A Quantitative Characterization Method and System for Positive Sequence Impedance of Equivalent Faults in New Energy Grid-Connected Converter Stations

Abstract

This invention discloses a method and system for quantitatively characterizing the equivalent fault positive-sequence impedance of a new energy grid-connected converter station. First, an equivalent composite sequence network of the system is established by combining the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to different fault types. Then, combining the weak feeder characteristics of the converter system and the topology of the fault composite sequence network, the expression for the positive-sequence voltage at the fault point is derived, and further, the expression for the positive-sequence voltage at the converter station bus is derived. The amplitude and phase changes of the positive-sequence voltage on the converter station bus side under different fault scenarios are studied. Based on the amplitude and phase changes of the positive-sequence voltage on the converter station bus side, the equivalent fault positive-sequence impedance of the converter system corresponding to different fault types is calculated, achieving a certain degree of quantitative characterization of the equivalent positive-sequence impedance of the converter system. This can provide theoretical guidance for the quantitative characterization of converter system fault characteristics, adaptive analysis of protection, and the formulation of new protection principles.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology, and in particular relates to a method and system for quantitative characterization of positive sequence impedance of equivalent faults in grid-connected converter stations of new energy sources. Background Technology

[0002] As the first line of defense in a power system, relay protection operates based on the system's fault characteristics. For traditional power frequency quantity protections such as abrupt change directional elements, current phase selection elements, and compensated distance protection, their protection principles all rely on the system's equivalent sequence impedance characteristics. However, in renewable energy grid-connected systems, the equivalent fault positive sequence impedance of converter stations is related to various factors such as system control strategies, fault types, and fault conditions. This differs significantly from the constant inductive sequence impedance of traditional synchronous machine systems, posing a significant challenge to many traditional protection systems that rely on the system's back-side impedance characteristics. To ensure the safe operation of the power system, it is necessary to conduct in-depth research on the equivalent fault positive sequence impedance characteristics of renewable energy grid-connected converters.

[0003] Current research on the equivalent sequence impedance of grid-connected converters for new energy sources can be divided into two categories: qualitative analysis and quantitative analysis. Previous qualitative analysis studies have largely relied on simulations, yielding concise but limited conclusions. Quantitative analysis, on the other hand, often uses the controlled variable method to analyze the impact of a single influencing factor on the fault sequence impedance, without fully considering the coupling relationships between these factors. Therefore, the derived results often deviate from actual results. In conclusion, the quantitative characterization of the fault equivalent positive sequence impedance of grid-connected converter stations for new energy sources requires further in-depth research. Summary of the Invention

[0004] This invention provides a method and system for quantitative characterization of the positive sequence impedance of equivalent faults in new energy grid-connected converter stations, which solves the technical problem that the characteristics of the equivalent fault sequence impedance of new energy converter stations are unclear and difficult to quantitatively characterize.

[0005] In a first aspect, the present invention provides a method for quantitatively characterizing the positive-sequence impedance of equivalent faults in a new energy grid-connected converter station, comprising: constructing an equivalent fault composite sequence network topology of the power system based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault type; deriving the positive-sequence voltage expression at the fault point of the power system based on the equivalent fault composite sequence network topology, thereby obtaining the changes in the amplitude and phase of the positive-sequence voltage at the fault point of the power system, wherein the fault point of the power system includes a minor three-phase symmetrical fault point and a severe three-phase symmetrical fault point; deriving the changes in the amplitude and phase of the positive-sequence voltage at the fault point of the power system and the fault ride-through guidelines of the grid-connected converter, thereby deriving the changes in the amplitude and phase of the positive-sequence voltage on the converter station bus side under different fault scenarios; and calculating the equivalent fault positive-sequence impedance of the converter station under different fault scenarios based on the changes in the amplitude and phase of the positive-sequence voltage on the converter station bus side under different fault scenarios, thus enabling quantitative characterization of the equivalent fault positive-sequence impedance of the converter station.

