A method and device for eliminating harmonics of a modular multilevel converter high-voltage direct current transmission

Abstract

This application provides a harmonic elimination method and apparatus for modular multilevel converter high-voltage direct current (HVDC) transmission, comprising: constructing a current and voltage measurement matrix based on the topology and electrical parameters of an electromagnetic current transformer, its secondary system, an electromagnetic voltage transformer, and its secondary system in the HVDC transmission system; constructing an HVDC transmission impedance model including current and voltage measurement components based on the main circuit topology of the HVDC transmission system and the current and voltage measurement matrix; analyzing the HVDC transmission impedance model under preset operating conditions to obtain the impedance matrix of the current and voltage measurement components; and determining the resonant frequency of the HVDC transmission using the impedance matrix of the current and voltage measurement components to perform harmonic elimination. This application can analyze the mismatch effects caused by the measurement components of the current transformer (CT) and its secondary system, and the current transformer (PT) and its secondary system, respectively, determine the system resonant frequency, and eliminate the resonance effect.

Description

Technical Field

[0001] This application relates to the field of high voltage direct current transmission, specifically a harmonic elimination method and apparatus for modular multilevel converter high voltage direct current transmission. Background Technology

[0002] Modular multi-level converter-high-voltage direct current (MMC-HVDC) transmission has unique advantages over other power transmission technologies and is widely used in inter-regional power transmission, offshore wind farm grid connection, and urban power grid upgrades. However, this technology faces many problems and challenges in practical applications, among which high-frequency resonance issues occur frequently and have become a key factor affecting the stable operation of the system, urgently requiring a solution.

[0003] The resonance problem of MMC-HVDC poses a serious threat to the system and is influenced by numerous complex factors, making its research extremely challenging. Research methods generally fall into two categories: state-space methods and impedance analysis. MMC-HVDCs contain numerous power electronic components, and their complex topology makes state-space modeling difficult, thus impedance analysis is more advantageous. However, many studies have not considered the interaction between the electromagnetic current transformer (CT) and its secondary system measurement components, the electromagnetic voltage transformer (PT) and its secondary system measurement components, and the MMC-HVDC. Due to the influence of the electromagnetic transformer and its secondary system measurement components, the actual signal received by the MMC-HVDC deviates from the ideal signal. This non-ideal measurement characteristic leads to a mismatch between the control system's reference signal and the actual operating conditions, resulting in a mismatch effect. As the system capacity continues to increase, the risk of resonance increases. Specifically, when the system is under light load or no-load conditions, the current amplitude is small, requiring high accuracy in the measurement components, which is often insufficient, leading to a significant increase in measurement deviation. This deviation, amplified by the closed-loop system, directly affects the accuracy of the control signal, thus triggering system resonance. When the system operates under heavy load, the current amplitude is large, the inherent accuracy of the measurement components is high, and the measurement deviation is relatively small; at the same time, the system's sensitivity to measurement accuracy decreases, and its tolerance to deviation increases accordingly. Therefore, under light load or no-load conditions, the accuracy characteristics of the electromagnetic current transformer (CT), electromagnetic voltage transformer (PT), and their secondary circuit measurement components directly affect the accuracy of system impedance modeling and are a crucial factor that cannot be ignored in resonance analysis.

[0004] This section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0005] To address the problems in the prior art, this application provides a harmonic elimination method and apparatus for modular multilevel converter high-voltage direct current transmission, which can analyze the mismatch effect caused by the measurement links of the CT and its secondary system, and the measurement links of the PT and its secondary system, determine the system resonant frequency, and eliminate the resonance effect.

[0006] To solve the above-mentioned technical problems, this application provides the following technical solution: In a first aspect, this application provides a harmonic suppression method for high-voltage direct current transmission using a modular multilevel converter, including: A current and voltage measurement matrix is ​​constructed based on the topology and electrical parameters of electromagnetic current transformers, current transformer secondary systems, electromagnetic voltage transformers, and voltage transformer secondary systems in high-voltage direct current transmission systems. Based on the main circuit topology of the high-voltage direct current transmission system and the current and voltage measurement matrix, a high-voltage direct current transmission impedance model considering the current and voltage measurement link is constructed. The impedance model of the high-voltage direct current transmission line is analyzed under the preset operating conditions to obtain the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links. The resonant frequency of high-voltage direct current transmission is determined by using the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, so as to perform harmonic elimination operation.

[0007] Further, the current and voltage measurement matrix includes a current measurement link matrix; the electrical parameters include the input current and output current of the electromagnetic current transformer and the current transformer secondary system measurement link; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: The input and output currents of the electromagnetic current transformer and its secondary system are measured. dq Coordinate transformation yields the input current. dq Components and output current dq Quantity; According to the input current dq Components and output current dq The components generate the current measurement element matrix.

[0008] Further, the current and voltage measurement matrix includes a voltage measurement link matrix; the electrical parameters include the input and output voltages of the electromagnetic voltage transformer and the voltage transformer secondary system measurement links; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: The input and output voltages of the electromagnetic voltage transformer and its secondary system are measured. dq Coordinate transformation yields the input voltage. dq Components and output voltage dq Quantity; According to the input voltage dq Components and output voltage dq The components generate the voltage measurement link matrix.

[0009] Furthermore, the construction of the HVDC transmission impedance model considering the current and voltage measurement links based on the main circuit topology of the HVDC transmission system and the current and voltage measurement matrix includes: A mathematical model for light no-load conditions is generated based on the main circuit topology. The current and voltage measurement matrix is ​​input into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model.

[0010] Furthermore, the step of generating a mathematical model under light no-load conditions based on the main circuit topology includes: Based on the input voltage dq Component determination of the three-phase AC current on the modular multilevel converter station dq Quantity; Based on the input voltage dq In the components d Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. d Axial components; Based on the input voltage dq In the components q Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. q Axial components; Based on the output voltage of the modular multilevel converter d Shaft component, output voltage of the modular multilevel converter q Shaft components and the three-phase AC current of the modular multilevel converter station dq The mathematical model under the light unloaded condition is constructed using components.

[0011] Furthermore, the high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the step of inputting the current and voltage measurement matrix into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model includes: The first virtual impedance is determined based on the proportional-integral control coefficient of the inner current loop, the delay coefficient generated by the control loop, the output current, and the matrix of the current measurement link. The second virtual impedance is determined based on the fundamental frequency angular velocity, transformer leakage inductance, output current, and current measurement array matrix. Based on the output current, the input voltage, the current measurement matrix, and the voltage measurement matrix, the third virtual impedance and the fourth virtual impedance are obtained. The system impedance matrix and the system gain matrix are constructed based on the first virtual impedance, the second virtual impedance, the third virtual impedance, the fourth virtual impedance, the current measurement link matrix, the voltage measurement link matrix, the voltage outer loop proportional-integral control coefficient, the current inner loop proportional-integral control coefficient, the compensation pair coefficient of the voltage feedforward link, and the delay coefficient generated by the control loop.

[0012] Furthermore, the HVDC transmission impedance model includes a system impedance matrix and a system gain matrix; analyzing the HVDC transmission impedance model under preset operating conditions yields impedance matrices considering current and voltage measurement stages, impedance matrices considering only current measurement stages, impedance matrices considering only voltage measurement stages, and impedance matrices not considering current and voltage measurement stages, including: By setting the current measurement element matrix and the voltage measurement element matrix in the system impedance matrix to identity matrices, the impedance matrix without considering the measurement elements is obtained. By setting the voltage measurement element matrix in the system impedance matrix to an identity matrix, an impedance matrix considering only the current measurement element is obtained. By setting the current measurement element matrix in the system impedance matrix to an identity matrix, an impedance matrix considering only the voltage measurement element is obtained. The impedance matrix considering the current and voltage measurement links is obtained based on the system impedance matrix, the system gain matrix, the current measurement link matrix, and the voltage measurement link matrix.

[0013] Furthermore, the step of determining the resonant frequency of the high-voltage direct current transmission using the impedance matrix considering the current and voltage measurement stages, the impedance matrix considering only the current measurement stages, the impedance matrix considering only the voltage measurement stages, and the impedance matrix not considering the current and voltage measurement stages, in order to perform harmonic cancellation operation, includes: By analyzing the main diagonal elements of the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, the positive sequence impedance relationship is obtained. The resonant frequency is determined using the positive sequence impedance relationship. The harmonic cancellation operation is performed at the resonant frequency using an active or passive filter.

[0014] Secondly, this application provides a harmonic suppression device for modular multilevel converter high-voltage direct current transmission, comprising: The measurement matrix construction unit is used to construct current and voltage measurement matrices based on the topology and electrical parameters of electromagnetic current transformers, current transformer secondary systems, electromagnetic voltage transformers, and voltage transformer secondary systems in high-voltage direct current transmission systems. Impedance model generation unit is used to construct an impedance model of the high voltage direct current transmission system that considers the current and voltage measurement links based on the main circuit topology of the high voltage direct current transmission system and the current and voltage measurement matrix. The impedance matrix analysis unit is used to analyze the impedance model of the high voltage direct current transmission under preset operating conditions, and obtain the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links. The resonant frequency determination unit is used to determine the resonant frequency of the high-voltage direct current transmission using the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, so as to perform harmonic cancellation operation.

[0015] Furthermore, the current and voltage measurement matrix includes a current measurement link matrix; the electrical parameters include the input current and output current of the electromagnetic current transformer and the current transformer secondary system measurement link; the measurement matrix construction unit includes: The current component calculation module is used to calculate the input and output currents of the electromagnetic current transformer and the measurement stage of the current transformer secondary system. dq Coordinate transformation yields the input current. dq Components and output current dq Quantity; A current matrix generation module is used to generate a current matrix based on the input current. dq Components and output current dq The components generate the current measurement element matrix.

