Variable admittance-based fault current limiting system and method for grid-forming converter

Abstract

Disclosed in the present invention are a variable admittance-based fault current limiting system and method for a grid-forming converter. The system comprises: a power calculation module, an excitation link module, a virtual rotor module, a coordinate transformation module, a dual-loop control module, and a space vector pulse width modulation module. The power calculation module is used for calculating active power and reactive power of a current power grid; the excitation link module is used for performing steady-state stepless variable susceptance control on the basis of the calculated reactive power, so as to adjust the electromotive force of the current power grid; the virtual rotor module is used for performing transient stepped variable conductance control on the basis of the calculated active power, so as to adjust the phase angle of the current power grid; the coordinate transformation module is used for converting the adjusted electromotive force and phase angle into electromotive force components in a direct current coordinate system; the dual-loop control module is used for generating and calculating a current instruction on the basis of the converted electromotive force components; and the space vector pulse width modulation module is used for generating a modulation signal to guide operation of a switching device.

Description

A fault current limiting system and method for grid-type converters with varying admittance Technical Field

[0001] This invention relates to the field of aero-engine demand analysis, and specifically to a fault current limiting system and method for a grid-type converter with variable admittance. Background Technology

[0002] With the large-scale integration of new energy power generation equipment into the grid, the proportion of the physical rotor inherent in synchronous generators is gradually decreasing. This results in a reduction in the system's immunity to disturbances. The absence of a rotor reduces the inertia of the power system, significantly decreasing its ability to resist wide-frequency oscillations and absorb harmonics. Furthermore, unlike traditional generators that regulate electromotive force through excitation and phase through rotor motion, new energy power electronic generation and consumption equipment, which relies on multiple control loops, increases the risks of frequency and voltage fluctuations and flicker. The combination and superposition of different switching devices also deteriorate the power quality of the system, posing significant crises and challenges to the large-scale grid integration of new energy.

[0003] In power systems, especially those with a high proportion of renewable energy, short-circuit faults are the most common and severe type of grid fault. Similar to synchronous machines, grid-connected converters actively stabilize their internal electromotive force during grid voltage dips and recoveries. Their inherent characteristics cause them to output extremely large currents to maintain voltage levels, especially during these rapid voltage dips and recoveries, which can lead to overcurrent. Grid-connected converters are essentially power electronic devices, and their current handling capacity depends on the current handling capability of their switching devices. Voltage dips and recoveries can easily damage these devices. Therefore, current limiting strategies during voltage dips and recovery are a crucial technology for the stable operation of grid-connected converters. How to ensure that grid-connected converters can stably support the grid while maintaining their overload capacity during fault ride-through, and guarantee the stable operation of the system without disconnecting from the grid, has become an urgent problem to be solved for renewable energy grid integration. Summary of the Invention

[0004] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0005] The purpose of this invention is to solve the above problems and provide a grid-type converter with variable admittance fault current limiting system and method. Based on the virtual rotor module and excitation link module, it provides configurable inertia and damping for the power grid. By simulating the inertia and damping characteristics externally, it has the external characteristics of a synchronous generator, which ensures the grid adaptability of new energy grid connection and makes it possible for large-scale multi-source heterogeneous new energy converters to be connected to the grid at the same time.

[0006] The technical solution of this invention is as follows:

[0007] This invention provides a fault current limiting system for a grid-type converter with varying admittance, comprising: a power calculation module, an excitation module, a virtual rotor module, a coordinate transformation module, a dual-loop control module, and a space vector pulse width modulation module; wherein...

[0008] The power calculation module is used to calculate the active and reactive power of the current power grid.

[0009] The excitation module is used to perform steady-state stepless susceptance control based on the calculated reactive power, thereby regulating the electromotive force of the current power grid.

[0010] The virtual rotor module is used to perform instantaneous stepped variable conductance control based on the calculated active power, thereby adjusting the phase angle of the current power grid.

