Flexible direct current system direct current circuit resonance modeling method, evaluation method and related device

Abstract

The invention discloses a flexible direct current system direct current circuit resonance modeling method, an evaluation method and a related device, and the method comprises the steps: firstly building a valve group monomer topology model based on the precise reduction of the physical structure of a converter valve, then converting the dynamic behavior of a control signal into a three-phase sine wave signal, and inputting the three-phase sine wave signal into a sub-module modulation link of a three-phase bridge arm, therefore, the real-time influence of the modulation process on the direct-current loop impedance is completely captured, and the model can truly reflect the coupling effect of the alternating-current power grid impedance on the direct-current loop resonance by combining the equivalent modeling of the actual impedance relation. Therefore, a valve group monomer equivalent model in which a flexible direct current transformer, alternating current power grid impedance and modulation process influence are introduced is constructed, a high-precision flexible direct current system direct current loop resonance model is constructed on the basis of the valve group monomer equivalent model, and the problem of insufficient resonance analysis precision caused by model simplification in the prior art is solved. And the accuracy of the resonance analysis model is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible direct current power transmission, in particular to a HVDC system DC loop resonance modeling method, a HVDC system DC loop resonance evaluation method and related devices. BACKGROUND

[0002] Resonance in DC system is one of the key problems in the operation of flexible direct current power transmission system. Resonance usually originates from the abnormal response of DC loop impedance at certain frequencies. When the impedance has a resonance point or the impedance value decreases significantly near these frequencies, the harmonic components may be amplified, leading to sustained oscillation, and even threatening the safety of the system.

[0003] For the flexible direct current power transmission system, the existing modeling method usually uses a simplified equivalent model, such as equivalent bridge arm reactor and sub-module capacitor, to represent the converter station. However, the current modeling method fails to fully consider the mutual influence between AC and DC systems, ignores the influence of HVDC transformer, AC grid impedance and modulation process on the DC loop impedance, resulting in insufficient model accuracy. In actual engineering application, the results output by the analysis model with insufficient accuracy often have obvious errors compared with the actual situation. SUMMARY

[0004] The present application provides a HVDC system DC loop resonance modeling method, a HVDC system DC loop resonance evaluation method and related devices, which are used to solve the technical problem of low accuracy of the existing resonance analysis model for the DC loop of the flexible direct current power transmission system.

[0005] To solve the above technical problem, the first aspect of the present application provides a HVDC system DC loop resonance modeling method, comprising:

[0006] A valve group single topology model is constructed, which is a three-phase structure, each phase containing upper and lower bridge arms, and each bridge arm containing a plurality of sub-modules and a bridge arm reactor;

[0007] Based on the valve group single topology model, the converter valve control signal is equivalent to a three-phase sinusoidal signal, and the sinusoidal signal is input into the sub-module modulation link of the three-phase bridge arm of the valve group single topology model;

[0008] According to the impedance relationship of the HVDC transformer and the AC grid, an equivalent impedance is constructed, and the equivalent impedance is connected in parallel between each pair of upper and lower bridge arms in the valve group single topology model to obtain a valve group single equivalent model;

[0009] Based on the valve group single equivalent model, a HVDC system DC loop resonance model is constructed according to the preset HVDC system DC loop structure information.

[0010] Preferably, based on the valve group monomer equivalent model, according to preset HVDC system DC loop structure information, the HVDC system DC loop resonance model is constructed, which comprises:

[0011] According to the preset HVDC system DC loop structure information, the scale information of each converter loop, the type of DC transmission line and the DC loop topology type of the HVDC system DC loop are determined;

[0012] According to the scale information of the converter loop, a certain number of valve group monomer equivalent models are connected in series to obtain a converter DC loop resonance analysis model;

[0013] According to the type of DC transmission line, the frequency response characteristics of the DC transmission line are determined, and a transmission line model is constructed based on the frequency response characteristics;

[0014] According to the converter DC loop resonance analysis model and the transmission line model, the HVDC system DC loop resonance model is constructed in combination with the DC loop topology type.

[0015] Preferably, the frequency response characteristics of the DC transmission line are determined according to the type of DC transmission line, which comprises:

[0016] According to the type of DC transmission line, the frequency response characteristics of the DC transmission line are determined by using a frequency-varying parameter model through curve fitting.

[0017] Preferably, the DC loop topology type comprises: a symmetric monopole topology type, a monopole ground topology type of a bipolar DC topology, a monopole metal topology type of a bipolar DC topology and a bipolar operation topology type.