[0006] Secondly, this invention provides a quantitative characterization system for the positive-sequence impedance of equivalent faults in a new energy grid-connected converter station, comprising: a construction module configured to construct an equivalent fault composite sequence network topology of the power system based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault type; a first derivation module configured to derive the positive-sequence voltage expression at the fault point of the power system based on the equivalent fault composite sequence network topology, thereby obtaining the changes in the amplitude and phase of the positive-sequence voltage at the fault point of the power system, wherein the fault point of the power system includes a minor three-phase symmetrical fault point and a severe three-phase symmetrical fault point; a second derivation module configured to derive the changes in the amplitude and phase of the positive-sequence voltage at the fault point of the power system and the fault ride-through guidelines of the grid-connected converter, thereby deriving the changes in the amplitude and phase of the positive-sequence voltage on the converter station bus side under different fault scenarios; and a calculation module configured to calculate the equivalent fault positive-sequence impedance of the converter station under different fault scenarios based on the changes in the amplitude and phase of the positive-sequence voltage on the converter station bus side under different fault scenarios, thereby quantitatively characterizing the equivalent fault positive-sequence impedance of the converter station.

[0007] Thirdly, an electronic device is provided, comprising: at least one processor, and a memory communicatively connected to the at least one processor, wherein the memory stores instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the steps of the quantitative characterization method for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations according to any embodiment of the present invention.

[0008] Fourthly, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the steps of the quantitative characterization method for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations according to any embodiment of the present invention.

[0009] This application presents a method and system for quantitative characterizing the equivalent fault positive-sequence impedance of a new energy grid-connected converter station. By combining the fault ride-through control strategy of the grid-connected converter and the fault boundary conditions corresponding to different fault types, an equivalent composite sequence network of the system is established. Subsequently, combining the weak feeder characteristics of the converter system and the topology of the system fault composite sequence network, the expression for the positive-sequence voltage at the fault point is derived. Based on this, the expression for the positive-sequence voltage at the converter station bus is derived, and the amplitude and phase changes of the positive-sequence voltage on the converter station bus side under different fault scenarios are studied. Finally, using the derived amplitude and phase changes of the positive-sequence voltage on the converter station bus side, the equivalent positive-sequence impedance of the converter system fault is calculated, realizing the quantitative characterization of the equivalent positive-sequence impedance of the converter system fault. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 A flowchart illustrating a quantitative characterization method for positive-sequence impedance of equivalent faults in a new energy grid-connected converter station, provided in an embodiment of the present invention;

[0012] Figure 2 A fault diagram of a photovoltaic system provided in an embodiment of the present invention;

[0013] Figure 3 This is an equivalent composite sequence network diagram of a system experiencing a phase A ground fault, provided in an embodiment of the present invention.

[0014] Figure 4 A schematic diagram of the equivalent fault positive sequence impedance fluctuation region of a converter system when a three-phase symmetrical fault occurs, provided in an embodiment of the present invention.

[0015] Figure 5 This is a schematic diagram of the equivalent fault positive sequence impedance fluctuation region of a converter system when a single-phase ground fault occurs, according to an embodiment of the present invention.

[0016] Figure 6 A structural block diagram of a quantitative characterization system for positive sequence impedance of equivalent faults in a new energy grid-connected converter station, provided in an embodiment of the present invention;

[0017] Figure 7 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0018] 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 embodiments of the present invention, 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.

[0019] Example 1

[0020] Please see Figure 1 The flowchart illustrates a quantitative characterization method for positive-sequence impedance of equivalent faults in a new energy grid-connected converter station according to this application.

[0021] like Figure 1 As shown, the method for quantitative characterization of positive sequence impedance of equivalent faults in new energy grid-connected converter stations provided by the present invention specifically includes steps S101-S104.

[0022] Step S101: Based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault types, construct the equivalent fault composite sequence network topology of the power system.

