A Resonance Suppression Method and System for Network Converter Systems Based on Sequence Impedance Reshaping

Abstract

This invention discloses a method and system for suppressing resonance in a grid-connected converter system based on sequence impedance reshaping. The method includes: obtaining linearized small signals of grid-side voltage, grid-side current, and converter-side current based on the active and reactive power control strategy of the grid-connected converter and the voltage-current dual closed-loop control principle; establishing a sequence impedance model of the output impedance of the grid-connected converter system based on a virtual synchronous generator; determining the system stability conditions based on the sequence impedance model and passive theory; and introducing an active damping feedback loop in the voltage control stage of the grid-connected converter to reshape the equivalent output impedance of the converter resonance control, reducing the non-passive region of the positive and negative sequence impedances, and thus suppressing the harmonic resonance of the grid-connected current of the grid-connected converter. This invention is the first to use a sequence impedance model for impedance reshaping in a grid-connected system, specifically introducing an equivalent series virtual damper and an equivalent notch filter feedback control loop in the converter system to reshape the sequence impedance waveform and thereby improve the stability and robustness of the system.

Description

Technical Field

[0001] This invention relates to the field of resonance suppression technology for grid converters, and in particular to a resonance suppression method and system for grid converter systems based on sequence impedance reshaping. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Grid-based control technology enables converter systems to regulate grid frequency and voltage while connected to the grid. With the increasing penetration of new energy sources in the power grid, its advantage of providing support to the grid-connected system and thus improving its stability has made it a current research hotspot. However, its more comprehensive control strategy also brings more possibilities for system instability and harmonic resonance.

[0004] To control harmonic resonance in complex grid-connected converter systems, given the complexity of their control models, most resonance suppression methods refer to grid-connected converter systems and begin harmonic analysis and suppression from the voltage and current closed-loop control components, lacking a global perspective. Furthermore, the state-space analysis methods used in some analysis methods that consider global impedance significantly increase the complexity of the modeling process. This modeling difficulty makes it hard to elucidate the stability mechanism of complex grid-connected converter systems. Consequently, existing methods such as virtual damping and notch filters are insufficient to specifically suppress the impact of harmonic resonance during grid connection. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a resonance suppression method and system for grid-connected converter systems based on sequence impedance reshaping. Starting with positive and negative sequence small signals and combining this with a grid-connected virtual synchronous generator control strategy, a sequence impedance model is established. By introducing a passive damping feedback loop to increase the system's passivity, and combining this with a notch filter to introduce an equivalent feedback loop, the system's sequence impedance model is specifically modified to suppress harmonic resonance. This reduces the non-passive region of the sequence impedance, thereby improving the stability of the grid-connected system and suppressing resonance.

[0006] In some implementations, the following technical solutions are adopted:

[0007] A resonance suppression method for a grid-type converter system based on sequence impedance reshaping includes:

[0008] Based on the active and reactive power control strategy of the grid-type converter and the voltage and current dual closed-loop control principle, the linearized small signals of grid-side voltage, grid-side current and converter-side current are obtained, and a sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator is established.

[0009] Based on the aforementioned sequence impedance model and combined with passivity theory, the conditions for system stability are determined.

[0010] Based on the condition of system stability, an active damping feedback loop is introduced into the voltage control stage of the grid-connected converter to reshape the equivalent output impedance of the converter resonance control, reduce the non-passive region of the output positive and negative sequence impedance, and achieve the suppression of grid-connected current harmonic resonance of the grid-connected converter.

[0011] As an optional approach, a sequence impedance model of the output impedance of a grid-type converter system based on a virtual synchronous generator is established. The specific process is as follows:

[0012] Based on the active and reactive power control strategy of the grid converter and the voltage and current dual closed-loop control principle, a nonlinear relationship model of the internal potential, output voltage and output current of the grid converter is established.

[0013] Positive-sequence and negative-sequence disturbance voltages are injected into the grid side of the grid-connected system, and the nonlinear model is subjected to harmonic linearization processing to obtain small signals of grid-side voltage, grid-side current and converter-side current, respectively.

[0014] By traversing the active and reactive power control processes and the voltage and current dual closed-loop control processes of the small-signal grid converter, a sequence impedance model of the positive-sequence and negative-sequence output impedance of the grid converter in a stationary coordinate system is established.

