Grid-forming converter fault current enhancement control method and device and electronic equipment

Abstract

This invention relates to the field of power electronic control technology, and discloses a method, device, and electronic equipment for enhancing fault current control in a grid-connected converter. The method includes: real-time monitoring of the voltage amplitude at the point of common coupling (PCC) and the grid frequency; determining a grid fault and recording the phase voltage reference value and voltage amplitude sag when the voltage amplitude meets the judgment criteria; determining the DC bus voltage reference value based on the phase voltage reference value and adjusting the converter's DC bus voltage amplitude to match the DC bus voltage reference value; switching the converter's modulation mode to an extremely low switching frequency mode, with its switching frequency consistent with the grid frequency; determining the reactive power reference value based on the voltage amplitude sag and controlling the converter to output reactive power according to this value to regulate the PCC voltage; and determining that the grid fault has been cleared and the converter has been restored to normal operating condition when the PCC voltage amplitude meets the recovery criteria. This invention significantly improves the fault current supply capability of grid-connected converters.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, specifically to a method, device, and electronic equipment for enhancing fault current control of grid-connected converters. Background Technology

[0002] With the large-scale integration of new energy sources into the power grid, the penetration rate of power electronic devices in power systems is continuously increasing. Grid-connected converters, due to their ability to simulate the dynamic characteristics of synchronous generators and stabilize grid voltage and frequency, have become important equipment in new power systems. According to grid standards and specifications, converters must maintain voltage and provide sufficient fault current when grid faults occur to ensure grid stability and the normal operation of traditional protection systems. However, the fault current supply capacity of existing grid-connected converters is limited by the thermal constraints of power semiconductor devices, and their transient overcurrent capacity is far lower than that of synchronous generators. This limitation stems from the compact and high-efficiency design of power electronic inverters, resulting in limited junction temperature margin. During transient faults, the surge in device losses can easily lead to excessive junction temperature, and even cause protection maloperation or failure to operate, thereby reducing the transient stability of the converter and the grid. Therefore, current limiting measures must be taken.

[0003] Limited fault current supply capacity and poor transient overcurrent capability due to thermal constraints of semiconductor devices affect grid stability and protection system operation. Traditional modulation control has high switching losses, and SVPWM control maintains a high switching frequency during faults, causing a surge in switching losses and rapid overheating of semiconductor device junctions, further limiting the potential for increasing fault current. Insufficient grid support capacity means that some technical solutions, while increasing fault current, cannot guarantee sufficient reactive power injection, affecting the grid voltage recovery speed and failing to meet grid specifications for fault ride-through. Summary of the Invention

[0004] This invention provides a fault current enhancement control method, device, and electronic equipment for grid-type converters to solve the problem that existing technologies cannot guarantee sufficient reactive power injection while enhancing fault current, resulting in slow grid voltage recovery.

[0005] In a first aspect, the present invention provides a fault current enhancement control method for a grid-type converter, the method comprising:

[0006] The system monitors the voltage amplitude and grid frequency at the point of common coupling (PCC) in real time. When the voltage amplitude is less than a first preset voltage amplitude and the duration exceeds a first preset duration, a grid fault is identified, and the phase voltage reference value and voltage amplitude sag are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude. The DC bus voltage reference value is determined based on the phase voltage reference value, and the DC bus voltage amplitude of the converter is adjusted to match the DC bus voltage reference value. The converter's modulation mode is switched to an extremely low switching frequency modulation mode, where the converter's switching frequency is consistent with the grid frequency. The reactive power reference value is determined based on the voltage amplitude sag, and the converter is controlled to output reactive power to the PCC based on the reactive power reference value to adjust the PCC voltage amplitude. When the PCC voltage amplitude recovers to a second preset voltage amplitude and the duration exceeds a second preset duration, the grid fault is cleared, and the converter is restored to normal operation.

