Distance protection method and system considering negative sequence suppression strategy of converters on two sides

Abstract

The invention provides a distance protection method and system in consideration of a negative sequence suppression strategy of converters on two sides. The method comprises the following steps: continuously acquiring voltage break variables, zero-sequence current and zero-sequence voltage at a protection installation position; the voltage break variable is used as a starting criterion of protection, the zero-sequence current and the zero-sequence voltage are used as action criteria of a zero-sequence direction element, the zero-sequence direction element is started when the voltage break variable is larger than a threshold value, and the fault direction is judged through the zero-sequence direction element; if the fault is judged to be a positive fault, judging whether a negative sequence suppression strategy of the converters on the two sides is successfully input or not by utilizing an outlet condition; if the exit condition is satisfied, combining the composite sequence network to obtain a fault point current; substituting the fault point current into the measurement impedance equation, constructing a binary equation set, and solving the binary equation set to obtain a fault distance; and if the fault distance is within the setting range, a tripping signal is triggered. Only local electric quantity is utilized, communication is not needed, and the defect that distance protection is greatly influenced by transition resistance is overcome.

Description

[0001] The present invention belongs to the field of line protection for new energy power stations transmitted through flexible DC systems, and specifically relates to a distance protection method considering the negative sequence suppression strategies of converters on both sides. Background Art

[0002] Flexible DC transmission technology is currently the main method for solving long-distance power transmission of large-scale renewable energy such as photovoltaic power. However, a double-ended weakly-fed system, which is a typical example, has characteristics such as 100% power electronics, weak support, and low immunity. When a fault occurs in a double-ended weakly-fed AC system, both systems at the two ends of the line are weakly-fed power sources, and the fault characteristics and protection requirements have undergone a fundamental transformation, resulting in weak anti-transition resistance ability and poor adaptability of distance protection. Summary of the Invention

[0003] The present invention provides a distance protection method and system considering the negative sequence suppression strategies of converters on both sides to improve the operating performance of distance protection.

[0004] The technical solution adopted by the present invention is as follows:

[0005] A distance protection method considering the negative sequence suppression strategies of converters on both sides includes the following steps:

[0006] Step 1: Continuously collect voltage mutation, zero-sequence current, and zero-sequence voltage at the protection installation location.

[0007] Step 2: Use the voltage mutation detected in Step 1 as the starting criterion for protection, and use the zero-sequence current and zero-sequence voltage as the operating criteria for the zero-sequence direction element. Compare the voltage mutation with a preset threshold value. When it is greater than the threshold value, start the zero-sequence direction element and use the zero-sequence direction element to determine the fault direction.

[0008] Step 3: If the zero-sequence direction element in Step 2 determines a forward fault, use the outlet condition to determine whether the negative sequence suppression strategies of the converters on both sides are successfully put into operation.

[0009] Step 4: If the outlet condition in Step 3 is satisfied, considering that the photovoltaic power station is equivalent to an open circuit under the negative sequence current suppression control strategy and the flexible DC power station is equivalent to a short circuit under the negative sequence voltage suppression control strategy, combine the composite sequence network to obtain the fault point current.

[0010] Step 5: Substitute the fault point current obtained in Step 4 into the measured impedance equation to construct a binary equation system with the fault distance and the transition resistance as unknowns, and solve the binary equation system to obtain the fault distance.

[0011] Step 6: Compare the fault distance calculated in Step 5 with the setting range. If it is within the setting range, trigger a tripping signal.

[0012] Further, Step 2 specifically includes:

[0013] Step 2.1: When the voltage dip detected at the protection terminal exceeds the set value, the protection is activated, as shown in the following formula: ΔU>ε, where ΔU is the voltage mutation and ε is the threshold value;

[0014] Step 2.2: The criterion for the zero-sequence directional element to determine a forward fault is:

[0015]

[0016] where is the zero-sequence voltage, is the zero-sequence current.

[0017] Furthermore, the threshold value ε = 0.1 kV.