[0015] After the small-signal traversal of the active and reactive power control process and the voltage and current dual closed-loop control process of the grid converter, the following is also included:

[0016] The small signal Δv of the dq axis grid-side voltage obtained after harmonic linearization is... d Δv q dq axis side current small signal Δi gd , Δi gq and the small signal Δi of the inverter side current d , Δi q Substituting the active frequency regulation, reactive voltage regulation, and current and voltage control processes into the equations of the main circuit of the converter, we obtain the sequence impedance models of the output impedance of the positive and negative sequence grid-type converter in the stationary coordinate system.

[0017] As an optional approach, based on the aforementioned sequence impedance model and combined with passive theory, the conditions for system stability are determined as follows: the system is stable when the positive and negative sequence impedance phases of the system output are both within the passive range.

[0018] As an optional solution, after introducing an active damping feedback loop, the voltage and current dual closed-loop control process becomes:

[0019]

[0020] Where ω1 is the rated angular frequency, L f For the series inductor on the converter side, s 2 K a This indicates the introduction of active damping feedback, where Ka is the active damping parameter; ΔU d (s), ΔU q (s) represent the small signals after linearization of the dq-axis modulated voltage, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) represent the reference current inputs for the linearized small-signal current loop of the dq-axis, Δi d , Δi q These are the inverter-side current small signals obtained after harmonic linearization, Δv and Δv, respectively. d (s), Δv q (s) represent the small-signal voltage on the dq axis network side obtained after harmonic linearization processing, Δi gd (s), Δi gq (s) represent the small signals of the dq axis grid-side current obtained after harmonic linearization processing.

[0021] As an optional solution, it is also possible to introduce a virtual notch filter into the voltage and current control stage of the grid converter so that the output positive and negative sequence impedances meet the phase margin requirements.

[0022] After introducing a virtual notch filter, the voltage and current dual closed-loop control process becomes:

[0023]

[0024] Where ω1 is the rated angular frequency, L f For the series inductor on the converter side, s 2 K a K represents the introduced active damping feedback. a For active damping parameters; G Nor (s) represents the notch filter model; ΔU d (s), ΔU q (s) represent the small signals after linearization of the dq-axis modulated voltage, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) represent the reference current inputs for the linearized small-signal current loop of the dq-axis, Δi d , Δi q These are the inverter-side current small signals obtained after harmonic linearization, Δv and Δv, respectively. d (s), Δv q (s) represent the small-signal voltage on the dq axis network side obtained after harmonic linearization processing, Δigd (s), Δi gq (s) represent the small signals of the dq axis grid-side current obtained after harmonic linearization processing.

[0025] In other embodiments, the following technical solutions are adopted:

[0026] A resonance suppression system for a grid-type converter system based on sequence impedance reshaping includes:

[0027] The model building module is used to obtain the linearized small signals of grid-side voltage, grid-side current and converter-side current based on the active and reactive power control strategy of the grid-type converter and the voltage and current dual closed-loop control principle, and to establish the sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator.

[0028] The stability analysis module is used to determine the conditions for system stability based on the order impedance model and the passive theory.

[0029] The resonance suppression module is used to introduce an active damping feedback loop into the voltage control stage of the grid-connected converter, based on the condition of system stability. This reshapes the equivalent output impedance of the converter's resonance control, reduces the non-passive region of the output positive and negative sequence impedance, and achieves the suppression of harmonic resonance of the grid-connected current of the grid-connected converter.

[0030] In other embodiments, the following technical solutions are adopted:

[0031] A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions, the instructions being adapted to be loaded and executed by the processor to perform the above-described resonance suppression method for a grid-type converter system based on sequence impedance reshaping.

[0032] In other embodiments, the following technical solutions are adopted:

[0033] A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of a terminal device of the above-described method for suppressing resonance in a grid-type converter system based on sequence impedance reshaping.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] (1) This invention targets grid-connected converter systems based on virtual synchronous generators. It establishes a system sequence impedance model using harmonic linearization and small-signal concepts, and determines the system stability conditions by combining passive theory. For the first time, the sequence impedance model is used to reshape the impedance of the grid-connected system. The invention specifically introduces an equivalent series virtual damper and an equivalent notch filter feedback control loop into the converter system to reshape the sequence impedance waveform, thereby improving the stability and robustness of the system.

