Island detection method, device, storage medium and converter system

Abstract

The present application provides an island detection method, device, storage medium and converter system. The method includes: real-time monitoring of whether the first AC frequency of the grid-type converter in normal operating mode falls within a preset first frequency range; if the first AC frequency does not fall within the first frequency range, then calculating the target active power command value according to the offset of the first AC frequency relative to the rated frequency of the system; adjusting the active power command value of the grid-type converter from the original value to the target active power command value; monitoring whether the second AC frequency of the grid-type converter after being adjusted to the target active power command value falls within a preset second frequency range; if it is monitored that the second AC frequency does not fall within the second frequency range, then identifying whether the second AC frequency within the first preset time period from the moment when the second AC frequency first crosses the limit does not fall within the second frequency range; if so, determining that an island occurs. The present application can improve the accuracy of island detection for grid-type converters.

Description

Technical Field

[0001] The present application relates to the field of electric power technology, and in particular to an island detection method, device, storage medium and converter system. Background Art

[0002] Renewable energy generation is accelerating its transformation from auxiliary power source to main power source. The "double high" (high proportion of new energy and high proportion of power electronic equipment) characteristics of the new power system have changed the stable form and operation characteristics of the power system. Problems such as reduced short-circuit capacity, reduced inertia, and lack of damping have brought challenges to the safe and stable operation of the future power system. With the continuous deepening of theoretical research on network control technology, the industry has generally believed that network control is a feasible solution to ensure the safe and stable operation of new power systems.

[0003] Among them, grid-connected converters are widely used in new power systems because they have voltage source output characteristics and can operate stably in both grid-connected mode and islanded mode without the need for control structure switching. However, when unplanned islanding occurs, the output voltage and frequency of the grid-connected converter are relatively stable, so the traditional method may not be able to detect the occurrence of islanding. Summary of the invention

[0004] The embodiments of the present application provide an island detection method, device, storage medium and converter system, which can improve the accuracy of island detection for a grid-type converter.

[0005] In a first aspect, the present application provides an island detection method, the method comprising:

[0006] Real-time monitoring of whether a first AC frequency of the grid-type converter in a normal operating mode falls within a preset first frequency range; the first frequency range is a normal operating frequency range of the grid-type converter;

[0007] If the first AC frequency does not fall within the first frequency range, calculating a target active power command value according to an offset of the first AC frequency relative to a rated frequency of the system;

[0008] Adjusting the active power command value of the grid-connected converter from an original value to the target active power command value;

[0009] monitoring whether the second AC frequency of the grid-connected converter after being adjusted to the target active power command value falls within a preset second frequency range; the second frequency range is a range of critical frequency for island protection;

[0010] If it is monitored that the second AC frequency does not fall within the second frequency range, identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit;

[0011] If so, it is determined that an island has occurred.

[0012] In one embodiment, the step of identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit includes:

[0013] Identify whether the second AC frequencies within the first preset time period from the moment when the second AC frequency crosses the limit for the first time are all greater than the upper limit value of the second frequency range, or whether they are all less than the lower limit value of the second frequency range.

[0014] In one embodiment, the method further comprises:

[0015] If the second AC frequency of the grid-type converter is within the second frequency range within a second preset time from the moment the target active power command value is adjusted, it is determined that islanding has not occurred, and the active power command value of the grid-type converter is adjusted to the original value.

[0016] In one embodiment, the step of calculating the target active power command value according to the offset of the first AC frequency relative to the system operating frequency includes:

[0017] The target active power command value is calculated based on the following formula:

[0018]

[0019] Among them, P ref is the target active power command value, m is the preset island detection coefficient, f is the first AC frequency, and f 1 is the system rated frequency, P 0 It is the original value of the active power command value.

[0020] In one embodiment, the value range of the island detection coefficient is:

[0021]

[0022] Among them, K p is the droop coefficient of the active synchronous control loop of the grid-connected converter.

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

[0024] If it is determined that an island has occurred, the island status will be reported.

[0025] In one embodiment, the method further comprises:

[0026] If the second AC frequency does not fall within the second frequency range, and the second AC frequencies within the first preset time period from the time when the second AC frequency first crosses the limit do not all fall within the second frequency range, it is determined that other types of disturbances occur.

