A subsynchronous oscillation control method based on real-time oscillation power ratio

Abstract

The present invention discloses a subsynchronous oscillation control method based on real-time oscillation power ratio, including: obtaining the instantaneous values ​​of three-phase voltage and current of each line element connected to the offshore wind power booster station and calculating the three-phase instantaneous power; performing frequency domain transformation on the three-phase instantaneous power to obtain the dominant oscillation modal frequency of each line element and the power frequency power and dominant oscillation modal oscillation power under the condition of frequency leakage; obtaining a set of line elements participating in the subsynchronous oscillation; calculating the real-time oscillation power ratio of each line element participating in the subsynchronous oscillation; sorting the line elements in the set according to the real-time oscillation power ratio, and performing graded excision on the line elements in the set in combination with multiple rounds of graded excision time constants to achieve subsynchronous oscillation control. The present invention can automatically identify the dominant oscillation modal frequency in the entire offshore wind power regional power grid and graded excision of the subsynchronous oscillation under the dominant oscillation modal frequency, and quickly calm the subsynchronous oscillation in the regional power grid.

Description

Technical Field

[0001] The present invention belongs to the technical field of subsynchronous oscillation control of electric power systems, and in particular relates to a subsynchronous oscillation control method based on real-time oscillation power ratio. Background Art

[0002] At present, with the deepening of my country's energy transformation process, the scale of new energy development and utilization has achieved unprecedented development. Offshore wind power is an important support for my country's energy transformation in the new era. In recent years, with the rapid development of deep-sea wind power development and utilization, offshore wind power has entered a stage of large-scale and commercial development. my country's offshore wind power development has made steady progress: the average annual new grid-connected scale from 2016 to 2018 was about 1,000MW, the new grid-connected scale in 2019 was 1,980MW, and the new grid-connected scale in 2020 was 3,060MW. By the end of 2020, the national offshore wind power grid-connected installed capacity reached 8,990MW. By optimizing the offshore wind power layout and carrying out deep-sea offshore wind power planning, offshore large-scale development and deep-sea demonstration development have been promoted, and offshore wind power base clusters have been built. The scale of offshore wind power development plans issued by various regions has reached 80 million kilowatts, and the cumulative installed capacity will exceed 200 million kilowatts by 2030.

[0003] In the early stage of offshore wind power development, large-scale offshore wind power grid-connected systems were mostly nearshore wind power that used AC transmission to connect to the onshore power grid. As the site selection of offshore wind farms gradually develops towards deep-sea areas, the installed capacity of a single wind turbine has further increased. At the same time, with the development of power electronics technology and flexible DC transmission technology, flexible DC transmission has been more widely used in large-scale offshore wind power grid-connected systems. In large-scale offshore flexible DC transmission grid-connected systems, the control characteristics such as wind turbine models and control parameters are obviously heterogeneous, and the control coupling between wind turbine clusters and wind turbine clusters and flexible DC transmission is complex. Under the interaction of complex multi-time scale control, wide-band oscillations may be caused, among which sub- / super-synchronous frequency band oscillations are the most prominent.

[0004] In 2014, the flexible direct current project of Shanghai Nanhui Wind Farm experienced oscillation when the wind farm was at high output, causing the converter to trip; the multi-terminal flexible direct current systems in Nan'ao, Guangdong, Zhoushan and Zhangbei, Zhejiang all experienced oscillation problems during commissioning and operation. When subsynchronous oscillation occurs, the AC voltage and DC voltage remain basically stable, but there are obvious subsynchronous frequency components in the AC current and DC current, which affects the commissioning and operation of the project. With the increasing scale of offshore wind power, the application of flexible direct current transmission projects in offshore wind power has been widely promoted and applied. The study of the mechanism of subsynchronous oscillation of large-scale offshore wind power grid-connected systems is currently a hot topic. At the same time, after the subsynchronous oscillation occurs, how to monitor the oscillation in real time through automatic control devices and quickly identify the source of disturbance and control the oscillation is also an urgent problem to be solved.

