A method and system for determining a flexible DC impedance boundary to avoid resonance with an AC system

Abstract

The present invention relates to a method and system for determining the boundary of a flexible direct current (DC) impedance that avoids resonance with an AC system. The method comprises: based on the characteristics of the grid structure data, traversing the operating conditions to be studied at a fixed frequency step size, calculating the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied; plotting the AC system impedance points at each frequency within a preset coordinate system, and constructing an AC envelope region within the coordinate system to envelop all AC system impedance points; within the AC envelope region, obtaining all possible flexible DC impedances for each frequency, and obtaining the boundary of the flexible DC system impedance feasible domain based on the criterion for avoiding resonance between the flexible DC system and the AC system. The present invention can define a feasible region for the flexible DC impedance in the early planning and design stage, or even in the engineering operation stage, and can be widely applied in the field of flexible direct current transmission technology.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current (DC) transmission, and in particular to a method and system for determining a DC impedance boundary for avoiding resonance with an AC system. Background Art

[0002] As more and more flexible DC transmission projects come into operation, problems such as AC system network harmonic amplification or oscillations between converters and the grid are becoming increasingly prominent. Essentially, these oscillations arise from the fast control characteristics and inherent link delays of flexible DC transmission systems, resulting in weak or negative damping in the impedance characteristics of their converters within certain frequency bands. Furthermore, due to the diverse operating modes of grid-connected AC systems, frequency-capacity effects in the transmission system can lead to significant variations in the system's equivalent harmonic impedance angle at different frequencies. Under certain operating conditions, the system impedance interacts with the flexible DC transmission system, causing harmonic current divergence.

[0003] To avoid broadband resonance with the AC power grid, extensive simulation and verification work is often required in the later stages of construction, especially during the commissioning phase. This involves reshaping or correcting the impedance characteristics of the flexible DC-AC system through methods such as secondary software control optimization or the addition of primary hardware damping devices. To identify the risk of resonance between the AC network and the flexible DC, a general approach is to perform electromagnetic transient modeling of the network under specific operating conditions and, through time-domain analysis, study the oscillations between the flexible DC-AC system under a single, given transmission power. While accurate, this approach is computationally intensive and inefficient, making it difficult to complete a comprehensive analysis of various operating modes within a reasonable timeframe. This makes it unsuitable for early-stage analysis, particularly during the planning and design phases.

[0004] At the current planning and design stage, there is very little public literature reporting on how to analyze flexible DC-grid resonance. In fact, it is very necessary to carry out multiple traversal calculations based on the planned grid data. From the perspective of avoiding the risk of grid resonance, the feasible range of flexible DC impedance can be defined in advance, laying a good foundation for the design of the flexible DC system main circuit and the optimization of the control strategy. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method and system for determining the boundary of flexible DC impedance to avoid resonance with the AC system, which can define the feasible area for flexible DC impedance in the early planning and design stage or even in the engineering operation stage.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions: a method for determining the impedance boundary of a flexible DC system to avoid resonance with an AC system, comprising: traversing the operating conditions to be studied according to a fixed frequency step size based on the characteristics of the power grid structure data, and calculating the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied; plotting the AC system impedance points at each frequency in a preset coordinate system, and constructing an AC envelope region within the coordinate system to envelop all AC system impedance points; within the AC envelope region, according to the criterion for avoiding resonance between the flexible DC system and the AC system, obtaining all possible flexible DC impedances for each frequency, thereby obtaining the feasible domain boundary of the flexible DC system impedance.

[0007] Furthermore, the calculation of the AC system impedance includes:

[0008] Determine the typical grid operating conditions required for AC system impedance scanning;

[0009] According to the geographical wiring diagram, determine the boundary nodes and external connection lines of the power grid in the area where the observation point is located;

[0010] Obtain grid data within the determined boundary nodes and external tie lines, and calculate harmonic impedance based on the grid data type;

[0011] From the minimum frequency to the maximum frequency, all frequency points are traversed with a fixed interval △f. For each frequency point f, the admittance matrix of the AC system containing power electronic components at the frequency f is solved, and the nodes of the AC system admittance matrix are numbered and optimized.