[0018] Furthermore, Step 3 specifically includes:

[0019] After the control strategy for suppressing negative sequence on both sides is put into operation, the protection on the PV station side and the VSC-HVDC converter back-to-back system side can export the fault distance only when the negative sequence network on the PV station side is in an open state and the negative sequence network on the VSC-HVDC converter back-to-back system side is in a short-circuit state;

[0020] When the control strategy for suppressing negative sequence on both sides is successfully implemented, there is When a fault occurs within the zone, there is There is

[0021]

[0022] where is the negative sequence voltage on the PV station side, is the negative sequence current at the fault point, is the negative sequence impedance of the line, Z L is the positive sequence impedance of the line, C 0 is the zero-sequence current distribution coefficient, is the zero-sequence current at the fault point, is the zero-sequence current on the PV station side;

[0023] The phase angle range of the zero-sequence current distribution coefficient is affected by the zero-sequence impedance of the line and the zero-sequence impedance of the transformer, so the range taken is

[0024] -5.2° ≤ ∠C 0 ≤ 7.4°

[0025] Considering a certain margin, the export condition of the PV station is:

[0026]

[0027] When the control strategy for suppressing negative sequence on both sides is successfully implemented, there is

[0028]

[0029] Among them is the negative sequence current on the VSC side, is the zero sequence current on the VSC side, is the current distribution coefficient on the VSC side;

[0030] The outlet conditions of the VSC converter station are:

[0031] Furthermore, step 4 specifically includes:

[0032] Step 4.1: According to the composite sequence network during single-phase grounding fault, the fault point current on the VSC side is deduced as:

[0033]

[0034] Step 4.2: According to the composite sequence network during single-phase grounding fault, the fault point current on the PV side is deduced as:

[0035]

[0036] Furthermore, in step 5 the fault point current obtained in step 4 is substituted into the measured impedance equation to construct a binary equation system with the fault distance and the transition resistance as unknowns, specifically including:

[0037] Step 5.1: Substitute the fault point current into the measured impedance equation on the VSC side to form a binary linear equation system to obtain the fault distance α. The measured impedance equation system on the VSC side is:

[0038]

[0039] Step 5.2: Substitute the fault point current into the measured impedance equation on the PV side to form a binary linear equation system to obtain the fault distance α. The measured impedance equation system on the PV side is:

[0040]

[0041] where the subscript X is the imaginary part of the complex number, and the subscript R is the real part of the complex number, is the measured impedance on the VSC side, is the measured impedance on the PV side, is the negative sequence impedance for protecting the full length of the line, K is the zero sequence current compensation coefficient, R f is the transition resistance, is the setting impedance, and α is the fault distance.

[0042] Furthermore, the setting range of the fault distance in step 6 is:

[0043] 0 ≤ α ≤ 1.

[0045] A distance protection system based on a negative-sequence suppression strategy considering converters on both sides, comprising: a computer-readable storage medium and a processor;

[0046] The computer-readable storage medium is used for storing executable instructions;

[0047] The processor is used for reading the executable instructions stored in the computer-readable storage medium and executing the distance protection method based on the negative-sequence suppression strategy considering converters on both sides.

[0048] A non-transitory computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the distance protection method based on the negative-sequence suppression strategy considering converters on both sides is implemented.

[0049] The present invention solves the problems that in a double-ended weak-feed scenario, the distance protection has weak ability to resist transition resistance and poor protection adaptability. The present invention adopts a negative-sequence current suppression control strategy for the photovoltaic side, a negative-sequence voltage suppression control strategy for the VSC-HVDC side, and a negative-sequence suppression control strategy for both converters. By analyzing the characteristics that the negative-sequence network on the photovoltaic side presents an open circuit and the negative-sequence network on the VSC-HVDC side presents a short circuit in the composite sequence network, only the local electrical quantities are used to obtain the fault current and the additional impedance angle at the fault point. Further, by separately writing equations for the real part and the imaginary part of the measurement impedance expression, a binary linear equation system with the transition resistance and the fault distance as unknowns is obtained, and the fault distance is solved to judge internal and external faults. Compared with the prior art, the present invention solves the problem of solving the fault current in the double-ended weak-feed scenario, eliminates the influence of the transition resistance on the distance protection, and improves the adaptability of the distance protection in the double-ended weak-feed scenario. In addition, the proposed scheme of the present invention has high accuracy, so the protection range can cover the full length of the line. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a flow chart of the present invention;

