A method and device for sub / super synchronous resonance identification and protection based on capacitor impedance characteristics

Abstract

The application provides a sub / super synchronous resonance identification method based on capacitor impedance characteristics, and is characterized in that at least comprises: collecting time domain discrete signals of capacitor branch current waveform and time domain signals of voltage waveform of a power supply bus in the same period; performing sliding window discrete Fourier transform to obtain corresponding fundamental voltage effective value and fundamental current effective value; calculating equivalent fundamental impedance; performing sliding window discrete Fourier transform again to obtain frequency spectrum distribution of the fundamental impedance array, and calculating to obtain the kurtosis coefficient of the frequency spectrum of the fundamental impedance; comparing with a preset judgment threshold to identify whether sub / super synchronous resonance occurs. The application also discloses corresponding protection methods and devices. By implementing the application, the accurate identification and protection of sub / super synchronous resonance in a power electronic distribution system are solved, and the effectiveness of sub / super synchronous resonance identification and prevention is improved.

Description

Technical Field

[0001] This invention relates to the field of broadband resonance suppression and protection in novel power distribution systems, and in particular to a method and apparatus for identifying and protecting subsynchronous / supersynchronous resonances based on capacitor impedance characteristics. Background Technology

[0002] In the context of new power system construction, the "dual-high" characteristics (high proportion of renewable energy and high proportion of power electronic equipment) of distribution systems are becoming increasingly prominent. The port dynamic characteristics of power electronic equipment differ significantly from those of traditional electromagnetic equipment, and the dynamic behavior between power electronic devices exhibits wide-frequency-domain interaction characteristics, leading to frequent secondary / supersynchronous resonance problems in power-electronic distribution systems. Secondary / supersynchronous resonance, through transmission, diffusion, and coupling, has a significant impact on the safety, stability, and economic operation of distribution systems, causing, for example, grid voltage fluctuations and excessive flicker, motor vibration, equipment protection activation, controller burnout, and production line interruptions. The occurrence of secondary / supersynchronous resonance is strongly correlated with the distribution system architecture, the number of power electronic devices, and their control parameters, exhibiting significant characteristics such as sporadic occurrence, variability, and uncertainty. Mainstream methods for suppressing secondary / supersynchronous resonance based on the port impedance reshaping of power electronic devices are difficult to achieve effective predictive control, with limited preventative effects, greatly increasing the difficulty of managing secondary / supersynchronous resonance. Therefore, how to quickly and accurately identify and protect against secondary / supersynchronous resonance is a new approach to solving this type of problem and a backup protection after impedance reshaping methods fail.

[0003] Currently, capacitor-based resonance protection primarily uses harmonic voltage or current in the capacitor branch as the protection criterion. For example, invention patent CN 110794291A uses harmonic current in the charging pile filter capacitor branch as the criterion, while also considering the influence of high-frequency harmonic current attraction effect, and performs weighted processing when the high-frequency harmonics are equivalent to the effective value of the fundamental current. This patent is mainly a protection strategy based on the safe operation of capacitors, but it is difficult to accurately determine whether the system has resonance. Protection against low-frequency oscillations in the system mainly uses the change trajectory of low-frequency oscillation power as the judgment basis. For example, invention patent CN 101237148A uses the change trajectory of active power in the tie line to detect low-frequency oscillations. When the difference between the power of the tie line at the sampling time and the average value of the previous 10 seconds is greater than the starting power threshold setting, and the set oscillation period, oscillation amplitude, and other conditions are met, the protection action is triggered. However, with the continuous increase in the penetration rate of distributed photovoltaics, the power fluctuation in the distribution system is increasing, and using power indicators as the resonance / oscillation criterion may lead to misjudgment.

[0004] Therefore, how to accurately identify and protect subsynchronous / supersynchronous resonances is an urgent problem to be solved. Summary of the Invention

[0005] The technical problem to be solved by this invention is to propose a method and device for identifying and protecting subsynchronous / supersynchronous resonances based on capacitor impedance characteristics, which solves the technical problem of accurate identification and protection of subsynchronous / supersynchronous resonances in power electronic distribution systems and improves the effectiveness of subsynchronous / supersynchronous resonance identification and prevention.

