Small-signal stability analysis method of grid-forming converter under virtual impedance current limiting
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-13
- Publication Date
- 2026-06-12
Smart Images
Figure CN122203201A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of grid-connected converter technology, specifically relating to a method for analyzing the small-signal stability of grid-connected converters under virtual impedance current limiting. Background Technology
[0002] With the large-scale integration of new energy power generation and power electronic equipment into power systems, power systems are gradually evolving towards an operating mode dominated by power electronic devices. Grid-type converters, capable of actively establishing voltage and frequency references, are considered one of the key pieces of equipment supporting the safe and stable operation of low-inertia power systems. However, limited by the current-carrying capacity of power semiconductor devices and filters, grid-type converters must possess effective current-limiting capabilities under conditions such as grid faults, voltage dips, or load surges to avoid system disconnection problems caused by device damage or protection actions. Therefore, introducing current-limiting mechanisms into grid-type converters has become a fundamental requirement in engineering applications.
[0003] In existing current limiting schemes for grid-connected converters, the virtual impedance-based current limiting method is widely used because it can suppress overcurrent without changing the main control structure of the grid. This method dynamically introduces virtual resistance and virtual reactance when the current approaches or exceeds a set threshold, thereby changing the equivalent output impedance characteristics of the converter and achieving current constraint. However, the introduction of virtual impedance not only affects the steady-state power distribution characteristics of the converter, but also significantly reshapes the impedance matching relationship between the converter and the grid, changing the frequency domain characteristics and control coupling characteristics of the system, thus having a significant impact on the small-signal stability of the system.
[0004] Existing small-signal stability analysis methods for grid-type converters are mostly based on the modeling premise of ignoring the influence of current limiting or assuming constant output impedance parameters. When virtual impedance dynamics are involved in current limiting, the analysis results are difficult to accurately reflect the actual impedance characteristic changes of the system. In addition, virtual impedance is usually triggered by nonlinear current amplitude calculation and filtering, and its dynamic behavior introduces additional frequency coupling and control delay, which limits the applicability of traditional small-signal stability criteria based on simplified models.
[0005] To address the aforementioned issues, this invention proposes a systematic small-signal stability analysis method that fully considers the dynamic characteristics of virtual impedance current limiting, in order to accurately evaluate the stability of grid-type converters under current-limiting conditions. Summary of the Invention
[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for analyzing the small-signal stability of grid-type converters under virtual impedance current limiting, thereby solving the problems in existing technologies.
[0007] The objective of this invention can be achieved through the following technical solutions: Small-signal stability analysis methods for grid-type converters under virtual impedance current limiting include: To obtain the following parameters for a grid-type converter under virtual impedance current limiting conditions: steady-state voltage vector at the common coupling point, steady-state output current vector, and steady-state phase angle difference between the controller rotating coordinate system and the grid synchronous coordinate system; In the controller rotating coordinate system, the adaptive virtual impedance current limiting link and voltage control link of the grid converter are linearized to establish its small-signal model in the controller rotating coordinate system. Based on the steady-state phase angle difference and active power droop control dynamics, a small-signal variable transformation relationship including phase angle disturbance terms is established between the controller rotating coordinate system and the power grid synchronous coordinate system, and the small-signal model under the controller rotating coordinate system is uniformly transformed to the power grid synchronous coordinate system. By combining the small-signal model after coordinate transformation with the electrical network constraint equations including filters and the power grid, eliminating internal variables, the closed-loop output impedance matrix of the grid-type converter, viewed from the common coupling point in the synchronous coordinate system of the power grid, is derived. Based on the closed-loop output impedance matrix and the equivalent impedance of the power grid, an open-loop transfer matrix is constructed for stability analysis. The generalized Nyquist criterion is then applied to analyze the eigenvalue trajectory of the open-loop transfer matrix to evaluate the small-signal stability of the grid-type converter under specific operating conditions.