[0036] (2) When analyzing the system stability mechanism, this invention uses sequence impedance modeling to ensure globality and accuracy while linearizing the nonlinear model to reduce the complexity of modeling.

[0037] (3) By introducing an active damping feedback loop, the present invention reshapes the equivalent output impedance of the converter resonance control, reduces its non-passive region, and increases the passivity of the system; at the same time, the virtual equivalent notch filter is introduced so that the output sequence impedance has sufficient phase margin when the system is connected to the grid, thereby improving the system stability and robustness and suppressing the system harmonic resonance.

[0038] (4) Compared with traditional passive and active damping methods, the present invention does not require hardware such as resistors and additional sensors, thus reducing system cost and losses.

[0039] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the virtual synchronous generator control system structure of the grid-type converter in an embodiment of the present invention;

[0041] Figure 2 This is a topology diagram of the main circuit of the grid-type converter in an embodiment of the present invention;

[0042] Figure 3 This is a topology diagram of the main circuit of the grid-type converter in an embodiment of the present invention;

[0043] Figure 4 This is a diagram of the positive and negative sequence small-signal equivalent circuit model of the grid-type converter system in an embodiment of the present invention;

[0044] Figure 5(a) is a block diagram of the series passive damping current and voltage control introduced into the grid-type converter system in an embodiment of the present invention;

[0045] Figure 5(b) is a block diagram of the equivalent active damping feedback loop control introduced into the grid-type converter system in an embodiment of the present invention;

[0046] Figure 6 This is a Bode plot of the output sequence impedance waveform of the grid converter system in this embodiment of the invention as a function of the active damping parameters.

[0047] Figure 7 This is a diagram showing the interaction characteristics of the system sequence impedance and grid-side inductance after selecting appropriate active damping parameters for the grid-type converter system in this embodiment of the invention.

[0048] Figure 8 This is a waveform diagram of the notch filter used in the grid converter system of this invention as parameters change;

[0049] Figure 9(a) is a block diagram of the notch filter voltage and current control introduced into the grid-type converter system in an embodiment of the present invention;

[0050] Figure 9(b) is a control block diagram of the equivalent notch filter feedback loop introduced into the grid converter system in an embodiment of the present invention;

[0051] Figure 10 Bode plot of the output sequence impedance as a function of parameters after introducing an equivalent notch filter feedback into the grid converter system in this embodiment of the invention;

[0052] Figure 11(a) is a waveform of the grid-side output current of the grid-type converter system before harmonic suppression in an embodiment of the present invention;

[0053] Figure 11(b) is a waveform diagram of the grid-side output current after the grid-type converter system uses active damping in an embodiment of the present invention;

[0054] Figure 11(c) is a waveform diagram of the grid-side output current after a notch filter is introduced into the grid-type converter system in an embodiment of the present invention.

[0055] Figure 11(d) shows the grid-side output current THD of the grid-type converter system after using active damping in an embodiment of the present invention;

[0056] Figure 11(e) shows the grid-side output current THD of the grid-type converter system after the introduction of a notch filter in an embodiment of the present invention. Detailed Implementation

[0057] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0058] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0059] Example 1

[0060] In one or more embodiments, a resonance suppression method for a grid-type converter system based on sequence impedance reshaping is disclosed, specifically including the following process:

[0061] S101: Based on the active and reactive power control strategy of grid-type converter and the voltage and current dual closed-loop control principle, through harmonic linearization processing, the small signals of grid-side voltage, grid-side current and converter-side current obtained after linearization are used to establish the sequence impedance model of the output impedance of the grid-type converter system.

[0062] Specifically, Figure 1 The structure of a virtual synchronous generator control system for a grid-type converter is presented, including: active power frequency regulation process, reactive power voltage regulation control process, and voltage and current dual closed-loop decoupling control process.

[0063] The active frequency modulation process is as follows:

[0064]

[0065] In the formula, θ is the phase angle of the internal potential of the virtual synchronous generator, ω1 is the rated angular frequency, and P ref Given the active power of the virtual synchronous generator, P act For the system to output active power, D p is the damping coefficient, and J is the moment of inertia of the virtual synchronous generator.

