Inverter modal admittance reconstruction damping control method and system

Abstract

The invention belongs to the technical field of power electronic grid-connected control, and relates to an inverter modal admittance reconstruction damping control method and system, and the method comprises the steps: enabling a TITO inverter output admittance model to be equivalent to a positive and negative sequence separated single-input single-output structure through a modeling decoupling module; the remodeling control module constructs a capacitor voltage feedback function with frequency selectivity; the transfer function solving module is used for obtaining a capacitor voltage feedback positive sequence channel transfer function and a capacitor voltage feedback negative sequence channel transfer function, and constructing a corresponding grid-connected current feedback transfer function; the frequency domain adjusting module introduces a frequency factor to equivalently replace an imaginary number unit; the robust optimization modeling module is used for constructing a parameter optimization model; and the parameter setting module is used for solving a frequency factor optimal value which enables the target function to take a maximum value by adopting a particle swarm algorithm. According to the invention, stable operation of the grid-connected system can be effectively maintained.

Description

A method and system for modal admittance reconfiguration damping control of inverters Technical Field

[0001] This invention relates to the field of power electronics grid-connected control technology, specifically to an inverter modal admittance reconfiguration damping control method and system. Background Technology

[0002] In existing technologies, the interaction between power electronic devices and grid impedance causes multi-frequency oscillations, which seriously affect the stable operation of grid-connected systems.

[0003] Current research on active damping technology mainly focuses on additional impedance control. Specifically, it distributes the damping control link to various control links through circuit structure and mathematical equivalence to reshape the inverter output admittance, effectively suppressing the oscillation mode at a specific frequency and improving the stability of the grid-connected inverter system to a certain extent.

[0004] However, the additional damping method based on fixed parameters still does not fully consider the frequency coupling effect between the grid impedance and the inverter, especially the mutual influence between positive and negative sequence modes. At the same time, because the grid impedance changes in real time over a wide frequency range due to factors such as line parameters and load switching, the existing method lacks the ability to actively adapt to the uncertainty of grid impedance. This leads to a decrease in damping effect and insufficient robustness under weak grid or variable operating conditions, making it difficult to ensure the safe and stable operation of high proportion of new energy grid connection in new power systems.

[0005] In view of this, it is very necessary to provide an inverter modal admittance reconfiguration damping control method and system to solve the above-mentioned defects in the prior art. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems in the prior art that do not consider the frequency coupling effect in the interaction between the power grid and the inverter, and that it is difficult to actively adapt to the wide range of changes in the power grid impedance. The invention provides a method and system for designing inverter modal admittance reconfiguration damping control to solve the technical problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: Firstly, the present invention provides a method for modal admittance reconfiguration damping control of an inverter, comprising the following steps: Step S1: Constructing a TITO inverter output admittance model incorporating frequency coupling effects, and using matrix operations to convert the TITO inverter output admittance model into a single-input single-output structure with positive and negative sequence separation; Step S2: Based on the single-input single-output structure with positive and negative sequence separation, introducing capacitor voltage feedback and grid-connected current parallel feedback, and constructing a frequency-selective capacitor voltage feedback function; Step S3: Based on the capacitor voltage feedback function, obtaining the positive-sequence channel transfer function and the negative-sequence channel transfer function of the capacitor voltage feedback, and constructing the corresponding grid-connected current feedback transfer function; Step S4: Introducing a frequency factor to equivalently replace the imaginary unit, obtaining an admittance reconfiguration transfer function model containing the frequency factor; Step S5: Using the minimum damping ratio among all closed-loop poles as the objective function, and the frequency factor as the tuning parameter, setting frequency constraints based on the maximum limiting grid impedance, and constructing a parameter optimization model; Step S6: Using a particle swarm optimization algorithm to solve for the optimal value of the frequency factor that maximizes the objective function.

[0008] Secondly, the present invention also provides an inverter modal admittance reconfiguration damping control system, comprising: a modeling and decoupling module for establishing a TITO inverter output admittance model considering frequency coupling, and using matrix operations to convert the TITO inverter output admittance model into a single-input single-output structure with positive and negative sequence separation; a reconfiguration control module for constructing a capacitor voltage feedback function with frequency selectivity; a transfer function solving module for obtaining the positive-sequence channel transfer function and the negative-sequence channel transfer function of the capacitor voltage feedback, and constructing the corresponding grid-connected current feedback transfer function; a frequency domain adjustment module for introducing a frequency factor to equivalently replace the imaginary unit; a robust optimization modeling module for constructing a parameter optimization model with the minimum damping ratio among all closed-loop poles as the objective function, the frequency factor as the tuning parameter, and frequency constraints set according to the maximum limiting grid impedance; and a parameter tuning module for using a particle swarm optimization algorithm to solve for the optimal value of the frequency factor that maximizes the objective function.