[0006] The technical solution adopted in this invention is to provide a subsynchronous / supersynchronous resonance identification method based on capacitor impedance characteristics, which includes at least the following steps:

[0007] Step S10: Real-time acquisition of the time-domain discrete signal of the capacitor branch current waveform and the time-domain signal of its power supply bus voltage waveform within the same time period;

[0008] Step S11: Perform a sliding window discrete Fourier transform on the collected voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS value and fundamental current RMS value of the voltage and current waveform time-domain discrete signals.

[0009] Step S12: Calculate the equivalent fundamental impedance based on the calculated effective values ​​of the fundamental voltage and fundamental current.

[0010] Step S13: Perform a sliding window discrete Fourier transform on the calculated fundamental impedance array again to obtain the spectral distribution of the fundamental impedance array, and calculate the kurtosis coefficient of the fundamental impedance spectrum.

[0011] Step S14: Compare the kurtosis coefficient calculation result with the preset judgment threshold to identify whether a subsynchronous / supersynchronous resonance has occurred.

[0012] Preferably, step S10 further includes:

[0013] On the secondary side of the capacitor branch current transformer and the secondary side of the capacitor power supply bus voltage transformer, the time-domain discrete signal i(k) of the capacitor branch current waveform and the time-domain discrete signal u(k) of the voltage waveform are sampled synchronously in real time, where: k is the number of the sampled voltage and current waveform time-domain discrete signal.

[0014] Preferably, step S11 further includes:

[0015] The collected voltage and current waveform time-domain discrete signals are subjected to a sliding window discrete Fourier transform to obtain the effective value of the fundamental frequency wave of the voltage and current waveform time-domain discrete signals. The window width of the Fourier transform is taken as 1 cycle, and the calculation formula is as follows:

[0016]

[0017]

[0018] Where U1 is the effective value of the fundamental voltage in the frequency domain; I1 is the effective value of the fundamental current in the frequency domain; N is the number of points of the time-domain discrete signal of the voltage or current waveform within one cycle; n is the number of the time-domain discrete signal of the waveform within the corresponding cycle; m is the number of the effective value of the fundamental wave in the frequency domain; j is the imaginary unit; and e is the natural constant.

[0019] Preferably, step S12 further includes:

[0020] Based on the calculated effective values ​​of the fundamental voltage and fundamental current, the equivalent fundamental impedance is calculated using the following formula:

[0021]

[0022] Where Z1 is the calculated equivalent fundamental impedance of the capacitor branch.

[0023] Preferably, step S13 further includes:

[0024] The calculated fundamental impedance array is then subjected to a sliding window discrete Fourier transform again to obtain the spectral distribution of the fundamental impedance array. The kurtosis coefficient of the fundamental impedance spectrum is then calculated, and the formula for calculating the kurtosis coefficient of the fundamental impedance spectral distribution is as follows:

[0025]

[0026] Where M is the number of data points in the fundamental impedance array. This represents the mean of the Z1 sample data.

[0027] Preferably, step S14 further includes:

[0028] Set the threshold for judging kurtosis coefficient as α. k If the calculated kurtosis coefficient is greater than or equal to the set judgment threshold, it can be determined that a primary / supersynchronous resonance has occurred; if the calculated kurtosis coefficient is less than the set judgment threshold, it can be determined that a primary / supersynchronous resonance has not occurred.

[0029] Accordingly, another aspect of the present invention also provides a subsynchronous / supersynchronous resonance protection method based on capacitor impedance characteristics, which further includes:

[0030] The aforementioned method for identifying subsynchronous / supersynchronous resonances based on capacitor impedance characteristics is used to identify subsynchronous / supersynchronous resonances in the capacitor branch.

[0031] When a secondary / supersynchronous resonance is detected in the capacitor branch, a secondary / supersynchronous resonance protection signal is sent to the capacitor switching switch to disconnect the capacitor and achieve secondary / supersynchronous resonance protection.

[0032] Accordingly, in another aspect, the present invention also provides a subsynchronous / supersynchronous resonance identification device, which includes at least: a measurement calculation module and a judgment module, wherein:

[0033] The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module.

[0034] The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred.