[0066] The reactive power voltage regulation control process is as follows:

[0067]

[0068] Among them, E m K represents the effective value of the virtual internal potential. i The integral coefficient of the virtual synchronous generator excitation, |v| ref The voltage is the RMS value of the rated voltage, |v| is the RMS value of the grid-connected voltage, and K q Q is the reactive power-voltage droop factor. ref Given the reactive power of the system, Q act It outputs reactive power to the system.

[0069] The voltage-current loop decoupling control process is as follows:

[0070]

[0071] Among them, C f For three-phase parallel capacitors, L f The inductor is connected in series on the converter side, and the capacitor voltage is v. abc v on the dq axis d v q Converter-side current i abc i is the value on the dq axis. d i q Grid-side current i gabc i is the value on the dq axis. gd i gqv dref v qref U is the output voltage of the dq axis during the reactive power regulation process. d U q These are the final dq-axis modulation voltages, G v (s), G i (s) are PI integral controllers for the voltage loop and current loop, respectively, with proportional coefficients K and K. pu K pi The integral coefficients are K iu K ii i dref i qref These are the outer loop outputs of the dq-axis voltage, which are also the small-signal reference current inputs for the linearization of the dq-axis current loop.

[0072] Figure 2 The grid-connected main circuit topology of the converter is given. First, harmonic linearization is performed on the grid-connected control system of the nonlinear grid-connected converter. Taking phase a as an example, the positive and negative sequence disturbance voltages injected on the grid side of the grid-connected system become:

[0073] v abc =V1cos(2πf1t)+V p cos(2πf p t+φ vp )+V n cos(2πf n t+φ vn (4)

[0074] In the formula, v abc The grid-side voltage (i.e., capacitor voltage), V1, V p V n These represent the amplitudes of its fundamental frequency, positive and negative disturbances, and negative sequence disturbance, respectively, f1 and f2. p f n These are the corresponding frequencies, φ vp φ vn These are the positive and negative sequence perturbation phase angles, respectively.

[0075] Similarly, for the grid-side current i gabc The amplitudes of the fundamental wave, positive and negative disturbances, and negative sequence disturbances are I, respectively. g1 I gp I gn The positive and negative sequence perturbation phase angles are φ. igp φ ign and the fundamental perturbation phase angle φ ig1 ;

[0076] For the converter-side current i abc The amplitudes of the fundamental wave, positive and negative disturbances, and negative sequence disturbances are I1, I2, and I3, respectively.p I n The phase angles of the positive and negative sequence disturbances are φ. ip φ in and the fundamental perturbation phase angle φ i1 .

[0077] For each voltage and current v at the disturbance point abc i gabc and i abc By performing Fourier transform and coordinate transform respectively, the voltage and current components in zero-sequence, positive-sequence, and negative-sequence states are obtained, thus yielding the small signals of each component. Considering the frequency shift effect during coordinate transform, the instantaneous output power P of the control system is calculated. act With Q act for:

[0078]

[0079] in,

[0080] P avg Q avg φ ig1 f and f represent the average active power, average reactive power, grid-side current fundamental disturbance phase angle, and frequency independent variables, respectively.

[0081] The small signal Δv of the dq axis grid-side voltage obtained after harmonic linearization is... d Δv q dq axis side current small signal Δi gd , Δi gq and the small signal Δi of the inverter side current d , Δi q By traversing the active and reactive power control loops and the voltage and current control loops of the system, small signals Δθ and Δv can be obtained. dqref , Δi dqref , ΔU dq :

[0082]

[0083] Where Δθ[f] is the small-signal change in the phase angle of the internal potential of the virtual synchronous generator, J is the moment of inertia of the virtual synchronous generator, and P... act_p P act_n These represent the instantaneous positive and negative sequence output power of the Virtual Synchronous Engine (VSG) system, respectively; Δv dref (s), Δv qref (s) represent the small-signal output voltage along the dq axis of the reactive voltage regulation process obtained after harmonic linearization, E m_p E m_n These represent the positive and negative sequence virtual internal potentials, respectively; Δidref (s), Δi qref (s) represent the reference current inputs for the linearized small-signal current loop of the dq-axis, Δv d (s), Δv q (s) represent the small-signal voltage on the dq axis network side obtained after harmonic linearization processing, Δi gd (s), Δi gq (s) represent the small-signal dq-axis grid-side current obtained after harmonic linearization; ΔU d (s), ΔU q (s) represent the small signals after linearization of the dq-axis modulated voltage, Δi d , Δi q These are the inverter-side current small signals obtained after harmonic linearization processing.