[0009] The modules work together to ensure that the inverter can effectively suppress oscillations and maintain the stable operation of the grid-connected system in weak grid environments and with a wide range of varying grid impedance.

[0010] The beneficial effects of this invention are that by establishing a TITO inverter output admittance model that includes the influence of frequency coupling, and equivalently representing a single-input single-output structure with positive and negative sequence separation, this invention improves the frequency coupling influence between the grid and the inverter, enhances the adaptability to grid impedance changes, reduces oscillation risk, and strengthens the stability of the inverter.

[0011] This invention enhances the damping characteristics of the inverter and improves its robustness under different grid impedance conditions by introducing frequency-selective capacitor voltage feedback and grid-connected current parallel feedback, thus solving the problem of insufficient damping in the prior art.

[0012] This invention introduces a frequency factor to equivalently replace the imaginary unit, thereby adjusting the frequency domain characteristics of the output impedance, making the inverter's damping performance adjustable and optimized, and improving its dynamic response capability under a wide range of grid impedance variations.

[0013] This invention provides an optimization basis for inverter damping characteristics by constructing a parameter optimization model with the minimum closed-loop damping ratio as the objective and combining it with grid impedance constraints. This improves the robust damping control of inverters in complex grid environments and enhances grid connection stability and disturbance rejection capability.

[0014] The inverter modal admittance reconfiguration damping control method proposed in this invention belongs to the paradigmatic method of reshaping the inverter output impedance by introducing electrical feedback in the form of additional damping channels. It has general applicability and is applicable to impedance reconfiguration of grid-connected inverters in addition to grid-connected inverters.

[0015] This invention takes into account the variable grid impedance in practical applications. By analyzing the capacitor voltage feedback function, it uses a particle swarm optimization algorithm to make the damping effect robust when connected to an uncertain grid impedance, thereby enhancing the inverter's adaptability to different grid connection conditions.

[0016] This invention addresses the technical problems of existing technologies that fail to consider the frequency coupling effect in the interaction between the grid and the inverter, and are difficult to actively adapt to a wide range of grid impedance variations, through technical measures such as modeling decoupling, admittance reshaping, introduction of frequency factors, and parameter optimization tuning. It achieves robust damping control and grid-connected stability improvement of the inverter under a wide range of grid impedance conditions, and has significant practical and engineering application value.

[0017] Therefore, it is evident that the present invention has outstanding substantive features and significant progress compared with the prior art, and the beneficial effects of its implementation are also obvious. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 is a flowchart of an inverter modal admittance reconfiguration damping control method; Figure 2 is a diagram showing the effect of frequency selection of capacitor voltage signal; Figure 3 is a graph showing the amplitude and phase frequency response curves of the inverter output impedance before and after admittance reconfiguration, Figure 3(a) is the amplitude frequency response, and Figure 3(b) is the phase frequency response; Figure 4 is a comparison of voltage and current waveforms before and after admittance reconfiguration, with damping control activated at t=1s, Figure 4(a) is a comparison of voltage waveforms before and after admittance reconfiguration, and Figure 4(b) is a comparison of current waveforms before and after admittance reconfiguration; Figure 5 is a comparison of Fourier analysis results before and after admittance reconfiguration, Figure 5(a) is a voltage and current waveform before admittance reconfiguration, and Figure 5(b) is a voltage and current waveform after admittance reconfiguration; Figure 6 is a block diagram of an inverter modal admittance reconfiguration damping control system. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments are explanations of the present invention, but the present invention is not limited to the following implementation methods.

[0021] Example 1: As shown in Figure 1, this example provides an inverter modal admittance reconfiguration damping control method, including the following steps: Step S1: Construct a TITO inverter output admittance model that includes frequency coupling effects, and use matrix operations to convert the TITO inverter output admittance model into a single-input single-output structure with positive and negative sequence separation; Step S2: Based on the single-input single-output structure with positive and negative sequence separation, introduce capacitor voltage feedback and grid current parallel feedback, and construct a capacitor voltage feedback function with frequency selectivity; Step S3: Based on the capacitor voltage feedback function, obtain the positive-sequence channel transfer function and the negative-sequence channel transfer function of capacitor voltage feedback, and construct the corresponding grid current feedback transfer function; Step S4: Introduce a frequency factor to equivalently replace the imaginary unit, and obtain an admittance reconfiguration transfer function model that includes the frequency factor; Step S5: Use the minimum damping ratio among all closed-loop poles as the objective function, the frequency factor as the tuning parameter, and set the frequency constraint condition according to the maximum limit grid impedance to construct a parameter optimization model; Step S6: Use the particle swarm optimization algorithm to solve for the optimal value of the frequency factor that maximizes the objective function.

