A high-speed protection method suitable for wind-solar power source collection line

Abstract

The application discloses a high-speed protection method suitable for a wind-solar-storage power source collection line, first analyzes a discharge circuit of a filter capacitor of a wind-solar-storage power source converter and a capacitor of a flexible direct current (HVDC) converter sub-module from the perspective of capacitor discharge, analyzes and obtains a fault characteristic difference of the wind-solar-storage power source and the HVDC converter in an initial fault stage; according to the fault characteristic difference of the wind-solar-storage power source and the HVDC converter in the initial fault stage, uses a time-frequency energy coefficient to measure a fault characteristic difference of short-circuit currents on both sides of the line; according to an amplitude error existing in currents on both sides of the line in normal operation, combines the time-frequency energy coefficient, and proposes a protection action criterion suitable for high-speed protection of the wind-solar-storage power source collection line, so that high-speed protection of the wind-solar-storage power source collection line is realized. The method proves a time-frequency characteristic difference of the HVDC converter and the wind-solar-storage power source, when a fault occurs in the collection line, the protection can rapidly and reliably act within 5 ms, and has strong resistance to transition resistance and system noise.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wind-solar-storage power source collection lines, and particularly relates to a high-speed protection method suitable for wind-solar-storage power source collection lines. BACKGROUND

[0002] In China, wind-solar-storage power source resources and energy demand present reverse distribution, so the existing project mainly adopts the grid-connected mode of alternating current collection and high-voltage flexible direct current transmission. In the alternating current collection system of the modular multi-level converter station connected with wind-solar-storage power sources, both ends are power electronic power sources, and the fault current presents the non-power frequency characteristics of limited amplitude and controlled phase angle, which leads to the decline of the action performance of the traditional fundamental quantity protection and the possibility of refusal to act, so it is necessary to study the high-speed protection principle suitable for wind-solar-storage power source collection lines.

[0003] The wind-solar-storage power source collection line of the prior art lacks a fault analysis model of the converter equipment, so in engineering application, only the protection configuration of the traditional synchronous system can be followed, the ratio type current differential protection is used as the main protection, and the protection setting value is adjusted by using the simulation test result. However, due to the essential difference between the fault characteristics of the power electronic equipment and the synchronous machine power source, the protection action performance is declined. In view of the problem of the decline of the action performance of the differential protection, many scholars propose to improve the action performance of the differential protection by adjusting the differential protection setting value or increasing auxiliary criteria, however, in the wind-solar-storage power source collection system, both sides of the collection line are power electronic equipment, the proportion of the power frequency component of the short-circuit current is small, and the improvement scheme based on the power frequency quantity is difficult to fundamentally solve the problem; another method is to construct protection by using the model difference between the line area fault and the area fault, however, the method involves derivative calculation, and the action performance is easily disturbed by environmental noise and measurement error. Therefore, it is urgent to study the high-speed protection scheme suitable for the wind-solar-storage power source collection line. SUMMARY

[0004] The purpose of the present application is to provide a high-speed protection method suitable for wind-solar-storage power source collection lines, which explores the difference in time-frequency characteristics between the flexible direct current converter and the wind-solar-storage power source, and the protection can quickly and reliably act within 5ms when the collection line fails, and has strong resistance to transition resistance and system noise.

[0005] The purpose of the present application is achieved by the following technical scheme:

[0006] A high-speed protection method suitable for wind-solar-storage power source collection lines, the method comprises:

[0007] Step 1, analyze the discharge circuit of the filter capacitor of the wind-solar-storage power source converter and the sub-module capacitor of the flexible direct current converter from the perspective of capacitor discharge, analyze and obtain the difference in fault characteristics between the wind-solar-storage power source and the flexible direct current converter at the initial stage of the fault;

[0008] Step 2, according to the fault characteristics difference of the initial wind-solar-storage power and the flexible direct current converter, the time-frequency energy coefficient is used to measure the fault characteristics difference of the short-circuit current on both sides of the line;

[0009] Step 3, according to the amplitude error of the current on both sides of the line in normal operation, combining the time-frequency energy coefficient in step 2, a protection action criterion suitable for high-speed protection of the wind-solar-storage power collection line is proposed, and the high-speed protection of the wind-solar-storage power collection line is realized by using the protection action criterion.

