Method and apparatus for suppressing direct-current overvoltage of flexible direct-current power grid, and computer device

Abstract

The present application relates to a method and apparatus for suppressing a direct-current overvoltage of a flexible direct-current power grid, and a computer device and a storage medium. The method comprises: when a fault occurs on an alternating-current side of an inverter station of a flexible direct-current power grid, acquiring a direct-current deviation amount of the inverter station; on the basis of the direct-current deviation amount, adjusting an original direct-current voltage reference value of an active power outer loop controller of the inverter station, so as to obtain a new direct-current voltage reference value; on the basis of the new direct-current voltage reference value, determining the number of sub-modules in a bridge arm of a converter valve of the inverter station; and according to the number of sub-modules, providing the sub-modules in the bridge arm of the converter valve, so as to suppress a direct-current overvoltage of the flexible direct-current power grid. By using the method, the costs of suppressing a direct-current overvoltage can be reduced.

Description

Method, device and computer equipment for suppressing DC overvoltage in flexible DC grid Technical Field

[0001] The present application relates to the field of power transmission and distribution technology, and in particular to a method, device, computer equipment, storage medium, and computer program product for suppressing direct current overvoltage in a flexible direct current grid. Background Art

[0002] In recent years, modular multilevel converter based high voltage direct current (MMC-HVDC) technology has developed rapidly. This technology uses fully controlled devices. Compared with traditional DC transmission, it has the advantages of independent control of active and reactive power, the ability to supply power to passive networks, and no commutation failure problems. It can output stable AC voltage and achieve decoupling between the sending and receiving ends. Therefore, it is widely used in fields such as power transmission from large-scale renewable energy power plants.

[0003] However, when a fault occurs at a receiving converter station or AC grid in a flexible DC grid, the active power input of the flexible DC grid will exceed its output. This unbalanced power will charge the capacitors of the flexible DC grid (MCC) submodules, causing the DC voltage to rise rapidly to the DC voltage protection set value within a few to tens of milliseconds. This can cause the converter station to lock out, or even cause a complete power outage, significantly impacting the system. Therefore, in engineering projects, energy dissipation devices are generally installed on the DC side of the converter station to suppress DC overvoltage, but these energy dissipation devices are costly.

[0004] Summary of the Invention

[0005] Based on this, it is necessary to provide a method, device, computer equipment, computer-readable storage medium and computer program product for suppressing DC overvoltage in a flexible DC grid to address the technical problem of high cost of the above-mentioned method for suppressing DC overvoltage in a flexible DC grid.

[0006] In a first aspect, the present application provides a method for suppressing DC overvoltage in a flexible DC grid. The method comprises:

[0007] When a fault occurs on the AC side of an inverter station of the flexible DC grid, obtaining a DC current deviation of the inverter station;

[0008] Based on the DC current deviation, an original DC voltage reference value of the active power outer loop controller of the inverter station is adjusted to obtain a new DC voltage reference value;

[0009] Determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0010] The submodules in the converter valve bridge arm are arranged according to the number of the submodules to suppress the DC overvoltage of the flexible DC grid.

[0011] In one embodiment, adjusting the original DC voltage reference value of the active power outer loop controller of the inverter station based on the DC current deviation to obtain a new DC voltage reference value includes:

[0012] Performing current-voltage conversion on the DC current deviation to obtain a DC voltage deviation;

[0013] Based on the DC voltage deviation, the original DC voltage reference value is adjusted to obtain a new DC voltage reference value.

[0014] In one embodiment, performing current-voltage conversion on the DC current deviation to obtain the DC voltage deviation includes:

[0015] Obtaining a transfer function of a proportional-integral link in the flexible direct current grid;

[0016] According to the transfer function of the proportional-integral link, the DC current deviation is subjected to current-voltage conversion processing to obtain the DC voltage deviation.

[0017] In one embodiment, adjusting the original DC voltage reference value based on the DC voltage deviation to obtain a new DC voltage reference value includes:

[0018] A difference is performed between the original DC voltage reference value and the DC voltage deviation, and the obtained difference is determined as a new DC voltage reference value.

