Series-parallel converter new energy transmission line fault analysis method and device

Abstract

The invention discloses a hybrid converter new energy transmission line fault analysis method and device. The method comprises the following steps: obtaining new energy station operation data and fault information data; respectively constructing a GFL fault equivalent model and a GFM fault equivalent model under different faults based on the operation data in combination with sequence component characteristics of the GFL and the GFM during the fault period; according to the fault equivalent model, a series-parallel system sending-out line equivalent sequence network used for different fault analysis is constructed through a network equivalence principle; deducing a mathematical relational expression of fault key electrical quantities by considering a fault response coupling relationship between the GFL and the GFM based on an equivalent sequence network and fault information data of a transmission line of each series-parallel system; and finally, solving by adopting an iterative algorithm to obtain a steady-state fault characteristic quantity. According to the method, the fault equivalent models of the GFL and the GFM are respectively constructed, the equivalent sequence network diagram of the sending-out line of the hybrid system is constructed, and the problems that the fault features in the GFL and GFM hybrid system are not clear and are difficult to quantitatively analyze are solved.

Description

Technical Field

[0001] This invention relates to the field of power system protection technology, specifically to a method and apparatus for fault analysis of new energy transmission lines using a hybrid converter. Background Technology

[0002] Driven by the "dual carbon" goal, new energy sources, represented by wind power and photovoltaics, are being integrated into the power system on a large scale. These new energy units are connected to the grid via power electronic converters, and their dynamic behavior differs fundamentally from that of traditional synchronous generators. Currently, the mainstream converter control strategies are mainly divided into two categories: grid-connected converters (GFLs) and grid-connected converters (GFMs). Grid-connected converters rely on grid voltage support and exhibit controlled current source characteristics, with limited fault output current amplitude, controlled phase, and rich harmonic content. Grid-connected converters, on the other hand, have voltage source characteristics, capable of autonomously constructing and supporting grid voltage, and the fault current they provide exhibits new characteristics in terms of amplitude and phase. In the future power grid, the hybrid operation of GFLs and GFMs will become a typical scenario. When a fault occurs in the transmission line of a new energy power plant, different types of converters in the hybrid system will exhibit complex and mutually influential transient and steady-state response characteristics.

[0003] Currently, research on fault models for single GFLs or single GFMs is relatively mature. However, systematic research methods are still lacking for fault modeling and characteristic analysis of transmission lines operating under mixed operation modes of the two. Existing technologies cannot accurately quantify the comprehensive impact of factors such as the ratio of GFLs to GFMs and control strategies on fault currents, leading to the risk of false tripping or failure to trip of relay protection devices based on traditional fault characteristics.

[0004] Therefore, there is an urgent need for a modeling and analysis method that can accurately characterize the fault characteristics of hybrid grid systems to support the safe and stable operation and protection configuration of new power systems. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a method and apparatus for fault analysis of new energy transmission lines in hybrid converter systems. By constructing fault equivalent models for GFL and GFM respectively, and building an equivalent sequence network diagram of the transmission lines of the hybrid system, the problem of unclear fault characteristics and difficulty in quantitative analysis in GFL and GFM hybrid systems is solved.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A fault analysis method for new energy transmission lines using a hybrid converter includes the following steps:

[0008] S1. Obtain operation data and fault information data of new energy power stations;

[0009] S2. Based on the aforementioned operational data, and combining the sequence component characteristics of GFL and GFM during the fault period, construct equivalent fault models for GFL and GFM under different fault conditions, respectively.

[0010] S3. Based on the GFL fault equivalent model and GFM fault equivalent model under different faults, construct the equivalent sequence network of the hybrid system transmission line for different fault analysis through the network equivalence principle.

[0011] S4. Based on the equivalent sequence network of the transmission lines of the hybrid system under different faults and the fault information data, taking into account the fault response coupling relationship between GFL and GFM, the mathematical relationship of the key electrical quantities of the fault is derived.

[0012] S5. Use an iterative algorithm to solve the mathematical relationship until the convergence condition is met, and then output the steady-state fault characteristic quantity.

[0013] As a preferred embodiment, the GFL fault equivalent model and GFM fault equivalent model under different faults specifically include:

[0014] For GFL, based on its control objectives and current limiting constraints during faults, the positive and negative sequence output current components of GFL are derived, thereby establishing an equivalent model of GFL. Among them, under symmetrical faults, GFL is equivalent to a positive sequence controlled current source model, and under asymmetrical faults, the positive sequence side of GFL is equivalent to a controlled current source model, and the negative sequence side is equivalent to an open circuit.