[0023] Step S102: Based on the equivalent fault composite sequence network topology, derive the positive sequence voltage expression at the fault point of the power system, and obtain the changes in the amplitude and phase of the positive sequence voltage at the fault point of the power system, wherein the fault point of the power system includes minor three-phase symmetrical fault points and severe three-phase symmetrical fault points.

[0024] In this embodiment, the expression for the positive sequence voltage at the point of a minor three-phase symmetrical fault in the power system is as follows:

[0025]

[0026] In the formula, R is the positive sequence voltage at the fault point. f For transition resistance, This is the positive-sequence fault current flowing through the fault point. The equivalent electromotive force of the conventional system at the opposite end of the converter station;

[0027] The expression for the positive sequence voltage at the point of severe three-phase symmetrical fault in a power system:

[0028]

[0029] In the formula, Z N1 Z represents the positive-sequence system impedance of the conventional system at the other end. LN1 The positive sequence line impedance from the fault point to the opposite busbar is given by k, which is a proportionality coefficient and a constant.

[0030] Step S103: Based on the changes in the amplitude and phase of the positive sequence voltage at the fault point in the power system and the fault ride-through guidelines of the grid-connected converter, derive the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios.

[0031] In this embodiment, the expression for the fault ride-through guideline of the grid-connected converter is:

[0032]

[0033] In the formula, i dref1 i is the d-axis reference value for the positive sequence current at the converter station's common point. qref1 P is the q-axis reference value for the positive sequence current at the converter station's common point. ref I is the active power reference value. rate I is the rated current of the converter station. max U1 is the maximum withstand current of the converter station, and U2 is the positive sequence voltage amplitude at the point of common. This is the per-unit value of the positive sequence voltage;

[0034] Specifically, the expression for the positive sequence voltage on the converter station bus side is:

[0035]

[0036] In the formula, This is the positive sequence voltage on the converter station bus side. This refers to the positive sequence current on the converter station bus side. Z is the positive sequence voltage at the fault point. Ld1 This is the positive sequence line impedance from the fault point to the converter station bus.

[0037] Step S104: Based on the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios, calculate the equivalent fault positive sequence impedance of the converter station under different fault scenarios, so as to quantitatively characterize the equivalent fault positive sequence impedance of the converter station.

[0038] In this embodiment, the expression for the positive-sequence impedance of the equivalent fault in the converter station is:

[0039]

[0040] In the formula, These are the fault components of the positive sequence voltage on the converter station bus side and the fault components of the positive sequence current on the converter station bus side, respectively.

[0041] In summary, the method in this embodiment establishes an equivalent composite sequence network of the system by combining the fault ride-through control strategy of the grid-connected converter and the fault boundary conditions corresponding to different fault types. Then, combining the weak feeder characteristics of the converter system and the topology of the system fault composite sequence network, the positive sequence voltage expression at the fault point is derived. Based on this, the positive sequence voltage expression at the converter station bus is derived, and the amplitude and phase changes of the positive sequence voltage on the converter station bus side under different fault scenarios are studied. Finally, using the derived amplitude and phase changes of the positive sequence voltage on the converter station bus side, the equivalent positive sequence impedance of the converter system fault is calculated, realizing the quantitative characterization of the equivalent positive sequence impedance of the converter system fault.

[0042] Example 2

[0043] The second embodiment of the present invention also proposes a method for quantitative characterization of the positive-sequence impedance of equivalent faults in a new energy grid-connected converter station. The method is implemented by software and / or hardware, and specifically includes steps S1-S3.

