Asymmetric short-circuit current calculation method and system for large-scale new energy station

Abstract

The application provides an asymmetric short-circuit current calculation method and system for large-scale new energy stations, and the method comprises the following steps: judging a fault type and a fault phase; constructing a fault composite sequence network; calculating negative sequence impedance of each new energy station, and calculating positive sequence initial voltage of each new energy station; calculating output short-circuit current of each new energy station; obtaining a simplified equivalent circuit through circuit simplification according to the fault composite sequence network; calculating positive sequence voltage of each new energy station; comparing the positive sequence voltage of each new energy station with the positive sequence initial voltage, judging whether a voltage difference meets convergence accuracy, solving output negative sequence current and zero sequence current of each new energy station according to a circuit equation; and outputting output phase current of each new energy station. The application overcomes the influence of a converter control on a phase selection element, can effectively shorten the iteration number, avoids the process of solving matrix inverse operation by using a node voltage method, has good engineering practicability and precision, and can be applied to large-scale new energy stations.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation technology, specifically relating to a method and system for calculating asymmetrical short-circuit current in large-scale new energy power plants. Background Technology

[0002] Building a new power system with an increasing proportion of renewable energy is a crucial step towards achieving dual-carbon goals, making the development and utilization of wind and solar power technologies a research hotspot. As the grid-connected capacity of renewable energy sources continues to increase, their post-fault disconnection has a growing impact on the power grid. Renewable energy units should possess a certain low-voltage ride-through capability. During low-voltage ride-through, it is necessary not only to inject a certain amount of positive-sequence reactive current into the grid but also to absorb negative-sequence reactive current to suppress the rise of negative-sequence voltage. Currently, relay protection setting calculations generally do not consider renewable energy sources or estimate currents at 1.2-1.5 times the rated current. With the increasing proportion of renewable energy, its impact on setting calculations becomes more significant. Inaccurate single-unit and cluster characteristics will directly lead to large errors in protection settings, posing challenges to the safe and stable operation of the new power system.

[0003] Current methods for calculating grid short-circuit currents involving renewable energy sources mostly employ a single-machine multiplication method to represent a cluster of renewable energy plants of the same type, without considering the impact of negative-sequence current components. While the single-machine multiplication method is suitable for scenarios where the terminal voltages of various renewable energy units within the same renewable energy plant are approximately equal, its accuracy is limited for large-scale renewable energy clusters. Furthermore, the probability of asymmetrical faults in renewable energy transmission lines is high, and the impact of their negative-sequence current components on the overall grid short-circuit current cannot be underestimated. In summary, current methods for calculating grid short-circuit currents involving renewable energy sources do not consider the impact of negative-sequence current components on the overall grid short-circuit current, and their accuracy needs further improvement when applied to large-scale renewable energy plants. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for calculating asymmetrical short-circuit current in large-scale renewable energy power plants, in order to solve the problem that current methods for calculating grid short-circuit current that take into account renewable energy do not consider the impact of negative sequence current components on the short-circuit current of the entire grid, and that the equivalent accuracy needs to be further improved when applied to large-scale renewable energy power plants.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants, specifically including the following steps:

[0007] S1. Calculate the correlation coefficient of fault transient voltage between each phase based on the three-phase fault transient voltage of the new energy collection bus; determine the fault type and fault phase based on the correlation coefficient of fault transient voltage between each phase and the three-phase current.

[0008] S2. Based on the fault type and fault phase, for single-phase ground faults, the fault phase is used as the reference phase; for two-phase ground faults and two-phase inter-phase faults, the non-fault phase is used as the reference phase. Construct a fault composite sequence network: calculate the negative sequence impedance of each new energy power station, open the positive sequence network of the new energy power station, and calculate the positive sequence initial voltage of each new energy power station.

[0009] S3. Based on the calculation model of positive sequence short-circuit current of new energy power stations, substitute the positive sequence initial voltage of each new energy power station to calculate the output short-circuit current of each new energy power station.

