Flexible DC power transmission line lightning stroke interference identification method based on instantaneous traveling wave power

Abstract

The invention discloses a flexible DC power transmission line lightning stroke interference identification method based on instantaneous traveling wave power. The method specifically comprises the following steps: step 1, calculating a line mode voltage reverse traveling wave and a line mode current reverse traveling wave; step 2, respectively obtaining a high-frequency component and a low-frequency component of a line mode voltage reverse traveling wave through a digital filter; a high-frequency component and a low-frequency component of a line-mode current reverse traveling wave; 3, calculating the absolute value of the product of the voltage and current reverse traveling wave high-frequency components to obtain an instantaneous traveling wave power high-frequency component; an instantaneous traveling wave power low-frequency component is obtained by calculating the absolute value of the product of the voltage and current reverse traveling wave low-frequency components; and 4, respectively calculating the ratio # imgabs0 # of the integral values of Ph (k1) and Pl (k1) in the time window of 1ms after the fault element is started, and judging whether lightning stroke interference occurs or not. According to the method, lightning stroke interference is identified according to the instantaneous traveling wave power frequency domain energy distribution difference, the method has high transition resistance resistance, and meanwhile, the requirement for the sampling frequency is low.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power systems and relates to a method for identifying lightning disturbance of flexible direct current transmission lines based on instantaneous traveling wave power. Background Art

[0002] In power systems, accurate identification of lightning disturbances is crucial to ensure the safe operation of transmission lines. Traditional lightning disturbance identification methods mainly rely on time domain features, but these methods have some obvious limitations.

[0003] First, methods based on time domain features usually focus on the trend of waveform changes. As mentioned in the literature, these methods may use the current change before and after lightning strikes or faults as features. However, there is a refraction and reflection process in the traveling wave after a lightning strike, and there may also be a zero crossing in the fault traveling wave, which makes the methods based on time domain features less reliable. In addition, these methods are greatly affected by the busbar structure, and the action performance needs to be improved under conditions of abnormal data transmission or noise interference. Secondly, time domain characteristics are more sensitive to the interference of transition resistance. The presence of transition resistance will lead to inaccurate impedance measurement of distance protection, which may cause protection refusal or malfunction. The size and nature of transition resistance have a significant impact on distance protection, especially in the case of short lines, where the impact is more serious.

[0004] In contrast, methods based on frequency domain features show significant advantages. Frequency domain methods usually use time-frequency analysis tools such as wavelet transform and Hilbert-Huang transform to reveal the energy distribution characteristics of faults and lightning disturbances. These methods can effectively distinguish between lightning disturbances and short-circuit faults because they focus on the spectral components of the signal rather than a single time domain indicator. Frequency domain features are less dependent on lightning parameters and transition resistance, so they have better adaptability and robustness. Summary of the invention

[0005] The purpose of the present invention is to provide a method for identifying lightning interference of flexible DC transmission lines based on instantaneous traveling wave power. The method identifies lightning interference according to the difference in frequency domain energy distribution of instantaneous traveling wave power, has high transition resistance capability, and has low sampling frequency requirements.

[0006] The technical solution adopted by the present invention is a method for identifying lightning interference of flexible direct current transmission lines based on instantaneous traveling wave power, which specifically includes the following steps:

[0007] Step 1: Calculate the line mode voltage reverse wave u b (k) and the line mode current reverse wave i b (k);

[0008] Step 2: Based on the calculation results of step 1, the high-frequency components u of the line-mode voltage reverse traveling wave are obtained through a digital filter. bh(k), low frequency component u bl (k); Line mode current reverse wave high frequency component i bh (k), low-frequency component i bl (k);

[0009] Step 3: Calculate the absolute value of the product of the voltage and current reverse wave high-frequency components to obtain the instantaneous traveling wave power high-frequency component P h (k); The instantaneous traveling wave power low-frequency component P is obtained by calculating the absolute value of the product of the voltage and current reverse traveling wave low-frequency components l (k);

[0010] Step 4: Calculate P h (k1), P l (k1) Ratio of the integral value within the time window of 1 ms after the faulty component is activated Determine whether lightning interference occurs.

