A Method for Calculating Short-Circuit Current in Wind-Solar-Storage Power Stations Based on Pseudo-Current Source Method and Equivalent Approximation

Abstract

This invention discloses a method for calculating short-circuit current in wind-solar-storage power stations based on the pseudo-current source method and equivalent approximation, comprising the following steps: Step S1, selecting a reference value; Step S2, inputting electrical parameters; Step S3, calculating network parameters; Step S4, calculating the short-circuit current provided by wind, solar, and energy storage power sources and the system based on the pseudo-current source method and equivalent approximation; Step S5, calculating the short-circuit current at each short-circuit point using the infinity calculation method. The short-circuit current calculation method for wind-solar-storage power stations proposed in this invention is suitable for equivalent calculation models under the special output conditions of wind power, photovoltaic, and energy storage power sources. It enables rapid and effective calculation of short-circuit currents at various voltage levels of busbars in wind farms, photovoltaic, energy storage, or combined wind-solar-storage power stations, demonstrating fast and efficient calculation and high application value.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation, and in particular to a method for calculating short-circuit current in wind, solar and energy storage power stations based on the pseudo-current source method of equivalent merging. Background Technology

[0002] Currently, with the increasing capacity of individual wind farms, photovoltaic power stations, energy storage power stations, or combined wind-solar-storage power stations, often reaching hundreds of thousands or even millions of kW, short-circuit current calculations are essential in the design and operation of new energy booster stations to limit the harm of short circuits and minimize the impact of faults. This calculation is crucial for assessing the thermal and dynamic stability of equipment and current-carrying conductors, selecting and setting relay protection devices, determining reasonable main wiring schemes, operating modes, current limiting measures, and ensuring that electrical equipment in the protection system is not damaged under the most severe short-circuit conditions, thus minimizing the damage caused by short-circuit faults. Currently, in wind power, photovoltaic, and energy storage projects, short-circuit current calculation methods are only applied to single power sources, and the algorithms used are relatively simple. In wind power projects, wind turbines are treated as synchronous generators, while in photovoltaic and energy storage projects, photovoltaic power sources are treated as actual current sources. Given that the current calculation methods have two problems: first, they are not applicable to short-circuit calculations for power plants with multiple renewable energy sources, such as wind-solar combined power plants, wind-storage combined power plants, photovoltaic-storage combined power plants, and wind-solar-storage combined power plants; second, by treating photovoltaic and energy storage power sources as actual current sources, the calculated values ​​for short-circuit currents in large-capacity, multi-transformer combined power plants become unacceptably large and clearly unreasonable. Applying this approach to the renewable energy sources in the system is even more unreasonable and inconsistent with reality. Therefore, this invention proposes a method for calculating the short-circuit current of wind-solar-storage power plants based on the current source method and equivalent merging. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging. This method is adapted to the equivalent calculation model for short-circuit current calculation under the special output conditions of wind power, photovoltaic and energy storage power sources. It can quickly and effectively calculate the short-circuit current of busbars at various voltage levels of wind farms, photovoltaic, energy storage or wind-solar-storage combined power stations, and has high application value.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by this invention is: a method for calculating the short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging, comprising the following steps:

[0005] Step S1, Reference value selection: The reference values ​​include the reference capacity, reference voltage, and reference current;

[0006] Step S2, Electrical Parameter Input: Electrical parameters include system parameters, main transformer parameters, wind power generation system parameters, photovoltaic power generation system parameters, energy storage system parameters, and collector line parameters;

[0007] Step S3, Network Parameter Calculation: Network parameter calculation includes the calculation of the per-unit impedance of the main transformer, the calculation of the per-unit impedance of the local step-up transformer, the conversion calculation of the per-unit impedance of the wind turbine + transformer box, and the calculation of the per-unit impedance of the collector line.

[0008] Step S4: Calculate the short-circuit current provided by wind, solar, energy storage and the system based on the pseudo-current source method and the equivalent approximation method: The short-circuit current provided by wind, solar, energy storage and the system includes the three-phase short-circuit current provided by the wind turbine generator, the three-phase short-circuit current provided by the photovoltaic power generation unit, the three-phase short-circuit current provided by the energy storage unit, and the three-phase short-circuit current provided by the system.

