A method and apparatus for detecting islands

Abstract

This application discloses an islanding detection method and apparatus. The method includes: monitoring the AC frequency of an inverter, which fluctuates within a preset range when the inverter is in normal control mode; when the instantaneous offset value of the AC frequency exceeds the preset range, the frequency before the instantaneous offset is taken as the first frequency; if the frequency in the first frequency data within a first preset time range is only greater than or only less than the first frequency, the AC frequency at the end of the first preset time is taken as the second frequency; continuously adjusting the output power of the inverter based on the change of the current AC frequency; and when the frequency in the second frequency data within a second preset time range is only greater than or only less than the second frequency, the inverter can be promptly instructed to report the islanding status. By using a two-step judgment method, the method distinguishes between islanding and normal load switching, avoiding the inverter actively adjusting the system voltage or frequency and improving the accuracy of islanding detection.

Description

Technical Field

[0001] This application relates to the field of communications, and more particularly to an islanding detection method and apparatus. Background Technology

[0002] Energy transition is a major trend in global energy development. With the coordinated development of new technologies on the power generation, grid, and load sides, traditional power systems will gradually evolve and move towards new energy power systems dominated by power electronic devices. Traditional power systems are dominated by large rotating generators, maintaining system voltage and frequency stability. A small number of power electronic devices control their own current based on the system's voltage and frequency, operating in grid-following mode. In new energy power systems, the proportion of rotating generators is decreasing, even to zero, while power electronic devices maintain system voltage and frequency stability, operating in grid-forming mode. During actual operation, power systems may experience faults due to various reasons, leading to isolated grids or systems.

[0003] Currently, islanding is determined by detecting whether small disturbances in the voltage, frequency, and power of the output current of power electronic devices cause a large deviation in system voltage or frequency. However, in grid forming mode, the system voltage or frequency may also experience a large instantaneous deviation when the normal load is switched on or off. In addition, grid forming mode is for the inverter to actively adjust the system voltage or frequency, resulting in low accuracy of islanding detection. Summary of the Invention

[0004] This application provides an island detection method and apparatus to reduce false positives and improve the accuracy of island detection.

[0005] The first aspect of this application provides an islanding detection method, comprising: real-time detection of the AC frequency of an inverter, wherein the AC frequency fluctuates within a preset range when the inverter is in normal control mode; when the AC frequency exceeds the preset range by an instantaneous offset value, and all frequencies in the first frequency data within a first preset time range are only greater than or only less than the first frequency, continuously adjusting the output power of the inverter according to the change in AC frequency, wherein the first frequency is the AC frequency before the instantaneous offset value exceeds the preset range, and the output power is used to influence the magnitude of the AC frequency; when all frequencies in the second frequency data within a second preset time range are only greater than or only less than the second frequency, reporting an islanding status, wherein the second frequency is the AC frequency at the end of the first preset time, and the islanding status indicates that the inverter has islanded.

[0006] In the aforementioned aspects, the AC frequency of the inverter is monitored. When the inverter is in normal control mode, this AC frequency fluctuates within a preset range. When the instantaneous deviation of the AC frequency exceeds the preset range, the AC frequency before the deviation is designated as the first frequency. The first frequency data within a first preset time range can be statistically analyzed. If the first frequency data is only greater than or only less than the first frequency, the AC frequency at the end of the first preset time is set as the second frequency. The inverter's output power is continuously adjusted based on the changes in the current AC frequency, causing the AC frequency to change. The AC frequency within a second preset time is then obtained as the second frequency data. When the second frequency data is still only greater than or only less than the first frequency, the inverter can be promptly instructed to report an islanding status, disconnecting the inverter from the local load. This secondary judgment method distinguishes between islanding and normal load switching, reducing false alarms and preventing the inverter from actively adjusting the system voltage or frequency, thus improving the accuracy of islanding detection.

[0007] In one possible implementation, before the above steps determine that the inverter has islanded, the method further includes: triggering a step of reporting the islanding status when the frequency in the second frequency data does not meet the preset frequency range.

[0008] In the above possible implementations, the islanding detection device may also report the islanding status only when it is determined that the frequencies in the second frequency data exceed the preset frequency range, even when all the frequencies in the second frequency data are distributed on one side of the second frequency, thereby improving the detection accuracy.

[0009] In one possible implementation, the above steps of continuously adjusting the inverter's output power according to changes in AC frequency include: increasing the output power when the AC frequency increases and decreasing the output power when the AC frequency decreases.