[0035] In another aspect, the present invention provides a subsynchronous / supersynchronous resonance protection device, which includes at least: a measurement and calculation module, a judgment module, and an execution module, wherein:

[0036] The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module.

[0037] The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred, and the judgment result is transmitted to the execution module.

[0038] The execution module is used to control the switching state of the capacitor switching switch. When it receives the subsynchronous / supersynchronous resonance signal transmitted from the judgment module, it sends a command to the capacitor switching switch to control the switching element to open. The input terminal of the execution module is connected to the output terminal of the judgment module, and its output terminal is connected to the capacitor switching switch.

[0039] Implementing the embodiments of the present invention has the following beneficial effects:

[0040] This invention proposes a method and device for identifying and protecting subsynchronous / supersynchronous resonances based on capacitor impedance characteristics. By utilizing the orthogonal characteristics of integer harmonics and the fundamental frequency within one power frequency cycle, the equivalent fundamental impedance of the capacitor branch calculated using a discrete Fourier transform with a single-cycle window width can effectively eliminate the influence of integer harmonics of the power grid on the subsynchronous / supersynchronous resonance detection results.

[0041] In this embodiment of the invention, capacitor impedance is used as the resonance criterion, which overcomes the influence of traditional grid voltage, current or power fluctuations on the subsynchronous / supersynchronous resonance detection results, making the detection results more reliable and accurate. In addition, the kurtosis system of the fundamental impedance spectrum distribution is used as the judgment index, which can avoid the influence of impedance changes during capacitor switching on the resonance judgment and effectively avoid malfunction of the protection device.

[0042] In this embodiment of the invention, by detecting and identifying subsynchronous / supersynchronous resonance in the capacitor branch, when subsynchronous / supersynchronous resonance is detected, the power grid architecture and parameters can be changed by cutting off the capacitor branch, thereby disrupting the subsynchronous / supersynchronous resonance conditions and achieving the effect of suppressing subsynchronous / supersynchronous resonance. Attached Figure Description

[0043] 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.

[0044] Figure 1 A flowchart illustrating an embodiment of a subsynchronous / supersynchronous resonance protection method based on capacitor impedance characteristics provided by the present invention;

[0045] Figure 2 for Figure 1 Application environment diagram;

[0046] Figure 3 This is a schematic diagram of the sliding window discrete Fourier transform involved in the present invention;

[0047] Figure 4 This is a comparison chart of the waveform trends of capacitor branch current and power supply bus voltage during subsynchronous / supersynchronous resonance, as described in an example of the present invention.

[0048] Figure 5 This is a comparison chart of the trends of capacitor branch current and fundamental effective value of power supply bus voltage when subsynchronous / supersynchronous resonance occurs in an example of the present invention;

[0049] Figure 6 This is a comparison chart showing the variation trend of the equivalent fundamental impedance and its fluctuation in the capacitor branch when subsynchronous / supersynchronous resonance occurs in an example of the present invention;

[0050] Figure 7 This is a spectral distribution diagram of the equivalent fundamental impedance fluctuation of the capacitor branch and its kurtosis coefficient when a subsynchronous / supersynchronous resonance occurs in an example of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0052] like Figure 1 The diagram shown illustrates the main flow of an embodiment of a subsynchronous / supersynchronous resonance identification method based on capacitor impedance characteristics provided by the present invention. (In conjunction with...) Figures 2 to 7 As shown, in this embodiment, the method includes at least the following steps:

[0053] Step S10: Real-time acquisition of the time-domain discrete signal of the capacitor branch current waveform and the time-domain signal of its power supply bus voltage waveform within the same time period;

[0054] In a specific example, step S10 further includes:

[0055] On the secondary side of the capacitor branch current transformer and the secondary side of the capacitor power supply bus voltage transformer, the time-domain discrete signal i(k) of the capacitor branch current waveform and the time-domain discrete signal u(k) of the voltage waveform are sampled synchronously in real time, where: k is the number of the sampled voltage and current waveform time-domain discrete signal, such as... Figure 2 As shown.

[0056] To ensure computational accuracy, the sampling rate f of the discrete-time signal is... s Generally, it should be ≥600Hz.

