Autonomous current sharing control method, device, terminal and storage medium for multiple power supplies

Abstract

The present invention provides a method, device, terminal and storage medium for autonomous current sharing control of multiple power supplies. The outputs of the multiple power supplies are all connected to a DC bus; the above-mentioned current sharing control method includes: obtaining the actual output current of the target power supply obtained by sampling; the target power supply is one of the multiple power supplies; according to the actual output current of the target power supply obtained by sampling, the target given voltage of the target power supply is corrected to obtain the given voltage value of the target power supply; according to the given voltage value of the target power supply, the target power supply is loop-controlled; the target given voltage of each power supply is the same, and the sum of the output currents of each power supply is fixed. The present invention corrects the target given voltage according to the actual output current, adjusts the output current, and the power supplies controlled by different control terminals autonomously share the current without establishing communication between the control terminals. The method is simple and effective.

Description

Technical Field

[0001] The present invention relates to the field of power supply technology, and in particular to a method, device, terminal and storage medium for autonomous current sharing control of multiple power supplies. Background Art

[0002] As global energy shortages and pollution become increasingly prominent, photovoltaics have been widely used as a clean and renewable energy source. A photovoltaic power station is a photovoltaic system that converts solar energy into electrical energy and transmits electricity to the power grid. In large and medium-sized photovoltaic power stations, multiple photovoltaic power sources are usually connected in parallel to the DC bus BUS and then connected to the grid through an inverter. For example, Figure 1 Since the total current of multiple photovoltaic power sources is constant, if the current of some channels is too low, it will inevitably cause the current of other channels to be too high. Long-term uneven current operation will cause the photovoltaic power source to age and reduce its reliability.

[0003] In existing technology, when there are many power supply paths, the resources of a single chip (control terminal) are limited, and these multiple power supply paths are usually controlled by two or more chips. When these multiple power supply paths are controlled by different chips, current sharing between the power supplies controlled by different chips requires communication between the chips, which is complex to set up. Summary of the Invention

[0004] The embodiments of the present invention provide a method, device, terminal and storage medium for autonomous current sharing control of multiple power sources to solve the problem that current sharing of multiple photovoltaic power sources requires communication and complex settings.

[0005] In a first aspect, an embodiment of the present invention provides an autonomous current sharing control method for multiple power supplies, wherein the outputs of the multiple power supplies are all connected to a DC bus; the current sharing control method includes:

[0006] Acquire the actual output current of the sampled target power supply, wherein the target power supply is one of the multiple power supplies;

[0007] Correcting the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling to obtain a given voltage value of the target power supply;

[0008] Performing loop control on the target power supply according to a given voltage value of the target power supply;

[0009] The target given voltages of the power supplies are the same, and the sum of the output currents of the power supplies is fixed.

[0010] In a second aspect, an embodiment of the present invention provides an autonomous current sharing control device for multiple power supplies, wherein the outputs of the multiple power supplies are all connected to a DC bus; the current sharing control device includes:

[0011] A current sampling module is used to obtain the actual output current of the target power supply obtained by sampling; wherein the target power supply is one of the multiple power supplies;

[0012] A voltage setting correction module is used to correct the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling, so as to obtain a given voltage value of the target power supply;

[0013] The loop control module is used to perform loop control on the target power supply according to the given voltage value of the target power supply; wherein the target given voltage of each power supply is the same, and the sum of the output currents of each power supply is fixed.

[0014] In a third aspect, an embodiment of the present invention provides a control terminal comprising a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the computer program, the steps of the autonomous current sharing control method for multiple power supplies provided in the first aspect or any possible implementation of the first aspect are implemented.

[0015] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it implements the steps of the autonomous current sharing control method for multiple power supplies provided in the first aspect or any possible implementation of the first aspect.

