Flexible direct-current line single-ended protection method and system based on initial voltage traveling wave characteristics

Abstract

A flexible direct-current line single-ended protection method and system based on initial voltage traveling wave characteristics. The method comprises: acquiring a fault voltage signal, determining whether a starting criterion is satisfied, and if yes, on the basis of the acquired signal, establishing an initial voltage traveling wave mathematical model under an internal / external fault; introducing a tangent envelope area ratio k to the initial voltage traveling wave mathematical model, to represent attenuation characteristics of an initial voltage traveling wave; on the basis of the tangent envelope area ratio, analyzing the relationship of the tangent envelope area ratio to transition resistance and a fault position; and comparing the tangent envelope area ratio with a set value to determine an internal / external fault. The tangent envelope area ratio of the initial voltage traveling wave is used to represent waveform morphological characteristics, so as to construct an internal / external identification criterion. The method is not affected by transition resistance in principle, can quickly and reliably identify a fault area, has strong sensitivity to high-resistance faults, and has a certain noise interference resistance capability. The present invention can be used for primary protection in flexible direct-current power transmission systems.

Description

Single-Ended Protection Method and System for Flexible DC Lines Based on Voltage First Traveling Wave Characteristics Technical Field

[0001] This invention belongs to the field of flexible DC line protection, and specifically relates to a single-ended quantity protection method and system for flexible DC lines based on the characteristics of the first traveling wave of voltage. Background Technology

[0002] High-voltage direct current (HVDC) transmission systems based on modular multilevel converters (MMCs) have been widely applied in renewable energy integration, long-distance power transmission, and cross-border power interconnection due to their advantages such as high power conversion capacity, high reliability, and excellent voltage quality. However, MMC-HVDC systems typically use overhead lines, which have a higher probability of failure, for power transmission. Furthermore, when a line fault occurs, the low damping of the DC system and the nonlinear response characteristics of the converter lead to rapid fault development and complex fault characteristics. Fast and reliable protection response is a prerequisite for ensuring the safe and stable operation of the system, but it also presents significant challenges. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for single-ended quantity protection of flexible DC lines based on the characteristics of the first traveling wave of voltage, so as to solve the problem that the existing single-ended quantity protection based on traveling wave is not sensitive enough to high-impedance faults.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides a single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage, comprising:

[0006] Collect fault voltage signals and determine whether they meet the start-up criteria. If they do, establish a mathematical model of the first traveling wave voltage under faults inside and outside the zone based on the collected signals.

[0007] The tangent envelope area ratio k is introduced into the mathematical model of the first traveling voltage wave to characterize the attenuation characteristics of the first traveling voltage wave.

[0008] The relationship between the tangent envelope area ratio and the transition resistance and fault location is analyzed based on the tangent envelope area ratio.

[0009] The ratio of the tangent envelope area is compared with the setting value to determine whether the fault is inside or outside the zone.

[0010] Optionally, the fault voltage signal is collected to determine whether the start-up criteria are met, including:

[0011] When a fault occurs on a flexible DC line, the voltage signal at the line protection installation point is collected to determine whether the start-up criterion is met. The start-up criterion is as follows:

[0012] (1)

[0013] In the formula: u# represents the voltage value at the protection installation point, the subscript # = p, n, where p and n represent the positive and negative terminals respectively; i represents the number of sampling points; Δset is the threshold for the activation criterion;

[0014] The three sampling points are continuously evaluated. If all three sampling points meet the activation criteria, the protection is activated.

[0015] Optionally, a mathematical model of the voltage first traveling wave under fault conditions inside and outside the area is established based on the acquired signals, including:

[0016] The voltage first traveling wave is defined as the first reverse traveling wave of voltage measured at the protection installation point. Considering the coupling between polar electrical quantities in the symmetrical bipolar system and the relatively stable line mode traveling wave, the line mode fault component voltage is used for analysis.

[0017] When an in-zone fault occurs, the first traveling voltage wave detected at the protection installation point M is:

[0018] (2)

[0019] In the formula, U f T(s) represents the initial voltage wave generated at the fault point; T(s) represents the transmission function of the voltage traveling wave on the DC line.

[0020] U f (s) is represented as:

[0021] (3)

[0022] In the formula, U dc Z is the DC voltage during normal system operation. c0 and Z c1 These are the zero-mode impedance and line-mode impedance of the line, respectively; R f For transition resistance;

[0023] The transfer function T(s) is:

[0024] (4)

[0025] In the formula: e -sx / v For transmission delay; k aτ is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave over a unit transmission distance; a denoted as the dispersion time constant per unit length of the line; x is the distance from the fault point to point M; v is the traveling wave propagation speed.