[0057] To utilize the Fast Fourier Transform (FFT) algorithm, the number of sampling points per cycle of the discrete-time signal can preferably be an integer multiple of 2, such as 16, 32, 64, 128, or 256 points, corresponding to sampling rates of 800Hz, 1600Hz, 3200Hz, 6400Hz, and 12800Hz, respectively. To adapt to existing microcomputer-based protection devices, the sampling rate of the discrete-time signal can also be adopted from commonly used microcomputer-based protection devices: 600Hz, 1000Hz, or 1200Hz, corresponding to 12, 20, or 24 sampling points per cycle, respectively. However, the Discrete Fourier Transform (DFT) algorithm should be used. Both the DFT and FFT are common knowledge in this field and will not be elaborated further.

[0058] Step S11: Perform a sliding window discrete Fourier transform on the collected voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS value and fundamental current RMS value of the voltage and current waveform time-domain discrete signals.

[0059] In a specific example, step S11 further includes:

[0060] The collected voltage and current waveform time-domain discrete signals are subjected to a sliding window discrete Fourier transform to obtain the effective value of the fundamental frequency wave of the voltage and current waveform time-domain discrete signals. The window width of the Fourier transform is taken as 1 cycle, and the calculation formula is as follows:

[0061]

[0062]

[0063] Where U1 is the effective value of the fundamental voltage in the frequency domain; I1 is the effective value of the fundamental current in the frequency domain; N is the number of points of the time-domain discrete signal of the voltage or current waveform within one cycle; n is the number of the time-domain discrete signal of the waveform within the corresponding cycle (the value range is 0 to N-1); m is the number of the effective value of the fundamental frequency (corresponding to the number of analysis); j is the imaginary unit; and e is the natural constant.

[0064] The sliding window step size for the sliding window discrete Fourier transform can be determined according to the actual analysis requirements and sampling frequency. Generally, C cycles can be selected, where C can be 1 / 6, 1 / 5, 1 / 4, 1 / 2 cycles, etc. However, it must be ensured that the number of discrete points s corresponding to the step size is a positive integer, i.e., s = N*C ∈ N. + For example, if the number of sampling points per cycle N = 64, the sliding step size C can be selected as 1 / 4 cycle or 1 / 2 cycle, with corresponding moving step sizes of s = 16 or s = 32 respectively.

[0065] Step S12: Calculate the equivalent fundamental impedance based on the calculated effective values ​​of the fundamental voltage and fundamental current.

[0066] In a specific example, step S12 further includes:

[0067] Based on the calculated effective values ​​of the fundamental voltage and fundamental current, the equivalent fundamental impedance is calculated using the following formula:

[0068]

[0069] Where Z1 is the calculated equivalent fundamental impedance of the capacitor branch.

[0070] Step S13: Perform a sliding window discrete Fourier transform on the calculated fundamental impedance array again to obtain the spectral distribution of the fundamental impedance array, and calculate the kurtosis coefficient of the fundamental impedance spectrum.

[0071] In a specific example, step S13 further includes:

[0072] The calculated fundamental impedance array is then subjected to a sliding window discrete Fourier transform again to obtain the spectral distribution of the fundamental impedance array. The kurtosis coefficient of the fundamental impedance spectrum is then calculated, and the formula for calculating the kurtosis coefficient of the fundamental impedance spectral distribution is as follows:

[0073]

[0074] Where M is the number of data points in the fundamental impedance array. This represents the mean of the Z1 sample data.

[0075] To better observe the spectral distribution characteristics of impedance fluctuations, the DC component should be removed when displaying the spectrum. This method is common knowledge and will not be elaborated further.

[0076] When performing a sliding window Fourier transform on the fundamental impedance array, to ensure the computational bandwidth, spectral resolution, and identification speed of subsynchronous / supersynchronous resonances, requirements should be placed on the sliding window width and the number of sliding window movement points, as follows:

[0077] Frequency resolution f r With sampling period T a The relation is f r =1 / T a , where f r The unit is Hz, T a The unit is seconds. To ensure frequency resolution, the sampling period of the impedance array for each calculation should be ≥1 second, then the corresponding frequency resolution is ≤1Hz;

[0078] To ensure rapid identification of subsynchronous / supersynchronous resonances, the number of points the sliding window moves should be minimized.