[0010] In the above possible implementation, the inverter is switched to islanding detection control mode, where the output power is in an unstable control state, and the output power is adjusted according to the positive feedback relationship between AC frequency and output power to improve the accuracy of islanding detection.

[0011] In one possible implementation, the output power is either active power or reactive power. Active power is the average value of the instantaneous power output by the inverter in one cycle, and reactive power is the power value of energy exchanged by the power source in one cycle.

[0012] In one possible implementation, the inverter operates in grid configuration mode, maintaining voltage and frequency stability of the photovoltaic power supply system.

[0013] A second aspect of this application provides an islanding detection device that can implement the methods described in the first aspect or any of the possible embodiments of the first aspect. The device includes corresponding units or modules for performing the described methods. The units or modules included in the device can be implemented in software and / or hardware. The device can be, for example, a network device, a chip, chip system, or processor that supports the network device in implementing the described methods, or a logic module or software capable of implementing all or part of the functions of the network device.

[0014] The third aspect of this application provides a photovoltaic power supply system, including: an inverter circuit and a controller, and an islanding detection device as described in claims 6-10, wherein the main circuit of the inverter is connected to the islanding detection circuit and the control circuit, and the control circuit is connected to the islanding detection device, wherein: the inverter circuit is used to convert DC power into AC power; the controller includes the islanding detection device described in the second aspect above.

[0015] A fourth aspect of this application provides a computer device, including: a processor coupled to a memory for storing instructions, which, when executed by the processor, cause the computer device to implement the methods described in the first aspect or any possible implementation thereof. The computer device may be, for example, a network device, or a chip or chip system supporting the implementation of the methods in a network device.

[0016] The fifth aspect of this application provides a computer-readable storage medium storing instructions that, when executed by a processor, implement the method provided in the first aspect or any possible implementation thereof. Attached Figure Description

[0017] Figure 1 A schematic diagram of the structure of a power system provided in this application embodiment;

[0018] Figure 2 This is a schematic diagram of the current island detection scheme provided in the embodiments of this application;

[0019] Figure 3 A flowchart illustrating an island detection method provided in an embodiment of this application;

[0020] Figure 4 This is a schematic diagram of a photovoltaic power supply system provided in an embodiment of this application;

[0021] Figure 5 A schematic diagram of a detection process provided in an embodiment of this application;

[0022] Figure 6 A timing diagram illustrating an island detection method provided in an embodiment of this application;

[0023] Figure 7 This is a schematic diagram illustrating a normal load switching scenario provided in an embodiment of this application;

[0024] Figure 8 This is a schematic diagram illustrating a possible islanding scenario provided in an embodiment of this application.

[0025] Figure 9 This is a schematic diagram illustrating a scenario where no islanding has occurred, as provided in an embodiment of this application.

[0026] Figure 10 This application provides a schematic diagram illustrating the confirmation of an islanding situation.

[0027] Figure 11 This is a schematic diagram of the structure of an island detection device provided in an embodiment of this application;

[0028] Figure 12 This is a schematic diagram of another photovoltaic power supply system provided in an embodiment of this application;

[0029] Figure 13 This is a schematic diagram of the structure of a computer device provided in an embodiment of this application. Detailed Implementation

[0030] This application provides an island detection method and apparatus to reduce false positives and improve the accuracy of island detection.

[0031] The embodiments of this application are described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. As those skilled in the art will recognize, with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0032] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0034] Furthermore, to better illustrate this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented without certain specific details. In some instances, methods, means, components, and circuits well-known to those skilled in the art have not been described in detail in order to highlight the main points of this application.

[0035] Figure 1 This is a schematic diagram of the structure of a power system provided in an embodiment of this application.

[0036] like Figure 1 As shown, the power system includes a DC power source 101, an inverter 102, and a power grid 103. The DC power source 101 is connected to the inverter 102, and the inverter 102 is connected to the power grid 103.

[0037] The DC power source device 101 includes one or more DC power sources, wherein the multiple DC power sources are connected in parallel, and any one of the DC power sources is used to provide DC power. This DC power source can be a photovoltaic cell, wind power cell, or other similar device. In the photovoltaic field, the DC power source included in the DC power source device can also be referred to as a photovoltaic panel.

[0038] Inverter 102 is used to convert the DC power output from DC source device 101 into AC power, and then transmit the converted AC power to grid 104 through step-up transformer 103. Inverter 102 includes one or more inverters, wherein multiple inverters are connected in parallel.