[0022] In step S1: Based on the concept of harmonic linearization, the output characteristics of the inverter under grid-connected operation are modeled using small signals to construct a TITO inverter output admittance model that includes the influence of frequency coupling; based on the generalized Nyquist criterion, the inverter output admittance is combined with the grid impedance to form the hysteresis matrix of the inverter grid-connected system; through matrix transformation and order reduction, the TITO inverter output admittance model is equivalently transformed into a SISO output structure in which the positive sequence channel and the negative sequence channel are independent.

[0023] TITO (Two-Input Two-Output) refers to the simultaneous existence of two input quantities and two output quantities, used to describe the mapping relationship between multiple variables. In the small-signal modeling of three-phase grid-connected inverters, the system is typically described in the dq coordinate system (direct-quadrature reference frame) or the sequence component coordinate system. In this case, the inverter output current is simultaneously affected by disturbances in both the d-axis voltage and the q-axis voltage, and there are significant cross-coupling relationships between different channels. The resulting output admittance model is usually represented in matrix form, with its off-diagonal elements reflecting inter-axis coupling and frequency coupling effects.

[0024] SISO (Single-Input Single-Output) refers to a system that contains only one input and one output, with no cross-coupling between them. After performing symmetrical component transformation and matrix order reduction on the TITO output admittance model of the inverter, the positive-sequence and negative-sequence components can be isolated, allowing the voltage and current relationships under each sequence component to be described in scalar form. In this case, both the positive-sequence and negative-sequence channels exhibit an SISO structure, facilitating the introduction of grid impedance and direct stability analysis.

[0025] The mathematical expression for the TITO inverter output admittance model can be expressed as: In the formula Indicates frequency as The positive sequence disturbance current with frequency is The influence of the positive sequence response voltage; Indicates frequency as The positive sequence disturbance current with frequency is The influence of negative sequence response voltage; Indicates frequency as The negative sequence disturbance current with frequency is The influence of the positive sequence response voltage; Indicates frequency as The negative sequence disturbance current with frequency is The influence of negative sequence response voltage. This represents the Laplace frequency domain operator, which is equivalent to the Laplace frequency domain operator in this frequency domain modeling. , The frequency of the disturbance current. The frequency shift of the Laplace frequency domain operator caused by inverter structural asymmetry can be equivalently represented in this frequency domain modeling as... ,in , The fundamental frequency, i.e. .

[0026] in, , , , The expression is as follows:

[0027] In the formula , is the transfer function expression between the output angle of the phase-locked loop and the q-axis component of the input grid-connected current; where The transfer function for the phase-locked loop is expressed as follows: , This is the transfer function for the inner current loop current feedback. , These are the expressions for the static operating point on the d-axis and q-axis, respectively. , , It is the capacitor current in the simulation model. It is the conjugate of the capacitor current. α is the grid-connected current, and α is the phase difference between the grid-connected voltage and the grid-connected current. All these values ​​are obtained from FFT measurements in the actual simulation model. ;in =50Hz, the physical meaning of which is the fundamental angular frequency; grid voltage The value is 310V; mains inductance 3mH; DC voltage of the power grid The voltage is set to 700V; the rated output power of the grid is 10kW. Inverter-side inductor... The inverter filter capacitor is 3mH. The inverter grid-side inductor is 12μF. The current is 0.5mH. Control system parameters include: current loop parameters. They are 4 / 100 respectively; PLL parameters The values ​​are 1.72 / 492 respectively; PWM pulse width modulation gain The value is 0.5; the decoupling coefficient of the inner current loop dq axis is set. The gain is 0.0027; to improve system stability, the capacitor current feedback gain is... The configuration is set to 10. The backlash matrix expression is: In the formula For grid admittance, where , It is the inductance of the power grid. for The grid admittance; The SISO admittance model for inverter positive and negative sequence decoupling considering frequency coupling effects is obtained: .

[0028] In step S2: In order to improve the grid-connected dynamic characteristics of the inverter and achieve admittance regulation, capacitor voltage feedback and grid-connected current parallel feedback are introduced in the inverter current inner loop control. Based on the positive and negative sequence decoupled SISO output structure, a frequency-selective capacitor voltage feedback positive sequence channel transfer function and capacitor voltage feedback negative sequence channel transfer function are constructed to reshape admittance for positive sequence disturbance components and negative sequence coupling, respectively.

[0029] The capacitor voltage feedback, after Park transform, yields an expression in the frequency domain that is used for current closed-loop regulation; the expression is:

[0030]

[0031] In the formula This is the base value of the capacitor voltage. , This represents the positive-sequence component of the capacitor voltage. This is the negative sequence component of the capacitor voltage.

