Island control method of converter multi-machine parallel system and converter multi-machine parallel system

Abstract

The application provides an island control method of a converter multi-machine parallel system and the converter multi-machine parallel system. The method controls all parallel converters through a parallel box in the converter multi-machine parallel system, so that the parallel box obtains power grid electrical signals in a grid-connected operation mode, and performs island detection according to the power grid electrical signals. If an island is detected, off-grid control signals are simultaneously sent to each converter, and the off-grid control signals are used to indicate that the working state of the corresponding converter is switched from the grid-connected mode to the off-grid mode. Through the above method, the application can avoid the problem that the multi-machines cannot normally realize island off-grid control due to inconsistent detection island time, so as to ensure that the converter multi-machine parallel system meets the grid-connected standard requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, and particularly relates to an island control method of a converter multi-machine parallel system and the converter multi-machine parallel system. BACKGROUND

[0002] For a converter, island detection and protection functions are required. When the single-machine power is small, the converter usually adopts multi-machine parallel expansion to meet market demand.

[0003] In the multi-machine parallel scene, the moment when the multiple converters in parallel detect an island is inconsistent. After the converter that detects the island first switches to an off-grid mode, the output voltage is mistaken for grid voltage by other converters, and it is thus considered that the grid is normal and cannot be switched to the off-grid mode. Finally, the island detection of the multi-machine parallel system fails, and the grid connection standard requirement cannot be met. SUMMARY

[0004] Embodiments of the present application provide an island control method of a converter multi-machine parallel system and the converter multi-machine parallel system, to solve the problem of island detection failure of the converter multi-machine parallel system in the prior art.

[0005] In a first aspect, embodiments of the present application provide an island control method of a converter multi-machine parallel system, the converter multi-machine parallel system comprising a parallel machine box and multiple converters; the AC side of each converter is connected to an AC bus, and the AC bus is connected to a power grid, and the parallel machine box is in communication connection with each converter.

[0006] The method is applied to the parallel machine box, and comprises the following steps.

[0007] In a grid-connected operation mode, a grid electrical signal is acquired, and island detection is performed according to the grid electrical signal.

[0008] If an island is detected, an off-grid control signal is simultaneously sent to each converter, and the off-grid control signal is used to instruct the working state of the corresponding converter to be switched from a grid-connected mode to an off-grid mode.

[0009] In a second aspect, embodiments of the present application provide an island control device of a converter multi-machine parallel system, the converter multi-machine parallel system comprising a parallel machine box and multiple converters; the AC side of each converter is connected to an AC bus, and the AC bus is connected to a power grid, and the parallel machine box is in communication connection with each converter. The device is applied to the parallel machine box and comprises the following steps.

[0010] An island detection module is configured to acquire a grid electrical signal in a grid-connected operation mode, and perform island detection according to the grid electrical signal.

[0011] The off-grid control module is configured to send an off-grid control signal to each of the plurality of converters if an island is detected, the off-grid control signal being configured to instruct the corresponding converter to switch from the grid-connected mode to the off-grid mode.

[0012] In a third aspect, an embodiment of the present application provides a parallel operation box, comprising an AC bus, a first switch, a second switch and a controller, the AC bus is connected with AC terminals of each of the plurality of converters, the first end of the first switch and the first end of the second switch are connected with the AC bus, the second end of the first switch is configured to connect with a power grid, and the second end of the second switch is configured to connect with a load.

[0013] The controller is configured to execute the island control method of the plurality of converters parallel operation system according to any one of the first aspect.

[0014] In a fourth aspect, an embodiment of the present application provides a plurality of converters parallel operation system, comprising a plurality of converters and a parallel operation box as described above.

[0015] The embodiment of the present application provides an island control method of a plurality of converters parallel operation system and the plurality of converters parallel operation system, the method sets a parallel operation box in the plurality of converters parallel operation system, controls all the parallel converters through the parallel operation box, and thus in the grid-connected operation mode, the parallel operation box acquires a power grid electrical signal and performs island detection according to the power grid electrical signal; if an island is detected, an off-grid control signal is sent to each of the plurality of converters, the off-grid control signal being configured to instruct the corresponding converter to switch from the grid-connected mode to the off-grid mode. Through the above method, the embodiment can avoid the problem that the plurality of converters cannot normally implement island off-grid control due to inconsistent detection time of the island, thereby ensuring that the plurality of converters parallel operation system meets the grid-connected standard requirement. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative labor.