[0012] The LU decomposition method is used to solve the AC network and obtain the AC system impedance at the observation point;

[0013] Traverse all operating modes and calculate the AC system impedance in all cases.

[0014] Furthermore, the AC envelope area adopts a fan-shaped envelope area.

[0015] Furthermore, the method for constructing the fan-shaped envelope area includes:

[0016] Traverse all AC system impedance points at harmonic frequencies to obtain the maximum and minimum values of the direct angles between the AC system impedance points and the zero coordinate;

[0017] Traverse all AC system impedance points at the harmonic frequency, and obtain the maximum and minimum distances between the AC system impedance points and coordinate zero as the maximum and minimum amplitudes;

[0018] Draw two rays from the coordinate origin with the angle obtained by subtracting the minimum angle from the maximum angle as the boundary;

[0019] Draw two concentric circles with the maximum and minimum amplitudes as radii and the origin of the coordinate system as the zero point;

[0020] The fan-shaped area formed by the intersection of the two drawn rays and the two concentric circles is the required fan-shaped envelope area.

[0021] Furthermore, when the boundary of the flexible direct impedance is difficult to determine or cannot be solved, a combination of multiple sectors is used to perform envelope determination.

[0022] Furthermore, the criteria for avoiding resonance between the flexible DC system and the AC system include: negative damping criterion, non-amplification criterion of key frequency harmonics, common connection point voltage distortion rate criterion and equipment harmonic current tolerance criterion.

[0023] Furthermore, the determination of the boundary of the flexible DC system impedance feasible region includes: comprehensively considering four criteria, or partially combining the four criteria, and finding the intersection of the flexible DC system impedance feasible regions obtained by each criterion to obtain the boundary of the flexible DC system impedance feasible region.

[0024] A flexible DC impedance boundary determination system for avoiding resonance with an AC system comprises: an AC system impedance calculation module, which traverses the operating conditions to be studied at a fixed frequency step size based on the characteristics of power grid structure data and calculates the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied; an AC envelope region construction module, which plots the AC system impedance points at each frequency within a preset coordinate system and constructs an AC envelope region within the coordinate system for enveloping all AC system impedance points; and a feasible region boundary determination module, which obtains all possible flexible DC impedances for each frequency within the AC envelope region based on a criterion for avoiding resonance between the flexible DC system and the AC system, thereby obtaining the feasible region boundary of the flexible DC system impedance.

[0025] A computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the above methods.

[0026] A computing device comprises: one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the above methods.

[0027] The present invention has the following advantages due to the adoption of the above technical solution:

[0028] 1. The present invention uses electromechanical transient program data as the main input condition, avoids electromagnetic transient modeling of large systems, can quickly traverse massive power grid operation modes, and has high calculation efficiency and fast simulation speed.

[0029] 2. The present invention uses a fan-shaped envelope to achieve regional coverage of impedance points under different operating modes of the AC power grid, which can effectively avoid the difficulty in predicting some risk frequency bands in advance due to the judgment of flexible direct current and system resonance risks in a single operating mode, and has the advantages of fast and comprehensive resonance risk assessment.

[0030] 3. The present invention adopts four criteria for avoiding resonance, which can systematically and comprehensively define the feasible impedance boundary range of flexible direct current (FDC). This lays a solid foundation for optimizing FDC main circuit parameters in the planning stage or early design stage, and optimizing FDC control parameters in the late design and debugging stages. The method is characterized by simple and easy steps, clear and concise operation, and strong feasibility.