[0032] Parallel feedback of grid-connected current enables direct adjustment of inverter output characteristics by adding a corresponding transfer function and superimposing it with the inner loop current.

[0033] Based on the parallel feedback of capacitor voltage and grid current, a frequency-selective capacitor voltage feedback function is constructed. The frequency-selective capacitor voltage feedback function is realized through a complex second-order resonator. Through two independent frequency selectors, namely a positive-sequence frequency selector and a negative-sequence frequency selector, the positive-sequence disturbance frequency component and the negative-sequence coupling frequency component are extracted. The amplitude and phase characteristics of the positive-sequence channel and the negative-sequence channel of the capacitor voltage are adjusted respectively, so that the inverter output impedance can be directionally controlled within the critical frequency range.

[0034] Capacitor voltage feedback function with frequency component selectivity The expression is: In the formula, This is the transfer function for the positive-sequence channel of capacitor voltage feedback. This is the transfer function for the negative sequence channel of capacitor voltage feedback. Center frequency Positive sequence frequency selector, Center frequency Negative sequence frequency selector.

[0035] Both the positive-sequence frequency selector and the negative-sequence frequency selector are implemented using a complex coefficient second-order resonant structure, and their specific expressions are as follows:

[0036]

[0037] in, , , , These are the quality factors of the positive-sequence resonant circuit and the negative-sequence resonant circuit, respectively. The capacitor voltage signals, after frequency component selection, enter the positive-sequence feedback channels. With negative order feedback channel Together with the newly added grid-connected current parallel feedback channel, it acts on the modulation stage to achieve directional reshaping and damping optimization of the inverter output admittance in the key oscillation frequency band. Figure 2 shows the effect of the capacitor voltage signal frequency selection. The complex coefficient second-order resonant stage determines the frequency selection characteristics, the positive-sequence channel and the negative-sequence channel of the capacitor voltage feedback determine the impedance reshaping direction, and the grid-connected current parallel feedback is used to assist in adjusting the overall stability margin of the system.

[0038] Thus, the small-signal d-axis and q-axis components of the AC modulation signal of the grid-connected inverter are obtained. , After inverse Park transformation to the stationary coordinate system abc, an additional modulation signal is generated. Taking phase a as an example, the positive sequence component and negative sequence component of the AC modulation signal are as follows:

[0039]

[0040] According to the superposition principle Based on the average circuit model of the three-phase grid-connected inverter, the inverter output admittance model after reshaping the modal admittance can be obtained.

[0041] The positive-sequence perturbation admittance after reshaping is shown in the following equation: The negative-order coupled admittance after reshaping is shown in the following equation: .

[0042] Through the above processing, the current inner loop control structure is reshaped, and the admittance characteristics of the capacitor voltage feedback positive sequence channel and the capacitor voltage feedback negative sequence channel are independently adjusted to form modal impedance control for a specific frequency, thereby optimizing the closed-loop dynamic performance of the inverter grid-connected system.

[0043] In step S3: by setting the reshaped positive-sequence disturbance admittance to zero, the transfer function expression of the positive-sequence channel in the capacitor voltage feedback can be solved; by setting the reshaped negative-sequence coupling admittance to zero, the transfer function expression of the negative-sequence channel in the capacitor voltage feedback can be solved; to compensate for the influence of the capacitor voltage feedback on the numerator of the grid-connected system closed-loop transfer function during admittance reshaping and to maintain the stability of the grid-connected system closed-loop performance, the transfer function of the grid-connected current parallel feedback channel is constructed as a linear function. In conjunction with the capacitor voltage feedback channel, it forms a comprehensive regulation effect on both positive-sequence admittance and negative-sequence admittance.

[0044] To make the transfer function expression of the capacitor voltage feedback positive sequence path Transfer function expression for negative-order channels It is feasible. Considering the dominant role of capacitor current in the high-frequency domain of modal admittance amplitude-frequency and phase-frequency characteristics, the transfer function expression of the positive-sequence channel of capacitor voltage feedback is given. The transfer function expression for the capacitor voltage feedback negative sequence channel After simplification, the simplified expression is shown below: , ; , The expression for the transfer function of the grid-connected current parallel feedback channel is: In the formula For grid-side inductive reactance, i.e. .

[0045] Through the above processing, the transfer functions of the positive-sequence channel and the negative-sequence channel of the capacitor voltage feedback were simplified by reducing their order, thus reducing the complexity of modeling.

