Net construction type converter system resonance suppression method and system based on sequence impedance remodeling

Abstract

The invention discloses a sequence impedance remodeling-based grid-forming converter system resonance suppression method and system, and the method comprises the steps: obtaining linearized grid-side voltage, grid-side current and converter-side current small signals based on the active and reactive power control strategy of a grid-forming converter and the voltage and current double-closed-loop control principle; establishing a sequence impedance model of the output impedance of the network construction type converter system based on the virtual synchronous generator; based on the sequence impedance model, combining a passivity theory to determine a system stability condition; in combination with the condition of system stability, an active damping feedback loop is introduced in a voltage control link of the grid-forming converter, equivalent output impedance of converter resonance control is remodeled, a non-passive area for outputting positive and negative sequence impedance is reduced, and grid-connected current harmonic resonance suppression of the grid-forming converter is realized. According to the method, a sequence impedance model is used for performing impedance remodeling of a grid-connected system for the first time, equivalent series virtual damping and a feedback control ring of an equivalent wave trap are specifically introduced into a converter system to perform sequence impedance waveform remodeling, and then the stability and robustness of the system are controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of resonance suppression of network-forming converters, and particularly to a method and system for suppressing resonance of a network-forming converter system based on sequence impedance reshaping. Background Art

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

[0003] The network-forming control technology enables the converter system to have the ability to adjust the grid-connected frequency and voltage while being grid-connected. With the increasing penetration rate of new energy in the power grid, its advantage of providing a certain supporting ability to the grid-connected system and thus improving the stability of the grid-connected system makes it a hot topic of current research. However, its more comprehensive control strategy also brings more possibilities for the system to become unstable and generate harmonic resonance.

[0004] In order to perform harmonic resonance control on a complex network-forming converter grid-connected system, considering the complexity of its control model, most resonance suppression methods will refer to the grid-following converter grid-connected system and start from the voltage and current closed-loop control part for harmonic analysis and suppression, lacking overall consideration; while in some analysis methods considering the overall impedance, the state space analysis method used will greatly increase the complexity of its modeling process, and the difficulty of modeling makes it difficult to clarify the stability mechanism of the complex network-forming converter grid-connected system. Furthermore, the use of existing virtual damping and notch filters is difficult to specifically suppress the influence of harmonic resonance during grid connection. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a method and system for suppressing resonance of a network-forming converter system based on sequence impedance reshaping. Starting from the positive and negative sequence small signals and combining with the network-forming virtual synchronous generator control strategy, a sequence impedance model of the output impedance of the network-forming converter system is established. By introducing a passive damping feedback loop to increase the passivity of the system and combining with a notch filter to introduce an equivalent feedback loop to specifically change the system sequence impedance model, the harmonic resonance of the system is suppressed, thereby reducing the non-passive region of the sequence impedance and improving the stability of the grid-connected system and suppressing resonance.

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

[0007] A method for suppressing resonance of a network-forming converter system based on sequence impedance reshaping, comprising:

[0008] Based on the active and reactive power control strategy of the network-forming converter and the principle of voltage and current double closed-loop control, the small signals of the grid-side voltage, grid-side current, and converter-side current after linearization are obtained, and a sequence impedance model of the output impedance of the network-forming converter system based on a virtual synchronous generator is established;

[0009] Based on the sequence impedance model and combined with the passivity theory, determine the conditions for system stability;

[0010] Combined with the conditions for system stability, introduce an active damping feedback loop in the voltage control link of the network-forming converter to reshape the equivalent output impedance of the converter's resonant control, reduce the non-passive region of the positive and negative sequence output impedances, and achieve the suppression of harmonic resonance in the grid-connected current of the network-forming converter.