[0051] Figure 2 is a composite sequence network for single-phase grounding fault under the negative-sequence suppression control strategy on both sides in the present invention;

[0052] Figure 3 is a schematic diagram of the negative-sequence current amplitudes at the protection installation points on the photovoltaic side and the VSC-HVDC side when a fault occurs at the midpoint of the line in the present invention;

[0053] Figure 4 is a schematic diagram of the negative-sequence voltage amplitudes at the protection installation points on the photovoltaic side and the VSC-HVDC side when a fault occurs at the midpoint of the line in the present invention;

[0054] Figure 5Schematic diagram for measuring the fault location under the condition of single-phase grounding fault at 20% of the line: (a) Metallic grounding; (b) Grounding through a 20 Ω transition resistor; (c) Grounding through a 50 Ω transition resistor; (d) Grounding through a 200 Ω transition resistor;

[0055] Figure 6 Schematic diagram for measuring the fault location under the condition of single-phase grounding fault at 40% of the line: (a) Metallic grounding; (b) Grounding through a 20 Ω transition resistor; (c) Grounding through a 50 Ω transition resistor; (d) Grounding through a 200 Ω transition resistor;

[0056] Figure 7 Schematic diagram for measuring the fault location under the condition of single-phase grounding fault at 60% of the line: (a) Metallic grounding; (b) Grounding through a 20 Ω transition resistor; (c) Grounding through a 50 Ω transition resistor; (d) Grounding through a 200 Ω transition resistor; Detailed implementation manners

[0057] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0058] As Figure 1 shown, the first aspect of the present invention provides a distance protection method considering the negative sequence suppression strategy of converters on both sides, including the following steps:

[0059] Step 1: Continuously collect the voltage mutation, zero-sequence current and zero-sequence voltage at the protection installation location;

[0060] Step 2: Use the voltage mutation detected in Step 1 as the starting criterion for the protection, and use the zero-sequence current and zero-sequence voltage as the action criteria for the zero-sequence direction element. Compare the voltage mutation with a preset threshold value. When it is greater than the threshold value, start the zero-sequence direction element, and use the zero-sequence direction element to judge the fault direction;

[0061] Step 2 specifically includes:

[0062] Step 2.1: When the magnitude of the voltage drop detected at the protection end exceeds the setting value, the protection starts, as shown in the following formula: ΔU>ε, where ΔU is the voltage mutation and ε is the threshold value, and the threshold value ε can be taken as 0.1 kV.

[0063] Step 2.2: The criterion for the zero-sequence direction element to judge a forward fault is:

[0064]

[0065] wherein is the zero-sequence voltage, is the zero-sequence current.

[0066] Step 3: If the zero-sequence direction element in Step 2 determines a forward fault, use the outlet condition to determine whether the negative-sequence suppression strategies of the converters on both sides are successfully put into operation; specifically, after the control strategies for negative-sequence suppression on both sides are put into operation, the protection on the photovoltaic power station side and the back-to-back converter side can only export the fault distance when the negative-sequence network on the photovoltaic power station side is in an open state and the negative-sequence network on the back-to-back converter side is in a short-circuit state;

[0067] When the negative-sequence suppression control strategies on both sides are successfully implemented, there is When a fault occurs within the zone, there is There is

[0068]

[0069] wherein is the negative-sequence voltage on the photovoltaic power station side, is the negative-sequence current at the fault point, is the negative-sequence impedance of the line, Z L is the positive-sequence impedance of the line, C 0 is the zero-sequence current distribution coefficient, is the zero-sequence current at the fault point, is the zero-sequence current on the photovoltaic power station side;

[0070] The phase angle range of the zero-sequence current distribution coefficient is affected by the zero-sequence impedance of the line and the zero-sequence impedance of the transformer, so the selected range is