[0005] The subsynchronous oscillation of large-scale offshore wind power grid-connected systems is related to the grid-connected wind power clusters and flexible DC control. The electrical control equipment layout design of the offshore wind power transmission system includes multiple points such as offshore wind farms, offshore booster substations, and onshore control centers. It is necessary to study effective hierarchical removal methods for the subsynchronous oscillations of offshore wind power grid-connected systems. Summary of the invention

[0006] In order to solve the deficiencies in the prior art, the present invention provides a subsynchronous oscillation control method based on real-time oscillation power ratio, which is suitable for subsynchronous oscillation control of large-scale offshore wind power grid-connected systems. When subsynchronous oscillation occurs in the offshore wind power grid-connected system, the oscillation power ratios of the submarine cables of multiple offshore booster stations in the grid-connected area can be calculated and sorted in real time, and the oscillation disturbance source can be controlled step by step accordingly. The dominant oscillation mode frequency in the entire offshore wind power regional power grid can be automatically identified and the subsynchronous oscillation under the dominant oscillation mode frequency can be graded and removed, and the subsynchronous oscillation in the regional power grid can be quickly calmed down, ensuring the rapid tracking and calming of oscillations in the sub / super synchronous frequency bands of the offshore wind power grid-connected system, and ensuring safe, stable and reliable offshore wind power new energy transmission.

[0007] The present invention adopts the following technical solution.

[0008] A subsynchronous oscillation control method based on real-time oscillation power ratio comprises the following steps:

[0009] Step 1: Obtain the instantaneous values ​​of three-phase voltage and current of each line element connected to the offshore wind power booster station and calculate the three-phase instantaneous power;

[0010] Step 2: Perform frequency domain transformation on the three-phase instantaneous power to obtain the frequency domain amplitude spectrum of the three-phase instantaneous power, and obtain the dominant oscillation mode frequency of each line element and the power frequency power and dominant oscillation mode oscillation power considering frequency leakage according to the frequency domain amplitude spectrum;

[0011] Step 3: align the dominant oscillation mode frequencies of each line element to obtain a set of line elements participating in subsynchronous oscillation;

[0012] Step 4: Calculate the real-time oscillation power ratio of each line element participating in the subsynchronous oscillation according to the power frequency power and the oscillation power of the dominant oscillation mode;

[0013] Step 5: Sort the circuit elements in the circuit element set according to the real-time oscillation power ratio, and perform hierarchical removal of the circuit elements in the circuit element set in combination with multiple rounds of hierarchical removal time constants to achieve sub-synchronous oscillation control.

[0014] Preferably, in step 1, the three-phase voltage and three-phase current signals of each line element connected to the offshore wind power booster station are sampled at a high sampling frequency and the time series and within the buffer time are calculated, and then the instantaneous power sequence within the three-phase instantaneous power buffer time is calculated.

[0015] Preferably, the high sampling frequency is 2000 Hz and the buffering time is 1 second;

[0016] The line components include submarine collection cables, SVG branches and lines on the step-up to low-voltage side.

[0017] Preferably, in step 2, the dominant oscillation mode frequency is obtained by:

[0018] For each line element, the envelope of the spectrum line amplitude in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum is searched for extreme points, and the amplitudes of the extreme points found are sorted and compared to obtain the frequency point with the largest amplitude as the dominant oscillation mode frequency of the corresponding line element.

[0019] Preferably, extreme points are searched for the envelope of the spectrum line amplitudes in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum, and in the process of sorting and comparing the amplitudes of the extreme points found, a threshold is set, and spectrum line amplitudes greater than the threshold are regarded as possible oscillation frequency points and participate in the sorting and comparison of extreme point amplitudes, while spectrum line amplitudes less than or equal to the threshold are not subject to subsequent sorting and comparison.

[0020] Preferably, the threshold is set according to the power frequency power, and is set to 1% of the power frequency power.

[0021] Preferably, in step 2, the power frequency power under the condition of frequency leakage is the sum of the three-phase instantaneous power amplitudes within the power frequency and its adjacent frequency intervals in the three-phase instantaneous power frequency domain amplitude spectrum.