[0010] S5. Based on the simplified equivalent circuit, calculate the positive sequence voltage of the new energy collection bus using the circuit equation, and calculate the positive sequence voltage of each new energy power station.

[0011] S6. Compare the positive sequence voltage of each new energy power station with the initial positive sequence voltage, and determine whether the voltage difference meets the convergence accuracy. If it does not meet the accuracy, substitute the current positive sequence voltage of each new energy power station into the positive sequence short-circuit current calculation model of the new energy power station, calculate the output short-circuit current of each new energy power station, and repeat steps S5 and S6 until the accuracy is met. Then, solve the output negative sequence current and zero sequence current of each new energy power station according to the circuit equation; output the output phase current of each new energy power station.

[0012] In some implementations, in S1, the expression for the three-phase fault transient voltage of the new energy collection bus is as follows: Formula (1) and Formula (2):

[0013] (1);

[0014] in, For each phase fault component voltage, , ;

[0015] The correlation coefficient of the transient voltage between phases is calculated using the following formula (2):

[0016] (2);

[0017] in, The correlation coefficient of transient voltage between phases during faults; When bc, ca, or ab, they represent the correlation coefficients of the fault transient voltages of phases BC, CA, or AB, respectively. For sampling points; The length of the data window.

[0018] Furthermore, in S1, if the following conditions are met... If it is determined to be a ground fault, The absolute values ​​are all greater than the set value. If the condition is met, it is determined to be a single-phase ground fault; otherwise, it is a two-phase ground fault. The fault was determined to be a phase-to-phase fault; among them, =0.8, , The calculation formula is as follows:

[0019] (3);

[0020] Among them, among them, For phase current fault components, , This is the zero-sequence current component. This represents the positive-sequence fault component current.

[0021] Furthermore, for single-phase ground faults, the faulty phase has a fault transient voltage correlation coefficient greater than the set value. The special phases; for a two-phase ground fault, the two phases corresponding to the minimum value of the fault transient voltage correlation coefficient are the fault phases; for a two-phase interphase fault, the two phases corresponding to the maximum value of the absolute value of the fault transient voltage correlation coefficient are the fault phases.

[0022] In some implementations, in S2, the negative sequence impedance of each new energy power station is calculated using the following formula (4):

[0023] (4);

[0024] in, Obtained from the low-voltage control strategy of new energy power stations, This is the negative sequence impedance from the mains power source to the fault point. For negative sequence short-circuit current in new energy power plants;

[0025] The positive-sequence initial voltage of each new energy power station is calculated according to the following formula (5):

[0026] (5);

[0027] in, This is the grid voltage. This is the positive-sequence impedance from the mains power source to the fault point. For transition resistance, , This is to determine the equivalent negative sequence impedance and zero sequence impedance of the entire network from the perspective of the fault point.

[0028] In some implementations, in S3, the calculation model for the positive sequence short-circuit current of the new energy power station is as follows:

[0029] (6);

[0030] in, 、 The first i Each unit in a new energy power station outputs short-circuit current with active and reactive components. N j For the first i The number of generating units in each new energy power station and These are expressions determined by the unit's low-voltage fault ride-through strategy.

[0031] In some implementations, in S4, the equivalent current source in the simplified equivalent circuit is... I eq for:

[0032] (7);

[0033] Simplified equivalent circuit equivalent impedance for:

[0034] (8);

[0035] in, The positive sequence impedance of the line from the new energy collection bus to the fault point.

[0036] In some implementations, in S5, the formula for calculating the positive sequence voltage of the new energy collection bus is:

[0037] (9);

[0038] The formula for calculating the positive sequence voltage of each new energy power station is as follows:

[0039] (10)

[0040] in, For the first i The positive sequence impedance of the line from the step-up bus to the collection bus of a new energy power station. For the first i The positive sequence impedance of the step-up transformer at a new energy power station For the first i The equivalent positive sequence impedance of the transformer box under the single-unit multiplication model of a new energy power station.