[0011] As an alternative solution, establish a sequence impedance model for the output impedance of the network-forming converter system based on the virtual synchronous generator. The specific process is as follows:

[0012] Based on the active and reactive power control strategy of the network-forming converter and the principle of double closed-loop voltage and current control, establish a non-linear relationship model for the internal electromotive force, output terminal voltage, and output current of the network-forming converter;

[0013] Inject positive and negative sequence disturbance voltages on the grid side of the grid-connected system, perform harmonic linearization processing on the non-linear model, and respectively obtain the small signals of the grid side voltage, grid side current, and converter side current;

[0014] Traverse the active and reactive power control process and the double closed-loop voltage and current control process of the network-forming converter with the small signals, and establish a sequence impedance model for the positive and negative sequence output impedances of the network-forming converter in the stationary coordinate system.

[0015] After traversing the active and reactive power control process and the double closed-loop voltage and current control process of the network-forming converter with the small signals, it further includes:

[0016] Substitute the dq-axis grid side voltage small signals Δv d 、Δv q ,the dq-axis grid side current small signals Δi gd 、Δi gq ,and the inverter side current small signals Δi d 、Δi q into the active frequency modulation, reactive power voltage regulation, and current voltage control processes respectively, and then substitute the obtained small signal model into the main circuit equation of the converter to obtain the sequence impedance model for the positive and negative sequence output impedances of the network-forming converter in the stationary coordinate system.

[0017] As an alternative solution, based on the sequence impedance model and combined with the passivity theory, determine the conditions for system stability, specifically: the system is stable when the phases of the positive and negative sequence output impedances of the system are within the passive range.

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

[0019]

[0020] where, ω 1 is the rated angular frequency, L f is the series inductance on the converter side, s 2 K a represents the introduced active damping feedback, and Ka is the active damping parameter; ΔU d (s), ΔU q (s) are the small signals after linearizing the dq-axis modulation voltage respectively, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) are the reference current inputs of the dq-axis current loop linearized small signals respectively, Δi d , Δi q are the small signals of the inverter side current obtained after harmonic linearization respectively, Δv d (s), Δv q (s) are the small signals of the dq-axis grid side voltage obtained after harmonic linearization respectively, Δi gd (s), Δi gq (s) are the small signals of the dq-axis grid side current obtained after harmonic linearization respectively.

[0021] As an alternative solution, it further includes: introducing a virtual notch filter in the voltage and current control link of the network-forming converter to make the output positive and negative sequence impedances meet the phase margin requirements.

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

[0023]

[0024] where, ω 1 is the rated angular frequency, L f is the series inductance on the converter side, s 2 K a represents the introduced active damping feedback, K a is the active damping parameter; G Nor (s) is the notch filter model; ΔU d (s), ΔU q (s) are the small signals after linearizing the dq-axis modulation voltage respectively, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) are the reference current inputs of the dq-axis current loop linearized small signals respectively, Δi d , Δi q are the small signals of the inverter side current obtained after harmonic linearization respectively, Δv d (s), Δv q(s) are the small-signal dq-axis grid-side voltages obtained after harmonic linearization processing, Δi gd (s), Δi gq (s) are the small-signal dq-axis grid-side currents obtained after harmonic linearization processing.

[0025] In some other embodiments, the following technical solution is adopted:

[0026] A resonant suppression system for a network-forming converter system based on sequence impedance reshaping, comprising:

[0027] A model construction module, configured to obtain the small-signal grid-side voltage, grid-side current, and converter-side current after linearization based on the active and reactive power control strategy of the network-forming converter and the voltage-current double closed-loop control principle, and establish a sequence impedance model of the output impedance of the network-forming converter system based on a virtual synchronous generator;

[0028] A stability analysis module, configured to determine the conditions for system stability based on the sequence impedance model in combination with the passivity theory;

[0029] A resonant suppression module, configured to introduce an active damping feedback loop into the voltage control link of the network-forming converter in combination with the conditions for system stability, reshape the equivalent output impedance of the converter resonant control, reduce the non-passive region of the positive and negative sequence output impedances, and achieve harmonic resonance suppression of the grid-connected current of the network-forming converter.

[0030] In some other embodiments, the following technical solution is adopted:

[0031] A terminal device, which includes a processor and a memory. The processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded and executed by the processor to perform the above-mentioned resonant suppression method for a network-forming converter system based on sequence impedance reshaping.