[0046] In step S4: to achieve controllability of the capacitor voltage and grid current feedback channel on the reshaped admittance frequency band characteristics, a frequency factor is introduced. and utilize The mathematical correspondence between the imaginary unit and the digital unit allows for the equivalent substitution of the imaginary unit in the positive-sequence transfer function and the negative-sequence transfer function of capacitor voltage feedback: specifically, a frequency factor is introduced. The mathematical relationship between the imaginary unit and the imaginary unit is: By equivalently replacing the imaginary units in the positive-sequence channel transfer function and the negative-sequence channel transfer function of capacitor voltage feedback, an admittance reshaping transfer function model including the frequency factor is obtained.

[0047] Through frequency factor The substitution method between the imaginary unit and the frequency factor allows the positive-sequence transfer function and the negative-sequence transfer function of the capacitor voltage feedback to explicitly reflect the change of the frequency factor. This facilitates the analysis of the frequency factor's regulatory effect on the system's dynamic characteristics and provides a technical basis for optimizing the stability and dynamic performance of the inverter grid-connected system.

[0048] In step S5: The closed-loop poles of the grid-connected inverter after reshaping the admittance are solved. The distribution of closed-loop poles after reshaping the admittance is taken as the analysis object. By examining the positions of all closed-loop poles in the complex plane, the pole with the weakest damping capability is selected as the key constraint factor for the stability of the grid-connected system. The minimum damping ratio corresponding to this pole is used as the performance evaluation index. Therefore, the minimum damping ratio in the set of closed-loop poles is constructed as the objective function to measure the overall damping level effect of the system after admittance reshaping. The objective function and frequency constraint conditions are shown in the following equation:

[0049] The impedance crossover frequency, The frequency corresponding to the minimum output impedance amplitude is defined. The frequency factor is used as a tuning parameter; by changing the value of the frequency factor, the output impedance characteristics of the inverter after reshaping the admittance and the distribution of closed-loop poles in the complex plane are affected. Using the frequency factor as an optimization variable, an overall improvement in the closed-loop pole damping ratio is achieved while satisfying constraints, thus forming a parameter optimization model centered on frequency factor tuning.

[0050] Frequency constraints are introduced into the parameter optimization model to ensure that the obtained frequency factor not only improves damping performance but also meets the physical and engineering limitations of grid-connected operation. The lower limit frequency of the frequency constraints is... The constraint is the crossover frequency at the maximum grid impedance that the inverter's own capacity should withstand and the inverter's output impedance after refactoring admittance. This is determined to avoid unfavorable impedance matching in the low-frequency range; upper frequency limit constraint. The frequency at which the inverter output impedance amplitude reaches its minimum value after reshaping the admittance is determined. To determine, the optimization results should be limited to a reasonable dynamic response range; and Together, they constitute the feasible search range for frequency factors.

[0051] By adjusting the frequency factor, the migration pattern of the closed-loop poles in the complex plane can be observed. Figure 3 compares the amplitude and phase frequency response curves of the inverter output impedance before and after admittance reshaping, reflecting the increase in the phase angle stability margin of the grid-connected system. This completes the frequency factor optimization modeling and analysis based on damping robustness.

[0052] Inverter positive sequence impedance with known grid coupling impedance For the closed-loop characteristic equation The characteristic roots are solved to obtain the closed-loop pole distribution, oscillation frequency, and damping ratio of the three-phase LCL inverter closed-loop grid-connected system.

[0053] The eigenvalues ​​corresponding to the closed-loop poles of the closed-loop characteristic equation can be expressed as: ; The first closed-loop grid-connected system for inverters There are several oscillation modes, in which... This is the attenuation coefficient of the oscillation mode. Oscillation frequency, oscillation mode Damping ratio The calculation formula is: Quantitative indicators for measuring the stability of inverter closed-loop grid-connected systems The above oscillation mode , ... The minimum damping ratio, i.e. .

[0054] By constructing a parameter optimization model with the minimum damping ratio of the closed-loop poles as the objective, the frequency factor as the adjustment means, and the grid impedance constraint as the basis, a systematic optimization basis is provided for the robust control design of the inverter grid-connected system.

[0055] In step S6: Under the premise of satisfying the given frequency constraints, a particle swarm optimization (PSO) algorithm is used to perform a global search for the frequency factor. The swarm of particles iteratively updates the frequency factor, gradually bringing the objective function closer to the optimal value. This yields the optimal frequency factor value that maximizes the objective function, enhancing the robustness of the inverter after reshaping the admittance to grid impedance uncertainties when connected to the grid under weak grid conditions. The optimal frequency factor obtained through the PSO algorithm is introduced into the inverter control structure after reshaping the admittance, adjusting the dynamic characteristics of the additional damping channel. By tuning the frequency factor, a control signal is generated, enabling the inverter's output impedance characteristics to adapt to a wide range of grid impedance changes during grid-connected operation. This maintains a sufficient damping level across a wide frequency range, enhancing the grid-connected system's adaptability to weak grid conditions and uncertain impedance conditions.