[0016] The embodiment of the present invention provides a method, device, terminal and storage medium for autonomous current sharing control of multiple power supplies. The outputs of the multiple power supplies are all connected to a DC bus; the above-mentioned current sharing control method includes: obtaining the actual output current of the target power supply obtained by sampling; the target power supply is one of the multiple power supplies; according to the actual output current of the target power supply obtained by sampling, the target given voltage of the target power supply is corrected to obtain the given voltage value of the target power supply; according to the given voltage value of the target power supply, the target power supply is loop-controlled; the target given voltage of each power supply is the same, and the sum of the output currents of each power supply is fixed. In the embodiment of the present invention, since the sum of the output currents of each power supply is fixed, the target given voltage of each power supply is the same, and the actual output voltage is also the same. For each power supply, the target given voltage can be corrected according to the actual output current to adjust the output current, so that the power supplies controlled by different chips (control terminals) can autonomously share the current, and there is no need to establish communication between chips. The method is simple and effective. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of the structure of a multi-channel power supply provided by an embodiment of the present invention;

[0019] Figure 2 This is a flow chart of an implementation method of an autonomous current sharing control method for multiple power supplies provided by an embodiment of the present invention;

[0020] Figure 3 1 is a schematic structural diagram of an autonomous current sharing control device for multiple power supplies provided by an embodiment of the present invention;

[0021] Figure 4 is a schematic diagram of a control terminal provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clear, specific embodiments will be described below with reference to the accompanying drawings.

[0024] See also Figure 2 , which shows a flowchart of the implementation of the autonomous current sharing control method of multiple power supplies provided by an embodiment of the present invention, and is described in detail as follows:

[0025] refer to Figure 1 , the outputs of multiple power supplies are all connected to the DC bus BUS; the above-mentioned current sharing control method includes:

[0026] S101: Acquire the actual output current of a sampled target power supply, wherein the target power supply is one of multiple power supplies;

[0027] S102: Correcting a target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling to obtain a given voltage value of the target power supply;

[0028] S103: performing loop control on the target power supply according to a given voltage value of the target power supply;

[0029] The target given voltages of the power supplies are the same, and the sum of the output currents of the power supplies is fixed.

[0030] refer to Figure 1 Since the interface resources and computing power of a control terminal are limited, when there are too many power supply channels, one control terminal may not be able to meet the demand (the control terminal can be a chip, for example, the chip interface is insufficient). Therefore, two or even more control terminals can be used to control multiple power supplies. If the output current of each power supply channel is to be balanced, communication between the control terminals needs to be established.

[0031] refer to Figure 1 , the sum of the output currents of each power supply is fixed, which is also the front-stage power limit. Therefore, if the feedback voltage of a power supply is too small, the output current of the power supply will be increased; if the feedback voltage of the power supply is too large, the output current of the power supply will be reduced. If the current is not evenly distributed among the power supplies due to sampling errors or other reasons, the given voltage of the target power supply can be corrected according to the actual output current. By adjusting the given voltage of the target power supply, the output current of the target power supply is affected, thereby achieving current sharing among the power supplies. In the above-mentioned current sharing control method, each power supply autonomously shares the current. When multiple power supplies are controlled by different control terminals, there is no need for communication between chips, and the control method is simple and effective. When multiple power supplies are controlled by the same chip, the above-mentioned method can also be used for current sharing.

[0032] Multiple power supplies can be controlled by the same control terminal or by at least two different control terminals. The number of power supplies controlled by each control terminal can be the same or different. For example, a total of 10 power supplies can be controlled by two control terminals, one controlling 4 and the other 6, respectively.

[0033] In a possible implementation, S102 may include:

[0034] S1021: Obtaining a correction coefficient of the target power supply;

[0035] S1022: Correcting the target given voltage of the target power supply according to the sampled actual output current of the target power supply and the correction coefficient of the target power supply to obtain a given voltage value of the target power supply.

[0036] If the actual output current of the target power supply is too high, the target set voltage of the target power supply can be corrected to reduce the target set voltage of the target power supply; conversely, if the actual output current is too low, the target set voltage can be increased. Specifically, the embodiment of the present invention corrects the target set voltage based on the actual output current and the correction factor.