[0079] The subsynchronous / supersynchronous frequency range is generally between 2Hz and 100Hz, and the frequency difference between it and the 50Hz power frequency after beating is less than 50Hz. Therefore, the maximum analysis frequency for the fundamental impedance array satisfies f max ≥50Hz corresponds to a sampling rate f of the impedance array. s_z ≥2f max ≥100Hz.

[0080] Step S14: Compare the kurtosis coefficient calculation result with the preset judgment threshold to identify whether a subsynchronous / supersynchronous resonance has occurred.

[0081] In a specific example, step S14 further includes:

[0082] Set the threshold for judging kurtosis coefficient as α. kIf the calculated kurtosis coefficient is greater than or equal to the set judgment threshold, it can be determined that a primary / supersynchronous resonance has occurred; if the calculated kurtosis coefficient is less than the set judgment threshold, it can be determined that a primary / supersynchronous resonance has not occurred.

[0083] More specifically, when the system does not experience subsynchronous / supersynchronous resonance, the calculated fundamental impedance is the fundamental impedance of the capacitor branch. Due to the existence of measurement errors, the obtained fundamental impedance fluctuates randomly around the actual fundamental impedance of the capacitor branch, and the obtained fundamental impedance spectrum is uniformly distributed with a corresponding kurtosis system < 3.

[0084] When the system experiences subsynchronous / supersynchronous resonance, due to the use of single-cycle Fourier transform, the frequency components of the subsynchronous / supersynchronous resonance leak, causing deviations in the calculation results of the fundamental effective value. Consequently, the calculated fundamental impedance fluctuates periodically around a certain frequency, and its spectrum has a dominant frequency of fluctuation within the 50Hz frequency range. The fluctuation frequency is the difference frequency between the subsynchronous / supersynchronous resonance frequency and the power frequency, and the corresponding kurtosis coefficient is much greater than 3.

[0085] To reduce misjudgment of subsynchronous / supersynchronous resonance, the judgment threshold for kurtosis coefficient can be appropriately increased; generally, α can be set. k =5~10.

[0086] Accordingly, another aspect of the present invention also provides a subsynchronous / supersynchronous resonance protection method based on capacitor impedance characteristics, which further includes:

[0087] The aforementioned method for identifying subsynchronous / supersynchronous resonances based on capacitor impedance characteristics is used to identify subsynchronous / supersynchronous resonances in the capacitor branch.

[0088] When a secondary / supersynchronous resonance is detected in the capacitor branch, a secondary / supersynchronous resonance protection signal is sent to the capacitor switching switch to disconnect the capacitor and achieve secondary / supersynchronous resonance protection.

[0089] To better illustrate the present invention, a specific embodiment is provided below for detailed description:

[0090] A substation has a 10kV busbar connected to an inductive load and a reactive power compensation capacitor bank. The total three-phase active power of the inductive load is 5MW, and the total three-phase inductive reactive power is 2Mvar. The total three-phase compensation capacity of the capacitor bank is 2Mvar, the loss is 0.5%, and the capacitive reactance is 50Ω. The grid frequency is 50Hz. A 5% 62.5Hz interharmonic voltage is applied to the 10kV power supply busbar. The current waveforms sampled at the power supply busbar and capacitor branch of the capacitor bank by the subsynchronous / supersynchronous resonance identification and protection device are as follows: Figure 4As shown, the sampling rate is 3200Hz, meaning 64 points are sampled per cycle. A sliding-window discrete Fourier transform is used, with a window width of 1 cycle and a window overlap of 0.5 cycles, resulting in a step size of 32 points. The trends of the fundamental voltage and fundamental current are shown below. Figure 5 As shown, due to spectral leakage, the calculated fundamental voltage and current fluctuate periodically around their true RMS values. The fundamental impedance is obtained from the calculated fundamental voltage and current, as shown below. Figure 6 As shown, due to spectral leakage, the calculated fundamental impedance also fluctuates periodically around the true value (50Ω). To better observe the spectral distribution of the fundamental impedance fluctuation component, the DC component of the fundamental impedance array is removed, and only its fluctuation component is subjected to Discrete Fourier Transform. The sampling period is 1 second, which corresponds to a frequency resolution of 1Hz. To ensure that the spectrum up to 50Hz can be analyzed, 100 fundamental impedance values ​​need to be sampled within the 1-second sampling period, that is, 2 fundamental impedance values ​​need to be sampled within each power frequency cycle. Therefore, a sliding window of 0.5 cycles is selected when calculating the effective values ​​of the fundamental voltage and current. Through Fourier analysis of the fundamental impedance array, the spectral distribution within 50Hz is obtained as follows: Figure 7 As shown, the calculated kurtosis coefficient is 18.3. The kurtosis coefficient judgment threshold is set to 10. If the calculated kurtosis coefficient is greater than the set threshold, it can be determined that the system has experienced subsynchronous / supersynchronous resonance. The execution module sends a disconnection command to the capacitor switching switch to disconnect the capacitor from the power grid.

