. When abnormal data occurs, it promptly reports to the main grid-connected switch. The local models for voltage amplitude, frequency, phase, and harmonics are independent of each other, and the anomaly reporting is also independent. Their respective anomaly analysis mechanisms are as follows:

[0063] a) Voltage amplitude: When the probability of a voltage amplitude appearing in the function is 0, it is immediately reported to the bus grid connection switch; when the probability density of the voltage amplitude in the range of [220-σ, 220-0.8σ] or [220+0.8σ, 220+σ] is greater than the normal value, it is immediately reported to the bus grid connection switch.

[0064] b) Voltage frequency: When the probability of a voltage frequency appearing in the function is 0, it should be reported to the bus grid connection switch immediately; when the probability of the voltage frequency in the range [50-σ, 50-0.8σ] or [50+0.8σ, 50+σ] is greater than the normal probability, it should be reported to the bus grid connection switch immediately.

[0065] c) Voltage Phase: A threshold for voltage phase change is set on the photovoltaic low-voltage grid-connected switch, which is adjustable between 1 and 60 degrees. When the voltage phase change value exceeds the threshold, it is immediately reported to the bus grid-connected switch. The bus grid-connected switch can adjust the voltage phase change threshold according to the phase data reported by the grid-connected switch.

[0066] d) Voltage Harmonics: A threshold for voltage harmonic distortion rate is set on the photovoltaic low-voltage grid-connected switch, which is adjustable between 0.5% and 30%. When the voltage harmonic distortion rate exceeds the threshold, it is immediately reported to the bus grid-connected switch. The bus grid-connected switch can adjust the voltage harmonic distortion rate threshold based on the voltage harmonics reported by the grid-connected switch.

[0067] 3) Wait for the bus grid connection switch to actively detect. Cooperate with the active detection and perform corresponding secondary detection based on the characteristic current injected by the bus switch. The detection method and result judgment are the same as in steps 1) and 2). The difference is that the secondary detection will only detect two of the following based on the bus grid connection switch: voltage amplitude, frequency, phase, and harmonics. The specific item to be measured will be issued by the bus grid connection switch. After the detection is completed, the corresponding results will be reported.

[0068] 4) After receiving the command from the bus grid-connected switch to disconnect the switch, the photovoltaic low-voltage grid-connected switch will trip; after receiving the command from the bus grid-connected switch not to disconnect the switch, it will maintain the status quo and continue to monitor.

[0069] (2) Active detection process of busbar grid connection switch

[0070] 1) The bus grid-connected switch establishes a decision function g(x) = w1x1 + w2x2 + w3x3 + w4x4 based on the voltage amplitude, frequency, phase and harmonics reported by the grid-connected switch, where x1, x2, x3 and x4 represent the values ​​of each parameter respectively; the bus grid-connected switch can assign corresponding weights according to the accuracy of the data reported by each parameter in order to quickly determine the problem.

[0071] The value w represents the weight of each variable, initially set to 0.25, therefore w1 + w2 + w3 + w4 = 1. The weight w is adjusted based on the accuracy of each island identification. The weight w uses a mean-based algorithm. Calculations are performed. Furthermore, each grid-connected switch has a different weight. Essentially, the bus grid-connected switches assign corresponding weights to each based on the data reported by the grid-connected switches.

[0072] When an isolated network occurs, multiple grid-connected switches (a, b, c, d, etc.) may report the issue. The bus grid-connected switch will add or subtract trust weights based on the accuracy of each switch. When multiple switches with high trust weights report together, secondary verification is not required, and the bus grid-connected switch can directly issue a command. When a switch with a low trust weight reports, the bus grid-connected switch will issue a secondary verification command.

[0073] 2) When the number of grid-connected switches operating in the system is N, and M grid-connected switches generate islanding data reports, if At that time, the main grid connection switch will directly issue commands to each grid connection switch to disconnect the grid connection switch. When the busbar switch sends a characteristic current I at a specific frequency to the transformer area bus, the change in the total harmonic distortion rate of the grid voltage caused by the characteristic current transmission shall not exceed 1%, the change in the odd harmonic voltage content rate shall not exceed 1%, and the change in the even harmonic voltage content rate shall not exceed 1%. After the characteristic current is transmitted, an islanding detection command is sent to all grid-connected switches. The detection content (amplitude, frequency, phase, harmonics) is distributed according to the weight value w of the grid-connected switch, with one switch having the largest weight w and the other having the smallest weight w. The data reported by the switch with the largest weight can be used as an important basis for the decision of the busbar grid-connected switch, while the data reported by the switch with the smallest weight is only considered as data of interest to the busbar grid-connected switch and is not used as the basis for the current judgment. For example, if the amplitude weight value of the No. 1 grid-connected switch is the largest and the harmonic weight value is the smallest; when the No. 1 switch reports islanding, during the secondary detection, the No. 1 grid-connected switch will only detect the amplitude and frequency of the characteristic current injected by the busbar grid-connected switch. The amplitude data will be used as an important basis for the decision of the busbar grid-connected switch, while the harmonic data will only be considered as data of interest to the busbar grid-connected switch.