[0015] For GFM, a virtual synchronous generator control strategy based on positive and negative sequence separation is adopted. Based on the amplitude of the virtual internal potential of GFM, an equivalent model of GFM is established. Under different fault conditions, the positive sequence side of GFM is equivalent to a controlled voltage source series impedance model, and the negative sequence side is equivalent to an open circuit.

[0016] As a preferred embodiment, the calculation formulas for the positive and negative sequence output current components of the GFL are as follows:

[0017]

[0018] In the formula, I GFLx_1 and I GFLx_2 These are the positive and negative sequence current components of the GFL output current, respectively; I + GFL θ is the output current limit value of the GFL; θ is the phase angle of the positive sequence current; x represents one of the three phases A, B, and C; δ x δ is the initial phase angle of the voltage; - The negative sequence component of the initial phase angle of the voltage; k u For grid voltage imbalance; E S_1 The positive sequence voltage amplitude measured by the power grid; P GFL Q is the reference value for the active power of the GFL;GFL This is the reference value for reactive power of GFL;

[0019] The formula for calculating the amplitude of the GFM virtual internal potential is as follows:

[0020]

[0021] E GFM =I GFM Z GFM_1 ;

[0022] In the formula, U represents the positive sequence voltage amplitude at the GFM grid connection point after the fault; + U represents the positive sequence voltage amplitude of the power grid. n Rated voltage; λ is the positive sequence voltage sag factor; E GFM Z represents the virtual internal potential of the GFM; p and q are intermediate coefficients; GFM I is the equivalent total impedance of the GFM; gf For GFM fault steady-state current limiting thresholds; E0 and U g0 These represent the equivalent output voltage of the virtual synchronous generator (GFM) and the grid voltage before the fault, respectively; I0 represents the current before the fault; I GFM Z represents the fault current of the GFM. GFM_1 This is the positive-sequence equivalent total impedance of the GFM.

[0023] As a preferred embodiment, the specific processing steps for constructing an equivalent sequence network for the transmission lines of a hybrid system for different fault analyses based on the network equivalence principle include:

[0024] Under symmetrical faults, based on Norton's theorem, the series impedance model of the controlled voltage source of GFM is equivalent to the parallel impedance model of the current source, and combined with the positive sequence controlled current source model of GFL to construct the positive sequence equivalent sequence network of the hybrid system.

[0025] Under asymmetric faults, based on the symmetric component method and combined with the fault equivalent models of GFL and GFM, positive sequence, negative sequence and zero sequence equivalent sequence networks of the hybrid system are constructed respectively.

[0026] As a preferred embodiment, the mathematical formulas for deriving the critical electrical quantities of the fault specifically include:

[0027] Under symmetrical faults in a hybrid system, based on the positive sequence equal value sequence network, the mathematical relationship between the short-circuit current on the renewable energy side, the short-circuit current on the AC grid side, and the voltage at the grid connection point on the renewable energy side is derived, and the current contribution coefficient and voltage distribution coefficient, which are the steady-state fault characteristic quantities, are calculated using the mathematical relationship.

[0028] Under asymmetrical faults in a hybrid system, mathematical relationships between the positive-sequence, negative-sequence, and zero-sequence current components at the fault point and the phase voltage at the grid connection point of the new energy source are derived based on the positive-sequence, negative-sequence, and zero-sequence equivalent sequence networks. The positive-sequence, negative-sequence, and zero-sequence current components at the fault point, as well as the phase voltage at the grid connection point of the new energy source, are calculated using these mathematical relationships as steady-state fault characteristic quantities.

[0029] As a preferred option, the formulas for calculating the short-circuit current on the renewable energy side and the short-circuit current on the AC grid side during a symmetrical fault in a hybrid system are as follows:

[0030]

[0031] In the formula, I M_1 and I N_1 These are the short-circuit currents on the renewable energy side and the AC grid side, respectively; I GFM_1 For the Norton equivalent GFM controlled current source, I GFL_1 The current supplied to GFL renewable energy, E S α1 represents the electromotive force of the power grid; α2, α3, and α4 are the current contribution coefficients of different power sources; m is the number of GFMs; n is the number of GFLs.

[0032] The formula for calculating the voltage at the grid connection point on the new energy side is:

[0033] U M_1 =β1(mI GFM_1 +nI GFL_1 )+β2E S ;

[0034] In the formula, U M_1 β1 and β2 are voltage at the grid connection point of the new energy side; β1 and β2 are voltage distribution coefficients.