[0007] The fault current enhancement control method for grid-connected converters provided by this invention accurately distinguishes between real grid faults and transient disturbances by real-time monitoring of the voltage amplitude and grid frequency at the point of common coupling (PCC), combined with a set voltage threshold and duration, thus preventing the control logic from being falsely triggered. After fault detection, the DC bus voltage is adjusted based on the recorded phase voltage reference value to provide sufficient voltage margin for the converter's output under fault conditions, meeting the basic conditions for subsequent voltage and current output. Furthermore, the converter's switching frequency is switched to an extremely low switching frequency modulation mode consistent with the grid frequency, significantly reducing switching losses and avoiding current limiting caused by overheating of devices under high fault current, thereby effectively enhancing the fault current. The corresponding reactive power reference value is determined based on the voltage amplitude drop, and reactive power is output, allowing for precise support of the PCC voltage according to the severity of the fault, improving the converter's voltage support capability and low-voltage ride-through capability. Finally, once the grid voltage meets the recovery conditions, the fault is cleared and normal operation is restored, avoiding shocks and oscillations during the recovery process.

[0008] In one alternative implementation, the converter includes a semiconductor switching device with a freewheeling diode connected in antiparallel across its terminals. In the ultra-low switching frequency modulation mode, the freewheeling diode clamps the voltage across the semiconductor switching device to zero, providing zero-voltage turn-on conditions for the semiconductor switching device.

[0009] The fault current enhancement control method for grid-type converters provided by this invention uses an anti-parallel connection of freewheeling diodes to precisely match the operating timing of semiconductor switching devices. This allows for timely clamping under extremely low switching frequency modulation modes, eliminating turn-on losses at their source. Eliminating turn-on losses effectively prevents performance degradation of semiconductor switching devices due to heat accumulation from loss conversion during operation. Simultaneously, the zero-voltage turn-on state significantly reduces the voltage stress experienced by the semiconductor switching devices during turn-on, minimizing the impact of electrical shocks on the internal structure of the devices.

[0010] In one optional implementation, determining the reactive power reference value based on the voltage amplitude sag includes: When the voltage amplitude sag meets the preset conditions, the reactive power reference value is calculated based on a preset multiple of the rated capacity of the converter; when the voltage amplitude sag does not meet the preset conditions, the reactive power reference value is set as a preset benchmark value. The preset conditions are determined based on the preset sag range of the rated voltage amplitude.

[0011] The fault current enhancement control method for grid-connected converters provided by this invention differentiates the reactive power reference value based on whether the voltage amplitude sag meets corresponding preset conditions, enabling precise matching of the reactive power output strategy with the actual fault severity of the power grid. By dividing fault conditions into preset sag ranges based on the rated voltage amplitude, different degrees of power grid fault severity can be clearly distinguished. For severe fault conditions, the reactive power reference value is calculated according to a preset multiple of the converter's rated capacity, which fully utilizes the converter's reactive power output capability and enhances its voltage support effect on the power grid. For milder fault conditions, the reactive power reference value is set as a preset benchmark value, which satisfies basic voltage regulation requirements while avoiding excessive reactive power output that could cause system operation fluctuations.

[0012] In one optional implementation, determining that the grid fault has been cleared and restoring the converter to normal operating condition includes: The DC bus voltage of the converter is adjusted to the rated DC bus voltage using ramp control; the extremely low switching frequency modulation mode is transitioned back to SVPWM linear modulation mode through an overmodulation stage; and the active and reactive power are adjusted to the rated operating values ​​according to the grid frequency.

[0013] The fault current enhancement control method for grid-connected converters provided by this invention restores the converter to normal operating conditions through a step-by-step, orderly control strategy, ensuring a smooth transition of the system during fault recovery. Using ramp control to regulate the DC bus voltage avoids sudden voltage surges, allowing the DC bus voltage to smoothly return to its rated value and ensuring stable and reliable operation of the DC side circuit. Simultaneously, by gradually adjusting active and reactive power to their rated operating values ​​in conjunction with the grid frequency, the power change process is made gradual and stable, preventing sudden power surges from impacting the grid and the converter.

[0014] In one optional implementation, determining the DC bus voltage reference value based on the phase voltage reference value includes: Determine the proportional relationship between the fundamental component of the phase voltage output by the converter and the DC bus voltage under the ultra-low switching frequency modulation mode; determine the reference value of the DC bus voltage based on the proportional relationship and the phase voltage reference value.