[0071] -5.2° ≤ ∠C 0 ≤ 7.4°

[0072] Taking into account a certain margin, the outlet condition of the photovoltaic power station is:

[0073]

[0074] When the negative-sequence suppression control strategies on both sides are successfully implemented, there is

[0075]

[0076] wherein is the negative-sequence current on the back-to-back converter side, is the zero-sequence current on the back-to-back converter side, is the current distribution coefficient on the back-to-back converter side;

[0077] The outlet condition of the back-to-back converter station is:

[0078] Step 4: If the exit conditions in Step 3 are met, utilize that the photovoltaic power station is equivalent to an open circuit under the negative-sequence current suppression control strategy and the flexible DC power station is equivalent to a short circuit under the negative-sequence voltage suppression control strategy, and combine the composite sequence network to obtain the fault point current;

[0079] Step 4 specifically includes:

[0080] Step 4.1: Deduce that the fault point current on the flexible DC side is expressed as:

[0081]

[0082] Step 4.2: Deduce that the fault point current on the photovoltaic side is expressed as:

[0083]

[0084] Step 5: Substitute the fault point current obtained in Step 4 into the measured impedance equation to construct a binary equation system with the fault distance and the transition resistance as unknowns, and obtain the fault distance by solving the binary equation system;

[0085] Specifically, substitute the fault point current into the measured impedance equation on the flexible DC side to form a binary linear equation system to obtain the fault distance α. The measured impedance equation system on the flexible DC side is:

[0086]

[0087] Substitute the fault point current into the measured impedance equation on the photovoltaic side to form a binary linear equation system to obtain the fault distance α. The measured impedance equation system on the photovoltaic side is:

[0088]

[0089] Where the subscript X is the imaginary part of the complex number and the subscript R is the real part of the complex number, is the measured impedance on the flexible DC side, is the measured impedance on the photovoltaic side, is the negative-sequence impedance of the full length of the protected line, K is the zero-sequence current compensation coefficient, R f is the transition resistance, is the setting impedance, and α is the fault distance.

[0090] Step 6: Compare the fault distance calculated in Step 5 with the setting range. If it is within the setting range, trigger a tripping signal. The setting range of the fault distance is: 0 ≤ α ≤ 1.

[0091] Such as Figure 2As shown in the figure, this is the composite sequence network diagram for single-phase grounding faults under the negative sequence suppression strategy for converters on both sides in this embodiment. Specifically, when the photovoltaic power station adopts the negative sequence current suppression control strategy, the negative sequence current of the photovoltaic power station is almost zero, but the negative sequence current on the VSC side is very large. As Figure 3 shown, at this time, the negative sequence network on the photovoltaic side is equivalent to an open circuit. When the VSC converter adopts the negative sequence voltage suppression control strategy, the negative sequence voltage on the VSC side is almost zero, but the negative sequence voltage on the photovoltaic side is very large. At this time, the negative sequence network on the VSC side is equivalent to a short circuit, as Figure 4 shown.

[0092] A typical photovoltaic power plant grid-connected system model was built in the PSCAD / EMTDC electromagnetic transient simulation platform. The system base voltage is 525 kV and the base capacity is 2000 MW. The operating characteristics of the distance protection under negative sequence suppression on both sides in a double-ended weakly-fed system were verified. A single-phase grounding fault occurred at 20% of the total line length from the photovoltaic side (i.e., 80% of the total line length from the VSC side), and the transition resistances were 0.01 Ω, 20 Ω, 50 Ω, and 200 Ω respectively. Under these conditions, the measurement of the fault location is as Figure 5 shown. As can be seen from Figure 5 it, when the transition resistance is small, the fault location measurement curve is relatively stable and the measurement effect is accurate. As the transition resistance increases, the photovoltaic fault location measurement curve fluctuates to some extent. This is because when the transition resistance is large, the negative sequence voltage is very small, so it is difficult to accurately track and measure the negative sequence voltage. However, the measurement results are still within the operating range of the distance protection, and the distance protection can operate correctly.