[0035] The formulas for calculating the positive-sequence, negative-sequence, and zero-sequence current components in a hybrid system under asymmetrical faults are as follows:

[0036]

[0037] In the formula, I MA and I NA These are the positive-sequence, negative-sequence, and zero-sequence current components from the renewable energy source and the AC grid side at the fault point; I MA_1 and I NA_1 These are the positive sequence currents on the renewable energy side and the AC grid side, respectively; I MA_2 and I NA_2 These are the negative sequence currents on the new energy side and the AC grid side, respectively; I MA_0 and I NA_0 These are the zero-sequence currents on the new energy side and the AC grid side, respectively.

[0038] The formula for calculating the phase voltage at the grid connection point on the new energy side is:

[0039] U M_A =h1(mI GFM_1 +nI GFL_1 )+h2E S ;

[0040] In the formula, U M_A h1 and h2 are the phase voltages at the grid connection point on the new energy side; h1 and h2 are both voltage distribution coefficients.

[0041] As a preferred embodiment, the convergence condition is that the voltage difference between the new energy side grid connection point calculated in two adjacent iterations meets a preset threshold, and the maximum number of iterations does not exceed a preset number.

[0042] A fault analysis device for new energy transmission lines using a hybrid converter includes:

[0043] The data acquisition module is used to acquire operation data and fault information data of new energy power stations;

[0044] The converter fault equivalent module is used to construct GFL fault equivalent models and GFM fault equivalent models under different faults based on the operating data collected by the data acquisition module and the sequence component characteristics of GFL and GFM during the fault.

[0045] The hybrid system sequence network construction module is used to construct equivalent sequence networks for hybrid system transmission lines for different fault analyses based on the GFL fault equivalent model and GFM fault equivalent model obtained by the converter fault equivalent module under different faults, and through the network equivalence principle.

[0046] The fault characteristic calculation module is used to derive the mathematical relationship between the fault key electrical quantities based on the equivalent sequence network of the hybrid system transmission line and the fault information data under different faults obtained by the hybrid system sequence network construction module, taking into account the fault response coupling relationship between GFL and GFM. The mathematical relationship is then solved by an iterative algorithm until the convergence condition is met, thereby outputting the steady-state fault characteristic quantity.

[0047] Compared with the prior art, the present invention has the following technical effects:

[0048] 1. This invention clarifies the electrical characteristics of two types of converters under fault conditions by establishing fault equivalent models for grid-connected converters (GFL) and grid-connected converters (GFM), respectively. A controlled current source model is established for GFL, and a controlled voltage source series impedance model is established for GFM. At the same time, the high impedance characteristics of both in negative sequence networks are clarified. This accurately describes the dynamic response of different types of converters and breaks through the limitation of traditional methods that simply equate new energy power plants to a single current source.

[0049] 2. This invention constructs an equivalent sequence network for the output lines of a hybrid system that considers the converter ratio. It constructs a positive sequence network under symmetrical faults and a composite equivalent sequence network under asymmetrical faults, thereby obtaining an analytical framework that can clearly reflect the interaction and proportional relationship between GFL and GFM. This simplifies the fault analysis of complex hybrid systems and can systematically consider the comprehensive influence of network topology, line parameters and converter control strategies.

[0050] 3. This invention derives mathematical relationships between fault characteristics, including current contribution coefficients and voltage distribution coefficients, expressing fault current and voltage as linear combinations of various power sources. This quantifies and traces fault characteristics. Furthermore, the introduced contribution coefficients allow engineers to intuitively assess the specific weights of the GFM and GFL in the fault current, as well as their support or drop in grid connection voltage. This provides a reliable basis for analyzing fault current distribution and evaluating relay protection sensitivity. Additionally, an iterative algorithm is used to solve the coupling relationship between converter control and system state, achieving steady-state calculation of grid connection voltage and fault current distribution. Attached Figure Description

[0051] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0052] Figure 1 This invention discloses a flowchart of a fault analysis method for new energy transmission lines using a hybrid converter.