[0011] The coordinate transformation module is used to convert the adjusted electromotive force and phase angle into electromotive force components in a DC coordinate system.

[0012] The dual-loop control module is used to generate and calculate current commands based on the converted electromotive force component.

[0013] The space vector pulse width modulation module is used to generate modulation signals to guide the operation of switching devices.

[0014] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention, when the power calculation module calculates the active power and reactive power of the current power grid, it first combines the phase angle in the current power grid to calculate the three-phase output current i oabc and voltage u oabc Converted to current components i in DC coordinate system respectively od i oq and voltage component u od u oq Then combine the current component i od i oq and voltage component u od u oq To calculate the active and reactive power in the current power grid.

[0015] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention, the grid-type converter variable admittance fault current limiting system further includes a notch filter; wherein, after calculating the active power and reactive power in the current power grid, the grid-type converter variable admittance fault current limiting system filters the active power and reactive power in the current power grid through the notch filter, thereby obtaining the filtered active power and reactive power.

[0016] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention, after calculating the active power and reactive power in the current power grid, the calculated active power and reactive power are transmitted to the virtual rotor module and the excitation link module respectively for steady-state stepless variable susceptance control and instantaneous stepped variable conductance control, thereby providing configurable phase angle and electromotive force for the dual-loop control module.

[0017] According to an embodiment of the grid-type converter fault current limiting system of the present invention, during steady-state stepless variable susceptance control, if a voltage drop in the current power grid is detected, the reactive power in the current power grid is steadily adjusted by adjusting the susceptance value after the voltage drop, thereby providing a configurable electromotive force for the dual-loop control module; wherein, the formula for adjusting the susceptance value after the voltage drop is as follows:

[0018] Where B represents the adjusted susceptance value,

[0019] k b This represents the voltage-susceptance adjustment coefficient.

[0020] u p This indicates the peak voltage detected in real time.

[0021] u peak This indicates a preset normal voltage value.

[0022] B ori This represents a preset susceptance value for normal operation.

[0023] According to an embodiment of the grid-type converter fault current limiting system of the present invention, when the virtual rotor module performs instantaneous stepped variable conductance control, it sets multiple admittance grade values ​​based on the positive sequence active current change rate, and then performs instantaneous stepped variable conductance control by setting the admittance grade values.

[0024] According to an embodiment of the grid-type converter fault current limiting system of the present invention, the virtual rotor module sets five admittance levels m1, m2, m3, m4, and m5 based on a preset virtual rotor formula to perform instantaneous stepped variable conductance control. The steps are as follows:

[0025] Step C1: Detect the voltage in the current power grid and calculate the positive sequence active current change rate dip / dt;

[0026] Step C2: Determine whether the calculated positive sequence active current change rate dip / dt is greater than m1 and less than m2; if yes, adjust the conductance value G to equal the instantaneous conductance GT1; if no, return to step C1 to continue calculating the positive sequence active current change rate dip / dt.

[0027] Step C3: Continue to determine whether the positive sequence active current change rate dip / dt is greater than m3 and less than m4; if yes, adjust the conductance value G to equal the instantaneous conductance GT2; if no, continue to set the conductance value G to equal the instantaneous conductance GT1.

[0028] Step C4: Continue to determine whether the positive sequence active current change rate dip / dt is greater than m5; if yes, determine that the sampling is incorrect; if no, continue to set the conductance value G to be equal to the instantaneous conductance GT2.

[0029] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention, when calculating the positive sequence active current change rate dip / dt of the current power grid, the grid-type converter variable admittance fault current limiting system first calculates the positive sequence active current and reactive current in the current power grid, and then calculates the positive sequence active current change rate dip / dt of the current power grid using the calculated positive sequence active current.

[0030] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention, the grid-type converter variable admittance fault current limiting system calculates the positive sequence active current and reactive current through the following steps:

[0031] Step D1: Calculate the fundamental components of the phase voltage and phase current within one fundamental cycle;

[0032] Step D2: Calculate the voltage vector component and current vector component of the fundamental positive sequence component based on the calculated fundamental components of the phase voltage and phase current.