[0027] In a second aspect, the present application provides an island detection device, the device comprising:

[0028] A first monitoring module is used to monitor in real time whether a first AC frequency of the grid-type converter in a normal operating mode falls within a preset first frequency range; the first frequency range is a normal operating frequency range of the grid-type converter;

[0029] a calculation module, configured to calculate a target active power command value according to an offset of the first AC frequency relative to a system rated frequency when the first AC frequency does not fall within the first frequency range;

[0030] An instruction value adjustment module, used for adjusting the active power instruction value of the grid-connected converter from an original value to the target active power instruction value;

[0031] A second monitoring module is used to monitor whether the second AC frequency of the grid-type converter after being adjusted to the target active power command value falls within a preset second frequency range; the second frequency range is a range of an island protection critical frequency;

[0032] A frequency over-limit judgment module, for, when it is detected that the second AC frequency does not fall within the second frequency range, identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit;

[0033] The island determination module is used to determine that an island occurs when it is identified that the second AC frequency does not fall into the second frequency range within a first preset time period since the second AC frequency first crosses the limit.

[0034] In a third aspect, the present application provides a storage medium storing computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of any of the above-mentioned island detection methods.

[0035] In a fourth aspect, the present application provides a converter system, comprising:

[0036] A grid-type converter is used to access the grid system via a switch unit;

[0037] A sampling unit, used for collecting the output voltage and output current of the grid-type converter;

[0038] A frequency detection unit, used for calculating the AC frequency of the grid-type converter based on the output voltage and output current collected by the sampling unit;

[0039] A control unit is used to obtain the AC frequency fed back by the frequency detection unit in real time, and execute the steps of any of the above-mentioned island detection methods.

[0040] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0041] The island detection method, device, storage medium and converter system provided by the present application monitor whether the AC frequency falls within the first frequency range when the grid-type converter is operating normally. When it is detected that it does not fall within the first frequency range, the active power command value of the grid-type converter is adjusted according to the offset of the first AC frequency relative to the rated frequency of the system, and the original value is adjusted to the target active power command value. Then, the AC frequency of the grid-type converter in the current mode is monitored to see whether it falls within the second frequency range. The first crossing moment is when it is detected that it does not fall within the second frequency range. It is identified whether the AC frequency within the first preset time period does not fall within the second frequency range to determine whether an island occurs. The island detection of the grid-type converter can be achieved without injecting a disturbance signal, and the occurrence of an island is determined by the AC frequency within the first preset time period, thereby eliminating misjudgments caused by other disturbances and improving the accuracy of unplanned island detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0043] Figure 1 is a structural block diagram of a converter system in one embodiment;

[0044] Figure 2 is a flow chart of an island detection method in one embodiment;

[0045] Figure 3 is a structural block diagram of an island detection device in one embodiment;

[0046] Figure 4 FIG. 1 is a diagram of the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0048] In some embodiments, the island detection method provided in the embodiments of the present application is applied to Figure 1 The control unit 140 in the converter system 100 shown. The converter system includes a grid-type converter 110, a sampling unit 120, a frequency detection unit 130 and a control unit 140. Among them, the grid-type converter 110 is used to access the power grid system through a switch unit; the sampling unit 120 is used to collect the output voltage and output current of the grid-type converter 110; the frequency detection unit 130 is used to calculate the AC frequency of the grid-type converter 110 based on the output voltage and output current collected by the sampling unit 120; the control unit 140 is used to obtain the AC frequency fed back by the frequency detection unit 130 in real time and execute the island detection method. The control unit 140 is also used to calculate the active and reactive power output by the grid-type converter 110 according to the output voltage and current signals collected by the sampling unit 120, and to generate a pulse trigger signal to control the switch device of the grid-type converter 110 through power synchronization control and voltage / current inner loop control.