[0010] It can be seen from the above technical solutions provided by the present application that the time-frequency characteristics difference of the flexible direct current converter and the wind-solar-storage power is verified, and when the fault occurs in the collection line, the protection can quickly and reliably act within 5ms, and has strong resistance to transition resistance and system noise. BRIEF DESCRIPTION OF DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0012] Figure 1 The flowchart of the high-speed protection method suitable for the wind-solar-storage power collection line provided by the embodiments of the present application is shown.

[0013] Figure 2 The discharge circuit diagram of the capacitor of the flexible direct current converter sub-module and the filter capacitor of the wind-solar-storage power converter is shown.

[0014] Figure 3 The system topology and fault position diagram of the wind-solar-storage power collection line of the example of the present application is shown.

[0015] Figure 4 The theoretical and simulation verification diagram of the discharge current of the capacitor of the flexible direct current converter sub-module and the filter capacitor of the wind-solar-storage power converter is shown.

[0016] Figure 5 The time-frequency diagram and the time-frequency energy coefficient diagram of the three-phase current when the midpoint of the collection line has a BC phase-to-phase fault. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0018] As Figure 1 shown is a high-speed protection method flow chart for wind-solar-storage power source collection line provided by the embodiment of the application, the method comprises:

[0019] Step 1, analyze the discharge circuit of the filter capacitor of the wind-solar-storage power source converter and the capacitor of the flexible direct current (DC) converter sub-module from the perspective of capacitor discharge, analyze and obtain the fault characteristic difference of the wind-solar-storage power source and the flexible DC converter in the initial stage of fault;

[0020] In this step, as Figure 2 shown is a discharge circuit diagram of the capacitor of the flexible DC converter sub-module and the filter capacitor of the wind-solar-storage power source converter, Figure 2 a is the discharge circuit of the capacitor of the flexible DC converter sub-module, Figure 2 b is the discharge circuit of the filter capacitor of the wind-solar-storage power source converter, according to the difference in charge and discharge of the capacitor of the flexible DC converter sub-module, it is deduced that there are three discharge circuits of the flexible DC converter; while the wind-solar-storage power source has only one discharge circuit of the filter capacitor; different capacitor discharge circuits can be equivalent to a second-order zero-input RLC series circuit, the difference lies in the equivalent parameters of the equivalent circuit, the discharge current of the second-order zero-input RLC series circuit is expressed as:

[0021] i=e -αt Acos(ωt+β)

[0022]

[0023] Wherein, i is the capacitor discharge current; α is the decay time constant; ω is the angular frequency; A is the capacitor current amplitude; β is the current phase angle; R, L and C are the equivalent electric group, inductance and capacitance parameters of the discharge circuit; t is the time; wherein the size of the decay time constant α and the angular frequency ω depends on the equivalent resistance, equivalent inductance and equivalent capacitance parameters of the input RLC series circuit; while the capacitor current amplitude A and the current phase angle β depend on the time decay constant, the angular frequency, the initial value of the capacitor voltage and the initial value of the inductance current; therefore the capacitor discharge current frequency depends on the resistance, capacitance and inductance parameters of the discharge circuit, which presents non-power frequency characteristics;

[0024] In the specific implementation, the equivalent inductance of the HVDC converter submodule capacitor discharge circuit is the sum of the converter bridge arm inductance and the line equivalent inductance, wherein the HVDC converter bridge arm inductance is generally 50-100 mH, and the line equivalent inductance is the sum of the inductance of the collection line converted to the high-voltage side through a transformer and the equivalent inductance of the converter transformer. The line equivalent inductance is relatively large, so the equivalent inductance of the HVDC converter submodule capacitor discharge circuit is very large, and the discharge frequency is relatively low. In combination with the actual parameters, the discharge current frequency of the HVDC converter submodule capacitor is 80-120 Hz. The equivalent inductance of the wind-solar-storage power converter filter capacitor discharge circuit is composed of the filter L2 inductance and the line inductance. In comparison with the large inductance of the HVDC converter bridge arm, the wind-solar-storage power converter filter L2 inductance is relatively small, and is approximately 0.1-3 mH. The line inductance converted to the low-voltage side of the wind-solar-storage power source is also very small. Therefore, the equivalent inductance of the wind-solar-storage power converter filter capacitor discharge circuit is very small, and the discharge frequency is very high. In combination with the actual parameters, the discharge current frequency of the wind-solar-storage power converter filter capacitor is 500-800 Hz.