[0017] Figure 1 is a structural schematic diagram of the plurality of converters parallel operation system provided by the embodiment of the present application;

[0018] Figure 2 is an implementation flowchart of the island control method of the plurality of converters parallel operation system provided by the embodiment of the present application;

[0019] Figure 3 is a structural schematic diagram of the island control device of the plurality of converters parallel operation system provided by the embodiment of the present application;

[0020] Figure 4 is a schematic diagram of a parallel box provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular sequences of acts, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.

[0022] In the description of the present application and the appended claims, the terms "first", "second", "third", etc. are used only to distinguish descriptions, and cannot be understood as indicating or implying relative importance.

[0023] In the present application, the reference "one embodiment" or "some embodiments" means that the specific features, structures or characteristics described in connection with the embodiment are included in one or more embodiments of the present application. Therefore, the statements "in one embodiment", "in some embodiments", "in other some embodiments", "in further some embodiments" and the like appearing in the present specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized. The terms "include", "contain", "have" and their variants mean "including but not limited to", unless otherwise specifically emphasized.

[0024] In addition, "a plurality of" mentioned in the embodiments of the present application should be interpreted as two or more.

[0025] In order to make the purpose, technical solutions and advantages of the present application clearer, specific embodiments will be described below with reference to the accompanying drawings.

[0026] Figure 1 The structure schematic diagram of the converter multi-machine parallel system provided by the embodiments of the present application is shown in FIG. 1. As shown in FIG. 1, the converter multi-machine parallel system includes a parallel box and a plurality of converters; the parallel box includes an AC bus, the AC side of each converter is connected to the AC bus, and the AC bus is used to connect a power grid, and the parallel box is in communication connection with each converter. Figure 1

[0027] The converter in the present embodiment can be an energy storage inverter, a photovoltaic inverter, or an AC-AC converter. The island control method of the converter multi-machine parallel system provided by the embodiments will be explained and described below taking the energy storage inverter as an example. ​

[0028] Specifically, as shown in Figure 1 The multi-machine parallel system of the converter includes a plurality of converters, switches corresponding to each converter, and a parallel box. The AC terminals of the plurality of energy storage inverters are connected to the AC bus AC-BUS in the parallel box through the corresponding switches KN1 and KN2, respectively. The parallel box further includes a first switch K1, a second switch K2, a third switch K3, and a controller. The AC bus AC-BUS is connected to the first ends of the first switch K1 and the second switch K2, the second end of the first switch K1 is connected to one end of a switching switch, the other end of the switching switch is connected to a power grid, the second end of the second switch K2 is connected to a load, the first end of the third switch K3 is connected to the second end of the first switch K1, and the second end of the third switch K3 is connected to the second end of the second switch K2. The switch of the AC terminal of each energy storage inverter can be an electromagnetic switch or a manual switch.

[0029] Each energy storage inverter includes a controller, and the corresponding converter circuit is controlled to work through the controller. The controller in the parallel box is in communication connection with the controllers of the energy storage inverters, and is used to control all the energy storage inverters to work from the upper layer. The first switch, the second switch, and the third switch can be electromagnetic switches or manual switches. When the first switch, the second switch, and the third switch are electromagnetic switches, the parallel box is in communication connection with the first switch and the second switch, and is used to control the switch states of the first switch and the second switch. The energy storage inverters can be in communication connection with the controllers of the energy storage inverters through CAN communication / RS485 communication.

[0030] The embodiment provides an island control method of a multi-machine parallel system of a converter. The execution subject of the method is a controller in a parallel box. The controller controls all the parallel converters through the parallel box of the multi-machine parallel system of the converter, and can avoid the problem that the multi-machines cannot normally realize island off-grid control due to inconsistent detection of island time, so as to ensure that the multi-machine parallel system of the converter meets the grid connection standard requirements.