[0018] Preferably, the impedance relationship between the HVDC transformer and the AC power grid is:

[0019]

[0020] In the formula, R t and L t are the equivalent resistance and equivalent reactance of the HVDC transformer respectively, is the equivalent impedance of the HVDC transformer and the AC power grid.

[0021] The second aspect of the present application provides a HVDC system DC loop resonance risk assessment method, which comprises:

[0022] Obtain a HVDC system DC loop resonance model, wherein the HVDC system DC loop resonance model is constructed according to the HVDC system DC loop resonance modeling method provided in the first aspect of the present application;

[0023] Based on the DC loop resonance model of the flexible DC system, an impulse voltage source is applied to the series unit in the DC loop resonance model of the flexible DC system. After obtaining the current response, the frequency domain characteristics of voltage and current are calculated by Fourier analysis to obtain the frequency characteristics of DC loop impedance.

[0024] Based on the DC circuit impedance frequency characteristics, a risk assessment is conducted in conjunction with a preset resonance criterion to identify potential resonance points based on the assessment results.

[0025] A third aspect of this application provides a DC loop resonance modeling device for a flexible DC system, comprising:

[0026] The valve group topology model construction unit is used to construct the valve group single-unit topology model. The valve group single-unit topology model is a three-phase structure. Each phase contains upper and lower bridge arms. Each bridge arm contains several sub-modules and a bridge arm reactor.

[0027] The valve group control equivalent unit is used to convert the converter valve control signal into a three-phase sine wave signal based on the valve group single-unit topology model, and input the sine wave signal into the sub-module modulation stage of the three-phase bridge arm of the valve group single-unit topology model respectively.

[0028] Impedance equivalent unit is used to construct equivalent impedance based on the impedance relationship between the flexible DC transformer and the AC power grid, and to connect the equivalent impedance in parallel between each pair of upper and lower bridge arms in the valve group single unit topology model to obtain the valve group single unit equivalent model.

[0029] The DC loop resonance model construction unit is used to construct the DC loop resonance model of the flexible DC system based on the equivalent model of the valve group unit and according to the preset DC loop structure information of the flexible DC system.

[0030] The fourth aspect of this application provides a device for assessing the resonant risk of a DC circuit in a flexible DC system, comprising:

[0031] A model acquisition unit is used to acquire a DC-DC resonant model of a flexible DC system, wherein the DC-DC resonant model of the flexible DC system is constructed by the DC-DC resonant modeling device of the flexible DC system as provided in the third aspect of this application;

[0032] An excitation application unit is used to apply an impulse voltage source to the series unit in the DC loop resonance model of the flexible DC system based on the DC loop resonance model of the flexible DC system. After obtaining the current response, the frequency domain characteristics of the voltage and current are calculated by Fourier analysis to obtain the frequency characteristics of the DC loop impedance.

[0033] The resonance risk assessment unit is used to perform risk assessment based on the impedance frequency characteristics of the DC circuit and in combination with preset resonance criteria, so as to identify potential resonance points according to the assessment results.

[0034] The fifth aspect of this application provides a DC loop resonance modeling terminal for a flexible DC system, comprising: a first memory and a first processor;

[0035] The first memory is used to store first program code, which corresponds to the DC loop resonance modeling method for flexible DC systems provided in the first aspect of this application;

[0036] The first processor is used to read and execute the first program code to implement the DC circuit resonance modeling method of the flexible DC system.

[0037] The sixth aspect of this application provides a DC circuit resonance risk assessment terminal for a flexible DC system, comprising: a second memory and a second processor;

[0038] The second memory is used to store second program code, which corresponds to the DC circuit resonance risk assessment method for flexible DC systems provided in the second aspect of this application;

[0039] The second processor is used to read and execute the second program code to implement the DC circuit resonance risk assessment method of the flexible DC system.

[0040] As can be seen from the above technical solutions, this application has the following advantages:

[0041] This solution first constructs a single-unit topology model of the valve group based on an accurate reconstruction of the physical structure of the converter valve. Then, by converting the dynamic behavior of the control signal into a three-phase sinusoidal signal input to the modulation stage of the three-phase bridge arm submodule, it ensures that the real-time impact of the modulation process on the DC loop impedance is fully captured. Combined with the equivalent modeling of the actual impedance relationship, the model can truly reflect the coupling effect of the AC grid impedance on the DC loop resonance. Thus, a single-unit equivalent model of the valve group is constructed, incorporating the effects of the flexible DC transformer, AC grid impedance, and modulation process. Based on this single-unit equivalent model of the valve group, a more accurate DC loop resonance model of the flexible DC system is constructed, solving the problem of insufficient resonance analysis accuracy caused by model simplification in the existing technology and improving the accuracy of the resonance analysis model. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a flowchart illustrating an embodiment of a DC loop resonance modeling method for a flexible DC system provided in this application.

