A method and system for locating an oscillation source of a flexible direct current power transmission system

Abstract

The application discloses a flexible direct current power transmission system oscillation source positioning method and system, and belongs to the technical field of power system automation. The positioning method comprises the following steps: in the case that the flexible direct current power transmission system is oscillating, the voltage waveforms of each port in the flexible direct current power transmission system are measured and frequency domain analysis is performed to obtain the oscillation frequency of the flexible direct current power transmission system; each port oscillation traveling wave component corresponding to the oscillation frequency is extracted from the voltage waveforms of each port of the flexible direct current power transmission system; the propagation time delay difference of each port oscillation traveling wave component in the flexible direct current power transmission system is analyzed; and according to the propagation time delay difference, the port where the oscillation traveling wave component first arrives is determined as the oscillation source. The application extracts the oscillation traveling wave component of a specific frequency and performs propagation time delay comparison, does not need to rely on the mutation wave head of the traveling wave, realizes accurate and effective positioning of the oscillation source of the flexible direct current power transmission system, and greatly improves the operation safety and working condition stability of the double-end and various flexible direct current power transmission systems.

Description

Technical Field

[0001] This invention belongs to the field of power system automation technology, specifically relating to a method and system for locating oscillation sources in a flexible DC transmission system. Background Technology

[0002] In recent years, the morphology and mechanism of power system oscillation problems have become significantly more complex. With the large-scale application of technologies such as new energy power sources, power electronic equipment, and flexible DC transmission, the dynamic characteristics of the system have gradually shifted from the traditional synchronous machine-dominated mode to a new "power electronic control-dominated" mode. The types of oscillations have expanded from the classic electromechanical low-frequency modes to a wider range of scenarios such as control-coupled oscillations, subsynchronous oscillations, supersynchronous oscillations, and AC / DC coupled oscillations.

[0003] Flexible direct current (DC) transmission systems have become an important component of modern power systems due to their advantages in long-distance, high-power transmission. However, the high proportion of power electronic equipment in DC systems results in low inertia and weak damping, leading to increasingly prominent system oscillation problems. Compared to traditional AC systems, DC systems have faster dynamic response speeds and more complex control modes, causing the excitation conditions, propagation paths, and manifestations of oscillations to exhibit significant nonlinear and multimodal characteristics. Oscillations not only affect power quality but can also cause system instability, and in severe cases, even lead to large-scale power outages. To ensure the safe and stable operation of DC systems, accurate oscillation source location is crucial. However, due to the multi-terminal characteristics of DC systems and the complexity of the power grid, the propagation paths of oscillation signals along the lines are diverse, posing numerous challenges to oscillation source location.

[0004] Traveling wave (TW) location methods are widely used in fault location scenarios. Their basic principle is that fault traveling waves have clear abrupt wavefronts. When a transient fault such as a short circuit or grounding occurs in the system, the fault point instantaneously generates a traveling wave signal containing a steep abrupt wavefront. This signal propagates rapidly along the line, generating another abrupt wavefront when it passes a measurement point at the end of the line. By detecting the time difference between the abrupt wavefronts arriving at different measurement points and combining this with the known wave velocity, the distance between the fault point and the measurement point can be directly calculated, thus locating the fault. However, directly applying the TW method to the location of oscillation sources in flexible DC transmission systems faces fundamental technical bottlenecks. Oscillating traveling waves in flexible DC transmission systems differ fundamentally from fault traveling waves in their behavior. Oscillating traveling waves exhibit periodic variations, and their waveforms show high similarity at different times, lacking the distinct abrupt wavefronts that can serve as trigger markers found in fault traveling waves. This inherent characteristic renders the traditional TW method, which relies on abrupt wavefront detection, unusable for direct application and unable to reliably locate oscillation sources. Summary of the Invention