[0015] The fault current enhancement control method for grid-type converters provided by this invention first determines the proportional relationship between the fundamental component of the converter output phase voltage and the DC bus voltage under extremely low switching frequency modulation mode. This ensures that the DC bus voltage always matches the target phase voltage, avoiding deviations from the expected output voltage due to unreasonable DC voltage settings. Furthermore, by combining the phase voltage reference value with the corresponding DC bus voltage reference value, the converter can stably output a voltage that meets the control target through precise determination of the DC bus voltage reference value, improving voltage control accuracy and operational stability, while providing reliable protection for power output and voltage support under subsequent fault conditions.

[0016] In one optional implementation, controlling the converter to output reactive power to the point of common coupling based on a reactive power reference value includes: Virtual impedance adjustment and voltage vector phase optimization are performed on the converter to enable the converter to preferentially output positive sequence reactive current to the point of common coupling.

[0017] The fault current enhancement control method for grid-connected converters provided by this invention improves the output characteristics of the converter under grid fault conditions by adjusting the virtual impedance and optimizing the voltage vector phase, thereby enhancing the balance and stability of the output current. The converter can more accurately and stably prioritize the output of positive-sequence reactive current to the point of common coupling, strengthening its support for grid voltage, improving reactive power utilization efficiency, and ultimately enhancing the converter's adaptability and grid-connected operation stability under asymmetrical grid faults.

[0018] Secondly, the present invention provides a fault current enhancement control device for a grid-type converter, the device comprising: The fault determination module is used to monitor the voltage amplitude and grid frequency of the point of common coupling in real time. When the voltage amplitude is less than the first preset voltage amplitude and the duration exceeds the first preset duration, a grid fault is determined and the phase voltage reference value and voltage amplitude drop are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude. The DC bus voltage dynamic adjustment module is used to determine the DC bus voltage reference value based on the phase voltage reference value and adjust the DC bus voltage amplitude of the converter to the DC bus voltage reference value. The converter mode switching module is used to switch the modulation mode of the converter to the ultra-low switching frequency modulation mode, in which the switching frequency of the converter is consistent with the grid frequency. The reactive power output module is used to determine the reactive power reference value based on the voltage amplitude drop and control the converter to output reactive power to the point of common coupling based on the reactive power reference value in order to adjust the voltage amplitude of the point of common coupling. The fault clearing module is used to determine that the grid fault has been cleared and restore the converter to normal operation when the voltage amplitude at the point of common coupling recovers to the second preset voltage amplitude and the duration exceeds the second preset duration.

[0019] Thirdly, the present invention provides an electronic device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the grid-type converter fault current enhancement control method described in the first aspect or any corresponding embodiment thereof.

[0020] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the grid-type converter fault current enhancement control method of the first aspect or any corresponding embodiment described above.

[0021] Fifthly, the present invention provides a computer program product, including computer instructions for causing a computer to execute the grid-type converter fault current enhancement control method described in the first aspect or any corresponding embodiment thereof. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1This is a schematic diagram of an application scenario according to an embodiment of the present invention; Figure 2 This is a schematic flowchart of a fault current enhancement control method for a grid-type converter according to an embodiment of the present invention; Figure 3 This is a structural block diagram of a grid-type converter fault current enhancement control device according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention and their authorization should be obtained in accordance with relevant laws and regulations through appropriate means.

[0026] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0027] As an optional application scenario of this invention, the specific application environment architecture or specific hardware architecture on which the execution of the grid-type converter fault current enhancement control method depends is described here. For example... Figure 1 As shown, the architecture system may include at least one terminal device and at least one server. Figure 1 The system is illustrated in the example, which includes a computer 101, a mobile terminal 102, and a server 103, and the terminal devices such as the computer 101 and the mobile terminal 102 are connected to the server 103 through a network 110.