[0044] Figure 2 This is a topological schematic diagram of the equivalent model of a valve group unit in an embodiment of a DC loop resonance modeling method for a flexible DC system provided in this application.

[0045] Figure 3 This is a schematic diagram of the topology of a DC circuit resonant model for a flexible DC system operating under unipolar conditions.

[0046] Figure 4 This is a schematic diagram of the DC loop resonant model topology of a flexible DC system operating under bipolar conditions.

[0047] Figure 5 This is a flowchart illustrating an embodiment of a DC circuit resonance risk assessment method for a flexible DC system provided in this application.

[0048] Figure 6 This is a schematic diagram of the architecture of an embodiment of a DC loop resonance modeling device for a flexible DC system provided in this application.

[0049] Figure 7 This is a schematic diagram of the architecture of an embodiment of a DC circuit resonance risk assessment device for a flexible DC system provided in this application. Detailed Implementation

[0050] This application provides a method for modeling and evaluating the resonance of DC circuits in flexible DC systems, as well as related devices, to address the technical problem that existing resonance analysis models for DC circuits in flexible DC systems have low accuracy, affecting the safety and reliability of flexible DC transmission systems.

[0051] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0052] First, a detailed description of an embodiment of a DC loop resonance modeling method for a flexible DC system provided in this application is as follows:

[0053] Please see Figure 1 This application provides an embodiment of a DC loop resonance modeling method for a flexible DC system, the steps of which include:

[0054] Step 101: Construct a single valve assembly topology model;

[0055] The valve group's individual topology model is a three-phase structure, with each phase containing upper and lower bridge arms, and each bridge arm containing several sub-modules and a bridge arm reactor.

[0056] Step 102: Based on the valve group single-unit topology model, the converter valve control signal is converted into a three-phase sine wave signal, and the sine wave signal is input into the sub-module modulation stage of the three-phase bridge arm of the valve group single-unit topology model respectively.

[0057] Step 103: Based on the impedance relationship between the flexible DC transformer and the AC power grid, construct the equivalent impedance and connect the equivalent impedance in parallel between each pair of upper and lower bridge arms in the valve group single-unit topology model to obtain the valve group single-unit equivalent model.

[0058] Step 104: Based on the equivalent model of the valve group unit, construct the resonant model of the DC circuit of the flexible DC system according to the preset DC circuit structure information of the flexible DC system.

[0059] It should be noted that the valve manifold individual topology model can be understood as a basic structure used to describe the electrical characteristics of the converter valve. It recreates the physical details of the converter valve through the design of the three-phase structure and the configuration of the upper and lower bridge arms. Specifically, the sub-modules in the bridge arms can be implemented in various ways, such as using half-bridge, full-bridge, or hybrid sub-modules. The choice of these sub-modules mainly depends on the specific engineering requirements and system design goals. Furthermore, the bridge arm reactors can be implemented using air-core or iron-core reactors, and their parameter design must meet the dynamic response requirements of the system.

[0060] The process of converting the converter valve control signal to a three-phase sinusoidal signal can be understood as a technique to simplify the control signal, facilitating subsequent analysis and calculation. Specifically, this process can extract the fundamental component using Fourier decomposition or suppress high-frequency components using a low-pass filter to obtain an approximate sinusoidal signal. This approach effectively reduces computational complexity while preserving the main characteristics of the control signal.

[0061] The impedance relationship between the flexible DC transformer and the AC power grid can be constructed in several ways, such as fitting impedance curves based on measured data or deriving equivalent parameters using theoretical formulas. Furthermore, the parallel operation of equivalent impedances can be performed using circuit simulation software or by directly calculating their equivalent values ​​analytically. This approach ensures that the model accurately reflects the impact of the AC side on the DC circuit.