[0074] 3) The busbar grid-connected switch statistics report results, which are only 0 or 1. 0 represents no islanding, and 1 represents islanding. Secondary detection is equivalent to each grid-connected switch voting based on its most weighted variable value, and the busbar grid-connected switch counts the number of votes. When the percentage of votes with a value of 1 is greater than or equal to 80%, a command to disconnect the grid-connected switch is issued; when the percentage of votes with a value of 1 is less than 80%, the system continues to operate. Each grid-connected switch's secondary detection is equivalent to an expert proficient in amplitude, frequency, phase, and harmonic detection. When N experts from different fields combine their votes, the accuracy of the results is significantly improved.

[0075] Example 2

[0076] In one or more embodiments, an anti-islanding photovoltaic low-voltage grid-connected switch is disclosed, comprising:

[0077] The local modeling module is used to create local models of the above parameters when the transformer area is in a non-islanded system.

[0078] The islanding detection module is used to input the amplitude, frequency, phase and harmonic content data of the bus side voltage acquired in real time into the corresponding local model. When a certain parameter is abnormal, it is reported to the bus grid-connected switch, so that the bus grid-connected switch can control each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection according to the number of reported abnormal data.

[0079] In other embodiments, an anti-islanding busbar grid-connected switch is disclosed, comprising:

[0080] The decision function module is used to establish a decision function based on the amplitude, frequency, phase and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter.

[0081] The anti-islanding control module is used to determine the number M of photovoltaic low-voltage grid-connected switches that report abnormal data. When the ratio of the number M to the total number N of photovoltaic low-voltage grid-connected switches is greater than a set threshold, the bus grid-connected switch sends a tripping action command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a characteristic current of a set frequency to the transformer area bus and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters, and sends corresponding action commands to each photovoltaic low-voltage grid-connected switch according to the detection results.

[0082] The specific implementation methods of the above modules have been described in detail in Example 1, and will not be repeated here.

[0083] Example 3

[0084] In one or more embodiments, an anti-islanding system based on a photovoltaic low-voltage grid-connected switch is disclosed, including at least one photovoltaic low-voltage grid-connected switch and a bus grid-connected switch as described in Embodiment 2; the photovoltaic low-voltage grid-connected switch and the bus grid-connected switch communicate with each other.

[0085] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. An anti-islanding method based on photovoltaic low-voltage grid-connected switches, comprising interconnected bus grid-connected switches and at least one photovoltaic low-voltage grid-connected switch; characterized in that, The anti-islanding method includes the following process: The photovoltaic low-voltage grid-connected switch monitors the amplitude, frequency, phase, and harmonic content of the bus-side voltage in real time, and establishes local models of the above parameters when the distribution area is in a non-islanded system. The photovoltaic low-voltage grid-connected switch inputs the amplitude, frequency, phase and harmonic content data of the bus side voltage acquired in real time into the corresponding local model. When a certain parameter is abnormal, it is reported to the bus grid-connected switch so that the bus grid-connected switch can control each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection based on the number of reported abnormal data. The number M of photovoltaic low-voltage grid-connected switches that report abnormal data is determined. When the ratio of the number M to the total number N of photovoltaic low-voltage grid-connected switches is greater than a set threshold, the bus grid-connected switch sends a tripping action command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a characteristic current of a set frequency to the transformer area bus and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters. Based on the detection results, the bus grid-connected switch sends a corresponding action command to each photovoltaic low-voltage grid-connected switch. The busbar grid-connected switch sends a characteristic current of a set frequency to the transformer substation busbar and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters, specifically including: After the busbar grid-connected switch sends a characteristic current of a set frequency to the transformer area busbar, it sends an islanding detection command to all photovoltaic low-voltage grid-connected switches. The detection content is issued according to the weight value w corresponding to the detection parameters of the photovoltaic low-voltage grid-connected switches. Each photovoltaic low-voltage grid-connected switch performs secondary detection of the set parameters based on the issued detection content.

2. The anti-islanding method based on a photovoltaic low-voltage grid-connected switch as described in claim 1, characterized in that, The bus grid-connected switch controls each photovoltaic low-voltage grid-connected switch to trip or perform secondary testing based on the number of reported abnormal data, specifically including: The bus grid-connected switch establishes a decision function based on the amplitude, frequency, phase, and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter.