[0049] In some embodiments, the control unit 140 includes a power calculation module, an island detection module, a voltage / current inner loop control module and a power synchronization control module. The power calculation module is used to calculate the active and reactive power output by the grid-type converter 110 based on the output voltage and output current collected by the sampling unit 120; the island detection module is used to execute the steps of the island detection method; the voltage / current inner loop control module and the power synchronization control are used to cooperate in generating a pulse trigger signal to control the switch device of the grid-type converter 110.

[0050] like Figure 2 As shown, an embodiment of the present application provides an island detection method, the method comprising:

[0051] Step S201 : monitoring in real time whether a first AC frequency of the grid-connected converter in a normal operation mode falls within a preset first frequency range.

[0052] The first frequency range is the normal operating frequency range of the grid-connected converter, which can be set according to the grid standard. For example, in some embodiments, it can be [49.8, 50.2 Hz].

[0053] Step S202: if the first AC frequency falls within the first frequency range, it is determined that islanding does not occur.

[0054] At this time, the process returns to step S201 to continue monitoring the first AC frequency.

[0055] Step S203: if the first AC frequency does not fall within the first frequency range, then calculating the target active power command value according to the offset of the first AC frequency relative to the system rated frequency.

[0056] The system rated frequency refers to the rated frequency of the power system in steady-state operation, such as 50 Hz or 60 Hz.

[0057] When the first AC frequency does not fall within the first frequency range, it may be a fluctuation generated under normal working conditions, or it may be an offset caused by disturbance, or an islanding may occur. Since the frequency of the grid-type converter is relatively stable, even if an islanding occurs, the offset is small, and it is impossible to make an accurate judgment at this time. In this embodiment, the target active power command value is calculated based on the offset of the first AC frequency relative to the rated frequency of the system to control the grid-type converter, aggravate the frequency offset of the grid-type converter, and then make a judgment.

[0058] Step S204: adjusting the active power command value of the grid-connected converter from the original value to the target active power command value.

[0059] Based on the droop characteristics of the grid-type converter, the frequency deviation of the grid-type converter can be aggravated by adjusting the active power command value to the target active power command value.

[0060] Step S205 , monitoring whether the second AC frequency of the grid-connected converter after being adjusted to the target active power command value falls within a preset second frequency range.

[0061] The second frequency range is the range of the critical frequency for island protection, and the specific range may be set according to the grid standard. For example, in some embodiments, the second frequency range may be [49.3, 50.5 Hz].

[0062] Step S206: if it is detected that the second AC frequency does not fall within the second frequency range, it is identified whether the second AC frequency does not fall within the second frequency range within a first preset time period from the time when the second AC frequency first crosses the limit.

[0063] The first over-limit moment refers to the moment when the second AC frequency is first identified as not falling within the second frequency range after the active power command value is adjusted to the target active power command value. Since normal operation or other types of disturbances may also cause the second AC frequency to exceed the limit, it is necessary to monitor the second AC frequency within the first preset time period to accurately determine whether an island occurs.

[0064] Step S207: If yes, it is determined that an island has occurred.

[0065] Step S208: if the second AC frequency does not fall within the second frequency range, and the second AC frequency does not fall within the second frequency range within the first preset time period from the time when the second AC frequency first crosses the limit, it is determined that other types of disturbances occur.

[0066] If other types of disturbances occur, the second AC frequency will exceed the limit, and the second AC frequency is an oscillating change. Therefore, if the second AC frequency within the first preset time period from the moment the second AC frequency first exceeds the limit does not fall into the second frequency range, that is, it partially falls into the second frequency range and partially exceeds the limit, it is determined that other types of disturbances have occurred. This embodiment observes the second AC frequency within a period of time by setting a time window, and makes a judgment based on the characteristics of the island state and the difference between other types of disturbances, thereby eliminating the situation where other types of disturbances are mistakenly judged as islands, thereby improving accuracy. In some embodiments, the first preset time period is 200ms.

[0067] Step S209: if the second AC frequency is within the second frequency range within the second preset time period from the moment when the grid-type converter is adjusted to the target active power command value, it is determined that islanding does not occur, and the active power command value of the grid-type converter is adjusted to the original value.