[0025] In the initial stage of the fault, the fault current of the HVDC converter is completely determined by the submodule capacitor discharge current, so the fault current of the HVDC converter is:

[0026]

[0027] wherein i M is the HVDC converter fault current; α M1 , α M2 and α M3 are the decay time constants of the three discharge circuits; ω M1 , ω M2 and ω M3 are the current angular frequencies of the three discharge circuits; A M1 , A M2 and A M3 are the capacitor current amplitudes of the three discharge circuits; β M1 , β M2 and β M3 are the capacitor current phase angles of the three discharge circuits; and t is the time.

[0028] The fault current of the wind-solar-storage power source is superimposed by the control response current and the filter capacitor discharge current, and is specifically:

[0029]

[0030] wherein i W is the wind-solar-storage power source fault current; ω W1 is the phase-locked loop detected angular frequency. The maximum frequency offset range of the phase-locked loop in engineering is -10%-10%, so the frequency of the wind-solar-storage power converter control response short-circuit current is 45-55 Hz; ωW2 is the discharge frequency of the filter capacitor; β W1 and β W2 are the phase angles of the control response current and the filter capacitor discharge current, respectively; B W1 and B W2 are the amplitudes of the control response current and the filter capacitor discharge current, respectively; t is time;

[0031] Therefore, the differences in the fault characteristics of the wind-photovoltaic storage power source and the flexible DC converter in the initial stage of the fault are as follows:

[0032] The short-circuit currents of the flexible DC converter and the wind-photovoltaic storage power source both present non-power frequency characteristics. The fault current of the flexible DC converter is completely determined by the discharge of the sub-module capacitor, and the equivalent inductance of the discharge loop is very large, and the discharge frequency is about 80-120 Hz. The fault current of the wind-photovoltaic storage power source is composed of the converter control response current and the filter capacitor discharge current. The frequency of the converter control response current deviates from the power frequency angle frequency due to the influence of the dynamic response of the phase-locked loop, and is about 45-55 Hz. The equivalent inductance of the filter capacitor discharge loop is very small, and the discharge frequency is relatively high, about 500-800 Hz.

[0033] Step 2, according to the differences in the fault characteristics of the wind-photovoltaic storage power source and the flexible DC converter in the initial stage of the fault, the time-frequency energy coefficient is used to measure the differences in the fault characteristics of the short-circuit currents on both sides of the line;

[0034] In this step, according to the differences in the fault characteristics of the wind-photovoltaic storage power source and the flexible DC converter in the initial stage of the fault, the modulus time-frequency energy coefficient is proposed as follows:

[0035]

[0036] In the formula, K M is the modulus time-frequency energy coefficient of the short-circuit current; n and m represent time and frequency, respectively; X and Y are the wavelet complex matrices of the short-circuit currents on both sides of the line; x ij and y ij are complex numbers; || represents the modulus operation;

[0037] The modulus time-frequency energy coefficient K M measures the differences in the wavelet coefficient matrices of the short-circuit currents. When the line is in normal operation or an external fault, the waveforms of the short-circuit currents on both sides of the line are consistent, and the modulus time-frequency energy coefficient K M is theoretically infinite, but in actual application, due to the existence of system noise, the short-circuit currents on both sides of the line cannot be completely consistent, so the modulus time-frequency energy coefficient K M is very large but not infinite. When an internal fault occurs, the frequency spectrum of the short-circuit currents on both sides of the line is very different, and the modulus time-frequency energy coefficient K M is very small, even less than 0, so the modulus time-frequency energy coefficient KM The internal and external faults can be distinguished;