[0028] Specifically, the terminal device can be a smartphone, tablet, laptop, PDA, desktop computer, game console, smart TV, smart wearable device, in-vehicle terminal, VR (Virtual Reality) device, AR (Augmented Reality) device, etc. Server 103 can be a standalone physical server, a server cluster, a distributed system, or a cloud server providing cloud services. Network 110 can be a wired or wireless network, examples of which include, but are not limited to, the Internet, corporate intranet, local area network, wide area network, mobile communication network, and combinations thereof.

[0029] According to an embodiment of the present invention, a method for enhancing fault current control of a grid-type converter is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0030] This embodiment provides a fault current enhancement control method for a grid-type converter, which can be used in the aforementioned mobile terminals, such as mobile phones and tablets. Figure 2 This is a flowchart of a fault current enhancement control method for a grid-type converter according to an embodiment of the present invention, such as... Figure 2 As shown, the process includes the following steps: Step S201: Monitor the voltage amplitude and grid frequency at the point of common coupling in real time. When the voltage amplitude is less than the first preset voltage amplitude and the duration exceeds the first preset duration, determine the grid fault and record the phase voltage reference value and voltage amplitude drop.

[0031] In one optional embodiment, the grid-connected converter senses the grid operating status in real time and determines whether a grid fault has occurred by measuring the voltage amplitude at the point of common coupling (PCC) and the grid frequency. Furthermore, it employs a combination of voltage amplitude mutation detection and duration determination. When the voltage amplitude is less than a first preset voltage amplitude and the duration exceeds a first preset duration, a grid fault is determined, and the phase voltage reference value and voltage amplitude drop are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude.

[0032] Among them, voltage amplitude sag is an electrical parameter characterizing the degree of voltage sag at the point of common coupling during a grid fault. Its value is the difference between the rated voltage amplitude and the real-time voltage amplitude at the point of common coupling, used to quantify the depth of the grid voltage sag. The phase voltage reference value is the target phase voltage amplitude used for closed-loop control of the converter during grid-connected operation, serving as a benchmark for converter output voltage regulation.

[0033] Specifically, the voltage amplitude and frequency at the point of common coupling (PCC) are monitored in real time. When the PCC voltage drops below 0.8 pu of the rated value, it is determined to be a power grid fault, which may be due to symmetrical or asymmetrical voltage drops. At the same time, the current phase voltage reference value is recorded. And voltage amplitude drop.

[0034] Step S202: Determine the DC bus voltage reference value based on the phase voltage reference value, and adjust the DC bus voltage amplitude of the converter to the DC bus voltage reference value.

[0035] In one optional embodiment, during a grid fault, to enable the converter to output a sufficiently high voltage to support the grid and provide a larger fault current, the DC bus voltage needs to be adjusted according to the phase voltage reference value. Only when the DC bus voltage reaches a level matching the phase voltage reference value can the converter have sufficient output voltage margin, thereby enabling it to output a sufficient fault current. The phase voltage reference value is a combined command value of the phase voltage amplitude and phase that the converter is expected to output within the current control cycle.

[0036] Step S203: Switch the modulation mode of the converter to the ultra-low switching frequency modulation mode. In the ultra-low switching frequency modulation mode, the switching frequency of the converter is consistent with the grid frequency.

[0037] In one optional embodiment, after the DC bus voltage is adjusted to the target reference value, the converter modulation mode smoothly transitions from SVPWM linear modulation through an overmodulation phase to an extremely low switching frequency modulation mode. The transition process employs optimized overmodulation techniques to ensure the continuity and stability of the voltage output. In this modulation mode, the converter output follows six discrete voltage vectors, and the switching frequency drops to match the grid frequency, achieving extremely low switching frequency operation.

[0038] Step S204: Determine the reactive power reference value based on the voltage amplitude drop, and control the converter to output reactive power to the point of common coupling based on the reactive power reference value, so as to adjust the voltage amplitude of the point of common coupling.

[0039] In an optional embodiment, in the event of a grid fault, the grid-type converter actively outputs reactive power to support the voltage amplitude at the point of common coupling, thereby restoring the voltage amplitude at the point of common coupling to its rated value.