[0005] The purpose of this invention is to address the problems in the prior art by providing a method and system for locating oscillation sources in flexible DC transmission systems. By extracting the oscillating traveling wave component at a specific frequency and comparing its propagation delay, the method achieves accurate and effective location of oscillation sources in flexible DC transmission systems without relying on the abrupt change wavefront of the traveling wave.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Firstly, a method for locating oscillation sources in a flexible DC transmission system is provided, comprising: When the flexible DC transmission system oscillates, the voltage waveforms at each port of the flexible DC transmission system are measured and frequency domain analysis is performed to obtain the oscillation frequency of the flexible DC transmission system. Extract the traveling wave components of each port oscillation frequency from the voltage waveforms at each port of the flexible DC transmission system; Analyze the differences in propagation time delay of the traveling wave components at each port in the flexible DC transmission system; Based on the difference in propagation time delay, the port where the oscillating traveling wave component arrives first is determined to be the oscillation source.

[0007] As a preferred embodiment, the flexible DC transmission system is a two-port flexible DC transmission system, which includes a three-phase AC power supply, a step-up transformer, a rectifier, a DC transmission line, an inverter, and a step-down transformer. The three-phase AC power supply is connected to the step-up transformer, which steps up the AC voltage provided by the three-phase AC power supply and connects it to the AC side of the rectifier. The rectifier converts the AC voltage into DC voltage and injects it into one end of the DC transmission line. The DC side of the inverter is connected to the other end of the DC transmission line, and the AC side of the inverter is connected to the step-down transformer, which is connected to the power grid. In the dual-port flexible DC transmission system, the rectifier side is the first port, and the inverter side is the second port.

[0008] As a preferred embodiment, the three-phase AC power supply provides 100kV AC voltage; the step-up transformer adopts a star-delta connection structure, wherein the end connected to the three-phase AC power supply adopts a star grounding structure, and the end connected to the rectifier adopts a delta structure; the DC transmission line consists of two parallel lines, and the voltage of the DC transmission line is 300kV; the step-down transformer adopts a delta-star connection structure, wherein the end connected to the inverter adopts a delta structure, and the end connected to the power grid adopts a star grounding structure.

[0009] As a preferred embodiment, the rectifier adopts a constant power control strategy, collects AC side voltage, current and DC voltage, and performs PWM modulation output according to active power reference value and reactive power reference value; the inverter adopts a constant DC voltage control strategy, performs closed-loop regulation of DC voltage, controls reactive power reference value, and collects AC side voltage, current and DC voltage for PWM modulation.

[0010] As a preferred embodiment, in the step of measuring the voltage waveforms of each port in the flexible DC transmission system and performing frequency domain analysis to obtain the oscillation frequency of the flexible DC transmission system when oscillation occurs, the voltage waveforms of each port in the flexible DC transmission system are subjected to fast Fourier transform or power spectrum analysis to obtain the signal spectrum of each port; the oscillation frequency of each port is determined based on the signal spectrum of each port, and the oscillation frequency is compared with the frequency of the pre-injected disturbance signal for confirmation.

[0011] As a preferred embodiment, the step of extracting the port oscillation traveling wave components corresponding to the oscillation frequency from the voltage waveforms at each port of the flexible DC transmission system includes: Frequency domain decomposition is performed on the voltage waveforms at each port to obtain voltage decomposed waveforms at different frequencies; Frequency domain analysis is performed on each voltage decomposition waveform, and the voltage decomposition waveforms with frequencies consistent with the oscillation frequency are selected as the oscillation traveling wave components of the corresponding ports.

[0012] As a preferred embodiment, the step of analyzing the propagation time delay differences of the oscillating traveling wave components at each port in the flexible DC transmission system includes: Calculate the cross-correlation function between the oscillating traveling wave components at different ports; The time delay between the oscillating traveling wave components at different ports is determined based on the peak value of the cross-correlation function. The order in which the oscillating traveling wave components propagate is determined by the sign of the time delay.

[0013] As a preferred approach, for a two-port flexible DC transmission system, the cross-correlation function between the oscillating traveling wave components at different ports is calculated using the following formula:

[0014] In the formula, This represents the cross-correlation value between the oscillating traveling wave components of the first port and the second port; This represents the oscillating traveling wave component of the first port after time shift; This represents the oscillating traveling wave component at the second port that has not undergone time shift; t This represents the time-integral variable, which changes from 0 to [value missing] during the integration process. ; Indicates the total length of the time window; Represents a time delay variable; The time delay variable corresponding to the maximum value of the cross-correlation function Determine the time delay, and determine the order of propagation of the oscillating traveling wave components based on the sign of the time delay.