[0032] In some other embodiments, the following technical solution is adopted:

[0033] A computer-readable storage medium, in which multiple instructions are stored, and the instructions are suitable for being loaded and executed by the processor of the terminal device to perform the above-mentioned resonant suppression method for a network-forming converter system based on sequence impedance reshaping.

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

[0035] (1) The present invention is directed to a grid-forming converter grid-connected system based on a virtual synchronous generator. By using harmonic linearization and small-signal ideas, a system sequence impedance model is established, and combined with passivity theory, the stability conditions of the system are determined. For the first time, the sequence impedance model is used for impedance reshaping of the grid-connected system, and an equivalent series virtual damping and a feedback control loop of an equivalent notch filter are specifically introduced into the converter system to reshape the sequence impedance waveform, thereby controlling the system stability and robustness.

[0036] (2) When analyzing the system stability mechanism, the present invention uses sequence impedance modeling, which linearizes the nonlinear model while ensuring globality and accuracy, reducing the modeling complexity.

[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, an equivalent virtual notch filter is introduced, so that there is sufficient phase margin in the output sequence impedance when the system is grid-connected, improving the system stability and robustness and suppressing 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, reducing the system cost and loss.

[0039] Other features and advantages of the additional aspects of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of this aspect. Brief Description of the Drawings

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

[0041] Figure 2 It is the main circuit topology diagram of the grid-forming converter in the embodiment of the present invention;

[0042] Figure 3 It is the main circuit topology diagram of the grid-forming converter in the embodiment of the present invention;

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

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

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

[0046] Figure 6It is the Bode diagram of the output sequence impedance waveform of the network-forming converter system in the embodiment of the present invention varying with the active damping parameter;

[0047] Figure 7 It is the interaction characteristic diagram of the system sequence impedance and the grid-side inductor after selecting a suitable active damping parameter in the network-forming converter system in the embodiment of the present invention;

[0048] Figure 8 It is the waveform diagram of the notch filter used in the network-forming converter system in the embodiment of the present invention varying with parameters;

[0049] Figure 9(a) is the voltage-current control block diagram of the network-forming converter system introducing a notch filter in the embodiment of the present invention;

[0050] Figure 9(b) is the control block diagram of the network-forming converter system introducing an equivalent notch filter feedback loop in the embodiment of the present invention;

[0051] Figure 10 It is the Bode diagram of the output sequence impedance of the network-forming converter system varying with parameters after introducing an equivalent notch filter feedback in the embodiment of the present invention;

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

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

[0054] Figure 11(c) is the grid-side output current waveform diagram of the network-forming converter system after introducing a notch filter in the embodiment of the present invention;

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

[0056] Figure 11(e) is the grid-side output current THD of the network-forming converter system after introducing a notch filter in the embodiment of the present invention. Detailed implementation manners

[0057] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

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

[0059] Embodiment 1

[0060] In one or more embodiments, a resonance suppression method for a network-forming converter system based on sequence impedance reshaping is disclosed, which specifically includes the following processes:

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

[0062] Specifically, Figure 1 The structure of the virtual synchronous generator control system of the network-forming converter is given, including: the active power frequency modulation process, the reactive power voltage regulation control process, and the voltage and current double closed-loop decoupling control process.

[0063] Among them, the active power frequency modulation process is specifically:

[0064]

[0065] In the formula, θ is the phase angle of the internal electromotive force of the virtual synchronous generator, ω 1 is the rated angular frequency, P ref is the given active power of the virtual synchronous generator, P act is the system 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 specifically:

[0067]

[0068] Among them, E m is the effective value of the virtual internal electromotive force, K i is the excitation integral coefficient of the virtual synchronous generator, |v| ref is the effective value of the rated voltage, |v| is the effective value of the grid-connected voltage, K q is the reactive power-voltage droop coefficient, Q ref is the system given reactive power, Q act is the system output reactive power.

