A method and device for obtaining a reference current of a net-following type converter
By acquiring the virtual impedance parameters after a grid fault and dynamically adjusting the converter reference current, the current distribution problem of grid-connected converters during grid faults is solved, achieving adaptive voltage support and safe operation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHANGSHA UNIVERSITY
- Filing Date
- 2023-05-22
- Publication Date
- 2026-06-02
AI Technical Summary
Existing grid-connected converters have difficulty effectively distributing positive/negative sequence active/reactive current within a safe current range during grid faults, resulting in poor voltage support and a lack of adaptive adjustment capabilities.
By acquiring the virtual impedance voltage drop, magnitude, and phase angle after a grid fault, the reference current of the converter is dynamically adjusted to achieve adaptive voltage support for symmetrical or asymmetrical faults.
It enables the converter to quickly stabilize at the optimal operating point under different fault scenarios, ensuring safe operation and providing balanced voltage support, adapting to different types of grid faults.
Smart Images
Figure CN116593822B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of converter control technology, specifically to a method and device for obtaining the reference current of a grid-connected converter. Background Technology
[0002] When a grid fault causes a voltage drop, grid connection specifications typically require grid-connected converters to have low-voltage ride-through capability. When the grid connection point voltage is at or above a given voltage profile, the grid-connected converter can maintain continuous operation. Clearly, outputting a larger fault current helps increase the grid connection point voltage of the grid-connected converter. However, the fault current tolerance capacity of grid-connected converters is limited, typically not exceeding twice the rated current. Therefore, designing a reasonable fault control strategy for grid-connected converters to achieve optimal voltage support within a safe current range is a pressing issue. The essence of this problem is how to rationally distribute the different components of the converter current (positive-sequence active / reactive, negative-sequence active / reactive) within a limited space.
[0003] In high-voltage power grids, line impedance is primarily inductive. Grid connection specifications typically require grid-connected converters to prioritize reactive current output to achieve good voltage support. More generally, setting the active / reactive current ratio of the converter output equal to the resistance / reactance ratio of the line impedance yields theoretically optimal voltage support. These are the two main fault voltage support strategies for grid-connected converters, which have two main problems: 1) They focus on the active / reactive current ratio allocation without providing a method for positive / negative sequence current allocation; 2) The active / reactive current allocation uses a fixed ratio and cannot adaptively adjust to changes in fault scenarios.
[0004] Therefore, it is desirable to have a technical solution to overcome or at least mitigate one of the aforementioned defects of the prior art. Summary of the Invention
[0005] The purpose of this invention is to provide a method for obtaining the reference current of a grid-connected converter to overcome or at least mitigate one of the above-mentioned defects in the prior art.
[0006] One aspect of the present invention provides a method for obtaining the reference current of a grid-connected converter for use in grid fault conditions, the method comprising:
[0007] Obtain the voltage drop across the virtual impedance of the converter after a power grid fault;
[0008] Obtain the magnitude of the virtual impedance;
[0009] Obtain the phase angle of the updated virtual impedance;
[0010] The reference current of the converter is obtained based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance.
[0011] Optionally, obtaining the voltage drop across the converter's virtual impedance after a grid fault includes:
[0012] Obtain the three-phase voltage at the converter's grid connection point before the grid fault;
[0013] Obtain the three-phase voltage at the converter's grid connection point after a grid fault;
[0014] The voltage drop across the virtual impedance of the converter after the grid fault is obtained based on the three-phase voltage at the converter's grid connection point before and after the grid fault.
[0015] Optionally, obtaining the magnitude of the virtual impedance includes:
[0016] The largest of the phase voltage drops of the virtual impedance is taken as the maximum value of the phase voltage drops of the virtual impedance.
[0017] Obtain the maximum allowable current value of the converter;
[0018] The magnitude of the virtual impedance is obtained based on the maximum value of the voltage drop in each phase of the virtual impedance and the maximum allowable current of the converter.
[0019] Optionally, obtaining the phase angle of the updated virtual impedance includes:
[0020] Obtain the phase angle of the virtual impedance in the initial period;
[0021] Get the current power frequency cycle number. If the current power frequency cycle number is greater than 3, get the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle.
[0022] Obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point during the (k-2)th power frequency cycle;
[0023] Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If so, then...
[0024] The phase angle of the updated virtual impedance is obtained using the first method.
[0025] Optionally, obtaining the phase angle of the updated virtual impedance further includes:
[0026] Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If not, then...
