Method and system for fault location of double-ended non-synchronous traveling wave of flexible dc power grid

Abstract

The application provides a method and system for fault location of double-ended non-synchronous traveling wave of a flexible DC power grid, the method comprising: collecting voltage and current data in the flexible DC power grid to calculate voltage and current of line mode and zero mode; constructing a fault line mode network, and constructing a fault equivalent simplified circuit after equivalent simplification to deduce an analytical expression of the voltage and current of the line mode and zero mode in the frequency domain; deducing a current anti-traveling wave frequency domain expression; converting the current anti-traveling wave frequency domain expression into a current anti-traveling wave front time domain expression; taking the current anti-traveling wave front time domain expression as a target function, performing parameter fitting on current anti-traveling wave front data, obtaining an optimal solution, and performing fault location. The application can accurately fit discrete traveling wave data measured at two ends of a line, accurately predict the location of a fault, does not require communication equipment and channels, can accurately predict the location of a fault under a near-end fault, improves the accuracy and reliability of prediction, and enhances adaptability in different new energy grid connection scenarios.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power control, and particularly relates to a method and system for double-end non-synchronous traveling wave fault location of a flexible DC power grid. BACKGROUND

[0002] At present, the flexible DC power transmission technology based on power electronic devices has become a key technology for realizing the grid connection of land and offshore wind power and photovoltaic and other renewable energy in a long-distance, large-capacity and high-efficiency condition, with economic and technical advantages. It effectively promotes the construction of large-scale AC / DC hybrid systems. However, due to the extremely complex environment of the DC line of the flexible DC power grid, human factors and natural factors can cause the insulation of the line to be damaged, and then a DC fault occurs. Once the fault occurs, the DC protection and DC circuit breaker will quickly cut off the fault current and isolate the fault line. In order to accurately calculate the location of the fault, reduce the impact of the fault on the system maintenance cost and economic loss, and improve the flexibility, operation efficiency and fault handling capability of the system, an accurate and reliable fault location technology is crucial.

[0003] As an improvement, in recent years, there has been a relatively large amount of research on DC fault location technology for flexible DC power grids. The main methods include the natural frequency method, the fault analysis method, the artificial intelligence method and the traveling wave method. However, the natural frequency method, the fault analysis method and the artificial intelligence method have their limitations in principle and performance, and are currently limited to the theoretical research stage, with no practical engineering application cases. The traveling wave method uses the transient traveling wave detected at the line protection to achieve the fault location, which can be divided into double-end traveling wave method and single-end traveling wave method. The key is to accurately identify the exact time of the arrival of the traveling wave at the protection measurement point in the reflection and refraction process, and to accurately analyze the discrete traveling wave data obtained by measurement to complete the identification of the wave head. Although the traveling wave method has been applied in engineering, the current method still has certain limitations, especially in the new power system with a high proportion of renewable energy and a large number of power electronic devices. For example, in the new power system, different line scenarios and parameters (such as DC submarine cables, DC overhead lines, and mixed lines of submarine cables and overhead lines) may cause errors in the calculation of the traveling wave velocity, thereby affecting the accuracy of the fault location result. The double-end traveling wave method relies on communication equipment and channels to synchronize the traveling wave data at both ends. The synchronization process may introduce certain errors, and the actual engineering investment is large. In addition, in the case where the channel is damaged, the double-end traveling wave method cannot be used. When a near-end fault occurs, the reflection and refraction of the traveling wave are extremely violent, resulting in relatively limited effective data available for fault location, which may cause the traveling wave head to be difficult to identify, thereby affecting the accuracy and reliability of the fault location result. Therefore, in summary, the current traveling wave fault location method relies on communication equipment and channels, has large errors and costs in fault location, and the reliability and accuracy in the case of near-end fault need to be further improved. SUMMARY

[0004] The purpose of the present application is to provide a method and system for double-end asynchronous traveling wave fault location of a flexible DC power grid, so as to solve the problem that the current traveling wave fault location method relies on communication equipment and channels, and the error and cost of fault location are large, and the reliability and accuracy under near-end fault need to be further improved.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] The present application provides a method for double-end asynchronous traveling wave fault location of a flexible DC power grid, comprising the following steps:

