A method and related device for calculating direct current bias current of a flexible direct transformer

Abstract

The application provides a flexible direct-current (DC) transformer DC bias current calculation method and related device, including obtaining a resonance analysis model of a DC loop of a flexible DC transmission system converter; the resonance analysis model is constructed based on the physical structure of the DC loop of the flexible DC transmission system converter; the impedance at 50Hz in the resonance analysis model is obtained through frequency scanning, and whether the impedance is less than a set threshold; if yes, time domain simulation calculation is performed by using a multi-terminal DC detailed electromagnetic transient simulation model to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used for simulating the electromagnetic transient process of the multi-terminal flexible DC transmission system. The DC loop resonance analysis model is constructed to judge the impedance at 50Hz, and then the electromagnetic transient simulation model is used to calculate the DC bias current, so that the DC bias risk of the flexible DC transformer can be effectively evaluated.

Description

Technical Field

[0001] This invention belongs to the field of transformer technology, specifically relating to a method and related apparatus for calculating the DC bias current of a flexible DC transformer. Background Technology

[0002] When the DC-side circuit impedance of a DC transmission system is low at 50Hz, the positive-sequence second harmonic on the AC side will cause an excessive DC component in the AC-side transformer, leading to transformer saturation, equipment heating and vibration, and affecting equipment safety. Based on the converter characteristics of traditional DC transmission systems, and the impedance-frequency characteristics of long-distance DC lines, smoothing reactors, and DC filters, the 50Hz impedance of the DC circuit and the magnitude of the transformer's DC bias current in a traditional DC transmission system can be clearly analyzed.

[0003] Currently, there are relatively mature research and calculation methods for the DC bias current of converter transformers in traditional DC transmission systems. However, there is still a lack of relevant calculation methods for the DC bias current of flexible DC transformers in flexible DC transmission systems. With the construction of new power systems, the application of flexible DC transmission will become increasingly widespread. Therefore, it is urgent to study calculation methods for the DC bias current of flexible DC transformers in flexible DC transmission systems. This method can be applied to the planning and design of flexible DC transmission systems, to predict the risk of excessive DC bias current in advance, and to ensure the safe and stable operation of the system and equipment. Summary of the Invention

[0004] In view of this, the present invention provides a method and related apparatus for calculating the DC bias current of a flexible DC transformer, so as to realize its application in the planning and design of flexible DC transmission systems, to predict the risk of excessive DC bias current in advance, and to ensure the safe and stable operation of the system and equipment.

[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for calculating the DC bias current of a flexible DC transformer, comprising the following steps:

[0007] A resonance analysis model of the DC circuit of the converter in a flexible DC transmission system is obtained; the resonance analysis model is constructed based on the physical structure of the DC circuit of the converter in a flexible DC transmission system.

[0008] The impedance at 50Hz in the resonance analysis model is obtained by frequency scanning, and it is determined whether the impedance at 50Hz is less than the set threshold. The set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC transformer.

[0009] If so, time-domain simulation calculations are performed using a multi-terminal DC detailed electromagnetic transient simulation model to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of a multi-terminal flexible DC transmission system.

[0010] Furthermore, the impedance at 50Hz in the resonance analysis model is obtained through frequency scanning, including:

[0011] A unit impulse voltage source is connected in series in the DC circuit of the converter of the flexible DC transmission system simulated by the resonance analysis model;

[0012] The current response of the DC circuit of the converter of the flexible DC transmission system is obtained, and Fourier calculations are performed on the voltage and current of the voltage source to obtain the frequency response of DC voltage and DC current at 50Hz.

[0013] The impedance amplitude of the DC circuit at 50Hz is calculated based on the frequency response of the DC voltage and DC current at 50Hz.

[0014] Furthermore, the impedance amplitude at 50Hz in the DC circuit is calculated using the following formula:

[0015]

[0016] In the formula, This represents the impedance amplitude at 50Hz in the DC circuit. This represents the frequency response at a DC voltage of 50Hz. This is the frequency response of the DC current at 50Hz.