[0022] Preferably, in step 2, the dominant oscillation mode oscillation power considering frequency leakage is the sum of the three-phase instantaneous power amplitudes within the dominant oscillation mode frequency and its adjacent frequency interval in the three-phase instantaneous power frequency domain amplitude spectrum.

[0023] Preferably, the adjacent frequencies are about 0.5 Hz.

[0024] Preferably, in step 3, within the sub-synchronous frequency band and the super-synchronous frequency band, the frequency band is subdivided with an integer frequency point as the center frequency and a 1 Hz range of 0.5 Hz around the center frequency as a frequency interval, and the subdivided frequency bands where the spectrum lines of the dominant oscillation mode amplitudes of the three-phase instantaneous power frequency domain of all line elements are located are counted, and the center frequency of the subdivided frequency band with the largest number of line elements falling into the subdivided frequency bands of the sub-synchronous frequency band and the super-synchronous frequency band is selected as the dominant oscillation mode frequency of this disturbance, and the line elements falling into the corresponding subdivided frequency band are the line elements that oscillate at the dominant oscillation mode frequency of this disturbance among the line elements connected to the offshore wind power booster station, forming a set of line elements of sub-synchronous oscillation.

[0025] Preferably, in step 5, the sorting results of the circuit elements are combined with multiple rounds of graded excision time constants to perform graded excision on the circuit elements in the circuit element set in the following manner: after the oscillation occurs, the timing starts, n rounds are preset, a fixed excision time is set for each round, and the time difference for graded excision is set for different rounds. The maximum number of circuit elements allowed to be excised is set for each round. After the timing reaches the time of any round, the circuit elements are excised one by one from the circuit queue of the latest sorting result, and it is ensured that the number of circuit elements excised in this round is not greater than the maximum number of circuit elements allowed to be excised.

[0026] The beneficial effects of the present invention are as follows:

[0027] The method of the present invention is mainly applied to offshore wind power grid-connected systems. The three-phase voltage and current signals of the line elements connected to the system are sampled in the time domain and the spectral line analysis is performed on the electrical quantities of the line elements in the frequency domain. The dominant oscillation mode frequency in the entire regional power grid is automatically identified through the spectral line analysis results. The sum of the spectral line amplitudes is calculated within the neighborhood frequency interval of the power frequency and the dominant oscillation mode frequency, and the sub-synchronous oscillation control is performed by dynamic sorting based on the ratio thereof. The present invention takes into account the coupled time-varying characteristics of the modal frequency during the actual on-site oscillation, comprehensively considers the spectral line power of the adjacent frequency interval under the power frequency and the dominant oscillation modal frequency during the oscillation disturbance, overcomes the influencing factors of frequency leakage, and can obtain the dominant oscillation modal frequency in the regional power grid in real time. At the same time, in the oscillation control process of the dominant oscillation modal frequency, the relative size relationship between the oscillation amplitude and the power frequency power amplitude under the dominant oscillation modal frequency is taken into account. It provides a new solution to the hierarchical removal of subsynchronous oscillations under the constraint of ensuring stable transmission of offshore wind power regional power grids. Under the constraint of ensuring stable transmission of offshore wind power, the hierarchical removal of oscillation disturbance sources can be reliably achieved, thereby ensuring the safe and stable operation of the sub / super synchronous frequency bands of the offshore wind power grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The flowchart of the subsynchronous oscillation control method based on the real-time oscillation power ratio of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0030] like Figure 1 As shown, the present invention provides a subsynchronous oscillation control method based on real-time oscillation power ratio, which adopts the power ratio within the dominant oscillation modal frequency interval within the sub- / super-synchronous frequency band within the regional power grid to the power at the power frequency as the main judgment basis, and is applied to the subsynchronous oscillation control of a large-scale offshore wind power grid-connected system. First, the three-phase voltage and current of each line element connected to the offshore wind power booster station are sampled in the time domain and the real-time three-phase instantaneous power time series is calculated; then, the power time series is transformed in the frequency domain to obtain the spectrum line amplitude sequence within the sub- and super-synchronous frequency bands, and the dominant oscillation frequency and the oscillation power at the corresponding dominant oscillation frequency are calculated in units of the connected element; finally, from the perspective of the entire regional power grid, the dominant oscillation modal frequencies of all connected element lines of the regional power grid are aligned to obtain the dominant oscillation modal frequency of the regional power grid (the dominant oscillation modal frequency of this disturbance), and the line set participating in the oscillation of the dominant oscillation modal frequency of this regional power grid is selected accordingly, and the ratio of the oscillation power in the neighborhood of the dominant oscillation modal frequency to the real-time oscillation power in the neighborhood of the power frequency is calculated, and dynamically sorted and graded. Until the subsynchronous oscillation disappears or the line is completely cut off. Specifically, the method comprises the following steps:

[0031] Step 1: Obtain the instantaneous values ​​of three-phase voltage and current of each line element connected to the offshore wind power booster station and calculate the three-phase instantaneous power;

[0032] Further preferably, the three-phase voltage and three-phase current of each line element connected to the offshore wind power booster station are sampled at a high sampling rate, and the instantaneous values ​​of the three-phase voltage and three-phase current of the line elements are calculated and the historical sampling data within 1 second are recorded, and the sampling frequency of the three-phase voltage and three-phase current of the connected line elements is 2000Hz. The three-phase instantaneous power sequence is calculated from the electrical quantity sampling data sequence within 1 second of each connected line element.

[0033] Step 2: Perform frequency domain transformation on the three-phase instantaneous power to obtain the frequency domain amplitude spectrum of the three-phase instantaneous power. According to the frequency domain amplitude spectrum, obtain the dominant oscillation mode frequency of each line element, as well as the power frequency power and the dominant oscillation mode oscillation power considering the frequency leakage;

[0034] (1) Based on the three-phase instantaneous power data of each line element within 1 second, the instantaneous power spectrum within the frequency range below 2 times the power frequency is calculated to obtain the three-phase instantaneous power frequency domain amplitude spectrum.

[0035] (2) The power frequency power under the condition of frequency leakage is the sum of the three-phase instantaneous power amplitudes in the power frequency and its adjacent frequency intervals in the three-phase instantaneous power frequency domain amplitude spectrum, specifically the sum of the spectrum amplitudes in a neighboring frequency interval with the power frequency 50 Hz as the center frequency in the three-phase instantaneous power frequency domain amplitude spectrum. That is, in the three-phase instantaneous power frequency domain amplitude spectrum sequence of the line element, the frequency interval with the power frequency 50 Hz as the center frequency and the deviation of 0.5 Hz around the power frequency 50 Hz is taken as its neighboring frequency interval, that is, the sum of the spectrum amplitudes in the interval [49.5 Hz, 50.5 Hz].

[0036] The sum of the spectrum line amplitudes in the frequency range of the power frequency and its neighboring frequency is used as the real-time power of the power frequency in the subsynchronous oscillation control criterion, and the frequency leakage factor is considered;

[0037] (3) The dominant oscillation mode frequency is obtained as follows:

[0038] For each line element, the envelope of the spectrum line amplitude in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum is searched for extreme points, and the amplitudes of the extreme points found are sorted and compared to obtain the frequency point with the largest amplitude as the dominant oscillation mode frequency of the corresponding line element;

[0039] The range of oscillation power frequency recognition in this process is the subsynchronous frequency band [2.5Hz, 47.5Hz] and the supersynchronous frequency band [52.5Hz, 97.5Hz].

[0040] The envelope of the spectrum line amplitude in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum is searched for extreme points, and the amplitudes of the extreme points found are sorted and compared. A threshold is set at 1% of the power frequency power. The spectrum line amplitudes greater than the threshold are regarded as possible oscillation frequency points and participate in the sorting and comparison of the extreme point amplitudes. The spectrum line amplitudes less than or equal to the threshold are not subject to subsequent sorting and comparison.

[0041] (4) The dominant oscillation mode oscillation power is the sum of the three-phase instantaneous power amplitudes within the dominant oscillation mode frequency and its adjacent frequency interval in the three-phase instantaneous power frequency domain amplitude spectrum, where the adjacent frequency refers to about 0.5 Hz.