[0039] The power grid 103 is used to draw power from the output of the inverter 102. The power that the power grid 103 draws from the output of the inverter 102 can also be called grid-connected power. In use... Figure 1 In the power system shown, the grid-connected power of grid 103 is constant. However, the output power of the DC source included in DC source device 101 is usually unstable. For example, the output power of photovoltaic cells differs between daytime and nighttime. Therefore, to ensure the stability of the grid-connected power of grid 103, the power system may also include an energy storage system (not shown in the figure), which is connected to inverter device 102.

[0040] Energy transition is a major trend in global energy development. With the coordinated development of new technologies on the power generation, grid, and load sides, traditional power systems will gradually evolve and move towards new energy power systems dominated by power electronic devices. Traditional power systems are dominated by large rotating generators, maintaining system voltage and frequency stability. A small number of power electronic devices control their own current based on the system's voltage and frequency, operating in grid-following mode. In new energy power systems, the proportion of rotating generators is decreasing, even to zero, while power electronic devices maintain system voltage and frequency stability, operating in grid-forming mode. During actual operation, power systems may experience faults due to various reasons, leading to isolated grids or systems.

[0041] The islanding effect of inverters refers to the situation where, when the grid-connected switch trips, the inverter fails to detect the power outage in time and disconnects itself from the grid, ultimately forming a self-sufficient islanded power generation system consisting of the inverter and the load. The islanding effect can cause the following harms to the power system and related personnel:

[0042] 1) The grid-connected switch and related equipment may be damaged due to out-of-step closing.

[0043] 2) Maintenance personnel who believe the line is not energized will be at risk of safety.

[0044] 3) The islanding effect may prevent faults from being cleared and interfere with the restoration of the power grid.

[0045] Current island detection solutions, such as Figure 2 As shown, the scheme includes a DC power supply 201, an inverter 202, an AC power grid 203, and a control device 204. The control device 204 includes a sampling unit 2041, a power calculation unit 2042, a frequency detection unit 2043, a power control unit 2044, and an islanding judgment unit 2045.

[0046] The sampling unit 2041 includes voltage sampling and current sampling, which is used to convert the AC current and AC voltage in the power system (high voltage system) into corresponding signals in the control system (low voltage system) at the AC port of the inverter, and to achieve electrical isolation between the two systems.

[0047] The functions of the power calculation unit 2042 and the frequency detection unit 2043 are to perform power calculation and AC frequency estimation based on the AC voltage and current signals sampled by the sampling unit, and to calculate the actual active power, reactive power and AC frequency of the inverter output.

[0048] The power control unit 2044 performs inverter output power control functions to ensure that the actual output power of the inverter meets control requirements, such as guaranteeing certain active power, reactive power, and power factor requirements. The power control unit also includes a modulation function, which converts the modulated wave output by the control unit into a semiconductor switching drive signal that matches the inverter topology, directly controlling the on / off state of the semiconductors in the inverter topology. Currently, the active power and reactive power values ​​input to the power control unit 2044 are required to be fixed values.

[0049] The islanding detection unit 2045 can determine whether islanding has occurred based on whether the amplitude, frequency, phase, and harmonics of the inverter output voltage are abnormal. Depending on the detection target, it can be further categorized into over / under voltage detection, over / under frequency detection, voltage phase jump detection, and voltage harmonic detection. However, the main drawback of this scheme is its relatively large detection blind zone. For example, when the distributed power supply and local load are well matched, keeping the islanded microgrid frequency within the 49.5-50.5Hz range, the aforementioned over / under frequency detection method will fail. To reduce the detection blind zone, the sensitivity of the device needs to be improved, but setting the threshold is difficult.

[0050] Another approach is to detect islanding by generating small disturbances in the voltage, frequency, and power of the output current of power electronic devices to determine whether it causes a large deviation in the system voltage or frequency. However, in grid forming mode, the system voltage or frequency may also experience a large instantaneous deviation when the normal load is switched on or off. In addition, grid forming mode is for the inverter to actively adjust the system voltage or frequency, resulting in low accuracy of islanding detection.

[0051] To address the above problems, this application provides an island detection method, as described below.

[0052] Please see Figure 3 ,like Figure 3 The diagram shown is a flowchart of an island detection method provided in an embodiment of this application. The method includes:

[0053] Step 301. The islanding detection device monitors the AC frequency of the inverter in real time. The AC frequency fluctuates within a preset range when the inverter is in normal control mode.