[0027] The second method is used to obtain the phase angle of the updated virtual impedance.
[0028] Optionally, obtaining the phase angle of the updated virtual impedance further includes:
[0029] Get the current power frequency cycle number. If the current power frequency cycle number is equal to 2, then...
[0030] The phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period plus the perturbation step size, or the phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period minus the perturbation step size.
[0031] Optionally, the first method is:
[0032] The phase angle of the updated virtual impedance is obtained using the following formula:
[0033] in,
[0034] The phase angle of the updated virtual impedance, k is the kth power frequency cycle. It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance is k-2 power frequency cycles, and sgn represents the sign function.
[0035] Optionally, the second method is:
[0036] The phase angle of the updated virtual impedance is obtained using the following formula:
[0037] in,
[0038] The phase angle of the updated virtual impedance, k is the kth power frequency cycle. It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance is k-2 power frequency cycles, and sgn represents the sign function.
[0039] Optionally, determining whether the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-1)th power frequency cycle and the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-2)th power frequency cycle satisfy preset conditions includes:
[0040] Determine U min [k-1]≥U min If [k-2] is true, then the preset condition is satisfied; where,
[0041] k is the kth power frequency cycle, U min [k-1] represents the minimum amplitude of the three-phase voltage at the converter grid connection point during the (k-1)th power frequency cycle, U min [k-2] is the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle.
[0042] Optionally, the reference current of the converter, obtained based on the voltage drop across the virtual impedance of the converter after the grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance, is obtained using the following formula:
[0043] in,
[0044] This represents the three-phase reference current of the converter. It is the three-phase voltage at the converter's grid connection point before the power grid fault. It is the three-phase voltage at the converter's grid connection point after a power grid fault.
[0045] This application also provides a reference current acquisition device for a grid-connected converter, the reference current acquisition device for the grid-connected converter comprising:
[0046] A voltage drop acquisition module is used to acquire the voltage drop acting on the virtual impedance of the converter after a power grid fault.
[0047] A module for obtaining the magnitude of virtual impedance, wherein the module is used to obtain the magnitude of virtual impedance;
[0048] The update module is used to obtain the phase angle of the updated virtual impedance;
[0049] A reference current acquisition module is used to acquire the reference current of the converter based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance.
[0050] Beneficial effects:
[0051] The reference current acquisition method for grid-connected converters described in this application has the following advantages:
[0052] 1. It enables grid-connected converters to adaptively handle different types of faults. For example, when a three-phase short-circuit fault occurs in the power grid, the converter automatically outputs a three-phase symmetrical current to provide balanced support for the voltage of each phase. When an asymmetrical fault occurs in the power grid, the fault phase current output by the converter is greater than that of the non-faulty phases, thus providing better voltage support for the faulty phase.
[0053] 2. This invention can ensure that the grid-connected converter is within a safe operating range, and can quickly search for and stabilize at the optimal operating point supported by the fault phase voltage under different fault scenarios. Attached Figure Description
[0054] Figure 1 This is a flowchart illustrating a method for obtaining the reference current of a grid-connected converter according to an embodiment of this application.
[0055] Figure 2 It is an electronic device used to achieve Figure 1 The method for obtaining the reference current of a grid-connected converter is shown.
[0056] Figure 3 This is a schematic diagram of the structure of a grid-connected converter control system according to an embodiment of this application.
[0057] Figure 4 This is a schematic diagram of the grid-connected converter connected to the power grid according to an embodiment of this application.
[0058] Figure 5 This is a schematic diagram of the process of adjusting the virtual impedance phase angle of the converter.
[0059] Figure 6 This is a schematic diagram of the virtual impedance modulus adjustment process of the converter.
[0060] Figure 7 This is a schematic diagram showing the maximum amplitude of the three-phase output current of the converter.
[0061] Figure 8 This is a schematic diagram showing the minimum value of the three-phase voltage amplitude at the converter's grid connection point. Detailed Implementation
[0062] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.
[0063] It should be noted that in the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0064] Figure 1 This is a flowchart illustrating a method for obtaining the reference current of a grid-connected converter according to an embodiment of this application.
[0065] like Figure 1 The reference voltage regulation method for the grid-connected converter shown is used in grid fault conditions. The reference current acquisition method for this grid-connected converter includes:
[0066] Step 1: Obtain the voltage drop across the virtual impedance of the converter after a grid fault;
[0067] Step 2: Obtain the magnitude of the virtual impedance;
[0068] Step 3: Obtain the phase angle of the updated virtual impedance;
[0069] Step 4: Obtain the reference current of the converter based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance.