[0016] Furthermore, the current and voltage measurement matrix includes a voltage measurement link matrix; the electrical parameters include the input and output voltages of the electromagnetic voltage transformer and the voltage transformer secondary system measurement link; the measurement matrix construction unit includes: The voltage component calculation module is used to calculate the input and output voltages of the electromagnetic voltage transformer and its secondary system measurement components. dq Coordinate transformation yields the input voltage. dq Components and output voltage dq Quantity; The voltage matrix generation module is used to generate a voltage matrix based on the input voltage. dq Components and output voltage dq The components generate the voltage measurement link matrix.

[0017] Furthermore, the impedance model generation unit includes: The light-load operating condition model generation module is used to generate a mathematical model under light-load operating conditions based on the main circuit topology. The impedance model generation module is used to input the current and voltage measurement matrix into the mathematical model under the light no-load condition to obtain the high-voltage direct current transmission impedance model.

[0018] Furthermore, the working condition model generation module includes: dq The component determination module is used to determine the input voltage. dq Component determination of the three-phase AC current on the modular multilevel converter station dq Quantity; d The axis component determination module is used to determine the input voltage. dq In the components d Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. d Axial components; q The axis component determination module is used to determine the input voltage. dq In the components q Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. q Axial components; The light-air model generation module is used to generate a model based on the output voltage of the modular multilevel converter. d Shaft component, output voltage of the modular multilevel converter q Shaft components and the three-phase AC current of the modular multilevel converter station dq The mathematical model under the light unloaded condition is constructed using components.

[0019] Furthermore, the high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the impedance model generation module includes: The first impedance determination module is used to determine the first virtual impedance based on the proportional-integral control coefficient of the current inner loop, the delay coefficient generated by the control loop, the output current, and the current measurement link matrix. The second impedance determination module is used to determine the second virtual impedance based on the fundamental frequency angular velocity, transformer leakage inductance, the output current and the current measurement link matrix. The three- and four-impedance determination module is used to obtain the third virtual impedance and the fourth virtual impedance based on the output current, the input voltage, the current measurement link matrix, and the voltage measurement link matrix. The impedance-gain matrix generation module is used to construct the system impedance matrix and the system gain matrix based on the first virtual impedance, the second virtual impedance, the third virtual impedance, the fourth virtual impedance, the current measurement link matrix, the voltage measurement link matrix, the voltage outer loop proportional-integral control coefficient, the current inner loop proportional-integral control coefficient, the compensation pair coefficient of the voltage feedforward link, and the delay coefficient generated by the control loop.

[0020] Furthermore, the high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the resonant frequency determination unit includes: The first matrix generation module is used to set the current measurement link matrix and the voltage measurement link matrix in the system impedance matrix as identity matrices to obtain the impedance matrix without considering the measurement links. The second matrix generation module is used to set the voltage measurement link matrix in the system impedance matrix as an identity matrix to obtain an impedance matrix that only considers the current measurement link. The third matrix generation module is used to set the current measurement link matrix in the system impedance matrix as an identity matrix to obtain an impedance matrix that only considers the voltage measurement link. The fourth matrix generation module is used to obtain the impedance matrix considering the current and voltage measurement links based on the system impedance matrix, the system gain matrix, the current measurement link matrix, and the voltage measurement link matrix.

[0021] Furthermore, the resonant frequency determination unit includes: The positive sequence relationship determination module is used to analyze the main diagonal elements of the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, respectively, to obtain the positive sequence impedance relationship. A resonant frequency determination module is used to determine the resonant frequency using the positive sequence impedance relationship; The harmonic cancellation operation execution module is used to perform harmonic cancellation operation at the resonant frequency using an active filter or a passive filter.

[0022] Thirdly, this application provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the harmonic elimination method for high-voltage direct current transmission of the modular multilevel converter.

[0023] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the harmonic elimination method for the modular multilevel converter high-voltage direct current transmission.

[0024] Fifthly, this application provides a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the harmonic suppression method for the modular multilevel converter high-voltage direct current transmission.

[0025] To address the problems in existing technologies, this application provides a method and apparatus for harmonic suppression in modular multilevel converter high-voltage direct current transmission. This method can accurately characterize the characteristics of the electromagnetic transformer measurement circuit by establishing a π-type equivalent circuit model, construct an impedance model of the MMC-HVDC islanded system including the CT, PT, and their secondary system measurement circuits, and perform stability analysis. It provides mathematical relationships for the impedance matrix under four different operating conditions and mathematical relationships for the resonant frequencies under three operating conditions including the measurement circuits. It also determines the high-frequency resonant frequencies of the MMC-HVDC islanded system excited by the CT, PT, and their secondary system measurement circuits, providing a technical basis for subsequent control and parameter optimization to suppress resonance induced by the measurement circuits. Attached Figure Description

[0026] 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.

[0027] Figure 1 This is a flowchart of the harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter in the embodiments of this application; Figure 2 This is one of the flowcharts for constructing the current and voltage measurement matrix in the embodiments of this application; Figure 3 This is the second flowchart of the process for constructing the current and voltage measurement matrix in the embodiments of this application; Figure 4 This is one of the flowcharts for constructing the high-voltage direct current transmission impedance model in the embodiments of this application; Figure 5 This is a flowchart of generating a mathematical model under light unloaded conditions in the embodiments of this application; Figure 6 This is the second flowchart of the high-voltage direct current transmission impedance model obtained in the embodiments of this application; Figure 7 This is a flowchart illustrating the process of obtaining the impedance matrix in an embodiment of this application; Figure 8 This is a flowchart illustrating the determination of the resonant frequency for high-voltage direct current transmission in an embodiment of this application; Figure 9 This is a structural diagram of the harmonic suppression device for high-voltage direct current transmission using a modular multilevel converter, as described in this application embodiment. Figure 10 This is a structural diagram of the measurement matrix construction unit in an embodiment of this application; Figure 11 This is a structural diagram of the measurement matrix construction unit in an embodiment of this application; Figure 12 This is a structural diagram of the impedance model generation unit in an embodiment of this application; Figure 13 This is a structural diagram of the working condition model generation module in an embodiment of this application; Figure 14 This is a structural diagram of the impedance model generation module in an embodiment of this application; Figure 15 This is one of the structural diagrams of the resonant frequency determination unit in the embodiments of this application; Figure 16 This is the second structural diagram of the resonant frequency determination unit in the embodiments of this application; Figure 17 This is a schematic diagram of the structure of the electronic device in the embodiments of this application; Figure 18 This invention provides a π-type equivalent model of CT and its secondary system in a stationary coordinate system. Figure 19 This invention provides a π-type equivalent model of CT and its secondary system in the dq-axis coordinate system. Figure 20 This invention provides an equivalent model of PT and its quadratic system in a stationary coordinate system in the π-type form. Figure 21 The input and output voltages of the measurement element provided by this invention; Figure 22 The ratio of the amplitude error to the phase difference of the output voltage in cases with and without a secondary system is provided by the present invention. Figure 23The topology diagram of the MMC-HVDC main circuit and measurement system provided by this invention; Figure 24A This invention provides one method for modeling the d-axis impedance of an MMC-HVDC islanded system that considers two measurement stages. Figure 24B This invention provides the second method for modeling the d-axis impedance of an MMC-HVDC islanded system, considering two measurement stages. Figure 24C This invention provides the third method for modeling the d-axis impedance of an MMC-HVDC islanded system, considering two measurement stages. Figure 24D This invention provides the fourth method for modeling the d-axis impedance of an MMC-HVDC islanded system, considering two measurement stages. Figure 25 This invention provides a modeling of the q-axis impedance of an MMC-HVDC islanded system considering two measurement stages. Figure 26 The matrix form of the impedance model of the MMC-HVDC islanded system is considered in this invention when two measurement links are taken into account; Figure 27 For the present invention to consider two measurement stages, the MMC-HVDC system in positive and negative sequence and C s Bode plot; Figure 28 For the present invention to consider two measurement stages, the MMC-HVDC system in positive and negative sequence Bode plot; Figure 29 This invention does not consider the measurement process when the MMC-HVDC system is in positive or negative sequence. and C s Bode plot; Figure 30 This invention does not consider the measurement process when the MMC-HVDC system is in positive or negative sequence. Bode plot; Figure 31 This invention considers only the measurement stages of CT and its secondary systems when the MMC-HVDC system is in positive and negative order. and C s Bode plot; Figure 32 This invention considers only the measurement stages of the PT and its secondary system when the MMC-HVDC system is in positive and negative sequence. and C s Bode plot; Figure 33For the present invention, the voltage and current waveforms of MMC-HVDC are considered when considering two measurement stages; Figure 34 The present invention does not consider the two measurement stages when presenting the voltage and current waveforms of MMC-HVDC. Figure 35 This invention only considers the measurement stages of the CT and its secondary system when presenting the MMC-HVDC voltage and current waveforms. Figure 36 This invention only considers the measurement links of the PT and its secondary system when the MMC-HVDC voltage and current waveforms are shown. Figure 37 This is a waveform diagram of the voltage and current of a converter station during high-frequency resonance according to the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0029] The information collected in the technical solution of this application is information and data authorized by the user or fully authorized by all parties. The collection, storage, use, processing, transmission, provision, disclosure and application of the relevant data all comply with the relevant laws, regulations and standards of the relevant countries and regions, necessary confidentiality measures have been taken, and they do not violate public order and good morals. Corresponding operation portals are provided for users to choose to authorize or refuse.