[0009] Step S5: Calculate the short-circuit current at each short-circuit point using the infinite calculation method. The short-circuit current at each short-circuit point includes the three-phase short-circuit current of the 500kV busbar of the substation, the three-phase short-circuit current of the 37kV busbar of the substation, the three-phase short-circuit current of the 37kV busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic, or energy storage local step-up transformer of the substation, the three-phase short-circuit current of the low-voltage side busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic, or energy storage local step-up transformer of the substation, the single-phase grounding short-circuit current of the 500kV busbar of the substation, and the short-circuit current flowing through the neutral point of the main transformer in the single-phase grounding fault.

[0010] A further improvement to the technical solution of the present invention is that the formula for calculating the per-unit value of the main transformer impedance in step S3 is as follows:

[0011]

[0012] Where: X T* - Per-unit value of short-circuit impedance of main transformer, U d % - Main transformer short-circuit impedance, S j -Base capacity, S e - Rated capacity of the main transformer.

[0013] A further improvement to the technical solution of this invention lies in the formula for calculating the per-unit value of the local step-up transformer impedance in step S3:

[0014] Where: X T-k* - Per-unit value of short-circuit impedance of local step-up transformer, U d-k % - Main transformer short-circuit impedance, S j -Base capacity, S e-k - Rated capacity of the main transformer.

[0015] A further improvement to the technical solution of this invention lies in the calculation formula for the per-unit value conversion of the equivalent impedance of the wind turbine and the transformer in step S3:

[0016]

[0017] Where: X WTS* - Per-unit equivalent impedance of the fan + transformer substation with a base capacity of 1000MVA, X WT* -Wind turbine generator set-Package transformer equivalent impedance per unit value, S j -Base capacity, P e - Rated capacity of wind turbine generator set, cosθ - Power factor of wind turbine generator set.

[0018] A further improvement to the technical solution of the present invention is that the calculation step of the per-unit value of the collector line impedance in step S3 is as follows:

[0019] Step a: Calculate the per-unit impedance of the collector line from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage. The calculation formula is as follows:

[0020]

[0021] Where: X Lmin* - The per-unit impedance of the collector line from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage; x - the impedance per unit length of the collector line; L min-k - The length (S) from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, solar power, or energy storage. j -Base capacity, - Reference voltage, 37kV;

[0022] Step b: Calculate the per-unit impedance of the wind farm's collector lines. The calculation formula is as follows:

[0023]

[0024] Where: X L* - Per-unit impedance of wind farm collector lines, x - impedance per unit length of collector line, L - average length of single-circuit collector line, S j -Base capacity, - Reference voltage, 37kV.

[0025] A further improvement to the technical solution of the present invention is that the calculation formula for the three-phase short-circuit current provided by the wind turbine generator set in step S4 is as follows:

[0026]

[0027]

[0028] in: -The three-phase short-circuit current supplied by the wind turbine generator to the 500kV bus, I j525 -500kV voltage level reference current, -The three-phase short-circuit current supplied by the wind turbine generator to the 37kV bus, I j37 -37kV voltage level reference current.

[0029] A further improvement to the technical solution of this invention lies in the following: the three-phase short-circuit current calculation formula provided by the photovoltaic power generation unit in step S4:

[0030]

[0031] in: - The three-phase short-circuit current provided by the photovoltaic power generation unit, K2 - The overcurrent factor of the photovoltaic inverter, S inv -Rated capacity of a single photovoltaic power generation unit, U e-2 - Voltage level of short-circuit current injection into the photovoltaic power generation unit.

[0032] A further improvement to the technical solution of the present invention is that the three-phase short-circuit current calculation formula provided by the energy storage unit in step S4 is as follows:

[0033]

[0034] in: - The three-phase short-circuit current provided by the energy storage unit, K3 - The overcurrent factor of the energy storage converter, S CN -Rated capacity of a single energy storage unit, U e-3 - Voltage level of short-circuit current injection into the energy storage unit.