[0054] In this embodiment, it should be noted that the inverter is an important component of the new energy power system. It converts the direct current (DC) generated by photovoltaic cells, wind turbines, and other power generation devices in the new energy power system into alternating current (AC) and feeds it to the power grid. The AC port of the inverter is used to transmit AC power to the grid. When the inverter experiences islanding, the AC frequency will change abruptly, exhibiting a significant shift within a short period. Therefore, islanding can be detected by the change in AC frequency. The islanding detection device can acquire and detect the AC frequency of the inverter's AC port in real time. The frequency is the number of times a periodic change occurs per unit time. The frequency of the AC power can be the frequency of the voltage or the frequency of the current. Example 1 of this application uses the voltage frequency as a case study. Figure 2 The sampling unit 2041 can collect the AC voltage at the inverter's AC port in real time and send it to the frequency detection unit 2043. The frequency detection unit 2043 estimates the AC frequency from the AC voltage and sends the estimated AC frequency to the islanding detection device. This embodiment applies to grid forming mode, where the inverter can maintain stable voltage and frequency in the photovoltaic power supply system. In normal control mode, the inverter will keep the AC frequency fluctuating within a preset range. Figure 2 The active and reactive power values ​​input to the medium power control unit 2044 are fixed values.

[0055] Step 302. When the AC frequency exceeds the preset range in an instantaneous offset value, and all frequencies in the first frequency data within the first preset time range are only greater than or only less than the first frequency, the output power of the inverter is continuously adjusted according to the change in AC frequency. The first frequency is the AC frequency before the instantaneous offset value exceeds the preset range, and the output power is used to influence the magnitude of the AC frequency.

[0056] In this embodiment, when the islanding detection device detects a momentary shift in the AC frequency and the momentary shift value exceeds the preset range of the AC frequency fluctuation, the inverter may become islanded. At this time, the frequency value of the AC frequency before the shift is the first frequency.

[0057] After an instantaneous shift in AC frequency, the islanding detection device can obtain first frequency data within a first preset time range. Specifically, it statistically analyzes the AC frequency values ​​within the first preset time range after an instantaneous shift exceeding the preset range, using these values ​​as the first frequency data. The device then compares the frequencies in the first frequency data with the first frequency itself. If the first frequency data contains both values ​​lower than and higher than the first frequency, it can be determined that the inverter is not islanded, and the power supply system is handling normal load switching, resulting in a sudden change in system power / voltage. If the frequencies in the first frequency data are only higher than or only lower than the first frequency (i.e., distributed only on one side of the waveform), it can be determined that the inverter is suspected of being islanded. In this case, the inverter's operating mode is changed from normal control mode to islanding detection control mode. The islanding detection device can use the currently acquired AC frequency as the second frequency, starting from this second frequency, and continuously adjust the inverter's output power based on subsequent changes in the acquired AC frequency, so that the AC frequency output by the inverter changes accordingly. In this system, the subsequently acquired AC frequency and the inverter's output power have a positive feedback relationship: when the AC frequency increases, the inverter's output power increases; when the AC frequency decreases, the inverter's output power decreases. For example, the islanding detection device can adjust... Figure 2 The power control unit inputs a power value to control the inverter's output power, where the input power value is the inverter's subsequent output power. The islanding detection device adjusts the inverter's output power based on changes in the AC frequency, which can be either active power or reactive power. It should be noted that active power output is the average instantaneous power emitted by the power supply within one cycle, representing the electrical power required to maintain the normal operation of the electrical equipment—that is, the power used to convert electrical energy into other forms of energy (mechanical energy, light energy, heat energy). Reactive power output is the power value exchanged between the magnetic field (or electric field) energy of the inductor (capacitor) and the power supply energy within one cycle. This embodiment uses active power output as an example.

[0058] Step 303. When all frequencies in the second frequency data within the second preset time range are only greater than or only less than the second frequency, the islanding detection device reports the islanding status. The second frequency is the AC frequency at the end of the first preset time. This islanding status indicates that the inverter has islanded.

[0059] In this embodiment, the islanding detection device can be set to a second preset time range. This second preset time range can be the same as or different from the first preset time range; no limitation is made here. After obtaining the currently acquired AC frequency as the second frequency, the islanding detection device can use this second preset time range as a time limit, adjusting the inverter's output power only within this time limit, and statistically analyzing the AC frequencies collected within this second preset time range as second frequency data. Then, the frequency in the second frequency data is compared with the second frequency. When no islanding occurs, the inverter is connected to the grid. In islanding detection mode, the frequency of the AC power output from the inverter's AC port will fluctuate around the second frequency, meaning its waveform will not be limited to one side of the second frequency. This allows for accurate detection of the absence of islanding. In other words, even if the inverter's AC frequency changes abruptly, the grid-connected inverter will not directly perform islanding protection, thus avoiding erroneous islanding protection caused by load switching in the power supply system.