[0062] The working principle of this application embodiment is as follows:

[0063] By constructing a single-unit topology model of the valve group, which adopts a three-phase structure design, each phase includes upper and lower bridge arms, and each bridge arm consists of several sub-modules and a bridge arm reactor, the physical details of the converter valve can be accurately reproduced. Furthermore, based on this topology model, the converter valve control signal is converted into a three-phase sinusoidal signal and input into the modulation stage of the sub-modules of the three-phase bridge arms, thereby ensuring that the real-time impact of the modulation process on the DC circuit impedance is fully captured. Specifically, based on the impedance relationship between the flexible DC transformer and the AC power grid, an equivalent impedance is constructed and connected in parallel between each pair of upper and lower bridge arms, resulting in... Figure 2 The valve group unit equivalent model shown is derived using actual impedance relationships to produce equivalent parameters, enabling the model to accurately reflect the coupling effect of AC grid impedance on DC circuit resonance. Finally, based on the valve group unit equivalent model, a complete flexible DC system DC circuit resonance model is constructed according to the pre-defined flexible DC system DC circuit structure information. By integrating equivalent units, flexible adaptation to different engineering scenarios is achieved, comprehensively incorporating the combined influence of flexible DC transformers, AC grids, and modulation control. This effectively solves the problem of insufficient accuracy caused by neglecting the interaction between AC and DC systems and the modulation process in existing modeling methods.

[0064] Based on the above basic embodiments, this application further proposes a specific implementation method for constructing a DC loop resonant model of a flexible DC system based on the equivalent model of a valve group unit, specifically including:

[0065] Based on the preset DC loop structure information of the flexible DC system, determine the scale information of each converter loop, the type of DC transmission line, and the DC loop topology type of the flexible DC system.

[0066] Based on the scale information of the converter circuit, a specific number of valve group unit equivalent models are connected in series to obtain the DC circuit resonance analysis model of the converter.

[0067] Based on the type of DC transmission line, determine the frequency response characteristics of the DC transmission line, and construct a transmission line model based on the frequency response characteristics;

[0068] Based on the DC loop resonance analysis model of the converter and the transmission line model, and combined with the DC loop topology type, a DC loop resonance model of the flexible DC system is constructed.

[0069] The converter loop scale information refers to the number and arrangement of submodules in the converter, which can be obtained by counting the total number of submodules in each bridge arm or by obtaining actual engineering parameters. DC transmission line type can be understood as including different forms such as cable lines and overhead lines, which can be distinguished by parameters such as line material, length, and laying method. DC loop topology type refers to the connection method of the flexible DC system, which can be determined through system design documents or actual wiring diagrams. The purpose of introducing these technical features is to ensure that the model can adapt to diverse engineering scenarios, thereby improving modeling accuracy and applicability.

[0070] Specifically, the above scheme constructs a high-precision DC loop resonance model by integrating the structural parameters and physical characteristics of the flexible DC system. First, based on the pre-defined DC loop structure information of the flexible DC system, the scale information of the converter loop, the type of DC transmission line, and the DC loop topology are clarified. This process ensures that the model can be customized for actual engineering boundary conditions. Second, based on the scale information of the converter loop, a specific number of valve group unit equivalent models are connected in series to realistically simulate the physical structure of a multi-module converter station. Simultaneously, DC reactors are connected in series to their corresponding positions when configuring them. Furthermore, the frequency response characteristics are determined according to the DC transmission line type, and a transmission line model is constructed. Finally, by combining the converter DC loop resonance analysis model, the transmission line model, and the DC loop topology, sub-models are dynamically combined to cover various operating conditions, thereby ensuring the consistency and reliability of the model in diverse engineering scenarios. Through this technical solution, the diversity of engineering configurations is effectively considered, improving the model's generalization ability and thus enhancing the accuracy and applicability of resonance analysis.

[0071] Based on this embodiment, this application further proposes that determining the frequency response characteristics of a DC transmission line according to its type includes: determining the frequency response characteristics of the DC transmission line by using a frequency-varying parameter model and curve fitting, based on the DC transmission line type.

[0072] In practical applications, frequency-varying parameter models refer to mathematical models that reflect the variation of parameters such as resistance and inductance of DC transmission lines with frequency. These models can be implemented using specialized algorithms based on the electrical characteristics of overhead lines or cables. Specifically, curve fitting can be understood as a technique for mathematical approximation using measured data or high-precision simulation results. Its purpose is to transform complex physical characteristics into quantifiable frequency domain functions, thereby ensuring that the model reflects both the actual frequency dependence of the line and the convenience of engineering applications.