[0093] A typical photovoltaic power plant grid-connected system model was built in the PSCAD / EMTDC electromagnetic transient simulation platform. The system base voltage is 525 kV and the base capacity is 2000 MW. The operating characteristics of the distance protection under negative sequence suppression on both sides in a double-ended weakly-fed system were verified. A single-phase grounding fault occurred at 40% of the total line length from the photovoltaic side (i.e., 60% of the total line length from the VSC side), and the transition resistances were 0.01 Ω, 20 Ω, 50 Ω, and 200 Ω respectively. Under these conditions, the measurement of the fault location is as Figure 6 shown. As can be seen from Figure 6 it, when the transition resistance is small, the fault location measurement curve is relatively stable and the measurement effect is accurate. As the transition resistance increases, the photovoltaic fault location measurement curve fluctuates to some extent. This is because when the transition resistance is large, the negative sequence voltage is very small, so it is difficult to accurately track and measure the negative sequence voltage. However, the measurement results are still within the operating range of the distance protection, and the distance protection can operate correctly.

[0094] A typical photovoltaic power plant grid-connected system model was built on the PSCAD / EMTDC electromagnetic transient simulation platform. The system base voltage is 525 kV and the base capacity is 2,000 MW. The operating characteristics of the distance protection in a double-ended weakly-fed system under negative-sequence suppression on both sides were verified. A single-phase ground fault occurred at 60% of the total line length from the photovoltaic side (i.e., 40% of the total line length from the flexible DC side), and the transition resistances were 0.01 Ω, 20 Ω, 50 Ω, and 200 Ω respectively. Under these conditions, the measurement of the fault location is as follows Figure 7 shown. It can be seen from Figure 7 that when the transition resistance is small, the fault location measurement curve is relatively stable and the measurement effect is accurate. As the transition resistance increases, the photovoltaic fault location measurement curve has certain fluctuations. This is because when the transition resistance is large, the negative-sequence voltage is very small, so it is difficult to accurately track and measure the negative-sequence voltage. However, the measurement result is still within the operating range of the distance protection, and the distance protection can operate correctly.

[0095] Compared with the prior art, the present invention can effectively improve the fault recognition ability in a double-ended weakly-fed system.

[0096] On the other hand, the present invention provides a distance protection system based on a negative-sequence suppression strategy considering converters on both sides, including: a computer-readable storage medium and a processor;

[0097] The computer-readable storage medium is used to store executable instructions;

[0098] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the distance protection method based on the negative-sequence suppression strategy considering converters on both sides described in the first aspect.

[0099] On the other hand, the present invention provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the distance protection method based on the negative-sequence suppression strategy considering converters on both sides described in the first aspect.

[0100] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented 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.

[0101] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing device generate means for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 in one or more blocks.

[0102] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 in one or more blocks.

[0103] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 in one or more blocks.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered by the protection scope of the claims of the present invention.

Claims

1. A distance protection method taking into account the negative sequence suppression strategy of converters on both sides, characterized in that: The steps include: Step 1: Continuously collect voltage mutation, zero-sequence current and zero-sequence voltage at the protection installation site; Step 2: The voltage mutation detected in step 1 is used as the starting criterion of the protection, and the zero-sequence current and zero-sequence voltage are used as the action criterion of the zero-sequence directional element. The voltage mutation is compared with the preset threshold value. When it is greater than the threshold value, the zero-sequence directional element is started, and the zero-sequence directional element is used to determine the fault direction; Step 3: If the zero-sequence directional element in step 2 is determined to be a forward fault, the exit conditions are used to determine whether the negative sequence suppression strategy of the converters on both sides is successfully put into use; Step 4: If the export conditions in step 3 are met, the PV station is equivalent to an open circuit under the negative sequence current suppression control strategy, and the flexible DC station is equivalent to a short circuit under the negative sequence voltage suppression control strategy, and the fault point current is obtained by combining the composite sequence network; Step 5: Substitute the fault point current obtained in step 4 into the measurement impedance equation, construct a binary equation group with the fault distance and transition resistance as unknown quantities, and obtain the fault distance by solving the binary equation group; Step 6: Compare the fault distance calculated in step 5 with the setting range. If it is within the setting range, a trip signal is triggered.