[0008] Furthermore, the process of linearizing the adaptive virtual impedance current limiting element of the grid converter includes: Obtain the steady-state current component and steady-state current amplitude in the controller's rotating coordinate system; linearize the output current amplitude at the steady-state operating point to obtain the small-signal quantity of the current amplitude. : in, This represents the steady-state current amplitude. The steady-state current component in the controller coordinate system. These are the small-signal disturbances corresponding to the current components in the controller's rotating coordinate system; Based on the small signal quantity of the current amplitude Calculate the small-signal voltage drop generated by the virtual impedance.
[0009] Furthermore, the transformation relationship of the small-signal variable including the phase angle disturbance term is as follows: in, and These are the small-signal variable vectors in the controller coordinate system and the power grid synchronization coordinate system, respectively. To correspond to the steady-state phase angle difference δ Rotation matrix of 0, J It is a constant antisymmetric matrix. This is the phase angle disturbance term.
[0010] Furthermore, the phase angle disturbance term Used to characterize the dynamic coupling relationship between phase angle disturbances caused by power control and voltage and current: in, The equivalent transfer function includes the active power droop coefficient and the power filtering stage. and These are the transposes of the steady-state voltage vector at the point of common coupling and the steady-state current vector of the power grid, respectively. and These are grid-side current disturbances and common-point voltage disturbances, respectively.
[0011] Furthermore, when the specific operating condition is a grid voltage sag, the process of constructing the open-loop transfer matrix for stability analysis is as follows: The closed-loop output impedance matrix of the grid converter As the source impedance, the equivalent impedance of the power grid, Zg(s), is used as the load impedance; the open-loop transfer matrix Build as: .
[0012] Furthermore, when the specific operating condition is a disturbance occurring at a common coupling point, the process of constructing the open-loop transfer matrix for stability analysis is as follows: Calculate the parallel equivalent impedance from the point of common coupling to the converter side and the grid side. ; The disturbance at the common coupling point is equivalent to the additional branch impedance connected to that point. The open-loop transfer matrix L( s ) is constructed as follows: .
[0013] Furthermore, the process of analyzing the eigenvalue trajectory of the open-loop transfer matrix using the generalized Nyquist criterion includes: Calculate the eigenvalues of the open-loop transfer matrix in the frequency domain; Plot the Nyquist trajectories of each eigenvalue as a function of frequency on the complex plane; Determine whether all feature value trajectories do not encircle the critical point (-1, j0); if so, the system is considered stable under the corresponding operating condition for small signals; otherwise, it is considered unstable.
[0014] The small-signal stability analysis device for a grid-type converter under virtual impedance current limiting performs the above-mentioned method, including: Phase angle difference calculation module: used to obtain the steady-state voltage vector at the common coupling point, the steady-state output current vector, and the steady-state phase angle difference between the controller rotating coordinate system and the grid synchronous coordinate system of the grid-type converter under the virtual impedance current limiting condition; Small-signal modeling module: used to linearize the adaptive virtual impedance current limiting link and voltage control link of the grid-type converter in the rotating coordinate system of the controller, and establish its small-signal model in the rotating coordinate system of the controller. Coordinate system transformation module: Based on the steady-state phase angle difference and active power droop control dynamics, it establishes a small-signal variable transformation relationship between the controller rotating coordinate system and the power grid synchronous coordinate system, including the phase angle disturbance term, and uniformly transforms the small-signal model under the controller rotating coordinate system to the power grid synchronous coordinate system; Closed-loop output impedance matrix derivation module: used to combine the small-signal model after coordinate transformation with the electrical network constraint equations including filters and power grid, eliminate internal variables, and derive the closed-loop output impedance matrix of the grid-type converter viewed from the common coupling point in the synchronous coordinate system of the power grid; Stability assessment module: Based on the closed-loop output impedance matrix and the equivalent impedance of the power grid, it constructs an open-loop transfer matrix for stability analysis, and applies the generalized Nyquist criterion to analyze the eigenvalue trajectory of the open-loop transfer matrix to evaluate the small-signal stability of the grid-type converter under specific operating conditions.