[0026] Ignoring the propagation delay of the traveling wave, the time-domain form of equation (2) is as follows:

[0027] (5)

[0028] In the formula: A1(R) f B1(t) and B1(t) are expressed as:

[0029] (6)

[0030] When a fault occurs outside the positive zone, the time-domain expression of the first traveling wave of the voltage at point M is:

[0031] (7)

[0032] in:

[0033] (8)

[0034] Right now:

[0035] (9)

[0036] Where: A2(R) f B1(t) and B2(t) are expressed as:

[0037] (10)

[0038] In the formula, l is the line length; before the reflected traveling wave is detected at point M, the amplitude of the first traveling wave at point M is 0; L dc This is the value of the current-limiting reactor.

[0039] Optionally, the tangent envelope area ratio k is introduced into the mathematical model of the first traveling voltage wave, including:

[0040] Tangents are constructed at the falling edge and the tail of the first wave, respectively. The intersection points O and Q of the tangents and the waveform, and the intersection point Y of the two tangents, form an envelope triangle region, which contains the steepness information of the waveform. The region formed by the line connecting the two tangent points and the waveform is the curve-enclosed region, which is contained within the envelope triangle region.

[0041] Let the area of ​​the region enclosed by the curve be S', and the area of ​​the enclosing triangle region be S; the ratio of the area of ​​the region enclosed by the curve to the area of ​​the enclosing triangle region is defined as the tangent-envelope area ratio, denoted as k, k<1;

[0042] (11)

[0043] Optionally, the relationship between the tangent envelope area ratio and the transition resistance and fault location can be analyzed based on the tangent envelope area ratio, including:

[0044] When a fault occurs within the zone, the waveform is at O(t) O u(t) O )) and Q (t Q u(t) Q The tangent at point )) is:

[0045] (12)

[0046] In the formula: k O and k Q Let the slopes of the two tangent lines be the discretized representation:

[0047] (13)

[0048] In the formula: Ts is the time interval between two adjacent sampling points;

[0049] make:

[0050] (14)

[0051] Combining equations (12) and (13), we obtain the intersection point Y(t) of the two tangents. k u k ):

[0052] (15)

[0053] Wherein, D1 is represented as:

[0054] (16)

[0055] Therefore, the area S of triangle ΔOYQ is:

[0056] (17)

[0057] Combining equations (6), we get:

[0058] (18)

[0059] The traveling wave curve between O and Q forms an irregular polygon; assume that each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t3, u3, u4), (t5, u5, u6), (t7, u7, u8), (t9, u9, u1), (t1, u1), (t1, u1), (t2, u2 ... i u i )…(t ns u ns ), n s Let (t1, u1) be the number of vertices; where (t1, u1) corresponds to (t... O u O ), (t ns u ns ) corresponds to (t) Q u Q The area S' of the curved trapezoid is expressed as:

[0060] (19)

[0061] In the formula: t ns+1 =t1,u ns+1 =u1;i=1,2...,n s , representing the i-th vertex;

[0062] Therefore, when there is a fault within the zone, the expression for k is:

[0063] (20)

[0064] The expressions for the tangent envelope area ratio of in-region faults and positive out-of-region faults are similar; when a positive out-of-region fault occurs, the intersection point Y(t) of the tangents on both sides of the first traveling wave of the voltage is... k u k )for:

[0065] (twenty one)

[0066] The area S of triangle ΔOYQ is:

[0067] (twenty two)

[0068] In summary, when a fault occurs outside the forward zone, the expression for k is:

[0069] (twenty three)

[0070] When a reverse fault occurs outside the region, the voltage first traveling wave measured by M is 0. At this time, the vertices of the polygon within ΔOYQ are (t1, 0), (t2, 0), and (t...). i ,0)...(t ns Substituting the coordinates of these vertices into equation (17), we get S' = 0; therefore, when a reverse fault occurs outside the region, we assume k = 0.

[0071] Optionally, the tangent envelope area ratio is compared with the setting value to determine whether the fault is inside or outside the zone, including:

[0072] The value of k is calculated using a sliding data window, where the maximum value of k is the most curved part of the traveling wave within the data window; the maximum value of k is then used. max To construct fault identification criteria:

[0073] (twenty four)

[0074] In the formula: k max k represents the maximum value of the ratio of the area of ​​the tangent envelope within the data window. set The threshold value is k. O_max K is the maximum value of k under the positive zone external metallic fault, and K1=1.2 is the reliability coefficient;

[0075] If the maximum value of the tangent envelope area ratio calculated in the data window is k max If equation (24) is satisfied, it is identified as an intra-regional fault; if the maximum value of the tangent envelope area ratio calculated in the data window is k max ≤k set If so, it is identified as an external fault.