[0084] according to Figure 2 The main circuit equation of the system can be obtained as follows:

[0085]

[0086] Among them, C f For three-phase parallel capacitors, L f For the series inductor on the converter side, v a v b v c The capacitor voltage (i.e., grid-side voltage v) in a three-phase stationary coordinate system abc ), i ga i gb i gc U represents the grid-side current in a three-phase stationary coordinate system. a U b U c The voltage is a three-phase modulated voltage in a stationary coordinate system.

[0087] Substituting the obtained small-signal model into (11) after coordinate transformation, the system sequence impedance model can be obtained as follows:

[0088]

[0089] The algebraic expressions in the formula are as follows:

[0090]

[0091]

[0092] in, (s and f are common variables in the frequency domain), K i K represents the integral excitation coefficient of the virtual synchronous generator. q The reactive power-voltage droop factor is used for the converter-side current i.abc The amplitudes of the fundamental wave, positive and negative disturbances, and negative sequence disturbances are I1, I2, and I3, respectively. p I n v abc For grid-side voltages, V1 and V p V n G represents the amplitudes of its fundamental frequency, positive and negative disturbances, and negative sequence disturbance, respectively. v [f]、G i [f] represents the PI integral controllers for the voltage loop and current loop, respectively, φ ig1 φ i1 The phase angle of the fundamental disturbance between the grid-side current and the converter-side current; and They represent The conjugate transpose and itself.

[0093] Figure 3 The image shows the sequence impedance of the system sequence impedance theoretical model and the sequence impedance verified by frequency sweep. The positive and negative sequence impedances of the model are represented by different colors. The derived sequence impedance model is in good agreement with the actual system output sequence impedance verification results, which proves the correctness of the theoretical model.

[0094] S102: Based on the aforementioned sequence impedance model and combined with passive theory, determine the conditions for system stability.

[0095] Figure 4 To model the positive and negative sequence small-signal equivalent circuit of the system, the three-phase converter is decomposed into positive and negative sequence subsystems, with positive and negative sequence voltage disturbance sources connected in series. The positive and negative sequence small-signal equivalent circuit includes the internal potential V of the positive and negative sequence virtual synchronous generator. vsgp With V vsgn The sequence impedance Z of the virtual synchronous generator vsgp With Z vsgn Positive and negative sequence grid impedance Z gp With Z gn and positive and negative sequence grid voltage V gp With V gn Partial series connection. Based on the equivalent circuit, the relationship between the grid-connected current and the converter system output impedance can be obtained as follows:

[0096]

[0097] As shown in (16), the stable state of the grid-connected current depends on the system impedance ratio. The system is stable when both the positive and negative sequence impedances meet the stability criterion. According to the passive theory, the system is stable when the output phase is within the range of [-90°, 90°]. Combining the system sequence impedance model, it can be seen that the system is stable when the phases of the positive and negative sequence impedances of the system output are within the passive range.

[0098] S103: In combination with the condition of system stability, an active damping feedback loop is introduced into the voltage control link of the grid-type converter to reshape the equivalent output impedance of the converter resonance control, reduce the non-passive region of the output positive and negative sequence impedance, and realize the suppression of grid-connected current harmonic resonance of the grid-type converter.

[0099] Figures 5(a) and 5(b) show the control block diagrams for introducing series passive damping in the converter voltage and current control loop and equating it with an active damping feedback loop. This reshapes the system output sequence impedance by increasing the system's passivity. The introduced current loop feedback can be simplified to s. 2 K a , will K a As active damping parameters, the parameters for active damping control are determined by combining the changes in the system sequence impedance model. At this point, the voltage-current dual closed-loop control process in the sequence impedance calculation model becomes:

[0100]

[0101] Figure 6 The curves showing the variation of the system's output sequence impedance with active damping parameters after introducing active damping are presented, where the solid line represents the positive sequence impedance and the dashed line represents the negative sequence output impedance. The proportion of the system's output sequence impedance in the passive region varies with the active damping parameters. Parameters that maximize the system's passive output sequence impedance within the passive region are selected to further improve the model and enhance system robustness. Based on... Figure 6 K can be selected as 0.1 or 0.2. a The parameters are such that the system sequence impedance is at its maximum in the passive region.

