Energy storage variable flow series compensation system, stability analysis method thereof and damping controller

Abstract

The invention relates to an energy storage variable flow series compensation system and a stability analysis method thereof, a damping controller and an energy storage system, which can collect a voltage signal arranged on a capacitor between an energy storage battery pack and a converter of the energy storage variable flow series compensation system, and judge whether an activation condition is met based on the voltage signal. And activating the self-adaptive adjustment filter under the condition that the activation condition is met, so that the damping controller is put into operation of the energy storage variable flow series compensation system. And the voltage synchronous controller determines an output phase angle signal required corresponding to a pulse width modulation signal for controlling the operation of the converter according to the subsynchronous frequency band voltage signal output by the self-adaptive adjustment filter and the initial voltage signal. According to the scheme, under the condition that the activation condition is met, the damping controller can be put into operation of the energy storage variable flow series compensation system, the damping level of an unstable subsynchronous resonance mode is improved, an original negative damping mode is corrected into a positive damping mode, and the stable operation capacity of the grid-forming type converter is improved.

Description

Technical Field

[0001] The present application relates to the technical field of electric energy transmission, and in particular to an energy storage converter series compensation system and a stability analysis method thereof, a damping controller, and an energy storage system. Background Art

[0002] With the development of science and technology, energy storage systems, as an important power system regulation resource, have brought great convenience to daily production and life. The energy storage battery pack of the energy storage system is generally connected to the AC power grid through the energy storage converter series compensation system. The converter in the energy storage converter series compensation system converts the stored energy into electric energy suitable for the grid demand and provides it to the power load in the AC power grid.

[0003] Among various types of converters, grid-type converters are gradually being used because they can improve the ability of energy storage systems to provide inertia and damping support for AC power grids. However, in related technologies, grid-type converters have poor stable operation capabilities. Summary of the invention

[0004] Based on this, it is necessary to provide an energy storage converter series compensation system and its stability analysis method, a damping controller, and an energy storage system to improve the stable operation capability of the grid-connected converter.

[0005] A damping controller includes a subsynchronous frequency tracker, an adaptive adjustment filter and a voltage synchronization controller, wherein the subsynchronous frequency tracker is used to obtain a voltage signal of a capacitor arranged between an energy storage battery group and an inverter of an energy storage inverter series compensation system, and activate the adaptive adjustment filter when it is determined according to 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 the voltage signal, and when activated, filters and adjusts the voltage signal, and outputs 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 according to 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

[0006] The damping controller can collect the voltage signal on the capacitor between the energy storage battery pack and the converter of the energy storage converter series compensation system, and judge whether the activation condition is met based on this, and activate the adaptive adjustment filter when the activation condition is met, so that the damping controller is put into operation in the energy storage converter series compensation system. After that, the voltage synchronization controller determines the output phase angle signal required for the pulse width modulation signal that controls the operation of the converter according to the sub-synchronous frequency band voltage signal output by the adaptive adjustment filter and the initial voltage signal. Through the above scheme, when the activation conditions are met, the damping controller can be put into operation in the energy storage converter series compensation system, improve the damping level of the unstable sub-synchronous resonance mode, correct the original negative damping mode to the positive damping mode, and improve the stable operation capability of the grid-type converter.

[0007] In some embodiments, the sub-synchronous 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 the voltage signal, and the decision module is also connected to the adaptive adjustment filter.

[0008] In the above scheme, the sub-synchronous 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.

[0009] 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 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.

[0010] 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 being able to accurately screen out the voltage signal in the sub-synchronous frequency band and improve the accuracy of damping suppression.

[0011] 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 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.

[0012] 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 damping-suppressing converter, and has high voltage synchronization control reliability.

[0013] 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.

[0014] 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, and verifies from two dimensions of frequency and amplitude to improve the accuracy of activation judgment.

[0015] In some embodiments, 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.

[0016] In the above scheme, when the frequency of the collected signal is between the upper limit and the lower limit of the set passband frequency, it is considered that the preset frequency condition is met to achieve damping suppression within the range of the set passband frequency, thereby improving the accuracy of damping suppression.

[0017] And / or, in some embodiments, the amplitude of the acquisition signal satisfies a preset amplitude condition, including: a ratio of the amplitude of the acquisition signal to a nominal amplitude is greater than or equal to a set threshold.

[0018] 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.

[0019] An energy storage current conversion series compensation system comprises a capacitor, a converter, a series compensation circuit and the above-mentioned damping controller, 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.

[0020] The 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.

[0021] In some embodiments, the energy storage converter series compensation system also includes a reactive control device, a voltage reference device and a pulse width generator, wherein the reactive 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.