[0041] In some implementations, in S6, the following formula (12) is used to determine whether the voltage difference meets the convergence accuracy:

[0042] (11);

[0043] in, and These are the current and the previously calculated number of... i Positive sequence voltage of a new energy power station. For convergence accuracy.

[0044] Each new energy power station outputs negative sequence current The calculation formula is:

[0045] (12);

[0046] in, .

[0047] The formula for calculating the zero-sequence current output of each new energy power station is as follows:

[0048] (13);

[0049] in, To output zero-sequence current, .

[0050] Output phase current of each new energy power station for:

[0051] (14);

[0052] in, .

[0053] This invention also provides an asymmetrical short-circuit current calculation system for large-scale renewable energy power plants. The system includes a fault phase selection module, an initial voltage calculation module, a short-circuit current calculation module, and a short-circuit current output module, wherein:

[0054] Therefore, the phase selection module is used to calculate the correlation coefficient of the fault transient voltage between each phase based on the three-phase fault transient voltage of the new energy collection bus, and to determine the fault type and fault phase based on the correlation coefficient and the three-phase current;

[0055] The initial voltage calculation module is used to construct a fault composite sequence network based on the fault type and fault phase, and calculate the positive sequence initial voltage of each new energy power station.

[0056] The short-circuit current calculation module is used to calculate the output short-circuit current of each new energy power station by substituting the positive-sequence initial voltage of each new energy power station into the positive-sequence short-circuit current calculation model. The Thevenin circuit containing the voltage source is equivalent to the Norton equivalent circuit. After simplifying the circuit, the positive-sequence voltage of the new energy bus and the positive-sequence voltage of each new energy power station are calculated iteratively using the circuit equations until the convergence accuracy is met. Based on the converged positive-sequence voltage, the output negative-sequence current and zero-sequence current of each new energy power station are solved by combining the circuit equations.

[0057] The short-circuit current output module is used to synthesize and output the output phase current of each new energy power station based on the calculated positive-sequence, negative-sequence, and zero-sequence currents.

[0058] Compared with the prior art, the present invention provides a method and system for calculating asymmetrical short-circuit current in large-scale new energy power plants, which has the following beneficial technical effects.

[0059] This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants, specifically including the following steps: S1. Calculate the correlation coefficient of fault transient voltage between each phase based on the three-phase fault transient voltage of the renewable energy collection bus; determine the fault type and fault phase based on the correlation coefficient of fault transient voltage between each phase and the three-phase current; S2. Based on the fault type and fault phase, for single-phase ground faults, use the fault phase as the reference phase; for two-phase ground faults and two-phase inter-phase faults, use the non-faulty phase as the reference phase, construct a fault composite sequence network; calculate the negative sequence impedance of each renewable energy power plant, open the positive sequence network of the renewable energy power plant, and calculate the positive sequence initial voltage of each renewable energy power plant; S3. Substitute the positive sequence initial voltage of each renewable energy power plant into the positive sequence short-circuit current calculation model of the renewable energy power plant. Calculate the output short-circuit current of each new energy power station; S4, based on the fault composite sequence network, the Thevenin circuit containing the voltage source is equivalent to the Norton equivalent circuit, and after circuit simplification, a simplified equivalent circuit is obtained; based on the simplified equivalent circuit, the positive sequence voltage of the new energy collection bus is calculated using the circuit equation, and the positive sequence voltage of each new energy power station is calculated; S5, compare the positive sequence voltage of each new energy power station with the initial positive sequence voltage, and determine whether the voltage difference meets the convergence accuracy. If not, substitute the current positive sequence voltage of each new energy power station into the calculation model of the positive sequence short-circuit current of the new energy power station, calculate the output short-circuit current of each new energy power station, and repeat steps S7 and S8 until the accuracy is met. Then, solve the output negative sequence current and zero sequence current of each new energy power station according to the circuit equation; output the output phase current of each new energy power station. Based on the above, this invention first realizes the judgment of fault type and fault phase in a short time through the transient voltage characteristics of three-phase faults, overcoming the influence of converter control on phase selection elements. Next, the initial voltage of each renewable energy power station is calculated based on the fault type and fault phase, effectively shortening the number of iterations and saving computational costs. Then, the output short-circuit current of each renewable energy power station is calculated using the short-circuit current calculation model. Furthermore, the fault composite sequence network is simplified based on the equivalent source theorem, avoiding the matrix inverse operation process of the nodal voltage method. This allows for rapid calculation of the voltage of each renewable energy power station based on the circuit equations until the voltages converge. Finally, expressions for the output negative-sequence current and zero-sequence current of each renewable energy power station are given, used to synthesize the output phase current of each renewable energy power station, completing the asymmetrical short-circuit current calculation process applicable to large-scale renewable energy power stations. The asymmetrical short-circuit current calculation method and system provided by this invention have good engineering practicality and accuracy, and can be applied to the practical calculation of asymmetrical short-circuit current in large-scale renewable energy power stations. Attached Figure Description