[0031] Specifically, referring to Figure 2 which shows an implementation flowchart of the island control method of the multi-machine parallel system of the converter provided by the embodiment, and the process is described in detail as follows:

[0032] S101: In a grid-connected operation mode, an electric grid electric signal is acquired, and island detection is performed according to the electric grid electric signal.

[0033] In the embodiment, after the parallel box is arranged in the parallel system, the parallel box receives the total active power target value and the total reactive power target value of the parallel system, and decomposes the total active power target value and the total reactive power target value into the active power given value and the reactive power given value corresponding to each energy storage converter according to the residual capacity percentage and the health state of the battery corresponding to each energy storage converter, and then sends the active power given value and the reactive power given value corresponding to each energy storage converter to the controller of the corresponding energy storage converter as the active loop given value and the reactive loop given value of the corresponding energy storage converter. After receiving the active power given value and the reactive power given value sent by the parallel box, each energy storage converter generates a pulse signal for controlling the energy storage converter according to the active power given value and the reactive power given value.

[0034] Specifically, the island effect refers to a self-provided power island phenomenon formed by a photovoltaic energy storage system supplying power to surrounding loads when the photovoltaic energy storage system fails to detect a power-off state in time and cannot quickly cut off the power supply from the power grid due to reasons such as a fault accident or power-off maintenance.

[0035] The island detection method includes an active detection method and a passive detection method. The active detection method refers to causing a certain disturbance in the output power, frequency or phase of the control converter. When the power grid is normally working, the disturbance cannot be detected due to the balancing effect of the power grid. Once the power grid fails, the disturbance output by the converter will quickly accumulate and exceed the allowed range, thereby triggering the island effect detection circuit. The passive detection method uses the changes in the voltage, frequency, phase or harmonics at the output end of the converter when the power grid is powered off to detect the island effect. However, when the output power of the photovoltaic system is balanced with the local load power, the passive detection method will lose the island effect detection capability, and there is a large non-detection zone (NDZ).

[0036] The embodiment is based on the active detection method to detect the island effect of the power grid electrical signal.

[0037] S102: If the island is detected, a off-grid control signal is sent to each converter, and the off-grid control signal is used to indicate that the working state of the corresponding converter is switched from the grid-connected mode to the off-grid mode.

[0038] Specifically, if the parallel box detects an island, i.e., the power grid fails or is powered off, the off-grid control signal is sent to all converters, and each converter switches the working state from the grid-connected state to the off-grid state according to the received off-grid control signal, thereby avoiding the problem that the island off-grid control cannot be normally implemented due to the inconsistent detection time of multiple machines, and ensuring that the multi-machine parallel system of the converter meets the grid-connected standard requirements.

[0039] In the embodiment, after the island is detected, the paralleling box is further configured to control the first switch and the third switch to be turned off.

[0040] In one embodiment, before S101, the paralleling box needs to detect whether the island function is in an enabled state, if the island function is in the enabled state, the subsequent steps are executed, if the island function is not in the enabled state, the island control is not performed.

[0041] In one possible embodiment, the specific implementation process of S101 includes:

[0042] The voltage signal between the AC bus and the power grid is obtained as a first voltage signal.

[0043] The island detection is performed according to the first voltage signal.

[0044] In the embodiment, the power grid electrical signal can include a voltage signal, a current signal and a power signal, a voltage transformer is arranged between the AC bus and the switching switch, the first voltage signal is obtained through the voltage transformer, and the paralleling box determines whether the island effect occurs in the multi-machine parallel system of the current converter through the first voltage signal.

[0045] In one possible implementation, the specific implementation process of S102 can further include:

[0046] If the island signal sent by any converter is detected, and the island effect is detected according to the first voltage signal, the off-grid control signal is sent to each converter at the same time; the first voltage signal is a voltage signal between the AC bus and the power grid; the island signal is a signal generated by the corresponding converter when the island is detected based on the second voltage signal; and the second voltage signal is a voltage signal on the AC side of the converter.