[0015] A computer storage medium storing a readable program, which, when executed, instructs a computing device to perform the above-described method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting.
[0016] An electronic device includes: a processor, a memory, a communication interface, and a communication bus, wherein the processor, the memory, and the communication interface communicate with each other through the communication bus; The memory is used to store at least one executable instruction that causes the processor to perform the operation corresponding to the small-signal stability analysis method of the network converter under virtual impedance current limiting as described above.
[0017] The beneficial effects of this invention are: 1. This invention addresses the problems of strong coupling in control loops, strong dependence on operating conditions, and difficulty in accurately characterizing traditional small-signal models in grid-type converters under virtual impedance current limiting. By performing unified small-signal modeling of virtual impedance current limiting, voltage control, and power droop control near the steady-state operating point, the complex nonlinear control system is equivalent to a port impedance model containing angular coupling effects, avoiding the modeling complexity and analysis difficulties brought about by directly establishing a high-dimensional state-space model.
[0018] 2. This invention effectively characterizes the dynamic coupling relationship between voltage, current and phase angle caused by power control by explicitly introducing the rotation transformation and phase angle disturbance terms between the controller coordinate system and the system synchronization coordinate system during the modeling process. This solves the problem of inaccurate stability determination caused by ignoring angular coupling in existing impedance analysis methods.
[0019] 3. Based on different operating conditions and fault scenarios, this invention flexibly selects appropriate impedance combinations to construct an open-loop transfer matrix, realizing unified analysis and judgment of stability under various typical scenarios such as normal grid-connected operation, asymmetrical faults, and load disturbances. This improves the versatility and engineering applicability of the stability analysis method, thus providing an effective theoretical basis for the design and tuning of virtual impedance current limiting parameters for grid-connected converters. Attached Figure Description
[0020] 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, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of the small-signal stability analysis method for the grid-type converter of the present invention; Figure 2 This is a system control structure and circuit block diagram of a grid-type converter in an embodiment of the present invention; Figure 3 A schematic diagram illustrating the difference between the dq coordinate system and the system synchronization coordinate system of a grid-type converter; Figure 4 A schematic diagram of coordinate transformation relationships in a unified small-signal coordinate system for grid-type converters; Figure 5 The equivalent output impedance Z of the grid-type converter, taking into account the virtual impedance dynamics, is... GFM The control block diagram; Figure 6 A schematic diagram of the equivalent impedance interconnected system in the dq coordinate system used for generalized Nyquist stability analysis; Figure 7Nyquist trajectory plot of characteristic values for a grid-type converter system under grid voltage sag conditions; Figure 8 The hardware-in-the-loop experimental results are shown for grid voltage sags. Figure 9 A schematic diagram of the equivalent impedance network under the condition of perturbation at the common coupling point; Figure 10 The Nyquist trajectory of the eigenvalues of a grid-type converter system under the disturbance condition at the point of common coupling; Figure 11 The diagram shows the hardware-in-the-loop test results for a three-phase ground fault. Figure 12 This is a comparison chart of the measured impedance spectrum and the theoretically calculated impedance spectrum at the common coupling point of a grid-type converter system. Detailed Implementation
[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0023] Example 1 This embodiment proposes a small-signal stability analysis method for grid-type converters under virtual impedance current limiting. The core of the method lies in establishing a closed-loop impedance model that accurately considers the dynamics of virtual impedance, and constructing a unified stability evaluation framework based on the generalized Nyquist criterion. Specifically, it can systematically analyze the system stability under various disturbances such as grid voltage sags and point-of-common coupling faults. Figure 1 The diagram shown is a schematic of the small-signal stability analysis method for grid-type converters based on the generalized Nyquist criterion proposed in this invention.