3. The anti-islanding method based on a photovoltaic low-voltage grid-connected switch as described in claim 2, characterized in that, Considering the weights of each parameter, a decision function is established, specifically including: The decision function is the sum of the product of each parameter value of a single photovoltaic low-voltage grid-connected switch and its weight; wherein, the bus grid-connected switch assigns corresponding weights to each photovoltaic low-voltage grid-connected switch based on the data reported by each photovoltaic low-voltage grid-connected switch.

4. The anti-islanding method based on a photovoltaic low-voltage grid-connected switch as described in claim 2, characterized in that, Based on the test results, corresponding action commands are sent to each photovoltaic low-voltage grid-connected switch, specifically including: When the number of photovoltaic low-voltage grid-connected switches that have become islanded exceeds the set threshold, the bus grid-connected switch sends a tripping command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a command to each photovoltaic low-voltage grid-connected switch to maintain the current action.

5. The anti-islanding method based on a photovoltaic low-voltage grid-connected switch as described in claim 1, characterized in that, Local models of the above parameters are established for each transformer station in a non-islanded system, specifically including: The local model of the voltage amplitude is a first-order Gaussian function, and the standard deviation of the function is the maximum voltage amplitude obtained by statistically analyzing the voltage amplitude fluctuation within a set time period collected in real time by the photovoltaic low-voltage grid-connected switch. The local model of the voltage frequency is a first-order Gaussian function, and the standard deviation of the function is the maximum value of the voltage frequency obtained by statistically analyzing the voltage frequency fluctuations within a set time period collected in real time by the photovoltaic low-voltage grid-connected switch. The local model of the voltage phase is a phase angle |T| with time interval T. φ2-φ The difference function of 1|; where, φ φ1 is the phase angle acquired at time T1, and φ2 is the phase angle acquired at time T2; the standard voltage phase angle change is calculated based on the time interval T. φ; According to | φ2-φ 1|- φ Calculate the voltage phase change value; The local model of the voltage harmonic content compares the data of each harmonic content with the standard data of each harmonic content to obtain the voltage harmonic distortion rate.

6. The anti-islanding method based on a photovoltaic low-voltage grid-connected switch as described in claim 5, characterized in that, When a certain parameter becomes abnormal, it is reported to the bus grid connection switch, specifically including: When the probability of a voltage amplitude or frequency appearing in its local model is 0, it is reported to the bus grid connection switch; when the probability density of voltage amplitude / frequency in a set range is greater than the set normal value, it is reported to the bus grid connection switch. When the voltage phase change value or harmonic distortion rate exceeds the set threshold, it is reported to the bus grid connection switch.

7. An anti-islanding photovoltaic low-voltage grid-connected switch, used to implement the anti-islanding method according to any one of claims 1-6, characterized in that, include: The local modeling module is used to create local models of the above parameters when the transformer area is in a non-islanded system. The islanding detection module is used to input the amplitude, frequency, phase and harmonic content data of the bus side voltage acquired in real time into the corresponding local model. When a certain parameter is abnormal, it is reported to the bus grid-connected switch, so that the bus grid-connected switch can control each photovoltaic low-voltage grid-connected switch to trip or perform secondary detection according to the number of reported abnormal data.

8. A grid-connected switch for an anti-islanding bus, used to implement the anti-islanding method according to any one of claims 1-6, characterized in that, include: The decision function module is used to establish a decision function based on the amplitude, frequency, phase and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter. The anti-islanding control module is used to determine the number M of photovoltaic low-voltage grid-connected switches that report abnormal data. When the ratio of the number M to the total number N of photovoltaic low-voltage grid-connected switches is greater than a set threshold, the bus grid-connected switch sends a tripping action command to each photovoltaic low-voltage grid-connected switch; otherwise, the bus grid-connected switch sends a characteristic current of a set frequency to the transformer area bus and controls each photovoltaic low-voltage grid-connected switch to perform secondary detection of set parameters, and sends corresponding action commands to each photovoltaic low-voltage grid-connected switch according to the detection results.

9. An anti-islanding system based on a photovoltaic low-voltage grid-connected switch, characterized in that, include: At least one photovoltaic low-voltage grid-connected switch as described in claim 7, and a busbar grid-connected switch as described in claim 8; The photovoltaic low-voltage grid-connected switch and the bus grid-connected switch communicate with each other.

10. An anti-islanding system based on a photovoltaic low-voltage grid-connected switch as described in claim 9, characterized in that, The bus grid-connected switch controls each photovoltaic low-voltage grid-connected switch to trip or perform secondary testing based on the number of reported abnormal data, specifically including: The bus grid-connected switch establishes a decision function based on the amplitude, frequency, phase, and harmonic content of the bus-side voltage detected in real time by each photovoltaic low-voltage grid-connected switch, taking into account the weight of each parameter.

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