[0007] S1, in the flexible DC power grid, the positive and negative pole protection voltages and the positive and negative pole protection currents at both ends of the line are collected, and the line mode voltage and the zero mode voltage, the line mode current and the zero mode current are calculated;

[0008] S2, combining the transmission line theory and the traveling wave theory of the power network, a fault line mode network is constructed, and after equivalent simplification, a fault equivalent simplified circuit is constructed, and the traveling wave frequency domain analytical expression of the line mode voltage and the zero mode voltage, the line mode current and the zero mode current is derived in combination with S1;

[0009] S3, based on the traveling wave frequency domain analytical expression of the line mode voltage and the zero mode voltage, the line mode current and the zero mode current, the current anti-traveling wave frequency domain expression is derived;

[0010] S4, according to Laplace inverse transform, the current anti-traveling wave frequency domain expression is converted into current anti-traveling wave front time domain expression;

[0011] S5, taking the current anti-traveling wave front time domain expression as the objective function, the current anti-traveling wave front data is parameter fitted, the optimal solution is obtained, and fault location is performed.

[0012] In some embodiments, in S1, the calculation of the line mode and zero mode voltage and the line mode and zero mode current adopts the following (1):

[0013]

[0014] Wherein, u (0) ,u (1) are the line mode voltage and the zero mode voltage, i (0) ,i (1) are the line mode current and the zero mode current.

[0015] In some embodiments, in S1, the positive and negative pole protection voltages and the positive and negative pole protection currents at both ends of the line are collected by a protection measurement device.

[0016] In some embodiments, in S2, the fault line-mode network is a MMC-MTDC system fault sequence network diagram, the MMC-type converter station is simplified by equivalence, and a fault equivalent simplified circuit is constructed.

[0017] Further, in S2, the traveling wave frequency domain analytical expression of the line-mode voltage and the zero-mode voltage, and the line-mode current and the zero-mode current is as follows formula (2):

[0018]

[0019] Wherein, wherein, i (1)MN (s) and u (1)MN (s) are the protection R MN The current and voltage frequency domain analytical expression, Z c(1) is the line-mode characteristic impedance of the line, L dc is the DC reactor at the end of the line, for describing the traveling wave transmission attenuation and distortion, k and τ are the line parameters, l is the fault distance, v (1) is the propagation speed of the traveling wave in the line-mode network, Δv F1 is the step signal.

[0020] Further, S3 is specifically: constructing the voltage and current anti-traveling wave expression as follows formula (4):

[0021]

[0022] Based on the voltage and current traveling wave expression, the current anti-traveling wave frequency domain expression as follows formula (5) is derived:

[0023]

[0024] In some embodiments, in S4, the current anti-traveling wave frequency domain expression and its specific parameters are as follows formula (6):

[0025]

[0026] Wherein, A MN and τ MN are the current anti-traveling wave front coefficients, T dMN is the transmission delay of i b(1)MN (t) propagating to the protection installation R MN through the fault distance l;

[0027] Based on formula (6), the current anti-traveling wave front time domain expression i b(1)NM (t) is derived as follows formula (7):

[0028]

[0029] Wherein, L is the total length of line MN.

[0030] In some embodiments, S5 is specifically: converting the voltage and current data in the protection fault recorder into anti-travel wave front data, using a nonlinear least square method, taking an anti-travel wave front time domain expression as an objective function, performing parameter fitting on the anti-travel wave front data, obtaining an optimal solution, and calculating the fault distance based on the optimal solution and line parameters.

[0031] In some embodiments, in S5, the fault distance is expressed as the following formula (8):

[0032]

[0033] Wherein, tau MN And tau NM is an anti-travel wave parameter, tau is a line parameter, and l is the fault distance.

[0034] The application also provides a flexible DC power grid double-end non-synchronous traveling wave fault distance measurement system, which comprises a network construction module, a data processing module and a data calculation module.

[0035] The network construction module is used for constructing a fault line model network and a fault equivalent simplified circuit; the data processing module is used for processing the collected voltage and current data; and the data calculation module is used for performing parameter fitting on the processed data and calculating the fault distance.

[0036] The flexible DC power grid double-end non-synchronous traveling wave fault distance measurement system is used to execute the flexible DC power grid double-end non-synchronous traveling wave fault distance measurement method.