[0031] In summary, the present invention can be widely applied in the field of flexible direct current transmission technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for determining a flexible DC impedance boundary to avoid resonance with an AC system in one embodiment of the present invention;

[0033] Figure 2a This is a diagram illustrating the interaction between the AC system and the flexible DC system under the influence of the system background harmonic voltage alone in one embodiment of the present invention;

[0034] Figure 2b This is a diagram illustrating the interaction between the AC system and the flexible DC system under the influence of harmonic voltage generated by the converter alone in one embodiment of the present invention;

[0035] Figure 3 is a schematic diagram of determining a fan-shaped envelope area in one embodiment of the present invention;

[0036] Figure 4 It is a feasible region of flexible direct impedance solved by considering only the negative damping criterion in one embodiment of the present invention;

[0037] Figure 5 This is the flexible direct impedance feasible region in one embodiment of the present invention, which only considers the non-amplification criterion of key frequency harmonics to solve. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0039] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0040] The present invention provides a method and system for determining the impedance boundary of a flexible DC system to avoid resonance with an AC system, comprising the following steps: 1) traversing the operating conditions to be studied at a fixed frequency step size according to the characteristics of the power grid structure, and calculating the equivalent harmonic impedance of the AC system as seen from the common connection point of the flexible DC system and the AC system within the studied frequency range; 2) plotting the AC system impedance points at each frequency in a preset coordinate system, and encircling all impedance points using a sector area or a combination of multiple sector areas; 3) for each frequency, according to four criteria for avoiding resonance between the flexible DC system and the AC system, including the negative damping criterion, the non-amplification criterion of key frequency harmonics, the common connection point voltage distortion rate criterion, and the equipment harmonic current tolerance criterion, all possible flexible DC system impedances are obtained, and an envelope interval of the flexible DC impedance feasible domain is constructed. The present invention uses a sector envelope form to achieve regional coverage of the impedance points under different operating modes of the AC power grid, can quickly traverse a large number of power grid operating modes, has the advantages of high computational efficiency and fast simulation speed, and can effectively avoid the problem of partial risk frequency bands caused by judging the risk of resonance between the flexible DC system and the system under a single operating mode.

[0041] In one embodiment of the present invention, Figure 1 As shown in FIG, a method for determining the flexible DC impedance boundary to avoid resonance with the AC system is provided. Figure 2a 、 Figure 2b As shown, the interaction between the AC system and the flexible DC system is given. In this embodiment, the method includes the following steps:

[0042] 1) According to the characteristics of the power grid structure data, the operating conditions to be studied are traversed at a fixed frequency step size, and the equivalent harmonic impedance of the AC system at the common connection point between the flexible DC system and the AC system (hereinafter referred to as the AC system impedance) is calculated within the frequency range to be studied.

[0043] 2) Plotting the AC system impedance points at each frequency in a preset coordinate system, and constructing an AC envelope region in the coordinate system to envelop all AC system impedance points.

[0044] 3) Within the AC envelope region, based on the criterion of avoiding resonance between the flexible DC system and the AC system, all possible flexible DC impedances are obtained for each frequency, and the envelope interval of the flexible DC impedance feasible domain is constructed, that is, the boundary of the flexible DC system impedance feasible domain is obtained.

[0045] In the above step 1), the grid structure data can be electromechanical transient data or electromagnetic transient data. Preferably, using electromechanical transient data can greatly improve the calculation efficiency, which is particularly suitable for ultra-large-scale AC power grids.

[0046] In this embodiment, the resonance risk study range is considered to be 0Hz to 2500Hz. Therefore, the frequency step size Δf can be preferably 10Hz (i.e., Δf = 10). On the one hand, it can quickly traverse the aforementioned resonance risk study range. On the other hand, a smaller frequency step size can avoid the omission of resonance risk frequencies during the traversal process. During use, the frequency step size can also be determined according to system requirements.