[0030] Provide users with corresponding operation entry points, allowing them to choose to agree to or reject the automated decision results; if the user chooses to reject, the process will proceed to the expert decision-making process.

[0031] In one embodiment, see Figure 1 In order to analyze the mismatch effects caused by the measurement links of the CT and its secondary system, and the PT and its secondary system, determine the system resonant frequency, and eliminate the resonance effect, this application provides a harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter, including: S101: Construct a current and voltage measurement matrix based on the topology and electrical parameters of electromagnetic current transformers, current transformer secondary systems, electromagnetic voltage transformers, and voltage transformer secondary systems in high-voltage direct current transmission systems. S102: Construct a high-voltage direct current transmission impedance model considering the current and voltage measurement links based on the main circuit topology of the high-voltage direct current transmission system and the current and voltage measurement matrix. S103: Analyze the impedance model of the high voltage direct current transmission line under the preset operating conditions to obtain the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links. S104: The resonant frequency of the high-voltage direct current transmission is determined by using the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, so as to perform harmonic cancellation operation.

[0032] Understandably, with the widespread application of modular multilevel converter (MMC) HVDC transmission technology in inter-regional power grids and offshore wind power grid integration, its high-frequency resonance problem is becoming increasingly prominent. Existing technologies often focus on the impedance characteristics of the converter itself or the AC system, neglecting the non-ideal transmission characteristics of the current transformer (CT) and power PT (PT) and their secondary system measurement components. Due to the influence of electromagnetic transformers and their secondary system measurement components, the actual signal received by the MMC-HVDC deviates from the ideal signal. This non-ideal transmission characteristic leads to an incorrect match between the control system's reference signal and the actual operating conditions, resulting in a mismatch effect. As system capacity gradually increases, resonance may occur; therefore, the measurement components of the CT, PT, and their secondary systems cannot be ignored in system impedance modeling and analysis.

[0033] To further reveal the impact of the CT and its secondary system measurement components, and the PT and its secondary system measurement components on the MMC-HVDC system, this application employs impedance analysis to analyze the mismatch effect and resonant frequency of the CT and its secondary system measurement components, and the PT and its secondary system measurement components on the MMC-HVDC system.

[0034] First, a current and voltage measurement matrix is ​​constructed based on the topology and electrical parameters of the electromagnetic current transformer, the secondary system of the current transformer, the electromagnetic voltage transformer, and the secondary system of the voltage transformer in the HVDC transmission system. Then, an HVDC transmission impedance model including the current and voltage measurement components is constructed based on the main circuit topology of the HVDC transmission system and the current and voltage measurement matrix. Next, the HVDC transmission impedance model is analyzed under preset operating conditions to obtain the impedance matrix of the current and voltage measurement components. Finally, the resonant frequency of the HVDC transmission is determined using the impedance matrix of the current and voltage measurement components to perform harmonic cancellation.

[0035] Specifically, firstly, an equivalent model of the electromagnetic voltage / current transformer and its secondary system measurement components is constructed, and an MMC-HVDC impedance model with non-ideal measurement components is established. The mismatch effect of the CT and its secondary system measurement components, and the PT and its secondary system measurement components on the MMC-HVDC impedance characteristics is analyzed. Then, an impedance model of the MMC-HVDC system considering the electromagnetic voltage / current transformer and its secondary system measurement components is established, and stability analysis is performed. Next, the impedance matrix relationships are analyzed under four conditions: considering two measurement components simultaneously, considering only the CT and its secondary system measurement components, considering only the PT and its secondary system measurement components, and not considering any measurement components. The relationships between different resonant frequencies under the three conditions considering measurement components are clarified, as well as the similarities and differences between considering a single measurement component and considering two measurement components. Finally, electromagnetic transient simulation experiments and field tests are conducted to verify the accuracy and reliability of the constructed MMC-HVDC islanded converter station impedance model and the proposed impedance matrix and resonant frequency relationships.

[0036] In this embodiment, the step of analyzing the mismatch effect of the measurement links of the CT and its secondary system, and the PT and its secondary system on the impedance characteristics of the MMC-HVDC includes: using a π-type lumped equivalent circuit to equivalently represent the CT and its secondary system, and the PT and its secondary system, respectively, to obtain the transfer function matrix. G cable (s) and H cable (s). Electromagnetic transient simulation experiments and field tests were conducted on an MMC-HVDC islanded system under light no-load conditions. The input voltage amplitude of the measurement circuit was 400V, and the frequency was 1.5kHz. The relative errors and phase differences of the amplitudes of the input and output voltages of the measurement circuit were obtained at different frequency bands. It was found that the secondary system of the measurement circuit generated system measurement deviations, causing inaccurate measurements and resulting in a mismatch between the measurement accuracy and the actual operating conditions, i.e., a mismatch effect. The mismatch effect leads to a mismatch in amplitude and phase between the actual signal and the control signal, which may induce high-frequency resonance and seriously affect the normal operation of the system.

[0037] In this embodiment of the application, the step of establishing an impedance model of an MMC-HVDC system considering two measurement stages includes: establishing mathematical models of the MMC-HVDC main circuit and control system, and using Ohm's theorem, the superposition theorem, and Thevenin's theorem to establish the system's impedance model respectively. d Shaft impedance model and system q Axial impedance modeling is performed to obtain the matrix form of the MMC-HVDC impedance model, which includes two measurement elements.

[0038] In this embodiment of the application, the steps for establishing the relationship of the impedance matrix under four conditions—considering both measurement stages simultaneously, considering only the CT and its secondary system measurement stages, considering only the PT and its secondary system measurement stages, and not considering any measurement stages—include: Let the impedance matrix Z vi Impedance matrix of CT and its secondary system measurement components G cable =I, PT and their secondary system measurement link matrix H cable =I, thus obtaining the impedance matrix without considering the measurement components. Z Let the impedance matrix Z vi middle H cable =I, G cable Without changing, we obtain the impedance matrix considering only the CT and its secondary system measurement components. Z i Similarly, let the impedance matrix Z vi middle G cable =I, H cable If the impedance remains unchanged, we can obtain the impedance matrix considering only the PT and its secondary system measurement components. Z v When the PT and its secondary system measurement link matrix H cable When the elements on the main diagonal are equal and the elements on the secondary diagonal are opposite, it is found that its impedance matrix satisfies... This indicates that the superposition of the measurement components corresponds to the multiplication of their impedance matrices.

[0039] In this embodiment of the application, the steps for establishing the relationship between different resonant frequencies considering three cases in the measurement process include: The condition for resonance in an MMC-HVDC system is that the magnitudes of the system's positive-sequence impedance and the grid-side impedance are equal, as shown in formula (14): (14) in Z vi,p It is the positive sequence impedance when both the CT and its secondary system measurement components and the PT and its secondary system measurement components are considered. Z i,p This refers to the positive-sequence impedance considering only the CT and its secondary system measurement stages. Z v,p This is the positive sequence impedance considering only the PT and its secondary system measurement components. i The resonant frequency of the MMC-HVDC system when only considering the CT and its secondary system measurement components. v To determine the resonant frequency of the system when only the PT and its secondary system are considered in the measurement process, vi To account for the resonant frequency of the system when considering both measurement elements, C s For AC side parasitic capacitance, 0 represents the angular frequency at the fundamental frequency (50Hz). The measurement stage is the cause of resonance or instability in the system, and resonance often occurs in the mid-frequency range, having a significant impact on the system and cannot be ignored in impedance modeling and analysis; the measurement stage has a smaller impact on the system's characteristics in the low-frequency and high-frequency ranges.

[0040] In the embodiments of this application, see Figure 18 , Figure 19 and Figure 20 The steps for analyzing a single measurement step versus considering the similarities and differences between two measurement steps include: Considering only the resonant frequency of the PT and its secondary system measurement circuit (corresponding to...) Figure 31 The frequency is higher than the resonant frequency considering only the CT and its secondary system measurement components (corresponding to...). Figure 32 This is due to the measurement links of the PT and its secondary system. L 3. C The value of 2 is relatively small, resulting in a high resonant frequency. When considering a single measurement element, its frequency is affected by... L and C The impact, L and C The smaller the value, the higher the resonant frequency. When considering two measurement components, the resonant frequency is always lower than the resonant frequency of considering only one measurement component; when the resonant frequency of one measurement component increases, the resonant frequencies of both measurement components also increase.

[0041] exist Figure 18 middle, I sa This is the input current of the secondary system. I ta For the output current, I L2a This refers to the current in the inductor branch. U ica , U oca These are the input voltage and the output voltage, respectively. R 1 and L 1 represents the resistance and inductance of the ECT secondary cable. C 1 is the grounding capacitor. Z This is the sampling resistor in the current measurement circuit.

[0042] exist Figure 19 middle, I sq Let q be the q-axis component of the input current of the secondary system. I tq This represents the q-axis component of the output current. I L2d The input current I of the secondary system L2a The d-axis component; U icq , U ocq These are the q-axis components of the input voltage and the output voltage, respectively. R 1 and L 1 represents the resistance and inductance of the ECT secondary cable. C 1 is the grounding capacitor. Z This is the sampling resistor in the current measurement circuit. s For the Laplace operator, ω 0 represents the angular frequency at the fundamental frequency (fundamental frequency is 50Hz).