[0015] As a preferred embodiment, the step of determining the port where the oscillating traveling wave component arrives first as the oscillation source based on the difference in propagation time delay includes: If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, the corresponding time delay is negative. Then it is determined that the oscillating traveling wave component of the first port leads the second port, and the oscillation source is located on the first port side. If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, and the corresponding time delay is positive, then it is determined that the oscillating traveling wave component of the second port leads the first port, and the oscillation source is located on the second port side.

[0016] Secondly, a flexible DC transmission system oscillation source location system is provided, comprising: The oscillation frequency determination module is used to measure the voltage waveforms at each port of the flexible DC transmission system and perform frequency domain analysis to obtain the oscillation frequency of the flexible DC transmission system when oscillation occurs. The oscillating traveling wave component extraction module is used to extract the oscillating traveling wave components of each port corresponding to the oscillation frequency from the voltage waveforms of each port of the flexible DC transmission system. The time delay analysis module is used to analyze the differences in propagation time delay of the oscillating traveling wave components at each port in the flexible DC transmission system. The oscillation source location module is used to determine the port where the oscillating traveling wave component arrives first as the oscillation source based on the difference in propagation time delay.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: Traditional traveling wave localization methods rely on the abrupt change front of the traveling wave to calculate time delay and locate the source. However, the oscillating traveling waves generated by flexible DC transmission systems do not have obvious abrupt change fronts, making it difficult for traditional methods to effectively capture the characteristics of the traveling waves and thus hindering accurate oscillation source localization. To address this, this invention abandons the reliance on the abrupt change front of the traveling wave. By measuring the voltage waveforms at each port of the flexible DC transmission system and performing frequency domain analysis, the oscillation frequency of the flexible DC transmission system is accurately determined. Based on this, the oscillating traveling wave components corresponding to the oscillation frequency of each port are extracted, precisely removing invalid interference signals and preserving the core oscillation characteristics. Based on frequency-domain fixed-frequency and time-domain accurate extraction of oscillating traveling wave components, this invention focuses on the propagation characteristics of oscillating traveling wave components at each port. By analyzing the differences in propagation time delay of oscillating traveling wave components at each port in the flexible DC transmission system, and using the principle that "the port where the oscillating traveling wave component arrives first is the oscillation source," the propagation sequence and direction of oscillating traveling waves at different ports are precisely quantified. This avoids the random errors of single-signal analysis and solves the positioning deviation problem caused by the strong coupling and feature ambiguity of oscillation signals in flexible DC transmission systems, significantly improving the accuracy and reliability of oscillation source positioning. This invention requires no complex algorithm modification or additional hardware equipment and can complete the entire analysis and positioning process based on the original port voltage measurement signals of the flexible DC transmission system, making it highly feasible for engineering implementation. This method can quickly and accurately trace the oscillation source in a flexible DC transmission system, providing a basis for subsequent oscillation suppression strategy formulation and fault control, effectively avoiding system fluctuations and equipment anomalies caused by the continuous spread of oscillations, and significantly improving the operational safety and stability of double-ended and various types of flexible DC transmission systems. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the topology of a dual-port flexible DC transmission system according to an embodiment of the present invention; Figure 2 A schematic diagram of the topology of a dual-port flexible DC transmission system after the addition of an oscillation source according to an embodiment of the present invention; Figure 3 Voltage waveform diagram of a dual-port flexible DC transmission system according to an embodiment of the present invention; Figure 4 The spectrum diagram of the voltage waveform at the first port after FFT transformation in this embodiment of the invention; Figure 5 Mode decomposition diagram of voltage waveform at the first port according to an embodiment of the present invention; Figure 6 Mode decomposition diagram of the voltage waveform at the second port in an embodiment of the present invention; Figure 7 Spectrum diagram of the voltage components of the first port in an embodiment of the present invention; Figure 8 Spectrum diagram of the voltage components of the second port in an embodiment of the present invention; Figure 9 Waveform similarity analysis diagram of oscillating traveling wave components S1 and S2 in an embodiment of the present invention; in, Figure 3 , Figures 5 to 9 All simulation graphs are directly output from MATLAB (Matrix Laboratory) or Simulink software. It is important to emphasize that... Figure 3 , Figures 5 to 9 These are the same image directly output by the simulation software, rather than a combination of different attached images. The various parts of the image are displayed together for easy comparison and analysis. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, those skilled in the art can obtain other embodiments without creative effort.