[0047] In step 1) above, the common connection point between the flexible DC and AC systems is used as the observation point. The method for calculating the AC system impedance at the observation point includes the following steps:

[0048] 1.1) Determine the typical grid operating conditions required for AC system impedance scanning;

[0049] In this embodiment, based on the basic operating mode and scanning range of the AC power grid to be studied, typical power grid operating conditions such as the normal mode, n-1 mode (i.e., disconnecting one AC line or one important component), and n-2 mode (i.e., disconnecting two AC lines or two important components) required for impedance scanning are determined.

[0050] 1.2) According to the geographical wiring diagram, determine the boundary nodes and external connection lines of the power grid in the area where the observation point is located.

[0051] In this embodiment, the observation point is the common connection point on the AC side of the DC system converter transformer;

[0052] 1.3) Obtain grid data within the determined boundary nodes and external tie lines, and calculate harmonic impedance based on the grid data type;

[0053] Among them, power grid data is divided into two categories. One is conventional component models including bus data, load data, generator data, line branch data, transformer data, switchable parallel branch data, etc.; the other is power electronic component data, including new energy units such as wind turbines, photovoltaics, and flexible direct current transmission systems.

[0054] For conventional component models, the harmonic model in the prior art can be used to continue the calculation.

[0055] For the power electronic component model, since its impedance characteristics are affected by the control system, the power electronic component model is first established in the electromagnetic transient software. Then, the excitation harmonic voltage source consistent with the scanning range in step 1.1) is injected into the original port in sequence, and the harmonic current generated by the port excitation is recorded. The impedance of the power electronic component is obtained according to formula (1):

[0056]

[0057] Where Z c(f) is the impedance of the power electronic component to be calculated at frequency f, U e(f) is the excitation voltage source voltage value of frequency f, I e(f) An excitation source of frequency f results in a corresponding harmonic current.

[0058] 1.4) From the minimum frequency f min To the maximum frequency f max , increase the step size Δf according to the set frequency, and traverse the frequency range [f min , f max ]; for each frequency point f, the admittance matrix of the AC system containing power electronic components at the frequency f is obtained, and the nodes of the AC system admittance matrix are numbered and optimized;

[0059] For various operating modes, from the minimum frequency f min To the maximum frequency f max , traverse all frequency points with a fixed interval Δf, and solve the admittance matrix of the AC system containing power electronic components for each frequency point f; number and optimize the nodes of the admittance matrix at each frequency point f; wherein, the power electronic components in step 1.3) are actually nonlinear impedances.

[0060] 1.5) Use the LU decomposition method to solve the AC network and obtain the AC system impedance at the observation point;

[0061] In this embodiment, calculating the harmonic impedance at a system node ultimately boils down to solving the nodal voltage equation for the AC system, which is essentially a system of linear algebraic equations. This invention employs the LU decomposition method. For the nodal voltage equation YV = I, the node admittance matrix Y is decomposed into the product of an L matrix and a U matrix. Through forward and back substitution, the solution is simplified. Ultimately, the AC system impedance at the observation point is obtained.

[0062] 1.6) Traverse all operating modes and calculate the AC system impedance in all cases.

[0063] In the above step 2), at each frequency point, the equivalent impedance of the AC system is plotted on a coordinate graph. Preferably, the AC envelope region of the present invention adopts a fan-shaped envelope region. Figure 3 As shown in FIG, a schematic diagram for determining the fan-shaped envelope area is given.

[0064] In this embodiment, the method for determining the sector envelope area includes the following steps:

[0065] 2.1) For a specific frequency f, traverse all the AC system impedance points at this frequency and obtain the maximum and minimum angles between the AC system impedance points and the zero coordinate:

[0066]

[0067] Where θ max(f) and θ min(f) are the maximum and minimum direct angles between the impedance point and the coordinate zero under all operating modes, respectively. Angle{0, Z} is the angle between the line segment between the calculated impedance point Z and the coordinate origin and the horizontal axis of the coordinate. The subscript f is the frequency. S is the set of all operating modes, and i is the i-th operating mode in the S set.