[0017] Furthermore, the threshold is set at 100 ohms.

[0018] Furthermore, time-domain simulation calculations are performed using a multi-terminal DC detailed electromagnetic transient simulation model, including:

[0019] Harmonic voltage sources are applied to the AC side of each end of the multi-terminal flexible DC transmission system to obtain the magnitude of the DC current component on the grid side of the flexible DC transformer at each end.

[0020] The magnitude of the DC current component on the grid side of each flexible DC transformer is obtained by geometric summation and calculation.

[0021] Furthermore, the magnitude of the DC bias current at each terminal is calculated according to the following formula:

[0022]

[0023] In the formula, I dcij Let i = 1, 2, ..., n, j = 1, 2, ..., n, where n is the number of ports in the multi-terminal flexible DC transmission system.

[0024] Furthermore, the resonant analysis model of the DC circuit of the converter in the flexible DC transmission system adopts a multi-valve group series structure.

[0025] Secondly, the present invention provides a device for calculating the DC bias current of a flexible DC transformer, comprising:

[0026] The model acquisition module is used to acquire the resonance analysis model of the DC circuit of the converter in the flexible DC transmission system; the resonance analysis model is constructed based on the physical structure of the DC circuit of the converter in the flexible DC transmission system.

[0027] The judgment module is used to obtain the impedance at 50Hz in the resonance analysis model through frequency scanning, and to determine whether the impedance at 50Hz is less than a set threshold. The set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC transformer.

[0028] The calculation module is used to perform time-domain simulation calculations using a multi-terminal DC detailed electromagnetic transient simulation model when the impedance is less than a set threshold at 50Hz, to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of a multi-terminal flexible DC transmission system.

[0029] Thirdly, the present invention provides a computer device, the device including a processor and a memory:

[0030] The memory is used to store computer programs and send the instructions of the computer programs to the processor;

[0031] The processor executes, according to the instructions of the computer program, a method for calculating the DC bias current of a flexible DC transformer, as described in the first aspect.

[0032] Fourthly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements a method for calculating the DC bias current of a flexible DC transformer as described in the first aspect.

[0033] In summary, this invention provides a method and related apparatus for calculating the DC bias current of a flexible DC transmission transformer. The method includes obtaining a resonance analysis model of the DC circuit of a flexible DC transmission system converter. This model is constructed based on the physical structure of the DC circuit of the converter. The impedance at 50Hz in the resonance analysis model is obtained through frequency scanning, and it is determined whether the impedance at 50Hz is less than a set threshold. The set threshold is determined based on the impedance value when the DC bias current becomes too large due to excessively low impedance, leading to saturation of the flexible DC transmission transformer. If so, a time-domain simulation calculation is performed using a multi-terminal detailed electromagnetic transient simulation model to obtain the DC bias current of the flexible DC transmission transformer. The multi-terminal detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of a multi-terminal flexible DC transmission system. This invention effectively assesses the DC bias risk of flexible DC transmission transformers by constructing a DC circuit resonance analysis model to determine the impedance at 50Hz and then using an electromagnetic transient simulation model to calculate the DC bias current. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart illustrating a method for calculating the DC bias current of a flexible DC transformer, provided as an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the DC circuit resonance analysis model of the converter in a flexible DC transmission system provided in an embodiment of the present invention.

[0037] Figure 3 A block diagram of a DC bias current calculation device for a flexible DC transformer provided in an embodiment of the present invention;

[0038] Figure 4 This is a block diagram of a computer device provided in an embodiment of the present invention. Detailed Implementation

[0039] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] Please see Figure 1 This invention provides a method for calculating the DC bias current of a flexible DC transformer, comprising the following steps:

[0041] S1: Obtain the resonance analysis model of the DC circuit of the converter in the flexible DC transmission system; the resonance analysis model is constructed based on the physical structure of the DC circuit of the converter in the flexible DC transmission system.