[0102] Figure 7 To obtain the interaction characteristics of the system sequence impedance and grid-side inductance when 0.2 is selected as the active damping parameter, and to ensure that the system has a phase margin of 30° when connected to the grid and to improve the system robustness, a virtual equivalent notch filter can be introduced.

[0103] Figure 8 The waveform of the notch filter is represented by its model G. Nor for:

[0104]

[0105] Where ξ is the notch width, ω2 is the notch center angular frequency, and ω2 is determined by the sequence impedance output waveform after adding active damping to the system and its intersection with the grid-side inductance. Figure 7 The output waveform of the system sequence impedance interacting with the power grid can be taken as 170Hz as the center angular frequency of the notch filter.

[0106] Figures 9(a) and 9(b) show the changes in the voltage and current control block diagrams of a grid-type converter system with a notch filter. By simulating the effect of a grid-side series notch filter, it is equivalent to adding a virtual notch filter control loop in the voltage and current control loop, thereby reshaping the system output sequence impedance waveform and ensuring sufficient phase margin in the output sequence impedance. The voltage and current dual closed-loop control process in the sequence impedance calculation model is as follows:

[0107]

[0108] Figure 10 To introduce the waveform of the system output sequence impedance as a function of the ξ parameter after the virtual notch filter feedback loop is introduced, the system output sequence impedance is basically in the passive region. The notch width of the notch filter can be selected as 0.4 or 0.6 depending on the system. At this time, the output impedance has a large phase margin, which can increase the stability and robustness of the system.

[0109] To verify the effectiveness of the control method disclosed herein, experimental simulations were conducted, and the simulation results are shown in Figures 11(a), 11(b), 11(c), 11(d), and 11(e). Figure 11(a) shows the grid-side output current waveform of the grid-type converter system before harmonic suppression, indicating severe harmonic phenomena in the current. In Figure 11(b), the introduction of an active damping feedback loop suppressed some of the output current harmonics. In Figure 11(c), the introduction of a virtual notch filter significantly suppressed the system output current resonance. Comparing Figure 11(d) and Figure 11(e), it can be seen that the introduction of a new feedback loop specifically reduced the current harmonic content after the introduction of active damping.

[0110] In summary, this embodiment reduces the difficulty of modeling while elucidating the stability mechanism of the system by combining passive theory. At the same time, it introduces a feedback loop to reshape the system impedance based on the sequence impedance model, thereby suppressing system harmonic resonance and improving system stability and robustness.

[0111] Example 2

[0112] In one or more embodiments, a resonance suppression system for a grid-type converter system based on sequence impedance reshaping is disclosed, comprising:

[0113] The model building module is used to obtain the linearized small signals of grid-side voltage, grid-side current and converter-side current based on the active and reactive power control strategy of the grid-type converter and the voltage and current dual closed-loop control principle, and to establish the sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator.

[0114] The stability analysis module is used to determine the conditions for system stability based on the order impedance model and the passive theory.

[0115] The resonance suppression module is used to introduce an active damping feedback loop into the voltage control stage of the grid-connected converter, based on the condition of system stability. This reshapes the equivalent output impedance of the converter's resonance control, reduces the non-passive region of the output positive and negative sequence impedance, and achieves the suppression of harmonic resonance of the grid-connected current of the grid-connected converter.

[0116] It should be noted that the specific implementation methods of the above modules are the same as those in Example 1, and will not be described in detail again.

[0117] Example 3

[0118] In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions adapted to be loaded by the processor and executed by the processor to perform the resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in Embodiment 1.

[0119] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor, etc.

[0120] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0121] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0122] Example 4

[0123] In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and executed by the resonance suppression method for a grid-type converter system based on sequence impedance reshaping described in Embodiment 1.

[0124] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for suppressing resonance in a grid-type converter system based on sequence impedance reshaping, characterized in that, include: Based on the active and reactive power control strategy of the grid-type converter and the voltage and current dual closed-loop control principle, the linearized small signals of grid-side voltage, grid-side current and converter-side current are obtained, and a sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator is established. Based on the aforementioned sequence impedance model and combined with the passive theory, the condition for system stability is determined as follows: the system is stable when both the positive and negative sequence impedance phases of the system output are within the passive range. Based on the condition of system stability, an active damping feedback loop is introduced into the voltage control stage of the grid-connected converter to reshape the equivalent output impedance of the converter resonance control, reduce the non-passive region of the output positive and negative sequence impedance, and achieve the suppression of grid-connected current harmonic resonance of the grid-connected converter.