[0021] A flexible direct current (HVDC) transmission system is a high-voltage direct current (HVDC) transmission system based on a voltage source converter (VSC). It can flexibly and bidirectionally transmit electrical energy and support the efficient and safe integration of new energy sources such as wind power and photovoltaics with the power grid. Oscillation refers to the phenomenon of periodic or near-periodic fluctuations in voltage, current, or power within a power system over time.

[0022] This invention proposes a method for locating oscillation sources in flexible DC transmission systems. The method utilizes oscillating traveling waves for oscillation source localization. The behavior of oscillating traveling waves differs fundamentally from that of fault traveling waves. Oscillating traveling waves exhibit periodic waveform characteristics and lack the distinct abrupt wavefronts characteristic of fault traveling waves. Furthermore, the oscillation waveforms at different times show a high degree of similarity. This characteristic renders traditional traveling wave localization methods, which rely on wavefront detection, unusable. The proposed oscillating traveling wave method analyzes the traveling wave delay and waveform similarity at different measurement points, and combines this with propagation path characteristics to infer the location of the oscillation source.

[0023] Specifically, the method for locating the oscillation source in a flexible DC transmission system according to an embodiment of the present invention includes the following steps: When the flexible DC transmission system oscillates, the voltage waveforms at each port of the flexible DC transmission system are measured and frequency domain analysis is performed to obtain the oscillation frequency of the flexible DC transmission system. Extract the traveling wave components of each port oscillation frequency from the voltage waveforms at each port of the flexible DC transmission system; Analyze the differences in propagation time delay of the traveling wave components at each port in the flexible DC transmission system; Based on the difference in propagation time delay, the port where the oscillating traveling wave component arrives first is determined to be the oscillation source.

[0024] In one possible implementation, embodiments of the present invention construct a dual-port flexible DC transmission system, such as... Figure 1 As shown, this dual-port flexible DC transmission system includes a three-phase AC power supply, a step-up transformer, a rectifier, a DC transmission line, an inverter, and a step-down transformer. A voltage source converter (VSC) is a general term for a power electronic device capable of generating voltage waveforms with controllable amplitude and phase, realizing the conversion of electrical energy between AC and DC. Further, the rectifier converts AC to DC; the inverter converts DC to AC; therefore, in this embodiment of the invention... Figure 1 and Figure 2 In this system, VSC1 represents the rectifier, and VSC2 represents the inverter. The three-phase AC power supply is connected to a step-up transformer, which raises the AC voltage provided by the three-phase AC power supply to a high voltage level suitable for DC transmission before connecting it to the AC side of rectifier VSC1. Rectifier VSC1 converts the AC voltage to DC voltage and injects it into one end of the DC transmission line. The DC side of inverter VSC2 is connected to the other end of the DC transmission line, and the AC side of inverter VSC2 is connected to a step-down transformer, which is connected to the power grid, reducing the AC voltage to a level acceptable to the grid before transmitting it to the grid. In this dual-port flexible DC transmission system, the rectifier VSC1 side is the first port, and the inverter VSC2 side is the second port.

[0025] Furthermore, in this embodiment of the invention, the three-phase AC power supply provides a 100kV AC voltage; the step-up transformer adopts a star-delta (Y-Δ) connection structure to achieve voltage matching and system isolation, with one end connected to the three-phase AC power supply using a star grounding structure and the other end connected to the rectifier VSC1 using a delta structure; the DC transmission line consists of two parallel lines, each 300km long, and uses a π-type equivalent model to simulate the line resistance, inductance, and capacitance to achieve stable DC power transmission, with the DC transmission line voltage being 300kV; the step-down transformer adopts a delta-star (Δ-Y) connection structure to ensure grid-side voltage matching and system isolation, with one end connected to the inverter VSC2 using a delta structure and the other end connected to the grid using a star grounding structure.