[0053] Figure 2 This is a general equivalent model diagram of faults in a grid-type converter in an embodiment of the present invention;

[0054] Figure 3 This is a general equivalent model diagram of faults in a grid-type converter in an embodiment of the present invention;

[0055] Figure 4 This is the equivalent sequence network diagram of symmetrical faults in the transmission line in this embodiment of the invention;

[0056] Figure 5 This is the equivalent sequence network diagram of a single-phase grounding fault in the transmitting line in this embodiment of the invention;

[0057] Figure 6 This is a schematic diagram of the structure of a hybrid converter new energy transmission line fault analysis device disclosed in this invention. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0059] The present invention will now be described in further detail with reference to the accompanying drawings.

[0060] Example 1:

[0061] With the increasing penetration rate of new energy sources, the fault characteristics of power systems have undergone fundamental changes: the short-circuit current characteristics dominated by traditional synchronous machines have been replaced by the controlled response of power electronic converters. Furthermore, grid-connected converters and grid-connected converters exhibit drastically different dynamic behaviors during faults; grid-connected converters exhibit controlled current source characteristics, while grid-connected converters exhibit voltage source characteristics. These two characteristics are coupled and mutually influential in hybrid operation scenarios, making the fault characteristics of transmission lines from new energy power plants complex and unclear. Existing analysis methods mostly target single-type converter systems, lacking systematic fault modeling and feature analysis tools that can simultaneously consider the characteristics and proportional relationships of both types of converters. This leads to the risk of maloperation or failure to operate of relay protection devices based on traditional fault characteristics, severely restricting the safe and stable operation of high-proportion new energy power grids.

[0062] Based on this, this invention proposes a fault analysis method and device for hybrid converters used in renewable energy transmission lines. It aims to address the problems of unclear fault characteristics and lack of systematic modeling and analysis when grid-connected (GFL) and grid-forming-middle (GFM) converters are connected to the grid after a high proportion of renewable energy integration. This method first establishes equivalent fault models for GFL and GFM converters respectively, clarifying the electrical characteristics under fault conditions for the two types of converters. Then, based on the equivalent fault models, it constructs an equivalent fault sequence network for hybrid system transmission lines considering the converter ratio, proposes symmetrical and asymmetrical fault characteristic analysis methods, and derives the mathematical relationships of key electrical quantities. Finally, it reveals the influence of converter ratio, fault type, and control strategy on fault current characteristics.

[0063] Specifically, the fault analysis method for new energy transmission lines using hybrid converters proposed in this invention, such as... Figure 1 As shown, it includes the following steps:

[0064] S1. Obtain operation data and fault information data of new energy power stations;

[0065] In practice, the operating data includes the rated power of GFL and GFM, output active / reactive power, current limit value, control strategy parameters, and positive / negative sequence component amplitude of grid connection point voltage; the fault information includes fault location, transition resistance, and fault type.

[0066] S2. Based on the aforementioned operational data, and combining the sequence component characteristics of GFL and GFM during the fault period, construct equivalent fault models for GFL and GFM under different fault conditions, respectively.

[0067] In practical implementation, for the GFL, based on its control objectives and current limiting constraints during the fault period, the positive and negative sequence output current components of the GFL are derived, thereby establishing an equivalent model of the GFL, such as... Figure 2 As shown; where, under symmetrical faults, the GFL is equivalent to a positive-sequence controlled current source model, and under asymmetrical faults, the positive-sequence side of the GFL is equivalent to a controlled current source model, and the negative-sequence side is equivalent to an open circuit.

[0068] The calculation formulas for the positive and negative sequence output current components of the GFL are as follows:

[0069]

[0070] In the formula, I GFLx_1 and I GFLx_2 These are the positive and negative sequence current components of the GFL output current, respectively; I + GFL θ is the output current limit value of the GFL; θ is the phase angle of the positive sequence current; x represents one of the three phases A, B, and C; δ x δ is the initial phase angle of the voltage; - The negative sequence component of the initial phase angle of the voltage; k u For grid voltage imbalance; E S_1 The positive sequence voltage amplitude measured by the power grid; P GFL Q is the reference value for the active power of the GFL; GFL This is the reference value for reactive power of GFL.

[0071] For the GFM, a voltage-current dual-closed-loop virtual synchronous generator (VSG) control strategy based on positive and negative sequence separation is adopted. This strategy incorporates power angle stabilization control, amplitude switching control, and virtual impedance current limiting control. Based on the amplitude of the GFM's virtual internal potential, an equivalent model of the GFM is established, such as... Figure 3 As shown; where, under different fault conditions, the positive sequence side of GFM is equivalent to a controlled voltage source series impedance model, and the negative sequence side is equivalent to an open circuit.