[0060] After islanding occurs, the unique frequency positive feedback characteristic of islanding can quickly disrupt the frequency of the AC output from the inverter's AC port in islanding detection mode. This results in frequencies in the second frequency data being either greater than or less than the second frequency, meaning the frequencies in the second frequency data are only distributed on one side of the second frequency in the waveform. This allows for accurate detection of islanding. Rapid detection of islanding reduces detection time, improves reliability and safety, and enables the reporting of islanding status for rapid islanding protection. The islanding protection operation can be: 1) the inverter switches to islanding mode and continues to operate, supplying power to the load (electrical load); 2) the inverter shuts down, meaning the inverter stops supplying power to the grid, for example, by stopping the output of AC power through the AC port of the grid-connected inverter. Of course, islanding protection can also be implemented in other ways in this application embodiment, and this application embodiment is not limited to these methods.

[0061] For example, such as Figure 4As shown, the photovoltaic power supply system includes an inverter, a transformer, and a load. The AC port of the inverter is connected to the transformer via a first switch, and the output of the transformer is connected to the power grid via a second switch, and the output of the transformer is also connected to the load. When the power grid fails, the second switch opens, disconnecting the photovoltaic power supply system from the power grid. At this time, the inverter continues to supply power to the load, resulting in islanding. When islanding is detected by the islanding detection method provided in this embodiment, the first switch can be opened to stop the output of AC power through the inverter's AC port. Thus, the inverter will not continue to supply power to the load, thereby achieving islanding protection. Optionally, after detecting islanding in the inverter, the islanding detection device in this embodiment can also report the islanding status to the upper-level controller, which can then disconnect the inverter from the local load, or control the inverter to enter other modes; this is not limited here.

[0062] In one example, the islanding detection device can also determine that the inverter is islanded only when all frequencies in the second frequency data are greater than or less than the second frequency, and the frequencies in the second frequency data are determined to be outside the preset frequency range, thereby improving the detection accuracy.

[0063] For example, if islanding does not occur, the frequency of the AC bus voltage will be stabilized by the main grid and gradually return to near its normal value without significant deviation. This means the obtained second frequency data will be distributed on both sides of the second frequency during the return process. However, if islanding occurs, meaning there is no support from the main grid, the frequency of the AC bus voltage will be continuously pulled off course by the inverter's frequency positive feedback mechanism until system protection is triggered, thus detecting the islanding phenomenon.

[0064] The island detection device in this application mainly targets... Figure 2 The islanding detection unit 2045 in the control device 204 has been improved. Specifically, the steps of the islanding detection method can be as follows: Figure 5The schematic diagram of the detection process is shown below. Step 501: The islanding detection device is in normal control mode and starts detection; Step 502: After detecting the frequency offset on the AC side of the inverter, the islanding detection device starts to collect frequency data for a duration of t1 and obtains the frequency value before the frequency offset as f0; Step 503: The islanding detection device judges the offset of the obtained frequency data. If the obtained frequency data fluctuates around f0, it is considered that no islanding has occurred, the detection ends, and step 501 is executed. If the obtained frequency data is greater than or less than f0, step 504 is executed; Step 504: The islanding detection device enters the islanding detection control mode, obtains the current frequency value f1, and controls the inverter to enter the active power instability control state. For example, the output active power P is in the frequency f positive feedback mode, that is, when the frequency... When frequency f increases, the active power input to the power control unit 2044 increases, causing the power control unit 2044 to control the inverter to increase its output active power. When frequency f decreases, the active power input to the power control unit 2044 decreases, causing the control unit 2044 to control the inverter to decrease its output active power. At the same time, frequency data with a duration of t2 is started to be counted. Step 505: Determine the offset of the obtained frequency data. If the obtained frequency data is distributed on both sides of f1, it is considered that no islanding has occurred, and the current detection ends. Return to step 501. If the obtained frequency data is all greater than or less than f1, and the frequency is greater than the lower limit or upper limit of the islanding detection frequency threshold, then proceed to step 506. Step 506: The islanding detection device confirms that islanding has occurred and disconnects the inverter from the local load.