[0044] S1, targeting Figure 2 In the system shown, when a minor ABCG fault occurs, the converter system can be equivalent to a negative resistor with a phase of -180°. At this time, the positive sequence current of the opposite end system and the positive sequence voltage at the protection installation point can be approximated as:

[0045]

[0046]

[0047] In the formula, This refers to the positive-sequence current flowing from the other end of the system to the fault point. Z represents the equivalent electromotive force of the conventional system at the opposite end of the converter station. N1 Z represents the positive-sequence system impedance of the conventional system at the other end. LN1 The positive sequence line impedance is from the fault point to the opposite bus. These are the positive sequence voltage and positive sequence current on the converter station bus side, respectively. Ld1 This represents the positive-sequence line impedance from the fault point to the converter station bus. R is the positive sequence voltage at the fault point. f For transition resistance, This is the positive sequence current flowing through the fault point;

[0048] From equation (2), we can see that The phase is approximately 0. Considering the converter system's weak ability to provide short-circuit current, when a minor ABCG fault occurs in the system... phase and Similarly, since there will be no huge jumps, k can be considered... u>0.8 (k u (This is the ratio of the positive-sequence voltage amplitude after a fault to the normal operating voltage amplitude.) The value range is [-30°, 15°] (This represents the phase change value before and after a positive sequence voltage fault).

[0049] However, when a severe ABCG fault occurs in the system, due to the weak feedback of the converter system... The value will be much greater than at this time and It can be represented as:

[0050]

[0051]

[0052] From equation (3), we can see that The phase is approximately -80°. Considering Mainly composed of Providing, can be considered The phase is approximately -80°, therefore The phase is also approximately -80°. Because and The amplitude is small, therefore The phase fluctuation may be large, so we assume k u When <0.2, The value range is [-120°, 90°], and the positive sequence q-axis current reference value I of the converter control system is taken into account when the voltage drops severely. qref It may approach the maximum withstand current I of the converter. max Therefore, for I qref =1.05I rate and I qref =sin80°I max Two scenarios were analyzed (I) rate (This refers to the rated current of the converter). And when 0.2... <k u When <0.8, at this time The phase generally lags behind the fault by 0°-80°, but due to the weak short-circuit current supply capability of the converter system (assuming I...), qref The maximum value is 1.05I. N ),therefore The phase will also not be the same as There is a significant gap, which is considered here. The value range is [-90°, 30°].

[0053] For single-phase ground faults, the converter is configured with current balance control to achieve fault ride-through. When a severe fault occurs in the system, taking a phase A ground fault (AG) as an example... Figure 2 Its faulty composite sequence network is shown, at this time and It can be represented as:

[0054]

[0055]

[0056] In the formula, Z LN2 Z N2 These are the negative sequence impedances of the line from the fault point to the bus of the opposite system and the equivalent negative sequence impedance of the opposite system, Z. ∑0 =(Z d0 +Z Ld0 )||(Z N0 +Z LN0 ), where the subscript "0" represents the zero-sequence impedance of the corresponding variable.

[0057] In equation (6), considering that the system voltage drop is not severe... The amplitude is relatively large, indicating that even if R f When the value is close to 0 It will also not experience a severe drop similar to the ABCG failure. In equation (6), when R f When the impedance is relatively small, considering that the positive and negative sequence impedance parameters of the line and the conventional system can be approximated as equal, It can be approximated by equation (7):

[0058]

[0059] When a high-resistance fault occurs in the AG circuit, the fault voltage drop is relatively small. It can be approximated as:

[0060]

[0061] Combined with formula (8), The phase can be approximated by (9). Furthermore, from equation (9), we can derive... The phase does not undergo a large jump before and after the fault.

[0062]

[0063] Based on the above analysis, for AG faults, it is assumed that when k u When >0.8, The value range is [-30°, 15°], when 0.4 <k u When <0.8, The value range is [-60°, 30°]. The analysis process for phase-to-phase faults and phase-to-ground faults is similar to that for single-phase ground faults, and will not be elaborated further by the author.

[0064] S2. Estimate using the positive sequence voltage and positive sequence current at the common point of the converter station. and The amplitude and phase relationship. The positive sequence voltage and positive sequence current at the converter station common point satisfy the fault ride-through guideline shown in equation (10):

[0065]

[0066] In the formula, i dref1 i is the d-axis reference value for the positive sequence current at the converter station's common point. qref1 P is the q-axis reference value for the positive sequence current at the converter station's common point. ref I is the active power reference value. rate I is the rated current of the converter. max U1 is the maximum withstand current of the converter, and U2 is the positive sequence voltage amplitude at the point of common. This is the per-unit value of the positive sequence voltage.