[0042] It should be noted that the DC circuit of a flexible DC transmission system converter typically consists of components such as inductors and capacitors. Inductors may originate from bridge arm reactors, and capacitors may come from flexible DC module capacitors, etc. The resonance analysis model is a circuit model constructed according to the actual connection method of these components, used to analyze the electrical characteristics of the DC circuit.

[0043] This step involves representing the inductors, capacitors, and other components in the DC circuit of the flexible DC transmission system converter using corresponding circuit models, thereby constructing a resonance analysis model. For example, if the DC circuit contains bridge arm reactors (inductors) and flexible DC module capacitors, the corresponding inductor and capacitor components are placed in the model according to their actual series or parallel connections.

[0044] S2: Obtain the impedance at 50Hz in the resonance analysis model by frequency scanning, and determine whether the impedance at 50Hz is less than the set threshold; the set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC.

[0045] It should be noted that the impedance at 50Hz is the circuit impedance obtained at a specific frequency of 50Hz when the DC circuit is frequency-scanned. It reflects the impedance characteristic of the DC circuit to current at a frequency of 50Hz.

[0046] This step involves frequency scanning of the resonance analysis model to obtain the impedance at 50Hz. The magnitude of the impedance at this frequency is closely related to whether the DC bias current will be too large. The threshold value is set based on past experience or theoretical calculations. When the impedance is less than this threshold, the DC bias current may become too large, leading to saturation of the flexible DC transformer.

[0047] S3: If so, then time-domain simulation calculations are performed using the multi-terminal DC detailed electromagnetic transient simulation model to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of the multi-terminal flexible DC transmission system.

[0048] It should be noted that the multi-terminal DC detailed electromagnetic transient simulation model is a model used to simulate the electromagnetic transient processes of multi-terminal flexible DC transmission systems. Electromagnetic transient processes refer to the rapid changes in voltage and current within a short period of time in a power system caused by switching operations, faults, etc. This model can accurately simulate the electrical behavior of various components in a multi-terminal system during these transient processes.

[0049] When it is determined that the impedance at 50Hz is less than the set threshold, indicating a risk of DC bias, this step utilizes a multi-terminal DC detailed electromagnetic transient simulation model for time-domain simulation calculations. In this model, by applying a harmonic voltage source of a specific frequency (e.g., 100Hz) to the AC side, the DC current components of the flexible DC transformer grid side at each terminal are obtained, and then the final DC bias current is obtained through geometric and other calculation methods.

[0050] This embodiment provides a method for calculating the DC bias current of a flexible DC transmission transformer. First, a resonance analysis model is constructed based on the physical structure of the DC circuit of the flexible DC transmission system. Then, the impedance at 50Hz is obtained by frequency scanning of this model, and the magnitude of the impedance is used to determine whether there is a risk of DC bias. If a risk exists, a detailed time-domain simulation calculation is performed using a multi-terminal DC detailed electromagnetic transient simulation model to finally obtain the DC bias current of the flexible DC transmission transformer. This method, by constructing a DC circuit resonance analysis model and obtaining the impedance at 50Hz, can predict the risk of excessive DC bias current leading to saturation of the flexible DC transmission transformer at an early stage, avoiding unnecessary complex calculations. After determining the existence of a risk, the time-domain simulation calculation using a multi-terminal DC detailed electromagnetic transient simulation model can accurately obtain the DC bias current of the flexible DC transmission transformer, providing reliable data support for the design, operation, and protection of flexible DC transmission systems.

[0051] In one embodiment, the DC loop resonance analysis model of the converter in a flexible DC transmission system is composed of an inductor and a capacitor connected in series. Here, the inductor L represents the bridge arm reactor, and the capacitor C represents the flexible DC module capacitor.

[0052] Generally, flexible DC transmission systems consist of multiple valve groups connected in series. If there are m valve groups connected in series, then there are m inductors and m capacitors connected in series. Simultaneously, if a smoothing reactor is configured in the flexible DC transmission system, then the reactor L... p Connect them in series to the corresponding positions to form a resonant analysis model of the DC circuit of the flexible DC converter.