[0019] In one embodiment, the converter valve bridge arm includes an upper bridge arm and a lower bridge arm;

[0020] The determining, according to the new DC voltage reference value, the number of submodules in the converter valve bridge arm of the inverter station includes:

[0021] Determining, according to the new DC voltage reference value, a first reference wave of an upper bridge arm and a second reference wave of a lower bridge arm in a bridge arm corresponding to each phase of the converter valve;

[0022] The number of submodules of the upper bridge arm corresponding to each phase is determined according to the first reference wave, and the number of submodules of the lower bridge arm corresponding to each phase is determined according to the second reference wave.

[0023] In one embodiment, determining the number of submodules of the upper bridge arm corresponding to each phase according to the first reference wave, and determining the number of submodules of the lower bridge arm corresponding to each phase according to the second reference wave, includes:

[0024] Get the capacitor voltage rating of the submodule;

[0025] Determining the number of submodules of the upper bridge arm corresponding to each phase based on the first reference wave and the capacitor voltage rated value;

[0026] The number of submodules of the lower bridge arm corresponding to each phase is determined based on the second reference wave and the capacitor voltage rated value.

[0027] In a second aspect, the present application also provides a device for suppressing DC overvoltage in a flexible DC grid. The device comprises:

[0028] An acquisition module, configured to acquire a DC current deviation of an inverter station of the flexible DC grid when a fault occurs on the AC side of the inverter station;

[0029] an adjustment module, configured to adjust an original DC voltage reference value of an active power outer loop controller of the inverter station based on the DC current deviation to obtain a new DC voltage reference value;

[0030] A determination module, configured to determine the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0031] The setting module is used to set the submodules in the converter valve bridge arm according to the number of submodules to suppress the DC overvoltage of the flexible DC grid.

[0032] In a third aspect, the present application further provides a computer device. The computer device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the following steps are performed:

[0033] When a fault occurs on the AC side of an inverter station of the flexible DC grid, obtaining a DC current deviation of the inverter station;

[0034] Based on the DC current deviation, an original DC voltage reference value of the active power outer loop controller of the inverter station is adjusted to obtain a new DC voltage reference value;

[0035] Determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0036] The submodules in the converter valve bridge arm are arranged according to the number of the submodules to suppress the DC overvoltage of the flexible DC grid.

[0037] In a fourth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the following steps:

[0038] When a fault occurs on the AC side of an inverter station of the flexible DC grid, obtaining a DC current deviation of the inverter station;

[0039] Based on the DC current deviation, an original DC voltage reference value of the active power outer loop controller of the inverter station is adjusted to obtain a new DC voltage reference value;

[0040] Determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0041] The submodules in the converter valve bridge arm are arranged according to the number of the submodules to suppress the DC overvoltage of the flexible DC grid.

[0042] In a fifth aspect, the present application further provides a computer program product. The computer program product includes a computer program that, when executed by a processor, implements the following steps:

[0043] When a fault occurs on the AC side of an inverter station of the flexible DC grid, obtaining a DC current deviation of the inverter station;

[0044] Based on the DC current deviation, an original DC voltage reference value of the active power outer loop controller of the inverter station is adjusted to obtain a new DC voltage reference value;

[0045] Determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0046] The submodules in the converter valve bridge arm are arranged according to the number of the submodules to suppress the DC overvoltage of the flexible DC grid.

[0047] The above-mentioned method, apparatus, computer device, storage medium, and computer program product for suppressing DC overvoltage in a flexible DC grid employs a method, apparatus, computer device, storage medium, and computer program product. When a fault occurs on the AC side of an inverter station in the flexible DC grid, the original DC voltage reference value of the inverter station's active power outer loop controller is adjusted based on the inverter station's DC current deviation. The number of submodules in the inverter station's converter valve bridge arm is determined based on the new DC voltage reference value obtained by the adjustment, and the submodules in the converter valve bridge arm are arranged accordingly. This method suppresses DC overvoltage in the flexible DC grid. This method applies the DC current deviation caused by the fault on the AC side of the inverter station to the number of submodules in the inverter valve bridge arm by adjusting the original DC voltage reference value of the inverter station's active power outer loop controller. This allows the number of submodules in the converter valve bridge arm to be adaptively adjusted based on the DC current deviation caused by the fault, thereby suppressing DC overvoltage caused by the fault. This eliminates the need for additional energy-consuming devices on the DC side of the converter station, thereby reducing the cost of suppressing DC overvoltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] FIG1 is a schematic diagram of a three-terminal flexible DC grid according to an embodiment;