[0073] In detail, this scheme effectively addresses the limitations of fixed-parameter models in resonance analysis by specifically addressing the frequency response characteristics of DC transmission lines. Due to fundamental differences in the electrical structures of different line types, the variation patterns of parameters such as resistance and inductance with frequency vary. Therefore, it is essential to select a suitable frequency-varying model based on the specific type to accurately reproduce the dynamic behavior of the line across a wide frequency range. Based on this, the frequency response characteristics are determined through curve fitting. This not only utilizes measured data or high-precision calculation results for mathematical approximation but also transforms complex physical characteristics into quantifiable frequency domain functions, thus avoiding frequency domain distortion problems caused by simplified models. The final determined frequency response characteristics are directly integrated into the resonance model, enabling DC loop impedance analysis to accurately capture the system's response characteristics at different frequencies, significantly improving the reliability of resonance risk assessment. Furthermore, this scheme, combined with the aforementioned process of constructing equivalent models for individual valve groups and DC loop resonance models for flexible DC transmission systems, forms a complete technical system, providing a reliable guarantee for accurately assessing the resonance risk of flexible DC transmission systems.

[0074] Furthermore, the DC loop topology types mentioned in the above embodiments may specifically include: symmetrical unipolar topology, unipolar maxima topology of bipolar DC topology, unipolar metallic topology of bipolar DC topology, and bipolar operating topology. The DC loop resonance analysis model topologies for single-stage and bipolar operating conditions of flexible DC transmission systems can be found in the respective references. Figure 3 and Figure 4 It should be noted that the DC reactor L shown in the figure p This is an optional component and can be omitted in some embodiments.

[0075] Specifically, the DC loop topology type refers to the specific circuit structure involved in constructing the DC loop resonant model of a flexible DC system. It can be implemented using various predefined topology configurations. In practical applications, the symmetrical unipolar topology type is a common simplified structure, characterized by achieving symmetrical operation of the DC system through a unipolar configuration. The unipolar polar topology type of bipolar DC topology is suitable for special operating conditions where the ground is used as the loop, reflecting changes in impedance characteristics under ground faults or specific conditions. The unipolar metallic topology type of bipolar DC topology is mainly used for configurations with metal conductors as loops, reflecting the design requirement of reducing environmental interference. The bipolar operating topology type is a key type for modeling the complex electrical coupling behavior of bipolar systems operating simultaneously, enhancing the model's versatility and thus meeting diverse engineering needs.

[0076] Furthermore, this application also proposes the impedance relationship between the flexible DC transformer and the AC power grid as follows:

[0077]

[0078] In the formula, R t and L t These are the equivalent resistance and equivalent reactance of a flexible DC transformer, respectively. This is the equivalent impedance of the flexible DC transformer and the AC power grid.

[0079] Among them, Z eq This refers to the combined impedance characteristics of a flexible DC transformer and an AC power grid at the resonant frequency. It can be expressed in complex form to accurately reflect the dynamic behavior of the system. In practical applications, R... t This can be understood as the main source of energy loss in a flexible DC transformer at its resonant frequency. Its specific implementation methods include, but are not limited to, experimental measurements or calculations based on physical parameters. Meanwhile, L... t The inductance characteristics of the flexible DC transformer were quantified, which can be determined by analyzing the transformer winding structure and material properties, with the aim of truly reflecting the dynamic response at high frequency resonance.

[0080] In detail, the above technical solution addresses the problem of insufficient impedance characteristic quantification in existing modeling methods by defining the impedance relationship between the flexible DC transformer and the AC power grid as a complex number, Zeq = Rt + jLt. Rt, as the equivalent resistance component, effectively captures the energy loss characteristics of the system at the resonant frequency, avoiding the distortion of the imaginary part of impedance caused by neglecting resistance in traditional simplified models. Lt, as the equivalent reactance component, reflects the dynamic behavior of inductance characteristics with frequency, ensuring that the suppression or amplification effect of the AC power grid and transformer on high-frequency resonance is accurately reflected when constructing the equivalent impedance. This mathematical expression directly relates physical parameters to the impedance frequency response, enabling precise simulation of the coupling effect between AC and DC systems when the equivalent impedance is connected in parallel to the valve group's individual topology model, thereby improving the DC loop resonance model's ability to identify potential resonance points. Furthermore, this solution, combined with the aforementioned construction of the valve group's individual topology model, parallel connection of equivalent impedances, and resonance model construction, further enhances the model's accuracy and applicability, providing a more reliable theoretical foundation for resonance risk assessment.