[0022] The above scheme combines the output phase angle signal and the modulation ratio reference value generated by the reactive power control device, generates a corresponding pulse width modulation signal for the converter through the voltage reference device and the pulse width generator, and improves the operating reliability of the converter.

[0023] In some embodiments, the reactive control device includes a reactive control module, a second adder and an auxiliary damping controller, the reactive 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.

[0024] 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, thereby controlling the generation of the pulse width modulation signal, which can effectively improve the accuracy of the modulation ratio reference value.

[0025] In some embodiments, the energy storage converter series compensation system also includes a first inductor and a first capacitor, wherein 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.

[0026] In the above scheme, the converter is connected to the series compensation circuit through the first inductor and the first capacitor, and the voltage transmission is made more stable and reliable through the first inductor and the first capacitor, further improving the operating reliability of the energy storage converter series compensation system.

[0027] 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 also connected to the converter, and an end of the second capacitor away from the second inductor is used to connect to an AC power grid.

[0028] 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 converter series compensation system, stabilizing the energy storage converter series compensation system, and reducing voltage fluctuations.

[0029] A stability analysis method based on the above-mentioned energy storage inverter series compensation system includes: when the adaptive adjustment filter is not activated, obtaining the overall state space model of the energy storage inverter series compensation system; 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 result.

[0030] The above scheme performs modal analysis on the energy storage converter series compensation system, constructs an overall state space model, and implements stability analysis of the energy storage converter series compensation system by solving the eigenvalues ​​of the overall state space model, and obtains stability analysis results, thereby providing data support for subsynchronous resonance theoretical analysis of the energy storage converter series compensation system constructed by the grid-connected converter.

[0031] In some embodiments, the operating status 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.

[0032] The above scheme adopts 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, so as to determine the overall state space model and improve the accuracy of the overall state space model.

[0033] In some embodiments, solving the eigenvalues ​​according to the overall state-space model to determine the stability analysis results includes: solving the eigenvalues ​​according to the overall state-space model to determine the eigenvalues; solving according to the eigenvalues ​​to determine the oscillation frequency and the damping ratio; determining the stability analysis results according to the oscillation frequency and the damping ratio.

[0034] The above scheme obtains the eigenvalue by solving the eigenvalue 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, which has the advantage of high accuracy of stability analysis.

[0035] In some embodiments, determining the stability analysis result based on the oscillation frequency and the damping ratio includes: 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 instability dominant parameter.

[0036] 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 (that is, instability), further performs participating factor analysis, finds the main factors causing subsynchronous resonance, and provides a theoretical basis for the construction of the damping controller.

[0037] 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

[0038] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0039] Figure 1 This is a schematic diagram of the damping controller structure in some embodiments of the present application;

[0040] Figure 2 This is a schematic diagram of the structure of a damping controller in some other embodiments of the present application;

[0041] Figure 3 This is a schematic diagram of the structure of the energy storage converter series compensation system in some embodiments of the present application;

[0042] Figure 4 A schematic flow chart of a stability analysis method for an energy storage inverter series compensation system in some embodiments of the present application;

[0043] Figure 5 This is a schematic diagram of the stability analysis process in some embodiments of the present application;

[0044] Figure 6 This is a schematic diagram of the stability analysis process in some other embodiments of the present application;

[0045] Figure 7 This is a schematic diagram of participation factors in some embodiments of the present application;

[0046] Figure 8 This is a schematic diagram of root locus analysis in some embodiments of the present application;

[0047] Fig. 9 This is a schematic diagram of the dynamic response of the damping controller in some embodiments of the present application;

[0048] Fig.10 Schematic diagram of waveforms for verifying different parameters of the damping controller in some embodiments of the present application. DETAILED DESCRIPTION

[0049] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field 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" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0051] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0052] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0053] 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).

[0054] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0055] At present, from the perspective of market development, energy storage systems and AC power grids are widely used in grid-connected operation. Sub-synchronous oscillation (SSO) of power system is an unstable condition caused by energy exchange of one or more specific frequencies between power generation units (synchronous machines, new energy units) and AC / DC power grids. Its specific frequency is usually lower than the synchronous frequency of the power grid, 50Hz. Early sub-synchronous oscillations were mainly caused by the interaction between the synchronous machine shaft system and the series compensation of the power grid. The SSO instability was caused by the complementarity between the natural torsional vibration frequency of the synchronous machine shaft system and the resonant frequency of the series compensation line, so it was also called sub-synchronous resonance (SSR). However, with the access of large-scale new energy and a large number of power electronic equipment, more SSO instability accidents dominated by new energy have been found in real projects. Its generation mechanism is different from the SSR dominated by the traditional synchronous machine shaft system, and it has more new oscillation characteristics and manifestations.