[0069] The decoupling control process of the voltage and current loops is specifically as follows:

[0070]

[0071] Among them, C f is the three-phase shunt capacitor, L f is the series inductor on the converter side, the capacitor voltage v abc in the dq axis is v d , v q , the converter-side current i abc in the dq axis is i d , i q , the grid-side current i gabc in the dq axis is i gd , i gq , v dref , v qref are the output voltages of the dq axis in the reactive power voltage regulation process, U d , U q are the final dq axis modulation voltages respectively, G v (s), G i (s) are the PI integral controllers of the voltage loop and the current loop respectively, and their proportionality coefficients are K pu , K pi respectively, and the integral coefficients are K iu , K ii respectively; i dref , i qref are the outputs of the dq axis voltage outer loop, that is, the linearized small-signal reference current inputs of the dq axis current loop.

[0072] Figure 2 Figure gives the main circuit topology of the converter grid connection. First, the harmonic linearization process is carried out on the grid connection control system of the non-linear grid-forming converter. For the positive and negative sequence disturbance voltages injected into the grid side of the grid connection system, taking phase a as an example, the grid side voltage becomes:

[0073] v abc =V 1 cos(2πf 1 t)+V p cos(2πf p t+φ vp )+V n cos(2πf n t+φ vn )(4)

[0074] In the formula, v abc is the grid side voltage (that is, the capacitor voltage), V 1 , V p , V n are the amplitudes of its fundamental wave, positive and negative disturbances, and negative sequence disturbances respectively, f1 and f p and f n are the corresponding frequencies, and φ vp and φ vn are the positive and negative sequence disturbance 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 disturbance are I g1 , I gp , I gn respectively, and the positive and negative sequence disturbance phase angles are φ igp , φ ign and the fundamental wave disturbance 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 disturbance are I 1 , I p , I n respectively, and the positive and negative sequence disturbance phase angles are φ ip , φ in and the fundamental wave disturbance phase angle φ i1 .

[0077] For the voltages and currents v abc , i gabc and i abc at the disturbance point, after performing Fourier transform and coordinate transformation on them respectively to convert them into voltage and current components under zero sequence, positive sequence, and negative sequence, their respective small signals are obtained. Then, considering the frequency offset effect in the coordinate transformation, the instantaneous output power P act and Q act of the control system are calculated as:

[0078]

[0079] where

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

[0081] After linearly processing the harmonics, the small signals Δv d , Δv q of the dq-axis grid-side voltage, the small signals Δi gd , Δi gq of the dq-axis grid-side current, and the small signals Δi d , Δi q, by traversing the active power, reactive power control loops and voltage and current control loops of the system, small signals Δθ and Δv can be obtained dqref , Δi dqref , ΔU dq :

[0082]

[0083] Among them, Δθ[f] is the small-signal change in the phase angle of the internal electromotive force of the virtual synchronous generator, J is the moment of inertia of the virtual synchronous generator, P act_p , P act_n are respectively the instantaneous positive and negative sequence output powers of the virtual synchronous generator (VSG) system; Δv dref (s), Δv qref (s) are respectively the small-signal output voltages of the dq axes in the reactive power regulation process obtained after harmonic linearization, E m_p , E m_n are respectively the positive and negative sequence virtual internal electromotive forces; Δi dref (s), Δi qref (s) are respectively the reference current inputs of the linearized small signals of the dq axis current loops, Δv d (s), Δv q (s) are respectively the small-signal grid-side voltages of the dq axes obtained after harmonic linearization, Δi gd (s), Δi gq (s) are respectively the small-signal grid-side currents of the dq axes obtained after harmonic linearization; ΔU d (s), ΔU q (s) are respectively the small-signals after linearization of the dq axis modulation voltages, Δi d , Δi q are respectively the small-signal inverter-side currents obtained after harmonic linearization.

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

[0085]

[0086] Among them, C f is the three-phase shunt capacitor, L f is the series inductor on the converter side, v a , v b , v c are the capacitor voltages in the three-phase stationary coordinate system (i.e., the grid-side voltage v abc ), i ga , i gb , i gc are the grid-side currents in the three-phase stationary coordinate system; U a , U b , U cis the three-phase modulated voltage in the stationary coordinate system.