[0053] DC transmission lines can be overhead lines or cables, and the analysis process is the same as for traditional DC transmission, using a frequency-dependent (Phase) model. Combined with the flexible DC converter model, a DC loop resonance analysis model for the flexible DC transmission system can be established. For multi-terminal flexible DC transmission systems, a corresponding model can be established based on the series and parallel connections of the converter stations. The DC loop resonance analysis model for a flexible DC transmission system is as follows: Figure 2 As shown.

[0054] In one embodiment, obtaining the impedance at 50Hz in the resonance analysis model by frequency scanning includes:

[0055] S21: A unit impulse voltage source is connected in series in the DC circuit of the converter of the flexible DC transmission system simulated by the resonance analysis model.

[0056] It should be noted that a unit impulse voltage source is connected in series in the DC circuit represented by the resonance analysis model. When this voltage source generates a momentary pulse, it will trigger a series of electromagnetic transient processes in the circuit, causing current to flow in the circuit.

[0057] S22: Obtain the current response of the DC circuit of the converter in the flexible DC transmission system, and perform Fourier calculations on the voltage and current of the voltage source to obtain the frequency response of the DC voltage and DC current at 50Hz.

[0058] It should be noted that, firstly, the current response of the DC circuit of the flexible DC transmission system converter under unit impulse voltage source excitation is obtained. Then, Fourier calculations are used to analyze the voltage source voltage and circuit current. Through this process, the DC voltage and DC current frequency responses at 50Hz can be selected. These responses contain information such as the amplitude and phase of the voltage and current at the 50Hz frequency.

[0059] S23: Calculate the impedance amplitude of the DC circuit at 50Hz based on the frequency response of the DC voltage and DC current at 50Hz.

[0060] It should be noted that, according to circuit theory, impedance is equal to the ratio of voltage to current. In the frequency domain, the impedance amplitude of a DC circuit at 50Hz can be calculated using the frequency response (amplitude) of the DC voltage and DC current at 50Hz.

[0061] In a further embodiment, the impedance amplitude at 50Hz in the DC circuit is calculated according to the following formula:

[0062]

[0063] In the formula, This represents the impedance amplitude at 50Hz in the DC circuit. This represents the frequency response at a DC voltage of 50Hz. This is the frequency response of the DC current at 50Hz.

[0064] In one embodiment, the threshold is set to 100 ohms. That is, if Z... HVDCmag (50) If it is greater than 100Ω, it indicates that the impedance of the DC circuit at 50Hz is relatively large, and the possibility of the flexible DC circuit saturating due to excessive DC bias current is low, so further detailed calculations are not necessary. If Z HVDCmag (50) If it is less than 100Ω, it indicates that the impedance of the DC circuit at 50Hz is small, and the DC bias current may be too large, which may cause the DC circuit to saturate. Further detailed calculations are needed.

[0065] In one embodiment, time-domain simulation calculations are performed using a multi-terminal DC detailed electromagnetic transient simulation model, including:

[0066] S31: Apply harmonic voltage sources to the AC side of each end of the multi-terminal flexible DC transmission system to obtain the magnitude of the DC current component on the grid side of each flexible DC transformer.

[0067] Harmonic voltage sources (e.g., 100Hz harmonic voltage sources) are applied to the AC side of each terminal in a multi-terminal flexible DC transmission system. Applying these voltage sources induces electromagnetic transient processes in the system, causing changes in the current on the grid side of each terminal's flexible DC transformer, including a DC current component. By simulating and monitoring this process using a detailed electromagnetic transient simulation model of the multi-terminal DC system, the magnitude of the DC current component on the grid side of each terminal can be accurately obtained. For example, when a 100Hz harmonic source is applied to terminal 1, the DC components at each terminal are I0, ... dc11 , I dc12 , … , I dc1n Therefore, it can be obtained that after applying harmonic sources to each terminal, the DC components at each terminal are I... dc11 , I dc12 , … , I dc1n ;I dc21 , I dc22 , … , I dc2n ;……;I dcn1 , I dcn2 , … , I dcnn .

