Energy-storage power-conversion series compensation system and stability analysis method therefor, and damping controller

Abstract

The present application relates to an energy-storage power-conversion series compensation system and a stability analysis method therefor, a damping controller, and an energy storage system, wherein a voltage signal on a capacitor arranged between an energy storage battery pack and a converter of the energy-storage power-conversion series compensation system can be collected, and whether an activation condition is met is determined based on the voltage signal; when the activation condition is met, an adaptive adjustment filter is activated to bring the damping controller into operation within the energy-storage power-conversion series compensation system. A voltage synchronization controller determines, on the basis of a sub-synchronous frequency band voltage signal output by the adaptive adjustment filter and an initial voltage signal, a required output phase angle signal corresponding to a pulse width modulation signal for controlling operation of the converter.

Description

Energy storage converter series compensation system and its stability analysis method and damping controller

[0001] Cross-references

[0002] This application refers to Chinese patent application No. 202311363676.2 filed on October 19, 2023, entitled “Energy Storage Converter Series Compensation System, Stability Analysis Method, and Damping Controller”, which is incorporated into this application in its entirety by reference. Technical Field

[0003] The present application relates to the field of electric energy transmission technology, and in particular to an energy storage converter series compensation system and its stability analysis method, a damping controller, and an energy storage system. Background Art

[0004] With the development of science and technology, energy storage systems, as a crucial power system regulation resource, have greatly facilitated electricity use in daily production and life. Energy storage battery packs are typically connected to the AC grid via a series-compensated energy storage system. The system's converters convert the stored energy into electricity suitable for grid demand and supply it to the AC grid's loads.

[0005] Among various converter types, grid-type converters are gaining popularity due to their ability to improve the inertia and damping support provided by energy storage systems to AC power grids. However, in related technologies, grid-type converters have relatively poor operational stability.

[0006] Summary of the Invention

[0007] Based on this, it is necessary to provide an energy storage converter series compensation system and its stability analysis method, damping controller, and energy storage system to improve the stable operation capability of the grid-type converter.

[0008] A damping controller includes a subsynchronous frequency tracker, an adaptive adjustment filter, and a voltage synchronization controller. The subsynchronous frequency tracker is used to obtain a voltage signal of a capacitor arranged between an energy storage battery pack and an inverter of an energy storage inverter series compensation system, and activates the adaptive adjustment filter when it is determined based on the voltage signal that an activation condition is met; the adaptive adjustment filter is connected to the subsynchronous frequency tracker and is used to receive a voltage signal, and when activated, filters and adjusts the voltage signal to output a subsynchronous frequency band voltage signal; the voltage synchronization controller is connected to the adaptive adjustment filter and the inverter and is used to receive an initial voltage signal and determine an output phase angle signal based on the subsynchronous frequency band voltage signal and the initial voltage signal; the output phase angle signal is used to generate a pulse width modulation signal to control the operation of the inverter

[0009] The damping controller collects the voltage signal on the capacitor between the energy storage battery pack and the converter of the energy storage converter series compensation system and, based on this signal, determines whether activation conditions are met. If so, it activates the adaptive adjustment filter, causing the damping controller to operate within the energy storage converter series compensation system. Subsequently, the voltage synchronization controller determines the required output phase angle signal corresponding to the pulse-width modulation signal controlling the converter's operation based on the subsynchronous frequency band voltage signal output by the adaptive adjustment filter and the initial voltage signal. This approach allows the damping controller to operate within the energy storage converter series compensation system if activation conditions are met, improving the damping level of unstable subsynchronous resonant modes, converting the original negative damping mode to a positive damping mode, and enhancing the stable operation of the grid-type converter.

[0010] In some embodiments, the subsynchronous frequency tracker includes an acquisition module, a fast Fourier analysis module, and a decision module connected in sequence. The acquisition module is used to obtain a voltage signal, and the decision module is further connected to an adaptive adjustment filter.

[0011] In the above scheme, the subsynchronous frequency tracker includes an acquisition module, a fast Fourier analysis module and a decision module. It performs fast Fourier analysis by acquiring voltage signals and uses the analysis results to determine whether to activate the adaptive adjustment filter, thereby having high tracking accuracy.

[0012] In some embodiments, the adaptive adjustment filter includes a low-pass filter, a high-pass filter, a band-pass filter and a gain amplifier connected in sequence, the low-pass filter is used to receive a voltage signal, the band-pass filter is also connected to a sub-synchronous frequency tracker, and the gain amplifier is also connected to a voltage synchronization controller.

[0013] In the above scheme, the adaptive adjustment filter performs low-pass filtering, high-pass filtering, band-pass filtering and gain processing on the voltage signal, thereby accurately screening out the voltage signal in the subsynchronous frequency band and improving the accuracy of damping suppression.

[0014] In some embodiments, the voltage synchronization controller includes a first subtractor, a second subtractor, a droop controller, a first adder, a multiplier and an integrator connected in sequence, the first subtractor is also used to receive a voltage signal, the second subtractor is also connected to an adaptive adjustment filter, the first subtractor is also used to receive an initial voltage signal, the first adder is also used to receive a system rated frequency, and the multiplier is also used to receive a system angular frequency reference value.

[0015] In the above scheme, the voltage synchronization controller can combine the system rated frequency, the system angular frequency reference value, the initial voltage signal, the voltage signal and the sub-synchronous frequency band voltage signal to perform synchronization control, output the output phase angle signal required by the converter when suppressing damping, and has high voltage synchronization control reliability.

[0016] In some embodiments, satisfying the activation condition includes: the acquisition signal frequency satisfies a preset frequency condition, and the acquisition signal amplitude satisfies a preset amplitude condition; wherein the acquisition signal frequency and the acquisition signal amplitude are determined by performing online Fourier analysis on the voltage signal.

[0017] The above scheme determines whether the activation conditions of the adaptive adjustment filter are met by verifying whether the frequency and amplitude of the collected signal meet the preset frequency conditions and preset amplitude conditions respectively. Verification is performed from two dimensions of frequency and amplitude to improve the accuracy of activation judgment.

[0018] In some embodiments, the acquisition signal frequency satisfies a preset frequency condition, including: the acquisition signal frequency is greater than or equal to a lower limit value of a set bandpass frequency, and is less than or equal to an upper limit value of the set bandpass frequency.

[0019] In the above scheme, when the frequency of the collected signal is between the upper limit and the lower limit of the set bandpass frequency, it is considered that the preset frequency condition is met, so as to achieve damping suppression within the range of the set bandpass frequency and improve the accuracy of damping suppression.

[0020] And / or, in some embodiments, the amplitude of the collected signal satisfies a preset amplitude condition, including: a ratio of the amplitude of the collected signal to the nominal amplitude is greater than or equal to a set threshold.

[0021] In the above scheme, when the ratio of the collected signal amplitude to the nominal amplitude is greater than or equal to the set threshold, it is considered that the preset amplitude condition is met, so as to achieve damping suppression when the collected signal amplitude is large, thereby improving the accuracy of damping suppression.

[0022] An energy storage current conversion series compensation system includes a capacitor, a converter, a series compensation circuit, and the above-mentioned damping controller. The first and second ends of the capacitor are respectively used to connect to an energy storage battery pack. The first end of the capacitor is also connected to the converter. The second end of the capacitor is also connected to the converter. The converter is also connected to the damping controller and the series compensation circuit. The series compensation circuit is used to connect to an AC power grid.

[0023] The above-mentioned energy storage converter series compensation system is connected to a damping controller at the converter. The damping controller can change the damping of the energy storage converter series compensation system in the event of subsynchronous resonance instability, thereby improving the operating stability of the energy storage converter series compensation system.

[0024] In some embodiments, the energy storage converter series compensation system further includes a reactive power control device, a voltage reference device, and a pulse width generator. The reactive power control device and the damping controller are respectively connected to the voltage reference device, and the pulse width generator is respectively connected to the voltage reference device and the converter.

[0025] The above scheme combines the output phase angle signal and the modulation ratio reference value generated by the reactive power control device to generate a corresponding pulse width modulation signal for the converter through the voltage reference device and the pulse width generator, thereby improving the operating reliability of the converter.