[0056] Under the control of a typical grid-following (GFL) converter, the subsynchronous oscillation mechanism of the energy storage system has been studied more clearly. It is generally believed that the grid-following converter will not be mutually coupled with the series compensation circuit arranged on the AC grid side to cause the SSR (Sub-Synchronous Resonance) phenomenon. At present, most of the research is based on the SSO stability analysis of the grid-following converter.

[0057] However, with the development of power systems, a grid-forming (GFM) converter based on DC Voltage Synchronization Control (DVSC) has been proposed. Through research, it is found that although the GFM converter can improve the ability of the energy storage system to provide inertia and damping support for the AC power grid, the GFM converter has poorer stable operation capability than the GFL converter.

[0058] In order to alleviate the problem of poor stable operation capability of GFM converter, considering the difference in operation mode between GFM converter and GFL converter, it is possible to verify whether this type of energy storage converter series compensation system will have SSR instability when GFM converter is connected to energy storage converter series compensation system. Through in-depth research, it is found that, unlike GFL converter type energy storage converter series compensation system, GFM converter type energy storage converter series compensation system does have SSR instability phenomenon, and the SSR instability phenomenon causes poor stable operation capability of GFM converter.

[0059] Based on the above considerations, the embodiment of the present application designs a damping controller, connects it to the GFM converter, 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 judges whether the activation condition is met based on this, and activates the adaptive adjustment filter when the activation condition is met, so that the damping controller is put into operation of the energy storage converter series compensation system. After that, the voltage synchronization controller determines the output phase angle signal required for the pulse width modulation signal that controls the operation of the converter according to the sub-synchronous frequency band voltage signal output by the adaptive adjustment filter and the initial voltage signal.

[0060] Through the implementation 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.

[0061] The damping controller of the embodiment of the present application is applied in an energy storage system, specifically, in an energy storage converter series compensation system between an energy storage module (which may be an energy storage battery pack) and an AC power grid of the energy storage system. Considering that the SSR instability phenomenon does not usually occur in a GFL converter, the energy storage converter series compensation system referred to in the embodiment of the present application specifically includes an energy storage converter series compensation system of the GFM converter type.

[0062] See also Figure 1 The 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 an inverter of an energy storage inverter series compensation system, and activate the adaptive adjustment filter 120 when it is determined according to the voltage signal that an activation condition is met; the adaptive adjustment filter 120 is a sub-synchronous frequency tracker 110, which 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 inverter, 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 inverter.

[0063] Specifically, the energy storage battery pack is a battery structure formed by connecting multiple batteries for storing and releasing electric energy. The 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 whose frequency is 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 theoretical output when the energy storage converter series compensation system is operating at rated power.

[0064] The sub-synchronous frequency tracker 110 (Sub-Synchronous Frequency Tracker, SFT) refers to 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 inverter series compensation system for operation based on the tracking processing result, and performs damping control on the energy storage inverter series compensation system. The adaptive adjustment filter 120 refers to 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 refers to 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 inverter series compensation system.

[0065] During the operation of the energy storage inverter series compensation system, the sub-synchronous frequency tracker 110 can collect the voltage signal of the capacitor set between the energy storage battery group and the converter in real time, track and process the voltage signal, and judge whether it is necessary to activate the adaptive adjustment filter 120 based on the result of the tracking process. It should be pointed out that the way in which the sub-synchronous frequency tracker 110 collects voltage signals is not unique. In one embodiment, a voltage collector can be set at the capacitor, and the voltage collector and the sub-synchronous frequency tracker 110 are both connected to the strong-weak current conversion board, and the sub-synchronous frequency tracker 110 obtains the voltage signal collected by the voltage collector from the strong-weak current conversion board.

[0066] If the activation condition is satisfied according to the result of the tracking process, it means that the energy storage inverter series compensation system will have SSR instability phenomenon, and the adaptive adjustment filter 120 will be activated to perform the next step of damping adjustment processing. If the activation condition is not satisfied according to the result of the tracking process, it means that the energy storage inverter series compensation system will not have SSR instability phenomenon, and there is no need to activate the adaptive adjustment filter 120 for damping adjustment, and it is only necessary to return to continue to obtain the voltage signal for analysis.

[0067] 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-electric-weak-electric conversion board in a separate manner) will be filtered, and finally the sub-synchronous frequency band voltage signal will be obtained and transmitted to the voltage synchronization controller 130. At the voltage synchronization controller 130, active synchronization control is performed in combination with the sub-synchronous frequency band voltage signal and the initial voltage signal, and finally the output phase angle signal is obtained. By analyzing the modulation of the output phase angle signal, the pulse width modulation signal required by the converter after the damping adjustment can be determined, and the converter is controlled to be turned on and off with the analyzed pulse width modulation signal, thereby changing the damping of the energy storage converter series compensation system. Thereby, the damping level of the unstable sub-synchronous resonance 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.