[0024] like Figure 2 As shown, the grid-connected converter system is connected to the power grid via an LC filter. Its outer loop control structure adopts an active-frequency P-... ω Droop and reactive-voltage QV droop control provide autonomous synchronization and voltage support capabilities. The active power control loop generates an internal reference angle. θ ref : in, ω n The rated angular frequency, K APC This is the active power droop coefficient. This is a low-pass filter. The reference value for the d-axis voltage output of the reactive power-voltage control loop is: To improve dynamic performance and suppress resonance, the inner loop employs single-loop voltage amplitude control (SLVM) and introduces an active damping resistor. R ad The critical overcurrent protection is achieved through adaptive virtual impedance. R v , X v To achieve this, its output current amplitude I omag Exceeding the preset threshold I th Activated at time: in, k R This is the gain coefficient. n X / R It is the ratio of reactance to resistance. G LPF,i ( s This is a current measurement filter. This design ensures effective current limiting during faults or large disturbances, while having a negligible impact on system performance during normal operation.
[0025] To accurately analyze the small-signal stability of the system, a closed-loop impedance model needs to be established. This modeling process begins with a clear definition of the coordinate system relationships. Figure 3 This diagram illustrates the difference between the dq coordinate system and the system synchronous coordinate system of a grid-connected converter. As shown, because the grid-connected converter autonomously generates frequency and voltage phase, there is a steady-state power angle difference between its internal control rotating coordinate system and the grid synchronous rotating coordinate system. δ 0= θ c - θ g .
[0026] After clarifying the steady-state differences, it is necessary to establish the dynamic relationship under small perturbations. Figure 4 This diagram illustrates the coordinate transformation relationship in a unified small-signal coordinate system for a grid-type converter. It describes the small-signal electrical quantities (such as...) in the controller coordinate system when the system is subjected to small disturbances. ) and small electrical signals in the system coordinate system (such as and small signal angle disturbance The transformation relationship between them. This relationship can be uniformly expressed as: in, T δ Let be a rotation matrix. J For antisymmetric matrices: This transformation relationship is the key bridge for subsequent dynamic and unified mapping of all control links to the system coordinate system for impedance analysis.
[0027] Based on the aforementioned coordinate system, all nonlinear control components, including dynamic virtual impedance (such as power calculation and current limiting logic), are linearized at the operating point. First, the internal angles of the controller... θ ref In the defined controller dq coordinate system, the virtual impedance element is linearized. The small-signal expression for the output current amplitude is: Based on this, the small-signal voltage drop generated by the virtual impedance can be expressed as: Among them, R v and X v This is a 2 × 2 matrix whose elements include coupling coefficients determined by the steady-state operating point current. Incorporating the active damping term, the equivalent output impedance matrix in the controller coordinate system is: Simultaneously, the single-loop voltage controller is linearized, and its output small-signal quantity can be expressed as a function of the PCC voltage and the grid current disturbance: in, H v c and H i c This is the transfer function matrix determined by the controller parameters and the steady-state operating point. The active power droop control dynamics are manifested as small-signal angular disturbances between the controller coordinate system and the grid synchronization coordinate system (superscript s). : This transformation not only completes the coordinate rotation, but more importantly, it introduces the dynamics of power... The resulting additional coupling term C δ This is the core of accurately capturing the synchronous dynamics of a grid-type converter on its impedance.
[0028] By applying the above transformations, the equivalent diagram of dynamically mapping the entire controller to the system coordinate system is shown below. Figure 4 As shown, and simultaneously with the physical network equations of the system (including LC filters and power grid connections): By systematically eliminating the internal potential of the inverter Output current and angle disturbance By considering internal variables, the equivalent output impedance matrix Z of the grid-type converter, which includes all control dynamics and virtual impedance effects, can ultimately be derived from the perspective of the PCC. GFM ( s ), which satisfies the following relation: By further combining the small-signal models of the aforementioned control elements and simplifying and performing algebraic elimination on the system equations, the equivalent output impedance Z can be obtained. GFM ( s The explicit analytic expression for ) is: Figure 5 The equivalent output impedance Z of the grid-type converter, taking into account the virtual impedance dynamics, is... GFM The control block diagram. It clearly shows Z in a structured way. GFM It is constructed by the aforementioned control elements (including dynamic virtual impedance, power droop control, single-loop voltage control, filters, etc.) through a closed loop of feedforward and feedback paths.