[0037] In a possible implementation, S1022 may include:

[0038] 1. Based on the actual output current of the target power supply obtained by sampling and the correction coefficient of the target power supply, the target given voltage of the target power supply is corrected in combination with the first formula to obtain the given voltage value of the target power supply;

[0039] The first formula can be:

[0040] U ref =U0-K*I

[0041] Among them, U ref is the given voltage value of the target power supply, U0 is the target given voltage of the target power supply, K is the correction coefficient of the target power supply, and I is the actual output current of the target power supply obtained by sampling.

[0042] In the embodiment of the present invention, the actual output current is multiplied by the correction coefficient as a correction amount to correct the given voltage value, thereby realizing autonomous current sharing.

[0043] In a possible implementation, multiple power supplies are controlled by at least two different control terminals; the above-mentioned current sharing control method may further include:

[0044] S104: Obtain the number of power supply channels controlled by the control terminal corresponding to the target power supply;

[0045] S105: Determine the proportional coefficient of the target power supply according to the number of power supply paths;

[0046] S106: Determine a correction coefficient of the target power source according to the proportional coefficient of the target power source.

[0047] In a possible implementation, S105 may include:

[0048] Determine the target power supply's proportionality factor based on the number of power supply paths and the second formula;

[0049] The second formula can be:

[0050]

[0051] Where k is the proportional coefficient of the target power supply, ΔU is the maximum voltage deviation, I0 is the rated output current of each power supply, and N is the number of power supplies.

[0052] For example, the control terminal corresponding to the target power supply controls 6 power supplies, the maximum voltage deviation is 15V, and the rated output current is 30A.

[0053] In a possible implementation, S106 may include:

[0054] 1. Determine the correction coefficient of the target power supply based on the proportional coefficient of the target power supply and the third formula;

[0055] The third formula can be:

[0056] K=k+m

[0057] Wherein, K is the correction coefficient of the target power supply, k is the proportional coefficient of the target power supply, and m is the proportional deviation value.

[0058] Wherein, m is a constant that can be set according to actual application requirements. Specifically, it can be determined based on sampling error and rated output current.

[0059] In a possible implementation, each power source may be a photovoltaic power source.

[0060] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0061] The following are device embodiments of the present invention. For details not fully described therein, reference may be made to the corresponding method embodiments described above.

[0062] Figure 3 The following is a schematic diagram showing the structure of an autonomous current sharing control device for multiple power supplies provided by an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0063] like Figure 1 As shown, the outputs of multiple power supplies are all connected to the DC bus BUS; refer to Figure 3 , the autonomous current sharing control device of multiple power supplies includes:

[0064] The current sampling module 21 is used to obtain the actual output current of the target power supply obtained by sampling; wherein the target power supply is one of the multiple power supplies;

[0065] The voltage setting correction module 22 is used to correct the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling, so as to obtain the given voltage value of the target power supply;

[0066] The loop control module 23 is used to perform loop control on the target power supply according to the given voltage value of the target power supply; wherein the target given voltages of the various power supplies are the same, and the sum of the output currents of the various power supplies is fixed.

[0067] In a possible implementation, the voltage setting correction module 22 may include:

[0068] A correction coefficient obtaining unit, used to obtain a correction coefficient of a target power source;

[0069] The given voltage output unit is used to correct the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling and the correction coefficient of the target power supply to obtain the given voltage value of the target power supply.

[0070] In a possible implementation, a given voltage output unit may be specifically used for:

[0071] According to the actual output current of the target power supply obtained by sampling and the correction coefficient of the target power supply, the target given voltage of the target power supply is corrected in combination with the first formula to obtain a given voltage value of the target power supply;

[0072] The first formula can be:

[0073] U ref =U0-K*I

[0074] Among them, U ref is the given voltage value of the target power supply, U0 is the target given voltage of the target power supply, K is the correction coefficient of the target power supply, and I is the actual output current of the target power supply obtained by sampling.

[0075] In a possible implementation, multiple power supplies are controlled by at least two different control terminals; the current sharing control device may further include:

[0076] A power supply path number acquisition module is used to obtain the number of power paths controlled by the control terminal corresponding to the target power supply;

[0077] A proportional coefficient determination module is used to determine the proportional coefficient of the target power supply according to the number of power supply paths;

[0078] The correction coefficient output module is used to determine the correction coefficient of the target power supply according to the proportional coefficient of the target power supply.