[0067] According to equation (10), the converter can be equivalent to a voltage-controlled current source, and the positive sequence voltage and positive sequence current satisfy a one-to-one correspondence. Therefore, it can be determined according to... Approximate estimation of amplitude and phase The amplitude and phase.

[0068] S3. The amplitude and phase changes of the positive sequence voltage on the converter station bus side under different fault scenarios, derived from step S1, and the voltage obtained in step S2. The equivalent fault positive-sequence impedance Z of the converter is calculated using equation (11). d1 :

[0069]

[0070] In the formula, These are the fault components of the positive sequence voltage on the converter station bus side and the fault components of the positive sequence current on the converter station bus side, respectively.

[0071] Figure 4 The black area in the image shows the equivalent fault positive sequence impedance fluctuation region of a converter system with a voltage level of 220kV and a transmission capacity of 175MW when a three-phase symmetrical fault occurs in the system. Figure 5 The black area in the diagram shows the fluctuation area of ​​the converter's equivalent positive sequence impedance when a single-phase ground fault occurs in the system.

[0072] Simulation verification:

[0073] A photovoltaic system with a transmission capacity of 175MW and a voltage level of 220kV was built in PSCAD / EMTDC software. The maximum withstand current of the converter was set to twice the rated current. The system topology is as follows. Figure 1 As shown. The system's fundamental frequency is 50Hz, the transformer substation's transformation ratio is 0.69kV / 35kV, the main transformer's transformation ratio is 35kV / 220kV, and the main transformer adopts a Y-type design. d The Δ connection method is used, with a transmission line length of 50km. The line is simulated using a Π model, and the positive sequence parameters per unit length are r1 = 0.06Ω / km, l1 = 0.127mH / km, and c0 = 0.005μF / km. Z N1 = (1.1 + j6.0)Ω. The sampling rate is set to 10kHz, and the full-wave Fourier algorithm is used to extract the power frequency signal.

[0074] Table 1 lists the calculated positive-sequence impedance of the converter station under different faults within the line (using fault steady-state data), combined with... Figure 3 and Figure 4 The positive-sequence impedance fluctuation range of the converter fault shown in Table 1 can be seen in Z. d1 The calculation results are all located in Figure 3 and Figure 4 The proposed method is effective in quantitatively characterizing the positive-sequence impedance of a converter fault because it is located within or near the boundary of the fault positive-sequence impedance fluctuation region.

[0075] Table 1 Z under different fault scenarios d1 Calculation results

[0076]

[0077] Example 3

[0078] Please see Figure 6 The diagram shows a structural block diagram of a quantitative characterization system for positive sequence impedance of equivalent faults in a new energy grid-connected converter station according to this application.

[0079] like Figure 6 As shown, the equivalent fault positive sequence impedance quantitative characterization system 200 for new energy grid-connected converter stations includes a construction module 210, a first derivation module 220, a second derivation module 230, and a calculation module 240.

[0080] The system includes the following modules: Construction module 210, configured to construct an equivalent fault composite sequence network topology for the power system based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault types; First derivation module 220, configured to derive the positive sequence voltage expression at the fault point of the power system based on the equivalent fault composite sequence network topology, obtaining the changes in the amplitude and phase of the positive sequence voltage at the fault point of the power system, wherein the fault point of the power system includes minor three-phase symmetrical fault points and severe three-phase symmetrical fault points; Second derivation module 230, configured to derive the changes in the amplitude and phase of the positive sequence voltage at the fault point of the power system and the fault ride-through guidelines of the grid-connected converter, deriving the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios; and Calculation module 240, configured to calculate the equivalent fault positive sequence impedance of the converter station under different fault scenarios based on the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios, thereby quantitatively characterizing the equivalent fault positive sequence impedance of the converter station.