[0026] In some embodiments, the reactive power control device includes a reactive power control module, a second adder, and an auxiliary damping controller. The reactive power control module and the auxiliary damping controller are respectively connected to the second adder, and the second adder is connected to the voltage reference device.

[0027] The above scheme combines the modulation ratio reference value generated by the reactive control module and the modulation ratio change value generated by the auxiliary damping controller for addition operation to obtain the actual modulation ratio reference value, which is used to control the generation of the pulse width modulation signal, and can effectively improve the accuracy of the modulation ratio reference value.

[0028] In some embodiments, the energy storage converter series compensation system further includes a first inductor and a first capacitor, the first end of the first inductor is connected to the converter, the second end of the first inductor is connected to the first end of the first capacitor and the series compensation circuit, and the second end of the first capacitor is grounded.

[0029] In the above solution, the converter is connected to the series compensation circuit through the first inductor and the first capacitor. The first inductor and the first capacitor make the voltage transmission more stable and reliable, further improving the operational reliability of the energy storage converter series compensation system.

[0030] In some embodiments, the series compensation circuit includes a second inductor and a second capacitor connected in series, an end of the second inductor away from the second capacitor is further connected to the converter, and an end of the second capacitor away from the second inductor is used to connect to the AC power grid.

[0031] In the above scheme, the series compensation circuit includes a second inductor and a second capacitor, and a series compensation circuit is formed by building the second inductor and the second capacitor, thereby improving the power factor of the energy storage and current conversion series compensation system, stabilizing the energy storage and current conversion series compensation system, and reducing voltage fluctuations.

[0032] A stability analysis method based on the above-mentioned energy storage converter series compensation system includes: obtaining an overall state space model of the energy storage converter series compensation system when the adaptive adjustment filter is not activated; wherein the overall state space model is determined by linearization processing based on an operating state model, and the operating state model is constructed based on modal analysis; and eigenvalues ​​are solved according to the overall state space model to determine the stability analysis results.

[0033] The above scheme performs modal analysis on the energy storage converter series compensation system when the adaptive adjustment filter is not activated and the voltage synchronization controller does not receive the subsynchronous frequency band voltage signal, constructs an overall state space model, and realizes stability analysis of the energy storage converter series compensation system by solving the eigenvalues ​​of the overall state space model. The stability analysis results are obtained, thereby providing data support for the subsynchronous resonance theoretical analysis of the energy storage converter series compensation system built with the grid-type converter.

[0034] In some embodiments, the operating state model includes at least one of a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model.

[0035] The above scheme uses one or more of the capacitor dynamic model, voltage droop control model, converter virtual power angle model, converter AC / DC voltage model, converter dynamic model, series compensation model and series compensation capacitor transient differential model for linearization processing, thereby determining the overall state space model and improving the accuracy of the overall state space model.

[0036] In some embodiments, performing eigenvalue solving according to the overall state space model to determine the stability analysis result includes: performing eigenvalue solving according to the overall state space model to determine the eigenvalue; performing solving according to the eigenvalue to determine the oscillation frequency and the damping ratio; and determining the stability analysis result according to the oscillation frequency and the damping ratio.

[0037] The above scheme obtains eigenvalues ​​by solving the eigenvalues ​​based on the overall state-space model, and combines the oscillation frequency and damping ratio obtained by the eigenvalue calculation to verify the subsynchronous resonance phenomenon of the energy storage converter series compensation system. It has the advantage of high accuracy in stability analysis.

[0038] In some embodiments, the stability analysis results are determined based on the oscillation frequency and the damping ratio, including: determining the target oscillation frequency and the target damping ratio when the energy storage converter series compensation system is unstable based on the oscillation frequency and the damping ratio; performing participation factor analysis based on the target oscillation frequency and the target damping ratio to determine the dominant instability parameters.

[0039] The above scheme, based on the oscillation frequency and damping ratio solved for each characteristic, finds the target oscillation frequency and target damping ratio when the energy storage converter series compensation system undergoes subsynchronous resonance (i.e., instability). It further performs a participating factor analysis to find the main factors causing subsynchronous resonance, providing a theoretical basis for the construction of the damping controller.

[0040] The present application also provides an energy storage system, including an energy storage battery pack and the above-mentioned energy storage converter series compensation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive work. In the drawings:

[0042] FIG1 is a schematic diagram of the structure of a damping controller in some embodiments of the present application;

[0043] FIG2 is a schematic diagram of the structure of a damping controller in some other embodiments of the present application;

[0044] FIG3 is a schematic diagram of the structure of an energy storage converter series compensation system in some embodiments of the present application;

[0045] FIG4 is a flow chart of a stability analysis method for an energy storage converter series compensation system according to some embodiments of the present application;

[0046] FIG5 is a schematic diagram of a stability analysis process in some embodiments of the present application;

[0047] FIG6 is a schematic diagram of a stability analysis process in some other embodiments of the present application;

[0048] FIG7 is a schematic diagram of participation factors in some embodiments of the present application;

[0049] FIG8 is a schematic diagram of root locus analysis in some embodiments of the present application;

[0050] FIG9 is a schematic diagram of the dynamic response of the damping controller in some embodiments of the present application;

[0051] FIG10 is a schematic diagram of waveforms for verifying different parameters of the damping controller in some embodiments of the present application.

[0052] Description of reference numerals:

[0053] 110 - Subsynchronous frequency tracker, 120 - Adaptive adjustment filter, 130 - Voltage synchronization controller; 111 - Acquisition module, 113 - Fast Fourier analysis module, 115 - Decision module; 121 - Low-pass filter, 123 - High-pass filter, 125 - Band-pass filter, 127 - Gain amplifier; 131 - First subtractor, 132 - Second subtractor, 133 - Droop controller, 134 - First adder, 135 - Multiplier, 136 - Integrator; 310 - Energy storage battery pack, 320 - Converter, 330 - Series compensation circuit, 340 - Damping controller; 410 - Reactive power control device, 420 - Voltage reference device, 430 - Pulse width generator; 411 - Reactive power control module, 412 - Auxiliary damping controller, 413 - Second adder. DETAILED DESCRIPTION

[0054] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0056] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0057] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0058] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0059] In the description of the embodiments of the present application, unless otherwise expressly specified or limited, technical terms such as "installed," "connected," "connected," and "fixed" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; internal connections between two components or interactions between two components. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present application based on specific circumstances.

[0060] Currently, energy storage systems are widely used in conjunction with AC power grids due to market developments. Sub-synchronous oscillation (SSO) in power systems is an instability condition caused by energy exchange between a generating unit (synchronous generator, renewable energy generator) and the AC / DC grid at one or more specific frequencies. These specific frequencies are typically 50 Hz (hertz) lower than the grid's synchronous frequency. Early sub-synchronous oscillations were primarily caused by the interaction between the synchronous generator shaft system and the series compensation of the grid. This SSO instability is caused by the complementary interaction between the natural torsional vibration frequency of the synchronous generator shaft system and the resonant frequency of the series compensation circuit, and is therefore also known as sub-synchronous resonance (SSR). However, with the large-scale integration of renewable energy and a large number of power electronic equipment, more SSO instability accidents driven by renewable energy have been discovered in real-world projects. Their generation mechanism differs from SSR driven by traditional synchronous generator shaft systems, and they exhibit more novel oscillation characteristics and manifestations.

[0061] Under the control of a typical grid-following (GFL) converter, the subsynchronous oscillation mechanism of energy storage systems has been studied more clearly. It is generally believed that the grid-following converter will not cause mutual coupling with the series compensation circuit set on the AC grid side to cause SSR (Sub-Synchronous Resonance). Currently, most research is based on the SSO stability analysis of grid-following converters.

[0062] However, with the development of power systems, a grid-forming (GFM) converter based on DC Voltage Synchronization Control (DVSC) has been proposed. Research has found that while GFM converters can improve the energy storage system's ability to provide inertia and damping support for the AC grid, they lack stable operating capabilities compared to GFL converters.