[0068] Return to step S201 and continue to monitor the first AC frequency. Since the active power command value of the grid-type converter is adjusted, the control unit controls it according to the adjusted active power command value, and the frequency change is a continuous change, so a time window of a second preset time length is set to observe the second AC frequency. If both are within the second frequency range, it is determined that the island has not occurred, avoiding misjudgment due to the lag of the frequency change. At this time, it indicates that the first AC frequency is over-limit and is a change under non-islanding disturbance, so the active power command value can be adjusted back to the original value to control the normal operation of the grid-type converter and continue monitoring.

[0069] The island detection method provided by the present application monitors whether the AC frequency falls into the first frequency range when the grid-type converter is operating normally. When it is detected that it does not fall into the first frequency range, the active power command value of the grid-type converter is adjusted according to the offset of the first AC frequency relative to the rated frequency of the system, and the original value is adjusted to the target active command value. Then, the AC frequency of the grid-type converter in the current mode is monitored to see whether it falls into the second frequency range. When it is detected that it does not fall into the second frequency range, it is the first time to cross the limit. It is identified whether the AC frequency within the first preset time does not fall into the second frequency range to determine whether an island occurs. The island detection of the grid-type converter can be achieved without injecting a disturbance signal, and the power quality of the system in the grid-connected mode will not be adversely affected. The occurrence of the island is judged by the AC frequency within the first preset time, and the misjudgment caused by other disturbances is eliminated, thereby improving the accuracy of unplanned island detection. On the other hand, since only the frequency needs to be monitored and the active power command value needs to be regulated, it can be applied to the original control system of the grid-type converter, which is simple to implement and highly adaptable.

[0070] In one embodiment, the step of identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit includes:

[0071] Identify whether the second AC frequencies within a first preset time period from the moment when the second AC frequency first crosses the limit are all greater than the upper limit value of the second frequency range, or whether they are all less than the lower limit value of the second frequency range.

[0072] In this embodiment, based on the frequency change characteristics of the grid-type converter in the island state, when an island occurs, the change in the second AC frequency should be a unidirectional over-limit rather than an oscillating change. By identifying whether the second AC frequency is greater than the upper limit value of the second frequency range within a first preset time period from the moment the second AC frequency first over-limits, or whether it is less than the lower limit value of the second frequency range, misjudgment caused by other factors can be further eliminated to improve the accuracy of island detection.

[0073] In one embodiment, the step of calculating the target active power command value according to the offset of the first AC frequency relative to the system operating frequency includes:

[0074] The target active power command value is calculated based on the following formula:

[0075]

[0076] Among them, P ref is the target active power command value, m is the preset island detection coefficient, f is the first AC frequency, and f 1 is the system rated frequency, P 0 It is the original value of the active power command value.

[0077] In one embodiment, the value range of the island detection coefficient is:

[0078]

[0079] Among them, K p is the droop coefficient of the active synchronous control loop of the grid-connected converter.

[0080] In this embodiment, the value range of the island detection coefficient is limited to avoid excessive adjustment when adjusting the active power command value, which may cause system instability. The larger the value of the island detection coefficient within this range, the smaller the island non-detection zone (NDZ), the shorter the detection time, but the smaller the stability margin of the grid-type converter. Those skilled in the art can make a selection according to actual needs.

[0081] In one embodiment, the method further comprises:

[0082] If it is determined that an island has occurred, the island status will be reported.

[0083] In this embodiment, when the control unit determines that an islanding occurs, it will report the islanding state to the superior control system and perform islanding protection in time. If the grid-type converter cannot detect the islanding state in time, the grid-connected switch and related equipment may be damaged due to out-of-step closing. In addition, it may also cause the fault to be unable to be cleared in time, affecting the restoration of the power grid to normal operating state. At the same time, maintenance personnel who believe that the line is not energized will be threatened. The islanding detection method provided by the present application can achieve timely and accurate detection, and can report in time when an islanding occurs, so as to perform islanding protection in time, avoid the occurrence of the above-mentioned hazards, and improve the stability and safety of system operation.

[0084] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0085] The following is a description of an island detection device provided in an embodiment of the present application. The island detection device described below and the island detection method described above can be referenced to each other.