[0049] FIG2 is a schematic flow chart of a method for suppressing DC overvoltage in a flexible DC grid according to one embodiment;

[0050] FIG3 is a schematic flow chart of the steps of adjusting the original DC voltage reference value in one embodiment;

[0051] FIG4 is a schematic flow chart of a method for suppressing DC overvoltage in a flexible DC grid according to another embodiment;

[0052] FIG5 is a structural block diagram of a method for suppressing DC overvoltage in a flexible DC grid according to one embodiment;

[0053] FIG6 is a curve diagram showing changes in a DC voltage reference value of an inverter station when a three-phase direct grounding fault occurs on the AC busbar of an inverter station in a three-terminal flexible DC grid in one embodiment;

[0054] FIG7 is a graph showing changes in the total number of upper and lower bridge arm submodules in operation in phase A of an inverter station when a three-phase direct grounding fault occurs on the AC busbar of the inverter station of a three-terminal flexible DC grid in one embodiment;

[0055] FIG8 is a simulated waveform diagram of the DC voltage on the rectifier side when a three-phase direct grounding fault occurs on the AC bus of an inverter station of a three-terminal flexible DC grid in one embodiment;

[0056] FIG9 is a structural block diagram of a device for suppressing DC overvoltage in a flexible DC grid according to one embodiment;

[0057] FIG10 is a diagram showing the internal structure of a computer device in one embodiment. DETAILED DESCRIPTION

[0058] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0059] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, such that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0060] Reference is made to Figure 1, which is a schematic diagram of a three-terminal flexible DC grid according to an embodiment. As shown in Figure 1, the flexible DC grid includes a rectifier station and an inverter station, wherein the inverter station includes inverter station 1 and inverter station 2. Both the rectifier station and the inverter station belong to converter stations. Specifically, the rectifier station is used to convert the AC power in the power grid into DC power, and transmit it to the inverter station through the DC transmission line; the inverter station converts the DC power into AC power to complete the transmission of electric energy. The application scenario of the present application is to suppress the DC overvoltage generated when a fault occurs on the AC side of the inverter station (i.e., the constant power converter station on the inverter side) (such as the three-phase direct grounding fault marked at the AC bus on the right side of the inverter station 1 as shown in Figure 1).

[0061] In one embodiment, as shown in FIG2 , a method for suppressing DC overvoltage in a flexible DC grid is provided, which can be applied to a processor in the flexible DC grid. In this embodiment, the method includes the following steps:

[0062] Step S210 : When a fault occurs on the AC side of an inverter station of the flexible DC grid, a DC current deviation of the inverter station is obtained.

[0063] The inverter station specifically refers to a constant power converter station on the inverter side of the flexible DC grid.

[0064] It can be understood that the inverter station is used to convert direct current into alternating current for power transmission. The location where the fault occurs in this application is the alternating current side of the inverter station, that is, the AC side.

[0065] Specifically, when a fault occurs on the AC side of an inverter station in a flexible DC grid, the inverter station's DC current measurement and reference value are obtained. The DC current deviation is calculated by subtracting the DC current reference value from the DC current measurement. The DC current reference value is a command value, obtained by dividing the inverter station's power command value by the voltage command value. If the rated power and rated voltage transmitted by the inverter station remain unchanged, the DC current reference value will also remain unchanged.

[0066] For example, when a three-phase direct grounding fault occurs on the AC busbar on the right side of inverter station 1 in FIG1 , the DC current measurement value of inverter station 1 and the DC current reference value can be obtained, and the DC current deviation can be obtained by subtracting the two values.

[0067] Step S220 : adjusting the original DC voltage reference value of the active power outer loop controller of the flexible DC grid based on the DC current deviation to obtain a new DC voltage reference value.

[0068] The original DC voltage reference value is a command value of the DC voltage. When the rated voltage of the converter does not change, this value is fixed and is taken as the rated DC voltage of the converter.

[0069] Specifically, when adjusting the original DC voltage reference value of the active power outer loop controller of the flexible DC grid based on the DC current deviation, direct adjustment cannot be performed due to the inconsistent units of current and voltage. Therefore, the DC current deviation must first be converted into a DC voltage deviation, and then the original DC voltage reference value must be adjusted according to the DC voltage deviation to obtain a new DC voltage reference value.