[0065] The timing diagram of the island detection method in this application is shown below. Figure 6 As shown, the system initially remains stable, with the inverter in normal control mode and the frequency unchanged. When the system experiences islanding or load switching, the system frequency fluctuates. After detecting the frequency offset, the frequency value before the offset is obtained as f0, and the first frequency offset judgment is initiated. At this time, the control mode remains unchanged.

[0066] There are two possible reasons for system frequency changes: normal load switching and islanding. If it's normal load switching, the frequency will be stabilized by the mains grid and return to near the rated frequency, thus causing the frequency to fluctuate. Figure 7 In the normal load switching scenario shown, the system frequency will be distributed above and below f0 due to the callback, indicating that islanding has not occurred and the inverter returns to normal control mode. If islanding has occurred, lacking the frequency stabilization capability of the main power grid, the system frequency is likely to remain consistently above or below f0, for example, as shown in the example below. Figure 8 The system appears to be in an islanding situation, with the system frequency consistently below f0.

[0067] However, due to the limited regulation capacity of the large power grid, even with normal load switching, the system frequency may remain below f0 within the t1 interval due to slow system regulation. Therefore, relying solely on... Figure 8 The situation is not enough to definitively conclude that the system has become islanded. Therefore, after t1, it is necessary to switch the inverter's control mode and perform further active detection to obtain the frequency value before the mode switch as f1.

[0068] At this point, two scenarios will still exist. Figure 8 The waveform will continue to develop into Figure 9 No island situation or Figure 10 This confirms the occurrence of islanding. If islanding has not occurred, the frequency will be stabilized by the main power grid and return to near the rated frequency, thus resulting in... Figure 9 In the scenario shown, the system frequency will be distributed above and below f1 due to the callback. In this case, islanding is not considered to have occurred, and the inverter returns to normal control mode. However, if islanding has occurred, due to the lack of frequency stabilization capability from the main power grid, the system frequency will be affected by the inverter's unstable control mode. The system frequency will be gradually pulled off course and unable to return to its normal value until it drops to the lower limit of the islanding detection frequency threshold fL. At this point, islanding is considered to have occurred. Figure 10 As shown.

[0069] This application embodiment monitors the AC frequency of the inverter in normal control mode. When the offset value of the AC frequency exceeds a preset range within a preset time, the AC frequency before the offset is taken as the first frequency. The first frequency data within the first preset time range can be statistically analyzed. If the first frequency data is only greater than or only less than the first frequency, the AC frequency at the end of the first preset time is set as the second frequency. The output power of the inverter is continuously adjusted by the change of the current AC frequency, so that the AC frequency changes, and the AC frequency within the second preset time is taken as the second frequency data. When the second frequency data is still only greater than or only less than the second frequency, the inverter can be promptly instructed to report the islanding status. Through a two-step judgment, the two situations of islanding and normal load switching are distinguished, reducing false judgments and avoiding the inverter actively adjusting the system voltage or frequency, thereby improving the accuracy of islanding detection.

[0070] The island detection method has been described above; the apparatus for implementing this method will be described below.

[0071] Please see Figure 11 ,like Figure 11 The diagram shown is a structural schematic of an island detection device provided in an embodiment of this application. The device 110 includes:

[0072] The detection unit 1101 is used to detect the AC frequency of the inverter in real time. The AC frequency fluctuates within a preset range when the inverter is in normal control mode.

[0073] The adjustment unit 1102 is used to continuously adjust the output power of the inverter according to the change of AC frequency when the instantaneous offset value of the AC frequency exceeds the preset range, and when all frequencies in the first frequency data within the first preset time range are only greater than or only less than the first frequency. The first frequency is the AC frequency before the instantaneous offset value exceeds the preset range, and the output power is used to affect the magnitude of the AC frequency.

[0074] The reporting unit 1103 is used to report the islanding status when all frequencies in the second frequency data within the second preset time range of the AC frequency are only greater than or only less than the second frequency. The islanding status indicates that the inverter has islanded.

[0075] Optionally, the device 110 further includes a judgment unit (not shown in the figure), which is specifically used to trigger the reporting unit 1103 when the frequency in the second frequency data does not meet the preset frequency range.

[0076] Optionally, the adjustment unit 1102 is specifically used to: increase the output power when the AC frequency increases; and decrease the output power when the AC frequency decreases.

[0077] Optionally, the output power can be either active power or reactive power. Active power is the average value of the instantaneous power output by the power supply in one cycle, while reactive power is the power value of energy exchanged by the inverter in one cycle.