[0079] In a possible implementation, the proportional coefficient determination module may be specifically configured to:

[0080] Determine the target power supply's proportionality factor based on the number of power supply paths and the second formula;

[0081] The second formula can be:

[0082]

[0083] Where k is the proportional coefficient of the target power supply, ΔU is the maximum voltage deviation, I0 is the rated output current of each power supply, and N is the number of power supplies.

[0084] In a possible implementation, the correction coefficient output module may be specifically used to:

[0085] Determine a correction factor for the target power source based on the proportional coefficient of the target power source and the third formula;

[0086] The third formula can be:

[0087] K=k+m

[0088] Wherein, K is the correction coefficient of the target power supply, k is the proportional coefficient of the target power supply, and m is the proportional deviation value.

[0089] In a possible implementation, each power source may be a photovoltaic power source.

[0090] Figure 4 Schematic diagram of the control terminal 3 provided by the embodiment of the present invention. Figure 4 As shown, the control terminal 3 of this embodiment includes: a processor 30 and a memory 31. The memory 31 is used to store a computer program 32, and the processor 30 is used to call and run the computer program 32 stored in the memory 31 to perform the steps in the above-mentioned embodiments of the autonomous current sharing control method for multiple power supplies, such as Figure 2 Alternatively, the processor 30 is used to call and run the computer program 32 stored in the memory 31 to implement the functions of each module / unit in the above-mentioned device embodiments, such as Figure 3 The functions of modules 21 to 23 are shown.

[0091] For example, the computer program 32 may be divided into one or more modules / units, one or more modules / units being stored in the memory 31 and executed by the processor 30 to implement the present invention. One or more modules / units may be a series of computer program instruction segments capable of implementing specific functions, and the instruction segments are used to describe the execution process of the computer program 32 in the control terminal 3. For example, the computer program 32 may be divided into Figure 3 Modules / units 21 to 23 are shown.

[0092] The control terminal 3 can be a computing device such as a desktop computer, a notebook, a palmtop computer, or a cloud server. The control terminal 3 can include, but is not limited to, a processor 30 and a memory 31. Those skilled in the art will understand that Figure 4 It is only an example of the control terminal 3 and does not constitute a limitation on the control terminal 3. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, the terminal may also include input and output devices, network access devices, buses, etc.

[0093] The processor 30 may be a central processing unit (CPU), or 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 may be a microprocessor or any conventional processor.

[0094] The memory 31 can be an internal storage unit of the control terminal 3, such as the hard disk or memory of the control terminal 3. The memory 31 can also be an external storage device of the control terminal 3, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a flash memory card, etc. equipped on the control terminal 3. Furthermore, the memory 31 can include both the internal storage unit of the control terminal 3 and an external storage device. The memory 31 is used to store computer programs and other programs and data required by the terminal. The memory 31 can also be used to temporarily store data that has been output or is about to be output.

[0095] Those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into one processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0096] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0097] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians 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 invention.

[0098] In the embodiments provided herein, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For example, the division of modules or units is merely a logical functional division. In actual implementation, other division methods may be used, such as multiple units or components being combined or integrated into another system, or some features being ignored or not implemented. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interface, or the indirect coupling or communication connection of devices or units may be electrical, mechanical, or other forms.