[0068] 2.2) For a specific frequency f, traverse all the AC system impedance points at that frequency and obtain the maximum and minimum distances between the AC system impedance points and coordinate zero as the maximum and minimum amplitudes:

[0069]

[0070] Where θ min(f) and R min(f) are the maximum and minimum amplitudes of the distance between the impedance point and the coordinate origin under all operating modes, |Z| is the amplitude of the calculated impedance point Z, the subscript f is the frequency, S is the set of all operating modes, and i is the i-th operating mode in the S set.

[0071] 2.3) Draw two rays from the origin, using the angle obtained by subtracting the minimum angle from the maximum angle as the boundary. 2.4) Draw two concentric circles with the maximum and minimum amplitudes as the radii and the origin as the zero point.

[0072] 2.5) The fan-shaped area formed by the intersection of the two drawn rays and the two concentric circles is the desired fan-shaped envelope area.

[0073] In step 2.2) above, if the AC system impedance point exhibits obvious regional characteristics or the determined sector coverage is too large, the flexible DC impedance boundary is difficult to determine or cannot be solved. In this case, the envelope can be determined by combining multiple sectors.

[0074] In step 3), the criteria used in this embodiment to avoid resonance between the flexible DC system and the AC system include the following four:

[0075] 3.1) The first criterion is the negative damping criterion, as follows:

[0076] Real(Z s(f) +Z m(f) )≥0 (4)

[0077] Among them, Zs(f) =X s(f) +jR s(f) , Z m(f) =X m(f) +jR m(f) , Z s(f) is the impedance of the AC system at frequency f, Z m(f) is the flexible direct impedance at frequency f, Real represents the real part, X s(f) The reactance of the AC system at the table frequency f (i.e. the imaginary part of the impedance Zs(f)), R s(f) represents the resistance of the AC system at frequency f (i.e. the imaginary part of the impedance Zs(f)), X m(f) R represents the reactance of the AC system at frequency f (i.e., the imaginary part of the impedance Zm(f)). m(f) It represents the resistance of the AC system at frequency f (i.e. the imaginary part of the impedance Zm(f)).

[0078] Preferably, the vector diagram method is used to draw the impedance feasible region of the flexible value system, such as Figure 4 shown.

[0079] 3.2) The second criterion is to not amplify the key frequency harmonics, as follows:

[0080]

[0081] Among them, Z s(f) =X s(f) +jR s(f) , Z m(f) =X m(f) +jR m(f) , Z s(f) is the impedance of the AC system at frequency f, Z m(f) is the flexible DC impedance at frequency f.

[0082] In order to obtain the feasible region of the flexible DC system impedance that satisfies formula (5), the vector diagram method is used to draw the following Figure 5 Impedance feasible region of the flexible system shown.

[0083] The feasible region for flexible direct impedance can be formed by the rays QM and QN and the area to their right. The lengths of segments AM, MO, BN, and ON are equal to half the minimum amplitude in step 2.2). QM is perpendicular to AO, and QN is perpendicular to OB.

[0084] 3.3) The third criterion is the voltage distortion rate criterion at the common connection point. The total voltage distortion rate at the common connection point should meet the following requirements:

[0085]

[0086]

[0087] Where k is the maximum harmonic order considered (usually 50), U N is the system fundamental voltage rating, U m(n) is the nth harmonic voltage generated by the flexible DC transmission system, σ is the total voltage distortion rate at the common connection point, n is the harmonic order (the fundamental frequency is 50 Hz), U p(n) is the nth harmonic voltage at the common connection point. s(n) is the AC system nth harmonic impedance, Z m(n) is the flexible nth harmonic impedance.

[0088] 3.4) The fourth criterion is the equipment harmonic current tolerance criterion, as follows:

[0089]

[0090]

[0091]

[0092]

[0093] Where, I n In order to consider the nth harmonic current under the combined effect of the system background harmonic voltage and the harmonic voltage generated by the converter, I s(n) To consider the nth harmonic current under the effect of system background harmonic voltage alone, I m(n) In order to consider the nth harmonic current under the action of the harmonic voltage generated by the converter, U s(n) is the nth system background harmonic voltage, and δ is the harmonic current tolerance capability of the equipment.