[0047] In the embodiment, the island effect can be detected through the electrical signal on the AC side of the converter, or through the electrical signal between the AC bus and the power grid. Since the converter may be misdetected due to abnormal output side power, and the paralleling box may be misdetected due to abnormal sampling device, the island effect is detected on the paralleling box side in the embodiment, and the island effect is detected when any converter detects the island effect, so that it is determined that the island effect occurs in the power grid.

[0048] Specifically, a voltage transformer is arranged at each converter output end to detect a voltage signal of the converter output end and serve as a second voltage signal, a controller of the converter acquires the second voltage signal collected by the corresponding voltage transformer, and judges whether the power grid is abnormal (power grid failure or power outage) according to the second voltage signal. If the power grid is detected to be abnormal, the power grid failure flag of the converter is set to TRUE, and an island signal carrying the power grid failure flag is generated, and then the island signal is sent to the parallel box. The parallel box also detects whether the island effect occurs according to the first voltage signal. If the island effect occurs and the island signal on any converter is monitored within a preset time before and after the time point of the occurrence of the island effect, the parallel box adjusts the working mode of the multi-converter parallel system from the grid-connected mode to the off-grid mode, and issues an off-grid control signal to each converter. After each converter receives the off-grid control signal issued by the parallel box, the working mode of each converter is switched to the off-grid mode.

[0049] The above method can collect the second voltage signal based on the original voltage sampling device on the converter side, and perform island detection using the original island detection logic on the converter side, thereby improving the detection accuracy of the island effect and expanding the applicability of the present application without changing the original control logic of the converter as much as possible.

[0050] In one possible embodiment, before the island detection is performed according to the first voltage signal, the island control method provided in the embodiment further includes:

[0051] S201: When the island signal sent by any converter is monitored, the tasks in the control task pool are suspended.

[0052] Correspondingly, the specific implementation process of the island detection according to the first voltage signal further includes:

[0053] If the island is not detected according to the first voltage signal within a first preset time length after the island signal is detected, the tasks in the task pool are controlled to resume running.

[0054] In the embodiment, when the active detection method is used to detect the island of the power grid, the converter side will first detect the occurrence of the island effect when the power grid is abnormal because the converter outputs a disturbance signal. At this time, the converter that detects the occurrence of the island effect sends the island signal to the parallel box. The parallel box can first switch the tasks in the task pool to the suspended state, i.e., pause the execution of the tasks in the task pool, so that the parallel box switches the working mode to the off-grid mode immediately after detecting the island effect, thereby improving the off-grid switching efficiency of the parallel system and reducing the time during which the parallel system remains in the grid-connected state after the occurrence of the island effect due to the large number of tasks of the parallel box.

[0055] When each converter detects that its working mode is switched from grid-connected mode to off-grid mode, an off-grid signal is sent to the parallel box, and the parallel box restores the tasks in the task pool to the running state after detecting the off-grid signals sent by all online converters.

[0056] In one possible embodiment, the specific implementation process of S201 includes:

[0057] When an island signal sent by any converter is monitored, a target task in the control task pool is suspended, and the target task is a task with an importance level not higher than that of the island control task.

[0058] In one possible embodiment, the specific implementation process of S102 includes:

[0059] If an island is detected, the time for sending an off-grid control signal to each converter is determined according to the communication time of the parallel box and each converter, so that the time for each converter to receive the off-grid control signal remains consistent.

[0060] Specifically, because different converters are placed in different positions and the communication time with the parallel box is also different, in order to ensure that the time for each converter to receive the control signal remains strictly consistent and avoid island detection failure, the parallel box first selects the maximum value of the communication time of all converters with the parallel box after generating the off-grid control signal, then calculates the time difference by subtracting the communication time of other converters from the maximum value, the parallel box first sends the off-grid control signal to the converter with the longest communication time, then takes the sending time of the off-grid control signal of the converter as the starting time, and sequentially counts the time difference corresponding to each converter, and sends the off-grid control signal to the corresponding converter when each count reaches, so that all converters can receive the off-grid control signal sent by the parallel box at the same time.