[0060] The accompanying drawings are provided to further understand the invention and constitute a part of this invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0061] Figure 1This is a flowchart illustrating the method for calculating asymmetrical short-circuit current in a large-scale renewable energy power plant according to the present invention.

[0062] Figure 2 This is a schematic diagram of the system model structure of an asymmetric short-circuit current calculation method for large-scale new energy power plants according to the present invention.

[0063] Figure 3 This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants and a power grid topology in the system containing large-scale renewable energy power plants.

[0064] Figure 4 This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants and a schematic diagram of a single-phase grounding fault circuit for calculating the positive sequence initial voltage of each renewable energy power plant in the system.

[0065] Figure 5 This is a schematic diagram of a two-phase fault circuit for calculating the positive sequence initial voltage of each new energy power station, which is a method for calculating the asymmetrical short-circuit current of a large-scale new energy power station according to the present invention.

[0066] Figure 6 This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants and a schematic diagram of a two-phase ground fault circuit for calculating the positive sequence initial voltage of each renewable energy power plant in the system.

[0067] Figure 7 This is a schematic diagram of a method for calculating asymmetrical short-circuit current in a large-scale renewable energy power plant and a composite sequence network for single-phase grounding faults in the system, as described in this invention.

[0068] Figure 8 This invention presents a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants and a schematic diagram of a composite sequence network for two-phase faults in the system.

[0069] Figure 9 This is a schematic diagram of a method for calculating asymmetrical short-circuit current in a large-scale new energy power plant and a composite sequence network for two-phase grounding faults in the system, as described in this invention.

[0070] Figure 10 This invention provides a method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants and a simplified equivalent circuit of composite sequence networks for different fault types in the system. Detailed Implementation

[0071] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0072] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0073] This invention provides a practical method for calculating the steady-state fault current of large-scale direct-drive wind farms. As the fault ride-through strategy of direct-drive wind farms reveals, the short-circuit current level is influenced by two factors: the voltage drop caused by the fault and the power output before the fault. The short-circuit current exhibits nonlinear controlled characteristics. For wind farms located close to each other with small electrical distances between turbines, the differences in wind speed and terminal voltage drop are minimal. Therefore, the short-circuit current provided by each direct-drive wind turbine in the same wind farm is approximately equal. Multiplying by a single turbine is quick and simple, and can be used to calculate the short-circuit current of the same wind farm. However, different wind farms exhibit significant differences in short-circuit current due to variations in geographical location and wind speed. Therefore, grouping and equalization are used to calculate the short-circuit current of multiple wind farms.