[0033] Step D3: Calculate the active power and reactive power of the fundamental positive sequence component based on the voltage vector component and current vector component of the fundamental positive sequence component.

[0034] Step D4: Calculate the effective values ​​of active current and reactive current based on the calculated active and reactive power of the fundamental positive sequence component.

[0035] According to an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention,

[0036] This invention also provides a fault current limiting method for a grid-type converter with varying admittance, comprising the following steps:

[0037] Step S1: Calculate the active and reactive power of the current power grid;

[0038] Step S2: Based on the calculated reactive power and active power, perform steady-state stepless variable susceptance control and stepped variable conductance control respectively, thereby adjusting the electromotive force and phase angle of the current power grid;

[0039] Step S3: Convert the adjusted electromotive force and phase angle into electromotive force components in the DC coordinate system;

[0040] Step S4: Calculate and generate the current command based on the converted electromotive force component.

[0041] The present invention also provides a computer-readable medium storing computer program code that, when executed by a processor, implements the method described above.

[0042] The present invention also provides a fault current limiting device for a grid-type converter with varying admittance, comprising:

[0043] Memory, used to store instructions that can be executed by a processor; and

[0044] A processor for executing the instructions to implement the method described above.

[0045] Compared with existing technologies, this invention offers the following advantages: For grid-connected converters with varying admittance faults, this invention provides configurable inertia and damping to the grid based on a virtual rotor module and an excitation module. A steady-state stepless variable susceptance control method is used for the conductance in the excitation module, enabling the control system to gradually converge to an overdamped state within a specific timeframe under varying external equivalent impedance. This ensures system stability and effectively limits the equivalent resistance (R) to match current limiting, thereby achieving stable output current during faults under overload conditions and providing sufficient stable reactive power support. Simultaneously, the active current change rate is detected at the moment of fault occurrence and recovery. Based on the magnitude of the active current change rate, instantaneous stepped variable conductance control is used in stages to limit the inrush current in the virtual rotor admittance module, effectively limiting the inrush current and avoiding shutdowns and grid disconnections caused by simulated inrushes. This ensures grid adaptability for new energy grid integration and makes it possible for large-scale multi-source heterogeneous new energy converters to be simultaneously connected to the grid. Attached Figure Description

[0046] The above-described features and advantages of the present invention will be better understood after reading the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings. In the drawings, components are not necessarily drawn to scale, and components having similar related characteristics or features may have the same or similar reference numerals.

[0047] Figure 1 is a system architecture diagram illustrating an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention.

[0048] Figure 2 is a control schematic diagram illustrating an embodiment of the grid-type converter variable admittance fault current limiting system of the present invention.

[0049] Figure 3 is a flowchart illustrating an embodiment of the instantaneous stepped variable conductance control of the present invention.

[0050] Figure 4 is a flowchart illustrating the steps of an embodiment of the present invention for calculating positive-sequence active and reactive currents.

[0051] Figure 5 is a flowchart illustrating the steps of an embodiment of the fault current limiting method for grid-type converters according to the present invention. Detailed Implementation

[0052] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are merely some examples or embodiments of this application. For those skilled in the art, these drawings can be applied to other similar scenarios without creative effort. Unless obvious from the context or otherwise specified, the same reference numerals in the drawings represent the same structures or operations.