[0061] In one possible embodiment, the specific implementation process of S102 includes:

[0062] If an island is detected, an off-grid control signal is sent to each converter at the same time, and the off-grid control signal is used to indicate that the working state of the corresponding converter is switched from the constant current mode to the constant voltage mode.

[0063] In this embodiment, in the off-grid mode, the converter outputs a stable voltage, and can provide a stable voltage to the load, and in the grid-connected mode, the converter outputs a stable current, and the output current flows into the power grid.

[0064] In one possible embodiment, the island control method provided in this embodiment further includes:

[0065] In the off-grid mode, it is judged whether the power grid is restored according to the power grid electrical signal.

[0066] If the power grid has been restored, each converter is simultaneously controlled to switch from the off-grid mode to the grid-connected mode.

[0067] In the embodiment, if it is detected that the power grid has been restored, the control box is also used to control the first switch and the third switch to be closed.

[0068] From the above embodiment, it can be seen that the embodiment proposes a control scheme for island detection and protection of a multi-converter parallel system, which can effectively solve the problems of inconsistent island detection pace of the parallel converters, abnormal island protection of the parallel system, and false detection of island protection due to abnormal power line of part of the converters, meets the demand of island detection standard for island function, is simple and reliable, can be directly added to the existing multi-converter parallel system, does not need to modify the converters, and has generalizability.

[0069] It should be understood that the size of the serial number of each step in the above embodiment does not mean the order of execution, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiment of the application.

[0070] The following is a device embodiment of the application, and for details not described in detail, reference can be made to the corresponding method embodiments described above.

[0071] Figure 3 A structure diagram of an island control device of a multi-converter parallel system provided by the embodiment of the application is shown, only parts related to the embodiment of the application are shown for ease of description, and details are described as follows:

[0072] As shown in Figure 3 The island control device 100 of the multi-converter parallel system includes:

[0073] The island detection module 110 is used to acquire a power grid electrical signal in a grid-connected operation mode, and perform island detection according to the power grid electrical signal.

[0074] The off-grid control module 120 is used to send an off-grid control signal to each converter if an island is detected, and the off-grid control signal is used to instruct the working state of the corresponding converter to switch from the grid-connected mode to the off-grid mode.

[0075] In one possible implementation, the island detection module 110 includes:

[0076] The voltage signal between the AC bus and the power grid is acquired as a first voltage signal.

[0077] The island detection is performed according to the first voltage signal.

[0078] In a possible implementation, the off-grid control module 120 comprises:

[0079] If an island signal sent by any of the converters is detected, and an island effect is detected according to a first voltage signal, an off-grid control signal is simultaneously sent to each of the converters; the first voltage signal is a voltage signal between the AC bus and the power grid; the island signal is a signal generated by the corresponding converter when an island is detected based on a second voltage signal; and the second voltage signal is a voltage signal on the AC side of the converter.

[0080] In a possible implementation, the island control device 100 of the converter multi-machine parallel system further comprises a task suspension module, configured to:

[0081] When an island signal sent by any of the converters is detected, a task in the task pool is controlled to be suspended; the island signal is a signal generated by the corresponding converter when an island is detected based on a second voltage signal; and the second voltage signal is a voltage signal on the AC side of the converter.

[0082] The island control device 100 of the converter multi-machine parallel system further comprises a task resumption module, configured to:

[0083] If an island is not detected according to the first voltage signal within a first preset time period after the island signal is detected, a task in the task pool is controlled to resume operation.

[0084] In a possible implementation, the off-grid control module 120 comprises:

[0085] If an island is detected, an off-grid control signal is simultaneously sent to each of the converters, and the off-grid control signal is used to instruct the corresponding converter to switch from the constant-current mode to the constant-voltage mode.

[0086] In a possible implementation, when an island signal sent by any of the converters is detected, the task suspension module controls a task in the task pool to be suspended, comprising:

[0087] When an island signal sent by any of the converters is detected, a target task in the task pool is controlled to be suspended, and the target task is a task with an importance level not higher than that of the island control task.