[0072] The formula for calculating the amplitude of the GFM virtual internal potential is as follows:

[0073]

[0074] The formula for calculating the fault current of GFM is:

[0075] E GFM =I GFM Z GFM_1 ;

[0076] In the formula, U represents the positive sequence voltage amplitude at the GFM grid connection point after the fault; + U represents the positive sequence voltage amplitude of the power grid. n Rated voltage; λ is the positive sequence voltage sag factor; E GFM Z represents the virtual internal potential of the GFM; p and q are intermediate coefficients; GFM I is the equivalent total impedance of the GFM; gf For GFM fault steady-state current limiting thresholds; E0 and U g0 These represent the equivalent output voltage of the virtual synchronous generator (GFM) and the grid voltage before the fault, respectively; I0 represents the current before the fault; I GFM Z represents the fault current of the GFM. GFM_1 This is the positive-sequence equivalent total impedance of the GFM.

[0077] This embodiment clarifies the electrical characteristics of two types of converters under fault conditions by establishing fault equivalent models for grid-connected converters and grid-connected converters respectively. A controlled current source model is established for GFL and a controlled voltage source series impedance model is established for GFM. At the same time, the high impedance characteristics of both in negative sequence networks are clarified. This accurately describes the dynamic response of different types of converters and breaks through the limitation of traditional methods that simply equate new energy power plants to a single current source.

[0078] S3. Based on the GFL fault equivalent model and GFM fault equivalent model under different faults, construct the equivalent sequence network of the hybrid system transmission line for different fault analysis through the network equivalence principle.

[0079] In practical implementation, under symmetrical fault conditions, based on Norton's theorem, the controlled voltage source series impedance model of the GFM is equivalent to a current source parallel impedance model, and combined with the positive-sequence controlled current source model of the GFL, a positive-sequence equivalent sequence network of a hybrid system containing m GFMs and n GFLs is constructed. The equivalent sequence network diagram of the symmetrical fault of the transmitting line is as follows. Figure 4 As shown;

[0080] Under asymmetrical fault conditions, this embodiment takes a single-phase ground fault as an example. Considering the influence of the zero-sequence component, based on the symmetrical component method and combined with the fault equivalent models of GFL and GFM, the positive-sequence, negative-sequence, and zero-sequence equivalent sequence networks of the hybrid system are constructed respectively. Among them, the negative-sequence network is equivalent to an open circuit due to the negative-sequence current suppression strategy of GFL and GFM, and the characteristics of the zero-sequence network are consistent with those of the traditional AC system. The equivalent sequence network diagram of the single-phase ground fault of the transmitting line is as follows: Figure 5 As shown.

[0081] This embodiment constructs an equivalent sequence network for the output lines of a hybrid system that considers the converter ratio. It constructs a positive sequence network under symmetrical faults and a composite equivalent sequence network under asymmetrical faults, thereby obtaining an analytical framework that can clearly reflect the interaction and proportional relationship between GFL and GFM. This simplifies the fault analysis of complex hybrid systems and can systematically take into account the comprehensive influence of network topology, line parameters and converter control strategies.

[0082] S4. Based on the equivalent sequence network of the transmission lines of the hybrid system under different faults and the fault information data, taking into account the fault response coupling relationship between GFL and GFM, the mathematical relationship of the key electrical quantities of the fault is derived.

[0083] In specific implementation, under symmetrical faults in hybrid systems, based on positive sequence equal value sequence networks, mathematical relationships are derived for the short-circuit current on the renewable energy side, the short-circuit current on the AC grid side, and the voltage at the renewable energy grid connection point. The current contribution coefficient and voltage distribution coefficient, which are steady-state fault characteristic quantities, are calculated using these mathematical relationships. These coefficients are affected by network topology, line impedance, GFM control strategy, and fault severity.

[0084] The formulas for calculating the short-circuit current on the renewable energy side and the short-circuit current on the AC grid side during a symmetrical fault in a hybrid system are as follows:

[0085]

[0086] In the formula, I M_1 and I N_1 These are the short-circuit currents on the renewable energy side and the AC grid side, respectively; I GFM_1 For the Norton equivalent GFM controlled current source, I GFL_1 The current supplied to GFL renewable energy, E S α1 represents the electromotive force of the power grid; α2, α3, and α4 are the current contribution coefficients of different power sources; m is the number of GFMs; n is the number of GFLs.

[0087] The formula for calculating the voltage at the grid connection point on the new energy side is:

[0088] U M_1 =β1(mI GFM_1 +nI GFL_1 )+β2E S ;

[0089] In the formula, U M_1 β1 and β2 are voltage at the grid connection point of the new energy side; β1 and β2 are voltage distribution coefficients.