[0063] To alleviate the poor operational stability of GFM converters, and considering the differences in operating modes between GFM and GFL converters, the GFM converter was connected to an energy storage converter series compensation system to verify whether this type of system would experience SSR instability. In-depth research revealed that, unlike the GFL converter-type energy storage converter series compensation system, the GFM converter-type energy storage converter series compensation system does experience SSR instability, and this SSR instability contributes to the poor operational stability of the GFM converter.

[0064] Based on the above considerations, the embodiments of the present application design a damping controller that is connected to a GFM converter. It collects the voltage signal on the capacitor between the energy storage battery pack and the converter of the energy storage converter series compensation system. Based on this signal, it determines whether activation conditions are met. If the activation conditions are met, it activates the adaptive adjustment filter to put the damping controller into operation in the energy storage converter series compensation system. Subsequently, the voltage synchronization controller determines the output phase angle signal required for the pulse width modulation signal that controls the converter operation based on the subsynchronous frequency band voltage signal output by the adaptive adjustment filter and the initial voltage signal.

[0065] Through the embodiment scheme of the present application, when the activation conditions are met, the damping controller can be put into operation in the energy storage converter series compensation system, and the voltage signal of the capacitor and the initial voltage signal can be combined for analysis and control to improve the damping level of the unstable subsynchronous resonant mode, correct the original negative damping mode to a positive damping mode, and improve the stable operation capability of the grid-type converter.

[0066] The damping controller of the embodiments of the present application is applied in an energy storage system. In some embodiments, it can be applied to an energy storage converter series compensation system between the energy storage module (which can be an energy storage battery pack) and the AC power grid of the energy storage system. Considering that GFL converters generally do not suffer from SSR instability, the energy storage converter series compensation system referred to in the embodiments of the present application refers to an energy storage converter series compensation system including a GFM converter type.

[0067] Please refer to Figure 1. An embodiment of the present application provides a damping controller, including a sub-synchronous frequency tracker 110, an adaptive adjustment filter 120 and a voltage synchronization controller 130. The sub-synchronous frequency tracker 110 is used to obtain a voltage signal of a capacitor arranged between an energy storage battery group and a converter of an energy storage converter series compensation system, and activate the adaptive adjustment filter 120 when it is determined based on the voltage signal that an activation condition is met; the adaptive adjustment filter 120 is connected to the sub-synchronous frequency tracker 110, and is used to receive a voltage signal, and when activated, filters and adjusts the voltage signal to output a sub-synchronous frequency band voltage signal; the voltage synchronization controller 130 is connected to the adaptive adjustment filter 120 and the converter, and is used to receive an initial voltage signal, and determine an output phase angle signal based on the sub-synchronous frequency band voltage signal and the initial voltage signal; the output phase angle signal is used to generate a pulse width modulation signal to control the operation of the converter.

[0068] The energy storage battery pack is a battery structure formed by connecting multiple batteries for storing and releasing electrical energy. Multiple batteries can be connected in series and / or in parallel, and there is no specific limitation. The energy storage converter series compensation system is a system that is arranged between the energy storage battery pack and the AC power grid, and converts the DC power output by the energy storage battery pack into AC power suitable for the AC power grid. The sub-synchronous frequency band voltage signal is a voltage signal with a frequency in the sub-synchronous frequency band in the voltage signal. The output phase angle signal is the phase angle required for the converter operation when the damping adjustment is achieved. The initial voltage signal is the voltage signal of the capacitor theoretically output when the energy storage converter series compensation system is operating at rated power.

[0069] The sub-synchronous frequency tracker 110 (SFT) is a device that tracks and processes the voltage signal of the capacitor and determines whether it is necessary to connect the damping controller to the energy storage converter series compensation system for operation based on the tracking processing result, thereby performing damping control on the energy storage converter series compensation system. The adaptive adjustment filter 120 is a device that can adjust the filter-related frequency according to actual needs and is activated by the sub-synchronous frequency tracker 110. The voltage synchronization controller 130 is a device that can perform synchronization control based on the initial voltage signal and the sub-synchronous frequency band voltage signal output by the adaptive adjustment filter 120 to determine the output phase angle signal required for pulse width modulation of the converter of the energy storage converter series compensation system.

[0070] During the operation of the energy storage inverter series compensation system, the subsynchronous frequency tracker 110 can collect the voltage signal of the capacitor disposed between the energy storage battery pack and the converter in real time, track and process the voltage signal, and use the tracking processing results to determine whether to activate the adaptive adjustment filter 120. It should be noted that the subsynchronous frequency tracker 110 is not limited to the method of collecting voltage signals. In some embodiments, a voltage collector can be provided at the capacitor, and both the voltage collector and the subsynchronous frequency tracker 110 can be connected to a high-voltage-low-voltage conversion board. The subsynchronous frequency tracker 110 obtains the voltage signal collected by the voltage collector from the high-voltage-low-voltage conversion board.

[0071] If the tracking results determine that the activation conditions are met, then the energy storage inverter series compensation system is experiencing SSR instability, and the adaptive adjustment filter 120 will be activated for the next step of damping adjustment. If the tracking results determine that the activation conditions are not met, then the energy storage inverter series compensation system is not experiencing SSR instability, and there is no need to activate the adaptive adjustment filter 120 for damping adjustment. The system can simply return to acquiring and analyzing the voltage signal.

[0072] When the adaptive adjustment filter 120 is activated, the input voltage signal (which can also be obtained by connecting the voltage collector and the adaptive adjustment filter 120 to the strong-current-weak-current conversion board in a separate manner) is filtered and processed, and the sub-synchronous frequency band voltage signal is finally obtained and transmitted to the voltage synchronization controller 130. At the voltage synchronization controller 130, active synchronous control is performed in combination with the sub-synchronous frequency band voltage signal and the initial voltage signal, and an output phase angle signal is finally obtained. By modulating and analyzing the output phase angle signal, the pulse width modulation signal required for the converter after damping adjustment can be determined, and the analyzed pulse width modulation signal is used to control the converter on and off, thereby changing the damping of the energy storage converter series compensation system. Thereby, the damping level of the unstable sub-synchronous resonant mode is improved, the original negative damping mode is corrected to the positive damping mode, and the stable operation capability of the grid-type converter is improved.

[0073] The damping controller described above can collect voltage signals from capacitors located between the energy storage battery pack and the converter of the energy storage converter series compensation system, and based on this information, determine whether activation conditions are met. If the activation conditions are met, the adaptive adjustment filter 120 is activated, causing the damping controller to operate in the energy storage converter series compensation system. Subsequently, the voltage synchronization controller 130 determines the required output phase angle signal corresponding to the pulse width modulation signal controlling converter operation based on the subsynchronous frequency band voltage signal output by the adaptive adjustment filter 120 and the initial voltage signal. This approach allows the damping controller to operate in the energy storage converter series compensation system if the activation conditions are met, improving the damping level of unstable subsynchronous resonant modes, correcting the original negative damping mode to a positive damping mode, and enhancing the stable operation of the grid-type converter.

[0074] Please refer to Figure 2. In some embodiments, the sub-synchronous frequency tracker 110 includes an acquisition module 111, a fast Fourier analysis module 113 and a decision module 115 connected in sequence. The acquisition module 111 is used to obtain the voltage signal. The decision module 115 is also connected to the adaptive adjustment filter 120.

[0075] The acquisition module 111 samples the voltage signal input to the subsynchronous frequency tracker 110. The fast Fourier analysis module 113 performs fast Fourier analysis on the input sampled signal to determine relevant characteristic parameters of the sampled signal, such as the sampled signal frequency and sampled signal amplitude, although specific details are not limited thereto. The decision module 115 determines whether the activation conditions are met to activate the adaptive adjustment filter 120. This module may be a comparator, etc., although specific details are not limited thereto.

[0076] It should be noted that the specific type of the acquisition module 111 is not limited, as long as it can accurately acquire the voltage signal within a period of time. For example, in some embodiments, the acquisition module 111 includes a rolling rectangle acquisition module. In actual scenarios, the voltage signal v dc It carries the broadband oscillation information of the energy storage converter series compensation system, including low-frequency oscillation, subsynchronous oscillation, supersynchronous oscillation, high-frequency oscillation information, etc. The rectangular window module collects the voltage signal v from time t to t+Δt through real-time rolling sampling. dc fluctuations, providing a basis for subsequent signal processing.