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

[0088]

[0089] The algebraic expressions in the formula are respectively:

[0090]

[0091]

[0092] Among them, (both s and f are common variables in the frequency domain), K i is the excitation integral coefficient of the virtual synchronous generator, and K q is the reactive power-voltage droop coefficient. For the converter-side current i abc , the amplitudes of the fundamental wave, positive and negative perturbations, and negative-sequence perturbations are I 1 , I p , I n respectively, v abc is the grid-side voltage, and V 1 , V p , V n are the amplitudes of its fundamental wave, positive and negative perturbations, and negative-sequence perturbations respectively. G v [f] and G i [f] are the PI integral controllers of the voltage loop and current loop respectively. φ ig1 , φ i1 are the fundamental wave perturbation phase angles of the grid-side current and converter-side current; and respectively represent 's conjugate transpose and itself.

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

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

[0095] Figure 4 are the positive and negative sequence small-signal equivalent circuit models of the system. The three-phase converter is decomposed into positive and negative sequence subsystems, and positive and negative sequence voltage perturbation sources are connected in series. The positive and negative sequence small-signal equivalent circuit includes the internal electromotive forces V vsgp and V vsgn of the positive and negative sequence virtual synchronous generators, and the sequence impedance Z of the virtual synchronous generatorvsgp With Z vsgn , positive and negative sequence grid impedances Z gp With Z gn and positive and negative sequence grid voltages V gp With V gn is connected in series with part of it. According to the equivalent circuit, the relationship between the grid-connected current and the output impedance of the converter system can be obtained as follows:

[0096]

[0097] It can be seen from (16) that the steady-state of the system grid-connected current depends on the system impedance ratio, and the system is stable when both positive and negative sequence impedances satisfy the stability criterion. According to the passivity theory, the system stability condition is that the output phases are all within the range of [-90°, 90°]. Combining with the system sequence impedance model, it can be known that: the system is stable when the phases of the positive and negative sequence output impedances of the system are all within the passive range.

[0098] S103: Combining the conditions for system stability, introduce an active damping feedback loop in the voltage control link of the grid-forming converter, reshape the equivalent output impedance of the converter resonance control, reduce the non-passive region of the output positive and negative sequence impedances, and realize the suppression of the grid-connected current harmonic resonance of the grid-forming converter.

[0099] Figure 5(a) and Figure 5(b) are the control block diagrams of introducing series passive damping in the voltage and current control links of the converter and equivalent it to an active damping feedback loop, and reshape the system output sequence impedance by increasing the system passivity. At this time, the current loop feedback introduced can be simplified to s 2 K a , take K a as the active damping parameter, and determine the parameters of the active damping control in combination with the change of the system sequence impedance model. At this time, the voltage and current double closed-loop control process in the sequence impedance calculation model becomes:

[0100]

[0101] Figure 6 is the change curve of the system output sequence impedance with the active damping parameter after introducing the active damping, where the solid line is the positive sequence impedance and the dashed line is the negative sequence output impedance. The proportion of the passive region occupied by the system output sequence impedance will change with the active damping parameter. Select the parameter that makes the passive output sequence impedance of the system the largest in the passive region to further improve the model and enhance the system robustness. According to Figure 6 in it, 0.1 or 0.2 can be selected as the parameter of K a , and at this time the passive region where the system sequence impedance is located is the largest.

[0102] Figure 7Figure 0 shows the interaction characteristics diagram of the system sequence impedance and the grid-side inductor when 0.2 is selected as the active damping parameter. To ensure that the system has a phase margin of 30° as much as possible when connected to the grid and improve the system robustness, a virtual equivalent notch filter can be introduced.