[0043] In this embodiment of the application, the steps for conducting electromagnetic transient simulation experiments and field tests include: On the simulation platform, a simulation model of the MMC-HVDC system under islanded, lightly unloaded conditions was constructed, considering the measurement links of the CT, PT, and their secondary systems. No components were added, and no simulation conditions were changed. During stable operation, the system suddenly generated resonance. In one experiment, FFT analysis showed that the resonant frequency was mainly concentrated around 1.5kHz, consistent with theoretical analysis and field tests.

[0044] In summary, the method provided in this application includes: Step S1: Establish a π-type equivalent model of the CT and its secondary system measurement components; Step S2: Establish a π-type equivalent model of the measurement components of PT and its secondary system; Step S3: Establish the mathematical model of the MMC-HVDC main circuit; Step S4: Based on the mathematical model of the MMC-HVDC main circuit, and combined with the π-type equivalent model of the CT, PT and their secondary system measurement links, construct the impedance model of the MMC-HVDC islanded system containing the CT, PT and secondary system measurement links. Step S5: Derive the matrix form of the system impedance model; Step S6: Establish the mathematical relationship of the impedance matrix under four operating conditions: considering two types of measurement links, not considering measurement links, considering the measurement links of CT and its secondary system, and considering the measurement links of PT and its secondary system. Step S7: Analyze the relationship between the resonant frequencies under three operating conditions, considering two types of measurement links: the measurement link of the CT and its secondary system, and the measurement link of the PT and its secondary system. Step S8: Using a simulation platform, electromagnetic transient model, and field tests, the accuracy and reliability of the constructed impedance model of the MMC-HVDC islanded converter station considering the measurement process, as well as the proposed impedance matrix relationship and resonant frequency relationship, are verified.

[0045] As described above, the harmonic suppression method for modular multilevel converter high-voltage direct current transmission provided in this application can accurately characterize the characteristics of the electromagnetic transformer measurement link by establishing a π-type equivalent circuit model, construct an impedance model of the MMC-HVDC islanded system including the CT, PT and their secondary system measurement links and perform stability analysis, give the mathematical relationship of the impedance matrix under four different operating conditions and the mathematical relationship of the resonant frequency under three operating conditions including the measurement link, and determine the high-frequency resonant frequency of the MMC-HVDC islanded system excited by the CT, PT and their secondary system measurement links, providing a technical basis for subsequent control and parameter optimization to suppress the resonance induced by the measurement link.

[0046] In one embodiment, see Figure 2 The current and voltage measurement matrix includes a current measurement link matrix; the electrical parameters include the input current and output current of the electromagnetic current transformer and the current transformer secondary system measurement link; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: S201: The input and output currents of the electromagnetic current transformer and its secondary system measurement circuit are measured... dq Coordinate transformation yields the input current. dq Components and output current dq Quantity; S202: Based on the input current dq Components and output current dq The components generate the current measurement element matrix.

[0047] Understandably, the first step is to establish a π-type equivalent model of the CT and its secondary system measurement components. Based on the actual situation of the converter station's secondary system, a single π-type lumped equivalent circuit is used to represent the CT and its secondary system. Taking phase A of the three-phase system as an example, the CT and its secondary system measurement components... abc Equivalent model in stationary coordinate system as follows Figure 18 As shown, where I sa This refers to the input current of the CT and its secondary system measurement circuit.U ica This refers to the input voltage of the CT and its secondary system measurement circuit. I L2a For the inductor branch current of the CT and its secondary system measurement circuit; U oca The output voltage of the CT and its secondary system measurement circuit; I ta The output current of the CT and its secondary system measurement circuit; R 1. L 2 represents the resistance and inductance of the measurement components of the CT and its secondary system; C 1 represents the capacitance of two branches in the measurement circuit of the CT and its secondary system; the parasitic capacitance is very small, approximately 3 × 10⁻⁶. - 7 F. The following are the parasitic capacitance parameters of the CT secondary cable. C The formula for calculating 1.

[0048] , Where G is the geometric factor, and the geometric factor G for a single-core cable is 1.2; The dielectric constant is 8, and the outer layer of the cable is insulated with polyvinyl chloride. Z This is the sampling resistor for the measurement stage of CT and its secondary system. It is generally set to 1-10Ω and is suitable for practical engineering scenarios.

[0049] CT and its secondary system measurement process dq Equivalent model in axial coordinate system as follows Figure 19 As shown, where I sd , I sq These represent the input current of the CT and its secondary system measurement circuit, respectively. d Axial components and q Axial components, I td , I tq These represent the output current. d Axial components and q axis. I td , I tq and I sd , I sq The relationship between them is: (15) in, The transfer function matrix of the CT and its secondary system measurement components;

[0050] Then, a π-type equivalent model of the PT and its secondary system measurement links is established.

[0051] Taking phase A as an example again, the equivalent model of the PT and its secondary system measurement components in the abc stationary coordinate system is as follows: Figure 20 As shown, Iiva is the input current of the PT and its secondary system measurement circuit; Usa is the input voltage; IL3a is the inductor branch current; Uta is the output voltage; R2 and L3 are the resistance and inductance of the inductor branch, respectively; and C2 is the branch capacitance. Compared to the length of the CT secondary cable, the PT secondary cable is relatively short, about half the length of the CT cable, therefore its lumped parameters... L 3 and C 2 is approximately L 2. C Half of 1, and the equivalent model of the PT and its secondary system measurement link does not have a sampling resistor Z; the equivalent model of the PT and its secondary system measurement link does not have a sampling resistor Z. Similar to the derivation method of the transfer function matrix of the CT and its secondary system measurement link, the transfer function matrix H of the PT and its secondary system measurement link can be obtained. cable The equation satisfies the following equation: (16) in, U sd , U sq These represent the input voltages of the EPT-ML. d Axial components and q Axial components, U td , U tq These represent the output voltages of the EPT-ML. d Axial components and q Axial components, and

[0052] exist Figure 20 middle, I iva This is the input current of the secondary system. U sa , U ta These are the input voltage and the output voltage, respectively. R 2 and L 3 represents the resistance and inductance of the secondary cable. C 2 is the grounding capacitor. IL3a This represents the current in the inductor branch.

[0053] As can be seen from the above description, the harmonic elimination method for modular multilevel converter high-voltage direct current transmission provided in this application can construct a current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system.

[0054] In one embodiment, see Figure 3 The current and voltage measurement matrix includes a voltage measurement link matrix; the electrical parameters include the input and output voltages of the electromagnetic voltage transformer and the voltage transformer secondary system measurement links; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: S301: The input and output voltages of the electromagnetic voltage transformer and its secondary system measurement circuit are measured. dq Coordinate transformation yields the input voltage. dq Components and output voltage dq Quantity; S302: Based on the input voltage dq Components and output voltage dq The components generate the voltage measurement link matrix.

[0055] Understandably, the next step is to establish a mathematical model for the MMC-HVDC main circuit.

[0056] In islanded operation mode, the topology of the MMC-HVDC main circuit and measurement system is as follows: Figure 23 As shown. Figure 23 middle, U cx ( x =a, b, c) represent the output voltages of the modular multilevel converter. U sx The three-phase voltage of the AC bus of the flexible DC transmission converter station. I sx For the AC output three-phase current of the flexible DC transmission converter station, L 0 represents the inductance of the modular multilevel converter bridge arm. I tx The three-phase measured current is obtained after the three-phase current on the AC side passes through the CT and its secondary system. U tx The three-phase measured voltage is obtained after the AC three-phase voltage passes through the PT and its secondary system. The transformer leakage inductance is... L 1.

[0057] See Figure 21 , Figure 22 and Figure 23 Based on the system architecture of MMC-HVDC, the main circuit and parasitic capacitance are obtained. C s The mathematical model of the loop in the stationary coordinate system, through Park The transformation yields the results of the flexible DC transmission converter station islanded renewable energy absorption system under light no-load conditions. dq The mathematical model in the axial coordinate system is: (17) in, s For the Laplace operator, ω 0 is the fundamental frequency ( f= angular velocity (50Hz) ω 0 = 2π f =100π). U sd , U sq These are the d-axis and q-axis components of the three-phase AC bus voltage of the flexible DC transmission converter station, respectively, and are also the input voltages of the PT and its secondary system measurement links; U cd , U cq These represent the d-axis and q-axis components of the output voltage of the modular multilevel converter, respectively. I sd , I sq These represent the d-axis and q-axis components of the three-phase AC current on the flexible DC transmission converter station, respectively, and also indicate the input current of the CT and its secondary system measurement components. L Transformer leakage inductance L It consists of 1 and half of the bridge arm inductance of MMC.

[0058] The control loop of a modular multilevel converter mainly consists of a voltage outer loop and a current inner loop. The voltage outer loop of a certain converter station uses constant AC voltage control, and its mathematical formula is: (18) in, I tdref , I tqref These are the d-axis and q-axis components of the reference current output from the outer voltage loop; G vpi It is a voltage outer loop proportional-integral controller. U sdref , U sqref These are the d-axis and q-axis components of the outer loop reference voltage.

[0059] The mathematical formula for the current inner loop control is: (19) in, G ipi It is a current inner-loop proportional-integral controller.

[0060] As can be seen from the above description, the harmonic elimination method for modular multilevel converter high-voltage direct current transmission provided in this application can construct a current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system.

[0061] In one embodiment, see Figure 4 The step of constructing a high-voltage direct current transmission impedance model considering the current and voltage measurement links based on the main circuit topology of the high-voltage direct current transmission system and the current and voltage measurement matrix includes: S401: Generate a mathematical model under light no-load conditions based on the main circuit topology; S402: Input the current and voltage measurement matrix into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model.