[0070] The reference current acquisition method for grid-connected converters described in this application has the following advantages:
[0071] 1. It enables grid-connected converters to adaptively handle different types of faults. For example, when a three-phase short-circuit fault occurs in the power grid, the converter automatically outputs a three-phase symmetrical current to provide balanced support for the voltage of each phase. When an asymmetrical fault occurs in the power grid, the fault phase current output by the converter is greater than that of the non-faulty phases, thus providing better voltage support for the faulty phase.
[0072] 2. This invention can ensure that the grid-connected converter is within a safe operating range, and can quickly search for and stabilize at the optimal operating point supported by the fault phase voltage under different fault scenarios.
[0073] In this embodiment, obtaining the voltage drop across the virtual impedance of the converter after a grid fault includes:
[0074] Obtain the three-phase voltage at the converter's grid connection point before the grid fault;
[0075] Obtain the three-phase voltage at the converter's grid connection point after a grid fault;
[0076] The voltage drop across the virtual impedance after the grid connection point failure is obtained based on the three-phase voltage of the converter connection point before the grid failure and the three-phase voltage of the converter connection point after the grid failure.
[0077] For example, It refers to the three-phase voltage at the converter's grid connection point before the power grid fault. This represents the three-phase voltage at the converter's grid connection point after a grid fault. It is the voltage drop acting on the virtual impedance.
[0078] In this embodiment, obtaining the magnitude of the virtual impedance includes:
[0079] The largest of the phase voltage drops of the virtual impedance is taken as the maximum value of the phase voltage drops of the virtual impedance.
[0080] Obtain the maximum allowable current value of the converter;
[0081] The magnitude of the virtual impedance is obtained based on the maximum voltage drop of each phase of the virtual impedance and the maximum allowable current of the converter.
[0082] For example, first calculate the magnitude of the voltage drop across each phase of the virtual impedance, and denote the maximum value (the maximum voltage drop across each phase of the virtual impedance) as ΔU. max ;
[0083] I lim This indicates the maximum allowable current value of the converter, which can be obtained through existing technology and will not be elaborated here.
[0084] The magnitude of the virtual impedance is obtained based on the maximum voltage drop of each phase of the virtual impedance and the maximum allowable current of the converter. Specifically, it is obtained using the following formula:
[0085] Among them, |Z S | represents the magnitude of the virtual impedance.
[0086] In this embodiment, obtaining the phase angle of the updated virtual impedance includes:
[0087] Obtain the phase angle of the virtual impedance in the initial period;
[0088] Get the current power frequency cycle number. If the current power frequency cycle number is greater than 3, get the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle.
[0089] Obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point during the (k-2)th power frequency cycle;
[0090] Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If so, then...
[0091] The phase angle of the updated virtual impedance is obtained using the first method.
[0092] In this embodiment, obtaining the phase angle of the updated virtual impedance further includes:
[0093] Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If not, then...
[0094] The second method is used to obtain the phase angle of the updated virtual impedance.
[0095] In this embodiment, the first method is:
[0096] The phase angle of the updated virtual impedance is obtained using the following formula:
[0097] in,
[0098] The phase angle of the updated virtual impedance, k is the kth power frequency cycle. It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance is k-2 power frequency cycles, and sgn represents the sign function.
[0099] In this embodiment, the second method is:
[0100] The phase angle of the updated virtual impedance is obtained using the following formula:
[0101] in,
[0102] The phase angle of the updated virtual impedance, k is the kth power frequency cycle. It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance is k-2 power frequency cycles, and sgn represents the sign function.
[0103] In this embodiment, determining whether the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-1)th power frequency cycle and the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-2)th power frequency cycle satisfy preset conditions includes:
[0104] Determine U min [k-1]≥U min If [k-2] is true, then the preset condition is satisfied; where,
[0105] k is the kth power frequency cycle, U min [k-1] represents the minimum amplitude of the three-phase voltage at the converter grid connection point during the (k-1)th power frequency cycle, U min [k-2] is the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle.
[0106] In this embodiment, obtaining the phase angle of the updated virtual impedance further includes:
[0107] Get the current power frequency cycle number. If the current power frequency cycle number is equal to 2, then...