[0053] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not specifically singular and may include plural forms. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0054] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of this application. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following drawings denote similar items; therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0055] In detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure will be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0056] In the description of this application, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is usually based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this application and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this application; the directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0057] This document discloses an embodiment of a grid-type converter variable admittance fault current limiting system. Figure 1 is a system architecture diagram illustrating an embodiment of the grid-type converter variable admittance fault current limiting system of this invention, and Figure 2 is a control schematic diagram illustrating an embodiment of the grid-type converter variable admittance fault current limiting system of this invention. As shown in Figures 1 and 2, in this embodiment, the grid-type converter variable admittance fault current limiting system includes a power calculation module, a notch filter, an excitation module, a virtual rotor module, a coordinate transformation module, a dual-loop control module, and a space vector pulse width modulation module. The power calculation module is used to calculate the active power P and reactive power Q of the current power grid. The excitation module is used to perform steady-state stepless variable admittance control based on the calculated reactive power Q, thereby adjusting the electromotive force E of the current power grid. The virtual rotor module is used to perform instantaneous stepped variable conductance control based on the calculated active power P, thereby adjusting the phase angle θ of the current power grid. The coordinate transformation module is used to convert the adjusted electromotive force E and phase angle θ into electromotive force components E in the DC coordinate system. q and E d The dual-loop control module is used to control the converted electromotive force component E. q and E d The current command is generated and calculated. The space vector pulse width modulation module is used to generate modulation signals to guide device operation.

[0058] Specifically, in this embodiment, when the power calculation module calculates the active power P and reactive power Q of the current power grid, it first combines the phase angle of the current power grid to calculate the three-phase output current i. oabc and voltage u oabc Converted to current components i in DC coordinate system respectively od i oq and voltage component u od u oqThen based on the current component i od i oq and voltage component u od u oq To calculate the active power P and reactive power Q in the current power grid.

[0059] In this system, the grid-type converter variable admittance fault current limiting system, after calculating the active power P and reactive power Q in the current power grid, also uses a notch filter to filter the calculated active power P and reactive power Q, thereby obtaining the filtered active power P. c and reactive power Q c Then the filtered active power P c and reactive power Q c The voltage is transmitted to the virtual rotor module and the excitation module respectively for instantaneous stepped conductance control and steady-state stepless susceptance control, thereby providing the dual-loop control module with configurable phase angle θ and electromotive force E. Thus, through the excitation module actively adjusting the generator terminal voltage and the virtual rotor module maintaining a stable power angle, the dual-loop control module achieves autonomous synchronization with the generator and demonstrates the frequency and voltage regulation capabilities of a synchronous generator.

[0060] In this embodiment, after the grid voltage drops, the voltage will remain at a low amplitude. At this time, the excitation module of the voltage source characteristic of the grid converter can be used to track the voltage without error. Without restriction, the reactive power will continue to increase until the voltage returns to normal. However, due to the limited current withstand capability of power electronics, it cannot perform more than 7 times the capability of a synchronous machine. Therefore, an auxiliary current loop is usually added to limit the current. However, when the equivalent impedance of the external grid at the PV node is low enough, the equivalent system of the converter with the current loop superimposed at the time of the fault will operate in an underdamped state, resulting in uncontrolled and gradually diverging current. Therefore, it is necessary to adjust the equivalent susceptance in the grid converter to adapt the entire system to the changing external impedance and readjust the grid converter system to an underdamped state.

[0061] Specifically, in this embodiment, when the excitation module performs steady-state stepless variable susceptance control, upon detecting a voltage dip in the current power grid, it can adjust the reactive power in the current power grid by adjusting the susceptance value after the voltage dip, thereby providing a configurable electromotive force for the dual-loop control module. The formula for adjusting the susceptance value after the voltage dip is as follows:

[0062] Where B represents the adjusted susceptance value, k b U represents the voltage-susceptance adjustment coefficient. p Indicates the real-time detected voltage peak value, u peakB represents a preset normal voltage value. ori This represents a preset susceptance value for normal operation. As shown in the formula above, after a voltage change, the excitation module can autonomously adjust its admittance, stabilizing the steady-state process control system and achieving effective current limiting. Because the admittance element in the excitation module is a forward differential element, its loop width is slightly larger than the current loop, allowing for appropriate filtering of the real-time detected voltage peaks to ensure a smooth transition of the controller state.