[0062] Among them, see Figure 5 The step of generating a mathematical model under light no-load conditions based on the main circuit topology includes: S501: Based on the input voltage dq Component determination of the three-phase AC current on the modular multilevel converter station dq Quantity; S502: Based on the input voltage dq In the components d Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. d Axial components; S503: Based on the input voltage dq In the components q Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. q Axial components; S504: Based on the output voltage of the modular multilevel converter d Shaft component, output voltage of the modular multilevel converter q Shaft components and the three-phase AC current of the modular multilevel converter station dq The mathematical model under the light unloaded condition is constructed using components.

[0063] Understandably, the next step is to construct an impedance model for the MMC-HVDC islanded system, including CT, PT, and secondary system measurement components.

[0064] When considering two measurement stages, the MMC-HVDC islanded system under light no-load conditions d The structural diagram of the shaft is divided into the control side and the system side, such as Figure 24A As shown, where, F V For compensation pairs in voltage feedforward circuits; G del It is the delay element generated by the control loop. Using Ohm's law, the superposition theorem, and Thevenin's theorem, the virtual impedance Z can be obtained. inner,d Z Fv,d Z sd,d The specific simplification process is as follows: Figure 24B , Figure 24C and Figure 24D As shown. The virtual impedance introduced by the d-axis component of the CT and its secondary system measurement circuit and the current inner loop PI controller. Z 1,d : ; Virtual impedance is introduced by the d-axis component of the coupling inductance in the measurement circuit and current inner loop of the CT and its secondary system. Z 2,d : ; CT and its secondary system measurement links, PT and its secondary system measurement links, and d-axis voltage feedforward introduction and Parallel virtual impedance Z Fv,d : ; The measurement links of CT and its secondary system, the measurement links of PT and its secondary system, and the virtual impedance introduced by the voltage outer loop are used to obtain equation (20), which contains... G vi and Z vi ) ; Circuit gain stage: . Using the same method as for d-axis impedance modeling, impedance modeling is performed on the q-axis to obtain the circuit gain element:

[0065] Furthermore, the matrix form of the system impedance model is constructed.

[0066] merge dshaft and q The impedance model of the shaft is used to obtain the matrix form of the MMC-HVDC impedance model, which includes two measurement elements, as follows: Figure 25 , Figure 26 As shown, the following equation holds:

[0067] exist Figure 25 middle, U sq This represents the q-axis component of the output voltage of the secondary system. I tq This represents the q-axis component of the output current. U sqref The q-axis component of the input voltage reference value. C 1 is the grounding capacitor. Z inner,q , Z Fv,q Z sd,q This is a virtual resistor. U 4 is an equivalent controlled voltage source. G 2 is the equivalent transfer function.

[0068] exist Figure 26 middle, G vpi For the proportional-integral element of the voltage outer loop controller, and, U sdref , U sqref These are the d-axis and q-axis components of the outer loop reference voltage. I td , I tq The d-axis and q-axis components of the three-phase current of the system are input to the controller after passing through the measurement circuit. G ipi For the inner loop proportional-integral controller, G del This is the transfer function for the delay element. U sd , U sq These are the d-axis and q-axis components of the three-phase AC bus voltage of the flexible DC transmission converter station, respectively. I sd , I sq These represent the d-axis and q-axis components of the three-phase current on the AC side of the flexible DC transmission converter station, respectively. s For the Laplace operator, ω 0 represents the angular frequency at the fundamental frequency (fundamental frequency is 50Hz). G cable Let be the transfer function of the current measurement circuit. Hcable This is the transfer function of the voltage measurement circuit. F V This is a compensation pair for the voltage feedforward circuit.

[0069] Further organization and simplification led to the following derivation d - q Impedance matrix of system in domain and system gain matrix They are as follows: ,

[0070] Then, the above impedance matrix and system gain matrix Depend on d - q The field is transformed into a positive / negative sequence field, as shown below: (twenty one) (twenty two) in, .

[0071] As can be seen from the above description, the harmonic elimination method for modular multilevel converter high-voltage direct current transmission provided in this application can generate a mathematical model under light no-load conditions based on the main circuit topology.

[0072] In one embodiment, see Figure 6 The high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the step of inputting the current and voltage measurement matrix into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model includes: S601: Determine the first virtual impedance based on the proportional-integral control coefficient of the current inner loop, the delay coefficient generated by the control loop, the output current, and the current measurement link matrix; S602: Determine the second virtual impedance based on the fundamental frequency angular velocity, transformer leakage inductance, the output current, and the current measurement link matrix; S603: Based on the output current, the input voltage, the current measurement matrix, and the voltage measurement matrix, the third virtual impedance and the fourth virtual impedance are obtained; S604: Construct the system impedance matrix and the system gain matrix based on the first virtual impedance, the second virtual impedance, the third virtual impedance, the fourth virtual impedance, the current measurement link matrix, the voltage measurement link matrix, the voltage outer loop proportional-integral control coefficient, the current inner loop proportional-integral control coefficient, the compensation pair coefficient of the voltage feedforward link, and the delay coefficient generated by the control loop.

[0073] Understandably, the following analysis will examine the relationship between the impedance matrices under four different conditions.

[0074] According to the impedance matrix model ,make G cable =I and H cable =I, that is G 11 =1、 G 12 =0、 G 21 =0、 G 22 =1、 H 11 =1、 H 12 =0、 H 21 =0、 H 22 =1, thus obtaining the impedance matrix of the MMC-HVDC system without considering the measurement components. Z ;make H cable =I, thus obtaining the system impedance matrix considering only the CT and its secondary system measurement components. Z i ;make G cable =I, thus obtaining the system impedance matrix considering only PT and its secondary system measurement components. Z v The following are examples:

[0075] When PT and its secondary system measurement link matrix H cable When the elements on the main diagonal are equal and the elements on the secondary diagonal are opposite, it is found that its impedance matrix satisfies... (twenty three) This indicates that the superposition of measurement elements corresponds to the multiplication of their impedance matrices, which facilitates subsequent generalization to the case of multiple measurement elements, simplifies the modeling process and subsequent resonance mechanism analysis.

[0076] From the formula It can be seen that the four impedance matrices in both positive and negative orders also satisfy the following conditions. (twenty four) If all four impedance matrices in both positive and negative sequences are diagonal matrices, then their positive sequence impedance satisfies the following condition: × = × (25) As can be seen from the above description, the harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter provided in this application can input the current and voltage measurement matrix into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model.

[0077] In one embodiment, see Figure 7 The high-voltage direct current (HVDC) transmission impedance model includes a system impedance matrix and a system gain matrix. Analyzing the HVDC transmission impedance model under preset operating conditions yields impedance matrices considering current and voltage measurement stages, impedance matrices considering only current measurement stages, impedance matrices considering only voltage measurement stages, and impedance matrices not considering current and voltage measurement stages, including: S701: Set the current measurement element matrix and the voltage measurement element matrix in the system impedance matrix to an identity matrix to obtain the impedance matrix without considering the measurement elements; S702: Set the voltage measurement link matrix in the system impedance matrix to an identity matrix to obtain an impedance matrix that only considers the current measurement link; S703: Set the current measurement element matrix in the system impedance matrix to an identity matrix to obtain an impedance matrix that only considers the voltage measurement element; S704: Obtain the impedance matrix considering the current and voltage measurement links based on the system impedance matrix, the system gain matrix, the current measurement link matrix, and the voltage measurement link matrix.

[0078] In one embodiment, see Figure 8 The method of determining the resonant frequency of high-voltage direct current transmission using the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, in order to perform harmonic cancellation operation, includes: S801: Analyze the main diagonal elements of the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links respectively to obtain the positive sequence impedance relationship. S802: Determine the resonant frequency using the positive sequence impedance relationship; S803: Perform harmonic cancellation operation at the resonant frequency using an active or passive filter.

[0079] It is understandable that we would analyze the relationship between resonant frequencies under the three operating conditions.

[0080] The condition for resonance in an MMC-HVDC system is that the magnitudes of the system's positive-sequence impedance and the grid-side impedance are equal, which can be obtained as follows: (26) in, i The resonant frequency of the MMC-HVDC system when only considering the CT and its secondary system measurement components. v To determine the resonant frequency of the system when only the PT and its secondary system are considered in the measurement process, vi The resonant frequency of the system is considered when both measurement elements are taken into account.

[0081] From formula (26), we can obtain: (27) Further simplification yields: (28) As described above, under preset operating conditions, the impedance model of the high-voltage direct current transmission is analyzed to obtain the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links. The resonant frequency of the high-voltage direct current transmission is determined using the impedance matrices considering the current and voltage measurement links, considering only the current measurement links, considering only the voltage measurement links, and not considering the current and voltage measurement links, so as to perform harmonic cancellation operation.

[0082] Simulation experiments, electromagnetic transient models, and field tests were used to verify the accuracy and reliability of the constructed impedance model of the MMC-HVDC islanded converter station considering the measurement process, as well as the proposed impedance matrix relationship and resonant frequency relationship, including: In simulation experiments, this invention obtained the Bode plot of the MMC-HVDC system considering two measurement stages, as shown below. Figure 27 and Figure 28 The impedance of the MMC-HVDC system considering two measurement stages is described above. With grid-side parasitic capacitance C s The Bode plot amplitudes intersect around 1.5 kHz, and the phase angles differ by more than 180°. This indicates that, considering both measurement elements, the system impedance and parasitic capacitance of the MMC-HVDC islanded converter station are related. C s The resonance condition is met in the mid-frequency range, causing the system to resonate at high frequencies, which leads to system instability. Figure 28 In the context of MMC-HVDC systems, two measurement stages are considered. The sudden drop and rise in amplitude and phase angle around 12kHz reduced the stability of the system at that specific frequency.