[0108] The phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period plus the perturbation step size, or the phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period minus the perturbation step size.
[0109] In this embodiment, the phase angle of the virtual impedance Updated once per power frequency cycle.
[0110] Let k represent the sequence number of the current power frequency cycle. At the beginning of the k-th power frequency cycle, for Update the value of , denoted as . At the end of the kth power frequency cycle, the amplitudes of the three-phase voltages at the converter grid connection point are compared, and the minimum value is denoted as U. min [k].
[0111] In this embodiment, the initial value of the phase angle of the virtual impedance in the initial period is... Set to 90°
[0112] Understandably, this value can also be selected as any other value as needed to obtain the sequence number of the current power frequency cycle. If the sequence number of the current power frequency cycle is equal to 2, that is... Set as or in It is the perturbation step size.
[0113] When k≥3, determine U min [k-1]≥U min Does [k-2] hold true?
[0114] If true, then it is determined by the following formula.
[0115]
[0116] If this is not true, then determine it using the following formula.
[0117]
[0118] In this embodiment, the reference current of the converter is obtained based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance using the following formula:
[0119] in,
[0120] In this formula, Indicates the three-phase reference current of the converter It is the three-phase voltage at the converter's grid connection point before the power grid fault. The three-phase voltage at the converter's grid connection point after a power grid fault. The subscripts A, B, and C correspond to phase A, phase B, and phase C in the power system, respectively. |Z S | and These represent the magnitude and phase angle of the converter's virtual impedance, respectively.
[0121] The following examples further illustrate this application in detail. It is understood that these examples do not constitute any limitation on this application.
[0122] See Figure 3 as well as Figure 4 The structure of the grid-connected converter control system in this application is as follows: Figure 3 As shown in the diagram. A schematic diagram of a grid-connected converter connected to the power grid is shown below. Figure 4 As shown.
[0123] The grid's rated voltage is 380V, and the system impedance is 0.2 + j1.5Ω. Line 1 and Line 2 are both 1km long, with an impedance per unit length of 0.6 + j0.16Ω / km. The converter's maximum allowable current is 60.8A, and its initial virtual impedance phase angle is set to 90°. Before the grid fault, the converter's output active power was 12kW.
[0124] At t = 0.06s, a two-phase metallic short circuit (A and B) occurs at the end of line 1. The process of adjusting the virtual impedance phase angle of the converter using the method of this application is as follows: Figure 5 As shown. The virtual impedance modulus adjustment process of the converter is as follows. Figure 6 As shown. The maximum amplitude of the three-phase output current of the converter is as follows. Figure 7 As shown, the current is accurately limited to near the maximum allowable value throughout the fault control process. The minimum value of the three-phase voltage amplitude at the converter grid connection point is as follows: Figure 8 As shown, during the fault control process, the voltage gradually increased from the initial 87V to a stable 118V.
[0125] In this embodiment,
[0126] The above formula can also be written in a more specific form:
[0127]
[0128] It can be seen that after a power grid fault, assuming that the voltage deviation of phase A is the largest, that is... middle If the amplitude is at its maximum, then the three-phase reference current generated by the converter will be at its maximum. middle, Its amplitude is the largest.
[0129] In summary, the amplitude of the three-phase output current of the converter is automatically proportional to the degree of reduction (deviation) of the three-phase voltage at the grid connection point, thus it can automatically adapt to different fault types.
[0130] Under three-phase short-circuit conditions, the voltage deviation of each phase is the same, so the current output by the converter is three-phase symmetrical, providing equal support (boost) to each phase voltage.
[0131] In the case of a two-phase short circuit, the voltage deviation of the faulty phase is significantly greater than that of the non-faulty phase. Therefore, the output current of the converter in the faulty phase is also significantly greater than that in the non-faulty phase, which can provide stronger support for the voltage of the faulty phase.
[0132] This application also provides a reference current acquisition device for a grid-connected converter. The reference current acquisition device for the grid-connected converter includes a voltage drop acquisition module, a virtual impedance magnitude acquisition module, an update module, and a reference current acquisition module.
[0133] The voltage drop acquisition module is used to acquire the voltage drop across the virtual impedance of the converter after a grid fault.
[0134] The virtual impedance magnitude acquisition module is used to obtain the magnitude of the virtual impedance;
[0135] The update module is used to obtain the phase angle of the updated virtual impedance;
[0136] The reference current acquisition module is used to acquire the reference current of the converter based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance.