[0011] The present invention is also characterized in that:

[0012] The specific process of step 1 is:

[0013] Step 1.1, after the protection start element is started, take 0.5ms before start and 1.0ms after start as the protection time window, read the voltage and current data in the data window, and read the positive voltage u at the protection installation location p (k), negative electrode voltage u n (k), positive electrode current i p (k), negative electrode current i n (k), respectively, and the average positive voltage u 10ms before the protection is started p0 , mean negative voltage u n0 , average positive current i p0 , mean negative electrode current i n0 Subtract, positive voltage fault component Δu p (k), negative pole voltage fault component Δu n (k), positive current fault component Δi p (k) and the negative current fault component Δi n (k), the calculation formula is shown in formula (1):

[0014]

[0015] Step 1.2: Calculate the line mode voltage fault component Δu1(k) and the line mode current fault component Δi1(k) within the time window using the following formula (2):

[0016]

[0017] Step 1.3, calculate the line mode voltage reverse wave u in the time window by the following formula (3): b (k):

[0018]

[0019] In the formula, Z c1 is the line mode wave impedance of the line;

[0020] Step 1.4, calculate the line mode current reverse wave i in the time window by the following formula (4): b (k):

[0021]

[0022] The specific process of step 2 is:

[0023] Step 2.1, construct the high-pass digital filter type, parameters and the low-pass digital filter type, parameters respectively;

[0024] Step 2.2, reverse the line mode voltage to u b (k) and the line mode current reverse wave i b (k) is substituted into the high-pass filter difference equation shown in equation (5), and u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. h [k-1], that is, the high-frequency component of the line-mode voltage reverse wave u bh (k), line mode current reverse wave high frequency component i bh (k); Reverse the line mode voltage traveling wave u b (k) and the line mode current reverse wave i b Substitute (k) into the differential equation of the low-pass filter shown in equation (5), and replace u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. l [k-1], that is, the low-frequency component u of the line-mode voltage reverse wave bl (k), line mode current reverse wave high frequency component i bl (k):

[0025]

[0026] Where: y h [k-1], y h [k-2], y h [k-3], y h [k-4], y h [k-5] is the output electrical quantity u calculated by the high-pass filter difference equation bh(k), i bh (k); y l [k-1], y l [k-2], y l [k-3], y l [k-4], y l [k-5] is the output electrical quantity u calculated by the low-pass filter difference equation bl (k), i bl (k); x[k], x[k-1], x[k–2], x[k–3], x[k–4], x[k-5] are the current and previous input electrical quantities u b (k), i b (k); k is the time domain sampling point.

[0027] The specific process of step 3 is:

[0028] Step 3.1: Calculate the absolute value of the product of the voltage and current reverse traveling wave high-frequency components from the time when the fault element starts to 1ms after starting by using formula (6) to obtain the instantaneous traveling wave power high-frequency component P h (k):

[0029] P h (k) = u bh (k) i bh (k) (6)

[0030] Step 3.2: Calculate the absolute value of the product of the voltage and current reverse traveling wave low-frequency components from the time when the fault element starts to 1ms after starting by using formula (7) to obtain the instantaneous traveling wave power low-frequency component P l (k):

[0031] P l (k) = u bl (k) i bl (k) (7).

[0032] The specific process of step 4 is:

[0033] Calculate P by formula (8) h (k1), P l (k1) The ratio between the integrated values ​​within the time window of 1 ms after the fault element is activated

[0034]

[0035] Where, 0≤k1≤N-1; N is the number of sampling points from the moment the faulty component starts to 1.0ms after starting;

[0036] like If When , it is judged as lightning interference.