[0090] Under asymmetrical faults, taking a single-phase ground fault as an example, based on the positive-sequence, negative-sequence, and zero-sequence equivalent sequence network, the expressions for the positive-sequence, negative-sequence, and zero-sequence current components at the fault point and the phase voltage at the grid connection point of the new energy side are derived to quantify the influence of three-sequence impedance coupling on fault characteristics. The positive-sequence, negative-sequence, and zero-sequence current components at the fault point, as well as the phase voltage at the grid connection point of the new energy side, are calculated as steady-state fault characteristic quantities using this mathematical relationship.

[0091] The formulas for calculating the positive-sequence, negative-sequence, and zero-sequence current components in a hybrid system under asymmetrical faults are as follows:

[0092]

[0093] In the formula, I MA and I NA These are the positive-sequence, negative-sequence, and zero-sequence current components from the renewable energy source and the AC grid side at the fault point; I MA_1 and I NA_1 These are the positive sequence currents on the renewable energy side and the AC grid side, respectively; I MA_2 and I NA_2 These are the negative sequence currents on the new energy side and the AC grid side, respectively; I MA_0 and I NA_0 These are the zero-sequence currents on the new energy side and the AC grid side, respectively.

[0094] The formula for calculating the phase voltage at the grid connection point on the new energy side is:

[0095] U M_A =h1(mI GFM_1 +nI GFL_1 )+h2E S ;

[0096] In the formula, U M_A h1 and h2 are the phase voltages at the grid connection point on the new energy side; h1 and h2 are both voltage distribution coefficients.

[0097] This embodiment derives the mathematical relationship between fault characteristics, including current contribution coefficient and voltage distribution coefficient, and expresses fault current and voltage as a linear combination of various power sources, thereby realizing the quantification and source tracing of fault characteristics. At the same time, through the introduction of contribution coefficients, engineers can intuitively evaluate the specific weights of GFM and GFL in the fault current, as well as their support or drop in grid connection voltage, thus providing a reliable basis for analyzing fault current distribution and evaluating relay protection sensitivity.

[0098] S5. Use an iterative algorithm to solve the mathematical relationship until the convergence condition is met, and then output the steady-state fault characteristic quantity.

[0099] In practice, the voltage difference at the grid connection point of the new energy side obtained from two adjacent iterations is less than 0.1% of the rated current, and the maximum number of iterations does not exceed 50.

[0100] In this embodiment, the iterative algorithm undertakes the numerical solution function within this framework. By processing the nonlinear constraints jointly constituted by the converter control strategy (such as the virtual impedance and internal potential regulation of GFM, and the current limiting and phase control of GFL) and the system fault conditions, it achieves steady-state calculation of the grid connection point voltage and fault current distribution.

[0101] Example 2:

[0102] This embodiment also discloses a fault analysis device for a hybrid converter-based new energy transmission line, the structure of which is as follows: Figure 6 As shown, it includes:

[0103] The data acquisition module is used to acquire operation data and fault information data of new energy power stations;

[0104] The converter fault equivalent module is used to construct GFL fault equivalent models and GFM fault equivalent models under different faults based on the operating data collected by the data acquisition module and the sequence component characteristics of GFL and GFM during the fault.

[0105] The hybrid system sequence network construction module is used to construct equivalent sequence networks for hybrid system transmission lines for different fault analyses based on the GFL fault equivalent model and GFM fault equivalent model obtained by the converter fault equivalent module under different faults, and through the network equivalence principle.

[0106] The fault characteristic calculation module is used to derive the mathematical relationship between the fault key electrical quantities based on the equivalent sequence network of the hybrid system transmission line and the fault information data under different faults obtained by the hybrid system sequence network construction module, taking into account the fault response coupling relationship between GFL and GFM. The mathematical relationship is then solved by an iterative algorithm until the convergence condition is met, thereby outputting the steady-state fault characteristic quantity.

[0107] The hybrid converter new energy transmission line fault analysis device provided in this embodiment is used to execute the hybrid converter new energy transmission line fault analysis method. Its principle and the technical effect achieved are the same as the hybrid converter new energy transmission line fault analysis method provided in this invention, and will not be repeated here.