[0076] Optional, when k max After satisfying criterion (24), the fault pole voltage is used to determine the fault pole and identify faults in the flexible DC line:

[0077] (25)

[0078] The expression for W in the formula is:

[0079] (26)

[0080] In the formula: Δu p ， n The positive and negative voltage components are represented by n, where n is the number of sampling points within the data window, and W is the number of sampling points within the data window. set The threshold is 1.2.

[0081] Secondly, the present invention provides a single-ended quantity protection system for flexible DC lines based on the characteristics of the first traveling wave of voltage, comprising:

[0082] The data acquisition module is used to acquire fault voltage signals and determine whether the start-up criteria are met. If they are met, a mathematical model of the first traveling wave of voltage under faults inside and outside the zone is established based on the acquired signals.

[0083] The feature characterization module is used to introduce the tangent envelope area ratio k into the mathematical model of the first traveling voltage wave to characterize the attenuation characteristics of the first traveling voltage wave.

[0084] The location relationship determination module is used to analyze the relationship between the tangent envelope area ratio and the transition resistance and fault location based on the tangent envelope area ratio.

[0085] The comparison output module is used to compare the ratio of the tangent envelope area with the set value to determine whether the fault is inside or outside the zone.

[0086] Thirdly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of a single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage.

[0087] Fourthly, the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of a single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage.

[0088] Compared with the prior art, the present invention has the following technical effects:

[0089] This invention uses the tangent envelope area ratio of the first traveling voltage wave to characterize waveform morphology and constructs an identification criterion for faults inside and outside the fault zone. In principle, this method is unaffected by transition resistance, can quickly and reliably identify fault areas, has strong sensitivity to high-resistance faults, and possesses a certain degree of noise interference resistance. It can be used for main protection in flexible DC transmission systems. Specifically, the method first acquires fault voltage and current signals to determine if the activation criterion is met; if so, it proceeds to the next step. A mathematical model of the first traveling voltage wave under faults inside and outside the fault zone is established, and the tangent envelope area ratio k is introduced to characterize the attenuation characteristics of the first traveling voltage wave. The expression for the tangent envelope area ratio is derived, and the relationship between the tangent envelope area ratio, transition resistance, and fault location is analyzed. Finally, the tangent envelope area ratio is compared with the setting value to determine whether the fault is inside or outside the fault zone. By introducing the tangent envelope area ratio as a key parameter for fault identification, rapid and reliable identification of faults inside and outside the fault zone in flexible DC transmission systems is achieved. Its technical effects are significant, and it has broad application prospects and promotional value.

[0090] Furthermore, the system first acquires the voltage signal at the time of the fault in real time. Using preset start-up criteria, it quickly determines whether further fault analysis is necessary, effectively reducing unnecessary calculation and analysis time and improving system response speed. Based on the characteristics of faults inside and outside the fault zone, a mathematical model of the first voltage wave is established, which accurately reflects the changing pattern of the first voltage wave at the time of the fault.

[0091] Furthermore, the tangent envelope area ratio k is introduced as a characteristic parameter to quantify the attenuation characteristics of the first voltage wave, and its sensitivity and effectiveness in fault area identification.

[0092] Furthermore, the expression for the tangent envelope area ratio is derived, and its relationship with transition resistance and fault location is analyzed in depth to determine whether the tangent envelope area ratio can be used as an effective criterion.

[0093] Furthermore, the stability and reliability of the tangent envelope area ratio under different fault conditions were verified through theoretical analysis and simulation experiments. The calculated tangent envelope area ratio was compared with a preset setting value. Based on the comparison results, it was determined whether the fault occurred inside or outside the protected area. This method is not affected by the transition resistance and can quickly and reliably identify the fault region, exhibiting strong sensitivity for high-resistance faults. Attached Figure Description

[0094] Figure 1 is a logic block diagram of the single-ended quantity protection method for flexible DC lines based on the voltage first traveling wave characteristics of the present invention.

[0095] Figure 2 shows the topology of the four-terminal flexible DC grid in the embodiment.

[0096] Figure 3 shows the simulation results of various fault conditions in the embodiment; among them, Figure (a) f0 is a fault outside the reverse zone, Figure (b) f1_200km is a fault occurring at the midpoint of Line 1, Figure (c) f1_400km is a fault occurring at the end of Line 1, and Figure (d) f2 is a fault inside the zone.