[0086] like Figure 3 As shown, the embodiment of the present application provides an island detection device 300, the device comprising:

[0087] The first monitoring module 301 is used to monitor in real time whether the first AC frequency of the grid-type converter in the normal operating mode falls within a preset first frequency range; the first frequency range is the normal operating frequency range of the grid-type converter;

[0088] A calculation module 302, configured to calculate a target active power command value according to an offset of the first AC frequency relative to a system rated frequency when the first AC frequency does not fall within the first frequency range;

[0089] The command value adjustment module 303 is used to adjust the active power command value of the grid-connected converter from the original value to the target active power command value;

[0090] The second monitoring module 304 is used to monitor whether the second AC frequency of the grid-type converter after being adjusted to the target active power command value falls within a preset second frequency range; the second frequency range is a range of the critical frequency of island protection;

[0091] The frequency over-limit judgment module 305 is used to identify whether the second AC frequency has not fallen into the second frequency range within a first preset time period since the second AC frequency first over-limited the second frequency range when the second AC frequency is monitored to not fall into the second frequency range;

[0092] The islanding determination module 306 is configured to determine that an islanding occurs when it is identified that the second AC frequency does not fall within the second frequency range within a first preset time period from the time when the second AC frequency first crosses the limit.

[0093] In one embodiment, the frequency limit crossing judgment module is configured to perform the following steps:

[0094] Identify whether the second AC frequencies within the first preset time period from the moment when the second AC frequency crosses the limit for the first time are all greater than the upper limit value of the second frequency range, or whether they are all less than the lower limit value of the second frequency range.

[0095] In one of the embodiments, the island determination module is further configured to perform the following steps:

[0096] If the second AC frequency of the grid-type converter is within the second frequency range within a second preset time from the moment the target active power command value is adjusted, it is determined that islanding has not occurred, and the active power command value of the grid-type converter is adjusted to the original value.

[0097] In one embodiment, the computing module is configured to perform the following steps:

[0098] The target active power command value is calculated based on the following formula:

[0099]

[0100] Among them, P ref is the target active power command value, m is the preset island detection coefficient, f is the first AC frequency, and f 1 is the system rated frequency, P 0 It is the original value of the active power command value.

[0101] In one embodiment, the island detection device further includes:

[0102] The reporting module is used to report the island status when it is determined that an island occurs.

[0103] In one of the embodiments, the island determination module is further configured to perform the following steps:

[0104] If the second AC frequency does not fall within the second frequency range, and the second AC frequency does not fall within the second frequency range within a first preset time period from the time when the second AC frequency first crosses the limit, it is determined that other types of disturbances occur.

[0105] The division of each module in the above-mentioned island detection device is only for illustration. In other embodiments, the island detection device can be divided into different modules as needed to complete all or part of the functions of the above-mentioned island detection device. Each module in the above-mentioned island detection device can be implemented in whole or in part by software, hardware and a combination thereof. Each of the above-mentioned modules can be embedded in or independent of the processor in the computer device in the form of hardware, or can be stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to each of the above modules.

[0106] In one embodiment, the present application further provides a storage medium storing computer-readable instructions. When the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the island detection method as described in any of the above embodiments.

[0107] In one embodiment, a control unit of the converter system stores computer-readable instructions, and when the one or more processors execute the computer-readable instructions, the steps of the islanding detection method as described in any of the above embodiments are performed.

[0108] In one embodiment, a computer device is provided as a control unit of a converter system. The computer device may be a terminal, and its internal structure diagram may be as shown in FIG. Figure 4 As shown. The computer device includes a processor, a memory, a communication interface, a display screen and an input device connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal in a wired or wireless manner, and the wireless manner can be achieved through WIFI, a mobile cellular network, NFC (near field communication) or other technologies. When the computer program is executed by the processor, an island detection method is implemented. The display screen of the computer device can be a liquid crystal display screen or an electronic ink display screen, and the input device of the computer device can be a touch layer covered on the display screen, or a key, trackball or touchpad set on the computer device housing, or an external keyboard, touchpad or mouse, etc.

[0109] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0110] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The processor involved in each embodiment provided in this application can be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, etc., but is not limited thereto.