[0108] In summary, this embodiment addresses the technical bottleneck of complex fault characteristics in transmission lines caused by the mixed operation of grid-connected and grid-connected converters after a high proportion of renewable energy is integrated into the power system, making traditional analysis methods inapplicable. It proposes a fault modeling and feature analysis solution. This method establishes refined fault equivalent models for the two types of converters, constructs an equivalent sequence network for the mixed system considering the converter composition ratio, derives analytical expressions for fault characteristics including current contribution coefficients and voltage distribution coefficients, and uses a convergent iterative algorithm for accurate solution. This achieves systematic quantitative analysis of key characteristics such as fault current amplitude and phase, and voltage sag. This method accurately reveals the coupling effect of converter type ratio, control parameter settings, and fault type on system fault characteristics, providing important theoretical basis and technical support for fault ride-through capability assessment and relay protection setting in high-proportion renewable energy power grids.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A fault analysis method for new energy transmission lines using a hybrid converter, characterized in that, Includes the following steps: S1. Obtain operation data and fault information data of new energy power stations; S2. Based on the aforementioned operational data, and combining the sequence component characteristics of GFL and GFM during the fault period, construct equivalent fault models for GFL and GFM under different fault conditions, respectively. S3. Based on the GFL fault equivalent model and GFM fault equivalent model under different faults, construct the equivalent sequence network of the hybrid system transmission line for different fault analysis through the network equivalence principle. S4. Based on the equivalent sequence network of the transmission lines of the hybrid system under different faults and the fault information data, taking into account the fault response coupling relationship between GFL and GFM, the mathematical relationship of the key electrical quantities of the fault is derived. S5. Use an iterative algorithm to solve the mathematical relationship until the convergence condition is met, and then output the steady-state fault characteristic quantity.

2. The fault analysis method for new energy transmission lines using a hybrid converter according to claim 1, characterized in that, In step S2, the GFL fault equivalent model and GFM fault equivalent model under different faults specifically include: For GFL, based on its control objectives and current limiting constraints during faults, the positive and negative sequence output current components of GFL are derived, thereby establishing an equivalent model of GFL. Among them, under symmetrical faults, GFL is equivalent to a positive sequence controlled current source model, and under asymmetrical faults, the positive sequence side of GFL is equivalent to a controlled current source model, and the negative sequence side is equivalent to an open circuit. For GFM, a virtual synchronous generator control strategy based on positive and negative sequence separation is adopted. Based on the amplitude of the virtual internal potential of GFM, an equivalent model of GFM is established. Under different fault conditions, the positive sequence side of GFM is equivalent to a controlled voltage source series impedance model, and the negative sequence side is equivalent to an open circuit.

3. The fault analysis method for new energy transmission lines using hybrid converters according to claim 2, characterized in that, The formulas for calculating the positive and negative sequence output current components of the GFL are as follows: In the formula, I GFLx_1 and I GFLx_2 These are the positive and negative sequence current components of the GFL output current, respectively; I + GFL This is the output current limit value for the GFL; θ is the phase angle of the positive sequence current; x represents one of the three phases A, B, and C; δ x δ is the initial phase angle of the voltage; - The negative sequence component of the initial phase angle of the voltage; k u For grid voltage imbalance; E S_1 The positive sequence voltage amplitude measured by the power grid; P GFL Q is the reference value for the active power of the GFL; GFL This is the reference value for reactive power of GFL; The formula for calculating the amplitude of the GFM virtual internal potential is as follows: E GFM =I GFM Z GFM_1 ; In the formula, U represents the positive sequence voltage amplitude at the GFM grid connection point after the fault; + U represents the positive sequence voltage amplitude of the power grid. n Rated voltage; λ is the positive sequence voltage sag factor; E GFM Z represents the virtual internal potential of the GFM; p and q are intermediate coefficients; GFM I is the equivalent total impedance of the GFM; gf For GFM fault steady-state current limiting thresholds; E0 and U g0 These represent the equivalent output voltage of the virtual synchronous generator (GFM) and the grid voltage before the fault, respectively; I0 represents the current before the fault; I GFM Z represents the fault current of the GFM. GFM_1 This is the positive-sequence equivalent total impedance of the GFM.

4. The fault analysis method for new energy transmission lines using hybrid converters according to claim 3, characterized in that, In step S3, the specific process of constructing an equivalent sequence network for the transmission lines of a hybrid system for different fault analyses using the network equivalence principle includes: Under symmetrical faults, based on Norton's theorem, the series impedance model of the controlled voltage source of GFM is equivalent to the parallel impedance model of the current source, and combined with the positive sequence controlled current source model of GFL to construct the positive sequence equivalent sequence network of the hybrid system. Under asymmetric faults, based on the symmetric component method and combined with the fault equivalent models of GFL and GFM, positive sequence, negative sequence and zero sequence equivalent sequence networks of the hybrid system are constructed respectively.