[0038] The proposed complex time-frequency energy coefficient is:

[0039]

[0040] In the formula, K F is the complex time-frequency energy coefficient of short-circuit current;

[0041] If the phase angle difference of the short-circuit currents on both sides of the line is greater than 90°, the complex time-frequency energy coefficient K F The phase angle information is considered, and the line time-frequency energy difference is well measured; when the phase angle difference of the short-circuit currents on both sides of the line is less than 90°, the modulus time-frequency energy coefficient K M The energy of the wavelet coefficient difference is taken after the modulus is taken, the fault phase time-frequency energy coefficient is smaller, and the protection effect is better, so the comprehensive modulus time-frequency energy coefficient K M and the complex time-frequency energy coefficient K F The protection is constructed, and the specific process is as follows:

[0042] K = min(K M , K F )

[0043] In the formula, K is the time-frequency energy coefficient of short-circuit current. The time-frequency energy coefficient K reflects the differences in the amplitude, phase angle and frequency of the short-circuit current, and the influence of the short-circuit current amplitude is reduced through the fractional operation, which is suitable for the scene that the short-circuit current amplitudes of the power electronic equipment power sources on both sides of the wind-solar-storage power source collection line are limited.

[0044] Step 3, according to the amplitude error existing in the currents on both sides of the line during normal operation, combining the time-frequency energy coefficient in step 2, a protection action criterion suitable for high-speed protection of the wind-solar-storage power source collection line is proposed, and the high-speed protection of the wind-solar-storage power source collection line is realized by using the protection action criterion.

[0045] In this step, during normal operation or external fault, the time-frequency energy coefficient K is very large, while during internal fault, the time-frequency energy coefficient K is very small, even lower than 0, so according to the amplitude error existing in the currents on both sides of the line during normal operation, the maximum is 10%, the protection setting value is obtained, specifically:

[0046] Suppose the short-circuit current time-domain signal is x = [x1, x2, …, x n-1 , x n ], considering the 10% amplitude error, the short-circuit current is x = [0.9x1, 0.9x2, …, 0.9x n-1 , 0.9x n ]; the wavelet transform is a linear transform, and the transform coefficient is M;

[0047] Considering the same error, the modulus time-frequency energy coefficient K M and the complex time-frequency energy coefficient K F are equal, the modulus time-frequency energy coefficient K M is taken as an example, and the specific process is as follows:

[0048]

[0049] Considering the amplitude error of 10%, the modulus time-frequency energy coefficient K M is 20; considering the margin coefficient of 0.9, the protection setting value is 18, and therefore the protection action criterion suitable for the wind-solar-storage power supply collection line high-speed protection is:

[0050] K < 18;

[0051] First, the time-frequency energy coefficient of the three-phase short-circuit current is calculated, if the time-frequency energy coefficient K of a phase is less than the protection setting value 18, it is determined that the phase is a fault phase; if the time-frequency energy coefficient K is greater than the protection setting value 18, it is determined that the phase is a non-fault phase;

[0052] Among them, if only one phase is determined as a fault phase, it is judged that the fault is a single-phase fault, and a single-phase tripping command is issued to cut off the fault phase, and the non-fault phase is normally operated; if two or three phases are determined as fault phases, it is judged that the fault is a two-phase or three-phase fault, and a three-phase tripping command is issued to directly trip the three phases.

[0053] It is worth noting that the contents not described in detail in the embodiments of the present application belong to the prior art known to those skilled in the art.