[0091] It is understood that, in this invention, since integer harmonics and the fundamental frequency are orthogonal within one power frequency cycle, the equivalent fundamental impedance of the capacitor branch calculated using the discrete Fourier transform with a single-cycle window width can effectively eliminate the influence of the power grid's integer harmonics on the subsynchronous / supersynchronous resonance detection results.

[0092] Because the grid voltage exhibits random fluctuations, the corresponding capacitor branch current also fluctuates randomly, but the capacitor branch impedance remains constant. Therefore, using capacitor impedance as the resonance criterion overcomes the influence of traditional grid voltage, current, or power fluctuations on the subsynchronous / supersynchronous resonance detection results, making the detection results more reliable and accurate. In addition, using the kurtosis system of the fundamental impedance spectrum distribution as the judgment index can avoid the influence of impedance changes during capacitor switching on the resonance judgment, effectively preventing malfunctions of protection devices.

[0093] Subsynchronous / supersynchronous resonance in power distribution systems is strongly correlated with the power distribution system architecture, the number of power electronic devices, and their control parameters. By detecting and identifying subsynchronous / supersynchronous resonance in capacitor branches, when subsynchronous / supersynchronous resonance is detected, the power grid architecture and parameters can be changed by disconnecting the capacitor branches, thereby disrupting the subsynchronous / supersynchronous resonance conditions and achieving the effect of suppressing subsynchronous / supersynchronous resonance.

[0094] Accordingly, another aspect of the present invention also provides a subsynchronous / supersynchronous resonance identification device, which includes at least: a measurement calculation module and a judgment module, as can be referred to Figure 2 As shown, where:

[0095] The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module.

[0096] The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred.

[0097] In another aspect, the present invention provides a subsynchronous / supersynchronous resonance protection device, which includes at least: a measurement and calculation module, a judgment module, and an execution module, as described above. Figure 2 As shown, where:

[0098] The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module.

[0099] The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred, and the judgment result is transmitted to the execution module.

[0100] The execution module is used to control the switching state of the capacitor switching switch. When it receives the subsynchronous / supersynchronous resonance signal transmitted from the judgment module, it sends a command to the capacitor switching switch to control the switching element to open. The input terminal of the execution module is connected to the output terminal of the judgment module, and its output terminal is connected to the capacitor switching switch.

[0101] For more details, please refer to and combine with the above. Figures 1 to 7 The details of this will not be elaborated here.

[0102] Implementing the embodiments of the present invention has the following beneficial effects:

[0103] This invention proposes a method and device for identifying and protecting subsynchronous / supersynchronous resonances based on capacitor impedance characteristics. By utilizing the orthogonal characteristics of integer harmonics and the fundamental frequency within one power frequency cycle, the equivalent fundamental impedance of the capacitor branch calculated using a discrete Fourier transform with a single-cycle window width can effectively eliminate the influence of integer harmonics of the power grid on the subsynchronous / supersynchronous resonance detection results.

[0104] In this embodiment of the invention, capacitor impedance is used as the resonance criterion, which overcomes the influence of traditional grid voltage, current or power fluctuations on the subsynchronous / supersynchronous resonance detection results, making the detection results more reliable and accurate. In addition, the kurtosis system of the fundamental impedance spectrum distribution is used as the judgment index, which can avoid the influence of impedance changes during capacitor switching on the resonance judgment and effectively avoid malfunction of the protection device.