[0074] In some embodiments, such as Figure 1 and Figure 3 As shown, the method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants according to the present invention includes the following steps:

[0075] S1. Calculate the correlation coefficient of the inter-phase fault transient voltage based on the three-phase fault transient voltage of the new energy collection bus. ;

[0076] S2. Based on the correlation coefficient of the transient voltage between each phase fault. And the three-phase current, to determine the fault type;

[0077] S3. Based on the correlation coefficient of the transient voltage between each phase fault. Determine the faulty phase;

[0078] like Figure 4 , Figure 5 and Figure 6 As shown, Figure 4 , Figure 5 and Figure 6 These are single-phase ground fault, two-phase fault, and two-phase ground fault, respectively; among them, Z 1 represents the impedance from the mains power source to the fault point. Z l The line impedance from the new energy collection bus to the fault point. Z lj For the first j The line impedance from the step-up bus to the collection bus of a new energy power station. Z thj The impedance of the step-up transformer. Z tlj The equivalent impedance of the transformer box under the single-machine multiplication model.

[0079] S4. Based on the fault type and fault phase, for single-phase ground faults, the fault phase is used as the reference phase; for two-phase ground faults and two-phase inter-phase faults, the non-faulty phase is used as the reference phase, constructing a fault composite sequence network: (The...) i Negative sequence impedance of a new energy power station The voltage is obtained from the low-voltage ride-through negative sequence control strategy. The positive sequence network of the renewable energy power station is left open, and the initial positive sequence voltage of each renewable energy power station is calculated. ;

[0080] S5. Based on the calculation model of the positive sequence short-circuit current of new energy power plants, substitute the initial positive sequence voltage of each new energy power plant. Calculate the output short-circuit current of each new energy power station. ;

[0081] like Figure 7 , Figure 8 and Figure 9 As shown, Figure 7 , Figure 8 and Figure 9 These are schematic diagrams of composite sequence networks for different fault types, namely single-phase ground fault, two-phase fault, and two-phase ground fault.

[0082] like Figure 10 As shown in Figure S6, based on the composite sequence network of different fault types, the Thevenin circuit containing the voltage source is equivalent to the Norton equivalent circuit, and after circuit simplification, a simplified equivalent circuit is obtained.

[0083] S7. Based on the simplified equivalent circuit, first calculate the positive sequence voltage of the new energy collection bus using the circuit equations. Then calculate the positive sequence voltage of each new energy power station. ;

[0084] S8. Compare the current positive sequence voltage of each new energy power station. With the positive sequence initial voltage of each new energy power station Determine if the voltage difference meets the convergence accuracy requirement. If not, adjust the current positive sequence voltage of each new energy power station. Substitute the positive sequence short-circuit current calculation model of the new energy power station into the calculation model, calculate the output short-circuit current of each new energy power station, repeat steps S7 and S8 until the condition is met, and then proceed to S9.

[0085] S9. Solve for the output negative sequence current of each renewable energy power station based on the circuit equations. and zero-sequence current ;

[0086] S10, Output phase current of each new energy power station .

[0087] As a specific implementation method, in S1 of the asymmetrical short-circuit current calculation method of the present invention, the expression for the fault transient voltage of the new energy collection bus is:

[0088] , (1);

[0089] in, For each phase fault component voltage, .

[0090] The formula for the correlation coefficient is:

[0091] (2);

[0092] in, The correlation coefficient between the transient voltages of each phase fault is given. For example, bc, ca, or ab. This represents the correlation coefficient between the fault transient voltages of phase B and phase C; n For sampling points; N The data window length is set to 5ms for calculation.

[0093] As a specific implementation method, in S2, the asymmetrical short-circuit current calculation method of the present invention, if the following conditions are met... If the correlation coefficient is determined to be a ground fault, then... The absolute values ​​are all greater than the set value. If the condition is met, it is determined to be a single-phase ground fault; otherwise, it is a two-phase ground fault. This was determined to be a phase-to-phase fault. =0.8, , for:

[0094] (3);

[0095] , This refers to the phase current fault component; This is the zero-sequence current component; This represents the positive-sequence fault component current.