[0029] Based on this impedance model, stability analysis can be performed on grid voltage sag conditions. Figure 6 This diagram illustrates the equivalent impedance interconnected system in the dq coordinate system used for generalized Nyquist stability analysis, treating the system as the converter output impedance Z. GFM ( s ) and grid impedance Z g ( s The interconnection of the system is defined as follows: The open-loop transfer matrix of this interconnected system is defined as: According to the generalized Nyquist criterion, the necessary and sufficient condition for the small-signal stability of the system is: when the frequency... ω As it changes from 0 to ∞, the open-loop transfer matrix L(j ω All eigenvalues λ i (j ω The Nyquist trajectories formed by (i=1,2) in the complex plane do not enclose the critical point (-1, j0). This method provides a rigorous mathematical tool for evaluating system stability within a multi-input multi-output framework.
[0030] The above method is applied to the stability assessment after a voltage sag in the power grid. After the voltage sag occurs and the system enters a new steady state, the impedance model Z is calculated based on this operating point. GFM ( s And construct the open-loop transfer matrix L( s By plotting L( sThe Nyquist trajectory of the eigenvalues is used for judgment.
[0031] To verify the effectiveness of this invention, experiments were conducted using the following system parameters. The main parameters of the grid-type converter system are shown in Table 1.
[0032] Table 1 Parameters of Grid-type Converter System Figure 7 The Nyquist trajectory diagram of the characteristic values of the grid-type converter system under grid voltage sag conditions is shown. Figure 7 (a) represents the steady-state operating condition. Figure 7 (b) in the diagram represents an unstable operating condition; such as Figure 7 As shown in (a), when the control parameters are set to the nominal values, neither of the two characteristic value trajectories encloses the critical point (-1, j0), indicating that the system remains stable after the disturbance. Figure 7 (b) shows when the controller is increased ω GLPFx The trajectory encircling the critical point indicates system instability.
[0033] To verify this analysis, a hardware-in-the-loop experiment was conducted. The experiment included applying a grid voltage sag disturbance at the PCC and running the system under both nominal control parameters and increased controller bandwidth conditions. The dynamic responses of the voltage and current at the common coupling point were recorded to compare the impact of different control parameters on system stability. The system parameters were consistent with those described above.
[0034] Figure 8 The hardware-in-the-loop experimental results for grid voltage sag are shown, including the voltage and current waveforms at the point of common coupling, where: Figure 8 (a) in the diagram represents the steady-state condition under the nominal control parameters. Figure 8 (b) represents the unstable operating condition with increased controller bandwidth; Figure 8 (a) shows that the system is operating stably under the nominal parameters. Figure 8 Figure 8 (b) shows that unstable oscillations occur after increasing the bandwidth, which is completely consistent with the frequency domain prediction.
[0035] Based on a similar inventive concept, embodiments of the present invention also provide a computer storage medium storing a readable program that, when run by a processor, can execute the above-described method for small-signal stability analysis of a network converter under virtual impedance current limiting.
[0036] Based on a similar inventive concept, this invention provides an electronic device, including: a processor, a memory, a communication interface, and a communication bus, wherein the processor, the memory, and the communication interface communicate with each other through the communication bus; The memory is used to store at least one executable instruction, which causes the processor to perform the operation corresponding to the above-described small-signal stability analysis method for network converters under virtual impedance current limiting.
[0037] Based on a similar inventive concept, embodiments of the present invention also provide a computer program product, including computer instructions, which instruct a computing device to perform the operations corresponding to the above-described small-signal stability analysis method for a grid-type converter under virtual impedance current limiting.