[0094] The third and fourth criteria need to be substituted into the calculation through step-by-step traversal method to determine the feasible region.

[0095] In the above step 3), the method for constructing the envelope interval of the flexible DC impedance feasible domain is: based on the actual system requirements, comprehensive consideration or partial combination of the first to fourth criteria, and then finding the intersection of the flexible DC system impedance feasible areas obtained by each criterion to obtain the boundary of the flexible DC system impedance feasible domain.

[0096] In one embodiment of the present invention, a system for determining a flexible DC impedance boundary for avoiding resonance with an AC system is provided, comprising:

[0097] The AC system impedance calculation module, based on the characteristics of the power grid structure data, traverses the operating conditions to be studied at a fixed frequency step size and calculates the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied;

[0098] An AC envelope region construction module plots the AC system impedance points at each frequency in a preset coordinate system and constructs an AC envelope region within the coordinate system to envelop all AC system impedance points;

[0099] The feasible region boundary determination module obtains all possible flexible DC impedances for each frequency within the AC envelope region, and obtains the feasible region boundary of the flexible DC system impedance based on the criterion of avoiding resonance between the flexible DC system and the AC system.

[0100] In the above embodiment, in the AC system impedance calculation module, the calculation of the AC system impedance includes:

[0101] Determine the typical grid operating conditions required for AC system impedance scanning;

[0102] According to the geographical wiring diagram, determine the boundary nodes and external connection lines of the power grid in the area where the observation point is located;

[0103] Obtain grid data within the determined boundary nodes and external tie lines, and calculate harmonic impedance based on the grid data type;

[0104] From the minimum frequency to the maximum frequency, all frequency points are traversed with a fixed interval △f. For each frequency point f, the admittance matrix of the AC system containing power electronic components at the frequency f is solved, and the nodes of the AC system admittance matrix are numbered and optimized.

[0105] The LU decomposition method is used to solve the AC network and obtain the AC system impedance at the observation point;

[0106] Traverse all operating modes and calculate the AC system impedance in all cases.

[0107] In the above embodiment, in the AC envelope region construction module, the AC envelope region adopts a fan-shaped envelope region.

[0108] The construction of the fan-shaped envelope area includes:

[0109] Traverse all AC system impedance points at harmonic frequencies to obtain the maximum and minimum values of the direct angles between the AC system impedance points and the zero coordinate;

[0110] Traverse all AC system impedance points at the harmonic frequency, and obtain the maximum and minimum distances between the AC system impedance points and coordinate zero as the maximum and minimum amplitudes;

[0111] Draw two rays from the coordinate origin with the angle obtained by subtracting the minimum angle from the maximum angle as the boundary;

[0112] Draw two concentric circles with the maximum and minimum amplitudes as radii and the origin of the coordinate system as the zero point;

[0113] The fan-shaped area formed by the intersection of the two drawn rays and the two concentric circles is the required fan-shaped envelope area.

[0114] In this embodiment, when the boundary of the flexible direct impedance is difficult to determine or cannot be solved, a combination of multiple sectors is used to determine the envelope.

[0115] In the above embodiment, in the feasible region boundary determination module, the criteria for avoiding resonance between the flexible DC system and the AC system include: negative damping criterion, non-amplification criterion of key frequency harmonics, common connection point voltage distortion rate criterion and equipment harmonic current tolerance criterion.

[0116] Among them, the determination of the feasible domain boundary of the flexible DC system impedance includes: comprehensively considering the four criteria, or partially combining the four criteria, finding the intersection of the feasible regions of the flexible DC system impedance obtained by each criterion, and obtaining the feasible domain boundary of the flexible DC system impedance.