[0099] Units described as separate components may or may not be physically separate, and 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 these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0100] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0101] If the integrated module / unit is implemented in the form of 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 present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and when the computer program is executed by the processor, it can implement the steps of the above-mentioned various method embodiments. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form, etc. Computer-readable media may include: any entity or device that can carry 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.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A method for autonomous current sharing control of multiple power supplies, characterized in that: The outputs of the multiple power supplies are all connected to the DC bus; the current sharing control method includes: Acquiring the actual output current of the sampled target power supply, wherein the target power supply is one of the multiple power supplies; Correcting the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling to obtain a given voltage value of the target power supply; performing loop control on the target power supply according to a given voltage value of the target power supply; The target given voltage of each power supply is the same, and the sum of the output currents of each power supply is fixed; The method of correcting the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling to obtain the given voltage value of the target power supply includes: Obtaining a correction coefficient of the target power source; Correcting the target given voltage of the target power supply according to the sampled actual output current of the target power supply and the correction coefficient of the target power supply to obtain a given voltage value of the target power supply; The multiple power supplies are controlled by at least two different control terminals; the current sharing control method further includes: Obtaining the number of power supplies controlled by the control terminal corresponding to the target power supply; Determining a proportional coefficient of the target power supply according to the number of power supplies; A correction coefficient of the target power is determined according to the proportional coefficient of the target power.

2. The autonomous current sharing control method for multiple power supplies according to claim 1, characterized in that: The step of correcting the target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling and the correction coefficient of the target power supply to obtain the given voltage value of the target power supply includes: According to the actual output current of the target power supply obtained by sampling and the correction coefficient of the target power supply, the target given voltage of the target power supply is corrected in combination with the first formula to obtain the given voltage value of the target power supply; The first formula is: U ref =U0-K*I Among them, U ref is the given voltage value of the target power supply, U0 is the target given voltage of the target power supply, K is the correction coefficient of the target power supply, and I is the actual output current of the target power supply obtained by sampling.

3. The autonomous current sharing control method for multiple power supplies according to claim 1, characterized in that: The determining the proportional coefficient of the target power supply according to the number of the power supplies includes: Determine the proportionality coefficient of the target power source according to the number of power sources and the second formula; The second formula is: Wherein, k is the proportional coefficient of the target power supply, ΔU is the maximum voltage deviation, I0 is the rated output current of each power supply, and N is the number of power supplies.

4. The autonomous current sharing control method for multiple power supplies according to claim 3, characterized in that: The determining the correction coefficient of the target power source according to the proportional coefficient of the target power source includes: Determining a correction coefficient of the target power source based on the proportional coefficient of the target power source in combination with a third formula; The third formula is: K=k+m Wherein, K is the correction coefficient of the target power, k is the proportional coefficient of the target power, and m is the proportional deviation value.

5. The autonomous current sharing control method for multiple power supplies according to any one of claims 1 to 4, characterized in that: All of the power sources are photovoltaic power sources.

6. An autonomous current sharing control device for multiple power supplies, characterized in that: The outputs of the multiple power supplies are all connected to the DC bus; the current sharing control device includes: A current sampling module, configured to obtain the actual output current of a target power supply obtained by sampling; wherein the target power supply is one of the multiple power supplies; a voltage setting correction module, configured to correct a target given voltage of the target power supply according to the actual output current of the target power supply obtained by sampling, so as to obtain a given voltage value of the target power supply; a loop control module, configured to perform loop control on the target power supply according to a given voltage value of the target power supply; wherein the target given voltages of the various power supplies are the same, and the sum of the output currents of the various power supplies is fixed; The voltage setting correction module includes: A correction coefficient obtaining unit, configured to obtain a correction coefficient of the target power source; a given voltage output unit, configured to correct a target given voltage of the target power supply according to the sampled actual output current of the target power supply and a correction coefficient of the target power supply, so as to obtain a given voltage value of the target power supply; The multiple power supplies are controlled by at least two different control terminals; the current sharing control device further includes: A power supply number acquisition module, configured to acquire the number of power supplies controlled by the control terminal corresponding to the target power supply; A proportional coefficient determination module, configured to determine the proportional coefficient of the target power source according to the number of power sources; The correction coefficient output module is used to determine the correction coefficient of the target power supply according to the proportional coefficient of the target power supply.

7. A control terminal, characterized in that: The system comprises a processor and a memory, wherein the memory is used to store a computer program, and the processor is used to call and run the computer program stored in the memory to execute the autonomous current sharing control method for multiple power supplies according to any one of claims 1 to 5.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the autonomous current sharing control method for multiple power supplies as described in any one of claims 1 to 5 is implemented.

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