[0037] The beneficial effect of the present invention is that the present invention identifies lightning interference based on the frequency domain energy distribution characteristics of the instantaneous traveling wave power of the single-ended quantity of the line. The method can be used in both a bounded flexible DC power grid and an unbounded flexible DC power grid, and the identification is rapid, has a strong ability to withstand transition resistance, and does not require a high sampling frequency. In the case of 0Ω, 500Ω transition resistance and at a sampling frequency of 50kHz, 25kHz, the lightning interference can still be well identified. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of a method for identifying lightning interference of flexible direct current transmission lines based on instantaneous traveling wave power of the present invention;

[0039] Figure 2 It is a simulation model diagram of a two-terminal true bipolar MMC flexible DC transmission system;

[0040] FIG3 (a) is a simulation verification stage, as shown in FIG3 , the instantaneous traveling wave power time domain waveform domain of the ground fault in the area at 250km of the bipolar flexible DC system with a transition resistance of 500Ω and the determination result of the flexible DC transmission line lightning interference identification method based on the instantaneous traveling wave power of the present invention;

[0041] FIG3(b) is a diagram of the frequency domain energy distribution ratio of the instantaneous traveling wave power time domain waveform of the bipolar flexible DC system at 250km in the area with an in-area ground fault and a transition resistance of 500Ω after wavelet decomposition in the simulation verification stage;

[0042] Figure 4 This is a simulation model diagram of a four-terminal MMC flexible DC transmission network;

[0043] Figure 5(a) is the simulation verification stage. Figure 4 The instantaneous traveling wave power time domain waveform domain of the lightning interference shielding failure in the four-terminal flexible DC power grid at 100km and the determination result of the lightning interference identification method of the flexible DC transmission line based on the instantaneous traveling wave power of the present invention;

[0044] Figure 5(b) is the simulation verification stage. Figure 4 The frequency domain energy distribution ratio diagram of the instantaneous traveling wave power time domain waveform of the lightning interference shielding failure in the four-terminal flexible DC power grid 100km away after wavelet decomposition;

[0045] Figure 6 This is a simulation model diagram of a four-terminal "mesh type" MMC flexible DC transmission network;

[0046] Figure 7(a) is the simulation verification stage. Figure 6The instantaneous traveling wave power time domain waveform domain of the four-terminal "mesh type" flexible DC system at 100km in the area for judging the lightning fault shielding failure and the judgment result of the flexible DC transmission line lightning interference identification method based on the instantaneous traveling wave power of the present invention;

[0047] Figure 7(b) is the simulation verification stage. Figure 6 The frequency domain energy distribution ratio of the instantaneous traveling wave power time domain waveform of the four-terminal "mesh-type" flexible DC system for lightning fault shielding judgment in the area 100km away after wavelet decomposition. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] The present invention is based on the method for identifying lightning interference in flexible DC transmission lines based on the frequency domain energy distribution of instantaneous traveling wave power. By analyzing the frequency domain characteristics of the traveling wave signal on the line after the lightning event occurs, the frequency domain energy distribution characteristics unique to lightning interference are extracted. Compared with the traditional time domain analysis method, frequency domain analysis can more comprehensively reflect the essential characteristics of lightning interference and effectively improve the recognition accuracy. In addition, the method can also achieve rapid response and real-time monitoring, significantly improving the reliability and safety of the flexible DC transmission system.

[0050] A lightning interference identification method for flexible DC transmission lines based on the energy distribution of instantaneous traveling wave power in frequency domain, such as Figure 1 As shown, the specific steps include:

[0051] Step 1: After the protection start element is started, take 0.5ms before start and 1.0ms after start as the protection time window, and read the voltage and current data within the time window. Calculate the positive voltage fault component Δu p (k), negative pole voltage fault component Δu n (k) and the negative current fault component Δi n (k), and then calculate the line mode voltage fault component Δu1(k) and line mode current fault component Δi1(k). Finally, the line mode voltage reverse wave u is calculated based on this. b (k), line mode current reverse wave i b (k); The specific process of step 1 is:

[0052] Step 1.1, after the protection start element is started, take 0.5ms before start and 1.0ms after start as the protection time window, and read the voltage and current data in the data window. Read the positive voltage u at the protection installation location p (k), negative electrode voltage u n (k), positive electrode current i p (k), negative electrode current i n(k), respectively, and the average positive voltage u 10ms before the protection is started p0 , negative electrode voltage average u n0 , average positive current i p0 , mean negative current i n0 Subtract, positive voltage fault component Δu p (k), negative pole voltage fault component Δu n (k), positive current fault component Δi p (k) and the negative current fault component Δi n (k), the calculation formula is shown in formula (1):

[0053]

[0054] Step 1.2, calculate the line mode voltage fault component Δu1(k) and the line mode current fault component Δi1(k) within the time window. The calculation formula is shown in formula (2):

[0055]

[0056] Step 1.3, calculate the line mode voltage reverse wave u in the time window b (k), the calculation formula is shown in formula (3):

[0057]

[0058] In the formula, Z c1 is the line mode wave impedance of the line.