[0081] It should be understood that Figure 6 The modules and references described in the document Figure 1 The steps described in the text correspond to those in the method described above. Therefore, the operations, features, and corresponding technical effects described above also apply to the method described in the text. Figure 6 The various modules in the document will not be described in detail here.

[0082] In other embodiments, the present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein when the program instructions are executed by a processor, the processor performs the quantitative characterization method for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations in any of the above method embodiments.

[0083] In one embodiment, the computer-readable storage medium of the present invention stores computer-executable instructions, which are configured as follows:

[0084] Based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault types, the equivalent fault composite sequence network topology of the power system is constructed.

[0085] Based on the equivalent fault composite sequence network topology, the expression for the positive sequence voltage at the fault point of the power system is derived, and the changes in the amplitude and phase of the positive sequence voltage at the fault point of the power system are obtained. The fault points of the power system include minor three-phase symmetrical fault points and severe three-phase symmetrical fault points.

[0086] Based on the changes in the amplitude and phase of the positive sequence voltage at the fault point in the power system and the fault ride-through guidelines of the grid-connected converter, the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios are derived.

[0087] Based on the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios, the equivalent fault positive sequence impedance of the converter station under different fault scenarios is calculated, so as to quantitatively characterize the equivalent fault positive sequence impedance of the converter station.

[0088] Computer-readable storage media may include a stored program area and a stored data area, wherein the stored program area may store an operating system and an application program required for at least one function; the stored data area may store data created based on the use of the quantitative characterization system for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations. Furthermore, the computer-readable storage medium may include high-speed random access memory, and may also include memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, the computer-readable storage medium may optionally include memory remotely disposed relative to a processor, which can be connected to the quantitative characterization system for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0089] Figure 7 This is a schematic diagram of the structure of the electronic device provided in the embodiment of the present invention, such as... Figure 7 As shown, the device includes a processor 310 and a memory 320. The electronic device may also include an input device 330 and an output device 340. The processor 310, memory 320, input device 330, and output device 340 can be connected via a bus or other means. Figure 7 Taking a bus connection as an example, the memory 320 is the computer-readable storage medium described above. The processor 310 executes various server functions and data processing by running non-volatile software programs, instructions, and modules stored in the memory 320, thereby implementing the quantitative characterization method for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations as described in the above method embodiment. The input device 330 can receive input digital or character information and generate key signal inputs related to user settings and function control of the quantitative characterization system for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations. The output device 340 may include a display screen or other display device.

[0090] The aforementioned electronic device can execute the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0091] In one implementation, the above-described electronic device is applied in a quantitative characterization system for positive-sequence impedance of equivalent faults in new energy grid-connected converter stations. As a client, it includes: at least one processor; and a memory communicatively connected to the at least one processor. The memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enable the at least one processor to:

[0092] Based on the fault ride-through control strategy of the grid-connected converter and the boundary conditions corresponding to the fault types, the equivalent fault composite sequence network topology of the power system is constructed.

[0093] Based on the equivalent fault composite sequence network topology, the expression for the positive sequence voltage at the fault point of the power system is derived, and the changes in the amplitude and phase of the positive sequence voltage at the fault point of the power system are obtained. The fault points of the power system include minor three-phase symmetrical fault points and severe three-phase symmetrical fault points.

[0094] Based on the changes in the amplitude and phase of the positive sequence voltage at the fault point in the power system and the fault ride-through guidelines of the grid-connected converter, the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios are derived.

[0095] Based on the changes in the amplitude and phase of the positive sequence voltage on the bus side of the converter station under different fault scenarios, the equivalent fault positive sequence impedance of the converter station under different fault scenarios is calculated, so as to quantitatively characterize the equivalent fault positive sequence impedance of the converter station.