5. The fault analysis method for new energy transmission lines using a hybrid converter according to claim 4, characterized in that, In step S4, the derivation of the mathematical relationship of the key electrical quantities of the fault specifically includes: Under symmetrical faults in a hybrid system, based on the positive sequence equal value sequence network, the mathematical relationship between the short-circuit current on the renewable energy side, the short-circuit current on the AC grid side, and the voltage at the grid connection point on the renewable energy side is derived, and the current contribution coefficient and voltage distribution coefficient, which are the steady-state fault characteristic quantities, are calculated using the mathematical relationship. Under asymmetrical faults in a hybrid system, mathematical relationships between the positive-sequence, negative-sequence, and zero-sequence current components at the fault point and the phase voltage at the grid connection point of the new energy side are derived based on the positive-sequence, negative-sequence, and zero-sequence equivalent sequence networks. The positive-sequence, negative-sequence, and zero-sequence current components at the fault point, as well as the phase voltage at the grid connection point of the new energy side, are calculated using these mathematical relationships as steady-state fault characteristic quantities.

6. The fault analysis method for new energy transmission lines using a hybrid converter according to claim 5, characterized in that, The formulas for calculating the short-circuit current on the renewable energy side and the short-circuit current on the AC grid side during a symmetrical fault in a hybrid system are as follows: In the formula, I M_1 and I N_1 These are the short-circuit currents on the renewable energy side and the AC grid side, respectively; I GFM_1 For the Norton equivalent GFM controlled current source, I GFL_1 The current supplied to GFL renewable energy, E S α1 represents the electromotive force of the power grid; α2, α3, and α4 are the current contribution coefficients of different power sources; m is the number of GFMs; n is the number of GFLs. The formula for calculating the voltage at the grid connection point on the new energy side is: U M_1 =β1(mI GFM_1 +nI GFL_1 )+β2E S ; In the formula, U M_1 β1 and β2 are voltage at the grid connection point of the new energy side; β1 and β2 are voltage distribution coefficients. The formulas for calculating the positive-sequence, negative-sequence, and zero-sequence current components in a hybrid system under asymmetrical faults are as follows: In the formula, I MA and I NA These are the positive-sequence, negative-sequence, and zero-sequence current components from the new energy source side and the AC grid side at the fault point, respectively. I MA_1 and I NA_1 These are the positive sequence currents on the renewable energy side and the AC grid side, respectively; I MA_2 and I NA_2 These are the negative sequence currents on the new energy side and the AC grid side, respectively; I MA_0 and I NA_0 These are the zero-sequence currents on the new energy side and the AC grid side, respectively. The formula for calculating the phase voltage at the grid connection point on the new energy side is: OR M_A =h1(mI GFM_1 +nI GFL_1 )+h2E S ; In the formula, U M_A h1 and h2 are the phase voltages at the grid connection point on the new energy side; h1 and h2 are both voltage distribution coefficients.

7. The fault analysis method for new energy transmission lines using a hybrid converter according to claim 6, characterized in that, In step S5, the convergence condition is that the voltage difference between the new energy side grid connection point calculated in two adjacent iterations meets the preset threshold, and the maximum number of iterations does not exceed the preset number.

8. A fault analysis device for new energy transmission lines using a hybrid converter, characterized in that, include: The data acquisition module is used to acquire operation data and fault information data of new energy power stations; The converter fault equivalent module is used to construct GFL fault equivalent models and GFM fault equivalent models under different faults based on the operating data collected by the data acquisition module and the sequence component characteristics of GFL and GFM during the fault. The hybrid system sequence network construction module is used to construct equivalent sequence networks for hybrid system transmission lines for different fault analyses based on the GFL fault equivalent model and GFM fault equivalent model obtained by the converter fault equivalent module under different faults, and through the network equivalence principle. The fault characteristic calculation module is used to calculate the equivalent sequence network of the hybrid system's outgoing lines and fault information data under different faults, based on the hybrid system sequence network construction module. It takes into account the fault response coupling relationship between GFL and GFM and derives the mathematical relationship of the key electrical quantities of the fault. An iterative algorithm is used to solve the mathematical relationship until the convergence condition is met, thereby outputting the steady-state fault characteristic quantity.

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