[0037] Compared with the prior art, the flexible DC power grid double-end non-synchronous traveling wave fault distance measurement method and system have the following beneficial technical effects.

[0038] The application provides a method for fault location of a double-ended asynchronous traveling wave of a flexible DC power grid, and specifically comprises the following steps: S1, in the flexible DC power grid, positive and negative protection voltages and positive and negative protection currents at both ends of a line are collected, and line-mode voltages and zero-mode voltages and line-mode currents and zero-mode currents are calculated; S2, a fault line-mode network is constructed in combination with a transmission line theory and a traveling wave theory of the power grid, a fault equivalent simplified circuit is constructed after equivalent simplification, and a traveling wave frequency domain analytical expression of the line-mode voltages and the zero-mode voltages and the line-mode currents and the zero-mode currents is derived; S3, a current anti-traveling wave frequency domain expression is derived based on the traveling wave frequency domain analytical expression of the line-mode voltages and the zero-mode voltages and the line-mode currents and the zero-mode currents; S4, the current anti-traveling wave frequency domain expression is converted into a current anti-traveling wave front time domain expression according to Laplace inverse transformation; and S5, parameter fitting is performed on current anti-traveling wave front data with the current anti-traveling wave front time domain expression as a target function, an optimal solution is obtained, and fault location is performed. Based on the above, the method can accurately fit discrete traveling wave data measured by a protection recording device at both ends of the line through reasonable design and parameter fitting, and then parameters of the current anti-traveling wave front time domain analytical expression containing fault distance information are obtained. The parameters are independently mapped with the fault distance and are not affected by fault conditions and boundary conditions. The parameters can be used to relatively accurately predict the position of the fault. The application does not need to rely on communication equipment and channels, does not need accurate traveling wave velocity values and detailed parameters of the line, can accurately predict the position of the fault under a near-end fault, improves the accuracy and reliability under the near-end fault, and enhances the adaptability under different new energy grid connection scenarios. Reliable technical support is provided for subsequent power grid maintenance. BRIEF DESCRIPTION OF DRAWINGS

[0039] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this application, illustrate embodiments of the application and serve to explain the principles of the application, and do not limit the application in any way.

[0040] Figure 1 A flowchart of the method in the method and system for fault location of a double-ended asynchronous traveling wave of a flexible DC power grid of the application;

[0041] Figure 2 A schematic diagram of a four-terminal flexible DC power grid in the method and system for fault location of a double-ended asynchronous traveling wave of a flexible DC power grid of the application.

[0042] Figure 3 A schematic diagram of a fault network current anti-traveling wave (a) and a Peterson fault equivalent circuit (b) in the method and system for fault location of a double-ended asynchronous traveling wave of a flexible DC power grid of the application.

[0043] Figure 4A parameter fitting result schematic diagram under an inter-pole short circuit fault in simulation of a flexible direct current power grid double-end non-synchronous traveling wave fault distance measurement method and system of the present application;

[0044] Figure 5 A parameter fitting accuracy evaluation result schematic diagram under different fault distances in simulation of a flexible direct current power grid double-end non-synchronous traveling wave fault distance measurement method and system of the present application;

[0045] Figure 6 A parameter fitting test result schematic diagram under 35 dB noise in simulation of a flexible direct current power grid double-end non-synchronous traveling wave fault distance measurement method and system of the present application. DETAILED DESCRIPTION

[0046] In order to make the objects, technical solutions, and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0048] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0049] In the description of the embodiments of the present application, it should also be noted that, unless explicitly defined and limited, if the terms “set”, “install”, “connect”, “connect” appear, they should be understood in a broad sense, for example, they can be fixedly connected, or detachably connected, or integrally connected; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0050] How to eliminate the dependence of the traveling wave method on the accurate wave speed value, improve the reliability and accuracy of the traveling wave method under the near-end fault, and how to analyze the time-frequency domain expression of the traveling wave and use the time-frequency domain parameters for fault distance measurement.