[0137] It is understandable that the above description of the method also applies to the description of the apparatus.
[0138] Figure 2 This is an exemplary structural diagram of an electronic device capable of implementing the reference current acquisition method for a grid-connected converter according to an embodiment of this application.
[0139] like Figure 2 As shown, the electronic device includes an input device 501, an input interface 502, a central processing unit 503, a memory 504, an output interface 505, and an output device 506. The input interface 502, central processing unit 503, memory 504, and output interface 505 are interconnected via a bus 507. The input device 501 and output device 506 are connected to the bus 507 via the input interface 502 and output interface 505, respectively, and thus connected to other components of the electronic device. Specifically, the input device 501 receives input information from the outside and transmits it to the central processing unit 503 via the input interface 502. The central processing unit 503 processes the input information based on computer-executable instructions stored in the memory 504 to generate output information, temporarily or permanently storing the output information in the memory 504, and then transmitting the output information to the output device 506 via the output interface 505. The output device 506 outputs the output information to the outside of the electronic device for user use.
[0140] In other words, Figure 2 The illustrated electronic device may also be implemented as including: a memory storing computer-executable instructions; and one or more processors, which can be coupled when executing the computer-executable instructions. Figure 1 The method for obtaining the reference current of a grid-type converter is described.
[0141] In one embodiment, Figure 2 The electronic device shown can be implemented as including: a memory 504 configured to store executable program code; and one or more processors 503 configured to run the executable program code stored in the memory 504 to execute the reference current acquisition method for the grid-connected converter in the above embodiments.
[0142] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.
[0143] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.
[0144] Computer-readable media include both permanent and non-permanent, removable and non-removable media, and information storage can be achieved by any method or technology. Information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, DVD or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transfer medium that can be used to store information accessible by a computing device.
[0145] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0146] Furthermore, it is clear that the word "comprising" does not exclude other units or steps. Multiple units, modules, or devices recited in a device claim may also be implemented by a single unit or overall device through software or hardware. The terms "first," "second," etc., are used to identify names, not to indicate any specific order.
[0147] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this application. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutively marked blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or the overall flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.
[0148] In this embodiment, the processor may be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.
[0149] Memory can be used to store computer programs and / or modules. The processor implements various functions of the device / terminal equipment by running or executing the computer programs and / or modules stored in the memory, and by accessing data stored in the memory. Memory can mainly include a program storage area and a data storage area. The program storage area can store the operating system, application programs required for at least one function (such as sound playback function, image playback function, etc.), etc.; the data storage area can store data created based on the use of the mobile phone (such as audio data, phonebook, etc.). In addition, memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disk, RAM, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one disk storage device, flash memory device, or other volatile solid-state storage device.
[0150] In this embodiment, if the modules / units integrated into the device / terminal equipment are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by hardware related to computer program instructions. The computer program can be stored in a computer-readable storage medium, and when the computer program is executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.
[0151] It should be noted that the content contained in a computer-readable medium may be appropriately added to or reduced according to the requirements of legislation and patent practice in the jurisdiction. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.
[0152] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.
Claims
1. A method for obtaining the reference current of a grid-connected converter, used in grid fault conditions, characterized in that, The method for obtaining the reference current of the grid-connected converter includes: Obtain the voltage drop across the virtual impedance of the converter after a power grid fault; Obtain the magnitude of the virtual impedance; Obtain the phase angle of the updated virtual impedance; The reference current of the converter is obtained based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance. The voltage drop across the converter's virtual impedance after a grid fault includes: Obtain the three-phase voltage at the converter's grid connection point before the grid fault; Obtain the three-phase voltage at the converter's grid connection point after a grid fault; The voltage drop acting on the virtual impedance of the converter after the grid fault is obtained based on the three-phase voltage of the converter connection point before and after the grid fault. The process of obtaining the magnitude of the virtual impedance includes: The largest of the phase voltage drops of the virtual impedance is taken as the maximum value of the phase voltage drops of the virtual impedance. Obtain the maximum allowable current value of the converter; The magnitude of the virtual impedance is obtained based on the maximum value of the voltage drop in each phase of the virtual impedance and the maximum allowable current of the converter. The phase angle for obtaining the updated virtual impedance includes: Obtain the phase angle of the virtual impedance in the initial period; Obtain the sequence number of the current power frequency cycle. If the sequence number of the current power frequency cycle is greater than 3, then obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle; where k is the kth power frequency cycle. Obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point during the (k-2)th power frequency cycle; Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If so, then... The phase angle of the updated virtual impedance is obtained using the first method.