[0088] As can be seen from the above embodiments, the embodiments propose a control device for island detection and protection of a converter multi-machine parallel system, which can effectively solve the problems of inconsistent island detection pace of the parallel converters, abnormal island protection of the parallel system, and false detection of island protection due to abnormal power lines of some converters, meet the demand of island detection standards for island function, and has simple and reliable scheme and generalizability.

[0089] Figure 4 is a schematic diagram of a parallel machine box provided by an embodiment of the present application. As shown in the figure, the parallel machine box 4 of this embodiment comprises a processor 40 and a memory 41. Figure 4 The memory 41 is configured to store a computer program 42, and the processor 40 is configured to invoke and run the computer program 42 stored in the memory 41 to perform the steps in the island control method embodiments of the parallel multi-converter system described above, such as steps 101-102 shown in the figure. Figure 2 Alternatively, the processor 40 is configured to invoke and run the computer program 42 stored in the memory 41 to implement the functions of the modules / units in the device embodiments described above, such as the functions of modules 110-120 shown in the figure. Figure 3

[0090] For example, the computer program 42 can be divided into one or more modules / units, which are stored in the memory 41 and executed by the processor 40 to complete the present application. The one or more modules / units can be a series of computer program instruction segments capable of completing a specific function, which are used to describe the execution process of the computer program 42 in the parallel machine box 4.

[0091] The parallel machine box 4 can include, but is not limited to, the processor 40 and the memory 41. Those skilled in the art can understand that Figure 4 The parallel machine box 4 is only an example and does not constitute a limitation on the parallel machine box 4, and can include more or fewer components than those shown, or combine certain components, or different components, for example, the parallel machine box can also include input / output devices, network access devices, buses, etc.

[0092] The processor 40 can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor.

[0093] ​The storage 41 can be an internal storage unit of the docking box 4, such as a hard disk or a memory of the docking box 4. The storage 41 can also be an external storage device of the docking box 4, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the docking box 4. Further, the storage 41 can also include both the internal storage unit and the external storage device of the docking box 4. The storage 41 is used to store the computer program and other programs and data required by the docking box. The storage 41 can also be used to temporarily store data that has been output or is to be output.

[0094] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above functional units and modules is exemplified, and in actual application, the above functions can be completed by different functional units and modules according to needs, that is, the internal structure of the apparatus is divided into different functional units or modules to complete all or part of the functions described above. Each functional unit and module in the embodiment can be integrated in one processing unit, or each unit can be physically present separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of software functional unit. In addition, the specific names of each functional unit and module are only for easy distinction, and do not limit the protection scope of the application. The specific working process of the units and modules in the system can refer to the corresponding process in the foregoing method embodiments, which will not be described here.

[0095] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described or recorded in detail in a certain embodiment can refer to the relevant description of other embodiments.

[0096] Those of ordinary skill in the art can appreciate that the units and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. A person skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0097] In the embodiments of the present application, it should be understood that the disclosed device / parallel box and method can be implemented in other manners. For example, the described device / parallel box embodiments are merely schematic. For example, the division of the modules or units is merely logical function division. There can be another division manner in actual implementation. For example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections between the units can be indirect couplings or communication connections through some interfaces, devices or units, and can be electrical, mechanical or in other forms.

[0098] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, i.e., can be located in one place, or can be distributed on a plurality of network units. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiments.

[0099] In addition, each functional unit in the various embodiments of the present application can be integrated into a processing unit, or each unit can be physically present separately, or two or more units can be integrated into one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0100] The integrated module / unit, if realized in the form of a software functional unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. When the processor executes the computer program, the steps of the island control method embodiment of the multi-machine parallel system of the various converters can be implemented. The computer program includes computer program code, which can be in the form of source code, object code, executable file or some intermediate form. The computer readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the contents included in the computer readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction, for example, in some jurisdictions, according to legislation and patent practice, the computer readable medium does not include electrical carrier signals and telecommunication signals.