[0097] Figure 4 is a flowchart of the single-ended quantity protection of flexible DC lines based on the voltage first traveling wave characteristics of the present invention. Embodiments of the present invention

[0098] The present invention will be further described below with reference to the accompanying drawings:

[0099] Example 1, please refer to Figures 1 and 4, the specific steps are as follows:

[0100] Step 1. Collect the fault voltage signal and determine whether it meets the start-up criteria. If it does, proceed to the next step.

[0101] Step 2. Establish a mathematical model of the first traveling voltage wave under faults inside and outside the zone;

[0102] Step 3. Introduce the tangent envelope area ratio k to characterize the attenuation characteristics of the first traveling voltage wave;

[0103] Step 4. Derive the expression for the tangent envelope area ratio and analyze the relationship between the tangent envelope area ratio and the transition resistance and fault location;

[0104] Step 5. Compare the tangent envelope area ratio with the setting value to determine whether the fault is within or outside the protection zone. In a flexible DC transmission system, when the protection device identifies a fault within the protection zone, it will send a trip signal to the DC circuit breakers at both ends of the line to isolate the faulty line. When the protection device identifies a fault outside the protection zone, the protection will reset and not operate.

[0105] The setting value is a pre-set value used by line protection devices to determine whether a fault has occurred and whether action is required. When electrical quantities (such as current, voltage, power, etc.) in the power system reach or exceed the set value, the line protection device will act according to predetermined logic, such as disconnecting the faulty circuit, to ensure the safe and stable operation of the power system.

[0106] An in-zone fault refers to a fault occurring within the protection zone set by a line protection device. For example, for a transmission line, if a line protection device is installed, the section of the line that the protection device is responsible for protecting is its protection zone. When a fault occurs on this section of the line, it is considered an in-zone fault.

[0107] An out-of-zone fault refers to a fault that occurs outside the protection zone set by the line protection device. For example, taking transmission line protection as an example, when a fault occurs on other equipment or lines outside the protection range of the line protection device, it is considered an out-of-zone fault.

[0108] Single-ended quantity protection refers to a relay protection method that uses only the electrical quantity information measured by the protection device on one side of the transmission line to realize fault judgment and protection action.

[0109] In step 1, when a fault occurs in the flexible DC line, the voltage signal at the line protection installation point is collected to determine whether the start-up criterion is met. The start-up criterion is as follows:

[0110] (1)

[0111] In the formula: u # This represents the voltage value at the protection installation point; the subscript # = p, n, where p and n represent the positive and negative terminals respectively; i represents the number of sampling points; Δset is the threshold for the activation criterion. This indicates the voltage difference at the protection installation point of two adjacent sampling points.

[0112] To ensure the anti-interference capability of the activation criterion, the three sampling points are continuously judged. If all three points satisfy the activation criterion of formula (1), then the protection is activated.

[0113] In step 2, a mathematical model of the first traveling voltage wave under faults inside and outside the protection zone is established. The first traveling voltage wave is defined as the first reverse traveling voltage wave measured at the protection installation point. Considering the coupling between polar electrical quantities in a symmetrical bipolar system and the relatively stable line-mode traveling wave, the line-mode fault component voltage is used for analysis unless otherwise specified below.

[0114] When an intra-zone fault occurs, the first traveling voltage wave detected at point M, where the protection is installed. for:

[0115] (2)

[0116] In the formula, U f (s) represents the line-mode fault component voltage at the fault point; T(s) is the transmission function of the voltage traveling wave on the DC line, where s represents the complex frequency domain;

[0117] U f (s) can be expressed as:

[0118] (3)

[0119] In the formula, U dc Z represents the DC voltage during normal operation of the flexible DC transmission system. c0 and Z c1 These are the zero-mode impedance and line-mode impedance of the line, respectively; R f This is the transition resistance.

[0120] The transfer function T(s) is:

[0121] (4)

[0122] In the formula: e -sx / v For transmission delay; k a τ is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave over a unit transmission distance; a denoted as the dispersion time constant per unit length of the line; x is the distance from the fault point to point M; and v is the traveling wave propagation speed.

[0123] Ignoring the propagation delay of the voltage traveling wave, the time-domain form of equation (2) can be expressed as follows:

[0124] (5)

[0125] In the formula: A1(R) f B1(t) and B1(t) are expressed as:

[0126] (6)

[0127] When a fault occurs outside the positive zone, the first traveling wave of the voltage at point M in the time domain... The expression is:

[0128] (7)

[0129] in:

[0130] (8)

[0131] Right now:

[0132] (9)

[0133] Where: A2(R) f B1(t) and B2(t) are expressed as:

[0134] (10)

[0135] In the formula, l is the line length; before the reflected traveling wave is detected at point M, the amplitude of the first traveling wave at point M is 0; L dc This is the value of the current-limiting reactor;

[0136] When a reverse fault occurs outside the fault zone, the initial voltage reverse traveling wave (first traveling wave) detected at point M is generated by the impedance discontinuity at the end of the line. Therefore, before the reflected traveling wave at the opposite end is detected at point M, the amplitude of the first traveling wave at point M is 0.