[0096] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of various embodiments or some parts of embodiments.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for quantitatively characterizing equivalent fault positive sequence impedance of a new energy grid-connected converter station, characterized in that, The method comprises the following steps: According to the boundary conditions corresponding to the fault ride-through control strategy of the grid-connected converter and the fault type, an equivalent fault composite sequence network topology of the power system is constructed; Based on the equivalent fault composite sequence network topology, an expression of the positive sequence voltage at the fault point of the power system is derived, and the amplitude and phase variation of the positive sequence voltage at the fault point of the power system are obtained, wherein the fault point of the power system includes a slight three-phase symmetric fault point and a serious three-phase symmetric fault point; According to the amplitude and phase variation of the positive sequence voltage at the fault point of the power system and the fault ride-through guide of the grid-connected converter, the amplitude and phase variation of the positive sequence voltage at the bus side of the converter station under different fault scenarios are derived; According to the amplitude and phase variation of the positive sequence voltage at the bus side of the converter station under different fault scenarios, the equivalent fault positive sequence impedance of the converter station under different fault scenarios is calculated, so as to quantitatively characterize the fault equivalent positive sequence impedance of the converter station.

2. The method according to claim 1, characterized in that, Wherein, The expression of the positive sequence voltage at the slight three-phase symmetric fault point of the power system is: wherein Vf is the positive sequence voltage at the fault point, R f Rt is the transition resistance, If is the positive sequence fault current flowing through the fault point, E is the equivalent electromotive force of the conventional system at the opposite end of the converter station; The expression of the positive sequence voltage at the serious three-phase symmetric fault point of the power system is: where Z N1 is the positive sequence system impedance of the opposite end conventional system, Z LN1 is the positive sequence line impedance from the fault point to the opposite end bus, and k is a proportional coefficient, which is a constant.

3. The method of claim 1, wherein the method is characterized in that, Wherein, The expression of the positive sequence voltage at the bus side of the converter station is: wherein is the positive sequence voltage at the busbar side of the converter station, is the positive sequence current at the busbar side of the converter station, is the positive sequence voltage at the fault point, Z Ld1 is the positive sequence line impedance from the fault point to the busbar of the converter station.

4. The method of claim 1, wherein, Wherein, The expression of the fault ride-through guide of the grid-connected converter is: where i dref1 is the d-axis reference value of the positive sequence current at the common point of the converter station, i qref1 is the q-axis reference value of the positive sequence current at the common point of the converter station, P ref is the active power reference value, I rate is the rated current of the converter, I max is the maximum withstand current of the converter, U1is the positive sequence voltage amplitude at the common point, is the per-unit value of the positive sequence voltage.

5. The method of claim 1, wherein, Wherein, The expression of the equivalent fault positive sequence impedance of the converter station is: In the formula, are the fault components of the positive sequence voltage at the converter station bus side and the positive sequence current at the converter station bus side, respectively.

6. A new energy grid-connected converter station equivalent fault positive sequence impedance quantitative characterization system, characterized in that, The method comprises the following steps: A construction module is configured to construct an equivalent fault composite sequence network topology of a power system according to boundary conditions corresponding to a fault ride-through control strategy of a grid-connected converter and a fault type; A first derivation module is configured to derive an expression of a positive sequence voltage at a fault point of the power system based on the equivalent fault composite sequence network topology, and obtain the amplitude and phase variation of the positive sequence voltage at the fault point of the power system, wherein the fault point of the power system includes a slight three-phase symmetric fault point and a serious three-phase symmetric fault point; A second derivation module is configured to derive the amplitude and phase variation of the positive sequence voltage at the bus side of the converter station under different fault scenarios according to the amplitude and phase variation of the positive sequence voltage at the fault point of the power system and the fault ride-through guide of the grid-connected converter; A calculation module is configured to calculate the equivalent fault positive sequence impedance of the converter station under different fault scenarios according to the amplitude and phase variation of the positive sequence voltage at the bus side of the converter station under different fault scenarios, so as to quantitatively characterize the fault equivalent positive sequence impedance of the converter station.

7. An electronic device, comprising: The method comprises the following steps: At least one processor and a memory connected in communication with the at least one processor, wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method of any one of claims 1 to 5.

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to implement the method of any one of claims 1 to 5.

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