[0063] In this embodiment, for grid-type converters, a severe imbalance in the power angle often occurs when dealing with voltage drops. This phenomenon is often accompanied by severe current spikes, easily leading to converter tripping or grid disconnection. Because this time is very short, mechanical components are difficult to adjust effectively without specific phase compensation, and specific phase compensation is often difficult to determine. For overcurrent caused by sudden voltage changes, large-resistance voltage division is the best protection for the converter. Therefore, effective admittance variation needs to be implemented in the grid-type converter to instantly offset voltage changes. However, relying solely on detecting the current peak value to determine admittance changes often has a significant time delay and is prone to false admittance jumps leading to self-oscillation. Therefore, in this embodiment, when the virtual rotor module performs instantaneous stepped conductance control, it sets multiple admittance grade values ​​based on the positive-sequence active current change rate, and then performs instantaneous stepped conductance control using these set admittance grade values.

[0064] The virtual rotor module, based on a preset virtual rotor formula, sets five admittance levels m1, m2, m3, m4, and m5 to perform instantaneous stepped variable conductance control. Figure 3 is a flowchart illustrating an embodiment of the instantaneous stepped variable conductance control of the present invention. The various steps of the instantaneous stepped variable conductance control will be described in detail below with reference to Figure 3.

[0065] Step C1: Detect the voltage in the current power grid and calculate the positive sequence active current change rate dip / dt.

[0066] In this embodiment, when calculating the positive-sequence active current change rate dip / dt of the current power grid, the grid-type converter variable admittance fault current limiting system first calculates the positive-sequence active current and reactive current in the current power grid (used to support the grid voltage during low-voltage breakdown). Then, it calculates the positive-sequence active current change rate dip / dt of the current power grid using the calculated positive-sequence active current. Figure 4 is a flowchart illustrating the steps of calculating the positive-sequence active current and reactive current in an embodiment of the present invention. The detailed steps for calculating the positive-sequence active current and reactive current are described in detail below with reference to Figure 4.

[0067] Step D1: Calculate the fundamental components of the phase voltage and phase current within one fundamental cycle.

[0068] In this embodiment, after measuring the phase voltage and phase current, the fundamental components of the phase voltage and phase current within one fundamental cycle are first calculated, for example, the fundamental cosine component u of phase voltage a. a·cos The fundamental sinusoidal component of phase a voltage u a·sin and the fundamental cosine component i of phase a current a·cos The fundamental sinusoidal component of phase a current i a·sin Wait. Using the fundamental cosine component u of phase a voltage... a·cos The fundamental sinusoidal component of phase a voltage u a·sin For example, the calculation formula is as follows:

[0069] Where f1 represents the fundamental frequency, u a Let U represent the phase voltage (a), and T represent one fundamental frequency period. Therefore, the effective value of its fundamental phase voltage, U... al The calculation formula is as follows:

[0070] Step D2: Calculate the voltage vector component and current vector component of the fundamental positive sequence component based on the calculated fundamental components of the phase voltage and phase current.

[0071] In this embodiment, after calculating the fundamental components of the phase voltage and phase current within the fundamental period through the above steps, the voltage vector component and current vector component of the fundamental positive sequence component are calculated based on the calculated fundamental components of the phase voltage and phase current, respectively. The calculation formulas are as follows:

[0072] Among them, u 1+,cos u represents the cosine component of the fundamental voltage in positive sequence. 1+,sin i represents the sinusoidal component of the fundamental voltage in positive sequence. 1+,cos i represents the cosine component of the fundamental current in positive sequence. 1+,sin It represents the sinusoidal component of the fundamental current in the positive sequence.

[0073] Step D3: Calculate the active power and reactive power of the fundamental positive sequence component based on the voltage vector component and current vector component of the fundamental positive sequence component.

[0074] In this embodiment, after calculating the voltage vector component and current vector component of the fundamental positive sequence component through the above steps, the active power P of the fundamental positive sequence component can be calculated based on the voltage vector component and current vector component of the fundamental positive sequence component. 1+ and reactive power Q 1+ The calculation formula is as follows:

[0075] Step D4: Calculate the effective values ​​of active current and reactive current based on the calculated active and reactive power of the fundamental positive sequence component.