[0026] Furthermore, the rectifier VSC1 adopts a constant power control strategy, which collects AC side voltage, current and DC voltage, and performs pulse width modulation (PWM) output according to the active power reference value and reactive power reference value to achieve stable DC power injection; the inverter VSC2 adopts a constant DC voltage control strategy, which performs closed-loop regulation of DC voltage and controls reactive power reference value at the same time. It collects AC side voltage, current and DC voltage and performs PWM modulation to achieve grid-side power output and DC voltage stability. The PWM control frequency is 10kHz.

[0027] In one possible implementation, please refer to Figure 2 In this embodiment of the invention, a known disturbance signal is introduced into the constructed dual-port flexible DC transmission system to cause the system to oscillate in a forced manner, which is used to simulate and verify the effectiveness of the method of the present invention.

[0028] Taking forced oscillation at the first port as an example, a three-phase symmetrical AC current source is connected in parallel between the power supply side and the rectifier VSC1 as the oscillation source. It is necessary to ensure that the amplitude and duration of the disturbance signal are within the safe operating range of the system, while not changing the original operating state of the system, so as to obtain a clear oscillation signal.

[0029] In this embodiment, the amplitude of the current source is set to 500A and the frequency to 30Hz. This AC disturbance current is injected into the dual-port flexible DC transmission system to cause low-frequency oscillations in the dual-port flexible DC transmission system, while ensuring that the disturbance signal will not cause the dual-port flexible DC transmission system to malfunction.

[0030] According to the oscillation source localization method of this invention, the voltage waveforms at each port of the flexible DC transmission system are measured and frequency domain analysis is performed to obtain the oscillation frequency of the flexible DC transmission system, specifically including: Voltage sensors are installed at each port of the flexible DC transmission system to measure the voltage waveform and ensure that the sampling accuracy meets the requirements of oscillation analysis.

[0031] The acquired voltage waveforms undergo preliminary filtering and noise reduction to eliminate high-frequency interference and measurement errors, providing a reliable data foundation for subsequent frequency domain analysis. The processed two-port voltage waveforms are shown below. Figure 3 As shown in the figure, the voltage waveform exhibits obvious periodic oscillation characteristics, with its amplitude changing rapidly within a certain range and peak and trough values ​​alternating. This indicates that the flexible DC transmission system oscillates at both ports, and the oscillating traveling wave propagates from the first port to the second port.

[0032] The acquired voltage waveform is subjected to Fast Fourier Transform (FFT) or other power spectrum analysis methods to obtain the signal spectrum of each port. Taking FFT as an example, after performing FFT on the voltage waveform of the first port, the resulting signal spectrum is as follows: Figure 4 As shown.

[0033] Identify oscillating components with significant amplitudes in the signal spectrum, determine the main oscillation frequency, and confirm this by comparing it with the frequency of known disturbance signals. This embodiment starts from... Figure 4 It can be seen that the system's power frequency of 50Hz is the main component, followed by a relatively high proportion of the 30Hz frequency component, proving that the flexible DC transmission system oscillates at 30Hz, which is consistent with the oscillation frequency previously injected into the flexible DC transmission system.

[0034] In one possible implementation, the step of extracting the port oscillation traveling wave component corresponding to the oscillation frequency from the port voltage waveform of the flexible DC transmission system includes: Frequency domain decomposition is performed on the voltage waveforms at each port to obtain voltage decomposed waveforms at different frequencies; Frequency domain analysis is performed on each voltage decomposition waveform, and the voltage decomposition waveforms with frequencies consistent with the oscillation frequency are selected as the oscillation traveling wave components of the corresponding ports.

[0035] Specifically, taking the mode decomposition method as an example, the voltage waveform at the first port is decomposed in the frequency domain into component signals corresponding to multiple different frequency components, such as... Figure 5 As shown.