[0103] Figure 8 Figure 4 shows the waveform of the notch filter's action, and its model G Nor is as follows:

[0104]

[0105] where ξ is the notch width, ω 2 is the notch center angular frequency, and ω 2 is determined by the output waveform of the system sequence impedance after adding active damping and its intersection with the grid-side inductor. From the interaction output waveform of the system sequence impedance and the power grid in Figure 7 , 170 Hz can be taken as the notch 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 the grid-forming converter system with the introduction of the notch filter. By simulating the effect of the series notch filter on the grid side and equivalent it in the voltage and current control loops, it is manifested as adding a virtual notch filter control loop, thereby reshaping the output waveform of the system sequence impedance to ensure that there is sufficient phase margin in its output sequence impedance. At this time, the voltage and current double closed-loop control process in the sequence impedance calculation model is as follows:

[0107]

[0108] Figure 10 Figure 28 shows the waveform of the system output sequence impedance varying with the ξ parameter after introducing the virtual notch filter feedback loop. At this time, the system output sequence impedance is basically in the passive region. 0.4 or 0.6 can be selected as the notch width of the notch filter according to 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 effect of the control method of the present disclosure, experimental simulations are carried out, and the simulation results are shown in Figures 11(a), 11(b), 11(c), 11(d), and 11(e). Figure 11(a) shows the waveform diagram of the grid-side output current of the grid-forming converter system before harmonic suppression, and the current contains serious harmonic phenomena; in Figure 11(b), part of the output current harmonics are suppressed by introducing the active damping feedback loop; in Figure 11(c), the system output current resonance is significantly suppressed by introducing the virtual notch filter; by comparing Figures 11(d) and 11(e), it can be found that the introduction of the new feedback loop specifically reduces the current harmonic content after introducing the active damping.

[0110] In summary, this embodiment reduces the modeling difficulty while clarifying the stability mechanism of the system in combination with the passivity theory. At the same time, according to the sequence impedance model, a feedback loop is introduced specifically to reshape the system impedance, thereby suppressing the system harmonic resonance and improving the system stability and robustness.

[0111] Embodiment 2

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

[0113] A model construction module, configured to obtain small signals of the grid-side voltage, grid-side current, and converter-side current after linearization based on the active and reactive power control strategy of the network-forming converter and the voltage-current double closed-loop control principle, and establish a sequence impedance model of the output impedance of the network-forming converter system based on a virtual synchronous generator;

[0114] A stability analysis module, configured to determine the conditions for system stability based on the sequence impedance model in combination with the passivity theory;

[0115] A resonance suppression module, configured to introduce an active damping feedback loop in the voltage control link of the network-forming converter in combination with the conditions for system stability, reshape the equivalent output impedance of the converter resonance control, reduce the non-passive region of the positive and negative sequence output impedances, and achieve the suppression of the grid-connected current harmonic resonance of the network-forming converter.

[0116] It should be noted that the specific implementation manners of the above modules are the same as those in Embodiment 1 and will not be elaborated here.

[0117] Embodiment 3

[0118] In one or more embodiments, a terminal device is disclosed, which includes a processor and a memory. The processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded and executed by the processor to perform the resonance suppression method for the network-forming converter system based on sequence impedance reshaping described in Embodiment 1.

[0119] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA, or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0120] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A part of the memory may also include a non-volatile random access memory. For example, the 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 circuit of the hardware in the processor or the instructions in the form of software.

[0122] Embodiment 4

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

[0124] Although the specific embodiments of the present invention are described above in conjunction with the accompanying drawings, it is not a limitation of the protection scope of the present invention. Those skilled in the art should understand that, based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.

Claims

1. A method for suppressing resonance of a grid-connected 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 double closed-loop control principle, the linearized grid-side voltage, grid-side current and converter-side current small signals are obtained, and the sequence impedance model of the output impedance of the grid-type converter system based on the virtual synchronous generator is established. Based on the sequence impedance model and combined with the passivity theory, the conditions for system stability are determined; In consideration of the system stability conditions, an active damping feedback loop is introduced into the voltage control link of the grid-connected converter to reshape the equivalent output impedance of the converter resonance control, reduce the non-passive area of ​​the output positive and negative sequence impedance, and realize the suppression of the harmonic resonance of the grid-connected current of the grid-connected converter.