[0035] A further improvement to the technical solution of the present invention is that the three-phase short-circuit current provided by the system in step S4 includes the following:

[0036] ①The formula for calculating the three-phase short-circuit current supplied by the system to the 500kV bus is as follows:

[0037]

[0038] in: -The three-phase short-circuit current supplied by the system to the 500kV bus, X S1* -500kV system positive sequence impedance per unit value, I j525 -500kV voltage level reference current;

[0039] ②The formula for calculating the three-phase short-circuit current supplied by the system to the 37kV bus is as follows:

[0040]

[0041] in: -The three-phase short-circuit current supplied by the system to the 37kV bus, I j37 -37kV voltage level reference current.

[0042] A further improvement to the technical solution of this invention is that the calculation formula for the three-phase short-circuit current of the 500kV busbar in step S5 is as follows:

[0043]

[0044] in: - Three-phase short-circuit current of the 500kV busbar at the substation, n1, n2, n3 - are the number of main transformers connected to wind power, photovoltaic power, and energy storage, respectively, N 1i N 2i N 3i - represents the number of wind power, photovoltaic, and energy storage units connected to the i-th main transformer, respectively. - These are the three-phase short-circuit currents supplied to the 500kV bus by the wind power, photovoltaic and energy storage units under the i-th main transformer, respectively, where i is the main transformer number;

[0045] The formula for calculating the three-phase short-circuit current of the 37kV busbar in the substation is as follows:

[0046]

[0047] in: - Three-phase short-circuit current of the 37kV busbar at the substation - The three-phase short-circuit current supplied to the 500kV busbar by the wind power, photovoltaic, and energy storage units under the first main transformer, respectively, N 11 N 21 N 31 - These represent the number of wind power, photovoltaic, and energy storage units connected to the first main transformer;

[0048] The formula for calculating the three-phase short-circuit current from the 35kV switchgear of the substation to the nearest 37kV busbar of the local step-up transformer for wind power, photovoltaic, or energy storage is as follows:

[0049]

[0050] in: - Three-phase short-circuit current from the 35kV switchgear of the substation to the 37kV busbar of the nearest local step-up transformer for wind power, photovoltaic or energy storage in the substation;

[0051] The formula for calculating the three-phase short-circuit current of the low-voltage side busbar from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage is as follows:

[0052]

[0053] in: -The three-phase short-circuit current from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest local step-up transformer for wind power, photovoltaic, or energy storage is I. j-k - These represent the reference currents on the low-voltage side of the local step-up transformer for wind power, photovoltaic, or energy storage, respectively, K. k - These are the overcurrent multiples for wind power, photovoltaic, or energy storage units, respectively;

[0054] The formula for calculating the single-phase ground fault current of the 500kV busbar in the substation is as follows:

[0055]

[0056] in: -Single-phase ground fault current of the 500kV busbar at the substation, X S2* -500kV system negative sequence impedance per unit value, X S0* -500kV system zero-sequence impedance per unit value, X T0* - Per-unit value of zero-sequence impedance of main transformer, n- Number of main transformers with neutral grounding;

[0057] Formula for calculating the total short-circuit current flowing through the neutral point of the main transformer during a single-phase ground fault:

[0058]

[0059] Among them: I n - Short-circuit current flows through the neutral point of the main transformer.

[0060] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0061] This invention proposes a short-circuit current calculation method for wind-solar-storage power stations based on the pseudo-current source method and equivalent merging. This method is adapted to the equivalent calculation model for short-circuit current calculation under the special output conditions of wind power, photovoltaic, and energy storage power sources, enabling rapid and effective calculation of short-circuit currents at various voltage levels of wind farms, photovoltaic, energy storage, or combined wind-solar-storage power stations. Compared to existing calculation methods that treat single-source new energy sources as true current sources, this invention addresses the problems of its applicability to short-circuit current calculations in combined power stations with multiple energy systems, and the irrationality of treating photovoltaic and energy storage as true current sources. It has high application value in current large-scale new energy base projects involving combined wind, solar, and energy storage power stations. Attached Figure Description

[0062] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0063] The present invention will be further described in detail below with reference to embodiments:

[0064] like Figure 1 As shown, the present invention will be further described in detail below with reference to the embodiments. The specific scheme is as follows: wind power capacity is 400MW, photovoltaic capacity is 1000MW, energy storage capacity is 150MW, and a 500kV step-up substation is constructed. The main transformer capacity is four 400MVA main transformers, and the voltage level is 500kV / 35kV.