[0054] In order to more clearly show the technical solutions provided by the present application and the technical effects generated, the protection method provided by the embodiments of the present application is described in detail below, as shown in Figure 3 The system topology and fault position of the wind-solar-storage power supply collection line are shown in the example of the present application, the capacity of the flexible direct current converter is 1100MW, the DC line voltage level is 400kV; three wind-solar-storage power supplies with capacities of 400MW, 300MW and 400MW are collected through a 40km AC collection line. The fault line is the 220kV collection line of the 300MW wind-solar-storage power supply station, and the fault positions are the flexible side zone outside, the flexible side near end, the line midpoint, the wind-solar-storage power supply side near end and the wind-solar-storage power supply side zone outside, which are defined as K1, K2, K3, K4 and K5 respectively. The fault types are set as A-phase ground fault, BC two-phase interphase short circuit, BCG two-phase ground fault and ABC three-phase short circuit, which are named as AG, BC, BCG and ABC respectively. The protection sampling frequency is 10kHz, and the protection time window is 5ms before and after the fault.

[0055] As shown in Figure 4Theoretical and simulation verification diagram of discharge current of VSC sub-module capacitor and VSC filter capacitor of wind-solar-storage power supply is shown by Figure 4 It can be seen that the calculated value and the simulation value of the discharge current of the four loops are consistent in trend, the error between the simulation value and the calculated value is very small, the error of the three discharge loops of the VSC sub-module capacitor is within 10%, and the error of the discharge loop of the VSC filter capacitor of the wind-solar-storage power supply is slightly larger, because the harmonic of the simulation value of the discharge current of the filter capacitor is large, and the distortion is large within 3-5 ms after the fault, but the change trend is consistent with the calculated value, which verifies the correctness of the theoretical derivation. Figure 4 It can be seen that the discharge current frequency of the VSC sub-module capacitor is low, which is about 80-120 Hz through theoretical calculation, and the discharge frequency of the VSC filter capacitor of the wind-solar-storage power supply is high, which is about 500-800 Hz through theoretical calculation within 5 ms after the fault, so the difference in time-frequency characteristics of the VSC fault current and the VSC fault current of the wind-solar-storage power supply can be used to construct the high-speed protection principle.

[0056] As shown in Figure 5 The three-phase current time-frequency diagram and time-frequency energy coefficient diagram of the BC phase-to-phase fault at the midpoint of the collection line are shown by Figure 5 It can be seen that the non-fault phase (A phase) is a through current, the short-circuit currents on both sides of the line are consistent, the time-frequency Figure 1 characteristics of the non-fault phase are very high, and the protection does not act, and the time-frequency diagrams of the fault phases are very different, among which the main frequency of the VSC fault current is about 80-120 Hz, and the frequency of the VSC fault current of the wind-solar-storage power supply is mainly 45-55 Hz and 500-800 Hz, so the time-frequency characteristics of the VSC fault current and the VSC fault current of the wind-solar-storage power supply are very different, and the time-frequency energy coefficient is very small, and the protection reliably acts.

[0057] To further verify the effectiveness of the method described in the embodiment of the application, tests are carried out under different fault positions, different fault types, etc., and tables 1-3 give all simulation results. Table 1 gives the time-frequency energy coefficients of various types of faults in the area; table 2 gives the time-frequency energy coefficients of A phase grounding and BC phase grounding faults at the midpoint of the collection line under different transition resistances; and table 3 gives the time-frequency energy coefficients of faults at the midpoint of the collection line under different intensity system noise:

[0058] Table 1

[0059]

[0060]

[0061] Table 2

[0062]

[0063] Table 3

[0064]

[0065]

[0066] The simulation results show that the protection can reliably and quickly identify various types of intra-zone and extra-zone faults, and can reliably act when the fault resistance is large, and has high sensitivity. The time-frequency energy coefficient adopts a fractional structure to process the time-frequency characteristics of the fault current, thereby reducing the influence of noise, so that the influence of noise on the protection system is small, and the protection system can still reliably act under a system noise of 20 dB.

[0067] To sum up, the protection method described in the embodiments of the present application reveals the differences in time-frequency characteristics of the flexible DC converter and the wind-solar-storage power converter, and when a fault occurs in the collection line, the protection can quickly and reliably act within 5 ms, has strong resistance to transition resistance and system noise, and is not affected by the operating conditions (such as capacity, operating mode, etc.) of the wind-solar-storage power grid-connected system and the control strategy of the inverter, and can avoid the risk that the existing phasor three-terminal differential protection cannot act correctly.