[0105] In this embodiment of the invention, by detecting and identifying subsynchronous / supersynchronous resonance in the capacitor branch, when subsynchronous / supersynchronous resonance is detected, the power grid architecture and parameters can be changed by cutting off the capacitor branch, thereby disrupting the subsynchronous / supersynchronous resonance conditions and achieving the effect of suppressing subsynchronous / supersynchronous resonance.

[0106] 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.

[0107] 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 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 for specifying modules in one or more boxes.

[0108] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for identifying subsynchronous / supersynchronous resonances based on capacitor impedance characteristics, characterized in that, It should include at least the following steps: Step S10: Real-time acquisition of the time-domain discrete signal of the capacitor branch current waveform and the time-domain signal of its power supply bus voltage waveform within the same time period; Step S11: Perform a sliding window discrete Fourier transform on the collected voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS value and fundamental current RMS value of the voltage and current waveform time-domain discrete signals. Step S12: Calculate the equivalent fundamental impedance based on the calculated effective values ​​of the fundamental voltage and fundamental current. Step S13: Perform a sliding window discrete Fourier transform on the calculated fundamental impedance array again to obtain the spectral distribution of the fundamental impedance array, and calculate the kurtosis coefficient of the fundamental impedance spectrum. Step S14: Compare the kurtosis coefficient calculation result with the preset judgment threshold to identify whether a subsynchronous / supersynchronous resonance has occurred. Step S11 further includes: The collected voltage and current waveform time-domain discrete signals are subjected to a sliding window discrete Fourier transform to obtain the effective value of the fundamental frequency wave of the voltage and current waveform time-domain discrete signals. The window width of the Fourier transform is taken as 1 cycle, and the calculation formula is as follows: Where U1 is the effective value of the fundamental voltage in the frequency domain; I1 is the effective value of the fundamental current in the frequency domain; N is the number of points of the time-domain discrete signal of the voltage or current waveform within one cycle; n is the number of the time-domain discrete signal of the waveform within the corresponding cycle; m is the number of the effective value of the fundamental wave in the frequency domain; j is the imaginary unit; and e is the natural constant.

2. The method as described in claim 1, characterized in that, Step S10 further includes: On the secondary side of the capacitor branch current transformer and the secondary side of the capacitor power supply bus voltage transformer, the time-domain discrete signal i(k) of the capacitor branch current waveform and the time-domain discrete signal u(k) of the voltage waveform are sampled synchronously in real time, where: k is the number of the sampled voltage and current waveform time-domain discrete signal.

3. The method as described in claim 2, characterized in that, Step S12 further includes: Based on the calculated effective values ​​of the fundamental voltage and fundamental current, the equivalent fundamental impedance is calculated using the following formula: in, The equivalent fundamental impedance of the capacitor branch is calculated.

4. The method as described in claim 3, characterized in that, Step S13 further includes: The calculated fundamental impedance array is then subjected to a sliding window discrete Fourier transform again to obtain the spectral distribution of the fundamental impedance array. The kurtosis coefficient of the fundamental impedance spectrum is then calculated, and the formula for calculating the kurtosis coefficient of the fundamental impedance spectral distribution is as follows: Where M is the number of data points in the fundamental impedance array. for The mean of the sample data.

5. The method as described in claim 4, characterized in that, Step S14 further includes: Set the threshold for judging kurtosis as follows: If the calculated kurtosis coefficient is greater than or equal to the set judgment threshold, it can be determined that a primary / supersynchronous resonance has occurred; if the calculated kurtosis coefficient is less than the set judgment threshold, it can be determined that a primary / supersynchronous resonance has not occurred.

6. A subsynchronous / supersynchronous resonance protection method based on capacitor impedance characteristics, characterized in that, Further includes: The capacitor branch is identified by the subsynchronous / supersynchronous resonance identification method based on capacitor impedance characteristics as described in any one of claims 1 to 5. When a secondary / supersynchronous resonance is detected in the capacitor branch, a secondary / supersynchronous resonance protection signal is sent to the capacitor switching switch to disconnect the capacitor and achieve secondary / supersynchronous resonance protection.