[0101] The above-described embodiments are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. An islanding control method for a multi-machine parallel converter system, characterized in that, The converter multi-machine parallel system includes a parallel box and multiple converters; the parallel box includes an AC bus, the AC side of each converter is connected to the AC bus, and the AC bus is used to connect to the power grid; the parallel box is communicatively connected to each converter. The method is applied to the parallel box, including: In grid-connected operation mode, the grid electrical signal is acquired, and islanding detection is performed based on the grid electrical signal; If an island is detected, an off-grid control signal is sent to each converter simultaneously. The off-grid control signal is used to indicate that the operating state of the converter should be switched from grid-connected mode to off-grid mode. If islanding is detected, an off-grid control signal is simultaneously sent to each converter, including: If an islanding signal is detected from any converter, the tasks in the task pool are switched to a suspended state based on the islanding signal. When an islanding effect is detected based on a first voltage signal, an off-grid control signal is simultaneously sent to each converter. The first voltage signal is the voltage signal between the AC bus and the power grid. The islanding signal is the signal generated when the converter detects islanding based on a second voltage signal. The second voltage signal is the voltage signal on the AC side of the converter.

2. The islanding control method for a multi-machine parallel converter system according to claim 1, characterized in that, The step of acquiring the power grid signal and performing islanding detection based on the power grid signal includes: The voltage signal between the AC bus and the power grid is acquired and used as the first voltage signal; Island detection is performed based on the first voltage signal.

3. The islanding control method for a multi-machine parallel converter system according to claim 1, characterized in that, The method further includes: If no island is detected based on the first voltage signal within a first preset time period after the island signal is detected, the tasks in the task pool are controlled to resume operation.

4. The islanding control method for a multi-machine parallel converter system according to claim 1, characterized in that, If islanding is detected, an off-grid control signal is simultaneously sent to each converter. This off-grid control signal indicates that the operating state of the converter should switch from grid-connected mode to off-grid mode, including: If an islanding is detected, an off-grid control signal is sent to each converter simultaneously. The off-grid control signal is used to indicate that the operating state of the corresponding converter is switched from constant current mode to constant voltage mode.

5. The islanding control method for a multi-machine parallel converter system according to claim 3, characterized in that, The step of suspending tasks in the control task pool when an islanding signal is detected from any converter includes: When an islanding signal is detected from any converter, the target task in the control task pool is suspended. The target task is a task whose importance level is no higher than that of the islanding control task.

6. An islanded control device for a multi-machine parallel converter system, characterized in that, The converter multi-machine parallel system includes a parallel box and multiple converters; the AC side of each converter is connected to an AC bus, and the AC bus is connected to the power grid; the parallel box is communicatively connected to each converter. The device is applied to the parallel unit box and includes: The islanding detection module is used to acquire grid electrical signals in grid-connected operation mode and perform islanding detection based on the grid electrical signals. The off-grid control module is used to send off-grid control signals to each converter simultaneously if islanding is detected. The off-grid control signals are used to indicate that the operating state of the corresponding converter is switched from grid-connected mode to off-grid mode. The off-grid control module includes: If an islanding signal is detected from any converter, the tasks in the task pool are switched to a suspended state based on the islanding signal. When an islanding effect is detected based on a first voltage signal, an off-grid control signal is simultaneously sent to each converter. The first voltage signal is the voltage signal between the AC bus and the power grid. The islanding signal is the signal generated when the converter detects islanding based on a second voltage signal. The second voltage signal is the voltage signal on the AC side of the converter.

7. A parallel box, characterized in that, It includes an AC bus, a first switch, a second switch, and a controller. The AC bus is connected to the AC terminals of each converter. The first terminal of the first switch and the first terminal of the second switch are both connected to the AC bus. The second terminal of the first switch is used to connect to the power grid, and the second terminal of the second switch is used to connect to the load. The controller is used to execute the islanding control method for a multi-machine parallel converter system as described in any one of claims 1 to 5.

8. A multi-machine parallel converter system, characterized in that, It includes multiple converters and a parallel unit box as described in claim 7.

9. The converter multi-machine parallel system as described in claim 8, characterized in that, The converter is used for: The system acquires the off-grid control signal sent by the parallel box and switches its own working state from parallel mode to off-grid mode according to the off-grid control signal.

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