[0078] Optionally, the inverter operates in grid configuration mode, maintaining the voltage and frequency stability of the photovoltaic power supply system.

[0079] The detection unit 1101 of the device 110 is used to perform Figure 3 In step 301 of the method embodiment, the adjustment unit 1102 of the device 110 is used to perform... Figure 3 In step 302 of the method embodiment, the reporting unit 1103 is used to execute... Figure 3 Step 303 in the method embodiment will not be repeated here.

[0080] This application provides a photovoltaic power supply system 120, the system structure of which is as follows: Figure 12 As shown, it includes an inverter circuit 1201 and a controller 1202, wherein:

[0081] Inverter circuit 1201 is used to convert DC power into AC power;

[0082] The controller 1202 includes a sampling unit 12021, a power calculation unit 12022, a frequency detection unit 12023, a power control unit 12024, and an islanding detection device 12025. The sampling unit 12021, power calculation unit 12022, frequency detection unit 12023, and power control unit 12024 are used to execute... Figure 2 The functions of the sampling unit 2041, power calculation unit 2042, frequency detection unit 2043, and power control unit 2044 are as follows:

[0083] The islanding detection device 12025 is used to detect the AC frequency of the inverter circuit 1201 from the frequency detection unit 12023 in real time. The inverter circuit 1201 is in normal control mode, and the AC frequency fluctuates within a preset range. When the AC frequency instantaneously deviates beyond the preset range, and all frequencies in the first frequency data within a first preset time range are only greater than or only less than the first frequency, the power control unit 12024 continuously adjusts the output power of the inverter circuit 1201 according to the change in AC frequency. The first frequency is the AC frequency before the instantaneous deviance exceeds the preset range, and the output power is used to influence the magnitude of the AC frequency. When all frequencies in the second frequency data within a second preset time range are only greater than or only less than the second frequency, an islanding status is reported. The second frequency is the AC frequency at the end of the first preset time. The islanding status indicates that the inverter 1201 has islanded and triggers inverter protection, such as disconnecting the inverter from the local load. The islanding detection device 12025 can achieve the above-mentioned... Figure 3 The island detection device in the method embodiments has the functions and / or performs the various steps.

[0084] Figure 13 The diagram shown illustrates a possible logical structure of a computer device 130 provided in an embodiment of this application. The computer device 130 includes a processor 1301, a communication interface 1302, a storage system 1303, and a bus 1304. The processor 1301, communication interface 1302, and storage system 1303 are interconnected via the bus 1304. In an embodiment of this application, the processor 1301 is used to control and manage the operations of the computer device 130; for example, the processor 1301 is used to execute... Figure 3 The steps performed by the island detection device in the method embodiment are described. Communication interface 1302 is used to support communication by computer device 130. Storage system 1303 is used to store program code and data of computer device 130.

[0085] The processor 1301 can be a central processing unit, a general-purpose processor, a digital signal processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. The processor 1301 can also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a digital signal processor and a microprocessor, etc. The bus 1304 can be a Peripheral Component Interconnect (PCI) bus or an Extended Industry Standard Architecture (EISA) bus, etc. The bus can be divided into address bus, data bus, control bus, etc. For ease of representation, Figure 13 Only one thick line is used in the diagram, but this does not mean that there is only one bus or one type of bus.

[0086] The detection unit 1101, adjustment unit 1102 and reporting unit 1103 in device 110 are equivalent to the processor 1301 in computer device 130.

[0087] The computer device 130 in this embodiment can correspond to the above-described... Figure 3 The island detection device in the method embodiment, the communication interface 1302 in the computer device 130 can realize the above-mentioned... Figure 3 For the sake of brevity, the functions of the island detection device and / or the various steps implemented in the method embodiments will not be described in detail here.

[0088] It should be understood that the division of units in the above device is merely a logical functional division. In actual implementation, they can be fully or partially integrated into a single physical entity, or they can be physically separated. Furthermore, all units in the device can be implemented entirely through software calls from processing elements; all units can be implemented entirely in hardware; or some units can be implemented through software calls from processing elements, and others in hardware. For example, each unit can be a separate processing element, or it can be integrated into a chip within the device. Alternatively, it can be stored as a program in memory, called and executed by a processing element of the device. Moreover, these units can be fully or partially integrated together, or implemented independently. The processing element mentioned here can also be called a processor, which can be an integrated circuit with signal processing capabilities. In the implementation process, each step of the above method or each of the above units can be implemented through integrated logic circuits in the processor element or through software calls from processing elements.