[0040] Step S205: When the voltage amplitude at the point of common coupling recovers to the second preset voltage amplitude and the duration exceeds the second preset duration, it is determined that the grid fault has been cleared and the converter is restored to normal operation.

[0041] In one optional embodiment, the PCC voltage is continuously monitored. When the PCC voltage recovers to a second preset voltage amplitude and the duration exceeds the second preset duration, it is determined that the power grid fault has been cleared, and the mode recovery process is initiated. The second preset voltage amplitude can be 0.9 pu or greater than the rated value, and the second preset duration can be 100 ms.

[0042] The fault current enhancement control method for grid-connected converters provided in this embodiment accurately distinguishes between real grid faults and transient disturbances by real-time monitoring of the voltage amplitude and grid frequency at the point of common coupling (PCC), combined with a set voltage threshold and duration, thus preventing the control logic from being falsely triggered. After fault detection, the DC bus voltage is adjusted based on the recorded phase voltage reference value to provide sufficient voltage margin for the converter's output under fault conditions, meeting the basic conditions for subsequent voltage and current output. Furthermore, the converter's switching frequency is switched to an extremely low switching frequency modulation mode consistent with the grid frequency, significantly reducing switching losses and avoiding current limiting caused by overheating of devices under high fault current, thereby effectively enhancing the fault current. The corresponding reactive power reference value is determined based on the voltage amplitude drop, and reactive power is output, allowing for precise support of the PCC voltage according to the fault severity, improving the converter's voltage support capability and low-voltage ride-through capability. Finally, once the grid voltage meets the recovery conditions, the fault is cleared and normal operation is restored, avoiding shocks and oscillations during the recovery process.

[0043] In some alternative implementations, the converter includes a semiconductor switching device with a freewheeling diode connected in antiparallel across its terminals. In the ultra-low switching frequency modulation mode, the freewheeling diode clamps the voltage across the semiconductor switching device to zero, providing zero-voltage turn-on conditions for the semiconductor switching device.

[0044] In one alternative embodiment, by connecting a freewheeling diode in antiparallel across the semiconductor switching device and utilizing the operating characteristics of the freewheeling diode in the extremely low switching frequency modulation mode, the voltage across the semiconductor switching device can be stably clamped to zero, thereby establishing the core operating condition for zero-voltage turn-on of the semiconductor switching device.

[0045] The fault current enhancement control method for grid-type converters provided in this embodiment uses an anti-parallel connection of freewheeling diodes to precisely match the operating timing of semiconductor switching devices. This allows for timely clamping in extremely low switching frequency modulation modes, eliminating turn-on losses at their source. Eliminating turn-on losses effectively prevents performance degradation of semiconductor switching devices due to heat accumulation from loss conversion during operation. Simultaneously, the zero-voltage turn-on state significantly reduces the voltage stress experienced by the semiconductor switching devices during turn-on, minimizing the impact of electrical shocks on the internal structure of the devices.

[0046] In some alternative implementations, the reactive power reference value is determined based on the voltage amplitude sag, including: When the voltage amplitude drop meets the preset conditions, the reactive power reference value is calculated based on the preset multiple of the converter's rated capacity.

[0047] In an optional embodiment, the preset condition is determined based on a preset drop range of the rated voltage amplitude, for example, the preset condition is met when the PCC voltage drops to 0.2-0.8 pu.

[0048] Specifically, when the voltage amplitude drop meets the preset conditions, it indicates that the current grid voltage drop is relatively deep and the grid fault is relatively serious. The reactive power is increased to 1.0-1.5 times the rated capacity according to the grid specifications, so that the converter outputs a large enough reactive power, thereby quickly increasing the voltage amplitude at the point of common coupling.

[0049] When the voltage amplitude drop does not meet the preset conditions, the reactive power reference value is set to the preset benchmark value.

[0050] In one optional embodiment, when the voltage amplitude drop does not meet the preset conditions, it indicates that the current grid voltage drop is relatively shallow and the grid fault is relatively minor, so there is no need for the converter to output a large amount of reactive power for voltage support. At this time, setting the reactive power reference value to a preset benchmark value enables the converter to output reactive power that meets basic regulation requirements.