[0096] Specifically, in step S3, for a single-phase ground fault, the faulty phase has a correlation coefficient greater than 1. The special phases; for a two-phase ground fault, the two phases corresponding to the minimum value of the correlation coefficient are the faulty phases; for a two-phase interphase fault, the two phases corresponding to the maximum value of the absolute value of the correlation coefficient are the faulty phases.

[0097] As a specific implementation method, in S4 of the asymmetric short-circuit current calculation method of the present invention, the negative sequence impedance of each new energy power station... Z i The calculation formula is:

[0098] (4);

[0099] in, Obtained from the low-voltage control strategy of new energy power stations, This is the negative sequence impedance from the mains power source to the fault point. This refers to the negative sequence short-circuit current of new energy power plants.

[0100] Positive sequence initial voltage of each new energy power station for:

[0101] (5);

[0102] in, U sys This is the grid voltage. This is the positive-sequence impedance from the mains power source to the fault point. R f For transition resistance, , This is to determine the equivalent negative sequence impedance and zero sequence impedance of the entire network from the perspective of the fault point.

[0103] As a specific implementation method, in S5 of the asymmetric short-circuit current calculation method of the present invention, the positive sequence short-circuit current calculation model for new energy power plants is as follows:

[0104] (6);

[0105] in, 、 The first iEach unit in a new energy power station outputs short-circuit current with active and reactive components. N j For the first i The number of generating units in each new energy power station and These are expressions determined by the unit's low-voltage fault ride-through strategy.

[0106] As a specific implementation method, in S6, the asymmetric short-circuit current calculation method of the present invention simplifies the equivalent current source in the equivalent circuit. I eq for:

[0107] (7);

[0108] Simplified equivalent circuit equivalent impedance Z eq for:

[0109] (8);

[0110] in, The positive sequence impedance of the line from the new energy collection bus to the fault point.

[0111] In a specific implementation method, the asymmetrical short-circuit current calculation method of the present invention includes, in S7, the positive sequence voltage of the new energy collection bus. The calculation formula is:

[0112] (9);

[0113] Positive sequence voltage of each new energy power station The calculation formula is:

[0114] (10);

[0115] in, For the first i The positive sequence impedance of the line from the step-up bus to the collection bus of a new energy power station. For the first i The positive sequence impedance of the step-up transformer at a new energy power station For the first i The equivalent positive sequence impedance of the transformer box under the single-unit multiplication model of a new energy power station.

[0116] As a specific implementation method, the convergence condition in S8 of the asymmetric short-circuit current calculation method of the present invention is:

[0117] (11);

[0118] in, and These are the current and the previously calculated number of... i Positive sequence voltage of a new energy power station. For convergence accuracy.

[0119] As a specific implementation method, in S9 of the asymmetric short-circuit current calculation method of the present invention, each new energy power station outputs negative sequence current. The calculation formula is:

[0120] (12);

[0121] in, .

[0122] The formula for calculating the zero-sequence current output of each new energy power station is as follows:

[0123] (13);

[0124] in, .

[0125] As a specific implementation method, in S10 of the asymmetric short-circuit current calculation method of the present invention, the output phase current of each new energy power station is... for:

[0126] (14);

[0127] in, .

[0128] like Figure 2 As shown, the present invention also provides an asymmetrical short-circuit current calculation system for large-scale renewable energy power plants. The system includes a fault phase selection module, an initial voltage calculation module, a short-circuit current calculation module, and a short-circuit current output module, wherein:

[0129] The fault phase selection module is used to determine the fault type and fault phase based on the transient voltage characteristics of a three-phase fault.

[0130] The initial voltage calculation module is used to calculate the initial voltage of each new energy power station based on the faulty phase;

[0131] The short-circuit current calculation module is used to solve the voltage of each new energy power station according to the circuit method, iterating until the voltage of each new energy power station converges, and outputting the output short-circuit current of each new energy power station from the short-circuit current calculation model of the new energy power station.