[0077] The fast Fourier analysis module 113 records the sampled signal as x(n), and the sampling time window Δt=N s / f s , where N s is the sampling point, f s is the sampling frequency, so the collected signal can be re-expressed as X(k):

[0078] Combining the above formula, the relevant characteristic parameters in the sampled signal can be solved, such as:

[0079] Among them, A i Indicates the amplitude of the collected signal, f i Indicates the acquisition signal frequency, φ i Indicates the phase of the acquisition signal, represents the real part of the acquired signal, Represents the imaginary part of the collected signal, N s Indicates the sampling point.

[0080] Finally, based on the results of the online fast Fourier analysis, decision module 115 determines whether to activate adaptive filter 120 according to the input signal. If adaptive filter 120 is activated, voltage synchronization controller 130 can perform synchronization control based on the subsynchronous frequency band voltage signal output by adaptive filter 120, thereby changing the damping of the energy storage and converter series compensation system and achieving subsynchronous resonance suppression. If adaptive filter 120 is not activated, voltage synchronization controller 130 can directly implement synchronization control based on the voltage signal.

[0081] In the above scheme, the subsynchronous frequency tracker 110 includes an acquisition module 111, a fast Fourier analysis module 113 and a decision module 115. It performs fast Fourier analysis on the acquired voltage signal and uses the analysis result to determine whether to activate the adaptive adjustment filter 120, thereby having high tracking accuracy.

[0082] Please continue to refer to Figure 2. In some embodiments, the adaptive adjustment filter 120 includes a low-pass filter 121, a high-pass filter 123, a band-pass filter 125 and a gain amplifier 127 connected in sequence. The low-pass filter 121 is used to receive the voltage signal, the band-pass filter 125 is also connected to the sub-synchronous frequency tracker 110, and the gain amplifier 127 is also connected to the voltage synchronization controller 130.

[0083] The low-pass filter 121 allows signals with frequencies below the low-pass frequency threshold to pass through, while blocking signals with frequencies above the low-pass frequency threshold. The high-pass filter 123 allows signals with frequencies above the high-pass frequency threshold to pass through, but blocks signals with frequencies below the high-pass frequency threshold. The bandpass filter 125 allows signals within a certain frequency band to pass through, while blocking signals outside of this frequency band. The gain amplifier 127 amplifies the input signal at a certain gain factor and then outputs it.

[0084] It is understandable that the way in which the low-pass filter 121 receives the voltage signal is not unique. In some embodiments, it is consistent with the way in which the sub-synchronous frequency tracker 110 obtains the voltage signal through the strong current-weak current conversion board, which will not be repeated here.

[0085] It should be pointed out that the solution of this embodiment needs to select the signal within the sub-synchronous frequency band through the low-pass filter 121, the high-pass filter 123 and the band-pass filter 125 in sequence. The signal output by the low-pass filter 121 needs to be filtered again by the high-pass filter 123. Therefore, the low-pass frequency threshold of the low-pass filter 121 needs to be set greater than the high-pass frequency threshold of the high-pass filter 123. Band-pass screening is performed again within the frequency band limited by the low-pass filter 121 and the high-pass filter 123 to obtain a signal within the sub-synchronous frequency band.

[0086] For example, in some embodiments, given that subsynchronous resonance generally occurs between 2 Hz and 45 Hz, the lower limit of the bandpass frequency range of the bandpass filter 125 can be set to approximately 2 Hz, such as 1.8 Hz, 2 Hz, or 2.2 Hz, and the upper limit of the bandpass frequency range can be set to approximately 45 Hz, such as 44 Hz, 46 Hz, etc., without specific limitation. Accordingly, the low-pass frequency threshold of the low-pass filter 121 needs to be set to be greater than or equal to 45 Hz, and the high-pass frequency threshold of the high-pass filter 123 needs to be set to be less than or equal to 2 Hz.

[0087] In the solution of this embodiment, the transfer function G of the low-pass filter 121 and the high-pass filter 123 is L (s), G H (s) can be expressed as:

[0088] Among them, ω L represents the angular frequency corresponding to the low-pass frequency threshold of the low-pass filter 121, which can be specifically set to ω L =2πf max ,ω L represents the angular frequency corresponding to the high-pass frequency threshold of the high-pass filter 123, which can be specifically set to ω L =2πf min , where f min The lower limit of the passband frequency range, f max The upper limit of the bandpass frequency range.

[0089] The transfer function G of the bandpass filter 125 is bp (s) can be expressed as: Where, the angular frequency ω sub =2πf sub , subsynchronous frequency f sub (ie, the sampling signal frequency) is acquired and detected by the sub-synchronous frequency tracker 110.

[0090] In summary, by measuring the difference Δv between the voltage signal and the initial voltage signal dc , passes through low-pass, high-pass, and band-pass filters 125 to obtain Δv dc Subsynchronous frequency band After amplification by the gain amplifier 127, the Furthermore, by adding the input terminal of the voltage synchronization controller 130 through feedforward control, the subsynchronous resonance damping support function can be effectively achieved. sub is the gain of the gain amplifier 127, which can be used as the damping coefficient of the damping controller.

[0091] In the above solution, the adaptive adjustment filter 120 performs low-pass filtering, high-pass filtering, band-pass filtering and gain processing on the voltage signal, thereby accurately screening out the voltage signal in the subsynchronous frequency band and improving the accuracy of damping suppression.

[0092] Please continue to refer to Figure 2. In some embodiments, the voltage synchronization controller 130 includes a first subtractor 131, a second subtractor 132, a droop controller 133, a first adder 134, a multiplier 135 and an integrator 136 connected in sequence. The first subtractor 131 is also used to receive the voltage signal, the second subtractor 132 is also connected to the adaptive adjustment filter 120, the first subtractor 131 is also used to receive the initial voltage signal, the first adder 134 is also used to receive the system rated frequency, and the multiplier 135 is also used to receive the system angular frequency reference value.

[0093] A subtractor is a device that subtracts the two signals input to the node to obtain a difference signal. A subtractor is a device that adds the two signals input to the node to obtain the sum of the superimposed signals. Droop controller 133 is a device that performs droop control on the input signal. Multiplier 135 is an electronic device that multiplies two unrelated analog signals (specifically, the system angular frequency reference value and the converter frequency in this embodiment of the application). Integrator 136 is a device that integrates the input signal with respect to time and outputs it.

[0094] It is understandable that the way in which the first subtractor 131 receives the voltage signal is not unique. In some embodiments, it is consistent with the way in which the subsynchronous frequency tracker 110 obtains the voltage signal through the strong current-weak current conversion board, which will not be repeated here.

[0095] Under the condition that the adaptive adjustment filter 120 is activated, the voltage signal and the initial voltage signal are subtracted in the first subtractor 131 to obtain the voltage variation Δv dc , voltage change Δv dc The subsynchronous frequency band voltage signal is simultaneously transmitted to the second subtractor 132 for subtraction, and the difference signal is output to the droop controller 133 for droop control, and the frequency change is output and compared with the system frequency rated value f c(0) The sum is added at the first adder 134 to determine the converter frequency f required by the converter. c . Then the converter frequency f c and the system angular frequency reference value ω B The two are simultaneously transmitted to the multiplier 135 for multiplication, and the result of the multiplication is output to the integrator 136 for processing to ultimately determine the output phase angle signal required by the converter.

[0096] When the adaptive adjustment filter 120 is not activated, the voltage signal and the initial voltage signal are subtracted in the first subtractor 131 to obtain the voltage variation Δv dc , voltage change Δv dc The output is sent to the droop controller 133 for droop control, and the frequency change is output and compared with the system frequency rating f c(0) The sum is added at the first adder 134 to determine the converter frequency f required by the converter. c . Then the converter frequency f c and the system angular frequency reference value ω B The two are simultaneously transmitted to the multiplier 135 for multiplication, and the result of the multiplication is output to the integrator 136 for processing to ultimately determine the output phase angle signal required by the converter.