[0042] Specifically, for each line element, based on the dominant oscillation mode frequency, the sum of the spectrum line amplitudes in the 0.5 Hz intervals on the left and right of the dominant oscillation mode frequency is calculated as the sum of the three-phase power in the dominant oscillation mode frequency and its adjacent frequency intervals;

[0043] The sum of the spectral line amplitudes in the frequency range of the dominant oscillation mode frequency and its neighborhood frequency is taken as the real-time power at the dominant oscillation mode frequency in the subsynchronous oscillation control criterion, and the frequency leakage factor is taken into account.

[0044] Step 3: align the dominant oscillation mode frequencies of each line element to obtain a set of line elements participating in subsynchronous oscillation;

[0045] Further preferably, within the sub-synchronous frequency band and the super-synchronous frequency band, the frequency band is subdivided with an integer frequency point as the center frequency and a 1 Hz range of 0.5 Hz around the center frequency as a frequency interval, and the subdivided frequency bands where the spectrum lines of the dominant oscillation mode amplitudes of the three-phase instantaneous power frequency domain of all line elements are located are counted, and the center frequency of the subdivided frequency band with the largest number of line elements falling in the subdivided frequency bands of the sub-synchronous frequency band and the super-synchronous frequency band is selected as the dominant oscillation mode frequency of this disturbance, and the line elements falling into the corresponding subdivided frequency band are the line elements that oscillate at the dominant oscillation mode frequency of this disturbance among the line elements connected to the offshore wind power booster station, forming a set of line elements of sub-synchronous oscillation.

[0046] The subsynchronous frequency range and the supersynchronous frequency range are divided into equal intervals, and the dominant oscillation modal frequencies of all line elements containing oscillation power in the regional power grid are aligned according to the divided frequency intervals. On this basis, the dominant oscillation modal frequency of this disturbance in the entire regional power grid is obtained, and the set of line elements containing the dominant oscillation modal frequency of this disturbance within the regional power grid is determined; the spectrum lines of the subsynchronous frequency range and the supersynchronous frequency range are spaced at 1Hz, with integer frequency points as the center frequency, and a range of 0.5Hz on the left and right as a frequency interval. The dominant oscillation modal frequencies of all access lines are aligned. Find the set of line elements in the entire regional power grid that participate in the oscillation at this dominant oscillation modal frequency.

[0047] Step 4: Calculate the real-time oscillation power ratio of each line element participating in the subsynchronous oscillation according to the power frequency power and the oscillation power of the dominant oscillation mode;

[0048] Further preferably, the dominant oscillation mode of the line element participating in the current disturbance of the regional power grid is ratioed to the power at the power frequency, and the real-time oscillation power ratio of the line element during the oscillation period is obtained as the main basis for subsynchronous oscillation control;

[0049] The power in the power frequency adjacent interval and the dominant oscillation mode frequency interval of the lines in the entire regional power grid that participated in this oscillation and whose dominant oscillation mode frequency is in the same frequency interval is recorded and the real-time oscillation power ratio of the oscillation power and the power frequency power is calculated.

[0050] Step 5: Sort the circuit elements in the circuit element set according to the real-time oscillation power ratio, and perform hierarchical removal of the circuit elements in the circuit element set in combination with multiple rounds of hierarchical removal time constants to achieve sub-synchronous oscillation control.

[0051] Further preferably, the real-time oscillation power ratios of the line elements participating in the dominant oscillation mode in the entire regional power grid are sorted in real time from large to small. The line elements with large oscillation power ratios are removed first; according to the pre-set real-time oscillation power ratio multi-round graded removal time constant, the line elements are removed step by step according to the sorted real-time oscillation power ratio and the multi-round graded removal time constant, so as to realize the control of subsynchronous oscillation in the regional power grid.