[0065] The method for calculating short-circuit current in wind, solar, and energy storage power stations based on the pseudo-current source method and equivalent approximation includes the following steps:

[0066] Step S1, Reference value selection: The reference values ​​include the reference capacity, reference voltage, and reference current;

[0067] Base capacity: S j =1000MVA;

[0068] Reference voltage: U j525 =525kV, U j37 =37kV, U j1.14 =1.14kV, U j0.8 =0.8kV, U j0.66 =0.66kV

[0069] Reference current: I j525 =1.0997kA,I j37 =15.6045kA, I j1.14 =506.4625kA, I j0.8 =721.7090kA, I j0.66 =874.7988kA.

[0070] Among them, 525kV and 37kV are the voltage of the substation, 1.14kV is the output voltage of the wind turbine generator, 0.8kV is the output voltage of the photovoltaic grid-connected inverter, and 0.66kV is the output voltage of the energy storage converter.

[0071] Step S2, Electrical Parameter Input: Electrical parameters include system parameters, main transformer parameters, wind power generation system parameters, photovoltaic power generation system parameters, energy storage system parameters, and collector line parameters;

[0072] (1) System parameters

[0073] System positive-sequence and negative-sequence impedance per unit: 0.0433

[0074] System zero-sequence impedance per unit: 0.0499

[0075] (2) Main transformer parameters

[0076] #1 Main Transformer Parameters

[0077] Rated capacity of main transformer (MVA): 400

[0078] Main transformer short-circuit impedance (%): 25

[0079] #2 Main Transformer Parameters

[0080] Rated capacity of main transformer (MVA): 400

[0081] Main transformer short-circuit impedance (%): 25

[0082] #3 Main Transformer Parameters

[0083] Rated capacity of main transformer (MVA): 400

[0084] Main transformer short-circuit impedance (%): 25

[0085] #4 Main Transformer Parameters

[0086] Rated capacity of main transformer (MVA): 400

[0087] Main transformer short-circuit impedance (%): 25

[0088] (3) Parameters of wind power generation system

[0089] Rated capacity of wind turbine generator set: 5MW

[0090] Wind turbine power factor: 0.95

[0091] Wind turbine generator set - transformer equivalent impedance per unit: 0.5

[0092] Rated capacity (MVA) of the local step-up transformer for wind turbine generator set: 5.5

[0093] Short-circuit impedance of local step-up transformer for wind turbine generator set (%): 8

[0094] Overcurrent factor K1 for wind turbine generator sets: 1.2 or 2 for converter type, 6 for asynchronous generators. Number of wind turbine generator sets under each main transformer:

[0095] Number of wind turbine generators under main transformer #1: 20

[0096] Number of wind turbine generators under main transformer #2: 20

[0097] Number of wind turbine generators under main transformer #3: 20

[0098] Number of wind turbine generators under main transformer #4: 20

[0099] (4) Photovoltaic power generation system parameters

[0100] Rated capacity of a single photovoltaic power generation unit (MW): 3.15

[0101] Rated AC output voltage (kV) of the photovoltaic grid-connected inverter: 0.8

[0102] Overcurrent factor K2 of photovoltaic inverter: 1.2

[0103] Rated capacity of on-site photovoltaic step-up transformer (MVA): 3.15

[0104] Photovoltaic on-site step-up transformer short-circuit impedance (%): 7

[0105] Number of photovoltaic power generation units under each main transformer:

[0106] Number of photovoltaic power generation units under main transformer #1: 79