[0081] The above is a detailed description of an embodiment of a DC loop resonance modeling method for a flexible DC system provided in this application. Based on the above embodiment, this application also provides a detailed description of an embodiment of a DC loop resonance risk assessment method for a flexible DC system, as follows:

[0082] Please see Figure 5 This application also discloses an embodiment of a method for assessing the resonance risk of a DC circuit in a flexible DC system, the steps of which include:

[0083] Step 201: Obtain the DC loop resonance model of the flexible DC system;

[0084] The DC-DC loop resonance model of the flexible DC system is constructed according to the DC-DC loop resonance modeling method of the flexible DC system provided in the above embodiments.

[0085] Step 202: Based on the DC loop resonance model of the flexible DC system, apply an impulse voltage source to the series unit in the DC loop resonance model of the flexible DC system. After obtaining the current response, calculate the frequency domain characteristics of voltage and current through Fourier analysis to obtain the frequency characteristics of DC loop impedance.

[0086] Step 203: Based on the DC loop impedance frequency characteristics and combined with the preset resonance criteria, conduct a risk assessment to identify potential resonance points based on the assessment results.

[0087] This embodiment, based on the DC loop resonance model of the flexible DC system constructed using the aforementioned modeling method, effectively solves the problem of inaccurate resonance risk assessment caused by neglecting the mutual influence of AC and DC systems in existing models by combining a high-precision resonance model with frequency domain analysis techniques. Specifically, this method fully incorporates the comprehensive influence of the flexible DC transformer, AC grid impedance, and modulation control when acquiring the DC loop resonance model of the flexible DC system, ensuring that the model can truly reflect the dynamic characteristics of the actual system. Furthermore, by applying an impulse voltage source to the series unit in the model and obtaining the current response, and using transient excitation to stimulate the system's broadband response, the impedance frequency characteristics can be accurately extracted directly from the time domain response, thus clearly revealing the location of the resonance point. Finally, risk assessment is performed based on the obtained DC loop impedance frequency characteristics combined with a preset resonance criterion, thereby improving the accuracy and engineering applicability of the risk assessment and ensuring the safe and stable operation of the flexible DC transmission system.

[0088] The above is a detailed description of the embodiments of the DC circuit resonance risk assessment method for flexible DC systems provided in this application. The following is a detailed description of the related embodiments of the DC circuit resonance modeling device for flexible DC systems, the DC circuit resonance risk assessment device for flexible DC systems, and related terminals provided in this application.

[0089] Please see Figure 6 This application provides an embodiment of a DC loop resonance modeling device for a flexible DC system, which comprises:

[0090] Valve group topology model building unit 301 is used to build valve group single unit topology model. The valve group single unit topology model is a three-phase structure. Each phase contains upper and lower bridge arms. Each bridge arm contains several sub-modules and a bridge arm reactor.

[0091] The valve group control equivalent unit 302 is used to convert the converter valve control signal into a three-phase sine wave signal based on the valve group single-unit topology model, and input the sine wave signal into the sub-module modulation link of the three-phase bridge arm of the valve group single-unit topology model respectively.

[0092] Impedance equivalent unit 303 is used to construct equivalent impedance based on the impedance relationship between the flexible DC transformer and the AC power grid, and connect the equivalent impedance in parallel between each pair of upper and lower bridge arms in the valve group single unit topology model to obtain the valve group single unit equivalent model.

[0093] The DC loop resonance model construction unit 304 is used to construct the DC loop resonance model of the flexible DC system based on the valve group single unit equivalent model and according to the preset DC loop structure information of the flexible DC system.

[0094] This embodiment combines the valve group's individual topology model with the equivalent processing of the converter valve control signal, and introduces equivalent modeling of the impedance relationship between the flexible DC transformer and the AC power grid. This solves the problem of insufficient accuracy caused by neglecting the interaction between AC and DC systems and the influence of the modulation process in existing modeling methods, thereby improving the applicability and accuracy of the model.

[0095] In one embodiment, the DC loop resonance model construction unit 304 is further configured to: determine the scale information of each converter loop, the type of DC transmission line, and the DC loop topology of the flexible DC system based on the preset DC loop structure information of the flexible DC system; connect a specific number of valve group unit equivalent models in series based on the scale information of the converter loop to obtain the converter DC loop resonance analysis model; determine the frequency response characteristics of the DC transmission line based on the type of DC transmission line, and construct the transmission line model based on the frequency response characteristics; and construct the flexible DC system DC loop resonance model based on the converter DC loop resonance analysis model and the transmission line model, combined with the DC loop topology.

[0096] Similarly, please see Figure 7 This application also discloses an embodiment of a DC circuit resonance risk assessment device for a flexible DC system, which comprises:

[0097] The model acquisition unit 401 is used to acquire the DC circuit resonance model of the flexible DC system, wherein the DC circuit resonance model of the flexible DC system is constructed by the aforementioned DC circuit resonance modeling device for the flexible DC system.