[0097] In the above scheme, the voltage synchronization controller 130 can combine the system rated frequency, the system angular frequency reference value, the initial voltage signal, the voltage signal and the sub-synchronous frequency band voltage signal to perform synchronization control, output the output phase angle signal required by the converter when suppressing damping, and has high voltage synchronization control reliability.

[0098] In some embodiments, satisfying the activation condition includes: the acquisition signal frequency satisfies a preset frequency condition, and the acquisition signal amplitude satisfies a preset amplitude condition; wherein the acquisition signal frequency and the acquisition signal amplitude are determined by performing online Fourier analysis on the voltage signal.

[0099] When analyzing whether activation conditions are met, decision module 115 employs different analysis methods depending on the input relevant characteristic parameters. This embodiment illustrates the solution using the example of relevant characteristic parameters including the sampled signal frequency and the sampled signal amplitude. Accordingly, decision module 115 pre-stores preset amplitude conditions and preset frequency conditions. The sampled signal frequency is compared and analyzed against the preset frequency conditions, and the sampled signal amplitude is compared and analyzed against the preset amplitude conditions. If both conditions are met, activation conditions are considered met.

[0100] The above scheme determines whether the activation conditions of the adaptive adjustment filter 120 are met by verifying whether the acquisition signal frequency and the acquisition signal amplitude meet the preset frequency conditions and the preset amplitude conditions respectively, and performs verification from two dimensions of frequency and amplitude to improve the accuracy of activation judgment.

[0101] In some embodiments, the acquisition signal frequency satisfies a preset frequency condition, including: the acquisition signal frequency is greater than or equal to a lower limit value of a set bandpass frequency, and is less than or equal to an upper limit value of the set bandpass frequency.

[0102] The solution of this embodiment needs to satisfy f min ≤f sub ≤f max , it is considered that the frequency of the collected signal meets the preset frequency condition. Among them, f min and f max They are used to set the upper and lower limits of the passband frequency, respectively. sub represents the frequency of the acquired signal analyzed by the fast Fourier analysis module 113. The set passband frequency is the frequency range corresponding to the frequency band signal allowed to pass by the bandpass filter 125 in the adaptive adjustment filter 120. For example, in some embodiments, the set passband frequency can be set to 2 Hz-45 Hz. Accordingly, the lower limit of the set passband frequency is 2 Hz, and the upper limit of the set passband frequency is 45 Hz.

[0103] In the above scheme, when the frequency of the collected signal is between the upper limit and the lower limit of the set bandpass frequency, it is considered that the preset frequency condition is met, so as to achieve damping suppression within the range of the set bandpass frequency and improve the accuracy of damping suppression.

[0104] In some embodiments, the amplitude of the collected signal satisfies a preset amplitude condition, including: a ratio of the amplitude of the collected signal to the nominal amplitude is greater than or equal to a set threshold.

[0105] The nominal amplitude is the ratio of the peak value of the effective signal to the average power of the signal. It is considered that the amplitude of the collected signal meets the preset amplitude condition, where A sub and A nom are the amplitude of the sampling signal waveform and the nominal value amplitude, T set A threshold is set to measure the subsynchronous resonance damping controller. When the subsynchronous oscillation degree exceeds a certain range, the subsynchronous resonance damping controller is activated.

[0106] In the above scheme, when the ratio of the collected signal amplitude to the nominal amplitude is greater than or equal to the set threshold, it is considered that the preset amplitude condition is met, so as to achieve damping suppression when the collected signal amplitude is large, thereby improving the accuracy of damping suppression.

[0107] In order to facilitate understanding of the technical solution of the present application, the present application is explained below in conjunction with more detailed embodiments.

[0108] During the operation of the energy storage converter series compensation system, the acquisition module 111 of the sub-synchronous frequency tracker 110 uses the strong-weak current conversion board and the voltage collector set on the capacitor to collect the voltage of the capacitor through the sliding rectangular window. The sampling signal of the capacitor voltage is then analyzed by the fast Fourier analysis module 113 of the sub-synchronous frequency tracker 110 to obtain the sampling signal frequency f sub and the sampling signal amplitude A sub , and transmits it to the decision module 115. The decision module 115 determines the nominal amplitude of the sampling signal according to the pre-stored nominal amplitude A nom , set the threshold T set , set the upper limit value f of the bandpass frequency max and set the lower limit of the passband frequency f min , analyze f min ≤f sub ≤f max as well as Whether they are established at the same time.

[0109] If both conditions are met, the activation condition is considered to be met, and the adaptive adjustment filter 120 will be activated, and the signal within the subsynchronous frequency band will be selected through the low-pass filter 121, the high-pass filter 123 and the band-pass filter 125 in sequence. After amplification by the gain amplifier 127, the The input terminal of the voltage synchronization controller 130 is further added through feedforward control.

[0110] At the voltage synchronization controller 130, the voltage signal and the initial voltage signal are subtracted in the first subtractor 131 to obtain the voltage variation Δv dc , voltage change Δv dc and subsynchronous frequency band voltage signal At the same time, it is transmitted to the second subtractor 132 for subtraction, and the difference signal is output to the droop controller 133 for droop control. The frequency change is output and compared with the system frequency rated value f c(0) The sum is added at the first adder 134 to determine the converter frequency f required by the converter. c . Then the converter frequency f c and the system angular frequency reference value ω B At the same time, they are transmitted to the multiplier 135 for multiplication, and the result of the multiplication is output to the integrator 136 for processing, and finally the output phase angle signal required by the converter is determined, thereby controlling the generation of the pulse width modulation signal.

[0111] If the activation condition is not met, the adaptive adjustment filter 120 is turned off, and the voltage signal and the initial voltage signal are subtracted in the first subtractor 131 to obtain the voltage variation Δv dc , voltage change Δv dc The output is sent to the droop controller 133 for droop control, and the frequency change is output and compared with the system frequency rating f c(0) The sum is added at the first adder 134 to determine the converter frequency f required by the converter. c . Then the converter frequency f c and the system angular frequency reference value ω B The two are simultaneously transmitted to the multiplier 135 for multiplication, and the result of the multiplication is output to the integrator 136 for processing to ultimately determine the output phase angle signal required by the converter.

[0112] Please refer to Figure 3. The present application also provides an energy storage and current conversion series compensation system, including a capacitor C, a converter 320, a series compensation circuit 330 and the above-mentioned damping controller 340 (the subsynchronous frequency tracker 110 and the adaptive adjustment filter 120 are not shown in the figure, and can be combined with Figure 2 for easier understanding). The first end and the second end of the capacitor C are respectively used to connect to the energy storage battery pack 310, the first end of the capacitor C is also connected to the converter 320, the second end of the capacitor C is also connected to the converter 320, the converter 320 is also connected to the damping controller 340 and the series compensation circuit 330, and the series compensation circuit 330 is used to connect to the AC power grid.

[0113] The series compensation circuit 330 is a series compensation circuit, which is a circuit used to improve the power factor of the energy storage converter series compensation system, stabilize the energy storage converter series compensation system and reduce voltage fluctuations. In the embodiment of the present application, the converter 320 specifically includes a grid-type converter. In the damping controller 340, the subsynchronous frequency tracker 110, the adaptive adjustment filter 120 and the voltage synchronization controller 130 can all perform voltage acquisition through the strong-weak current conversion board and the voltage collector provided at the capacitor C; the specific structure and implementation principle of the damping controller 340 are as shown in the above-mentioned embodiments and drawings, and will not be repeated here.

[0114] The above-mentioned energy storage converter series compensation system is connected to the damping controller 340 at the converter 320. The damping controller 340 can change the damping of the energy storage converter series compensation system in the event of subsynchronous resonance instability, thereby improving the operating stability of the energy storage converter series compensation system.

[0115] Please refer to Figure 3. In some embodiments, the energy storage and current conversion series compensation system also includes a reactive power control device 410, a voltage reference device 420 and a pulse width generator 430. The reactive power control device 410 and the damping controller 340 are respectively connected to the voltage reference device 420, and the pulse width generator 430 is respectively connected to the voltage reference device 420 and the converter 320.