2. The reference current acquisition method for a grid-connected converter as described in claim 1, characterized in that, The step of obtaining the phase angle of the updated virtual impedance further includes: Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If not, then... The second method is used to obtain the phase angle of the updated virtual impedance.
3. The reference current acquisition method for a grid-connected converter as described in claim 1, characterized in that, The step of obtaining the phase angle of the updated virtual impedance further includes: Get the current power frequency cycle number. If the current power frequency cycle number is equal to 2, then... The phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period plus the perturbation step size, or the phase angle of the updated virtual impedance is the phase angle of the virtual impedance in the initial period minus the perturbation step size.
4. The reference current acquisition method for a grid-connected converter as described in claim 1, characterized in that, The first method is: The phase angle of the updated virtual impedance is obtained using the following formula: ;in, The phase angle of the updated virtual impedance, k is the kth power frequency cycle, and Δ φ It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance for k-2 power frequency cycles, and sgn represent the sign function; the second method is: The phase angle of the updated virtual impedance is obtained using the following formula: ;in, The phase angle of the updated virtual impedance, k is the kth power frequency cycle, and Δ φ It is the perturbation step size, The phase angle of the virtual impedance for k-1 power frequency cycles. The phase angle of the virtual impedance is k-2 power frequency cycles, and sgn represents the sign function.
5. The reference voltage regulation method for a grid-connected converter as described in claim 1, characterized in that, The step of determining whether the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-1)th power frequency cycle and the minimum values of the amplitudes of the three-phase voltages at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions includes: judge U min [ k -1]≥ U min [ k If -2] is true, then the preset condition is satisfied; where, k is the kth power frequency cycle. U min [ k [-1] represents the minimum amplitude of the three-phase voltage at the converter grid connection point during the (k-1)th power frequency cycle. U min [ k [-2] represents the minimum amplitude of the three-phase voltage at the converter grid connection point during the (k-2)th power frequency cycle.
6. The reference voltage regulation method for a grid-connected converter as described in claim 1, characterized in that, The reference current of the converter, which is obtained based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance, is obtained using the following formula: ;in, This represents the three-phase reference current of the converter. It is the three-phase voltage at the converter's grid connection point before the power grid fault. It is the three-phase voltage at the converter's grid connection point after a power grid fault.
7. A reference current acquisition device for a grid-connected converter, characterized in that, The reference current acquisition device for the grid-connected converter includes: A voltage drop acquisition module is used to acquire the voltage drop acting on the virtual impedance of the converter after a power grid fault. A module for obtaining the magnitude of virtual impedance, wherein the module is used to obtain the magnitude of virtual impedance; The update module is used to obtain the phase angle of the updated virtual impedance; A reference current acquisition module is used to acquire the reference current of the converter based on the voltage drop across the virtual impedance of the converter after the power grid fault, the magnitude of the virtual impedance, and the phase angle of the virtual impedance. The voltage drop across the converter's virtual impedance after a grid fault includes: Obtain the three-phase voltage at the converter's grid connection point before the grid fault; Obtain the three-phase voltage at the converter's grid connection point after a grid fault; The voltage drop acting on the virtual impedance of the converter after the grid fault is obtained based on the three-phase voltage of the converter connection point before and after the grid fault. The process of obtaining the magnitude of the virtual impedance includes: The largest of the phase voltage drops of the virtual impedance is taken as the maximum value of the phase voltage drops of the virtual impedance. Obtain the maximum allowable current value of the converter; The magnitude of the virtual impedance is obtained based on the maximum value of the voltage drop in each phase of the virtual impedance and the maximum allowable current of the converter. The phase angle for obtaining the updated virtual impedance includes: Obtain the phase angle of the virtual impedance in the initial period; Obtain the sequence number of the current power frequency cycle. If the sequence number of the current power frequency cycle is greater than 3, then obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle; where k is the kth power frequency cycle. Obtain the minimum value of the amplitude of the three-phase voltage at the converter grid connection point during the (k-2)th power frequency cycle; Determine whether the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-1)th power frequency cycle and the minimum amplitude of the three-phase voltage at the converter grid connection point in the (k-2)th power frequency cycle meet preset conditions. If so, then... The phase angle of the updated virtual impedance is obtained using the first method.