[0098] Excitation application unit 402 is used to apply an impulse voltage source to the series unit in the DC loop resonance model of the flexible DC system based on the DC loop resonance model of the flexible DC system. After obtaining the current response, the frequency domain characteristics of voltage and current are calculated by Fourier analysis to obtain the frequency characteristics of DC loop impedance.

[0099] The resonance risk assessment unit 403 is used to perform risk assessment based on the DC loop impedance frequency characteristics and a preset resonance criterion, so as to identify potential resonance points based on the assessment results.

[0100] This embodiment combines a high-fidelity model that incorporates the effects of flexible DC transformers, AC grid impedance, and modulation control with frequency domain analysis methods. This solves the problem of insufficient model accuracy caused by neglecting the interaction between AC and DC systems in existing modeling methods, thereby improving the accuracy and reliability of resonance risk assessment.

[0101] In another embodiment, this application also discloses an embodiment of a DC-DC loop resonance modeling terminal for a flexible DC system, comprising: a first memory and a first processor; the first memory is used to store first program code, the first program code corresponding to the above-described DC-DC loop resonance modeling method for a flexible DC system; the first processor is used to read and execute the first program code to implement the DC-DC loop resonance modeling method for a flexible DC system.

[0102] By embedding high-precision modeling methods into an executable program and integrating it into the first memory and first processor, the modeling process is automated and standardized. Specifically, the terminal can automatically execute a complete modeling process, including the construction of the valve group's individual topology model, control signal equivalence, and impedance equivalence, effectively avoiding the problem of overlooking key factors such as flexible DC transformers, AC grid impedance, and modulation control that may occur during manual operation. This approach not only ensures the accuracy of the DC loop resonance analysis model but also provides a reliable foundation for risk assessment in engineering applications.

[0103] Similarly, this application also discloses an embodiment of a DC-DC loop resonance risk assessment terminal for a flexible DC system, comprising: a second memory and a second processor; the second memory is used to store second program code, which corresponds to the aforementioned DC-DC loop resonance risk assessment method for a flexible DC system; the second processor is used to read and execute the second program code to implement the DC-DC loop resonance risk assessment method for a flexible DC system.

[0104] By co-designing the second memory and the second processor, and combining them with a risk assessment process based on a high-precision resonant model, the problem of inaccurate assessment caused by neglecting the interaction between AC and DC systems in traditional modeling methods is solved. Specifically, this terminal can perform analysis based on a resonant model that considers the influence of flexible DC transformers, AC grid impedance, and modulation processes, thereby improving model accuracy and practical assessment capabilities, and ultimately enhancing the safety and reliability of flexible DC transmission systems.

[0105] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the terminals, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0106] In the several embodiments provided in this application, it should be understood that the disclosed terminals, devices, and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between devices or units through some interfaces, and may be electrical, mechanical, or other forms.

[0107] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0108] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0109] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0110] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0111] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0112] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for modeling DC loop resonance in a flexible DC system, characterized in that, include: Construct a valve group unit topology model. The valve group unit topology model is a three-phase structure. Each phase contains upper and lower bridge arms. Each bridge arm contains several sub-modules and a bridge arm reactor. Based on the valve group single-unit topology model, the converter valve control signal is converted into a three-phase sine wave signal, and the sine wave signal is respectively input into the sub-module modulation stage of the three-phase bridge arm of the valve group single-unit topology model; Based on the impedance relationship between the flexible DC transformer and the AC power grid, an equivalent impedance is constructed, and the equivalent impedance is connected in parallel between each pair of upper and lower bridge arms in the valve group single-unit topology model to obtain the valve group single-unit equivalent model. Based on the equivalent model of the valve group unit, and according to the preset DC loop structure information of the flexible DC system, a DC loop resonance model of the flexible DC system is constructed.

2. The method for modeling DC loop resonance in a flexible DC system according to claim 1, characterized in that, Based on the equivalent model of the valve group unit, and according to the preset DC loop structure information of the flexible DC system, the DC loop resonance model of the flexible DC system is constructed as follows: Based on the preset DC loop structure information of the flexible DC system, determine the scale information of each converter loop, the type of DC transmission line, and the DC loop topology type of the flexible DC system. Based on the scale information of the converter circuit, a specific number of equivalent models of the valve group units are connected in series to obtain the DC circuit resonance analysis model of the converter. Based on the type of DC transmission line, determine the frequency response characteristics of the DC transmission line, and construct a transmission line model based on the frequency response characteristics; Based on the converter DC loop resonance analysis model and the transmission line model, and combined with the DC loop topology type, a flexible DC system DC loop resonance model is constructed.