[0068] S32: Perform geometric summation and calculation on the DC current components of the grid side of each flexible DC transformer to obtain the magnitude of the DC bias current at each end.

[0069] The magnitudes of the DC current components on the grid side of each flexible DC transformer obtained in step S31 are geometrically calculated to obtain the magnitudes of the DC bias current at each end.

[0070] In a further embodiment, the magnitude of the DC bias current at each terminal is calculated according to the following formula:

[0071]

[0072] In the formula, I dcij Let i = 1, 2, ..., n, j = 1, 2, ..., n, where n is the number of ports in the multi-terminal flexible DC transmission system.

[0073] This embodiment provides a method for calculating the DC bias current of a flexible DC transmission transformer in a flexible DC transmission system. It clarifies whether detailed calculation of the DC bias current is necessary by using an impedance criterion at 50Hz in the DC circuit, and then calculates the magnitude of the DC bias current in detail using electromagnetic transient simulation and geometric summation methods. This method can be applied to the planning and design of flexible DC transmission systems, allowing for early prediction of the DC bias current of the transformer. If the current is too large, suppression measures need to be added to ensure the safe and stable operation of the system and equipment.

[0074] Based on the same inventive concept, this application also provides a flexible DC transformer DC bias current calculation device for implementing the aforementioned method for calculating the DC bias current of a flexible DC transformer. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in the embodiments of the flexible DC transformer DC bias current calculation device provided below can be found in the limitations of the flexible DC transformer DC bias current calculation method described above, and will not be repeated here.

[0075] Please see Figure 3 This invention also provides a device for calculating the DC bias current of a flexible DC transformer, comprising:

[0076] The model acquisition module is used to acquire the resonance analysis model of the DC circuit of the converter in the flexible DC transmission system; the resonance analysis model is constructed based on the physical structure of the DC circuit of the converter in the flexible DC transmission system.

[0077] The judgment module is used to obtain the impedance at 50Hz in the resonance analysis model through frequency scanning, and to determine whether the impedance at 50Hz is less than a set threshold. The set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC transformer.

[0078] The calculation module is used to perform time-domain simulation calculations using a multi-terminal DC detailed electromagnetic transient simulation model when the impedance is less than a set threshold at 50Hz, to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of a multi-terminal flexible DC transmission system.

[0079] Furthermore, the impedance at 50Hz in the resonance analysis model is obtained through frequency scanning, including:

[0080] A unit impulse voltage source is connected in series in the DC circuit of the converter of the flexible DC transmission system simulated by the resonance analysis model;

[0081] The current response of the DC circuit of the converter of the flexible DC transmission system is obtained, and Fourier calculations are performed on the voltage and current of the voltage source to obtain the frequency response of DC voltage and DC current at 50Hz.

[0082] The impedance amplitude of the DC circuit at 50Hz is calculated based on the frequency response of the DC voltage and DC current at 50Hz.

[0083] Furthermore, the impedance amplitude at 50Hz in the DC circuit is calculated using the following formula:

[0084]

[0085] In the formula, This represents the impedance amplitude at 50Hz in the DC circuit. This represents the frequency response at a DC voltage of 50Hz. This is the frequency response of the DC current at 50Hz.

[0086] Furthermore, the threshold is set at 100 ohms.

[0087] Furthermore, time-domain simulation calculations are performed using a multi-terminal DC detailed electromagnetic transient simulation model, including:

[0088] Harmonic voltage sources are applied to the AC side of each end of the multi-terminal flexible DC transmission system to obtain the magnitude of the DC current component on the grid side of the flexible DC transformer at each end.

[0089] The magnitude of the DC current component on the grid side of each flexible DC transformer is obtained by geometric summation and calculation.