[0056] Using the maximum grid impedance that a 10kVA inverter can withstand as the grid connection condition, simulation verification was conducted to reshape the admittance and introduce an additional damping channel with damping robustness. Damping control was applied at t=1s. The voltage and current waveforms before and after admittance reshaping are shown in Figure 4, and Figure 5 shows the comparison of the voltage Fourier analysis results before and after admittance reshaping. Simulation results show that the optimized frequency factor can significantly improve the system's suppression capability under oscillation conditions, verifying the effectiveness and robustness of the proposed optimization parameter method in weak grid connection scenarios.

[0057] Example 2: As shown in Figure 6, this example provides an inverter modal admittance reconfiguration damping control system, including: a modeling and decoupling module 1 establishes a TITO inverter output admittance model in the dq coordinate system based on the harmonic linearization method; based on the generalized Nyquist criterion, the inverter output admittance is combined with the grid impedance to construct the hysteresis matrix of the grid-connected system; matrix reduction operation is performed on it to transform the complex TITO inverter output admittance model into an equivalent SISO structure in which the positive-sequence channel and the negative-sequence channel are independent; the frequency domain coupling mechanism of the grid-connected inverter under disturbance is revealed; the complex multivariable channels are decoupled into independent channels that are easy to analyze; and key mathematical models and characteristic roots are provided for subsequent stability assessment and directional control design.

[0058] The reshaping control module 2 introduces capacitor voltage feedback and grid-connected current feedback in the inner current loop. Through two independent frequency selectors, namely a positive-sequence frequency selector and a negative-sequence frequency selector, it extracts the positive-sequence disturbance frequency component and the negative-sequence coupling frequency component. These components are then processed by independently designed capacitor voltage feedback positive-sequence channel transfer functions and capacitor voltage feedback negative-sequence channel transfer functions, respectively. After inverse Park transformation, an additional modulation signal is generated. By reshaping the inverter output impedance, the admittance characteristics of the positive-sequence disturbance channel and the negative-sequence coupling channel can be adjusted separately and independently, providing the grid-connected system with directional impedance regulation capability within a specific frequency band.

[0059] The transfer function solution module 3 sets the positive-sequence coupling admittance in the reshaped admittance model to zero, and parsely obtains the expression for the positive-sequence channel transfer function of the capacitor voltage feedback. It then sets the negative-sequence coupling admittance to zero and solves for the expression for the negative-sequence channel transfer function of the capacitor voltage feedback. This simplifies both the positive and negative-sequence channels, reducing model complexity. A linear form of the grid-connected current parallel feedback channel transfer function is constructed to compensate for the impact of the introduced capacitor voltage feedback on the numerator of the closed-loop transfer function. The mathematical expressions for each feedback channel are precisely determined, achieving the expected decoupling goal and laying a theoretical foundation for constructing a stable and controllable closed-loop system.

[0060] The frequency domain adjustment module 4 introduces a frequency factor, which, through its mathematical relationship with the imaginary unit, effectively replaces the imaginary unit term in the reduced-order transfer function. The frequency factor is introduced as a freely adjustable parameter, providing an effective means to finely control the inverter's output impedance characteristics in the frequency domain and thus optimize the system's dynamic response.

[0061] Robust optimization modeling module 5 uses the minimum damping ratio among all closed-loop poles of the system after reshaping the admittance as the objective function. The frequency factor is a tuning parameter. Based on the grid impedance adapted to the inverter after resetting admittance, upper and lower limit constraints are set for the frequency factor: the upper limit is determined by the frequency at the minimum amplitude of the inverter output impedance after resetting admittance, and the lower limit is determined by the crossover frequency between the maximum grid impedance that the inverter's own capacity should bear and the output impedance of the inverter after resetting admittance. By changing the frequency factor, the migration law of the closed-loop poles in the complex plane can be observed. The stability improvement problem is transformed into a mathematical optimization problem with clear physical constraints, providing a rigorous modeling framework for systematically seeking optimal damping performance in an uncertain grid environment.

[0062] The parameter tuning module 6 employs a particle swarm optimization algorithm to perform a global search for the frequency factor under the constraint of the frequency factor. Through iterative calculation, it finally obtains the optimal value of the frequency factor that maximizes the objective function, dynamically adjusts the characteristics of the additional damping channel, and generates control signals to drive the inverter to operate. This enables the grid-connected system to maintain a high level of damping under a wide range of grid impedance changes, enhancing the grid-connected system's adaptability and robustness to weak grids and impedance uncertainties.

[0063] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The methods disclosed in the embodiments are described simply because they correspond to the systems disclosed in the embodiments; relevant details can be found in the method section.