[0038] Example 2 This embodiment illustrates how to apply the unified impedance modeling and stability analysis framework established in Embodiment 1 to common point of coupling (PCC) disturbance conditions, such as three-phase grounding faults. Figure 9 As shown, the fault is equivalent to an additional impedance branch Z. branch ( s The circuit is connected to the PCC. At this time, the equivalent impedance Z on the converter side as seen from the PCC is... PCC ( s ) is Z GFM ( s ) and grid impedance Z g ( s Parallel connection of ) For this scenario, a new open-loop transfer matrix is constructed: At the steady-state operating point after a three-phase ground fault, the generalized Nyquist criterion is applied for analysis. The analysis process includes: firstly, the three-phase ground fault at the PCC is equivalent to an additional impedance branch connected to the common coupling point, thereby changing the equivalent impedance characteristics seen by the converter; then, based on the established system small-signal impedance model, the Nyquist trajectory of the system eigenvalues is calculated, and the results are analyzed at the nominal low-pass filter bandwidth. ω GLPFx The system is compared under two control parameter conditions: increased bandwidth and increased bandwidth. Furthermore, the stability margin and its changing trend are judged by observing the relative positional relationship between the eigenvalue Nyquist trajectory and the critical point 1+j0. Finally, the PCC voltage and current response are verified by combining the time-domain simulation results to confirm the accuracy of frequency domain stability analysis in predicting the stability and instability behavior of the system.
[0039] The eigenvalue Nyquist trajectory of a grid converter system under common coupling point disturbance conditions is as follows: Figure 10 As shown, Figure 10 In the diagram, (a) and (b) represent steady-state and unstable operating conditions, respectively; for example... Figure 10 As shown in (a), when the relevant control parameter is the low-pass filter bandwidth ωGLPFx When L is the nominal value, s The eigenvalue trajectory remains stable. However, when the value increases... ω GLPFx Afterwards, as Figure 10 As shown in (b), the eigenvalue trajectory clearly moves toward the critical point and forms an encirclement, indicating that the system is unstable.
[0040] Figure 11 The diagram shows the hardware-in-the-loop test results for a three-phase ground fault, including the voltage and current waveforms at the point of common coupling, where: Figure 11 (a) in the figure represents the steady-state condition under nominal parameters. Figure 11 (b) in the figure represents the unstable operating condition under the condition of increasing the bandwidth of the low-pass filter; Figure 11 (a) shows that the system remained stable after a fault under nominal parameters. Figure 11 (b) shows that after increasing the filter bandwidth, continuous oscillations occurred and then the system became unstable.
[0041] To fundamentally verify the theoretical impedance model Z established in this invention GFM ( s To ensure the accuracy of the impedance spectrum, impedance spectrum measurements were performed at the PCC point. Figure 12 This figure shows a comparison between the measured impedance spectrum and the theoretically calculated impedance spectrum at the common coupling point of a grid-type converter system. As shown, over a wide frequency range, the theoretically calculated curve and the measured data agree in both amplitude and phase, proving that the theoretically calculated curve matches the measured data in both amplitude and phase. Figure 5 And the accuracy of the closed-loop impedance model described by the formula above.
[0042] In summary, this invention establishes an accurate small-signal impedance model incorporating virtual impedance dynamics and applies the generalized Nyquist criterion to achieve a systematic and quantitative assessment of the small-signal stability of grid-connected converters under various typical grid disturbances. This method not only accurately predicts stability but also clearly reveals the intrinsic influence mechanism of controller parameters (such as the bandwidth of the virtual impedance filter) on the system stability margin, providing crucial theoretical tools and practical guidance for the safe and stable operation of grid-connected converters and the optimized design of controller parameters in high-proportion renewable energy power systems.