[0051] As Figure 1As shown, the present application provides a method for locating a double-ended asynchronous traveling wave fault of a flexible DC power grid, comprising the following steps:

[0052] S1, in the flexible DC power grid, the positive and negative protection voltages and currents at both ends of the line are collected, and the line mode voltage and zero mode voltage, line mode current and zero mode current are calculated;

[0053] S2, combining the transmission line theory and traveling wave theory of the power network, a fault line mode network is constructed, and after equivalent simplification, a fault equivalent simplified circuit is constructed, and the traveling wave frequency domain analytical expression of the line mode voltage and zero mode voltage, line mode current and zero mode current is derived in combination with S1;

[0054] S3, based on the traveling wave frequency domain analytical expression of the line mode voltage and zero mode voltage, line mode current and zero mode current, the current anti-traveling wave frequency domain expression is derived;

[0055] S4, according to Laplace inverse transform, the current anti-traveling wave frequency domain expression is converted into current anti-traveling wave front time domain expression;

[0056] S5, taking the current anti-traveling wave front time domain expression as the objective function, the current anti-traveling wave front data is parameter fitted, the optimal solution is obtained, and fault location is performed.

[0057] The present application aims at the deficiencies of the prior art, and through the parameter fitting algorithm, the discrete traveling wave data measured by the line end protection recording device can be accurately fitted, and then the traveling wave time domain analytical expression parameters containing fault distance information are obtained. These parameters are independently mapped with the fault distance and are not affected by the fault conditions and boundary conditions. Using these parameters can accurately predict the location of the fault. This helps to quickly repair the fault and reduce the economic loss and impact on the safe and stable operation of the system. The present application improves the accuracy and efficiency of fault location through the design of the overall calculation method, and is expected to improve the overall stability of the power grid.

[0058] Specifically, the present application is realized by the following ways:

[0059] Step 1: in the flexible DC power grid, the positive and negative voltage and current u p ,u n and i p ,i n measured by the line end protection measuring device are used to calculate the line mode and zero mode voltage and current u (0) ,u (1) and i (0) ,i (1) , and the specific calculation is as follows:

[0060]

[0061] Step 2: Establishing the MMC-MTDC system fault sequence network diagram, simplifying the MMC converter station, constructing the fault equivalent simplified circuit, solving the line mode voltage and current traveling wave frequency domain analytical expression obtained by the line MN two-end protection measurement under the in-zone fault, and solving the line mode voltage and current traveling wave frequency domain analytical expression obtained by the line MN two-end protection measurement under the in-zone fault MN The measured voltage and current traveling wave is as follows:

[0062]

[0063] Where, i (1)MN (s) and u (1)MN (s) are the protection R MN current and voltage frequency domain analytical expressions. Z c(1) is the line mode characteristic impedance of the line. L dc is the line end DC reactor. for describing the traveling wave transmission attenuation and distortion. Parameters k and τ are line parameters. l is the fault distance. v (1) is the propagation speed of the traveling wave in the line mode network. According to the superposition theorem, Δv F1 can be regarded as a step signal, and its physical meaning is the initial voltage value of the fault point line mode, which is determined by the fault type, the size of the transition resistance, and the line rated voltage. Δv F1 The calculation of different fault types is as follows:

[0064]

[0065] Where, V f is the line rated DC voltage. Z c(1) and Z c(0) are the line mode and zero mode traveling wave characteristic impedances, respectively. R f is the size of the transition resistance (only considering the transition resistance as linear.

[0066] Step 3: Although the voltage and current traveling waves contain the fault distance l, the backward traveling wave is more suitable for fault location because: the expression of the backward traveling wave is simpler than that of the voltage and current, the direction of the backward traveling wave is from the fault point to the line end protection installation, the backward traveling wave is not affected by the boundary reflection of the line end, and the backward traveling wave is only the initial step voltage signal of the fault point after the traveling wave transmission process, containing more pure fault distance information. According to the traveling wave theory, combined with the voltage and current traveling waves i (1)MN (s) and u (1)MN (s), and the line mode characteristic impedance Z c(1) , the voltage and current backward traveling waves can be solved as shown in the following formula:

[0067]

[0068] Combining the voltage current travelling wave expression, the protection R MN The measured current anti-travelling wave frequency domain expression i b(1)MN (s) is as follows:

[0069]

[0070] Step 4: According to the inverse Laplace transform, the protection R MN The measured current anti-travelling wave front time domain expression i b(1)MN (t) and its specific parameters are as follows:

[0071]

[0072] Where A MN and τ MN are the current anti-travelling wave front coefficients. T dMN represents the transmission delay of i b(1)MN (t) propagating to the protection installation R MN through the fault distance l. Considering the symmetry of the system, the current anti-travelling wave front time domain expression i b(1)NM (t) measured by the protection R NM of line MN close to the bus N is:

[0073]

[0074] Where L is the total length of line MN.