[0051] The grid-connected converter fault current enhancement control method provided in this embodiment determines the reactive power reference value differently based on whether the voltage amplitude sag meets the corresponding preset conditions, enabling precise matching of the reactive power output strategy with the actual fault severity of the power grid. By dividing the fault conditions based on a preset sag range of the rated voltage amplitude, different degrees of power grid fault severity can be clearly distinguished. For severe fault conditions, the reactive power reference value is calculated according to a preset multiple of the converter's rated capacity, which can fully utilize the converter's reactive power output capability and enhance the voltage support effect on the power grid. For milder fault conditions, the reactive power reference value is set as a preset benchmark value, which can meet the basic voltage regulation requirements while avoiding excessive reactive power output that could cause system operation fluctuations.

[0052] In some alternative implementations, determining that the grid fault has been cleared and restoring the converter to normal operating condition includes: The DC bus voltage of the converter is adjusted to the rated DC bus voltage using ramp control.

[0053] The extremely low switching frequency modulation mode is transitioned back to the SVPWM linear modulation mode through an overmodulation phase.

[0054] Based on the grid frequency, the active and reactive power are adjusted to their rated operating values.

[0055] In one optional embodiment, after determining that the grid fault has been cleared, the mode recovery process is initiated. First, the DC bus voltage reference value is gradually restored to the rated value, and the recovery process uses ramp control to avoid voltage surges. Simultaneously, the modulation mode transitions from extremely low switching frequency modulation through an over-modulation phase back to SVPWM linear modulation mode, and the switching frequency is gradually increased to the rated value. Reactive power output is restored to normal operating level, and active power is gradually restored according to the grid frequency regulation characteristics to ensure that the converter smoothly switches to normal operating state and avoids secondary impact on the grid caused by mode switching.

[0056] The fault current enhancement control method for grid-type converters provided in this embodiment restores the converter to normal operating conditions through a step-by-step, orderly control strategy, ensuring a smooth transition of the system during fault recovery. Using ramp control to regulate the DC bus voltage avoids sudden voltage surges, allowing the DC bus voltage to smoothly return to its rated value and ensuring stable and reliable operation of the DC side circuit. Simultaneously, by gradually adjusting active and reactive power to their rated operating values ​​in conjunction with the grid frequency, the power change process is made gradual and stable, preventing sudden power surges from impacting the grid and the converter.

[0057] In some optional implementations, determining the DC bus voltage reference value based on the phase voltage reference value includes: Step a1: Determine the ratio between the fundamental component of the phase voltage output by the converter and the DC bus voltage under the extremely low switching frequency modulation mode.

[0058] In an optional embodiment, under the ultra-low switching frequency modulation mode, the fundamental component of the converter output phase voltage has a fixed proportional relationship with the DC bus voltage, that is, the amplitude of the fundamental phase voltage is... DC bus voltage of times.

[0059] Step a2: Determine the DC bus voltage reference value based on the proportional relationship and the phase voltage reference value.

[0060] In an alternative embodiment, the phase voltage reference value required during a fault is synthesized in this modulation mode. The DC bus voltage needs to be dynamically adjusted to the matching value. The calculation formula is as follows:

[0061] The fault current enhancement control method for grid-type converters provided in this embodiment first determines the proportional relationship between the fundamental component of the converter output phase voltage and the DC bus voltage under extremely low switching frequency modulation mode. This ensures that the DC bus voltage always matches the target phase voltage, avoiding deviations from the expected output voltage due to unreasonable DC voltage settings. Furthermore, by combining the phase voltage reference value with the corresponding DC bus voltage reference value, the converter can stably output a voltage that meets the control target through accurate determination of the DC bus voltage reference value, improving voltage control accuracy and operational stability, while providing reliable protection for power output and voltage support under subsequent fault conditions.

[0062] In some alternative implementations, controlling the converter to output reactive power to the point of common coupling based on a reactive power reference value includes: Virtual impedance adjustment and voltage vector phase optimization are performed on the converter to enable the converter to preferentially output positive sequence reactive current to the point of common coupling.