[0059] Step 1.4, calculate the line mode current reverse wave i in the time window b (k), the calculation formula is shown in formula (4):

[0060]

[0061] In the formula, Z c1 is the line mode wave impedance of the line.

[0062] Step 2: Take the line mode voltage reverse wave u from step 1 b (k) is opposite to the line mode current traveling wave i b (k), the line mode voltage reverse wave high frequency component u is obtained through digital filter. bh (k), low frequency component u bl (k); Line mode current reverse wave high frequency component i bh (k), low-frequency component i bl (k); The specific process of step 2 is:

[0063] Step 2.1, according to the energy distribution of the instantaneous traveling wave power in the fault and interference, the energy distribution in the range of 0 to 1.5kHz is significantly different. Therefore, 0 to 1.5kHz is defined as the low frequency band, and above 1.5kHz is defined as the high frequency band. Construct the type and parameters of the high-pass digital filter: Chebyshev II high-pass filter, stopband cutoff frequency 1.5kHz, passband cutoff frequency 2.5kHz, stopband attenuation 30dB, passband fluctuation 1dB. Construct the type and parameters of the low-pass digital filter: Chebyshev II low-pass filter, stopband cutoff frequency 1.0kHz, passband cutoff frequency 1.5kHz, stopband attenuation 30dB, passband fluctuation 1dB.

[0064] Step 2.2, reverse the line mode voltage to u b (k) and the line mode current reverse wave i b (k) is substituted into the high-pass filter difference equation shown in equation (5), and u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. h [k-1], that is, the high-frequency component of the line-mode voltage reverse wave u bh (k), line mode current reverse wave high frequency component i bh (k); Reverse the line mode voltage traveling wave u b (k) and the line mode current reverse wave i b Substitute (k) into the differential equation of the low-pass filter shown in equation (5), and replace u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. l [k-1], that is, the low-frequency component u of the line-mode voltage reverse wave bl (k), line mode current reverse wave high frequency component i bl (k):

[0065]

[0066] Where: y h [k-1], y h [k-2], y h [k-3], y h [k-4], y h [k-5] is the output electrical quantity u calculated by the high-pass filter difference equation bh (k), i bh (k); y l [k-1], y l [k-2], y l [k-3], y l [k-4], y l[k-5] is the output electrical quantity u calculated by the low-pass filter difference equation bl (k), i bl (k); x[k], x[k-1], x[k–2], x[k–3], x[k–4], x[k-5] are the current and previous input electrical quantities u b (k), i b (k); k is the time domain sampling point.

[0067] Step 3: Calculate the absolute value of the product of the voltage and current reverse wave high-frequency components to obtain the instantaneous traveling wave power high-frequency component P h (k); The instantaneous traveling wave power low-frequency component P is obtained by calculating the absolute value of the product of the voltage and current reverse traveling wave low-frequency components l (k).

[0068] The specific process of step 3 is:

[0069] Step 3.1: Calculate the absolute value of the product of the voltage and current reverse traveling wave high-frequency components from the time when the fault element starts to 1ms after starting by using formula (6) to obtain the instantaneous traveling wave power high-frequency component P h (k):

[0070] P h (k) = u bh (k) i bh (k)(6)

[0071] Step 3.2: Calculate the absolute value of the product of the voltage and current reverse traveling wave low-frequency components from the time when the fault element starts to 1ms after starting by using formula (7) to obtain the instantaneous traveling wave power low-frequency component P l (k):

[0072] P l (k) = u bl (k) i bl (k)(7).

[0073] Step 4: Calculate P h (k1), P l (k1) Ratio of the integral value within the time window of 1 ms after the faulty component is activated The specific process of step 4 is:

[0074] Calculate P by formula (8) h (k1), P l (k1) The ratio between the integrated values ​​within the time window of 1 ms after the fault element is activated

[0075]

[0076] Where, 0≤k1≤N-1; N is the number of sampling points from the time the faulty component starts to 1.0ms after starting.