[0076] In this embodiment, the active power and reactive power of the fundamental positive-sequence component are calculated through the above steps. The effective value of the active current I p1+ and the effective value of the reactive current I q1+ can be calculated by the following formula:

[0077] Step C2: Determine whether the calculated rate of change of positive-sequence active current dip / dt is greater than m1 and less than m2; if so, adjust the conductance value G to be equal to the instantaneous conductance GT1; if not, return to Step C1 to continue calculating the rate of change of positive-sequence active current dip / dt.

[0078] Step C3: Continue to determine whether the rate of change of positive-sequence active current dip / dt is greater than m3 and less than m4; if so, adjust the conductance value G to be equal to the instantaneous conductance GT2; if not, continue to set the conductance value G to be equal to the instantaneous conductance GT1.

[0079] Step C4: Continue to determine whether the rate of change of positive-sequence active current dip / dt is greater than m5; if so, determine that the sampling is incorrect; if not, continue to set the conductance value G to be equal to the instantaneous conductance GT2.

[0080] In this embodiment, after comprehensively considering factors such as the current-carrying capacity level of the converter, the leakage reactance of the transformer, and the LC parameters of the converter, five admittance grading values m1, m2, m3, m4, and m5 are set to perform instantaneous stepped variable-conductance control. Among them, if m1 < dip / dt < m2, then adjust the conductance value G = GT1. Then continue to judge. If m3 < dip / dt < m4, then continue to adjust the conductance value G = GT1. And continue to judge. If m5 < dip / dt, then determine that the sampling is incorrect. Since the rate of change of current is generally not affected by sampling spike interference, this method of using the rate of change of positive-sequence active current (dip / dt) to detect and determine the grading value of the admittance can not only effectively limit the current spike but also well achieve a smooth transition in the transient process.

[0081] This specification also discloses an embodiment of a method for fault current limiting by variable admittance of a network-forming converter. Fig. 5 is a flowchart showing the steps of an embodiment of the method for fault current limiting by variable admittance of the network-forming converter of the present invention. Please refer to Fig. 5. The following is a detailed description of each step of the method for fault current limiting by variable admittance of the network-forming converter.

[0082] Step S1: Calculate the active power and reactive power of the current power grid.

[0083] Step S2: Perform steady-state stepless variable susceptance control and stepped variable-conductance control respectively according to the calculated reactive power and active power, so as to adjust the electromotive force and phase angle of the current power grid;

[0084] Step S3: Convert the adjusted electromotive force and phase angle into electromotive force components in the DC coordinate system;

[0085] Step S4: Calculate and generate the current command based on the converted electromotive force component.

[0086] In this embodiment, when limiting the current of a grid-type converter with variable admittance fault, it is first necessary to calculate the active power P and reactive power Q of the current power grid. Then, based on the calculated reactive power Q and active power P, steady-state stepless variable admittance control and stepped variable conductance control are performed respectively, thereby adjusting the electromotive force E and phase angle θ of the current power grid.

[0087] In this process, after calculating the active power P and reactive power Q in the current power grid, the calculated active power P and reactive power Q are filtered to obtain the filtered active power P. c and reactive power Q c Then, based on the filtered active power P c and reactive power Q c Instantaneous stepped conductance control and steady-state stepless susceptance control are performed separately, providing configurable phase angle θ and electromotive force E for the dual-loop control. Thus, by actively adjusting the excitation link of the generator terminal voltage and maintaining a stable power angle with a virtual rotor, the dual-loop control achieves autonomous synchronization with the generator and demonstrates the frequency and voltage regulation capabilities of a synchronous generator.

[0088] This specification also provides a computer-readable medium storing computer program code that, when executed by a processor, implements the variable admittance fault current limiting method for grid-type converters as described above.