[0052] The method of performing graded removal of the line elements in the line element set by combining the sorting results of the line elements with the multi-round graded removal time constants is as follows: after the oscillation occurs, the timing starts, and n rounds are preset. A fixed removal time, i.e., the action time, is set for each round. The times of different rounds ensure a certain level difference, i.e., there is a graded removal time difference. The maximum number of line elements allowed to be removed is set for each round. After the timing reaches the action time of any round, the line elements are removed one by one from the line queue of the latest real-time oscillation power ratio sorting result, and it is ensured that the number of line elements removed in this round is not greater than the maximum number of line elements allowed to be removed.

[0053] Example 1

[0054] According to the above process, the main implementation steps of a subsynchronous oscillation control method based on real-time oscillation power ratio of the present invention are as follows:

[0055] Step 1: Sample the three-phase voltage and three-phase current signals of each line element connected to the offshore wind power booster station at a sampling frequency of 2000 Hz and calculate the time series sum within the one-second buffer time, and then calculate the instantaneous power series of the three-phase instantaneous power within the one-second buffer time;

[0056] Step 2: Perform frequency domain transformation on the instantaneous power sequence within the one-second buffer time, and then search for the extreme points of the envelope of the frequency domain amplitude spectrum of the access component to obtain the dominant oscillation mode frequency of the access component and the oscillation power amplitude in the frequency neighborhood interval, and the power frequency power.

[0057] In this embodiment, six submarine collection cables, two SVG branches and one line to the low-voltage side of the boost transformer on a section of busbar connected to an offshore wind power boost station are taken as an example for explanation.

[0058] The dominant oscillation mode frequencies and corresponding oscillation powers of all nine connected line elements are shown in Table 1:

[0059] Table 1 Access line power and oscillation power values

[0060]

[0061] In this embodiment, the amplitude of the spectrum line after the frequency domain transformation of the circuit element is set to 1% of the power frequency power as a threshold in the process of searching for the dominant oscillation mode frequency. The spectrum line greater than the threshold is regarded as a possible oscillation frequency point to participate in the extreme point comparison. The spectrum line less than the threshold is not calculated for the oscillation power ratio and is not involved in the subsequent sorting.

[0062] Step 3: Align the dominant oscillation modal frequencies of the access lines in the region, find the dominant oscillation modal frequency of the regional power grid (the dominant oscillation modal frequency of this disturbance), and control the oscillation at this frequency as the control object.

[0063] According to the data in Table 1, the dominant oscillation mode frequency of the regional power grid is 15.0Hz, and the lines involved in this oscillation are:

[0064] 35kV collection cable 1; 35kV collection cable 2; 35kV collection cable 3; 35kV collection cable 4; 35kV collection cable 5; step-up to low voltage side line;

[0065] Step 4: Calculate the real-time oscillation power ratio. As shown in Table 1, it can be basically determined that the oscillation with the dominant oscillation modal frequency of 15 Hz exists in most of the collection lines and the low-voltage side lines of the step-up transformer. The SVG branch does not participate in this 15 Hz oscillation. The dominant oscillation modal frequency of 75.1 Hz displayed by the 35 kV collection cable 6 is not in the same frequency interval as most of the aforementioned lines and is not controlled in this oscillation control process.

[0066] Step 5: Based on the line set obtained in step 4 and the real-time oscillation power ratio calculated in Table 1, sort them according to the real-time oscillation power ratio. The result after sorting from large to small is shown in Table 2:

[0067] Table 2 Line oscillation power ratio and dynamic ranking results of the dominant oscillation mode in the participating area

[0068] Access line name Real-time oscillation power ratio Real-time oscillation power ratio sorting 35kV collection cable 1 0.092 2 35kV collection cable 2 0.168 1 35kV collection cable 3 0.014 4 35kV collection cable 4 0.003 6 35kV collection cable 5 0.006 5 Boost to low voltage side 0.081 3

[0069] In this embodiment, the calculation and sorting of the oscillation power ratios adopts timed interrupt interval cyclic calculation and dynamic sorting, and the oscillation sources are cut off in stages according to the dynamic changes of the oscillation and the dynamic sorting results.