[0068] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims. The information disclosed in the background section of the present application is merely intended to deepen the understanding of the overall background technology of the present application, and should not be regarded as acknowledging or implying in any form that the information constitutes the prior art known to those skilled in the art.

Claims

1. A high-speed protection method suitable for wind-solar power storage source collection lines, characterized in that, The method comprises: Step 1, analyzing the discharge circuit of the filter capacitor of the wind-solar-storage power converter and the capacitor of the flexible direct current (HVDC) converter sub-module from the perspective of capacitor discharge, and analyzing and obtaining the fault characteristic difference between the wind-solar-storage power converter and the HVDC converter in the initial stage of the fault; In the step 1, According to the difference in the charging and discharging of the capacitor of the HVDC converter sub-module, it is derived that the HVDC converter has three discharge circuits, while the wind-solar-storage power converter has only one discharge circuit of the filter capacitor; different capacitor discharge circuits can be equivalent to a second-order zero-input RLC series circuit, the difference lies in the equivalent parameters of the equivalent circuit, and the discharge current of the second-order zero-input RLC series circuit is expressed as: i = e -αt A cos (ωt + β) Wherein, i is the capacitor discharge current; alpha is the decay time constant; omega is the angular frequency; A is the capacitor current amplitude; beta is the current phase angle; R, L and C are the equivalent electric group, inductance and capacitance parameters of the discharge circuit respectively; t is the time; wherein the size of the decay time constant alpha and the angular frequency omega depends on the equivalent resistance, equivalent inductance and equivalent capacitance parameters of the input RLC series circuit; and the capacitor current amplitude A and the current phase angle beta depend on the time decay constant, the angular frequency, the initial value of the capacitor voltage and the initial value of the inductance current; therefore, the capacitor discharge current frequency depends on the resistance, capacitance and inductance parameters of the discharge circuit, and presents a non-power frequency characteristic; In the initial stage of the fault, the fault current of the HVDC converter is completely determined by the sub-module capacitor discharge current, so the fault current of the HVDC converter is: where i M is the fault current of the LCC; α M1 , α M2 , and α M3 are the decay time constants of the three discharge circuits; ω M1 , ω M2 , and ω M3 are the current angular frequencies of the three discharge circuits; A M1 , A M2 , and A M3 are the capacitance current amplitudes of the three discharge circuits; β M1 , β M2 , and β M3 are the capacitance current phase angles of the three discharge circuits; t is time; The fault current of the wind-solar-storage power converter is superimposed by the control response current and the filter capacitor discharge current, and is specifically: Wherein, i W is the fault current of the wind-solar-storage power supply; ω W1 is the angular frequency detected by the phase-locked loop, and the maximum frequency offset range of the phase-locked loop in engineering is-10% to 10%, so the frequency of the wind-solar-storage power supply converter control response to the short-circuit current is 45 to 55 Hz; ω W2 is the filter capacitor discharge frequency; β W1 and β W2 are the phase angles of the control response current and the filter capacitor discharge current, respectively; B W1 and B W2 are the amplitudes of the control response current and the filter capacitor discharge current, respectively; t is time; Therefore, in the initial stage of the fault, the fault characteristic difference between the wind-solar-storage power converter and the HVDC converter is: The short-circuit current of the HVDC converter and the wind-solar-storage power converter both presents a non-power frequency characteristic, wherein the fault current of the HVDC converter is completely determined by the sub-module capacitor discharge, and the equivalent inductance of the discharge circuit is large; the fault current of the wind-solar-storage power converter is composed of the converter control response current and the filter capacitor discharge current, wherein the converter control response current is affected by the dynamic response of the phase-locked loop, the current frequency will deviate from the power frequency angular frequency, the equivalent inductance of the filter capacitor discharge circuit is small, and the discharge frequency is high; Step 2, according to the fault characteristic difference between the wind-solar-storage power converter and the HVDC converter in the initial stage of the fault, the time-frequency energy coefficient is used to measure the fault characteristic difference of the short-circuit current on both sides of the line; Step 3, according to the amplitude error existing in the currents on both sides of the line in normal operation, combining the time-frequency energy coefficient in step 2, a protection action criterion suitable for the high-speed protection of the wind-solar-storage power converter collection line is proposed, and the high-speed protection of the wind-solar-storage power converter collection line is realized by using the protection action criterion.