[0132] The short-circuit current output module is used to synthesize and output the phase current of each new energy power station.

[0133] This invention relates to a method and system for calculating asymmetrical short-circuit current in large-scale renewable energy power plants. It determines the fault type and faulty phase based on the transient voltage characteristics of a three-phase fault. Then, it calculates the initial voltage of each renewable energy power plant based on the fault type and faulty phase. Next, it calculates the output short-circuit current of each renewable energy power plant using a short-circuit current calculation model. Finally, it calculates the voltage of each renewable energy power plant based on circuit equations until the voltages of all renewable energy power plants converge, thus completing the asymmetrical short-circuit current calculation process applicable to large-scale renewable energy power plants. It is suitable for large-scale renewable energy power plants, has good calculation accuracy, and has certain practical significance.

[0134] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Those skilled in the art can readily implement the present invention according to the description and above. However, any modifications, alterations, or variations made by those skilled in the art without departing from the scope of the present invention, based on the disclosed technical content, are equivalent embodiments of the present invention. Furthermore, any equivalent changes, alterations, or variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants, characterized in that, Includes the following steps: S1. Calculate the correlation coefficient of fault transient voltage between each phase based on the three-phase fault transient voltage of the new energy collection bus; determine the fault type and fault phase based on the correlation coefficient of fault transient voltage between each phase and the three-phase current. The expressions for the transient voltage of the three-phase fault at the new energy collection bus are as follows: (1) and (2): （1）； in, For each phase fault component voltage, , ; The correlation coefficient of the transient voltage between phases is calculated using the following formula (2): （2）； in, The correlation coefficient of transient voltage between phases during faults; When bc, ca, or ab, they represent the correlation coefficients of the fault transient voltages of phases BC, CA, or AB, respectively. For sampling points; To set the length of the data window; If satisfied If it is determined to be a ground fault, The absolute values ​​are all greater than the set value. If the condition is met, it is determined to be a single-phase ground fault; otherwise, it is a two-phase ground fault. The fault was determined to be a phase-to-phase fault; among them, =0.8, , The calculation formula is as follows: （3）； in, For phase current fault components, , This is the zero-sequence current component. This represents the positive-sequence fault component current. S2. Based on the fault type and fault phase, for single-phase ground faults, the fault phase is used as the reference phase; for two-phase ground faults and two-phase inter-phase faults, the non-fault phase is used as the reference phase. Construct a fault composite sequence network: calculate the negative sequence impedance of each new energy power station, open the positive sequence network of the new energy power station, and calculate the positive sequence initial voltage of each new energy power station. The negative sequence impedance of each new energy power station is calculated using formula (4): （4）； in, Obtained from the low-voltage control strategy of new energy power stations, This is the negative sequence impedance from the mains power source to the fault point. For negative sequence short-circuit current in new energy power plants; The positive-sequence initial voltage of each new energy power station is calculated according to the following formula (5): （5）； in, This is the grid voltage. This is the positive-sequence impedance from the mains power source to the fault point. For transition resistance, , To determine the equivalent negative-sequence impedance and zero-sequence impedance of the entire network from the perspective of the fault point; S3. Based on the calculation model of positive sequence short-circuit current of new energy power stations, substitute the positive sequence initial voltage of each new energy power station to calculate the output short-circuit current of each new energy power station. S4. Based on the fault composite sequence network, the Thevenin circuit containing the voltage source is equivalent to the Norton equivalent circuit, and after circuit simplification, a simplified equivalent circuit is obtained. S5. Based on the simplified equivalent circuit, calculate the positive sequence voltage of the new energy collection bus using the circuit equation, and calculate the positive sequence voltage of each new energy power station. The formula for calculating the positive sequence voltage of the new energy collection bus is: （9）； The formula for calculating the positive sequence voltage of each new energy power station is as follows: （10）； in, For the first i The positive sequence impedance of the line from the step-up bus to the collection bus of a new energy power station. For the first i The positive sequence impedance of the step-up transformer at a new energy power station For the first i Equivalent positive sequence impedance of a box-type transformer under a single-unit multiplication model of a new energy power station; S6. Compare the positive sequence voltage of each new energy power station with the initial positive sequence voltage, and determine whether the voltage difference meets the convergence accuracy. If it does not meet the accuracy, substitute the current positive sequence voltage of each new energy power station into the positive sequence short-circuit current calculation model of the new energy power station, calculate the output short-circuit current of each new energy power station, and repeat steps S5 and S6 until the accuracy is met. Then, solve the output negative sequence current and zero sequence current of each new energy power station according to the circuit equation; output the output phase current of each new energy power station.