[0111] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0112] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0113] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can refer to each other.

[0114] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An island detection method, characterized in that: The method comprises: Real-time monitoring of whether a first AC frequency of the grid-type converter in a normal operating mode falls within a preset first frequency range; the first frequency range is a normal operating frequency range of the grid-type converter; If the first AC frequency does not fall within the first frequency range, calculating a target active power command value according to an offset of the first AC frequency relative to a rated frequency of the system; Adjusting the active power command value of the grid-connected converter from an original value to the target active power command value; monitoring whether the second AC frequency of the grid-connected converter after being adjusted to the target active power command value falls within a preset second frequency range; the second frequency range is a range of critical frequency for island protection; If it is monitored that the second AC frequency does not fall within the second frequency range, identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit; If so, it is determined that an island has occurred.

2. The island detection method according to claim 1, characterized in that: The identifying whether the second AC frequency does not fall into the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit includes: Identify whether the second AC frequencies within the first preset time period from the moment when the second AC frequency crosses the limit for the first time are all greater than the upper limit value of the second frequency range, or whether they are all less than the lower limit value of the second frequency range.

3. The island detection method according to claim 1, characterized in that: The method further comprises: If the second AC frequency of the grid-type converter is within the second frequency range within a second preset time from the moment the target active power command value is adjusted, it is determined that islanding has not occurred, and the active power command value of the grid-type converter is adjusted to the original value.

4. The island detection method according to claim 1, characterized in that: The calculating the target active power command value according to the offset of the first AC frequency relative to the system operating frequency includes: The target active power command value is calculated based on the following formula: Among them, P ref is the target active power command value, m is the preset island detection coefficient, f is the first AC frequency, f1 is the system rated frequency, and P0 is the original value of the active power command value.

5. The island detection method according to claim 4, characterized in that: The value range of the island detection coefficient is: Among them, K p is the droop coefficient of the active synchronous control loop of the grid-connected converter.

6. The island detection method according to any one of claims 1 to 5, characterized in that: The method further comprises: If it is determined that an island has occurred, the island status will be reported.

7. The island detection method according to claim 1, characterized in that: The method further comprises: If the second AC frequency does not fall within the second frequency range, and the second AC frequencies within the first preset time period from the time when the second AC frequency first crosses the limit do not all fall within the second frequency range, it is determined that other types of disturbances occur.

8. An island detection device, characterized in that: The device comprises: A first monitoring module is used to monitor in real time whether a first AC frequency of the grid-type converter in a normal operating mode falls within a preset first frequency range; the first frequency range is a normal operating frequency range of the grid-type converter; a calculation module, configured to calculate a target active power command value according to an offset of the first AC frequency relative to a system rated frequency when the first AC frequency does not fall within the first frequency range; An instruction value adjustment module, used for adjusting the active power instruction value of the grid-connected converter from an original value to the target active power instruction value; A second monitoring module is used to monitor whether the second AC frequency of the grid-type converter after being adjusted to the target active power command value falls within a preset second frequency range; the second frequency range is a range of an island protection critical frequency; A frequency over-limit judgment module, for, when it is detected that the second AC frequency does not fall within the second frequency range, identifying whether the second AC frequency does not fall within the second frequency range within a first preset time period from the moment when the second AC frequency first crosses the limit; The island determination module is used to determine that an island occurs when it is identified that the second AC frequency does not fall into the second frequency range within a first preset time period since the second AC frequency first crosses the limit.

9. A storage medium, characterized in that: The storage medium stores computer-readable instructions, and when the computer-readable instructions are executed by one or more processors, the one or more processors execute the steps of the island detection method according to any one of claims 1 to 7.

10. A converter system, characterized in that: include: A grid-type converter is used to access the grid system via a switch unit; A sampling unit, used for collecting the output voltage and output current of the grid-type converter; A frequency detection unit, used for calculating the AC frequency of the grid-type converter based on the output voltage and output current collected by the sampling unit; A control unit is used to obtain the AC frequency fed back by the frequency detection unit in real time, and execute the steps of the island detection method according to any one of claims 1 to 7.

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