[0036] Mode decomposition can adaptively decompose a signal into several intrinsic mode functions (IMFs), each IMF representing a frequency component of the signal. The expression for the signal mode decomposition is as follows:

[0037] In the formula, x ( t () represents the signal to be decomposed; Indicates the first i indivual IMF Quantity; n express IMF The quantity of the components; r ( t ) represents the residual.

[0038] Modal decomposition is performed on the voltage waveform at the second port, decomposing it into component signals corresponding to multiple different frequency components, such as... Figure 6 As shown. Figure 5 and Figure 6 The first row shows the voltage waveforms at the first and second ports, respectively. The following rows show the voltage waveforms at the first and second ports decomposed from the first and second port voltage waveforms. IMF Quantity.

[0039] right Figure 5 and Figure 6 The individual component signals from the two decomposed ports are subjected to a Fast Fourier Transform (FFT) to obtain the frequency of each component, such as... Figure 7 and Figure 8 As shown, the frequency of each component is clearly represented in the spectrum.

[0040] Analyze the frequency of each component, and based on the obtained oscillation frequency, at the first port. IMF The voltage decomposition waveform that is consistent with or closest to the target frequency is selected from the components, and this voltage decomposition waveform is taken as the oscillating traveling wave component S1. The oscillating traveling wave component S2 of the second port is found in the same way.

[0041] from Figure 7 As can be seen, the frequency of the IMF5 component is closest to 30Hz. Figure 8 As can be seen, the frequency of the IMF2 5 component is closest to 30Hz. Therefore, the IMF5 component is used as the oscillating traveling wave component S1, and the IMF2 5 component is used as the oscillating traveling wave component S2.

[0042] In one possible implementation, the step of analyzing the propagation time delay differences of the traveling wave components at each port in the flexible DC transmission system includes: Calculate the cross-correlation function between the oscillating traveling wave components at different ports; The time delay between the oscillating traveling wave components at different ports is determined based on the peak value of the cross-correlation function. The order in which the oscillating traveling wave components propagate is determined by the sign of the time delay.

[0043] Furthermore, a sequence correlation analysis was performed on the oscillating traveling wave components S1 and S2, and the calculation expression of the cross-correlation function is as follows:

[0044] In the formula, This represents the cross-correlation value between the oscillating traveling wave components of the first port and the second port; This represents the oscillating traveling wave component of the first port after time shift; This represents the oscillating traveling wave component at the second port that has not undergone time shift; t This represents the time-integral variable, which changes from 0 to [value missing] during the integration process. ; Indicates the total length of the time window; Represents a time delay variable; The time delay variable corresponding to the maximum value of the cross-correlation function Determine the time delay, and determine the order of propagation of the oscillating traveling wave components based on the sign of the time delay.

[0045] In one possible implementation, the step of determining the port where the oscillating traveling wave component arrives first as the oscillation source based on the propagation delay difference includes: If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, the corresponding time delay is negative. Then it is determined that the oscillating traveling wave component of the first port leads the second port, and the oscillation source is located on the first port side. If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, and the corresponding time delay is positive, then it is determined that the oscillating traveling wave component of the second port leads the first port, and the oscillation source is located on the second port side.

[0046] In this embodiment, if C 12 Maximum τ If the value is negative, it indicates that the oscillating traveling wave component S1 needs to be shifted to the right to overlap with the oscillating traveling wave component S2. The oscillating traveling wave component S1 leads the oscillating traveling wave component S2, and the oscillation reaches the first port first. Therefore, the oscillation source is the rectifier VSC1. like C 12 Maximum τ If the value is positive, it indicates that the oscillating traveling wave component S1 needs to be shifted to the left to overlap with the oscillating traveling wave component S2. The oscillating traveling wave component S1 lags behind the oscillating traveling wave component S2. The oscillation reaches the second port first, so the oscillation source is the inverter VSC2.