2. The method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants according to claim 1, characterized in that, In S1, for a single-phase ground fault, the faulty phase is one in which the correlation coefficient of the fault transient voltage is greater than the set value. The special phases; for a two-phase ground fault, the two phases corresponding to the minimum value of the fault transient voltage correlation coefficient are the fault phases; for a two-phase interphase fault, the two phases corresponding to the maximum value of the absolute value of the fault transient voltage correlation coefficient are the fault phases.

3. The method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants according to claim 1, characterized in that, In S3, the calculation model for the positive sequence short-circuit current of the new energy power station is as follows: （6）； in, 、 The first i Each unit in a new energy power station outputs short-circuit current with active and reactive components. No. i The number of generating units in each new energy power station and These are expressions determined by the unit's low-voltage fault ride-through strategy.

4. The method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants according to claim 1, characterized in that, In S4, the simplified equivalent circuit is used to define the equivalent current source. I eq for: （7）； Simplified equivalent circuit equivalent impedance for: （8）； in, The positive sequence impedance of the line from the new energy collection bus to the fault point.

5. The method for calculating asymmetrical short-circuit current in large-scale renewable energy power plants according to claim 1, characterized in that, In S6, the following formula (12) is used to determine whether the voltage difference meets the convergence accuracy requirement: （11）； in, and These are the current and the previously calculated number of... i Positive sequence voltage of a new energy power station. For convergence accuracy; Each new energy power station outputs negative sequence current The calculation formula is: （12）； in, ; The formula for calculating the zero-sequence current output of each new energy power station is as follows: （13）； in, To output zero-sequence current, ; Output phase current of each new energy power station for: （14）； in, .

6. The system upon which the asymmetric short-circuit current calculation method for large-scale renewable energy power plants according to any one of claims 1-5 is based, characterized in that, The system includes a fault phase selection module, an initial voltage calculation module, a short-circuit current calculation module, and a short-circuit current output module, wherein: Therefore, the phase selection module is used to calculate the correlation coefficient of the fault transient voltage between each phase based on the three-phase fault transient voltage of the new energy collection bus, and to determine the fault type and fault phase based on the correlation coefficient and the three-phase current; The initial voltage calculation module is used to construct a fault composite sequence network based on the fault type and fault phase, and calculate the positive sequence initial voltage of each new energy power station. The short-circuit current calculation module is used to calculate the output short-circuit current of each new energy power station by substituting the positive-sequence initial voltage of each new energy power station into the positive-sequence short-circuit current calculation model. The Thevenin circuit containing the voltage source is equivalent to the Norton equivalent circuit. After simplifying the circuit, the positive-sequence voltage of the new energy bus and the positive-sequence voltage of each new energy power station are calculated iteratively using the circuit equations until the convergence accuracy is met. Based on the converged positive-sequence voltage, the output negative-sequence current and zero-sequence current of each new energy power station are solved by combining the circuit equations. The short-circuit current output module is used to synthesize and output the output phase current of each new energy power station based on the calculated positive-sequence, negative-sequence, and zero-sequence currents.

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