2. A method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 1, characterized in that: The sequence impedance model of the output impedance of the grid-connected converter system based on the virtual synchronous generator is established. The specific process is as follows: Based on the active and reactive power control strategy of grid-type converter and the voltage and current double closed-loop control principle, a nonlinear relationship model among the internal potential, output voltage and output current of the grid-type converter is established. Injecting positive-sequence and negative-sequence disturbance voltages on the grid side of the grid-connected system, performing harmonic linearization processing on the nonlinear model, and obtaining small signals of the grid-side voltage, grid-side current, and converter-side current respectively; The small signal is passed through the active and reactive power control process and the voltage and current double closed-loop control process of the grid-forming converter to establish a sequence impedance model of the positive-sequence and negative-sequence grid-forming converter output impedance in a stationary coordinate system.

3. A method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 2, characterized in that: After the small signal traverses the active and reactive power control process and the voltage and current double closed-loop control process of the grid-forming converter, the method further includes: The small voltage signal Δv on the dq axis grid side obtained after harmonic linearization processing d , Δv q , dq axis grid side current small signal Δi gd , Δi gq , and the inverter side current small signal Δi d , Δi q , respectively substitute the active frequency regulation, reactive voltage regulation and current and voltage control processes, and then substitute the obtained small signal model into the converter main circuit equation to obtain the sequence impedance model of the positive-sequence and negative-sequence grid-type converter output impedance in the stationary coordinate system.

4. A method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 1, characterized in that: Based on the sequence impedance model and combined with the passivity theory, the conditions for system stability are determined, specifically: the system is stable when the phases of the positive and negative sequence impedances output by the system are both within the passive range.

5. The method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 1, characterized in that: After the active damping feedback loop is introduced, the voltage and current double closed-loop control process becomes: Where ω1 is the rated angular frequency, L f is the series inductance on the converter side, s 2 K a represents the introduced active damping feedback, Ka is the active damping parameter; ΔU d (s), ΔU q (s) are small signals after linearization of dq axis modulation voltage, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) are the reference current inputs of the linearized small signals of the dq axis current loop, Δi d , Δi q are the inverter side current small signal obtained after harmonic linearization processing, Δv d (s), Δv q (s) are the small voltage signals on the dq axis grid side obtained after harmonic linearization processing, Δi gd (s), Δi gq (s) are the small current signals on the dq axis grid side obtained after harmonic linearization processing.

6. A method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 1, characterized in that: Also includes: A virtual notch filter is introduced into the voltage and current control link of the grid-type converter to make the output positive and negative sequence impedance meet the phase margin requirement.

7. A method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping according to claim 6, characterized in that: After the introduction of the virtual notch filter, the voltage and current dual closed-loop control process becomes: Where ω1 is the rated angular frequency, L f is the series inductance on the converter side, s 2 K a represents the active damping feedback introduced, K a is the active damping parameter; G Nor (s) is the notch filter model; ΔU d (s), ΔU q (s) are small signals after linearization of dq axis modulation voltage, G i (s) is the current loop transfer function, Δi dref (s), Δi qref (s) are the reference current inputs of the linearized small signals of the dq axis current loop, Δi d , Δi q are the inverter side current small signal obtained after harmonic linearization processing, Δv d (s), Δv q (s) are the small voltage signals on the dq axis grid side obtained after harmonic linearization processing, Δi gd (s), Δi gq (s) are the small current signals on the dq axis grid side obtained after harmonic linearization processing.

8. 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 grid-side voltage, grid-side current and converter-side current small signals based on the active and reactive power control strategy of the grid-type converter and the voltage and current double 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; A stability analysis module, used to determine the conditions for system stability based on the sequence impedance model combined with passivity theory; The resonance suppression module is used to introduce an active damping feedback loop in the voltage control link of the grid-connected converter in combination with the system stability conditions, reshape the equivalent output impedance of the converter resonance control, reduce the non-passive area of ​​the output positive and negative sequence impedance, and realize the suppression of the harmonic resonance of the grid-connected current of the grid-connected converter.

9. A terminal device, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executing the method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a plurality of instructions, characterized in that: The instructions are suitable for being loaded by a processor of a terminal device and executing the method for suppressing resonance of a grid-connected converter system based on sequence impedance reshaping as described in any one of claims 1 to 7.

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