[0083] Impedance matrix of MMC-HVDC system under light no-load conditions, without considering measurement components and parasitic capacitance C s Characteristics such as Figure 29 As shown, the Bode plot amplitude curves of the two systems intersect near 2.7 kHz. The phase angle differences at the intersection point under positive and negative sequences are 170° and 168°, respectively, both less than 180°. Therefore, the MMC-HVDC system is stable and does not resonate under light no-load conditions, without considering the measurement components. Figure 29 and Figure 27 In contrast, it was found that the system resonated after the measurement element was added, with the resonant frequency around 1.5 kHz.

[0084] Figure 30 The gain matrix of the MMC-HVDC system is shown under light no-load conditions, without considering the measurement process. Its characteristics include consistent positive and negative sequence impedances, a continuously decreasing amplitude that remains at -14.2dB with increasing frequency, and a phase angle that first decreases with increasing frequency, reaching a minimum of -42.6° at 238Hz, and then continuously increasing and remaining near 0°. Figure 30 and Figure 31 Comparison, Figure 31 A sudden drop and rise in amplitude and phase angle occur around 12kHz, while Figure 30 This phenomenon was not observed. This indicates that the introduction of the measurement element has a significant impact on the dynamic characteristics of the system, and may lead to a decrease in the stability of the system at a specific frequency.

[0085] When only considering the CT and its secondary system measurement components, the impedance of the MMC-HVDC system is... Bode diagrams in positive and negative order are as follows: Figure 31 As shown. With Figure 29 compared to, Figure 31 Impedance of MMC-HVDC System With grid-side parasitic capacitance C S The amplitude curves intersect near 2kHz in the mid-frequency band, and the phase angle difference is more than 180°, indicating that the system resonates in the mid-frequency band when only the CT and its secondary system measurement components are considered. In the low-frequency and high-frequency bands, the CT and its secondary system measurement components have little effect on the system phase and amplitude, and can be ignored.

[0086] When only the PT and its secondary system measurement components are considered, the impedance of the MMC-HVDC system is... Bode diagrams in positive and negative order are as follows: Figure 32 As shown. With Figure 29 compared to, Figure 32 The amplitude and phase oscillated repeatedly around 8kHz, causing system instability. At low and high frequencies, the influence of the PT and its secondary system measurement components on the system phase and amplitude is negligible.

[0087] Compare Figure 31 and Figure 32 It was found that the resonant frequency of the measurement circuit considering only the PT and its secondary system is higher than that considering only the CT and its secondary system. This is because the resonant frequency of the measurement circuit considering only the PT and its secondary system... L 3. C The value of 2 is relatively small, resulting in a high resonant frequency. Therefore, it can be concluded that when considering a single measurement element, its frequency is affected by... L and C The impact, L and C The smaller the value, the higher the resonant frequency.

[0088] Taking all factors into consideration Figure 27 , Figure 31 and Figure 32 , can be obtained vi =1.5kHz i =2 kHz v =8kHz, substituting into formula (17) holds true, indicating that the simulation results are consistent with the theoretical analysis of the resonant frequency. When considering two measurement elements, the resonant frequency is always less than the resonant frequency of considering only one measurement element; when the resonant frequency of one measurement element increases, the resonant frequencies of both measurement elements will also increase.

[0089] Referring to Table 1, simulation models of flexible DC transmission converter stations under four operating conditions and their islanded renewable energy consumption modes are constructed in the simulation platform. The specific parameters of the models are as follows. This model ignores the system delay.

[0090] Table 1 Simulation Modeling Parameters

[0091] The voltage and current waveforms of the MMC-HVDC islanded system considering the measurement stages of the CT, PT, and their secondary systems are as follows: Figure 33 As shown. Ignoring the measurement components, the voltage and current waveforms are as follows. Figure 34 As shown, resonance does not occur at this time. The voltage and current waveforms of the MMC-HVDC islanded system, considering only the CT and its secondary system measurement stages, are as follows: Figure 35 As shown, resonance occurred. Considering only the PT and its secondary system measurement components, the system's voltage and current waveforms are as follows: Figure 36As shown, after considering the measurement stage, the waveforms of the output voltage and current amplitudes of the MMC-HVDC system diverge rapidly. Without protection activation, the output current can reach as high as 2kA, indicating that the MMC-HVDC system has resonated. FFT analysis shows that the resonant frequency is mainly concentrated around 1.5kHz, consistent with previous analysis results. This demonstrates the accuracy and rationality of the conclusion proposed in this paper that the measurement stage can induce high-frequency resonance in the flexible DC system. By analyzing the impedance modeling of different measurement stages and their impact on the system's dynamic characteristics, the influence of the measurement stages on the stability of the MMC-HVDC system is verified.

[0092] In short, Figures 33 to 36 The results show that introducing a measurement element will excite high-frequency resonance in the MMC-HVDC islanded system. Figure 33 , Figure 35 and Figure 36 The output voltage and output current waveforms were subjected to Fast Fourier Transform to calculate the resonant frequencies. vi =1.5kHz, i =2kHz and v =8kHz, consistent with the Bode plot analysis results above, demonstrating the accuracy of the resonance mechanism proposed in this invention.

[0093] During the commissioning of a converter station, a high-frequency resonant voltage and current fault occurred on the empty bus under islanded operation conditions. The recorded waveform is as follows: Figure 37 As shown. Figure 37 (Left side) shows the AC system voltage waveform of the converter station when resonance occurs. Figure 37 (Right side) shows the current waveform. When the system resonates, the waveform of the system current amplitude rises divergently. Within 0.55s to 0.75s, the current amplitude can reach 50A without protection, and there is a continuous upward trend. FFT analysis shows that the resonant frequency is about 1.5kHz, which is consistent with the Bode plot analysis results, indicating the accuracy of the resonance mechanism proposed in this invention.

[0094] Based on the same inventive concept, this application also provides a harmonic suppression device for modular multilevel converter high-voltage direct current (HVDC) transmission, which can be used to implement the method described in the above embodiments, as described in the following embodiments. Since the principle of the harmonic suppression device for modular multilevel converter HVDC transmission is similar to the harmonic suppression method for modular multilevel converter HVDC transmission, the implementation of the harmonic suppression device for modular multilevel converter HVDC transmission can refer to the implementation of the software performance benchmark determination method, and repeated details will not be elaborated further. As used below, the terms "unit" or "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the system described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0095] In one embodiment, see Figure 9 In order to analyze the mismatch effect caused by the measurement links of CT and its secondary system and PT and its secondary system respectively, determine the system resonant frequency, and eliminate the resonance effect, this application provides a harmonic elimination device for modular multilevel converter high voltage DC transmission, including: a measurement matrix construction unit 901, an impedance model generation unit 902, an impedance matrix analysis unit 903, and a resonant frequency determination unit 904.

[0096] The measurement matrix construction unit 901 is used to construct a current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the secondary system of the current transformer, the electromagnetic voltage transformer and the secondary system of the voltage transformer in the high voltage direct current transmission system. Impedance model generation unit 902 is used to construct an impedance model of the high voltage direct current transmission system that considers the current and voltage measurement links based on the main circuit topology of the high voltage direct current transmission system and the current and voltage measurement matrix. Impedance matrix analysis unit 903 is used to analyze the impedance model of the high voltage direct current transmission under preset operating conditions to obtain the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links. The resonant frequency determination unit 904 is used to determine the resonant frequency of the high voltage direct current transmission using the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, so as to perform harmonic cancellation operation.

[0097] In one embodiment, see Figure 10The current and voltage measurement matrix includes a current measurement link matrix; the electrical parameters include the input current and output current of the electromagnetic current transformer and the current transformer secondary system measurement link; the measurement matrix construction unit 901 includes: a current component calculation module 1001 and a current matrix generation module 1002.

[0098] The current component calculation module 1001 is used to calculate the input and output currents of the electromagnetic current transformer and the measurement stage of the current transformer secondary system. dq Coordinate transformation yields the input current. dq Components and output current dq Quantity; Current matrix generation module 1002 is used to generate a current matrix based on the input current. dq Components and output current dq The components generate the current measurement element matrix.

[0099] In one embodiment, see Figure 11 The current and voltage measurement matrix includes a voltage measurement link matrix; the electrical parameters include the input voltage and output voltage of the electromagnetic voltage transformer and the voltage transformer secondary system measurement link; the measurement matrix construction unit 901 includes a voltage component calculation module 1101 and a voltage matrix generation module 1102.

[0100] Voltage component calculation module 1101 is used to calculate the input and output voltages of the electromagnetic voltage transformer and the secondary system measurement stage of the voltage transformer. dq Coordinate transformation yields the input voltage. dq Components and output voltage dq Quantity; Voltage matrix generation module 1102 is used to generate a voltage matrix based on the input voltage. dq Components and output voltage dq The components generate the voltage measurement link matrix.

[0101] In one embodiment, see Figure 12 The impedance model generation unit 902 includes: a light air condition model generation module 1201 and an impedance model generation module 1202.

[0102] The light-load and no-load operating condition model generation module 1201 is used to generate a mathematical model under light-load and no-load operating conditions based on the main circuit topology. Impedance model generation module 1202 is used to input the current and voltage measurement matrix into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model.

[0103] In one embodiment, see Figure 13The working condition model generation module 1201 includes: dq Component determination module 1301 d Shaft component determination module 1302 q Axis component determination module 1303 and light hollow model generation module 1304.