[0089] This specification also provides a method for limiting the current of a grid-type converter with varying admittance faults, comprising storing an instruction memory executable by a processor, and a processor for executing the instructions in the instruction memory to implement the method for limiting the current of a grid-type converter with varying admittance faults as described above.

[0090] The prior description of this disclosure is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not intended to be limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0091] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. To clearly illustrate this interchangeability between hardware and software, the various illustrative components, blocks, modules, circuits, and steps are described above in a generalized manner in terms of their functionality. Whether such functionality is implemented as hardware or software depends on the specific application and the design constraints imposed on the overall system. Those skilled in the art may implement the described functionality in different ways for each specific application, but such implementation decisions should not be construed as departing from the scope of the invention.

[0092] The various illustrative logic blocks, modules, and circuits described in conjunction with the embodiments disclosed herein can be implemented or performed using a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. The general-purpose processor may be a microprocessor, but in alternatives, it may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration.

[0093] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of both. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor such that the processor can read and write information to / from the storage medium. In an alternative, the storage medium may be integrated into the processor. The processor and storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In an alternative, the processor and storage medium may reside as discrete components in the user terminal.

[0094] In one or more exemplary embodiments, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software as a computer program product, the functionality may be stored or transmitted as one or more instructions or code on or through a computer-readable medium. A computer-readable medium includes both computer storage media and communication media, encompassing any medium that facilitates the transfer of a computer program from one location to another. A storage medium may be any available medium accessible to a computer. By way of example and not limitation, such a computer-readable medium may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and is accessible to a computer. Any connection is also legitimately referred to as a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of a medium. As used in this article, disk and disc include compact discs (CDs), laser discs, optical discs, digital multi-purpose discs (DVDs), floppy disks, and Blu-ray discs. Disks typically reproduce data magnetically, while discs reproduce data optically using lasers. Combinations of these should also be included within the scope of computer-readable media.

Claims

1. A fault current limiting system for a grid-type converter with variable admittance, characterized in that, include: The system includes a power calculation module, an excitation module, a virtual rotor module, a coordinate transformation module, a dual-loop control module, and a space vector pulse width modulation module; among these, The power calculation module is used to calculate the active and reactive power of the current power grid. The excitation module is used to perform steady-state stepless susceptance control based on the calculated reactive power, thereby adjusting the electromotive force of the current power grid. The virtual rotor module is used to perform instantaneous stepped variable conductance control based on the calculated active power, thereby adjusting the phase angle of the current power grid. The coordinate transformation module is used to convert the adjusted electromotive force and phase angle into electromotive force components in a DC coordinate system. The dual-loop control module is used to generate and calculate current commands based on the converted electromotive force components. The space vector pulse width modulation module is used to generate modulation signals to guide the operation of switching devices.

2. The grid-type converter variable admittance fault current limiting system according to claim 1, characterized in that, When calculating the active and reactive power of the current power grid, the power calculation module first combines the phase angle of the current power grid to calculate the three-phase output current i. oabc and voltage u oabc Converted to current components i in DC coordinate system respectively od i oq and voltage component u od u oq Then combine the current component i od i oq and voltage component u od u oq To calculate the active and reactive power in the current power grid.

3. The grid-type converter variable admittance fault current limiting system according to claim 2, characterized in that, The grid-type converter variable admittance fault current limiting system also includes a notch filter; wherein, after calculating the active power and reactive power in the current power grid, the grid-type converter variable admittance fault current limiting system filters the active power and reactive power in the current power grid through the notch filter, thereby obtaining the filtered active power and reactive power.

4. The grid-type converter variable admittance fault current limiting system according to claim 2, characterized in that, After calculating the active and reactive power in the current power grid, the grid-type converter variable admittance fault current limiting system transmits the calculated active and reactive power to the virtual rotor module and the excitation link module respectively for steady-state stepless variable susceptance control and instantaneous stepped variable conductance control, thereby providing configurable phase angle and electromotive force for the dual-loop control module.