3. The method for modeling DC loop resonance in a flexible DC system according to claim 2, characterized in that, Determining the frequency response characteristics of the DC transmission line based on its type includes: Based on the type of DC transmission line, a frequency-varying parameter model is used, and the frequency response characteristics of the DC transmission line are determined by curve fitting.

4. The method for modeling DC loop resonance in a flexible DC system according to claim 2, characterized in that, The DC circuit topology types include: symmetrical unipolar topology, unipolar polarity topology of bipolar DC topology, unipolar metallic topology of bipolar DC topology, and bipolar operating topology.

5. The method for modeling DC loop resonance in a flexible DC system according to claim 1, characterized in that, The impedance relationship between the flexible DC transformer and the AC power grid is as follows: In the formula, R t and L t These are the equivalent resistance and equivalent reactance of a flexible DC transformer, respectively. This is the equivalent impedance of the flexible DC transformer and the AC power grid.

6. A method for assessing the resonance risk of a flexible DC system's DC circuit, characterized in that, include: Obtain a DC-DC resonant model of a flexible DC system, wherein the DC-DC resonant model of the flexible DC system is constructed according to the DC-DC resonant modeling method of a flexible DC system as described in any one of claims 1 to 5; Based on the DC loop resonance model of the flexible DC system, an impulse voltage source is applied to the series unit in the DC loop resonance model of the flexible DC system. After obtaining the current response, the frequency domain characteristics of voltage and current are calculated by Fourier analysis to obtain the frequency characteristics of DC loop impedance. Based on the DC circuit impedance frequency characteristics, a risk assessment is conducted in conjunction with a preset resonance criterion to identify potential resonance points based on the assessment results.

7. A DC circuit resonance modeling device for a flexible DC system, characterized in that, include: The valve group topology model construction unit is used to construct the valve group single-unit topology model. The valve group single-unit topology model is a three-phase structure. Each phase contains upper and lower bridge arms. Each bridge arm contains several sub-modules and a bridge arm reactor. The valve group control equivalent unit is used to convert the converter valve control signal into a three-phase sine wave signal based on the valve group single-unit topology model, and input the sine wave signal into the sub-module modulation stage of the three-phase bridge arm of the valve group single-unit topology model respectively. Impedance equivalent unit is used to construct equivalent impedance based on the impedance relationship between the flexible DC transformer and the AC power grid, and to connect the equivalent impedance in parallel between each pair of upper and lower bridge arms in the valve group single unit topology model to obtain the valve group single unit equivalent model. The DC loop resonance model construction unit is used to construct the DC loop resonance model of the flexible DC system based on the equivalent model of the valve group unit and according to the preset DC loop structure information of the flexible DC system.

8. A device for assessing the risk of DC circuit resonance in a flexible DC system, characterized in that, include: The model acquisition unit is used to acquire the DC circuit resonance model of the flexible DC system, wherein the DC circuit resonance model of the flexible DC system is constructed by the DC circuit resonance modeling device of the flexible DC system as described in claim 7; An excitation application unit is used to apply an impulse voltage source to the series unit in the DC loop resonance model of the flexible DC system based on the DC loop resonance model of the flexible DC system. After obtaining the current response, the frequency domain characteristics of the voltage and current are calculated by Fourier analysis to obtain the frequency characteristics of the DC loop impedance. The resonance risk assessment unit is used to perform risk assessment based on the impedance frequency characteristics of the DC circuit and in combination with preset resonance criteria, so as to identify potential resonance points according to the assessment results.

9. A DC circuit resonance modeling terminal for a flexible DC system, characterized in that, include: First memory and first processor; The first memory is used to store first program code, which corresponds to the DC loop resonance modeling method for flexible DC systems as described in any one of claims 1 to 5; The first processor is used to read and execute the first program code to implement the DC circuit resonance modeling method of the flexible DC system.

10. A terminal for assessing the resonant risk of a flexible DC system's DC circuit, characterized in that, include: Second memory and second processor; The second memory is used to store second program code, which corresponds to the DC circuit resonance risk assessment method for flexible DC systems as described in claim 6; The second processor is used to read and execute the second program code to implement the DC circuit resonance risk assessment method of the flexible DC system.

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