[0117] The system provided in this embodiment is used to execute the above-mentioned method embodiments. Please refer to the above-mentioned embodiments for specific processes and detailed contents, which will not be repeated here.

[0118] A computing device provided in one embodiment of the present invention may be a terminal and may include: a processor, a communications interface, a memory, a display screen, and an input device. The processor, communications interface, and memory communicate with each other via a communications bus. The processor is configured to provide computing and control capabilities. The memory includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system and a computer program. When the computer program is executed by the processor, the computer program implements a method for determining a flexible direct impedance boundary that avoids resonance with an AC system. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The communications interface is configured to communicate with an external terminal via wired or wireless communication. The wireless communication may be implemented via Wi-Fi, a management network, NFC (near field communication), or other technologies. The display screen may be a liquid crystal display or an electronic ink display screen. The input device may be a touch layer covering the display screen, or may be a key, trackball, or touchpad provided on the housing of the computing device, or may be an external keyboard, touchpad, or mouse. The processor can call the logic instructions in the memory to execute the following method: according to the characteristics of the power grid structure data, traverse the operating conditions to be studied according to a fixed frequency step size, and calculate the AC system impedance at the common connection point of the flexible DC system and the AC system within the frequency range to be studied; draw the points of the AC system impedance at each frequency in a preset coordinate system, and construct an AC envelope area in the coordinate system to envelop all AC system impedance points; within the AC envelope area, obtain all possible flexible DC impedances for each frequency, and obtain the feasible domain boundary of the flexible DC system impedance based on the criterion of avoiding resonance between the flexible DC system and the AC system.

[0119] In addition, the logical instructions in the above-mentioned memory can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0120] Those skilled in the art will understand that the structure of the above-mentioned computing device is only a partial structure related to the solution of the present application, and does not constitute a limitation on the computing device to which the solution of the present application is applied. The specific computing device may include more or fewer components, or combine certain components, or have a different component arrangement.

[0121] In one embodiment of the present invention, a computer program product is provided, comprising a computer program stored on a non-transitory computer-readable storage medium, the computer program comprising program instructions. When the program instructions are executed by a computer, the computer can execute the methods provided by the above-mentioned method embodiments, for example, comprising: traversing the operating conditions to be studied according to a fixed frequency step size based on the characteristics of the power grid structure data, and calculating the AC system impedance at the common connection point of the flexible DC system and the AC system within the frequency range to be studied; plotting the points of the AC system impedance at each frequency in a preset coordinate system, and constructing an AC envelope region within the coordinate system for enveloping all AC system impedance points; within the AC envelope region, obtaining all possible flexible DC impedances for each frequency, and obtaining the feasible domain boundary of the flexible DC system impedance based on the criterion for avoiding resonance between the flexible DC system and the AC system.

[0122] In one embodiment of the present invention, a non-transitory computer-readable storage medium is provided, which stores server instructions, and the computer instructions enable a computer to execute the methods provided in the above embodiments, for example, including: traversing the operating conditions to be studied according to a fixed frequency step size based on the characteristics of the power grid structure data, and calculating the AC system impedance at the common connection point of the flexible DC system and the AC system within the frequency range to be studied; plotting the points of the AC system impedance at each frequency in a preset coordinate system, and constructing an AC envelope region within the coordinate system for enveloping all AC system impedance points; within the AC envelope region, obtaining all possible flexible DC impedances for each frequency, and obtaining the feasible domain boundary of the flexible DC system impedance based on the criterion for avoiding resonance between the flexible DC system and the AC system.

[0123] The above embodiment provides a computer-readable storage medium, whose implementation principle and technical effects are similar to those of the above method embodiment, and will not be repeated here.