[0070] Step S230: Determine the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value.

[0071] In a specific implementation, after obtaining a new DC voltage reference value, the new DC voltage reference value can be used as the DC voltage in the converter valve bridge arm reference wave calculation module in the inverter station, and the bridge arm reference wave is calculated based on the new DC voltage reference value, thereby realizing adaptive adjustment of the converter valve bridge arm reference wave. The number of sub-modules is further determined based on the calculated reference wave, so that the number of sub-modules can also be adaptively and dynamically adjusted according to the DC voltage deviation caused by a fault on the AC side of the inverter station of the flexible DC grid.

[0072] Step S240 : setting the submodules in the converter valve bridge arm according to the number of submodules to suppress DC overvoltage in the flexible DC grid.

[0073] Specifically, after determining the number of submodules in the converter valve bridge arm, the submodules can be set according to the number of submodules. Since the number of submodules is equivalent to the DC voltage deviation caused by a fault on the AC side of the inverter station of the flexible DC grid, adaptive adjustment is performed, thereby suppressing the DC overvoltage of the flexible DC grid.

[0074] The above-mentioned method for suppressing DC overvoltage in a flexible DC grid involves adjusting the original DC voltage reference value of the inverter station's active power outer loop controller based on the inverter station's DC current deviation when a fault occurs on the AC side of the flexible DC grid. The number of submodules in the inverter station's converter valve bridge arm is determined based on the new DC voltage reference value obtained by the adjustment, and the submodules in the converter valve bridge arm are arranged accordingly. This method suppresses DC overvoltage in the flexible DC grid. This method applies the DC current deviation caused by the fault on the inverter station's AC side to the number of submodules in the inverter station's converter valve bridge arm by adjusting the original DC voltage reference value of the inverter station's active power outer loop controller. This allows the number of submodules in the converter valve bridge arm to be adaptively adjusted based on the DC current deviation caused by the fault, thereby suppressing DC overvoltage caused by the fault. This eliminates the need for additional energy-consuming devices on the DC side of the converter station, thereby reducing the cost of suppressing DC overvoltage.

[0075] In an exemplary embodiment, as shown in FIG3 , in step S220 , adjusting the original DC voltage reference value of the active power outer loop controller of the inverter station based on the DC current deviation to obtain a new DC voltage reference value includes:

[0076] Step S310, performing current-voltage conversion processing on the DC current deviation to obtain a DC voltage deviation;

[0077] Step S320 : adjusting the original DC voltage reference value based on the DC voltage deviation to obtain a new DC voltage reference value.

[0078] Specifically, the current-voltage conversion process for the DC current deviation may include: converting the DC current deviation into a DC voltage deviation through a proportional-integral controller, and then adjusting the original DC voltage reference value based on the DC voltage deviation to obtain a new DC voltage reference value.

[0079] Furthermore, in an exemplary embodiment, in the above step S320, the original DC voltage reference value is adjusted based on the DC voltage deviation to obtain a new DC voltage reference value, including: performing a difference processing on the original DC voltage reference value and the DC voltage deviation, and determining the obtained difference as the new DC voltage reference value.

[0080] Specifically, based on the DC voltage deviation, the relationship for adjusting the original DC voltage reference value can be expressed as: U ref_real =U ref -ΔU ref (1)

[0081] Among them, U ref is the original DC voltage reference value, ΔU ref is the DC voltage deviation, U ref_real is the new DC voltage reference value.

[0082] In the above embodiment, by converting the DC current deviation of the inverter station when a fault occurs into a DC voltage deviation, the DC voltage deviation is added to the active power outer loop controller, and subtracted from the original DC voltage reference value to obtain a new DC voltage reference value, thereby reducing the original DC voltage reference value of the active power outer loop controller, so that the number of sub-modules in the converter valve bridge arm of the inverter station can be adjusted according to the new DC voltage reference value, thereby achieving the suppression of DC overvoltage in the flexible DC grid.

[0083] In an exemplary embodiment, in the above-mentioned step S310, the DC current deviation is subjected to current-voltage conversion processing to obtain the DC voltage deviation, including: obtaining the transfer function of the proportional-integral link in the flexible DC grid; and performing current-voltage conversion processing on the DC current deviation according to the transfer function of the proportional-integral link to obtain the DC voltage deviation.