[0064] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0065] In the embodiments provided by this invention, it should be understood that the disclosed systems and methods can be implemented in other ways. For example, the system embodiments described above are merely illustrative. For instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between systems or units may be electrical, mechanical, or other forms.

[0066] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0067] In addition, the functional modules in the various embodiments of the present invention can be integrated into one processing unit, or each module can exist physically separately, or two or more modules can be integrated into one unit.

[0068] Similarly, in the various embodiments of the present invention, each processing unit can be integrated into a functional module, or each processing unit can exist physically, or two or more processing units can be integrated into a functional module.

[0069] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0070] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0071] The above-disclosed embodiments are merely preferred embodiments of the present invention, but the present invention is not limited thereto. Any non-creative variations that can be conceived by those skilled in the art, as well as any improvements and modifications made without departing from the principles of the present invention, should fall within the protection scope of the present invention.

Claims

1. A method for modal admittance reconfiguration damping control of an inverter, characterized in that, Includes the following steps: Step S1: Construct a TITO inverter output admittance model incorporating frequency coupling effects. Through matrix operations, the TITO inverter output admittance model is equivalent to a single-input, single-output structure with positive and negative sequence separation. S2: Based on the single-input, single-output structure with positive and negative sequence separation, introduce capacitor voltage feedback and grid-connected current parallel feedback, and construct a frequency-selective capacitor voltage feedback function. S3: Based on the capacitor voltage feedback function, obtain the positive-sequence channel transfer function and the negative-sequence channel transfer function of the capacitor voltage feedback, and construct the corresponding grid-connected current feedback transfer function. S4: Introduce a frequency factor to equivalently replace the imaginary unit, obtaining an admittance reshaping transfer function model containing the frequency factor. S5: Using the minimum damping ratio among all closed-loop poles as the objective function and the frequency factor as the tuning parameter, set frequency constraints based on the maximum limiting grid impedance, and construct a parameter optimization model. S6: Use a particle swarm optimization algorithm to solve for the optimal value of the frequency factor that maximizes the objective function.

2. The inverter modal admittance reconfiguration damping control method according to claim 1, characterized in that, In step S1: small-signal modeling is performed on the output characteristics of the inverter under grid-connected operation conditions to construct a TITO inverter output admittance model that includes the influence of frequency coupling; the inverter output admittance is combined with the grid impedance to form the hysteresis matrix of the inverter grid-connected system; through matrix transformation and order reduction processing, the TITO inverter output admittance model is equivalently transformed into a SISO output structure in which the positive sequence channel and the negative sequence channel are independent.

3. The inverter modal admittance reconfiguration damping control method according to claim 2, characterized in that, The mathematical expression for the TITO inverter output admittance model can be expressed as: The backlash matrix expression is: ;make The TITO inverter output admittance model is transformed into an equivalent SISO output structure through matrix transformation and order reduction: 。 4. The inverter modal admittance reconfiguration damping control method according to claim 3, characterized in that, In step S2: Capacitor voltage feedback and grid-connected current parallel feedback are introduced into the inverter current inner loop control. Frequency-selective positive-sequence and negative-sequence transfer functions of the capacitor voltage feedback are constructed to reshape the admittance for the positive-sequence disturbance component and negative-sequence coupling, respectively. The reshaped positive-sequence disturbance admittance is shown in the following equation: The negative-order coupled admittance after reshaping is shown in the following equation: 。 5. The inverter modal admittance reconfiguration damping control method according to claim 4, characterized in that, In step S3: by setting the reshaped positive-sequence coupling admittance to zero, the transfer function expression of the positive-sequence channel in the capacitor voltage feedback can be solved; by setting the reshaped negative-sequence coupling admittance to zero, the transfer function expression of the negative-sequence channel in the capacitor voltage feedback can be solved; the transfer function of the grid-connected current parallel feedback channel is constructed as a linear function. In coordination with the capacitor voltage feedback channel; the transfer function expression for the capacitor voltage feedback positive sequence channel. The transfer function expression for the capacitor voltage feedback negative sequence channel After simplification, the simplified expression is shown below: ， ； ， The expression for the transfer function of the grid-connected current parallel feedback channel is: In the formula For grid-side inductive reactance, i.e. 。 6. The inverter modal admittance reconfiguration damping control method according to claim 5, characterized in that, In step S4: a frequency factor is introduced. The mathematical relationship between the imaginary unit and the imaginary unit is: By equivalently replacing the imaginary units in the positive-sequence channel transfer function and the negative-sequence channel transfer function of capacitor voltage feedback, an admittance reshaping transfer function model containing a frequency factor is obtained.