[0068] The damping controller can collect the voltage signal on the capacitor between the energy storage battery group and the converter of the energy storage converter series compensation system, and judge whether the activation condition is met based on this, and activate the adaptive adjustment filter 120 when the activation condition is met, so that the damping controller is put into operation in the energy storage converter series compensation system. After that, the voltage synchronization controller 130 determines the output phase angle signal required for the pulse width modulation signal that controls the operation of the converter according to the sub-synchronous 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 can be put into operation in the energy storage converter series compensation system, improve the damping level of the unstable sub-synchronous resonance mode, correct the original negative damping mode to the positive damping mode, and improve the stable operation capability of the grid-type converter.

[0069] See also 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 a voltage signal, and the decision module 115 is also connected to an adaptive adjustment filter 120.

[0070] Specifically, the acquisition module 111 is a module for sampling the voltage signal of the input subsynchronous frequency tracker 110. The fast Fourier analysis module 113 is a module for performing fast Fourier analysis on the input sampling signal to determine the relevant characteristic parameters in the sampling signal, such as analyzing the sampling signal frequency and sampling signal amplitude, etc., which are not specifically limited. The decision module 115 is a module for determining whether the activation condition is met to activate the adaptive adjustment filter 120, which can be a comparator, etc., which are not specifically limited.

[0071] It should be noted that the specific type of the acquisition module 111 is not unique, as long as it can accurately acquire the voltage signal within a period of time. For example, in a more detailed embodiment, the sampling module includes a rolling rectangular sampling module. In an actual scenario, the voltage signal v dc It carries the broadband oscillation information of the energy storage inverter 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.

[0072] 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 restated as X(k):

[0073]

[0074] Combining the above formula, the relevant characteristic parameters in the sampled signal can be solved, for example:

[0075]

[0076] 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.

[0077] Finally, based on the online fast Fourier analysis results, the decision module 115 determines whether to activate the adaptive adjustment filter 120 according to the input signal. When the adaptive adjustment filter 120 is activated, the voltage synchronization controller 130 can perform synchronization control in combination with the sub-synchronous frequency band voltage signal output by the adaptive adjustment filter 120, thereby changing the damping of the energy storage inverter series compensation system to achieve sub-synchronous resonance suppression. When the adaptive adjustment filter 120 is not activated, the voltage synchronization controller 130 can directly achieve synchronization control according to the voltage signal.

[0078] In the above scheme, the sub-synchronous frequency tracker 110 includes an acquisition module 111, a fast Fourier analysis module 113 and a decision module 115, and performs fast Fourier analysis by acquiring voltage signals to determine whether to activate the adaptive adjustment filter 120 based on the analysis results, thereby having high tracking accuracy.

[0079] Please continue reading 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.

[0080] Specifically, the low-pass filter 121 is a device that allows signals with frequencies lower than the low-pass frequency threshold to pass through, and blocks signals with frequencies higher than the low-pass frequency threshold from passing through. The high-pass filter 123 is a device that allows signals with operating frequencies higher than the high-pass frequency threshold to pass through, but blocks signals with frequencies lower than the high-pass frequency threshold from passing through. The band-pass filter 125 is a device that allows signals within a certain frequency band to pass through, and signals beyond the frequency band cannot pass through. The gain amplifier 127 is a device that amplifies the input signal with a certain gain multiple and then outputs it.

[0081] It is understandable that the way in which the low-pass filter 121 receives the voltage signal is not unique. In one embodiment, 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.

[0082] It should be pointed out that the scheme 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, it is necessary to set the low-pass frequency threshold of the low-pass filter 121 to be greater than the high-pass frequency threshold of the high-pass filter 123, and perform band-pass screening again within the frequency band limited by the low-pass filter 121 and the high-pass filter 123, so as to obtain the signal within the sub-synchronous frequency band.

[0083] For example, in a more detailed embodiment, considering that subsynchronous resonance generally occurs in the range of 2 Hz-45 Hz, the lower limit of the bandpass frequency range of the bandpass filter 125 can be set at about 2 Hz, such as 1.8 Hz, 2 Hz or 2.2 Hz, etc., and the upper limit of the bandpass frequency range can be set at about 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.

[0084] 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:

[0085]

[0086]

[0087] 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 ωL=2πfmin, where fmin is the lower limit of the passband frequency range, and f max The upper limit of the passband frequency range.

[0088] 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 fsub (that is, the sampling signal frequency) is acquired and detected by the sub-synchronous frequency tracker 110.