[0124] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0125] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0126] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for determining a flexible DC impedance boundary to avoid resonance with an AC system, characterized in that: include: According to the characteristics of the power grid structure data, the operating conditions to be studied are traversed at a fixed frequency step size, and the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied is calculated; Plotting the AC system impedance points at each frequency in a preset coordinate system, and constructing an AC envelope region in the coordinate system for enveloping all AC system impedance points; In the AC envelope region, according to the criterion of avoiding resonance between the flexible DC system and the AC system, all possible flexible DC impedances are obtained for each frequency, and then the feasible region boundary of the flexible DC system impedance is obtained; The AC envelope area adopts a fan-shaped envelope area; The method for constructing the fan-shaped envelope area includes: Traverse all AC system impedance points at harmonic frequencies to obtain the maximum and minimum values of the direct angles between the AC system impedance points and the zero coordinate; Traverse all AC system impedance points at the harmonic frequency, and obtain the maximum and minimum distances between the AC system impedance points and coordinate zero as the maximum and minimum amplitudes; Draw two rays from the coordinate origin with the angle obtained by subtracting the minimum angle from the maximum angle as the boundary; Draw two concentric circles with the maximum and minimum amplitudes as radii and the origin of the coordinate system as the zero point; The intersection of the two drawn rays and the two concentric circles is used as the boundary, and the fan-shaped area formed is the fan-shaped envelope area required; Four criteria for avoiding resonance between the flexible DC system and the AC system are used, including: negative damping criterion, non-amplification of key frequency harmonics criterion, common connection point voltage distortion rate criterion and equipment harmonic current tolerance criterion, to determine or solve the boundary of the flexible DC impedance in the fan-shaped envelope area.

2. The method for determining a flexible DC impedance boundary to avoid resonance with an AC system according to claim 1, wherein: The calculation of the AC system impedance includes: Determine the typical grid operating conditions required for AC system impedance scanning; According to the geographical wiring diagram, determine the boundary nodes and external connection lines of the power grid in the area where the observation point is located; Obtain grid data within the determined boundary nodes and external tie lines, and calculate harmonic impedance based on the grid data type; From the minimum frequency to the maximum frequency, all frequency points are traversed with a fixed interval △f. For each frequency point f, the admittance matrix of the AC system containing power electronic components at the frequency f is solved, and the nodes of the AC system admittance matrix are numbered and optimized. use The decomposition method is used to solve the AC network and obtain the AC system impedance at the observation point; Traverse all operating modes and calculate the AC system impedance in all cases.

3. The method for determining a flexible DC impedance boundary to avoid resonance with an AC system according to claim 1, wherein: When the boundary of the flexible direct impedance is difficult to determine or cannot be solved, a combination of multiple sectors is used to determine the envelope.

4. The method for determining a flexible DC impedance boundary to avoid resonance with an AC system according to claim 1, wherein: The determination of the boundary of the flexible DC system impedance feasible region includes: comprehensively considering four criteria, or partially combining the four criteria, and finding the intersection of the flexible DC system impedance feasible regions obtained by each criterion to obtain the boundary of the flexible DC system impedance feasible region.

5. A system for determining a flexible DC impedance boundary for avoiding resonance with an AC system, for implementing the method for determining a flexible DC impedance boundary for avoiding resonance with an AC system as claimed in any one of claims 1 to 4, characterized in that: include: The AC system impedance calculation module, based on the characteristics of the power grid structure data, traverses the operating conditions to be studied at a fixed frequency step size and calculates the AC system impedance at the common connection point between the flexible DC system and the AC system within the frequency range to be studied; An AC envelope region construction module plots the AC system impedance points at each frequency in a preset coordinate system and constructs an AC envelope region within the coordinate system to envelop all AC system impedance points; The feasible region boundary determination module calculates all possible flexible DC impedances for each frequency within the AC envelope region based on the criterion of avoiding resonance between the flexible DC system and the AC system, and then obtains the feasible region boundary of the flexible DC system impedance.

6. A computer-readable storage medium storing one or more programs, characterized in that: The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any one of the methods of claims 1 to 4 .

7. A computing device, characterized in that include: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the methods according to claims 1 to 4.

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