[0116] Reactive power control device 410 is a device that regulates and controls reactive power in an electric power system to maintain system stability and reliability. Voltage reference device 420 generates the required duty cycle for a pulse-width modulation signal based on the output phase angle signal and the modulation ratio reference value output by reactive power control device 410. Pulse width generator 430 generates a pulse-width modulation signal based on the input duty cycle signal.

[0117] In the energy storage inverter series compensation system, the damping controller 340 performs synchronous control based on the voltage signal of capacitor C and can be considered the active power control circuit. To improve the operational reliability of the energy storage inverter series compensation system, this embodiment also includes a reactive power control device 410 in addition to active power control. This reactive power control device manages and controls the flow of reactive power.

[0118] In this embodiment, reactive power control is used to generate a pulse width modulation signal corresponding to the modulation ratio reference value required for regulating converter 320. The modulation ratio reference value and the output phase angle signal are then transmitted to voltage reference device 420, which analyzes and determines the required duty cycle for the pulse width modulation signal. Finally, the required duty cycle is transmitted to pulse width generator 430, which generates a corresponding pulse width modulation signal to control converter 320.

[0119] The above solution combines the output phase angle signal and the modulation ratio reference value generated by the reactive power control device 410 to generate a corresponding pulse width modulation signal for the converter 320 through the voltage reference device 420 and the pulse width generator 430, thereby improving the operating reliability of the converter 320.

[0120] Please continue to refer to Figure 3. In some embodiments, the reactive control device 410 includes a reactive control module 411, a second adder 413 and an auxiliary damping controller 412. The reactive control module 411 and the auxiliary damping controller 412 are respectively connected to the second adder 413, and the second adder 413 is connected to the voltage reference device 420.

[0121] The reactive power control module 411 is used to implement reactive power control and determine the modulation ratio reference value. The auxiliary damping controller 412 assists in damping control, outputting a modulation ratio variation value to suppress oscillations other than subsynchronous resonance in the energy storage converter series compensation system. The reactive power control module 411 performs reactive power regulation and control to obtain a modulation ratio reference value. This value is then added to the modulation ratio variation value output by the auxiliary damping controller 412 in a second adder 413 to determine the modulation ratio reference value.

[0122] The above scheme combines the modulation ratio reference value generated by the reactive power control module 411 and the modulation ratio change value generated by the auxiliary damping controller 412 to perform an addition operation to obtain the actual modulation ratio reference value, thereby controlling the generation of the pulse width modulation signal, which can effectively improve the accuracy of the modulation ratio reference value.

[0123] Please refer to Figure 3. In some embodiments, the energy storage converter series compensation system further includes a first inductor and a first capacitor. The first end of the first inductor is connected to the converter 320, the second end of the first inductor is connected to the first end of the first capacitor and the series compensation circuit 330, and the second end of the first capacitor is grounded.

[0124] In the solution of this embodiment, a first inductor and a first capacitor are further provided between the converter 320 and the series compensation circuit 330. The first end of the first capacitor, the second end of the first inductor, and the common connection point of the series compensation circuit 330 serve as a grid connection point. Correspondingly, the voltage at this point serves as the grid connection point voltage.

[0125] In the above solution, the converter 320 is connected to the series compensation circuit 330 through the first inductor and the first capacitor. The first inductor and the first capacitor make the voltage transmission more stable and reliable, further improving the operational reliability of the energy storage converter series compensation system.

[0126] It should be noted that the specific structure of the series compensation circuit 330 is not unique. Please refer to Figure 3. In some embodiments, the series compensation circuit 330 includes a second inductor and a second capacitor connected in series, and the end of the second inductor away from the second capacitor is also connected to the converter 320, and the end of the second capacitor away from the second inductor is used to connect to the AC power grid.

[0127] In the solution of this embodiment, the series compensation circuit 330 specifically includes a second inductor and a second capacitor connected in series, and the series compensation function is achieved through the second inductor and the second capacitor.

[0128] In the above solution, the series compensation circuit 330 includes a second inductor and a second capacitor, and a series compensation circuit is formed by the second inductor and the second capacitor, thereby improving the power factor of the energy storage and current conversion series compensation system, stabilizing the energy storage and current conversion series compensation system, and reducing voltage fluctuations.

[0129] Please refer to FIG. 4 . The present application further provides a stability analysis method based on the above-mentioned energy storage converter series compensation system, including step 402 and step 404 .

[0130] Step 402 : When the adaptive adjustment filter is not activated, the overall state space model of the energy storage converter series compensation system is obtained.

[0131] Step 404 : performing eigenvalue solution based on the overall state space model to determine the stability analysis result.

[0132] The energy storage converter series compensation system is shown in the above-mentioned embodiments and drawings, wherein the overall state space model is determined by linearization processing based on the operating state model, and the operating state model is constructed based on modal analysis. The stability analysis proposed in the embodiment of the present application refers to subsynchronous resonance stability analysis. When the adaptive adjustment filter 120 is not activated, that is, the damping controller 340 is not activated, the voltage synchronization controller 130 in the damping controller 340 does not have a subsynchronous frequency band voltage signal input for synchronous control.

[0133] In actual scenarios, the overall state space model of the energy storage converter 320 can be pre-constructed and stored in the processor. When there is a need for stability analysis, it can be directly obtained from the processor. In another embodiment, the overall state space model may not be constructed in advance. When there is a need for stability analysis, after the operating state model is constructed based on modal analysis, linearization processing is further performed based on the operating state model to determine the overall state space model. After determining the overall state space model, the eigenvalue solution of the differential-algebraic equations represented by the overall state space model is performed, and the stability analysis result is determined by the final solution result, that is, whether the energy storage converter series compensation system has subsynchronous resonance instability at this time, and when subsynchronous resonance instability exists, what are the main factors causing subsynchronous resonance instability, etc.

[0134] In the above scheme, when the adaptive adjustment filter 120 is not activated and the voltage synchronization controller 130 does not receive the sub-synchronous frequency band voltage signal, a modal analysis is performed on the energy storage converter series compensation system, an overall state space model is constructed, and the stability analysis of the energy storage converter series compensation system is realized by solving the eigenvalues ​​of the overall state space model. The stability analysis results are obtained, thereby providing data support for the sub-synchronous resonance theoretical analysis of the energy storage converter series compensation system constructed by the grid-type converter 320.

[0135] It should be noted that the specific types of operating state models are not unique and may vary depending on the actual structure of the energy storage converter series compensation system. In some embodiments, the operating state model includes at least one of a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model.

[0136] The operating state model can be one or more of a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model. In some embodiments, the operating state model also includes a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model.

[0137] The capacitor dynamic model is the dynamic equation of the capacitor C during operation, which can be expressed as: Where C represents the capacitance of capacitor C, v dc Represents the voltage signal, P r represents the output power of the energy storage battery group 310, P c It is understood that without considering the loss of the converter 320, the power output from the capacitor C to the converter 320 should be consistent with the output power of the converter 320, that is, the output power of the converter 320 can be equivalently expressed as P c .

[0138] The voltage droop control model is the voltage droop control equation of the voltage synchronization controller 130 in the damping controller 340, which can be specifically expressed as: dc -v dc(0) =K dc (f c -f c(0) ), where v dc(0) Represents the initial voltage signal, K dcrepresents the droop coefficient of the droop controller 133 in the voltage synchronous controller 130, f c Indicates the frequency of the converter 320, f c(0) Indicates the system frequency rating.

[0139] The converter virtual power angle model is the virtual power angle equation of the converter 320 under voltage synchronization control, which can be specifically expressed as:

[0140] Among them, δ c Indicates the output phase angle signal, H dc represents the virtual inertia constant, ω B Indicates the system angular frequency reference value, v dc(0) Represents the initial voltage signal, K dc represents the droop coefficient of the droop controller 133 in the voltage synchronous controller 130, f c Indicates the frequency of the converter 320, f c(0) Indicates the system frequency rating, P r represents the output power of the energy storage battery group 310, P c represents the output power of the converter 320 .

[0141] After this, the relationship between the converter AC voltage and DC voltage can be determined, that is, the converter AC and DC voltage model, which can be expressed as: v c =mv dc , where v c Indicates AC voltage, v dc represents the DC voltage signal, and m represents the modulation ratio reference value.