[0070] Assume that 6 rounds of excision are set, and the time constants of graded excision in the 6 rounds are set as follows:

[0071] The first round of excision time was 5 s;

[0072] The second round of excision lasted 10 s;

[0073] The third round of excision lasted 15 s;

[0074] The fourth round of excision lasted 20 s;

[0075] The fifth round of excision time was 25 s;

[0076] The sixth round of excision lasted 30 s;

[0077] The number of circuit elements that can be removed in any round is set to 1.

[0078] Assuming that the dynamic sorting results remain unchanged during the oscillation period, the expected action results are as follows based on the dynamic sorting results in Table 2:

[0079] The first round of cutting takes 5 seconds to cut off the 35kV collection cable 2;

[0080] The second round of cutting time is 10s to cut off the 35kV collection cable 1;

[0081] The third round of removal takes 15 seconds to remove the boost-to-low pressure side;

[0082] The fourth round of cutting time is 20s to cut off the 35kV collection cable 3;

[0083] The fifth round of cutting time is 25s and the 35kV collection cable 5 is cut off;

[0084] The sixth round of cutting time is 30s and the 35kV collection cable 4 is cut off;

[0085] The actual cut-off result when oscillation occurs will change according to the progress of the oscillation and the dynamic changes of the electrical main connection topology; for example, in this embodiment, after the third round of cut-off of the low-voltage side of the step-up transformer, the 35kV collection cable 3, 35kV collection cable 5, and 35kV collection cable 4 are no longer electrically connected to the step-up transformer, and the oscillation situation will change. The specific action result depends on the dynamic sorting result of the real-time oscillation power ratio.

[0086] The beneficial effects of the present invention are as follows:

[0087] The method of the present invention is mainly applied to offshore wind power grid-connected systems. The three-phase voltage and current signals of the line elements connected to the system are sampled in the time domain and the spectral line analysis is performed on the electrical quantities of the line elements in the frequency domain. The dominant oscillation mode frequency in the entire regional power grid is automatically identified through the spectral line analysis results. The sum of the spectral line amplitudes is calculated within the neighborhood frequency interval of the power frequency and the dominant oscillation mode frequency, and the sub-synchronous oscillation control is performed by dynamic sorting based on the ratio thereof. The present invention takes into account the coupled time-varying characteristics of the modal frequency during the actual on-site oscillation, comprehensively considers the spectral line power of the adjacent frequency interval under the power frequency and the dominant oscillation modal frequency during the oscillation disturbance, overcomes the influencing factors of frequency leakage, and can obtain the dominant oscillation modal frequency in the regional power grid in real time. At the same time, in the oscillation control process of the dominant oscillation modal frequency, the relative size relationship between the oscillation amplitude and the power frequency power amplitude under the dominant oscillation modal frequency is taken into account. It provides a new solution to the hierarchical removal of subsynchronous oscillations under the constraint of ensuring stable transmission of offshore wind power regional power grids. Under the constraint of ensuring stable transmission of offshore wind power, the hierarchical removal of oscillation disturbance sources can be reliably achieved, thereby ensuring the safe and stable operation of the sub / super synchronous frequency bands of the offshore wind power grid-connected system.

[0088] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0089] A computer-readable storage medium may be a tangible device that can hold and store instructions used by an instruction execution device. A computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples of computer-readable storage media (a non-exhaustive list) include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure in a groove on which instructions are stored, and any suitable combination of the foregoing. As used herein, a computer-readable storage medium is not to be interpreted as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse through a fiber optic cable), or an electrical signal transmitted through a wire.