[0090] Furthermore, the magnitude of the DC bias current at each terminal is calculated according to the following formula:

[0091]

[0092] In the formula, I dcij Let i be the DC component of the i-th port when a harmonic voltage source is applied to the j-th port in a multi-terminal flexible DC transmission system, where i = 1, 2, ..., n, and n is the number of ports in the multi-terminal flexible DC transmission system.

[0093] Furthermore, the resonant analysis model of the DC circuit of the converter in the flexible DC transmission system adopts a multi-valve group series structure.

[0094] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments 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. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0095] Reference Figure 4 The present invention also provides a computer device, including: a memory and a processor, and a computer program stored in the memory, wherein when the computer program is executed on the processor, it implements the method for calculating the DC bias current of a flexible DC transformer as described in any of the above methods.

[0096] The computer device may be a desktop computer, laptop, handheld computer, or cloud server, etc. This computer device may include, but is not limited to, a processor and memory. Those skilled in the art will understand that... Figure 4 The examples of computer devices are merely examples and do not constitute a limitation on computer devices. They may include more or fewer components than shown in the illustration, or combinations of certain components, or different components. For example, they may also include input / output devices, network access devices, etc.

[0097] The processor referred to can be a Central Processing Unit (CPU), but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0098] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard drive or RAM. In other embodiments, the memory may be an external storage device of the computer device, such as a plug-in hard drive, Smart Media Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, the memory may include both internal and external storage units of the computer device. The memory is used to store the operating system, applications, bootloader, data, and other programs, such as the program code of the computer program. The memory can also be used to temporarily store data that has been output or will be output.

[0099] This invention also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the method for calculating the DC bias current of a flexible DC transformer as described in any of the above methods.

[0100] In this embodiment, 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, all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include at least: any entity or device capable of carrying computer program code to a photographing device / terminal device, a recording medium, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium. Examples include USB flash drives, portable hard drives, magnetic disks, or optical disks. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electrical carrier signals or telecommunication signals.

[0101] This invention provides a computer program product, including a computer program that, when executed by a processor, implements the method for calculating the DC bias current of a flexible DC transformer as described in any of the above methods.

[0102] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0103] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0104] In the embodiments disclosed in this application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are merely illustrative. For instance, the division of modules or 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 displayed or discussed mutual coupling or direct coupling or communication connection may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention 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 the present invention.

Claims

1. A method for calculating the DC bias current of a flexible DC transformer, characterized in that, Includes the following steps: A resonance analysis model of the DC circuit of the converter in a flexible DC transmission system is obtained; wherein, the inductor and capacitor elements in the DC circuit of the converter in the flexible DC transmission system are represented by the corresponding circuit models, and then the resonance analysis model is constructed. The impedance at 50Hz in the resonance analysis model is obtained by frequency scanning, and it is determined whether the impedance at 50Hz is less than a set threshold. The set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC circuit. If so, time-domain simulation calculations are performed using a multi-terminal DC detailed electromagnetic transient simulation model to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of a multi-terminal flexible DC transmission system. The impedance at 50Hz in the resonance analysis model is obtained by frequency scanning, including: A unit impulse voltage source is connected in series in the DC circuit of the converter of the flexible DC transmission system simulated by the resonance analysis model. The current response of the DC circuit of the converter of the flexible DC transmission system is obtained, and Fourier calculation is performed on the voltage and current of the voltage source to obtain the frequency response of DC voltage and DC current at 50Hz. The impedance amplitude of the DC circuit at 50Hz is calculated based on the frequency response of the DC voltage and DC current at 50Hz. The impedance amplitude at 50Hz in the DC circuit is calculated according to the following formula: ； In the formula, This refers to the impedance amplitude at 50Hz in the DC circuit. This represents the frequency response at a DC voltage of 50Hz. The frequency response of DC current at 50Hz; Time-domain simulation calculations were performed using a multi-terminal DC detailed electromagnetic transient simulation model, including: Harmonic voltage sources are applied to the AC side of each end of the multi-terminal flexible DC transmission system to obtain the magnitude of the DC current component on the grid side of the flexible DC transformer at each end. The magnitudes of the DC current components on the grid side of the flexible DC transformer at each end are geometrically summed and calculated to obtain the magnitudes of the DC bias current at each end. The magnitude of the DC bias current at each terminal is calculated according to the following formula: ； In the formula, I dcij The DC component of the i-th port when a harmonic voltage source is applied to the j-th port in the multi-terminal flexible DC transmission system, i=1,2,…,n, j=1,2,…,n, where n is the number of ports in the multi-terminal flexible DC transmission system.