[0137] In step 3, the tangent envelope area ratio k is introduced to characterize the attenuation characteristics of the first traveling voltage wave. The specific steps are as follows:

[0138] Tangents are constructed at the falling edge and the tail of the first traveling wave, respectively. The intersection points O and Q of the tangents with the first traveling wave waveform and the intersection point Y of the two tangents form an envelope triangle region, which contains the steepness information of the waveform. The region formed by the line connecting the two tangent points and the waveform is called the curve-enclosed region, which is contained within the envelope triangle region. The tangent point refers to the intersection point of the tangent and the first traveling wave waveform.

[0139] Let the area of ​​the region enclosed by the curve be S', and the area of ​​the enclosing triangle region be S. The ratio of the area of ​​the region enclosed by the curve to the area of ​​the enclosing triangle region is defined as the tangent-envelope area ratio, denoted as k, where k < 1.

[0140] (11)

[0141] In step 4, the expression for the tangent envelope area ratio is derived, and the relationship between the tangent envelope area ratio and the transition resistance and fault location is analyzed. The specific steps are as follows:

[0142] When a fault occurs within the region, the waveform at the intersection point O(t) of the tangent and the first traveling wave waveform. O u(t) O )) and Q (t Q u(t) Q The tangent at point )) is:

[0143] (12)

[0144] In the formula: b O ,b Q respectively in u(t) O ) and u(t) Q The intercept voltage parameter on the waveform indicates the position of the intersection point between the tangent and the first traveling wave, where t is the time variable and k is the voltage level. O and k Q The slopes of the two tangent lines;

[0145] k O and k Q Let the slopes of the two tangent lines be the discretized representation:

[0146] (13)

[0147] In the formula: T s This represents the time interval between two adjacent sampling points.

[0148] make:

[0149] (14)

[0150] Combining formulas (12) and (13), the intersection point Y(t) of the two tangents can be obtained. k u k ):

[0151] (15)

[0152] Wherein, D1 is represented as:

[0153] (16)

[0154] Therefore, the area S of triangle ΔOYQ is:

[0155] (17)

[0156] Combining equations (6), we get:

[0157] (18)

[0158] The traveling wave curve between points O and Q forms an irregular polygon. Assume each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t3, u4), (t5, u5), (t6, u6), (t7, u7), (t8, u8), (t9, u9), (t1, u1), (t1, u1), (t2, u2 ... i u i )…(t ns u ns ), n s Let (t1, u1) be the number of vertices; where (t1, u1) corresponds to (t... O u O ), (t ns u ns ) corresponds to (t) Q u Q The area S' of the curved trapezoid is expressed as:

[0159]

[0160] (19)

[0161] In the formula: t ns+1 =t1,u ns+1 =u1;i=1,2...,n s , representing the i-th vertex.

[0162] Therefore, when a fault occurs within the positive region, the expression for the tangent envelope area ratio k is:

[0163] (20)

[0164] When a fault occurs within the forward region, the expressions for the ratio of the tangent envelope area of ​​the fault within and outside the forward region are similar, and the structure of the time-domain expression for the first traveling voltage wave is also similar. Therefore, the derivation of k is also similar. At this time, the intersection point Y(t) of the tangents on both sides of the first traveling voltage wave is... k u k )for:

[0165] (twenty one)

[0166] The area S of triangle ΔOYQ is:

[0167] (twenty two)

[0168] In summary, when a fault occurs outside the positive region, the expression for the tangent envelope area ratio k is:

[0169] (twenty three)

[0170] When a reverse fault occurs outside the region, the first traveling wave of the voltage measured at point M is 0. Therefore, the vertices of the polygon within ΔOYQ at this time are (t1, 0), (t2, 0), and (t...). i ,0)...(t ns Substituting the coordinates of these vertices into equation (17), we get S' = 0; therefore, when a reverse fault occurs outside the region, we assume k = 0.

[0171] A forward fault refers to a fault within the protection range where the current direction is consistent with the preset direction of the protection, and the protection should operate. A reverse fault refers to a fault outside the protection range where the current direction is opposite to the preset direction of the protection, and the protection should be blocked.

[0172] In summary, the distortion degree of the voltage first traveling wave is closely related to the fault location. When the traveling wave propagation distance is very short, the area enclosed by the curve is relatively large, and k is close to 1. As the fault distance increases, the waveform attenuation increases, and the value of k decreases. Moreover, as shown in equations (20) and (23), the expression for k does not include the transition resistance term and is only related to the fault location. Theoretically, using the ratio of the tangent envelope area to k to identify faults inside and outside the fault zone has strong robustness against the transition resistance.