[0063] In one optional embodiment, virtual impedance adjustment and voltage vector phase optimization are performed on the converter to ensure that positive-sequence reactive current is preferentially output to the PCC connection point. Virtual impedance adjustment is a control method that adjusts the impedance value of a virtual impedance element equivalently constructed through a control algorithm within the converter control loop. Voltage vector phase optimization is a control method that rationally plans and corrects the phase, angle, and timing of the output voltage vector during converter modulation and voltage control, enabling the voltage vector to track an ideal trajectory. Furthermore, the reactive power output response time is ≤20ms.

[0064] The fault current enhancement control method for grid-connected converters provided in this embodiment improves the converter's output characteristics under grid fault conditions by performing virtual impedance adjustment and voltage vector phase optimization, thereby enhancing the balance and stability of the output current. The converter can more accurately and stably prioritize the output of positive-sequence reactive current to the point of common coupling, strengthening its support for grid voltage, improving reactive power utilization efficiency, and ultimately enhancing the converter's adaptability and grid-connected operation stability under asymmetrical grid faults.

[0065] This embodiment also provides a grid-type converter fault current enhancement control device, which is used to implement the above embodiments and preferred embodiments; details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0066] This embodiment provides a fault current enhancement control device for a grid-type converter, such as... Figure 3 As shown, it includes: The fault determination module 301 is used to monitor the voltage amplitude and grid frequency of the point of common coupling in real time. When the voltage amplitude is less than the first preset voltage amplitude and the duration exceeds the first preset duration, the grid fault is determined and the phase voltage reference value and voltage amplitude drop are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude. The DC bus voltage dynamic adjustment module 302 is used to determine the DC bus voltage reference value based on the phase voltage reference value, and adjust the DC bus voltage amplitude of the converter to the DC bus voltage reference value; The converter mode switching module 303 is used to switch the modulation mode of the converter to an extremely low switching frequency modulation mode, in which the switching frequency of the converter is consistent with the grid frequency. The reactive power output module 304 is used to determine the reactive power reference value based on the voltage amplitude drop and control the converter to output reactive power to the point of common coupling based on the reactive power reference value in order to adjust the voltage amplitude of the point of common coupling. The fault clearing module 305 is used to determine that the grid fault is cleared and restore the converter to normal operation when the voltage amplitude at the point of common coupling recovers to the second preset voltage amplitude and the duration exceeds the second preset duration.

[0067] The grid-type converter fault current enhancement control device provided in this embodiment of the invention can execute the grid-type converter fault current enhancement control method provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as in the corresponding embodiments described above, and will not be repeated here.

[0068] Figure 4 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0069] The following is a detailed reference. Figure 4 This diagram illustrates a structural schematic suitable for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 401, which can perform various appropriate actions and processes according to a program stored in read-only memory (ROM) 402 or a program loaded from memory 408 into random access memory (RAM) 403. The RAM 403 also stores various programs and data required for the operation of the electronic device. The processor 401, ROM 402, and RAM 403 are interconnected via a bus 404. An input / output (I / O) interface 405 is also connected to the bus 404.

[0070] Typically, the following devices can be connected to I / O interface 405: input devices 406 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 407 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 408 including, for example, magnetic tapes, hard disks, etc.; and communication devices 409. Communication device 409 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 4 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0071] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 409, or installed from a memory 408, or installed from a ROM 402. When the computer program is executed by the processor 401, it performs the functions defined in the grid-type converter fault current enhancement control method of the embodiments of the present invention.

[0072] Figure 4 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0073] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that the computer, processor, microprocessor controller, or programmable hardware includes storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the grid-type converter fault current enhancement control method shown in the above embodiments is implemented.