[0089] In summary, by measuring the difference Δv between the voltage signal and the initial voltage signal dc , through low-pass, high-pass, and band-pass filters 125 to obtain Δv dc Subsynchronous frequency band After amplification by gain amplifier 127, we get Further, by adding the input end of the voltage synchronous controller 130 through feedforward control, the subsynchronous resonance damping support function is effectively realized. sub is the gain of the gain amplifier 127, which can be used as the damping coefficient of the damping controller.

[0090] In the above scheme, the adaptive adjustment filter 120 performs low-pass filtering, high-pass filtering, band-pass filtering and gain processing on the voltage signal, thereby being able to accurately screen out the voltage signal in the sub-synchronous frequency band and improve the accuracy of damping suppression.

[0091] Please continue reading Figure 2In 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 a voltage signal, the second subtractor 132 is also connected to the adaptive adjustment filter 120, the first subtractor 131 is also used to receive an initial voltage signal, the first adder 134 is also used to receive a system rated frequency, and the multiplier 135 is also used to receive a system angular frequency reference value.

[0092] Specifically, the subtractor is a device that subtracts the two signals input to the node to obtain a difference signal. The subtractor is a device that adds the two signals input to the node to obtain the sum of the superimposed signals. The droop controller 133 is a device that performs droop control on the input signal. The multiplier 135 is an electronic device that multiplies two unrelated analog signals (the embodiment of the present application specifically includes the system angular frequency reference value and the converter frequency). The integrator 136 is a device that integrates the input signal over time and outputs it.

[0093] It is understandable that the way in which the first subtractor 131 receives the voltage signal is not unique. In one embodiment, 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.

[0094] 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 change 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 first adder 134 adds the frequency f required by the converter to determine the converter frequency f 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, so as to finally determine the output phase angle signal required by the converter.

[0095] 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 rated value f c(0)The first adder 134 adds the frequency f required by the converter to determine the converter frequency f 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, so as to finally determine the output phase angle signal required by the converter.

[0096] 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, and output the output phase angle signal required by the converter when suppressing damping, which has high voltage synchronization control reliability.

[0097] 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.

[0098] Specifically, when the decision module 115 analyzes whether the activation condition is met, the analysis method will be different according to the different relevant characteristic parameters input. The solution of this embodiment is explained by taking the relevant characteristic parameters including the acquisition signal frequency and the acquisition signal amplitude as an example. Correspondingly, the decision module 115 pre-stores the preset amplitude condition and the preset frequency condition, and needs to compare and analyze the sampling signal frequency with the preset frequency condition, and compare and analyze the sampling signal amplitude with the preset amplitude condition. When both meet the corresponding conditions, it is considered that the activation condition is met.

[0099] The above scheme determines whether the activation condition of the adaptive adjustment filter 120 is met by verifying whether the acquisition signal frequency and the acquisition signal amplitude meet the preset frequency condition and the preset amplitude condition respectively, and verifies from two dimensions of frequency and amplitude to improve the accuracy of activation judgment.

[0100] 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 passband frequency, and is less than or equal to an upper limit value of a set passband frequency.

[0101] Specifically, the solution of this embodiment needs to satisfy f min ≤f sub ≤f max , it is considered that the collected signal frequency meets the preset frequency condition. Among them, f min and f max are used to set the upper and lower limits of the passband frequency, f subrepresents the frequency of the collected signal analyzed by the fast Fourier analysis module 113. The set passband frequency is the frequency range value corresponding to the frequency band signal allowed to pass by the bandpass filter 125 in the adaptive adjustment filter 120. For example, in a more detailed embodiment, the set passband frequency can be set to 2Hz-45Hz, and accordingly, the lower limit value of the passband frequency is set to 2Hz, and the upper limit value of the passband frequency is set to 45Hz.

[0102] In the above scheme, when the frequency of the collected signal is between the upper limit and the lower limit of the set passband frequency, it is considered that the preset frequency condition is met to achieve damping suppression within the range of the set passband frequency, thereby improving the accuracy of damping suppression.

[0103] 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 a nominal amplitude is greater than or equal to a set threshold.

[0104] Specifically, 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.

[0105] 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.

[0106] 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.

[0107] During the operation of the energy storage inverter series compensation system, the acquisition module 111 of the sub-synchronous frequency tracker 110 acquires the voltage of the capacitor through a sliding rectangular window by using the strong-weak current conversion board and the voltage collector set on the capacitor. Then, the fast Fourier analysis module 113 of the sub-synchronous frequency tracker 110 analyzes the sampling signal frequency f sub and the sampling signal amplitude A sub , and transmitted to the decision module 115. The decision module 115 determines the nominal amplitude A of the sampling signal according to the pre-stored nom , set the threshold T set , set the upper limit value f of the passband 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.

[0108] 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 sub-synchronous 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 gain amplifier 127, we get The input terminal of the voltage synchronous controller 130 is further added through feedforward control.