[0089] In one example, a unit in any of the above devices can be one or more integrated circuits configured to implement the methods described above, such as: one or more application-specific integrated circuits (ASICs), or one or more digital signal processors (DSPs), or one or more field-programmable gate arrays (FPGAs), or a combination of at least two of these forms of integrated circuits. As another example, when a unit in the device can be implemented in the form of a processing element scheduler, the processing element can be a general-purpose processor, such as a central processing unit (CPU) or other processor capable of calling programs. Furthermore, these units can be integrated together to implement a system-on-a-chip (SOC).

[0090] In another embodiment of this application, a computer-readable storage medium is also provided, which stores computer-executable instructions. When the processor of the device executes the computer-executable instructions, the device executes the method executed by the island detection device in the above method embodiment.

[0091] In another embodiment of this application, a computer program product is also provided, which includes computer-executable instructions stored in a computer-readable storage medium. When the processor of the device executes the computer-executable instructions, the device performs the method executed by the islanding detection device in the above-described method embodiments.

[0092] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0093] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0094] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0095] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0096] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. An island detection method, characterized in that, include: The AC frequency of the inverter is detected in real time, and the AC frequency fluctuates within a preset range when the inverter is in normal control mode. When the AC frequency deviates from the preset range by an instantaneous offset value, and all frequencies in the first frequency data within the first preset time range are only greater than or only less than the first frequency, the output power of the inverter is continuously adjusted according to the change of the AC frequency. The first frequency is the AC frequency before the instantaneous offset value exceeds the preset range, and the output power is used to influence the magnitude of the AC frequency. When all frequencies in the second frequency data within the second preset time range are only greater than or only less than the second frequency, an islanding status is reported. The second frequency is the AC frequency at the end of the first preset time. The islanding status indicates that the inverter has islanded.

2. The method according to claim 1, characterized in that, Before reporting the island status, the method further includes: When the frequency in the second frequency data does not meet the preset frequency range, the step of reporting the island status is triggered.

3. The method according to any one of claims 1-2, characterized in that, The step of continuously adjusting the output power of the inverter according to the change of the AC frequency includes: When the AC frequency increases, the output power is increased; When the AC frequency decreases, the output power is reduced.

4. The method according to any one of claims 1-2, characterized in that, The output power is either active power or reactive power. The active power is the average value of the instantaneous power output by the power supply in one cycle, and the reactive power is the power value of energy exchanged by the inverter in one cycle.

5. The method according to any one of claims 1-2, characterized in that, The inverter operates in grid configuration mode and is used to maintain the voltage and frequency stability of the photovoltaic power supply system.

6. An island detection device, characterized in that, include: The detection unit is used to detect the AC frequency of the inverter in real time, and the AC frequency fluctuates within a preset range when the inverter is in normal control mode. An adjustment unit is used to continuously adjust the output power of the inverter according to the change of the AC frequency when the instantaneous offset value of the AC frequency exceeds the preset range, and when all frequencies in the first frequency data within a first preset time range are only greater than or only less than the first frequency. The first frequency is the AC frequency before the instantaneous offset value exceeds the preset range, and the output power is used to affect the magnitude of the AC frequency. The reporting unit is used to report an islanding status when all frequencies in the second frequency data within the second preset time range of the AC frequency are only greater than or only less than the second frequency, where the second frequency is the AC frequency at the end of the first preset time, and the islanding status indicates that the inverter has islanded.

7. The apparatus according to claim 6, characterized in that, The device further includes a judgment unit, which is specifically used for: When the frequency in the second frequency data does not meet the preset frequency range, the reporting unit is triggered.

8. The apparatus according to any one of claims 6-7, characterized in that, The adjustment unit is specifically used for: When the AC frequency increases, the output power is increased; When the AC frequency decreases, the output power is reduced.

9. The apparatus according to any one of claims 6-7, characterized in that, The output power is either active power or reactive power. The active power is the average value of the instantaneous power output by the power supply in one cycle, and the reactive power is the power value of energy exchanged by the inverter in one cycle.

10. The apparatus according to any one of claims 6-7, characterized in that, The inverter operates in grid configuration mode, and maintains the voltage and frequency stability of the photovoltaic power supply system.

11. A photovoltaic power supply system, characterized in that, include: Inverter circuit and controller, The inverter circuit is used to convert DC power into AC power. The controller includes the island detection device as described in any one of claims 6-10.

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