[0077] Step 5: If If When , it is judged as lightning interference.

[0078] The specific process of step 5 is:

[0079] like If When , it is judged as lightning interference. With threshold By contrast, as shown in formula (9), according to The relationship between the magnitude of the threshold value and the value of the lightning disturbance is used as the criterion for identifying lightning disturbances.

[0080]

[0081] The threshold value is selected based on the difference in the instantaneous traveling wave power frequency domain distribution when a fault occurs and when lightning strikes interfere, as well as the simulation test results.

[0082] As attached Figure 2 As shown in the figure, it is a simulation model diagram of a double-terminal flexible DC transmission system. In the figure, the current limiting reactor L=0.2H, MMC1 and MMC2 are modular converters, P1 and P2 are line boundary protection measurement points, f1, f2 and f3 are disturbance occurrence locations, the rated voltage of this system is ±500kV, the rated transmission capacity is 3000MVA, the total length of the transmission line is 500km, and the overhead line frequency variable parameter model is adopted. The line wave impedance is Z c0 =320Ω、Z c1 =260Ω. When simulating the system, the sampling frequency is 100kHz, and the 1.2 / 50μs standard lightning current model is used to simulate lightning strikes. The full text takes the line Line1, P1 measuring point as an example, and the fault distance is the distance from the fault point to the measuring point P1. Figure 1 The identification process is used to identify the ground fault.

[0083] Example 1

[0084] As shown in Figure 3(a), Figure 2 When a positive ground fault with a transition resistance of 500Ω occurs at 250 km from the protection measuring point P1 in the double-terminal flexible DC transmission system shown in the figure, the line mode voltage reverse wave simulation value measured at the protection measuring point is shown in the figure. After the protection element is started, the line mode voltage reverse wave data of the 50 sampling points before the start and the 100 sampling points after the start are read. Calculation The value is determined as a fault and the protection is activated. Figure 3(b) shows the frequency domain energy distribution bar graph of the instantaneous traveling wave power, which proves the correctness of the protection principle.

[0085] As attached Figure 4 As shown in the figure, it is a simulation model diagram of a four-terminal MMC flexible DC transmission network. In the figure, the current limiting reactor L = 0.2H, MMC1, MMC2, MMC3, MMC4 are modular converters, P1 and P2 are line boundary protection measurement points, f1 is the disturbance location, the rated voltage between MMC1 and MMC2 is ±500kV, the rated transmission capacity is 3000MVA, the total length of the transmission line is 207.9km, and the overhead line frequency variable parameter model is adopted. The line wave impedance is Z c0 =310Ω、Z c1 =250Ω. When simulating the system, the sampling frequency is 100kHz, and the 1.2 / 50μs standard lightning current model is used to simulate lightning strikes. The structure of the four-terminal flexible DC power grid is highly symmetrical. The full text takes Line 1, P1 measuring point as an example. The fault distance is the distance from the fault point to the measuring point P1. Figure 1 The identification process is used to identify lightning interference.

[0086] Example 2

[0087] As shown in Figure 5(a), Figure 4 The line mode voltage reverse wave simulation value measured at the protection measuring point when a lightning shielding failure occurs 100 km away from the protection installation in the four-terminal MMC flexible DC transmission network shown in the figure. After the protection element is started, the line mode voltage reverse wave data of the 50 sampling points before the start and the 100 sampling points after the start are read. Calculation The value is determined to be lightning interference, and the protection is turned on. Figure 5(b) shows the frequency domain energy distribution bar graph of the instantaneous traveling wave power, which proves the correctness of the protection principle.