[0047] The waveform similarity of oscillating traveling wave components S1 and S2 is as follows: Figure 9 As shown, from Figure 9 It can be seen that τ is negative when the correlation is maximum, indicating that the signal at the first port leads the signal at the second port, and the oscillation arrives at the first port first. The oscillation source is on the VSC1 side of the rectifier, which is consistent with the set oscillation source position.

[0048] The method described in this invention can effectively extract the oscillating traveling wave component from the voltage waveforms at each port, and achieve precise location of the oscillation source by analyzing the differences in the propagation delay of the traveling wave in the system. This oscillation source location method further enhances the operational safety and stability of dual-port flexible DC transmission systems, provides strong support for future oscillation control and power regulation of flexible DC transmission systems, and improves the overall system reliability and safety.

[0049] Another embodiment of the present invention also proposes an oscillation source location system for a flexible DC transmission system, comprising: The oscillation frequency determination module is used to measure the voltage waveforms at each port of the flexible DC transmission system and perform frequency domain analysis to obtain the oscillation frequency of the flexible DC transmission system when oscillation occurs. The oscillating traveling wave component extraction module is used to extract the oscillating traveling wave components of each port corresponding to the oscillation frequency from the voltage waveforms of each port of the flexible DC transmission system. The time delay analysis module is used to analyze the differences in propagation time delay of the oscillating traveling wave components at each port in the flexible DC transmission system. The oscillation source location module is used to determine the port where the oscillating traveling wave component arrives first as the oscillation source based on the difference in propagation time delay.

[0050] Another embodiment of the present invention also proposes an electronic device, including a processor and a memory, wherein the processor is used to execute a computer program stored in the memory to implement the aforementioned method for locating oscillation sources in a flexible DC transmission system.

[0051] Another embodiment of the present invention provides a computer-readable storage medium storing at least one instruction that, when executed by a processor, implements the method for locating the oscillation source of a flexible DC transmission system.

[0052] The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable storage medium can include any entity or device capable of carrying the computer program code, a medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately added or removed according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals. For ease of explanation, the above content only shows the parts related to the embodiments of the present invention; for specific technical details not disclosed, please refer to the method section of the embodiments of the present invention. This computer-readable storage medium is non-transitory and can be stored in storage devices formed by various electronic devices, enabling the execution process described in the method of the embodiments of the present invention.

[0053] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, 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.

[0054] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It should 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.

[0055] 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.

[0056] 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.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for locating an oscillation source in a flexible DC transmission system, characterized in that, include: When a flexible DC transmission system oscillates, the voltage waveforms at each port of the flexible DC transmission system are measured and frequency domain analysis is performed to obtain the oscillation frequency of the flexible DC transmission system; fast Fourier transform or power spectrum analysis is performed on the voltage waveforms at each port of the flexible DC transmission system to obtain the signal spectrum of each port; and the oscillation frequency of each port is determined based on the signal spectrum of each port. The traveling wave components of each port oscillation frequency are extracted from the voltage waveforms of each port of the flexible DC transmission system. Specifically, the voltage waveforms of each port are decomposed in the frequency domain to obtain voltage decomposed waveforms of different frequencies. Frequency domain analysis is performed on each voltage decomposed waveform, and the voltage decomposed waveforms with the same frequency as the oscillation frequency are selected as the traveling wave components of the corresponding port. Analyze the differences in propagation time delay of the traveling wave components at each port in the flexible DC transmission system; Based on the difference in propagation time delay, the port where the oscillating traveling wave component arrives first is determined to be the oscillation source.

2. The method for locating the oscillation source of a flexible DC transmission system according to claim 1, characterized in that, The flexible DC transmission system is a dual-port flexible DC transmission system, which includes a three-phase AC power supply, a step-up transformer, a rectifier, a DC transmission line, an inverter, and a step-down transformer. The three-phase AC power supply is connected to the step-up transformer, which steps up the AC voltage provided by the three-phase AC power supply and connects it to the AC side of the rectifier. The rectifier converts the AC voltage into DC voltage and injects it into one end of the DC transmission line. The DC side of the inverter is connected to the other end of the DC transmission line, and the AC side of the inverter is connected to the step-down transformer, which is connected to the power grid. In the dual-port flexible DC transmission system, the rectifier side is the first port, and the inverter side is the second port.