[0090] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0091] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages, such as Smalltalk, C++, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be customized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements 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 subsynchronous oscillation control method based on real-time oscillation power ratio, characterized in that: The method comprises the following steps: Step 1: Obtain the instantaneous values ​​of three-phase voltage and current of each line element connected to the offshore wind power booster station and calculate the three-phase instantaneous power; Step 2: Perform frequency domain transformation on the three-phase instantaneous power to obtain the three-phase instantaneous power frequency domain amplitude spectrum, and obtain the dominant oscillation mode frequency of each line element and the power frequency power and dominant oscillation mode oscillation power under the condition of frequency leakage according to the frequency domain amplitude spectrum; wherein, the power frequency power under the condition of frequency leakage is the sum of the three-phase instantaneous power amplitudes within the power frequency and its adjacent frequency interval in the three-phase instantaneous power frequency domain amplitude spectrum; the dominant oscillation mode oscillation power under the condition of frequency leakage is the sum of the three-phase instantaneous power amplitudes within the dominant oscillation mode frequency and its adjacent frequency interval in the three-phase instantaneous power frequency domain amplitude spectrum; Step 3: align the dominant oscillation mode frequencies of each line element to obtain a set of line elements participating in subsynchronous oscillation; Step 4: Calculate the real-time oscillation power ratio of each line element participating in the subsynchronous oscillation according to the power frequency power and the oscillation power of the dominant oscillation mode; Step 5: Sort the circuit elements in the circuit element set according to the real-time oscillation power ratio, and perform hierarchical removal of the circuit elements in the circuit element set in combination with multiple rounds of hierarchical removal time constants to achieve sub-synchronous oscillation control.

2. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 1, characterized in that: In step 1, the three-phase voltage and three-phase current signals of each line element connected to the offshore wind power booster station are sampled at a high sampling frequency and the time series and within the buffer time are calculated, and then the instantaneous power sequence within the three-phase instantaneous power buffer time is calculated.

3. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 2, characterized in that: The high sampling frequency is 2000Hz and the buffer time is 1 second; The line components include submarine collection cables, SVG branches and lines on the step-up to low-voltage side.

4. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 1, characterized in that: In step 2, the dominant oscillation mode frequency is obtained as follows: For each line element, the envelope of the spectrum line amplitude in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum is searched for extreme points, and the amplitudes of the extreme points found are sorted and compared to obtain the frequency point with the largest amplitude as the dominant oscillation mode frequency of the corresponding line element.

5. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 4, characterized in that: The envelope of the spectrum line amplitude in the subsynchronous frequency band and the supersynchronous frequency band in the frequency domain amplitude spectrum is searched for extreme points, and the amplitudes of the extreme points found are sorted and compared. A threshold is set, and the spectrum line amplitudes greater than the threshold are regarded as possible oscillation frequency points and participate in the sorting and comparison of the extreme point amplitudes. The spectrum line amplitudes less than or equal to the threshold are not subject to subsequent sorting and comparison.

6. A subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 5, characterized in that: The threshold is set according to the power frequency power and is set to 1% of the power frequency power.

7. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 1, characterized in that: Adjacent frequencies are 0.5 Hz to the left and right.

8. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 1, characterized in that: In step 3, within the sub-synchronous frequency band and the super-synchronous frequency band, the frequency band is subdivided with an integer frequency point as the center frequency and a 1 Hz range of 0.5 Hz around the center frequency as a frequency interval, and the subdivided frequency bands where the spectrum lines of the dominant oscillation mode amplitudes of the three-phase instantaneous power frequency domain of all line elements are located are counted, and the center frequency of the subdivided frequency band with the largest number of line elements falling in the subdivided frequency bands of the sub-synchronous frequency band and the super-synchronous frequency band is selected as the dominant oscillation mode frequency of this disturbance, and the line elements falling into the corresponding subdivided frequency band are the line elements that oscillate at the dominant oscillation mode frequency of this disturbance among the line elements connected to the offshore wind power booster station, forming a set of line elements of sub-synchronous oscillation.

9. The subsynchronous oscillation control method based on real-time oscillation power ratio according to claim 1, characterized in that: In step 5, the sorting results of the circuit elements are combined with the multi-round graded removal time constants to perform graded removal of the circuit elements in the circuit element set in the following manner: after the oscillation occurs, the timing starts, n rounds are preset, a fixed removal time is set for each round, the time difference of graded removal is set for different rounds, the maximum number of circuit elements allowed to be removed is set for each round, and after the timing reaches the time of any round, the circuit elements are removed one by one from the circuit queue of the latest sorting result, and it is ensured that the number of circuit elements removed in this round is not greater than the maximum number of circuit elements allowed to be removed.

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