[0088] As attached Figure 6 As shown in the figure, it is a simulation model diagram of a four-terminal "mesh type" MMC flexible DC transmission network. In the figure, the current limiting reactor L = 0.2H, MMC1, MMC2, MMC3, MMC4 are modular converters, P1 and P2 are line boundary protection measurement points, f1 is the disturbance location, the rated voltage between MMC1 and MMC2 is ±500kV, the rated transmission capacity is 3000MVA, the total length of the transmission line is 207.9km, and the overhead line frequency variable parameter model is adopted. The line wave impedance is Z c0 =310Ω、Z c1=250Ω. When simulating the system, the sampling frequency is 100kHz, and the 1.2 / 50μs standard lightning current model is used to simulate lightning strikes. The four-terminal "mesh-type" flexible DC power grid has a highly symmetrical structure. The full text takes Line 1, P1 measuring point as an example. The fault distance is the distance from the fault point to the measuring point P1. According to the attached Figure 1 The identification process is used to identify lightning faults.

[0089] Example 3

[0090] As shown in Figure 7(a), Figure 6 In the four-terminal "mesh-type" flexible direct current transmission system shown in the figure, when a ground fault occurs 100 km away from the protection installation, the line mode voltage reverse wave simulation value measured at the protection measurement point. After the protection element is started, the line mode voltage reverse wave data of the 50 sampling points before the start and the 100 sampling points after the start are read. Calculation The value is determined as a fault and the protection is activated. Figure 7(b) shows the frequency domain energy distribution bar graph of the instantaneous traveling wave power, which proves the correctness of the protection principle.

[0091] In order to fully verify the influence of fault distance, transition resistance, sampling frequency and system type on the protection method, ground fault and lightning interference simulations were carried out at the beginning, end and midpoint of the bipolar DC transmission system, four-terminal flexible DC grid and four-terminal "mesh type" flexible DC grid. The lightning interference identification method was verified based on the simulation results.

[0092] From Table 1, we can get the simulation data of different fault distances and transition resistances on the bipolar flexible DC transmission line. From the data in the time window, we can get: when lightning interference occurs, Less than 5; in the event of a ground fault, Greater than 5. Lightning interference can be identified at different fault distances.

[0093] Table 1 Simulation results of different fault distances and transition resistances

[0094]

[0095] From Table 2, we can get the simulation data of the four-terminal flexible DC power grid and the four-terminal "mesh type" flexible DC power grid. From the data in the time window, we can get: when lightning interference occurs, Less than 5; in the event of a ground fault, Greater than 5. Lightning interference can be identified under different transition resistance grounding faults.

[0096] Table 2 Simulation results of different system types

[0097]

[0098] From Table 3, we can get the simulation data of the four-terminal flexible DC power grid and the four-terminal "mesh type" flexible DC power grid under the condition of ground fault and lightning interference. From the data in the time window, we can get: when lightning interference occurs, Less than 5; in the event of lightning faults and ground faults, Greater than 5. The sampling frequency has no significant effect on the protection performance and can effectively identify lightning interference.

[0099] Table 3 Simulation results of different sampling frequencies

[0100]

[0101] The present invention utilizes that when a fault occurs, the low-frequency energy of the instantaneous traveling wave power accounts for a high proportion, while when lightning interference occurs, the high-frequency energy of the instantaneous traveling wave power accounts for a high proportion. The high and low frequency components of the instantaneous traveling wave power are extracted by a digital filter, and the proportion of the high and low frequency components is calculated accordingly. This method identifies lightning interference based on the difference in energy distribution in the frequency domain of the instantaneous traveling wave power. The frequency domain protection principle is combined with the time domain algorithm extraction, so that the method can be quickly identified, has a strong ability to withstand transition resistance, and does not require a high sampling frequency. At the same time, due to its lightning identification principle constructed by reverse traveling waves, it can be used in both bounded flexible DC power grids and unbounded flexible DC power grids.

Claims

1. A method for identifying lightning interference of flexible DC transmission lines based on instantaneous traveling wave power, characterized in that: The specific steps include: Step 1: Calculate the line mode voltage reverse wave u b (k) and the line mode current reverse wave i b (k); Step 2: Based on the calculation results of step 1, the high-frequency components u of the line-mode voltage reverse traveling wave are obtained through a digital filter. bh (k), low frequency component u bl (k); Line mode current reverse wave high frequency component i bh (k), low-frequency component i bl (k); Step 3: Calculate the absolute value of the product of the voltage and current reverse wave high-frequency components to obtain the instantaneous traveling wave power high-frequency component P h (k); The instantaneous traveling wave power low-frequency component P is obtained by calculating the absolute value of the product of the voltage and current reverse traveling wave low-frequency components. l (k); Step 4: Calculate P h (k1), P l (k1) Ratio of the integral value within the time window of 1 ms after the faulty component is activated Determine whether lightning interference occurs.