[0109] 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 change 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, and the frequency change is output and compared with the system frequency rated value f c(0) The first adder 134 adds the frequency f required by the converter to determine the converter frequency f 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, so as to control the generation of the pulse width modulation signal.

[0110] If it is determined that 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 change 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 rated value f c(0) The first adder 134 adds the frequency f required by the converter to determine the converter frequency f 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, so as to finally determine the output phase angle signal required by the converter.

[0111] See also Figure 3The present application also provides an energy storage 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 reference to Figure 2 For ease of understanding), the first end and the second end of the capacitor C are respectively used to connect to the energy storage battery group 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.

[0112] Specifically, 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 scheme of the embodiment of the present application, the converter 320 specifically includes a grid-type converter 320. In the damping controller 340, the sub-synchronous frequency tracker 110, the adaptive adjustment filter 120 and the voltage synchronization controller 130 can all perform voltage collection through the strong current-weak current conversion board and the voltage collector arranged 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.

[0113] The above 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.

[0114] See also Figure 3 In some embodiments, the energy storage converter series compensation system further 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.

[0115] Specifically, the reactive power control device 410 is a device that maintains the stability and reliability of the power system by regulating and controlling reactive power. The voltage reference device 420 is a device that generates the duty cycle required for the pulse width modulation signal according to the output phase angle signal and the modulation ratio reference value output by the reactive power control device 410. The pulse width generator 430 is a device that realizes the generation of the pulse width modulation signal according to the input duty cycle signal.

[0116] In the energy storage inverter series compensation system, the damping controller 340 performs synchronous control according to the voltage signal of the capacitor C, and this part can be regarded as an active power control circuit. In order to improve the operational reliability of the energy storage inverter series compensation system, the scheme of this embodiment, in addition to the active power control, also needs to set a reactive power control device 410, through which the reactive power flow is managed and controlled.

[0117] In the solution of this embodiment, reactive power control can generate a pulse width modulation signal corresponding to the required modulation ratio reference value for regulating the converter 320. The modulation ratio reference value and the output phase angle signal are then transmitted to the voltage reference device 420, which analyzes and determines the duty cycle required for the pulse width modulation signal. Finally, the required duty cycle is transmitted to the pulse width generator 430, which generates a corresponding pulse width modulation signal to control the operation of the converter 320.

[0118] The above scheme, combined with the output phase angle signal and the modulation ratio reference value generated by the reactive power control device 410, generates 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.

[0119] Please continue reading 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.

[0120] Specifically, the reactive power control module 411 is a device for realizing the reactive power control function to determine the modulation ratio reference value. The auxiliary damping controller 412 is a device for assisting the damping control and outputting the modulation ratio variation value to suppress other oscillations in the energy storage converter series compensation system except for the subsynchronous resonance. The reactive power control module 411 performs reactive power regulation control to obtain the modulation ratio reference value, and adds it to the modulation ratio variation value output by the auxiliary damping controller 412 in the second adder 413 to determine the modulation ratio reference value.

[0121] The above scheme combines the modulation ratio reference value generated by the reactive control module 411 and the modulation ratio change value generated by the auxiliary damping controller 412 for 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.

[0122] See also Figure 3In some embodiments, the energy storage converter series compensation system further includes a first inductor and a first capacitor, wherein 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.

[0123] Specifically, in the solution of this embodiment, a first inductor and a first capacitor are further arranged between the converter 320 and the series compensation circuit 330, and 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, and correspondingly, the voltage at this point serves as the grid connection point voltage.

[0124] In the above scheme, the converter 320 is connected to the series compensation circuit 330 through the first inductor and the first capacitor. The voltage transmission is made more stable and reliable through the first inductor and the first capacitor, further improving the operating reliability of the energy storage converter series compensation system.

[0125] It should be noted that the specific structure of the series compensation circuit 330 is not unique. Figure 3 In some embodiments, the series compensation circuit 330 includes a second inductor and a second capacitor connected in series, an end of the second inductor away from the second capacitor is also connected to the converter 320, and an end of the second capacitor away from the second inductor is used to connect to the AC power grid.

[0126] Specifically, 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 realized by the second inductor and the second capacitor.

[0127] In the above scheme, the series compensation circuit 330 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 converter series compensation system, stabilizing the energy storage converter series compensation system, and reducing voltage fluctuations.

[0128] Please refer to Figure 4 The present application also provides a stability analysis method based on the above energy storage converter series compensation system, including step 402 and step 404.

[0129] Step 402: When the adaptive adjustment filter is not activated, the overall state space model of the energy storage inverter series compensation system is obtained.

[0130] Step 404, performing eigenvalue solution according to the overall state space model to determine the stability analysis result.