[0173] In step 5, the tangent envelope area ratio is compared with the setting value to determine whether the fault is inside or outside the zone. The specific steps are as follows:

[0174] The value of k is calculated using a sliding data window, where the maximum value of k is the most curved part of the traveling wave within the data window. Therefore, the maximum value of k is used... max To construct fault identification criteria:

[0175] (twenty four)

[0176] In the formula: k max k represents the maximum value of the ratio of the area of ​​the tangent envelope within the data window. set To set the threshold, k O_max This represents the maximum value of k under positive out-of-zone metallic faults. K1 = 1.2 is the reliability coefficient. If the maximum value of k is the tangent envelope area ratio calculated in the data window... maxIf equation (24) is satisfied, it is identified as an intra-regional fault; if the maximum value of the tangent envelope area ratio calculated in the data window is k max ≤k set If so, it is identified as an external fault.

[0177] In step 6, the fault pole is determined using the fault pole voltage, thereby identifying faults in the flexible DC line.

[0178] Fault pole voltage typically refers to the abnormal voltage condition of a faulty pole (positive, negative, or a phase) in a flexible DC line; fault pole typically refers to a faulty pole (positive, negative, or a phase) in a flexible DC line.

[0179] When k max After satisfying criterion (24), the fault pole voltage is used to determine the fault pole:

[0180] (25)

[0181] The expression for W in the formula is:

[0182] (26)

[0183] In the formula: Δu p ， n The positive and negative voltage components are represented by n, where n is the number of sampling points within the data window, and W is the number of sampling points within the data window. set The set value is 1.2.

[0184] Using fault voltage to determine the fault location is a quick and accurate way to identify the fault location in flexible DC lines, ensuring system safety, reducing the scope of power outages, improving power supply reliability, and guiding subsequent maintenance.

[0185] Example 2: A ±520 kV four-terminal flexible DC power grid model is established as shown in Figure 2. MMC1-MMC3 employ constant active and reactive power control, while MMC4 employs constant DC voltage and reactive power control. f0, f1, and f2 represent reverse external faults, internal faults, and forward external faults, respectively. Specific parameters of the system are shown in Table 1. The DC line adopts a frequency-varying parameter model, with a line length of 400 km and Ldc of 150 mH. The protection sampling frequency is 50 kHz. set=0.49. Positive grounding faults were set at different locations f0, f1, and f2, with transition resistances of 0.1Ω, 200Ω, 400Ω, and 600Ω, respectively, to verify the proposed protection performance. Simulation results for various fault scenarios are shown in Figure 3, and protection operation status is shown in Table 1. In the table, f1_200 km and f1_400 km represent faults occurring at the midpoint and end of Line 1, respectively.

[0186]

[0187] As shown in Table 1, the proposed protection method can correctly distinguish between faults inside and outside the protection zone and has good resistance to transition resistance.

[0188] Example 3: A ±520 kV four-terminal flexible HVDC transmission system model was established as shown in Figure 2. 30 dB Gaussian white noise was added to the sampled signal to verify the impact of noise interference on the proposed protection scheme. The simulation results are shown in Table 2.

[0189] Table 2. Protection Action Results under 30 dB Noise Interference

[0190]

[0191] Simulation results show that the addition of noise does indeed affect the waveform and the ratio of the tangent envelope area. The envelope triangle is determined by 5 sampling points, and k is calculated using a sliding window algorithm. max This reduces noise interference to some extent, and the proposed protection can reliably identify faults inside and outside the zone under 30 dB noise interference.

[0192] In another embodiment of the present invention, a single-ended quantity protection system for flexible DC lines based on the characteristics of the first traveling voltage wave is provided. This system can be used to implement the aforementioned single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling voltage wave. The system includes: a data acquisition module for acquiring fault voltage signals and determining whether the activation criterion is met; if so, establishing a mathematical model of the first traveling voltage wave under faults inside and outside the fault zone based on the acquired signals; a feature characterization module for introducing a tangent envelope area ratio k into the mathematical model of the first traveling voltage wave to characterize the attenuation characteristics of the first traveling voltage wave; a positional relationship determination module for analyzing the relationship between the tangent envelope area ratio, transition resistance, and fault location based on the tangent envelope area ratio; and a comparison output module for comparing the tangent envelope area ratio with a setting value to determine whether the fault is inside or outside the fault zone.