2. The resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in claim 1, characterized in that, The sequence impedance model of the output impedance of a grid-connected converter system based on a virtual synchronous generator is established. The specific process is as follows: Based on the active and reactive power control strategy of the grid converter and the voltage and current dual closed-loop control principle, a nonlinear relationship model of the internal potential, output voltage and output current of the grid converter is established. Positive-sequence and negative-sequence disturbance voltages are injected into the grid side of the grid-connected system, and the nonlinear model is subjected to harmonic linearization processing to obtain small signals of grid-side voltage, grid-side current and converter-side current, respectively. By traversing the active and reactive power control processes and the voltage and current dual closed-loop control processes of the small-signal grid converter, a sequence impedance model of the positive-sequence and negative-sequence output impedance of the grid converter in a stationary coordinate system is established.

3. The resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in claim 2, characterized in that, After the small-signal traversal of the active and reactive power control process and the voltage and current dual closed-loop control process of the grid converter, the following is also included: The small signal of the dq axis grid-side voltage obtained after harmonic linearization , dq axis grid side current small signal , and inverter-side current small signal , Substituting the active frequency regulation, reactive voltage regulation, and current and voltage control processes into the equations of the main circuit of the converter, we obtain the sequence impedance models of the output impedance of the positive and negative sequence grid-type converter in the stationary coordinate system.

4. The resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in claim 1, characterized in that, After introducing an active damping feedback loop, the voltage and current dual closed-loop control process becomes: ； in, The rated angular frequency, For the series inductor on the converter side, This indicates the introduction of active damping feedback. These are active damping parameters; , These are the small signals after linearization of the dq-axis modulated voltage, respectively. The current loop transfer function, , These are the reference current inputs for the small-signal linearization of the dq-axis current loop, respectively. , These are the small-signal inverter-side currents obtained after harmonic linearization processing. , These are the small-signal dq-axis grid-side voltages obtained after harmonic linearization processing. , These are the small signals of the dq axis grid-side current obtained after harmonic linearization processing.

5. The resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in claim 1, characterized in that, Also includes: A virtual notch filter is introduced into the voltage and current control stage of the grid converter to ensure that the output positive and negative sequence impedances meet the phase margin requirements.

6. The resonance suppression method for a grid-type converter system based on sequence impedance reshaping as described in claim 5, characterized in that, After introducing a virtual notch filter, the voltage and current dual closed-loop control process becomes: ； in, The rated angular frequency, For the series inductor on the converter side, This indicates the introduction of active damping feedback. These are active damping parameters; This is a notch filter model; , These are the small signals after linearization of the dq-axis modulated voltage, respectively. The current loop transfer function, , These are the reference current inputs for the small-signal linearization of the dq-axis current loop, respectively. , These are the small-signal inverter-side currents obtained after harmonic linearization processing. , These are the small-signal dq-axis grid-side voltages obtained after harmonic linearization processing. , These are the small signals of the dq axis grid-side current obtained after harmonic linearization processing.

7. A resonance suppression system for a grid-type converter system based on sequence impedance reshaping, characterized in that, include: The model building module is used to obtain the linearized small signals of grid-side voltage, grid-side current and converter-side current based on the active and reactive power control strategy of the grid-type converter and the voltage and current dual closed-loop control principle, and to establish the sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator. The stability analysis module is used to determine the conditions for system stability based on the sequence impedance model and the passive theory. Specifically, the system is stable when the positive and negative sequence impedance phases of the system output are both within the passive range. The resonance suppression module is used to introduce an active damping feedback loop into the voltage control stage of the grid-connected converter, based on the condition of system stability. This reshapes the equivalent output impedance of the converter's resonance control, reduces the non-passive region of the output positive and negative sequence impedance, and achieves the suppression of harmonic resonance of the grid-connected current of the grid-connected converter.

8. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed by the resonant suppression method for a grid converter system based on sequence impedance reshaping as described in any one of claims 1-6.

9. A computer-readable storage medium storing a plurality of instructions, characterized in that, The instructions are adapted to be loaded by the processor of the terminal device and executed by the resonance suppression method for a grid converter system based on sequence impedance reshaping as described in any one of claims 1-6.

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