2. The method for identifying lightning disturbance of flexible direct current transmission lines based on instantaneous traveling wave power according to claim 1 is characterized in that: The specific process of step 1 is as follows: Step 1.1, after the protection start element is started, take 0.5ms before start and 1.0ms after start as the protection time window, read the voltage and current data in the data window, and read the positive voltage u at the protection installation location p (k), negative electrode voltage u n (k), positive electrode current i p (k), negative electrode current i n (k), respectively, and the average positive voltage u 10ms before the protection is started p0 , negative electrode voltage average u n0 , average positive current i p0 , mean negative electrode current i n0 Subtract, positive voltage fault component Δu p (k), negative pole voltage fault component Δu n (k), positive current fault component Δi p (k) and the negative current fault component Δi n (k), the calculation formula is shown in formula (1): Step 1.2: Calculate the line mode voltage fault component Δu1(k) and the line mode current fault component Δi1(k) within the time window using the following formula (2): Step 1.3, calculate the line mode voltage reverse wave u in the time window by the following formula (3): b (k): In the formula, Z c1 is the line mode wave impedance of the line; Step 1.4, calculate the line mode current reverse wave i in the time window by the following formula (4): b (k):

3. The method for identifying lightning disturbance of flexible DC transmission lines based on instantaneous traveling wave power according to claim 2 is characterized in that: The specific process of step 2 is: Step 2.1, construct the high-pass digital filter type, parameters and the low-pass digital filter type, parameters respectively; Step 2.2, reverse the line mode voltage to u b (k) and the line mode current reverse wave i b (k) is substituted into the high-pass filter difference equation shown in equation (5), and u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. h [k-1], that is, the high-frequency component of the line-mode voltage reverse wave u bh (k), line mode current reverse wave high frequency component i bh (k); Reverse the line mode voltage traveling wave u b (k) and the line mode current reverse wave i b Substitute (k) into the differential equation of the low-pass filter shown in equation (5), and replace u b (k) and i b (k) is used as the input electrical quantity x[k], and the output high-frequency electrical component y is obtained. l [k-1], that is, the low-frequency component u of the line-mode voltage reverse wave bl (k), line mode current reverse wave high frequency component i bl (k): Where: y h [k-1], y h [k-2], y h [k-3], y h [k-4], y h [k-5] is the output electrical quantity u calculated by the high-pass filter difference equation bh (k), i bh (k); y l [k-1], y l [k-2], y l [k-3], y l [k-4], y l [k-5] is the output electrical quantity u calculated by the low-pass filter difference equation bl (k), i bl (k); x[k], x[k-1], x[k–2], x[k–3], x[k–4], x[k-5] are the current and previous input electrical quantities u b (k), i b (k); k is the time domain sampling point.

4. The method for identifying lightning disturbance of flexible DC transmission lines based on instantaneous traveling wave power according to claim 3 is characterized in that: The specific process of step 3 is as follows: Step 3.1: Calculate the absolute value of the product of the voltage and current reverse traveling wave high-frequency components from the time when the fault element starts to 1ms after starting by using formula (6) to obtain the instantaneous traveling wave power high-frequency component P h (k): P h (k)=u bh (k)·i bh (k) (6) Step 3.2: Calculate the absolute value of the product of the voltage and current reverse traveling wave low-frequency components from the time when the fault element starts to 1ms after starting by using formula (7) to obtain the instantaneous traveling wave power low-frequency component P l (k): P l (k)=u bl (k)·i bl (k) (7)。 5. The method for identifying lightning disturbance of flexible DC transmission lines based on instantaneous traveling wave power according to claim 4 is characterized in that: The specific process of step 4 is as follows: Calculate P by formula (8) h (k1), P l (k1) The ratio between the integrated values ​​within the time window of 1 ms after the fault element is activated Where, 0≤k1≤N-1; N is the number of sampling points from the moment the faulty component starts to 1.0ms after starting; like If When , it is judged as lightning interference.

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