2. The high-speed protection method for the wind-solar-storage power source collection line according to claim 1, characterized in that, In the step 2, according to the fault characteristic difference between the wind-solar-storage power converter and the HVDC converter in the initial stage of the fault, the modulus time-frequency energy coefficient is proposed as: where K M is the short circuit current modulus time-frequency energy coefficient; n and m represent time and frequency, respectively; X and Y are the short circuit current wavelet complex matrices on both sides of the line; x ij and y ij are complex numbers; || represents the modulus operation; The modulus time-frequency energy coefficient K M The modulus time-frequency energy coefficient K M Theoretically, it is infinite, but in actual application, due to the existence of system noise, the short-circuit currents on both sides of the line cannot be completely consistent, so the modulus time-frequency energy coefficient K M is very large but not infinite; and when the internal fault occurs, the short-circuit current spectrum on both sides of the line is quite different, so the modulus time-frequency energy coefficient K M is very small, even lower than 0, so the modulus time-frequency energy coefficient K M can be used to distinguish internal and external faults. The complex time-frequency energy coefficient is proposed as: In the formula, K F is the short-circuit current complex frequency energy coefficient; If the phase angle difference of short-circuit current on both sides of the line is greater than 90°, the complex time-frequency energy coefficient K F The phase angle information is considered, and the line time-frequency energy difference is well measured. When the phase angle difference of short-circuit current on both sides of the line is less than 90°, the modulus time-frequency energy coefficient K M The energy of the wavelet coefficient difference is taken first, and then the time-frequency energy coefficient of the fault phase is smaller, and the protection effect is better, so the comprehensive modulus time-frequency energy coefficient K M and the complex time-frequency energy coefficient K F The protection is constructed, and the specific is as follows: K = min(K M ,K F ) In the formula, K is the time-frequency energy coefficient of the short-circuit current, the time-frequency energy coefficient K reflects the difference in the amplitude, phase angle and frequency of the short-circuit current, and the influence of the short-circuit current amplitude is reduced through the fractional operation.

3. The high-speed protection method for the wind-solar-storage power source collection line according to claim 2, characterized in that, In the step 3, the time-frequency energy coefficient K is large in normal operation or out-zone fault, and is small in in-zone fault, even lower than 0, so the protection setting value is obtained according to the amplitude error of the current existing on both sides of the line in normal operation, specifically: Let short circuit current time domain signal be: x = [x1, x2, …, x n-1 , x n ], considering 10% amplitude error, short circuit current is: x = [0.9x1, 0.9x2, …, 0.9x n-1 , 0.9x n ]; wavelet transform is a linear transform, let transform coefficient be M; Considering the same error, the modulus time-frequency energy coefficient K M and the complex quantity time-frequency energy coefficient K F are equal, taking the modulus time-frequency energy coefficient K M as an example, the specific is as follows: Considering 10% of the amplitude error, the modulus time-frequency energy coefficient K M is 20; considering the margin coefficient of 0.9, the protection setting value is 18, and thus the protection action criterion suitable for the wind-solar-storage power supply collection line high-speed protection is: K＜18； First, the time-frequency energy coefficient of three-phase short-circuit current is calculated, if the time-frequency energy coefficient K of a phase is less than the protection setting value 18, the phase is determined as a fault phase; If the time-frequency energy coefficient K is greater than the protection setting value 18, it is determined as a non-fault phase; If only one phase is determined as a fault phase, the fault is judged as a single-phase fault, and a single-phase trip command is issued to remove the fault phase, and the non-fault phase is in normal operation; If two or three phases are determined as fault phases, the fault is judged as a two-phase or three-phase fault, and a three-phase trip command is issued to directly trip the three phases.

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