[0104] dq Component determination module 1301 is used to determine the component based on the input voltage. dq Component determination of the three-phase AC current on the modular multilevel converter station dq Quantity; d The axis component determination module 1302 is used to determine the axis component based on the input voltage. dq In the components d Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. d Axial components; q The axis component determination module 1303 is used to determine the axis component based on the input voltage. dq In the components q Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. q Axial components; The light-air model generation module 1304 is used to generate a model based on the output voltage of the modular multilevel converter. d Shaft component, output voltage of the modular multilevel converter q Shaft components and the three-phase AC current of the modular multilevel converter station dq The mathematical model under the light unloaded condition is constructed using components.

[0105] In one embodiment, see Figure 14 The high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the impedance model generation module 1202 includes: a first impedance determination module 1401, a second impedance determination module 1402, a third and fourth impedance determination module 1403, and an impedance gain matrix generation module 1404.

[0106] The first impedance determination module 1401 is used to determine the first virtual impedance based on the current inner loop proportional-integral control coefficient, the delay coefficient generated by the control loop, the output current and the current measurement link matrix. The second impedance determination module 1402 is used to determine the second virtual impedance based on the fundamental frequency angular velocity, transformer leakage inductance, the output current and the current measurement link matrix. The three- and four-impedance determination module 1403 is used to obtain the third virtual impedance and the fourth virtual impedance based on the output current, the input voltage, the current measurement link matrix and the voltage measurement link matrix. The impedance-gain matrix generation module 1404 is used to construct the system impedance matrix and the system gain matrix based on the first virtual impedance, the second virtual impedance, the third virtual impedance, the fourth virtual impedance, the current measurement link matrix, the voltage measurement link matrix, the voltage outer loop proportional-integral control coefficient, the current inner loop proportional-integral control coefficient, the compensation pair coefficient of the voltage feedforward link, and the delay coefficient generated by the control loop.

[0107] In one embodiment, see Figure 15 The high-voltage direct current transmission impedance model includes a system impedance matrix and a system gain matrix; the resonant frequency determination unit 904 includes: a first matrix generation module 1501, a second matrix generation module 1502, a third matrix generation module 1503 and a fourth matrix generation module 1504.

[0108] The first matrix generation module 1501 is used to set the current measurement link matrix and the voltage measurement link matrix in the system impedance matrix as identity matrices to obtain the impedance matrix without considering the measurement links. The second matrix generation module 1502 is used to set the voltage measurement link matrix in the system impedance matrix as an identity matrix to obtain an impedance matrix that only considers the current measurement link. The third matrix generation module 1503 is used to set the current measurement link matrix in the system impedance matrix as an identity matrix to obtain an impedance matrix that only considers the voltage measurement link. The fourth matrix generation module 1504 is used to obtain the impedance matrix considering the current and voltage measurement links based on the system impedance matrix, the system gain matrix, the current measurement link matrix, and the voltage measurement link matrix.

[0109] In one embodiment, see Figure 16 The resonant frequency determination unit 904 includes: a positive sequence relationship determination module 1601, a resonant frequency determination module 1602, and a harmonic cancellation operation execution module 1603.

[0110] The positive sequence relationship determination module 1601 is used to analyze the main diagonal elements of the impedance matrix considering the current and voltage measurement links, the impedance matrix considering only the current measurement links, the impedance matrix considering only the voltage measurement links, and the impedance matrix not considering the current and voltage measurement links, respectively, to obtain the positive sequence impedance relationship. The resonant frequency determination module 1602 is used to determine the resonant frequency using the positive sequence impedance relationship; The harmonic cancellation operation execution module 1603 is used to perform harmonic cancellation operation at the resonant frequency using an active filter or a passive filter.

[0111] From a hardware perspective, in order to analyze the mismatch effects caused by the measurement links of the CT and its secondary system, and the measurement links of the PT and its secondary system, determine the system resonant frequency, and eliminate the resonance effect, this application provides an embodiment of an electronic device for implementing all or part of the harmonic elimination method for the modular multilevel converter high-voltage direct current transmission. The electronic device specifically includes the following components: The system comprises a processor, a memory, a communications interface, and a bus; wherein the processor, memory, and communications interface communicate with each other via the bus; the communications interface is used to realize information transmission between the harmonic suppression device of the modular multilevel converter high-voltage direct current transmission and core business systems, user terminals, and related databases and other related equipment; the logic controller can be a desktop computer, tablet computer, or mobile terminal, etc., and this embodiment is not limited to these. In this embodiment, the logic controller can be implemented with reference to the embodiments of the harmonic suppression method and the harmonic suppression device of the modular multilevel converter high-voltage direct current transmission in the embodiments, the contents of which are incorporated herein, and repeated details will not be described again.

[0112] It is understood that the user terminal may include smartphones, tablet computers, network set-top boxes, portable computers, desktop computers, personal digital assistants (PDAs), in-vehicle devices, smart wearable devices, etc. Among these, the smart wearable devices may include smart glasses, smartwatches, smart bracelets, etc.

[0113] In practical applications, the harmonic suppression method for modular multilevel converter HVDC transmission can be partially executed on the electronic device side as described above, or all operations can be completed in the client device. The choice can be made based on the processing capabilities of the client device and the limitations of the user's usage scenario. This application does not impose any limitations on this. If all operations are completed in the client device, the client device may further include a processor.

[0114] The aforementioned client device may have a communication module (i.e., a communication unit) that can communicate with a remote server to achieve data transmission. The server may include a server on the task scheduling center side; in other implementation scenarios, it may also include a server on an intermediate platform, such as a server on a third-party server platform that has a communication link with the task scheduling center server. The server may include a single computer device, a server cluster consisting of multiple servers, or a distributed server structure.

[0115] Figure 17 This is a schematic block diagram illustrating the system configuration of the electronic device 9600 according to an embodiment of this application. Figure 17 As shown, the electronic device 9600 may include a central processing unit 9100 and a memory 9140; the memory 9140 is coupled to the central processing unit 9100. It is worth noting that... Figure 17 This is an example; other types of structures can also be used to supplement or replace this structure to achieve telecommunications functions or other functions.

[0116] In one embodiment, the harmonic suppression method for modular multilevel converter HVDC transmission can be integrated into a central processing unit 9100. The central processing unit 9100 can be configured to perform the following control: S101: Determine the fitness of individuals in subpopulations within the initial population using a pre-built fitness prediction model; wherein each individual is composed of a set of allocation ratios for product dispatching points; S102: Convert the initial fitness variables corresponding to each fitness into initial gene variables; S103: Use the initial gene variables to complete the evolution of the subpopulation, and obtain the superior individuals corresponding to the subpopulation and the superior gene variables corresponding to the superior individuals; S104: According to the preset fusion and reproduction cycle, the excellent individuals are fused and reproduced using the excellent gene variables to obtain the optimal network point allocation ratio.

[0117] As can be seen from the above description, the harmonic elimination method for high-voltage direct current transmission using modular multilevel converters provided in this application can obtain the optimal branch allocation ratio in a concurrent high-performance computing system using a multi-population genetic algorithm. It can realize concurrent design based on a multi-population genetic algorithm under a high-performance computing system, improve algorithm performance and global optimal solution search capability, and more efficiently schedule and allocate the resources and products required by each branch of the financial institution.

[0118] In another embodiment, the harmonic elimination device for modular multilevel converter high-voltage direct current transmission can be configured separately from the central processing unit 9100. For example, the harmonic elimination device for modular multilevel converter high-voltage direct current transmission can be configured as a chip connected to the central processing unit 9100, and the function of the harmonic elimination method for modular multilevel converter high-voltage direct current transmission can be realized through the control of the central processing unit.

[0119] like Figure 17 As shown, the electronic device 9600 may further include: a communication module 9110, an input unit 9120, an audio processor 9130, a display 9160, and a power supply 9170. It is worth noting that the electronic device 9600 does not necessarily need to include these components. Figure 17 All components shown; in addition, the electronic device 9600 may also include Figure 17 For components not shown, please refer to existing technologies.

[0120] like Figure 17 As shown, the central processing unit 9100, sometimes also referred to as a controller or operating control, may include a microprocessor or other processor device and / or logic device, which receives inputs and controls the operation of various components of the electronic device 9600.

[0121] The memory 9140 may be, for example, one or more of a cache, flash memory, hard drive, removable media, volatile memory, non-volatile memory, or other suitable devices. It may store the aforementioned failure-related information, and also store a program for executing that information. The central processing unit 9100 may execute the program stored in the memory 9140 to perform information storage or processing, etc.

[0122] Input unit 9120 provides input to central processing unit 9100. Input unit 9120 may be, for example, a keypad or touch input device. Power supply 9170 provides power to electronic device 9600. Display 9160 displays images and text. Display may be, for example, an LCD display, but is not limited thereto.

[0123] The memory 9140 can be a solid-state memory, such as a read-only memory (ROM), random access memory (RAM), a SIM card, etc. It can also be a memory that retains information even when power is off, can be selectively erased, and contains more data; examples of this type of memory are sometimes referred to as EPROMs. The memory 9140 can also be some other type of device. The memory 9140 includes a buffer memory 9141 (sometimes referred to as a buffer). The memory 9140 may include an application / function storage unit 9142 for storing application programs and function programs or processes for executing the operation of the electronic device 9600 via the central processing unit 9100.

[0124] The memory 9140 may also include a data storage unit 9143 for storing data, such as contacts, digital data, pictures, sounds, and / or any other data used by the electronic device. The driver storage unit 9144 of the memory 9140 may include various drivers for the electronic device's communication functions and / or for performing other functions of the electronic device (such as messaging applications, address book applications, etc.).