[0084] Among them, the proportional integral link (PI link) is a controller commonly used in control systems. The transfer function of the PI link can be expressed as: G PI (s)=Kp+Ki / s, where Kp is the proportional gain, Ki is the integral gain, and s is a complex variable.

[0085] Specifically, according to the transfer function of the proportional-integral link, the method for converting the DC current deviation into voltage is as follows: multiplying the transfer function of the proportional-integral link by the DC current deviation, and taking the resulting product as the DC voltage deviation. The calculation formula can be expressed as: ΔU ref =G PI (s)·(I dcref -I dcm ) (2)

[0086] Among them, I dcref is the DC current reference value, I dcm is the DC current measurement value, (I dcref -I dcm ) is the DC current deviation, G PI (s) is the transfer function of the PI link, ΔUref is the DC voltage deviation.

[0087] In this embodiment, when the DC current deviation is converted into current and voltage, the transfer function of the proportional-integral link is used to perform current-voltage conversion on the DC current deviation to obtain a DC voltage deviation. The fast response and stability of the transfer function of the proportional-integral link are utilized to achieve efficient conversion of the DC current deviation to the DC voltage deviation, so as to facilitate the subsequent determination of the number of sub-modules in the converter valve bridge arm based on the DC voltage deviation.

[0088] In an exemplary embodiment, in the above step S230, determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value includes:

[0089] Step S2301, determining a first reference wave of an upper bridge arm and a second reference wave of a lower bridge arm in a bridge arm corresponding to each phase of a converter valve according to a new DC voltage reference value;

[0090] Step S2302 : determining the number of submodules of the upper bridge arm corresponding to each phase according to the first reference wave, and determining the number of submodules of the lower bridge arm corresponding to each phase according to the second reference wave.

[0091] Specifically, the converter valve bridge arm includes an upper bridge arm and a lower bridge arm. The converter valve is an MCC (Modular Multilevel Converter) converter valve with three phases. Therefore, the number of submodules of the upper bridge arm and the lower bridge arm of each phase needs to be calculated.

[0092] For any phase, the first reference wave of the upper bridge arm and the second reference wave of the lower bridge arm in the phase can be determined based on the new DC voltage reference value, the instantaneous value of the phase voltage output by the current vector controller, and the phase voltage amplitude output by the circulating current suppression controller. The specific calculation method is shown in formula (3). pref_j =U ref_real -u cj +u cir_j ,j=a,b,cu nref_j =U ref_real +u cj +u cir_j ,j=a,b,c (3)

[0093] Among them, u pref_j and u nref_j are the first reference wave of the upper bridge arm and the second reference wave of the lower bridge arm in one phase, u cj is the instantaneous value of the phase voltage output by the current vector controller, u cir_j is the phase voltage amplitude output by the circulating current suppression controller.

[0094] After obtaining the first reference wave and the second reference wave, the number of submodules of the upper bridge arm corresponding to each phase can be calculated using the first reference wave, and the number of submodules of the lower bridge arm corresponding to each phase can be determined based on the second reference wave.

[0095] Further, in an exemplary embodiment, the specific implementation method of step S2302 of determining the number of sub-modules of the upper bridge arm corresponding to each phase according to the first reference wave, and determining the number of sub-modules of the lower bridge arm corresponding to each phase according to the second reference wave is: obtaining the capacitor voltage rating of the sub-module; determining the number of sub-modules of the upper bridge arm corresponding to each phase based on the first reference wave and the capacitor voltage rating; determining the number of sub-modules of the lower bridge arm corresponding to each phase based on the second reference wave and the capacitor voltage rating.

[0096] In a specific implementation, the number of submodules of the upper bridge arm corresponding to each phase can be obtained by dividing the first reference wave of the upper bridge arm by the capacitor voltage rating, and the number of submodules of the lower bridge arm corresponding to each phase can be obtained by dividing the second reference wave of the lower bridge arm by the capacitor voltage rating, which can be expressed as follows:

[0097] Among them, N pj and N nj are the number of submodules put into use in the upper bridge arm and lower bridge arm in one phase, U SM_ave is the rated value of the submodule capacitor voltage, and [] indicates rounding.