3. The method for locating the oscillation source of a flexible DC transmission system according to claim 2, characterized in that, The three-phase AC power supply provides 100kV AC voltage; the step-up transformer adopts a star-delta connection structure, wherein the end connected to the three-phase AC power supply adopts a star grounding structure, and the end connected to the rectifier adopts a delta structure; the DC transmission line consists of two parallel lines, and the voltage of the DC transmission line is 300kV; the step-down transformer adopts a delta-star connection structure, wherein the end connected to the inverter adopts a delta structure, and the end connected to the power grid adopts a star grounding structure.

4. The method for locating the oscillation source of a flexible DC transmission system according to claim 2, characterized in that, The rectifier adopts a constant power control strategy, which collects AC side voltage, current and DC voltage, and performs PWM modulation output according to active power reference value and reactive power reference value; the inverter adopts a constant DC voltage control strategy, which performs closed-loop regulation of DC voltage, controls reactive power reference value, and collects AC side voltage, current and DC voltage for PWM modulation.

5. The method for locating the oscillation source of a flexible DC transmission system according to claim 1, characterized in that, The steps for analyzing the propagation time delay differences of the traveling wave components at each port in the flexible DC transmission system include: Calculate the cross-correlation function between the oscillating traveling wave components at different ports; The time delay between the oscillating traveling wave components at different ports is determined based on the peak value of the cross-correlation function. The order in which the oscillating traveling wave components propagate is determined by the sign of the time delay.

6. The method for locating the oscillation source in a flexible DC transmission system according to claim 5, characterized in that, For a two-port flexible DC transmission system, the cross-correlation function between the oscillating traveling wave components at different ports is calculated using the following formula: In the formula, This represents the cross-correlation value between the oscillating traveling wave components of the first port and the second port; This represents the oscillating traveling wave component of the first port after time shift; This represents the oscillating traveling wave component at the second port that has not undergone time shift; t This represents the time-integral variable, which changes from 0 to [value missing] during the integration process. ; Indicates the total length of the time window; Represents a time delay variable; The time delay variable corresponding to the maximum value of the cross-correlation function Determine the time delay, and determine the order of propagation of the oscillating traveling wave components based on the sign of the time delay.

7. The method for locating the oscillation source of a flexible DC transmission system according to claim 6, characterized in that, The step of determining the port where the oscillating traveling wave component arrives first as the oscillation source based on the difference in propagation time delay includes: If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, the corresponding time delay is negative. Then it is determined that the oscillating traveling wave component of the first port leads the second port, and the oscillation source is located on the first port side. If the cross-correlation function between the oscillating traveling wave components of the first port and the second port reaches its maximum value, the corresponding time delay is positive. Then, it is determined that the oscillating traveling wave component of the second port leads the first port, and the oscillation source is located on the second port side.

8. A oscillation source positioning system for a flexible DC transmission system, characterized in that, include: The oscillation frequency determination module is used to measure the voltage waveforms at each port of the flexible DC transmission system and perform frequency domain analysis to obtain the oscillation frequency of the flexible DC transmission system when oscillation occurs; to perform fast Fourier transform or power spectrum analysis on the voltage waveforms at each port of the flexible DC transmission system to obtain the signal spectrum of each port; and to determine the oscillation frequency of each port based on the signal spectrum of each port. The oscillating traveling wave component extraction module is used to extract the oscillating traveling wave components of each port corresponding to the oscillation frequency from the voltage waveforms of each port of the flexible DC transmission system. Specifically, the voltage waveforms of each port are decomposed in the frequency domain to obtain voltage decomposed waveforms of different frequencies. Frequency domain analysis is performed on each voltage decomposed waveform to select the voltage decomposed waveforms with the same frequency as the oscillation frequency as the oscillating traveling wave components of the corresponding port. The time delay analysis module is used to analyze the differences in propagation time delay of the oscillating traveling wave components at each port in the flexible DC transmission system. The oscillation source location module is used to determine the port where the oscillating traveling wave component arrives first as the oscillation source based on the difference in propagation time delay.

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