[0043] Example 3 This embodiment proposes a small-signal stability analysis device for a grid-type converter under virtual impedance current limiting, specifically including: Phase angle difference calculation module: used to obtain the steady-state voltage vector at the common coupling point, the steady-state output current vector, and the steady-state phase angle difference between the controller rotating coordinate system and the grid synchronous coordinate system of the grid-type converter under the virtual impedance current limiting condition; Small-signal modeling module: used to linearize the adaptive virtual impedance current limiting link and voltage control link of the grid-type converter in the rotating coordinate system of the controller, and establish its small-signal model in the rotating coordinate system of the controller. Coordinate system transformation module: Based on the steady-state phase angle difference and active power droop control dynamics, it establishes a small-signal variable transformation relationship between the controller rotating coordinate system and the power grid synchronous coordinate system, including the phase angle disturbance term, and uniformly transforms the small-signal model under the controller rotating coordinate system to the power grid synchronous coordinate system; Closed-loop output impedance matrix derivation module: used to combine the small-signal model after coordinate transformation with the electrical network constraint equations including filters and power grid, eliminate internal variables, and derive the closed-loop output impedance matrix of the grid-type converter viewed from the common coupling point in the synchronous coordinate system of the power grid; Stability assessment module: Based on the closed-loop output impedance matrix and the equivalent impedance of the power grid, it constructs an open-loop transfer matrix for stability analysis, and applies the generalized Nyquist criterion to analyze the eigenvalue trajectory of the open-loop transfer matrix to evaluate the small-signal stability of the grid-type converter under specific operating conditions.
[0044] The methods of the present invention can be implemented in hardware, firmware, or as software or computer code that can be stored in a recording medium (such as a CD-ROM, RAM, floppy disk, hard disk, or magneto-optical disk), or as computer code originally stored on a remote recording medium or a non-transitory machine-readable medium and subsequently stored on a local recording medium, downloaded via a network. Thus, the methods described herein can be processed by software stored on a recording medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware (such as an ASIC or FPGA). It is understood that the computer, processor, microprocessor controller, or programmable hardware includes storage components (e.g., RAM, ROM, flash memory, etc.) capable of storing or receiving software or computer code that, when accessed and executed by the computer, processor, or hardware, implements the methods described herein. Furthermore, when a general-purpose computer accesses the code used to implement the methods shown herein, the execution of the code transforms the general-purpose computer into a dedicated computer for performing the methods shown herein.
[0045] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A method for analyzing the small-signal stability of a grid-type converter under virtual impedance current limiting, characterized in that, include: To obtain the following parameters for a grid-type converter under virtual impedance current limiting conditions: steady-state voltage vector at the common coupling point, steady-state output current vector, and steady-state phase angle difference between the controller rotating coordinate system and the grid synchronous coordinate system; In the controller rotating coordinate system, the adaptive virtual impedance current limiting link and voltage control link of the grid converter are linearized to establish its small-signal model in the controller rotating coordinate system. Based on the steady-state phase angle difference and active power droop control dynamics, a small-signal variable transformation relationship including phase angle disturbance terms is established between the controller rotating coordinate system and the power grid synchronous coordinate system, and the small-signal model under the controller rotating coordinate system is uniformly transformed to the power grid synchronous coordinate system. By combining the small-signal model after coordinate transformation with the electrical network constraint equations including filters and the power grid, eliminating internal variables, the closed-loop output impedance matrix of the grid-type converter, viewed from the common coupling point in the synchronous coordinate system of the power grid, is derived. Based on the closed-loop output impedance matrix and the equivalent impedance of the power grid, an open-loop transfer matrix is constructed for stability analysis. The generalized Nyquist criterion is then applied to analyze the eigenvalue trajectory of the open-loop transfer matrix to evaluate the small-signal stability of the grid-type converter under specific operating conditions.
2. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 1, characterized in that, The process of linearizing the adaptive virtual impedance current limiting element of a grid converter includes: Obtain the steady-state current component and steady-state current amplitude in the controller's rotating coordinate system; linearize the output current amplitude at the steady-state operating point to obtain the small-signal quantity of the current amplitude. : in, This represents the steady-state current amplitude. The steady-state current component in the controller coordinate system. These are the small-signal disturbances corresponding to the current components in the controller's rotating coordinate system; Based on the small signal quantity of the current amplitude Calculate the small-signal voltage drop generated by the virtual impedance.
3. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 1, characterized in that, The transformation relationship of the small-signal variable containing the phase angle disturbance term is as follows: in, and These are the small-signal variable vectors in the controller coordinate system and the power grid synchronization coordinate system, respectively. To correspond to the steady-state phase angle difference δ Rotation matrix of 0, J It is a constant antisymmetric matrix. This is the phase angle disturbance term.
4. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 3, characterized in that, The phase angle disturbance term Used to characterize the dynamic coupling relationship between phase angle disturbances caused by power control and voltage and current: in, The equivalent transfer function includes the active power droop coefficient and the power filtering stage. and These are the transposes of the steady-state voltage vector at the common coupling point and the steady-state current vector of the power grid, respectively. and These are the grid-side current disturbance and the common coupling point voltage disturbance, respectively.
5. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 1, characterized in that, When the specific operating condition is a grid voltage sag, the process of constructing the open-loop transfer matrix for stability analysis is as follows: The closed-loop output impedance matrix of the grid converter As the source impedance, the equivalent impedance of the power grid, Zg(s), is used as the load impedance; the open-loop transfer matrix Build as: 。 6. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 1, characterized in that, When the specific operating condition is a disturbance occurring at a common coupling point, the process of constructing the open-loop transfer matrix for stability analysis is as follows: Calculate the parallel equivalent impedance from the common coupling point to the converter side and the grid side. ; The disturbance at the common coupling point is equivalent to the additional branch impedance connected to that point. The open-loop transfer matrix L( s ) is constructed as follows: 。 7. The method for small-signal stability analysis of a grid-type converter under virtual impedance current limiting according to claim 5 or 6, characterized in that, The process of analyzing the eigenvalue trajectories of the open-loop transfer matrix using the generalized Nyquist criterion includes: Calculate the eigenvalues of the open-loop transfer matrix in the frequency domain; Plot the Nyquist trajectories of each eigenvalue as a function of frequency on the complex plane; Determine whether all feature value trajectories do not encircle the critical point (-1, j0); if so, the system is considered stable under the corresponding operating condition for small signals; otherwise, it is considered unstable.
8. A small-signal stability analysis device for a grid-type converter under virtual impedance current limiting, comprising the method described in any one of claims 1-7, characterized in that, include: Phase angle difference calculation module: used to obtain the steady-state voltage vector at the common coupling point, the steady-state output current vector, and the steady-state phase angle difference between the controller rotating coordinate system and the grid synchronous coordinate system of the grid-type converter under the virtual impedance current limiting condition; Small-signal modeling module: used to linearize the adaptive virtual impedance current limiting link and voltage control link of the grid-type converter in the rotating coordinate system of the controller, and establish its small-signal model in the rotating coordinate system of the controller. Coordinate system transformation module: Based on the steady-state phase angle difference and active power droop control dynamics, it establishes a small-signal variable transformation relationship between the controller rotating coordinate system and the power grid synchronous coordinate system, including the phase angle disturbance term, and uniformly transforms the small-signal model under the controller rotating coordinate system to the power grid synchronous coordinate system; Closed-loop output impedance matrix derivation module: used to combine the small-signal model after coordinate transformation with the electrical network constraint equations including filters and power grid, eliminate internal variables, and derive the closed-loop output impedance matrix of the grid-type converter viewed from the common coupling point in the synchronous coordinate system of the power grid; Stability assessment module: Based on the closed-loop output impedance matrix and the equivalent impedance of the power grid, it constructs an open-loop transfer matrix for stability analysis, and applies the generalized Nyquist criterion to analyze the eigenvalue trajectory of the open-loop transfer matrix to evaluate the small-signal stability of the grid-type converter under specific operating conditions.
9. A computer storage medium storing a readable program, characterized in that, When the program runs, it can instruct the computing device to perform the small-signal stability analysis method for a grid-type converter under virtual impedance current limiting as described in any one of claims 1-7.
10. An electronic device, characterized in that, include: The processor, memory, communication interface, and communication bus are provided, wherein the processor, memory, and communication interface communicate with each other via the communication bus. The memory is used to store at least one executable instruction, which causes the processor to perform the operation corresponding to the small-signal stability analysis method of the grid converter under virtual impedance current limiting as described in any one of claims 1-7.