[0098] In the above embodiment, by using the new DC voltage reference value as the DC voltage in the reference wave calculation module of the converter valve bridge arm in the inverter station, since the new DC voltage reference value is smaller than the original DC voltage reference value, the reference wave is positively correlated with the DC voltage reference value, and the number of sub-modules invested in the upper and lower bridge arms is also positively correlated with the reference wave. Therefore, by adjusting the DC voltage reference value, the reference wave of the entire converter valve bridge arm can be reduced, and the number of sub-modules invested in the converter valve bridge arm can be reduced. Therefore, by reducing the number of sub-modules invested in the converter valve bridge arm, the DC overvoltage can be suppressed.

[0099] In one embodiment, in order to facilitate those skilled in the art to understand the embodiments of the present application, the following will be described with reference to specific examples in the accompanying drawings. Referring to FIG4 , a complete flow diagram of a method for suppressing DC overvoltage in a flexible DC grid is shown, including the following steps:

[0100] Step S410 : When a fault occurs on the AC side of an inverter station of the flexible DC grid, a DC current deviation of the inverter station is obtained.

[0101] Step S420 : Converting the DC current deviation into a DC voltage deviation through the transfer function of the PI link.

[0102] Step S430 : Subtract the original DC voltage reference value in the active power outer loop controller of the inverter station from the DC voltage deviation to obtain a new DC voltage reference value.

[0103] Step S440 : determining a first reference wave of an upper bridge arm and a second reference wave of a lower bridge arm in the bridge arm corresponding to each phase of the converter valve according to the new DC voltage reference value.

[0104] Step S450 : determining the number of sub-modules of the upper bridge arm corresponding to each phase based on the first reference wave and the capacitor voltage rating of the sub-module.

[0105] Step S460 : determining the number of submodules of the lower bridge arm corresponding to each phase based on the second reference wave and the capacitor voltage rating.

[0106] Refer to Figure 5, which is a structural block diagram of a method for suppressing DC overvoltage in a flexible DC grid in one embodiment. As shown in Figure 5, the inverter station (or receiving-end constant power converter station, flexible DC inverter-side constant power converter station) adopts classic current vector control, including outer loop power control and inner loop current control. In the active power outer loop controller, the DC current reference value I dcref With the DC current measurement value I dcm After the difference is made, the DC voltage reference value deviation ΔU is generated through the PI link ref and subtracted from the original DC voltage reference value as the new DC voltage reference value U ref_real In steady state, the active power outer loop controller can control the DC voltage of the inverter station to U ref_real , control the DC current to I dcref , so that the active power of the inverter station can be controlled at P dc =U ref_real I dcref . Constant reactive power control is adopted in the reactive outer loop control diagram. In order to effectively suppress the DC overvoltage caused by a fault on the AC side of the inverter station, the present application provides a method for adaptively adjusting the reference wave of the converter valve bridge arm to suppress the DC overvoltage of flexible DC transmission. First, the DC current deviation of the constant power converter station on the inverter side is passed through the PI link to obtain the deviation of the DC voltage reference value; then the DC voltage reference value deviation is added to the active power outer loop controller, and subtracted from the original DC voltage reference value as a new DC voltage reference value; finally, the new DC voltage reference value is used as the DC voltage in the converter valve bridge arm reference wave in the constant power converter station on the inverter side, thereby realizing adaptive adjustment of the bridge arm reference wave.

[0107] In an exemplary embodiment, taking the three-terminal flexible DC grid shown in FIG1 as an example, the DC overvoltage suppression method proposed in this application is applied to the inverter-side constant power converter station, that is, the inverter station 1 shown in FIG1 . Initially, the system operates in a stable state. At t = 0.5s, a three-phase direct grounding fault occurs at the AC bus of the inverter station 1, and the fault time is 0.1s. FIG6 shows the DC voltage reference value U output by the active power outer loop controller of the inverter station 1. ref_real Figure 7 shows the waveform of the total number of upper and lower bridge arm submodules in operation in phase A of inverter station 1, and Figure 8 shows the simulated waveform of the DC voltage on the rectifier side. As can be seen from the figures, when a fault occurs, the method proposed in this application can adaptively adjust the bridge arm reference waveform by lowering the DC voltage reference value, thereby reducing the number of submodules in operation in the converter valve bridge arm and ultimately suppressing DC overvoltage.

[0108] It should be understood that, although the various steps in the flowcharts involved in the various embodiments described above are displayed in sequence according to the instructions of the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the flowcharts involved in the various embodiments described above can include multiple steps or multiple stages, and these steps or stages are not necessarily executed and completed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of steps or stages in other steps.