7. The inverter modal admittance reconfiguration damping control method according to claim 6, characterized in that, In step S5: Solve for the closed-loop poles of the grid-connected inverter after reshaping the admittance, and construct the minimum damping ratio in the set of closed-loop poles as the objective function. The objective function and frequency constraints are shown in the following equation: ; Form a parameter optimization model with frequency factor tuning as the core; Lower limit frequency of frequency constraint conditions The constraint is the crossover frequency at the maximum grid impedance that the inverter's own capacity should withstand and the inverter's output impedance after refactoring admittance. Confirmed, upper limit frequency constraint The frequency at which the inverter output impedance amplitude reaches its minimum value after reshaping the admittance is determined. Sure, and Together, they constitute the feasible search range for frequency factors.

8. The inverter modal admittance reconfiguration damping control method according to claim 7, characterized in that, In step S6: Under the premise of satisfying the predetermined frequency constraints, the particle swarm algorithm is used to perform a global search for the frequency factor, and the swarm particles are iteratively updated to make the objective function gradually approach the optimal value, so as to obtain the optimal value of the frequency factor that makes the objective function reach its maximum value; the optimal frequency factor obtained by the particle swarm algorithm is introduced into the inverter control structure after reshaping the admittance to adjust the dynamic characteristics of the additional damping channel; and a control signal is generated by tuning the frequency factor.

9. An inverter modal admittance reconfiguration damping control system, characterized in that, include: The modeling and decoupling module (1), the reshaping control module (2), the transfer function solving module (3), the frequency domain adjustment module (4), the robust optimization modeling module (5), and the parameter tuning module (6) are used to establish a TITO inverter output admittance model considering frequency coupling, and to convert the TITO inverter output admittance model into a single-input single-output structure with positive and negative sequence separation through matrix operations; the reshaping control module (2) is used to construct a capacitor voltage feedback function with frequency selectivity; the transfer function solving module (3) is used to obtain the positive sequence channel transfer function and the negative sequence channel transfer function of capacitor voltage feedback, and to construct the corresponding grid-connected current feedback transfer function; the frequency domain adjustment module (4) is used to introduce a frequency factor to replace the imaginary unit; the robust optimization modeling module (5) is used to construct a parameter optimization model with the minimum damping ratio among all closed-loop poles as the objective function, the frequency factor as the tuning parameter, and the frequency constraint condition set according to the maximum limit grid impedance; the parameter tuning module (6) uses the particle swarm optimization algorithm to solve for the optimal value of the frequency factor that maximizes the objective function.

10. The inverter modal admittance reconfiguration damping control system according to claim 9, characterized in that, The modeling and decoupling module (1) establishes the TITO inverter output admittance model in the dq coordinate system based on the harmonic linearization method. Based on the generalized Nyquist criterion, it combines the inverter output admittance with the grid impedance to construct the hysteresis matrix of the grid-connected system. It performs matrix order reduction operation on the inverter to transform the complex TITO inverter output admittance model into an equivalent SISO structure where the positive-sequence channel and the negative-sequence channel are independent. The reshaping control module (2) introduces capacitor voltage feedback and grid-connected current feedback in the current inner loop. Through two independent positive-sequence component selectors and negative-sequence component selectors, it extracts the positive-sequence disturbance frequency component and the negative-sequence coupling frequency component. These components are processed through the positive-sequence channel transfer function and the negative-sequence channel transfer function of the capacitor voltage feedback, respectively. After inverse Park transformation, an additional modulation signal is generated. The transfer function solving module (3) sets the positive-sequence coupling admittance in the reshaping admittance model to zero and parses the expression of the positive-sequence channel transfer function of the capacitor voltage feedback. Setting the negative-sequence coupling admittance to zero, the expression for the transfer function of the negative-sequence channel of capacitor voltage feedback is solved. The transfer functions of the positive-sequence channel and the negative-sequence channel of capacitor voltage feedback are simplified to construct a linear form of the grid-connected current parallel feedback channel transfer function. The robust optimization modeling module (5) takes the minimum damping ratio among all closed-loop poles of the system after reshaping the admittance as the objective function. The frequency factor is a tuning parameter; based on the grid impedance adapted by the inverter after resetting the admittance, the upper and lower limit constraints of the frequency factor are set: the upper limit is determined by the frequency at the minimum amplitude of the inverter output impedance after resetting the admittance, and the lower limit is determined by the crossover frequency at the maximum grid impedance that the inverter itself should bear and the inverter output impedance after resetting the admittance; the parameter tuning module (6) adopts the particle swarm algorithm to perform a global search of the frequency factor under the constraint of the frequency factor; through iterative calculation, the optimal value of the frequency factor that maximizes the objective function is obtained, the characteristics of the additional damping channel are dynamically adjusted, and a control signal is generated to drive the inverter to run.

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