[0075] Step 5: The current anti-travelling wave i b(1)MN (t) and the coefficient A b(1)NM of i MN (t) A NM and τ MN τ NM both contain fault distance information. However, the size of A MN and A NM is affected by the coupling of fault type and transition resistance size in addition to fault distance. Therefore, the anti-travelling wave parameters τ MN and τ NM are more suitable for fault location. If the specific values of τ MN and τ NM can be obtained by parameter fitting of the discrete data obtained by protection measurement, since the line parameter τ is a constant, the fault distance can be represented as:

[0076]

[0077] The voltage and current data in the protection fault recorder are discrete data, so the calculated current anti-travelling wave front is also discrete data, and the data density is determined by the sampling frequency. In order to fit the specific τ MN and τNM Numerical analysis is required to solve a nonlinear least squares problem. Using the time-domain expression of the inverse traveling wavefront as the objective function, parameter fitting is performed on discrete data to find the optimal solution. The obtained optimal solution τ is then used... MN and τ NM The parameter τ is used for fault location.

[0078] The following detailed description of the ranging method and system for two-terminal asynchronous traveling wave faults in the flexible DC power grid of the present invention will be provided through specific embodiments.

[0079] Step 1: Assuming that the DC line MN between bus M and bus N is a faulty line, use the positive and negative voltage and current u obtained from the protection at both ends of the line. p ,u n and i p i n The line-mode and zero-mode voltage and current u are calculated using the formula (1) above. (0) ,u (1) and i (0) i (1) ;

[0080] like Figure 2 and Figure 3 As shown, step 2: for Figure 2 The fault analysis of the MMC-MTDC system shown is performed. Since line MN is the faulty line, the focus of fault location measurement is on protection R. MN and R NM Analysis of the obtained data. Figure 3 (a) defines the direction of the current reverse traveling wave and the schematic diagram in the faulty line. Figure 3 (b) is the Peterson equivalent circuit for the line-mode network. The MMC converter station is simplified to an equivalent series RLC impedance, denoted as Z. MMC The specific calculation is as follows:

[0081]

[0082] Among them, R arm and R on These are the equivalent resistance of the MMC converter station bridge arm and the on-resistance of the IGBT, respectively. arm C is the equivalent inductance of the bridge arm of an MMC type converter station. sm R is the equivalent capacitance of the half-bridge submodule. N is the number of bridge arm submodules in the converter station. The specific value depends on the specific parameters of the converter station. In the model used in this invention, R eq =0.907mΩ, L eq =3.33mH, C eq =0.45×10 3 μF.

[0083] The equivalent simplified circuit of the fault is constructed, and the analytical expression of the line-mode voltage and the current traveling wave at the two ends of the line MN under the fault in the region is solved, so that the protection R MN The measured voltage and current traveling wave are taken as an example, and the frequency domain expression thereof is as formula (2) shown above:

[0084] Step 3: According to the traveling wave theory, the voltage and current traveling waves i (1)MN (s) and u (1)MN (s) are combined with the line-mode characteristic impedance Z c(1) The voltage and current counter-traveling waves can be solved, as shown in formula (4);

[0085] The voltage and current counter-traveling waves can be solved, as shown in formula (4); MN The frequency domain expression of the measured current counter-traveling wave i b(1)MN (s) is specifically as formula (5) shown.

[0086] Step 4: In the test system, the total length L of the line MN is set to 200 km.

[0087] Step 5: Based on the fault distance formula (8); in order to fit the parameters τ MN and τ NM , the present application uses the Adaptive Multi-step Levenberg-Marquardt (AMLM) algorithm to take the parameter fitting of i b(1)MN (t) as an example, and defines the optimization target and error function based on the AMLM algorithm optimization fitting as:

[0088]

[0089] Wherein, the error of the H(x) optimization target is i b(1)MN , x is equal to [A MN , τ MN ] 1×2 , and is a two-dimensional vector, that is, the parameter to be solved.