5. The grid-type converter variable admittance fault current limiting system according to claim 4, characterized in that, During steady-state stepless variable susceptance control, if a voltage dip in the current power grid is detected, the reactive power in the current power grid is steadily adjusted by adjusting the susceptance value after the voltage dip, thereby providing a configurable electromotive force for the dual-loop control module. The formula for adjusting the susceptance value after the voltage dip is as follows: Where B represents the adjusted susceptance value, k b This represents the voltage-susceptance adjustment coefficient. u p This indicates the peak voltage detected in real time. u peak This indicates a preset normal voltage value. B ori This represents a preset susceptance value for normal operation.

6. The grid-type converter variable admittance fault current limiting system according to claim 4, characterized in that, When performing instantaneous stepped conductance control, the virtual rotor module sets multiple admittance levels based on the positive sequence active current change rate, and then performs instantaneous stepped conductance control by using the set admittance levels.

7. The grid-type converter variable admittance fault current limiting system according to claim 4, characterized in that, The virtual rotor module, based on a preset virtual rotor formula, sets five admittance levels m1, m2, m3, m4, and m5 to perform instantaneous stepped variable conductance control. The steps are as follows: Step C1: Detect the voltage in the current power grid and calculate the positive sequence active current change rate dip / dt; Step C2: Determine whether the calculated positive sequence active current change rate dip / dt is greater than m1 and less than m2; if yes, adjust the conductance value G to equal the instantaneous conductance GT1; if no, return to step C1 to continue calculating the positive sequence active current change rate dip / dt. Step C3: Continue to determine whether the positive sequence active current change rate dip / dt is greater than m3 and less than m4; if yes, adjust the conductance value G to equal the instantaneous conductance GT2; if no, continue to set the conductance value G to equal the instantaneous conductance GT1. Step C4: Continue to determine whether the positive sequence active current change rate dip / dt is greater than m5; if yes, determine that the sampling is incorrect; if no, continue to set the conductance value G to be equal to the instantaneous conductance GT2.

8. The grid-type converter variable admittance fault current limiting system according to claim 7, characterized in that, When calculating the positive sequence active current change rate dip / dt of the current power grid, the grid-type converter variable admittance fault current limiting system first calculates the positive sequence active current and reactive current in the current power grid, and then calculates the positive sequence active current change rate dip / dt of the current power grid using the calculated positive sequence active current.

9. The grid-type converter variable admittance fault current limiting system according to claim 4, characterized in that, The grid-type converter variable admittance fault current limiting system calculates the positive-sequence active and reactive currents through the following steps: Step D1: Calculate the fundamental components of the phase voltage and phase current within one fundamental cycle; Step D2: Calculate the voltage vector component and current vector component of the fundamental positive sequence component based on the calculated fundamental components of the phase voltage and phase current. Step D3: Calculate the active power and reactive power of the fundamental positive sequence component based on the voltage vector component and current vector component of the fundamental positive sequence component. Step D4: Calculate the effective values ​​of active current and reactive current based on the calculated active and reactive power of the fundamental positive sequence component.

10. A fault current limiting method for a grid-type converter with variable admittance, characterized in that, Includes the following steps: Step S1: Calculate the active and reactive power of the current power grid; Step S2: Based on the calculated reactive power and active power, perform steady-state stepless variable susceptance control and stepped variable conductance control respectively, thereby adjusting the electromotive force and phase angle of the current power grid; Step S3: Convert the adjusted electromotive force and phase angle into electromotive force components in the DC coordinate system; Step S4: Calculate and generate the current command based on the converted electromotive force component.

11. A computer-readable medium storing computer program code, characterized in that, The computer program code implements the method of claim 10 when executed by a processor.

12. A fault current limiting device for a grid-type converter with variable admittance, characterized in that, include: Memory is used to store instructions that can be executed by the processor; as well as A processor for executing the instructions to implement the method as described in claim 10.

Images