2. The distance protection method according to claim 1, characterized in that: Step 2 specifically includes: Step 2.1: When the protection terminal detects that the voltage drop exceeds the set value, the protection is activated, as shown in the following formula: ΔU>ε, where ΔU is the voltage mutation amount and ε is the threshold value; Step 2.2: The criterion for determining that the zero-sequence directional element is a forward fault is: in is the zero sequence voltage, is the zero sequence current.

3. The distance protection method according to claim 2 taking into account the negative sequence suppression strategy of converters on both sides is characterized in that: The threshold value ε=0.1 kV.

4. The distance protection method according to claim 1, characterized in that: Step 3 specifically includes: After the control strategy of negative sequence suppression on both sides is put into use, the negative sequence network on the photovoltaic station side needs to be in an open circuit state, and the negative sequence network on the back side of the flexible DC converter system needs to be in a short circuit state, so that the protection on the photovoltaic side and the flexible DC side can export the fault distance; When the negative sequence suppression control strategy on both sides is successfully implemented, there is When an internal fault occurs, there is a have in is the negative sequence voltage on the photovoltaic side, is the negative sequence current at the fault point, is the line negative sequence impedance, Z L is the line positive sequence impedance, C0 is the zero sequence current distribution coefficient, is the zero-sequence current at the fault point, is the zero-sequence current on the photovoltaic side; The phase angle range of the zero-sequence current distribution coefficient is affected by the zero-sequence impedance of the line and the zero-sequence impedance of the transformer, so the range is -5.2°≤∠C0≤7.4° Considering a certain margin, the export conditions of the photovoltaic station are: When the negative sequence suppression control strategy on both sides is successfully implemented, there is in is the negative sequence current on the flexible DC side, is the zero-sequence current on the flexible DC side, is the current distribution coefficient of the flexible DC side; The exit conditions of the flexible DC converter station are:

5. The distance protection method according to claim 4 taking into account the negative sequence suppression strategy of converters on both sides is characterized in that: Step 4 specifically includes: Step 4.1: According to the composite sequence network of a single-phase grounding fault, the fault point current on the flexible DC side is expressed as: Step 4.2: According to the composite sequence network of a single-phase grounding fault, the fault point current on the photovoltaic side is expressed as:

6. The distance protection method according to claim 5 taking into account the negative sequence suppression strategy of converters on both sides is characterized in that: In step 5, the fault point current obtained in step 4 is substituted into the measurement impedance equation to construct a binary equation group with the fault distance and transition resistance as unknown quantities, specifically including: Step 5.1: Substitute the fault point current into the measurement impedance equation of the flexible DC side to form a set of two-variable linear equations to obtain the fault distance α. The measurement impedance equation set of the flexible DC side is: Step 5.2: Substitute the fault point current into the measured impedance equation on the photovoltaic side to form a set of two-variable linear equations to obtain the fault distance α. The measured impedance equation set on the photovoltaic side is: The subscript X is the imaginary part of the complex number, and the subscript R is the real part of the complex number. Measure the impedance of the flexible straight side. Measure the impedance on the photovoltaic side, To protect the negative sequence impedance of the entire line, K is the zero sequence current compensation coefficient, R f is the transition resistance, is the setting impedance, and α is the fault distance.

7. The distance protection method according to claim 6 taking into account the negative sequence suppression strategy of converters on both sides is characterized in that: The setting range of the fault distance in step 6 is: 0≤α≤1。 8. A distance protection system based on a negative sequence suppression strategy taking into account converters on both sides, comprising: A computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium, and execute the distance protection method based on the negative sequence suppression strategy taking into account the converters on both sides according to any one of claims 1-7.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the distance protection method based on a negative sequence suppression strategy taking into account converters on both sides as described in any one of claims 1 to 7 is implemented.

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