[0090] The iteration vector of the AMLM algorithm is defined as formula (11) shown below:

[0091]

[0092] Wherein, the criterion r k ≥ p0 is used to control the adaptive iteration step size δ k The size of the kth iteration. p0 is a very small positive number, and is set to 0.0001.

[0093] The adaptive iteration step size δ k is defined as:

[0094]

[0095] where I is a 2x2 identity matrix. k is the AMLM algorithm parameter. G k is the Jacobian matrix.

[0096] Define λ k and G k as follows:

[0097]

[0098] where G k is the Jacobian matrix The parameters are set as follows: p1=0.50, p2=0.25, p3=0.75, c1=4.0, c2=0.25, β1=10 -5 , β min =10 -8 . When the criterion is satisfied, it indicates that the AMLM algorithm converges, the current iteration k is the optimal solution x k =[A MN,k ,τ MN,k ], the iteration is completed, and the anti- wave front i b(1)MN of the optimal parameters A MN and τ MN is successfully fitted. The parameter fitting step for i b(1)NM is consistent with the fitting for i b(1)MN above.

[0099] The accuracy of the parameter fitting is evaluated. The statistical index R 2 is used by the present application to evaluate the fitting accuracy, which is defined as follows:

[0100] where SSR is the regression sum of squares, and SST is the total sum of squares.

[0101] After the currents i b(1)MN (t) and i b(1)NM (t) at the installation places of the two-side protections of the fault line MN are fitted, the fault distance formula (8) above is obtained.

[0102] In the case of a near-end fault, the protection device closer to the fault point measures a shorter wavefront data window for the current reverse traveling wave, containing less data. Therefore, the accuracy of its fitting and ranging results is lower than that of far-end protection. To overcome the influence of near-end faults, this invention first compares the fitting accuracy of the protection devices on both sides of the fault before performing fault location. This invention considers the practical application scenario of fault location, namely, after the fault is identified by the DC protection system and the fault current is isolated by the circuit breaker, which is a post-processing rather than a real-time operation, requiring only analysis of the fault waveform data. Therefore, this invention does not rely on additional communication equipment and devices to exchange measurement data. The final ranging calculation expression is as follows:

[0103]

[0104] The definition of measurement error is:

[0105] Among them, l * To predict the distance to the fault.

[0106] The present invention further verifies the effectiveness and feasibility of the ranging method and system for double-ended asynchronous traveling wave faults in flexible DC power grids through the following simulation.

[0107] like Figure 2 As shown, the present invention builds a simulation system based on the PSCAD / EMTDC simulation platform, and the specific parameters of the system are shown in Table 1 below:

[0108] Table 1: Test System Parameters

[0109]

[0110]

[0111] like Figure 4 As shown, Figure 4 The AMLM algorithm is used to analyze the current reverse traveling wave i under different fault distances. b(1)MN The fitting results for (t) indicate that the fault type is an inter-electrode metallic short-circuit fault. The results demonstrate that the employed AMLM can accurately fit discrete data.

[0112] like Figure 5 As shown, Figure 5 The results of parameter fitting using the AMLM algorithm under different fault distances and fault types are presented for a 200km long DC submarine cable. The results show that the AMLM algorithm can accurately fit discrete current back-traveling waves, and its accuracy is unaffected by fault type or fault distance.

[0113] like Figure 6 As shown,Figure 6 The results of parameter fitting under 35dB Gaussian white noise interference are given.

[0114] The following table 2 is the fault distance measurement result in line MN.

[0115] Table 2 fault distance measurement result

[0116]

[0117]

[0118] From the results in table 2, it is shown that the distance measurement method of the application can reliably and accurately calculate the fault distance, and has better applicability.

[0119] In summary, the distance measurement method and system of the application for double-end asynchronous traveling wave fault of flexible DC power grid can improve the accuracy and reliability under near-end fault condition without relying on communication equipment and channel, without accurate traveling wave velocity value and detailed parameters of the line, and enhance the adaptability under different new energy grid connection scenarios. The calculation operation of the method is convenient and easy to implement, and has the characteristics of high reliability and strong adaptability.

[0120] Finally, it should be noted that: the above is only the preferred embodiment of the application, and does not limit the application in any form; any ordinary technical personnel in the industry can implement the application according to the description and the above; however, any equivalent changes, modifications and evolution of the above disclosed technical content without departing from the technical solution of the application are equivalent embodiments of the application; at the same time, any equivalent changes, modifications and evolution of the above embodiments according to the essence of the application are still within the protection scope of the technical solution of the application.