7. A subsynchronous / supersynchronous resonance identification device, characterized in that, It should include at least: a measurement and calculation module and a judgment module, wherein: The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module. The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred. The measurement and calculation module detects the capacitor branch current and the capacitor power supply bus voltage in the following manner, and calculates the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch: A sliding window discrete Fourier transform is performed on the collected voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS value and fundamental current RMS value of the voltage and current waveform time-domain discrete signals; Calculate the equivalent fundamental impedance based on the calculated effective values ​​of the fundamental voltage and fundamental current. The calculated fundamental impedance array is subjected to a sliding window discrete Fourier transform again to obtain the spectral distribution of the fundamental impedance array, and the kurtosis coefficient of the fundamental impedance spectrum is calculated. Specifically, performing a sliding-window discrete Fourier transform on the acquired voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS values ​​and fundamental current RMS values ​​of the voltage and current waveform time-domain discrete signals is as follows: The collected voltage and current waveform time-domain discrete signals are subjected to a sliding window discrete Fourier transform to obtain the effective value of the fundamental frequency wave of the voltage and current waveform time-domain discrete signals. The window width of the Fourier transform is taken as 1 cycle, and the calculation formula is as follows: Where U1 is the effective value of the fundamental voltage in the frequency domain; I1 is the effective value of the fundamental current in the frequency domain; N is the number of points of the time-domain discrete signal of the voltage or current waveform within one cycle; n is the number of the time-domain discrete signal of the waveform within the corresponding cycle; m is the number of the effective value of the fundamental wave in the frequency domain; j is the imaginary unit; and e is the natural constant.

8. A subsynchronous / supersynchronous resonance protection device, characterized in that, It includes at least: a measurement calculation module, a judgment module, and an execution module, wherein: The measurement and calculation module is used to detect the capacitor branch current and the capacitor power supply bus voltage, calculate the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch, and transmit the obtained kurtosis coefficient to the judgment module; the input terminal of the measurement and calculation module is respectively connected to the secondary signals of the capacitor power supply bus voltage transformer and the capacitor branch current transformer, and its output terminal is connected to the input terminal of the judgment module. The judgment module is used to receive the kurtosis coefficient calculation result from the measurement and calculation module and compare it with the set kurtosis coefficient judgment threshold. When the kurtosis coefficient calculation result is greater than or equal to the set judgment threshold, it is determined that a subsynchronous / supersynchronous resonance has occurred, and the judgment result is transmitted to the execution module. The execution module is used to control the switching state of the capacitor switching switch. When it receives the subsynchronous / supersynchronous resonance signal transmitted from the judgment module, it sends a command to the capacitor switching switch to control the switching element to open. The input terminal of the execution module is connected to the output terminal of the judgment module, and its output terminal is connected to the capacitor switching switch. The measurement and calculation module detects the capacitor branch current and the capacitor power supply bus voltage in the following manner, and calculates the kurtosis coefficient of the fundamental impedance spectrum distribution of the capacitor branch: A sliding window discrete Fourier transform is performed on the collected voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS value and fundamental current RMS value of the voltage and current waveform time-domain discrete signals; Calculate the equivalent fundamental impedance based on the calculated effective values ​​of the fundamental voltage and fundamental current. The calculated fundamental impedance array is subjected to a sliding window discrete Fourier transform again to obtain the spectral distribution of the fundamental impedance array, and the kurtosis coefficient of the fundamental impedance spectrum is calculated. Specifically, performing a sliding-window discrete Fourier transform on the acquired voltage and current waveform time-domain discrete signals to obtain the corresponding fundamental voltage RMS values ​​and fundamental current RMS values ​​of the voltage and current waveform time-domain discrete signals is as follows: The collected voltage and current waveform time-domain discrete signals are subjected to a sliding window discrete Fourier transform to obtain the effective value of the fundamental frequency wave of the voltage and current waveform time-domain discrete signals. The window width of the Fourier transform is taken as 1 cycle, and the calculation formula is as follows: Where U1 is the effective value of the fundamental voltage in the frequency domain; I1 is the effective value of the fundamental current in the frequency domain; N is the number of points of the time-domain discrete signal of the voltage or current waveform within one cycle; n is the number of the time-domain discrete signal of the waveform within the corresponding cycle; m is the number of the effective value of the fundamental wave in the frequency domain; j is the imaginary unit; and e is the natural constant.

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