[0193] In another embodiment of the present invention, a computer device is provided, comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a central processing unit, a digital signal processor, an application-specific integrated circuit (ASIC), a programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, and is suitable for loading and executing one or more instructions from the computer storage medium to implement corresponding method flows or functions. The processor described in this embodiment can be used in the operation of a single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage.

[0194] In another embodiment of the present invention, a storage medium is provided, specifically a computer-readable storage medium, which is a memory device in a computer device for storing programs and data. The computer-readable storage medium includes both built-in storage media in the computer device and extended storage media supported by the computer device. The computer-readable storage medium provides storage space and stores the operating system of the terminal. The computer-readable storage medium can be a high-speed RAM memory or an unstable memory, such as at least one disk storage device. This storage space also stores one or more instructions suitable for loading and execution by a processor. These instructions are one or more computer programs (including program code) to implement the corresponding steps of the single-ended quantity protection method for flexible DC lines based on the voltage first traveling wave characteristics described in the above embodiments.

[0195] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0196] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

Claims

1. A single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage, characterized in that, include: Collect fault voltage signals and determine whether they meet the start-up criteria. If they do, establish a mathematical model of the first traveling wave voltage under faults inside and outside the zone based on the collected signals. The tangent envelope area ratio k is introduced into the mathematical model of the first traveling voltage wave to characterize the attenuation characteristics of the first traveling voltage wave. The relationship between the tangent envelope area ratio and the transition resistance and fault location is analyzed based on the tangent envelope area ratio. The ratio of the tangent envelope area is compared with the setting value to determine whether the fault is inside or outside the zone.

2. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 1, characterized in that, Collect fault voltage signals and determine whether the start-up criteria are met, including: When a fault occurs on a flexible DC line, the voltage signal at the line protection installation point is collected to determine whether the start-up criterion is met. The start-up criterion is as follows: (1) In the formula: u # This indicates the voltage value at the protection installation point, with subscripts #=p, n; p and n represent the positive and negative terminals respectively; i represents the number of sampling points; Δset is the threshold for the activation criterion. The three sampling points of the flexible DC line are continuously judged. If all three sampling points meet the start-up criteria, the protection is activated.

3. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 1, characterized in that, A mathematical model of the voltage first traveling wave under fault conditions inside and outside the area is established based on the collected signals, including: The voltage first traveling wave is defined as the first reverse traveling wave of voltage measured at the protection installation location; When an intra-zone fault occurs, the first traveling voltage wave detected at point M, where the protection is installed. for: (2) In the formula, U f (s) represents the line-mode fault component voltage at the fault point; T(s) represents the transmission function of the voltage traveling wave on the DC line; Among them, U f (s) is represented as: (3) In the formula, U dc Z represents the DC voltage during normal operation of the flexible DC transmission system. c0 and Z c1 These are the zero-mode impedance and line-mode impedance of the line, respectively; R f For transition resistance; The transfer function T(s) of the voltage traveling wave on a DC line is: (4) In the formula: e -sx / v For transmission delay; k a τ is the attenuation coefficient per unit length of the line, reflecting the attenuation of the voltage traveling wave over a unit transmission distance; a denoted as the dispersion time constant per unit length of the line; x is the distance from the fault point to point M; v is the traveling wave propagation speed. Ignoring the propagation delay of the voltage traveling wave, the time-domain form of equation (2) is as follows: (5) In the formula: A1(R) f B1(t) and B1(t) are expressed as: (6) When a fault occurs outside the positive zone, the first traveling wave of the voltage at point M in the time domain... The expression is: (7) in: (8) Right now: (9) Where: A2(R) f B1(t) and B2(t) are expressed as: (10) In the formula, l is the line length; before the reflected traveling wave is detected at point M, the amplitude of the first traveling wave at point M is 0; L dc This is the value of the current-limiting reactor.

4. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 1, characterized in that, The mathematical model of the first traveling wave of voltage introduces the tangent envelope area ratio k, including: Tangents are constructed at the falling edge and the tail of the first traveling wave of the voltage. The intersection points O and Q of the tangents with the first traveling wave waveform and the intersection point Y of the two tangents are connected to form an envelope triangle region, which contains the steepness information of the waveform. The region formed by the line connecting the two tangent points and the waveform is the curve-enclosed region, which is contained within the envelope triangle region. The tangent point refers to the intersection point of the tangent and the first traveling wave waveform. Let the area of ​​the region enclosed by the curve be S', and the area of ​​the enclosing triangle region be S; the ratio of the area of ​​the region enclosed by the curve to the area of ​​the enclosing triangle region is defined as the tangent-envelope area ratio, denoted as k, k<1; (11)。 5. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 1, characterized in that, Analysis of the relationship between the tangent envelope area ratio, transition resistance, and fault location based on the tangent envelope area ratio includes: When a fault occurs within the region, the waveform at the intersection point O(t) of the tangent and the first traveling wave waveform... O u(t) O )) and Q (t Q u(t) Q The tangent at point )) is: (12) In the formula: b O b Q respectively in u(t) O ) and u(t) Q The intercept voltage parameter on the waveform represents the position of the intersection of the tangent and the first traveling wave, where t is the time variable, and u(t) is the voltage parameter on the first traveling wave. O ) and u(t) Q ) are the voltage dependent variables at intersection points O and Q, respectively, k O and k Q The slopes of the two tangent lines; slope k O and k Q The discretization is represented as: (13) In the formula: Ts is the time interval between two adjacent sampling points; make: (14) Combining equations (12) and (13), we obtain the intersection point Y(t) of the two tangents. k u k ): (15) Wherein, D1 is represented as: (16) Therefore, the area S of triangle ΔOYQ is: (17) Combining equations (6), we get: (18) The traveling wave curve between intersection points O and Q forms an irregular polygon; assume that each vertex of this polygon has coordinates (t1, u1), (t2, u2), (t3, u3, u4), (t5, u5, u6), (t7, u7, u8), (t9, u9, u1), (t1, u1), (t1, u1), (t2, u2 ... i u i )…(t ns u ns ), Let (t1, u1) be the number of vertices; where (t1, u1) corresponds to (t... O u O ), (t ns u ns ) corresponds to (t) Q u Q The area S' of the curved trapezoid is expressed as: (19) In the formula: t ns+1 =t1,u ns+1 =u1;i=1,2...,n s , representing the i-th vertex; Therefore, when a fault occurs within the positive region, the expression for the tangent envelope area ratio k is: (20) When a fault occurs outside the positive region, the intersection point Y(t) of the tangents on both sides of the first traveling wave of the voltage is... k u k )for: (21) The area S of triangle ΔOYQ is: (22) In summary, when a fault occurs outside the forward zone, the expression for k is: (23) When a reverse fault occurs outside the region, the first traveling wave of the voltage measured at point M is 0. Therefore, the vertices of the polygon within ΔOYQ at this time are (t1, 0), (t2, 0), and (t...). i ,0)...(t ns Substituting the coordinates of these vertices into formula (17), we get S'=0; therefore, when a reverse zone fault occurs, k=0.

6. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 5, characterized in that, The ratio of the tangent envelope area is compared with the setting value to determine whether the fault is inside or outside the zone, including: The tangent envelope area ratio k is calculated using a sliding data window, where the maximum value of k is the most curved portion of the traveling wave within the data window; the maximum value of k is then used. max To construct fault identification criteria: (24) In the formula: k max k represents the maximum value of the ratio of the area of ​​the tangent envelope within the data window. set k is the setpoint value. O_ma x K is the maximum value of k under the positive zone external metallic fault, and K1=1.2 is the reliability coefficient; If the maximum value of the tangent envelope area ratio calculated in the data window is k max If equation (24) is satisfied, it is identified as an intra-zone fault; If the maximum value of the tangent envelope area ratio calculated in the data window is k max ≤k set If so, it is identified as an external fault.

7. The single-ended quantity protection method for flexible DC lines based on the characteristics of the first traveling wave of voltage as described in claim 6, characterized in that, When k max After satisfying criterion (24), the fault pole voltage is used to determine the fault pole and identify faults in the flexible DC line, specifically: (25) The expression for W in the formula is: (26) In the formula: Δu p,n The positive and negative voltage components are represented by n, where n is the number of sampling points within the data window, and W is the number of sampling points within the data window. set The set value is 1.

2.

8. A single-ended quantity protection system for flexible DC lines based on the characteristics of the first traveling wave of voltage, characterized in that, include: The data acquisition module is used to acquire fault voltage signals and determine whether the start-up criteria are met. If they are met, a mathematical model of the first traveling wave of voltage under faults inside and outside the zone is established based on the acquired signals. The feature characterization module is used to introduce the tangent envelope area ratio k into the mathematical model of the first traveling voltage wave to characterize the attenuation characteristics of the first traveling voltage wave. The location relationship determination module is used to analyze the relationship between the tangent envelope area ratio and the transition resistance and fault location based on the tangent envelope area ratio. The comparison output module is used to compare the ratio of the tangent envelope area with the set value to determine whether the fault is inside or outside the zone.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the flexible DC line single-ended quantity protection method based on the voltage first traveling wave characteristics as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the single-ended quantity protection method for flexible DC lines based on the voltage first traveling wave characteristics as described in any one of claims 1 to 7.

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