[0142] The converter dynamic model refers to the dynamic equations of the converter 320 and the shunt capacitor. The corresponding equations when finally organized into a dq coordinate system can be specifically expressed as:

[0143] in, represents the d-axis component of the output current of the converter 320, represents the q-axis component of the output current of the converter 320, L c represents the inductance value of the first inductor, represents the d-axis component of the AC voltage, The q-axis component of the AC voltage, represents the d-axis component of the grid connection point voltage, represents the q-axis component of the grid-connected point voltage, C1 represents the capacitance value of the first capacitor, represents the d-axis component of the current input to the AC grid, It represents the q-axis component of the current input to the AC grid.

[0144] The series compensation model refers to the series compensation degree of the AC system containing the series compensation device, which is specifically expressed as: Among them, SCL represents the series compensation level, L l represents the inductance of the second inductor in the series compensation circuit 330, C l represents the capacitance value of the second capacitor in the series compensation circuit 330, ω B Indicates the system angular frequency reference value.

[0145] The series compensation capacitor transient differential model refers to the electromagnetic transient differential equation of the second capacitor in the series compensation circuit 330, which can be specifically expressed as:

[0146] Among them, L l represents the inductance of the second inductor in the series compensation circuit 330, C l represents the capacitance value of the second capacitor in the series compensation circuit 330, represents the d-axis component of the equivalent voltage of the AC grid, The q-axis component of the equivalent voltage of the AC grid, The d-axis component representing the voltage value of the second capacitor, The q-axis component representing the voltage value of the second capacitor, represents the d-axis component of the grid connection point voltage, represents the q-axis component of the grid-connected point voltage, represents the d-axis component of the current input to the AC grid, It represents the q-axis component of the current input to the AC grid.

[0147] The above scheme uses one or more of the capacitor dynamic model, voltage droop control model, converter virtual power angle model, converter AC / DC voltage model, converter dynamic model, series compensation model and series compensation capacitor transient differential model for linearization processing, thereby determining the overall state space model and improving the accuracy of the overall state space model.

[0148] Referring to FIG. 5 , in some embodiments, step 404 includes step 502 , step 504 , and step 506 .

[0149] Step 502: performing eigenvalue solution based on the overall state space model to determine the eigenvalue.

[0150] Step 504 : Solve the eigenvalues ​​to determine the oscillation frequency and damping ratio.

[0151] Step 506: Determine the stability analysis result according to the oscillation frequency and the damping ratio.

[0152] In the solution of this embodiment, the operating state model includes a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model. By linearizing each of the above models at the equilibrium point, the following differential-algebraic equation system is obtained:

[0153] in, and They represent the coefficient matrix after linearization, Δy represents the output variable matrix, and Δx represents the state variable matrix. There are 10 variables in total, which can be expressed as:

[0154] After that, the system is subjected to eigenvalue analysis, where the droop coefficient K dc The value is set to 41.7 (per unit), and the system series compensation SCL is selected to be 68%. The calculated eigenvalues, oscillation frequencies, and damping ratios are shown in the following table:

[0155] It can be clearly observed from the table above that the energy storage converter series compensation system has 10 eigenvalues ​​corresponding to different oscillation modes. The oscillation frequencies are distributed between 7.13Hz and 316.06Hz, representing high-frequency oscillation modes (316.06Hz, 216.14Hz), super-synchronous oscillation mode (83.57Hz), sub-synchronous oscillation mode (16.22Hz), and low-frequency oscillation mode (7.13Hz). Most of the oscillation modes in the table are stable, but there is an unstable mode λ in the system that requires special attention. 9,10 = 0.2 ± j101.9, with a positive real part and an imaginary frequency of 101.9 rad (16.22 Hz), indicating a subsynchronous oscillation mode. Based on the established model and eigenvalue analysis, an important phenomenon was discovered: SSR instability also occurs in the energy storage-converter series compensation system of the grid-connected converter 320.

[0156] The above scheme obtains eigenvalues ​​by solving the eigenvalues ​​based on the overall state-space model, and combines the oscillation frequency and damping ratio obtained by the eigenvalue calculation to verify the subsynchronous resonance phenomenon of the energy storage converter series compensation system. It has the advantage of high accuracy in stability analysis.

[0157] Referring to FIG. 6 , in some embodiments, step 506 includes step 602 and step 604 .

[0158] Step 602 : Determine the target oscillation frequency and target damping ratio when the energy storage converter series compensation system is unstable based on the oscillation frequency and the damping ratio.

[0159] Step 604 : Perform participation factor analysis based on the target oscillation frequency and the target damping ratio to determine the instability dominant parameter.

[0160] Taking the above table as an example, in order to reveal the dominant system link that causes SSR instability in the energy storage converter series compensation system, the instability mode λ 9，10 The participation factor analysis shown in Figure 7 was performed. The horizontal axis of Figure 7 represents the order of the state variables, while the vertical axis represents the specific value of the participation factor after normalization. As can be seen from Figure 7, the state variable Δv dc , Δδ c 、 The participation in the instability mode is high. Specifically, the two state variables with the highest participation Δv dc and Δδ c , which is strongly related to the voltage synchronous controller 130 in FIG7 , and the four state variables with the second highest participation This phenomenon is strongly correlated with the dynamics of the series compensation circuit 330 in the AC power grid shown in Figure 7. Explained from the perspective of the dominant system dynamics, this new type of SSR instability is caused by the interaction between the voltage synchronization controller 130 of the converter 320 and the series compensation circuit 330. Within the subsynchronous frequency band, significant energy exchange occurs between the two dominant links, ultimately resulting in unstable output power of the energy storage system.

[0161] The above scheme, based on the oscillation frequency and damping ratio solved respectively under each characteristic, finds the target oscillation frequency and target damping ratio when the energy storage converter series compensation system occurs subsynchronous resonance (i.e., instability), further performs a participating factor analysis on it, finds the main factors causing subsynchronous resonance, and provides a theoretical basis for the construction of the damping controller 340.

[0162] Furthermore, in order to verify the effectiveness of the proposed damping controller 340, the droop coefficient K dc Set to 41.7, the system series compensation degree SCL is selected as 68%. For example, the system dynamic equation of the damping controller 340 is added to the system state space model, and the characteristic values ​​are recalculated under the same working conditions and organized as shown in the following table, where the damping coefficient D sub The value is 0.25:

[0163] It can be seen from the table that after the damping controller 340 of the embodiment of the present application is connected, the damping ratio of each oscillation mode of the energy storage converter series compensation system is significantly improved compared with the above table. In particular, there is a characteristic value λ of subsynchronous instability 9,10 After adding the proposed damping controller 340, the real part of the eigenvalue becomes negative and the damping ratio is increased to 0.398%, which fully verifies the effectiveness of the proposed damping controller 340.

[0164] To further illustrate the damping coefficient D of the damping controller 340 sub The root locus analysis of the influence of SSR instability was carried out based on the state space method as shown in Figure 8. sub The value varies from 0.1 to 0.3. Due to the negative damping effect of the SSR instability of the system under study, the damping coefficient cannot be arbitrarily given to stabilize the unstable mode of the system. sub When it increases from 0.1 to 0.3, the real part of the eigenvalue of the SSR instability mode of interest moves from right to left, and the system moves from the right half plane unstable region to the left half plane stable region. In particular, the critical damping coefficient D sub is 0.15.

[0165] In order to verify the theoretical calculation results of the above eigenvalue analysis and root locus analysis and further fully reflect the dynamic response characteristics of the proposed damping controller 340, Figures 9 and 10 respectively show the SSR oscillation time domain response diagram after the proposed control scheme is put into use and the system time domain response diagram under different operating parameters.