[0131] The energy storage inverter series compensation system is as shown in the above-mentioned embodiments and the accompanying 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. Specifically, 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.

[0132] In actual scenarios, the overall state space model of the energy storage converter 320 can be pre-constructed and stored in the processor, and directly obtained from the processor when there is a need for stability analysis. In other embodiments, 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 eigenvalues ​​of the differential-algebraic equations represented by the overall state space model are solved, and the stability analysis results are determined with the final solution results, that is, whether there is sub-synchronous resonance instability in the energy storage converter series compensation system at this time, and when there is sub-synchronous resonance instability, what are the main factors causing sub-synchronous resonance instability, etc.

[0133] 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 result is 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.

[0134] It should be noted that the specific type of the operating state model is not unique. In combination with the actual structure of the energy storage converter series compensation system, the operating state model will also be different. 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 and DC voltage model, a converter dynamic model, a series compensation model, and a series compensation capacitor transient differential model.

[0135] Specifically, the operating status 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 a more specific embodiment, the operating status 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.

[0136] The capacitor dynamic model is the dynamic equation of the capacitor C during operation, which can be specifically expressed as: Where C represents the capacitance of capacitor C, v dc Represents 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 .

[0137] 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 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, fc (0) Indicates the system frequency rating.

[0138] 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:

[0139]

[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 represents 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 that, 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 specifically 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, which are finally arranged into the corresponding equation form in the dq coordinate system form, which can be specifically expressed as:

[0143]

[0144]

[0145] 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-connected 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, Represents the q-axis component of the current input to the AC grid.

[0146] The series compensation model refers to the series compensation degree of the AC system containing a series compensation device, which is specifically expressed as: Where, SCL represents the series compensation level (SCL), L l represents the inductance value 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.

[0147] 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:

[0148]

[0149]

[0150] Among them, L l represents the inductance value 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-connected 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, Represents the q-axis component of the current input to the AC grid.

[0151] The above scheme adopts 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, so as to determine the overall state space model and improve the accuracy of the overall state space model.

[0152] See also Figure 5 In some embodiments, step 404 includes step 502 , step 504 , and step 506 .

[0153] Step 502, performing eigenvalue solution according to the overall state space model to determine the eigenvalue.

[0154] Step 504, solving according to the eigenvalue to determine the oscillation frequency and the damping ratio.

[0155] Step 506: Determine the stability analysis result according to the oscillation frequency and the damping ratio.

[0156] Specifically, the solution of this embodiment takes the operating state model including the capacitor dynamic model, the voltage droop control model, the converter virtual power angle model, the converter AC and DC voltage model, the converter dynamic model, the series compensation model and the series compensation capacitor transient differential model as an example, and linearizes the above models at the equilibrium point, and finally obtains the following differential-algebraic equation group:

[0157]

[0158] in, and They represent the coefficient matrix after linearization, Δy represents the output variable matrix, and Δx represents the state variable matrix, which includes 10 variables in total and can be expressed as:

[0159]

[0160] After that, the system is subjected to eigenvalue analysis, where the droop coefficient K dc Set to 41.7 (per unit value), the system series compensation SCL is selected as 68%, and the calculated eigenvalues, oscillation frequencies, and damping ratios are shown in the following table:

[0161]

[0162] It can be clearly observed from the above table that the energy storage inverter series compensation system has 10 eigenvalues ​​corresponding to different oscillation modes. The oscillation frequency is distributed between 7.13Hz and 316.06Hz, representing high-frequency oscillation mode (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 special attention should be paid to the fact that there is an unstable mode λ in the system. 9,10 =0.2±j101.9, the real part of its eigenvalue is positive, and the oscillation frequency of the imaginary part is 101.9rad (16.22Hz), which belongs to the subsynchronous oscillation mode. Based on the established model and eigenvalue analysis, an important phenomenon is found here: the SSR instability phenomenon also exists in the energy storage conversion series compensation system of the grid-type converter 320.

[0163] The above scheme obtains the eigenvalue by solving the eigenvalue 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, which has the advantage of high accuracy of stability analysis.

[0164] See also Figure 6 , in some embodiments, step 506 includes step 602 and step 604 .

[0165] Step 602: Determine the target oscillation frequency and target damping ratio when the energy storage converter series compensation system is unstable according to the oscillation frequency and the damping ratio.

[0166] Step 604: Perform participation factor analysis according to the target oscillation frequency and the target damping ratio to determine the instability dominant parameter.