Claims

1. A method for fault location of double-ended non-synchronous traveling wave faults in a flexible HVDC grid, characterized in that, Comprise the following steps: S1, in the flexible DC power grid, the positive and negative protection voltage and the positive and negative protection current of the line two ends are collected, and the line mode voltage and the zero mode voltage, the line mode current and the zero mode current are calculated; S2, combining the transmission line theory and the traveling wave theory of the power network, a fault line mode network is constructed, and a fault equivalent simplified circuit is constructed after equivalent simplification, and the traveling wave frequency domain analytical expression of the line mode voltage and the zero mode voltage, the line mode current and the zero mode current is derived; The fault line mode network is the fault sequence network diagram of the MMC-MTDC system, the MMC type converter station is equivalent and simplified, and the fault equivalent simplified circuit is constructed; The traveling wave frequency domain analytical expression of the line mode voltage and the zero mode voltage, the line mode current and the zero mode current is as follows formula (2): （2）； wherein, and to protect current and voltage frequency domain analytical expressions, is the line mode characteristic impedance, is the line end DC reactor, for describing the travelling wave transmission attenuation and distortion, k and is the line parameter, is the fault distance, is the travelling wave on-line mode network propagation speed, is the step signal; S3, based on the traveling wave frequency domain analytical expression of the line mode voltage and the zero mode voltage, the line mode current and the zero mode current, the current anti-traveling wave frequency domain expression is derived; S4, according to Laplace inverse transformation, the current anti-traveling wave frequency domain expression is converted into the current anti-traveling wave front time domain expression; S5, taking the current anti-traveling wave front time domain expression as the objective function, the parameter fitting of the current anti-traveling wave front data is carried out, the optimal solution is obtained, and fault distance measurement is carried out.

2. The method of claim 1, wherein, In the S1, the line mode and zero mode voltage and the line mode and zero mode current are calculated by using the following (1): （1）； wherein Vlineand Vzeroare the line mode voltage and the zero mode voltage, respectively, Ilineand Izeroare the line mode current and the zero mode current, respectively.

3. The method of claim 1, wherein, In the S1, the positive and negative protection voltage and the positive and negative protection current of the line two ends are collected by the protection measuring device.

4. The method of claim 3, wherein, The S3 is specifically: the voltage and current anti-traveling wave expression of the following formula (4) is constructed: （4）； Based on the voltage and current traveling wave expression, the current anti-traveling wave frequency domain expression of the following formula (5) is derived: （5）。 5. The method of claim 4, wherein, In the S4, the current anti-traveling wave frequency domain expression and its specific parameters are as follows formula (6): （6）； wherein, and is a current traveling wave front coefficient, is the transmission delay over the fault distance propagating to the protection installation . Based on equation (6), the current anti-traveling wave front time-domain expression of equation (7) is derived as follows : （7）； Wherein, L is the total length of the line MN.

6. The method of claim 1, wherein, The S5 is specifically: the voltage and current data in the protection fault recorder are converted into anti-traveling wave front data, the non-linear least square method is used, the anti-traveling wave front time domain expression is taken as the objective function, the parameter fitting of the anti-traveling wave front data is carried out, the optimal solution is obtained, and the fault distance is calculated based on the optimal solution and the line parameters.

7. The method of claim 5, wherein the method of locating a double-ended unsynchronized traveling wave fault of a flexible HVDC grid is characterized by, In the S5, the fault distance is expressed as follows formula (7): （8）； wherein, and is a counter wave parameter, is a line parameter, is a fault distance.

8. A system for fault location of double-ended non-synchronized traveling wave faults in a flexible HVDC grid, characterized in that, The system comprises a network construction module, a data processing module and a data calculation module; wherein: The network construction module is used for constructing the fault line mode network, and the fault equivalent simplified circuit is constructed; the data processing module is used for data processing of the collected voltage and current data; the data calculation module is used for parameter fitting of the processed data, and the fault distance is calculated; The double-end asynchronous traveling wave fault distance measurement system of the flexible DC power grid is used to execute the double-end asynchronous traveling wave fault distance measurement method of the flexible DC power grid in any one of claims 1-7.

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