2. The method for calculating the DC bias current of a flexible DC transformer according to claim 1, characterized in that, The set threshold is 100 ohms.

3. The method for calculating the DC bias current of a flexible DC transformer according to claim 1, characterized in that, The resonant analysis model of the DC circuit of the converter in the flexible DC transmission system adopts a multi-valve group series structure.

4. A device for calculating the DC bias current of a flexible DC transformer, characterized in that, include: The model acquisition module is used to acquire the resonance analysis model of the DC circuit of the converter of the flexible DC transmission system; wherein, the inductor and capacitor elements in the DC circuit of the converter of the flexible DC transmission system are represented by the corresponding circuit models, and then the resonance analysis model is constructed. The judgment module is used to obtain the impedance at 50Hz in the resonance analysis model through frequency scanning, and to determine whether the impedance at 50Hz is less than a set threshold; the set threshold is determined based on the impedance value when the DC bias current is too large due to the impedance being too small, resulting in the saturation of the flexible DC transformer. The calculation module is used to perform time-domain simulation calculations using a multi-terminal DC detailed electromagnetic transient simulation model when the impedance is less than a set threshold at 50Hz, to obtain the DC bias current of the flexible DC transformer; the multi-terminal DC detailed electromagnetic transient simulation model is used to simulate the electromagnetic transient process of the multi-terminal flexible DC transmission system. The impedance at 50Hz in the resonance analysis model is obtained by frequency scanning, including: A unit impulse voltage source is connected in series in the DC circuit of the converter of the flexible DC transmission system simulated by the resonance analysis model. The current response of the DC circuit of the converter of the flexible DC transmission system is obtained, and Fourier calculation is performed on the voltage and current of the voltage source to obtain the frequency response of DC voltage and DC current at 50Hz. The impedance amplitude of the DC circuit at 50Hz is calculated based on the frequency response of the DC voltage and DC current at 50Hz. The impedance amplitude at 50Hz in the DC circuit is calculated according to the following formula: ； In the formula, This refers to the impedance amplitude at 50Hz in the DC circuit. This represents the frequency response at a DC voltage of 50Hz. The frequency response of DC current at 50Hz; Time-domain simulation calculations were performed using a multi-terminal DC detailed electromagnetic transient simulation model, including: Harmonic voltage sources are applied to the AC side of each end of the multi-terminal flexible DC transmission system to obtain the magnitude of the DC current component on the grid side of the flexible DC transformer at each end. The magnitudes of the DC current components on the grid side of the flexible DC transformer at each end are geometrically summed and calculated to obtain the magnitudes of the DC bias current at each end. The magnitude of the DC bias current at each terminal is calculated according to the following formula: ； In the formula, I dcij The DC component of the i-th port when a harmonic voltage source is applied to the j-th port in the multi-terminal flexible DC transmission system, i=1,2,…,n, j=1,2,…,n, where n is the number of ports in the multi-terminal flexible DC transmission system.

5. A computer device, characterized in that, The device includes a processor and a memory: The memory is used to store computer programs and send the instructions of the computer programs to the processor; The processor executes a method for calculating the DC bias current of a flexible DC transformer according to the instructions of the computer program as described in any one of claims 1-3.

6. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, which, when executed by a processor, implements a method for calculating the DC bias current of a flexible DC transformer as described in any one of claims 1-3.

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