[0167] Specifically, 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, for the instability mode λ 9，10 Attached Figure 7The participating factor analysis is shown in Figure 2. Figure 7 The horizontal axis represents the order of the state variables, while the vertical axis represents the specific value of the participation factor after normalization. Figure 7 It can be seen that 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 , with attached Figure 7 The voltage synchronous controller 130 is strongly correlated with the four state variables with the second highest participation With attached Figure 7 The series compensation circuit 330 of the AC power grid is strongly correlated. From the perspective of the dominant dynamic link of the system, the instability phenomenon of the new SSR is caused by the interaction between the voltage synchronization controller 130 of the converter 320 and the series compensation circuit 330. In the sub-synchronous frequency band, there is obvious energy exchange between the two dominant links, which ultimately manifests as the instability of the output power of the energy storage system.

[0168] 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 participating factor analysis, finds the main factors causing subsynchronous resonance, and provides a theoretical basis for the construction of the damping controller 340.

[0169] 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 SCL is selected to be 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 condition and organized as shown in the following table, where the damping coefficient D sub The value is 0.25:

[0170]

[0171] 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.

[0172] To further explain the damping coefficient D of the damping controller 340 sub The influence of SSR instability was studied based on the state space method. Figure 8 The root locus analysis is shown in Figure 2. sub The value varies from 0.1 to 0.3. Due to the negative damping effect of SSR instability in the studied system, 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 enters the left half plane stable region from the right half plane unstable region. In particular, the critical damping coefficient D sub is 0.15.

[0173] 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, Fig. 9 and Fig.10 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 are shown respectively.

[0174] Attached Fig. 9 In the system disturbance setting, at t = 20s, 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 put into operation at t = 21.5s, and the damping coefficient D sub is 0.25. Fig. 9 It can be observed that 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 illustrate 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.

[0175] In order to verify the adaptability and robustness of the damping controller 340 under multiple working conditions, the attached Fig.10 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 is 0.25. Fig.10 It can be seen that in the wide range of K dc(16-40) and SCL (64%-78%), the proposed control scheme can fully exert its SSR suppression function. After the divergent SSR oscillation occurs in the system, the damping controller 340 can quickly restore the system to a normal stable operating state. The above simulation results are highly consistent with the theoretical calculation and analysis results, which further fully verifies the effectiveness, adaptability and robustness of the proposed scheme.

[0176] 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.

[0177] Specifically, the energy storage inverter series compensation system is as shown in the above-mentioned embodiments and drawings, and will not be described in detail here. The above-mentioned energy storage system is provided with a damping controller 340 in the energy storage inverter series compensation system between the energy storage battery group 310 and the AC power grid, which can collect the voltage signal on the capacitor C between the energy storage battery group 310 and the converter 320 of the energy storage inverter series compensation system, and judge whether the activation condition is met based on this, and activate the adaptive adjustment filter 120 when the activation condition is met, so that the damping controller 340 is put into operation of the energy storage inverter series compensation system. After that, the voltage synchronization controller 130 determines the output phase angle signal required for the pulse width modulation signal that controls the operation of the converter 320 according to the sub-synchronous 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 to improve the damping level of the unstable subsynchronous resonance mode, correct the original negative damping mode to a positive damping mode, and improve the stable operation capability of the grid-type converter 320.

[0178] 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 replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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, characterized in that: include: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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 3, characterized in that: 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, characterized in that: The acquisition signal frequency satisfies the preset frequency condition, which includes: the acquisition signal frequency is greater than or equal to the lower limit of the set passband frequency, and is less than or equal to the upper limit of the set passband frequency; And / or, the amplitude of the collected signal meets a preset amplitude condition, including: a ratio of the amplitude of the collected signal to a nominal amplitude is greater than or equal to a set threshold.

7. An energy storage converter series compensation system, characterized in that: It comprises a capacitor, an inverter, a series compensation circuit and the damping controller according to any one of claims 1 to 6, 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 inverter, the second end of the capacitor is also connected to the inverter, the inverter 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.

8. The energy storage converter series compensation system according to claim 7, characterized in that: It 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.

9. The energy storage converter series compensation system according to claim 8, characterized in that: 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.

10. The energy storage converter series compensation system according to any one of claims 7 to 9, characterized in that: It also includes a first inductor and a first capacitor, wherein a first end of the first inductor is connected to the converter, a second end of the first inductor is connected to a first end of the first capacitor and the series compensation circuit, and a second end of the first capacitor is grounded.

11. The energy storage converter series compensation system according to any one of claims 7 to 10, characterized in that: 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.

12. A stability analysis method for the energy storage converter series compensation system according to any one of claims 7 to 11, characterized in that: include: 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.

13. The stability analysis method according to claim 12, characterized in that: 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.

14. The stability analysis method according to claim 12, characterized in that: 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.

15. The stability analysis method according to claim 14, characterized in that: 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.

16. An energy storage system, characterized in that: It comprises an energy storage battery pack and the energy storage current conversion series compensation system as described in any one of claims 7-11.

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