[0109] Based on the same inventive concept, embodiments of the present application also provide a flexible DC grid DC overvoltage suppression device for implementing the aforementioned flexible DC grid DC overvoltage suppression method. The solution provided by this device is similar to the solution described in the aforementioned method. Therefore, the specific limitations of one or more embodiments of the flexible DC grid DC overvoltage suppression device provided below can be found in the aforementioned limitations of the flexible DC grid DC overvoltage suppression method and are not further elaborated here.

[0110] In one embodiment, as shown in FIG9 , a device for suppressing DC overvoltage in a flexible DC grid is provided, comprising: an acquisition module 910 , an adjustment module 920 , a determination module 930 , and a setting module 940 , wherein:

[0111] An acquisition module 910 is configured to acquire a DC current deviation of an inverter station when a fault occurs on the AC side of the inverter station of the flexible DC grid;

[0112] An adjustment module 920 is configured to adjust an original DC voltage reference value of an active power outer loop controller of an inverter station based on the DC current deviation to obtain a new DC voltage reference value;

[0113] A determination module 930 is configured to determine the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value;

[0114] The setting module 940 is configured to set the submodules in the converter valve bridge arm according to the number of submodules, so as to suppress the DC overvoltage of the flexible DC grid.

[0115] In one embodiment, the adjustment module 920 is further configured to perform current-voltage conversion on the DC current deviation to obtain a DC voltage deviation; and adjust the original DC voltage reference value based on the DC voltage deviation to obtain a new DC voltage reference value.

[0116] In one embodiment, the adjustment module 920 is further configured to obtain a transfer function of a proportional-integral link in the flexible DC grid; and perform current-to-voltage conversion on the DC current deviation according to the transfer function of the proportional-integral link to obtain a DC voltage deviation.

[0117] In one embodiment, the adjustment module 920 is further configured to perform a difference process between the original DC voltage reference value and the DC voltage deviation, and determine the obtained difference as a new DC voltage reference value.

[0118] In one embodiment, the bridge arm of the converter valve includes an upper bridge arm and a lower bridge arm; the determination module 930 is further used to determine the first reference wave of the upper bridge arm and the second reference wave of the lower bridge arm in the bridge arm corresponding to each phase of the converter valve according to the new DC voltage reference value; determine the number of sub-modules of the upper bridge arm corresponding to each phase according to the first reference wave, and determine the number of sub-modules of the lower bridge arm corresponding to each phase according to the second reference wave.

[0119] In one embodiment, the determination module 930 is further used to obtain the capacitor voltage rating of the sub-module; determine the number of sub-modules of the upper bridge arm corresponding to each phase based on the first reference wave and the capacitor voltage rating; and determine the number of sub-modules of the lower bridge arm corresponding to each phase based on the second reference wave and the capacitor voltage rating.

[0120] Each module in the flexible DC grid DC overvoltage suppression device described above can be implemented in whole or in part through software, hardware, or a combination thereof. Each module can be embedded in or independent of a processor in a computer device in hardware form, or stored in a computer device memory in software form, so that the processor can call and execute the corresponding operations of each module.

[0121] In one embodiment, a computer device is provided. The computer device may be a terminal, and its internal structure diagram may be as shown in FIG10 . The computer device includes a processor, memory, a communication interface, a display screen, and an input device connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The communication interface of the computer device is used to communicate with an external terminal via wired or wireless communication. The wireless communication may be achieved via Wi-Fi, a mobile cellular network, NFC (near field communication), or other technologies. When the computer program is executed by the processor, a method for suppressing DC overvoltage in a flexible DC power grid is implemented. The display screen of the computer device may be a liquid crystal display or an electronic ink display screen. The input device of the computer device may be a touch layer covering the display screen, or may be a key, trackball, or touchpad provided on the computer device housing, or may be an external keyboard, touchpad, or mouse.

[0122] Those skilled in the art will understand that the structure shown in FIG10 is merely a block diagram of a portion of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than shown in the figure, or combine certain components, or have a different arrangement of components.

[0123] In one embodiment, a computer device is further provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps in the above method embodiments when executing the computer program.

[0124] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0125] In one embodiment, a computer program product is provided, including a computer program, which implements the steps in the above method embodiments when executed by a processor.