[0074] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0075] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A method for enhancing fault current control in a grid-type converter, characterized in that, The method includes: Real-time monitoring of the voltage amplitude and grid frequency at the point of common coupling; when the voltage amplitude is less than a first preset voltage amplitude and the duration exceeds a first preset duration, a grid fault is determined and the phase voltage reference value and voltage amplitude drop are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude. The DC bus voltage reference value is determined based on the phase voltage reference value, and the DC bus voltage amplitude of the converter is adjusted to the DC bus voltage reference value. The modulation mode of the converter is switched to an extremely low switching frequency modulation mode, wherein the switching frequency of the converter is consistent with the grid frequency in the extremely low switching frequency modulation mode. The reactive power reference value is determined based on the voltage amplitude drop, and the converter is controlled to output reactive power to the point of common coupling based on the reactive power reference value, so as to adjust the voltage amplitude of the point of common coupling. When the voltage amplitude at the common connection point recovers to the second preset voltage amplitude and the duration exceeds the second preset duration, the power grid fault is determined to be cleared and the converter is restored to normal operation.

2. The method according to claim 1, characterized in that, The converter includes a semiconductor switching device, and a freewheeling diode is connected in antiparallel across the two ends of the semiconductor switching device; In the extremely low switching frequency modulation mode, the freewheeling diode clamps the voltage across the semiconductor switching device to zero, providing zero-voltage turn-on conditions for the semiconductor switching device.

3. The method according to claim 1, characterized in that, Determining the reactive power reference value based on the voltage amplitude sag includes: When the voltage amplitude drop meets the preset conditions, the reactive power reference value is calculated according to a preset multiple of the rated capacity of the converter; When the voltage amplitude drop does not meet the preset conditions, the reactive power reference value is set as a preset benchmark value. The preset conditions are determined based on the preset drop range of the rated voltage amplitude.

4. The method according to claim 1, characterized in that, Determining whether a power grid fault has been cleared and restoring the converter to normal operating condition includes: Ramp control is used to regulate the DC bus voltage of the converter to the rated DC bus voltage; The extremely low switching frequency modulation mode is transitioned back to the SVPWM linear modulation mode through an overmodulation phase. Based on the grid frequency, the active and reactive power are adjusted to their rated operating values.

5. The method according to claim 1, characterized in that, Determining the DC bus voltage reference value based on the phase voltage reference value includes: Determine the proportional relationship between the fundamental component of the phase voltage output by the converter and the DC bus voltage under the extremely low switching frequency modulation mode; The DC bus voltage reference value is determined based on the stated proportional relationship and the stated phase voltage reference value.

6. The method according to claim 1, characterized in that, Controlling the converter to output reactive power to the point of common coupling according to the reactive power reference value includes: Virtual impedance adjustment and voltage vector phase optimization are performed on the converter to enable the converter to preferentially output positive sequence reactive current to the point of common coupling.

7. A fault current enhancement control device for a grid-type converter, characterized in that, The device includes: The fault determination module is used to monitor the voltage amplitude and grid frequency of the point of common coupling in real time. When the voltage amplitude is less than a first preset voltage amplitude and the duration exceeds the first preset duration, a grid fault is determined and the phase voltage reference value and voltage amplitude drop are recorded. The first preset voltage amplitude is determined based on the rated voltage amplitude. The DC bus voltage dynamic adjustment module is used to determine the DC bus voltage reference value based on the phase voltage reference value, and adjust the DC bus voltage amplitude of the converter to the DC bus voltage reference value; A converter mode switching module is used to switch the modulation mode of the converter to an ultra-low switching frequency modulation mode, wherein the switching frequency of the converter is consistent with the grid frequency in the ultra-low switching frequency modulation mode. The reactive power output module is used to determine a reactive power reference value based on the voltage amplitude drop, and control the converter to output reactive power to the point of common coupling based on the reactive power reference value, so as to adjust the voltage amplitude of the point of common coupling. The fault clearing module is used to determine that the grid fault is cleared and restore the converter to normal operation when the voltage amplitude of the common connection point recovers to the second preset voltage amplitude and the duration exceeds the second preset duration.

8. An electronic device, characterized in that, include: The system includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the fault current enhancement control method for a grid-type converter as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to execute the fault current enhancement control method for the grid-type converter as described in any one of claims 1 to 6.

10. A computer program product, characterized in that, It includes computer instructions for causing a computer to execute the fault current enhancement control method for a grid-type converter as described in any one of claims 1 to 6.

Images