[0166] In FIG9 , the system disturbance is set as follows: at t=20s (seconds), the energy storage converter series compensation system is put into the series compensation circuit 330, SCL increases from 0 to 70%, and at the same time, the droop coefficient K dc The damping controller 340 is set to 40. It is put into operation at t = 21.5s, and the damping coefficient D sub is 0.25. As can be seen from Figure 9, when the system SCL rises, the output power of the converter 320 shows a divergent SSR oscillation phenomenon, and its three-phase AC voltage also produces distortion within the sub-synchronous frequency band. However, after the damping controller 340 is put into operation, the active power output by the converter 320 converges rapidly in a short period of time and returns to a new equilibrium stability point. The sub-synchronous distortion of the converter's three-phase AC voltage also disappears rapidly and returns to normal power frequency operation. The above electromagnetic transient time-domain simulation results fully demonstrate that the damping controller 340 of the embodiment of the present application can significantly improve the damping level of the SSR instability mode, correct the original negative damping mode to a positive damping mode, and greatly improve the stable operation capability of the grid-connected energy storage converter 320.

[0167] In order to verify the adaptability and robustness of the damping controller 340 under multiple working conditions, FIG10 shows different voltage droop coefficients K dc The dynamic response characteristics of the system under different series compensation SCL, where the damping coefficient D sub As shown in Figure 10, K fluctuates over a wide range. dcIn both the SCL (16-40%) and SCL (64%-78%) scenarios, the proposed control scheme fully demonstrates its SSR suppression capabilities. After divergent SSR oscillations occur, engaging the damping controller 340 quickly restores the system to normal, stable operation. These simulation results closely correspond to theoretical analysis, further validating the effectiveness, adaptability, and robustness of the proposed scheme.

[0168] The present application also provides an energy storage system, including an energy storage battery pack and the above-mentioned energy storage converter series compensation system.

[0169] The energy storage converter series compensation system is described in the various embodiments and accompanying figures above and will not be further described here. The energy storage system, located between the energy storage battery pack 310 and the AC power grid, includes a damping controller 340. This controller collects the voltage signal across capacitor C, located between the energy storage battery pack 310 and the converter 320 of the energy storage converter series compensation system, and based on this voltage signal, determines whether activation conditions are met. If the activation conditions are met, the adaptive adjustment filter 120 is activated, causing the damping controller 340 to enter operation of the energy storage converter series compensation system. Subsequently, the voltage synchronization controller 130 determines the required output phase angle signal corresponding to the pulse width modulation signal for controlling the converter 320 based on the subsynchronous frequency band voltage signal output by the adaptive adjustment filter 120 and the initial voltage signal. Through the above scheme, when the activation conditions are met, the damping controller 340 can be put into operation in the energy storage converter series compensation system, thereby improving the damping level of the unstable subsynchronous resonance mode, correcting the original negative damping mode to a positive damping mode, and improving the stable operation capability of the grid-type converter 320.

[0170] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A damping controller, comprising: A subsynchronous frequency tracker, used to obtain a voltage signal of a capacitor disposed between an energy storage battery group and a converter of an energy storage converter series compensation system, and activate an adaptive adjustment filter when it is determined according to the voltage signal that an activation condition is met; An adaptive adjustment filter, connected to the sub-synchronous frequency tracker, configured to receive the voltage signal, and filter and adjust the voltage signal when activated, and output a sub-synchronous frequency band voltage signal; A voltage synchronization controller is connected to the adaptive adjustment filter and the converter, and is used to receive an initial voltage signal and determine an output phase angle signal according to the sub-synchronous frequency band voltage signal and the initial voltage signal; the output phase angle signal is used to generate a pulse width modulation signal to control the operation of the converter.

2. The damping controller according to claim 1, wherein: The sub-synchronous frequency tracker includes an acquisition module, a fast Fourier analysis module and a decision module which are connected in sequence. The acquisition module is used to obtain the voltage signal, and the decision module is also connected to the adaptive adjustment filter.

3. The damping controller according to claim 1 or 2, wherein: The adaptive adjustment filter includes a low-pass filter, a high-pass filter, a band-pass filter and a gain amplifier connected in sequence, the low-pass filter is used to receive the voltage signal, the band-pass filter is also connected to the sub-synchronous frequency tracker, and the gain amplifier is also connected to the voltage synchronization controller.

4. The damping controller according to any one of claims 1 to 3, wherein: The voltage synchronization controller includes a first subtractor, a second subtractor, a droop controller, a first adder, a multiplier and an integrator connected in sequence, the first subtractor is also used to receive the voltage signal, the second subtractor is also connected to the adaptive adjustment filter, the first subtractor is also used to receive the initial voltage signal, the first adder is also used to receive the system rated frequency, and the multiplier is also used to receive the system angular frequency reference value.

5. The damping controller according to any one of claims 1 to 4, wherein: Meeting the activation condition includes: the acquisition signal frequency meets the preset frequency condition, and the acquisition signal amplitude meets the preset amplitude condition; wherein the acquisition signal frequency and the acquisition signal amplitude are determined by performing online Fourier analysis on the voltage signal.

6. The damping controller according to claim 5, wherein: The acquisition signal frequency satisfies a preset frequency condition, which includes: the acquisition signal frequency is greater than or equal to a lower limit value of a set passband frequency, and is less than or equal to an upper limit value of the set passband frequency.

7. The damping controller according to claim 5, wherein: The acquisition signal amplitude satisfies a preset amplitude condition, including: a ratio of the acquisition signal amplitude to a nominal amplitude is greater than or equal to a set threshold.

8. An energy storage current conversion series compensation system, comprising a capacitor, a converter, a series compensation circuit and a damping controller according to any one of claims 1 to 7, wherein the first end and the second end of the capacitor are respectively used to connect to an energy storage battery pack, the first end of the capacitor is also connected to the converter, the second end of the capacitor is also connected to the converter, the converter is also connected to the damping controller and the series compensation circuit, and the series compensation circuit is used to connect to an AC power grid.

9. The energy storage converter series compensation system according to claim 8, wherein: The energy storage current conversion series compensation system also includes a reactive power control device, a voltage reference device and a pulse width generator. The reactive power control device and the damping controller are respectively connected to the voltage reference device, and the pulse width generator is respectively connected to the voltage reference device and the converter.

10. The energy storage converter series compensation system according to claim 9, wherein: The reactive power control device comprises a reactive power control module, a second adder and an auxiliary damping controller. The reactive power control module and the auxiliary damping controller are respectively connected to the second adder, and the second adder is connected to the voltage reference device.

11. The energy storage converter series compensation system according to any one of claims 8 to 10, wherein: The energy storage current conversion series compensation system also includes a first inductor and a first capacitor, the first end of the first inductor is connected to the converter, the second end of the first inductor is connected to the first end of the first capacitor and the series compensation circuit, and the second end of the first capacitor is grounded.

12. The energy storage converter series compensation system according to any one of claims 8 to 11, wherein: The series compensation circuit includes a second inductor and a second capacitor connected in series, wherein one end of the second inductor away from the second capacitor is also connected to the converter, and one end of the second capacitor away from the second inductor is used to connect to an AC power grid.

13. A stability analysis method for the energy storage converter series compensation system according to any one of claims 8 to 12, comprising: When the adaptive adjustment filter is not activated, an overall state space model of the energy storage inverter series compensation system is obtained; wherein the overall state space model is determined by linearization processing based on the operating state model, and the operating state model is constructed based on modal analysis; The eigenvalue solution is performed according to the overall state space model to determine the stability analysis result.

14. The stability analysis method according to claim 13, wherein: The operating state model includes at least one of a capacitor dynamic model, a voltage droop control model, a converter virtual power angle model, a converter AC / DC voltage model, a converter dynamic model, a series compensation model and a series compensation capacitor transient differential model.

15. The stability analysis method according to claim 13 or 14, wherein: The performing eigenvalue solving according to the overall state space model to determine the stability analysis result includes: Performing eigenvalue solving according to the overall state space model to determine eigenvalues; Solving according to the characteristic value to determine the oscillation frequency and the damping ratio; A stability analysis result is determined according to the oscillation frequency and the damping ratio.

16. The stability analysis method according to claim 15, wherein: Determining the stability analysis result according to the oscillation frequency and the damping ratio includes: Determining a target oscillation frequency and a target damping ratio when the energy storage converter series compensation system is unstable according to the oscillation frequency and the damping ratio; A participation factor analysis is performed according to the target oscillation frequency and the target damping ratio to determine the instability dominant parameter.

17. An energy storage system, comprising an energy storage battery pack and the energy storage converter series compensation system according to any one of claims 8 to 12.

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