[0126] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with the relevant laws, regulations and standards of relevant countries and regions.

[0127] Those skilled in the art will appreciate that all or part of the processes in the above-mentioned embodiment methods can be implemented by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, database or other media used in the embodiments provided in this application may include at least one of non-volatile and volatile memory. Non-volatile memory may include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory may include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in the various embodiments provided herein may include at least one of a relational database and a non-relational database. Non-relational databases may include, but are not limited to, distributed databases based on blockchains. The processor involved in the various embodiments provided herein may be, but are not limited to, a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic unit, a data processing logic unit based on quantum computing, and the like.

[0128] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0129] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present application. It should be noted that variations and improvements may be made by those skilled in the art without departing from the spirit of the present application, and such variations and improvements are within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A method for suppressing direct current overvoltage in a flexible direct current grid, characterized in that: The method comprises: When a fault occurs on the AC side of an inverter station of the flexible DC power grid, obtaining a DC current deviation of the inverter station; Based on the DC current deviation, an original DC voltage reference value of the active power outer loop controller of the inverter station is adjusted to obtain a new DC voltage reference value; Determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value; The submodules in the converter valve bridge arm are arranged according to the number of the submodules to suppress the DC overvoltage of the flexible DC grid.

2. The method according to claim 1, characterized in that: The adjusting, based on the DC current deviation, the original DC voltage reference value of the active power outer loop controller of the inverter station to obtain a new DC voltage reference value comprises: Performing current-voltage conversion processing on the DC current deviation to obtain a DC voltage deviation; Based on the DC voltage deviation, the original DC voltage reference value is adjusted to obtain a new DC voltage reference value.

3. The method according to claim 2, characterized in that The step of performing current-voltage conversion processing on the DC current deviation to obtain a DC voltage deviation comprises: Obtaining a transfer function of a proportional-integral link in the flexible DC power grid; According to the transfer function of the proportional-integral link, the DC current deviation is subjected to current-voltage conversion processing to obtain the DC voltage deviation.

4. The method according to claim 2, characterized in that: The adjusting the original DC voltage reference value based on the DC voltage deviation to obtain a new DC voltage reference value includes: A difference process is performed between the original DC voltage reference value and the DC voltage deviation, and the obtained difference is determined as a new DC voltage reference value.

5. The method according to claim 1, characterized in that The converter valve bridge arm comprises an upper bridge arm and a lower bridge arm; The step of determining the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value includes: Determine, according to the new DC voltage reference value, a first reference wave of an upper bridge arm and a second reference wave of a lower bridge arm in the bridge arm corresponding to each phase of the converter valve; The number of submodules of the upper bridge arm corresponding to each phase is determined according to the first reference wave, and the number of submodules of the lower bridge arm corresponding to each phase is determined according to the second reference wave.

6. The method according to claim 5, characterized in that The determining, according to the first reference wave, the number of submodules of the upper bridge arm corresponding to each phase, and the determining, according to the second reference wave, the number of submodules of the lower bridge arm corresponding to each phase, comprises: Get the capacitor voltage rating of the submodule; Determining the number of submodules of the upper bridge arm corresponding to each phase based on the first reference wave and the capacitor voltage rated value; Based on the second reference wave and the capacitor voltage rated value, the number of submodules of the lower bridge arm corresponding to each phase is determined.

7. A device for suppressing direct current overvoltage in a flexible direct current grid, characterized in that: The device comprises: An acquisition module, used for acquiring a DC current deviation of an inverter station in a flexible DC power grid when a fault occurs on an AC side of the inverter station; An adjustment module, configured to adjust an original DC voltage reference value of an active power outer loop controller of the inverter station based on the DC current deviation to obtain a new DC voltage reference value; A determination module, used to determine the number of submodules in the converter valve bridge arm of the inverter station according to the new DC voltage reference value; A setting module is used to set the submodules in the converter valve bridge arm according to the number of submodules to suppress the DC overvoltage of the flexible DC power grid.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method for suppressing direct current overvoltage in a flexible direct current grid according to any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for suppressing direct current overvoltage in a flexible direct current grid according to any one of claims 1 to 6 are implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method for suppressing direct current overvoltage in a flexible direct current grid according to any one of claims 1 to 6 are implemented.

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