[0125] The communication module 9110 is a transmitter / receiver that sends and receives signals via the antenna 9111. The communication module (transmitter / receiver) 9110 is coupled to the central processing unit 9100 to provide input signals and receive output signals, which is the same as in a conventional mobile communication terminal.

[0126] Based on different communication technologies, multiple communication modules 9110 can be configured in the same electronic device, such as cellular network modules, Bluetooth modules, and / or wireless LAN modules. The communication module (transmitter / receiver) 9110 is also coupled to a speaker 9131 and a microphone 9132 via an audio processor 9130 to provide audio output via the speaker 9131 and receive audio input from the microphone 9132, thereby realizing typical telecommunications functions. The audio processor 9130 may include any suitable buffer, decoder, amplifier, etc. Additionally, the audio processor 9130 is also coupled to a central processing unit 9100, enabling on-device recording via the microphone 9132 and on-device playback of stored sound via the speaker 9131.

[0127] Embodiments of this application also provide a computer-readable storage medium capable of implementing all steps of the harmonic suppression method for modular multilevel converter high-voltage direct current transmission with a server or client execution subject in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all steps of the harmonic suppression method for modular multilevel converter high-voltage direct current transmission with a server or client execution subject in the above embodiments. For example, when the processor executes the computer program, it implements the following steps: S101: Determine the fitness of individuals in subpopulations within the initial population using a pre-built fitness prediction model; wherein each individual is composed of a set of allocation ratios for product dispatching points; S102: Convert the initial fitness variables corresponding to each fitness into initial gene variables; S103: Use the initial gene variables to complete the evolution of the subpopulation, and obtain the superior individuals corresponding to the subpopulation and the superior gene variables corresponding to the superior individuals; S104: According to the preset fusion and reproduction cycle, the excellent individuals are fused and reproduced using the excellent gene variables to obtain the optimal network point allocation ratio.

[0128] As can be seen from the above description, the harmonic elimination method for high-voltage direct current transmission using modular multilevel converters provided in this application can obtain the optimal branch allocation ratio in a concurrent high-performance computing system using a multi-population genetic algorithm. It can realize concurrent design based on a multi-population genetic algorithm under a high-performance computing system, improve algorithm performance and global optimal solution search capability, and more efficiently schedule and allocate the resources and products required by each branch of the financial institution.

[0129] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, apparatus, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0130] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (devices), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0131] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0132] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0133] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter, characterized in that, include: A current and voltage measurement matrix is ​​constructed based on the topology and electrical parameters of electromagnetic current transformers, current transformer secondary systems, electromagnetic voltage transformers, and voltage transformer secondary systems in high-voltage direct current transmission systems. Based on the main circuit topology of the high-voltage direct current transmission system and the current and voltage measurement matrix, a high-voltage direct current transmission impedance model including the current and voltage measurement link is constructed. The impedance matrix of the current and voltage measurement link is obtained by analyzing the impedance model of the high-voltage direct current transmission under the preset operating conditions. The impedance matrix of the current and voltage measurement circuit is used to determine the resonant frequency of the high-voltage direct current transmission in order to perform harmonic cancellation operation.

2. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 1, characterized in that, The current and voltage measurement matrix includes a current measurement link matrix; the electrical parameters include the input current and output current of the electromagnetic current transformer and the current transformer secondary system measurement link; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: The input and output currents of the electromagnetic current transformer and its secondary system are measured. dq Coordinate transformation yields the input current. dq Components and output current dq Quantity; According to the input current dq Components and output current dq The components generate the current measurement element matrix.

3. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 1, characterized in that, The current and voltage measurement matrix includes a voltage measurement link matrix; the electrical parameters include the input and output voltages of the electromagnetic voltage transformer and the voltage transformer secondary system measurement links; the construction of the current and voltage measurement matrix based on the topology and electrical parameters of the electromagnetic current transformer, the current transformer secondary system, the electromagnetic voltage transformer, and the voltage transformer secondary system in the high-voltage direct current transmission system includes: The input and output voltages of the electromagnetic voltage transformer and its secondary system are measured. dq Coordinate transformation yields the input voltage. dq Components and output voltage dq Quantity; According to the input voltage dq Components and output voltage dq The components generate the voltage measurement link matrix.

4. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 3, characterized in that, The construction of a high-voltage direct current (HVDC) transmission impedance model, including current and voltage measurement components, based on the main circuit topology of the HVDC transmission system and the current and voltage measurement matrix includes: A mathematical model for light no-load conditions is generated based on the main circuit topology. The current and voltage measurement matrix is ​​input into the mathematical model under light no-load conditions to obtain the high-voltage direct current transmission impedance model.

5. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 4, characterized in that, The step of generating a mathematical model under light no-load conditions based on the main circuit topology includes: Based on the input voltage dq Component determination of the three-phase AC current on the modular multilevel converter station dq Quantity; Based on the input voltage dq In the components d Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. d Axial components; Based on the input voltage dq In the components q Shaft component, input current dq The component determines the output voltage of the modular multilevel converter. q Axial components; Based on the output voltage of the modular multilevel converter d Shaft component, output voltage of the modular multilevel converter q Shaft components and the three-phase AC current of the modular multilevel converter station dq The mathematical model under the light unloaded condition is constructed using components.

6. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 4, characterized in that, The high-voltage direct current (HVDC) transmission impedance model includes a system impedance matrix and a system gain matrix; the step of inputting the current and voltage measurement matrices into the mathematical model under light no-load conditions to obtain the HVDC transmission impedance model includes: The first virtual impedance is determined based on the proportional-integral control coefficient of the inner current loop, the delay coefficient generated by the control loop, the output current, and the matrix of the current measurement link. The second virtual impedance is determined based on the fundamental frequency angular velocity, transformer leakage inductance, output current, and current measurement array matrix. Based on the output current, the input voltage, the current measurement matrix, and the voltage measurement matrix, the third virtual impedance and the fourth virtual impedance are obtained. The system impedance matrix and the system gain matrix are constructed based on the first virtual impedance, the second virtual impedance, the third virtual impedance, the fourth virtual impedance, the current measurement link matrix, the voltage measurement link matrix, the voltage outer loop proportional-integral control coefficient, the current inner loop proportional-integral control coefficient, the compensation pair coefficient of the voltage feedforward link, and the delay coefficient generated by the control loop.

7. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 1, characterized in that, The impedance matrix of the current and voltage measurement stage includes an impedance matrix containing the current and voltage measurement stage, an impedance matrix containing only the current measurement stage, an impedance matrix containing only the voltage measurement stage, and an impedance matrix not containing the current and voltage measurement stage; the high-voltage direct current (HVDC) transmission impedance model includes a system impedance matrix and a system gain matrix; analyzing the HVDC transmission impedance model under preset operating conditions yields the impedance matrices containing the current and voltage measurement stage, the impedance matrices containing only the current measurement stage, the impedance matrices containing only the voltage measurement stage, and the impedance matrices not containing the current and voltage measurement stage, including: By setting the current measurement element matrix and the voltage measurement element matrix in the system impedance matrix to identity matrices, the impedance matrix that does not contain measurement elements is obtained. Set the voltage measurement element matrix in the system impedance matrix to an identity matrix to obtain an impedance matrix that only contains the current measurement element; Set the current measurement element matrix in the system impedance matrix to an identity matrix to obtain an impedance matrix that only contains voltage measurement elements; The impedance matrix containing the current and voltage measurement elements is obtained based on the system impedance matrix, the system gain matrix, the current measurement element matrix, and the voltage measurement element matrix.

8. The harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter according to claim 6, characterized in that, The process of determining the resonant frequency of high-voltage direct current transmission using impedance matrices containing current and voltage measurement elements, impedance matrices containing only current measurement elements, impedance matrices containing only voltage measurement elements, and impedance matrices not containing current and voltage measurement elements, in order to perform harmonic cancellation operations, includes: By analyzing the main diagonal elements of the impedance matrices containing current and voltage measurement elements, the impedance matrices containing only current measurement elements, the impedance matrices containing only voltage measurement elements, and the impedance matrices not containing current and voltage measurement elements, the positive sequence impedance relationship is obtained. The resonant frequency is determined using the positive sequence impedance relationship. The harmonic cancellation operation is performed at the resonant frequency using an active or passive filter.

9. A harmonic suppression device for modular multilevel converter high-voltage direct current transmission, characterized in that, include: The measurement matrix construction unit is used to construct current and voltage measurement matrices based on the topology and electrical parameters of electromagnetic current transformers, current transformer secondary systems, electromagnetic voltage transformers, and voltage transformer secondary systems in high-voltage direct current transmission systems. Impedance model generation unit is used to construct an impedance model of the high voltage direct current transmission system that includes current and voltage measurement links based on the main circuit topology of the high voltage direct current transmission system and the current and voltage measurement matrix. Impedance matrix analysis unit is used to analyze the impedance model of the high voltage direct current transmission line under preset operating conditions to obtain the impedance matrix of the current and voltage measurement link; The resonant frequency determination unit is used to determine the resonant frequency of the high-voltage direct current transmission using the impedance matrix of the current and voltage measurement link, so as to perform harmonic elimination operation.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the harmonic elimination method for high-voltage direct current transmission using a modular multilevel converter as described in any one of claims 1 to 8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the harmonic suppression method for high-voltage direct current transmission using a modular multilevel converter as described in any one of claims 1 to 8.

12. A computer program product comprising a computer program / instructions, characterized in that, When executed by a processor, the computer program / instruction implements the steps of the harmonic suppression method for high-voltage direct current transmission of a modular multilevel converter as described in any one of claims 1 to 8.

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