[0107] Number of photovoltaic power generation units under main transformer #2: 80

[0108] Number of photovoltaic power generation units under main transformer #3: 79

[0109] Number of photovoltaic power generation units under main transformer #4: 80

[0110] (5) Energy storage system parameters

[0111] Rated capacity of a single energy storage unit (MW): 2.5

[0112] Rated AC output voltage (kV) of energy storage converter: 0.66

[0113] Overcurrent factor K3 of the energy storage converter: 1.2

[0114] Rated capacity (MVA) of on-site energy storage booster transformer: 2.75

[0115] Short-circuit impedance of local step-up transformer for energy storage (%): 7

[0116] Number of energy storage units under each main transformer:

[0117] Number of energy storage units under main transformer #1: 15

[0118] Number of energy storage units under main transformer #2: 15

[0119] Number of energy storage units under main transformer #3: 15

[0120] Number of energy storage units under main transformer #4: 15

[0121] (6) Collector line parameters

[0122] Parameters of the nearest collector line to the substation (A)

[0123] Length of the collector line (km) from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage: 0.17

[0124] The nearest collector line impedance per unit length (Ω / km): 0.4

[0125] Parameters of the collector line for Wind Farm B

[0126] Average length of collector lines under main transformer #1 (km): 5

[0127] Average length of collector lines under main transformer #2 (km): 5

[0128] Average length of collector lines under main transformer #3 (km): 5

[0129] Average length of collector lines under main transformer #4 (km): 5

[0130] Impedance per unit length of the collector line (Ω / km): 0.4

[0131] Step S3, Network Parameter Calculation: Network parameter calculation includes the calculation of the per-unit impedance of the main transformer, the calculation of the per-unit impedance of the local step-up transformer, the conversion calculation of the per-unit impedance of the wind turbine + transformer box, and the calculation of the per-unit impedance of the collector line.

[0132] (1) Calculation of per-unit value of main transformer impedance

[0133] Calculation formula:

[0134] in:

[0135] X T* - Per-unit value of short-circuit impedance of main transformer

[0136] U d % - Main transformer short-circuit impedance (%)

[0137] S j - Baseline Capacity (MVA)

[0138] S e - Rated capacity of main transformer (MVA)

[0139] The calculation results based on formula (1) are as follows:

[0140] #1 Main transformer short-circuit impedance per unit: 0.625

[0141] #2 Main transformer short-circuit impedance per unit: 0.625

[0142] #3 Main transformer short-circuit impedance per unit: 0.625

[0143] #4 Main transformer short-circuit impedance per unit: 0.625

[0144] (2) Calculation of per-unit impedance of local step-up transformer

[0145] Calculation formula:

[0146] in:

[0147] X T-k* - Per-unit value of short-circuit impedance of local step-up transformer

[0148] U d-k % - Main transformer short-circuit impedance (%)

[0149] S j - Baseline Capacity (MVA)

[0150] S e-k - Rated capacity of main transformer (MVA)

[0151] k - power source type, where 1 indicates wind turbine generator, 2 indicates photovoltaic, and 3 indicates energy storage. The calculation results based on formula (2) are as follows:

[0152] Per-unit short-circuit impedance of local step-up transformer for wind turbine generator set: X T-1* =14.5455

[0153] Per-unit value of short-circuit impedance of photovoltaic local step-up transformer: X T-2* =22.2222

[0154] Per-unit value of short-circuit impedance of local step-up transformer for energy storage: X T-3* =25.4545

[0155] (3) Calculation of per-unit equivalent impedance of fan + transformer substation

[0156] Calculation formula:

[0157] in:

[0158] X WTS* - Per-unit equivalent impedance of fan + transformer substation with a base capacity of 1000MVA

[0159] X WT* -Wind turbine generator set-Equivalent impedance per unit value of transformer substation

[0160] S j - Baseline Capacity (MVA)

[0161] P e - Rated capacity of wind turbine generator set (MW)

[0162] cosθ - Power factor (MVA) of wind turbine generator.

[0163] The result calculated according to formula (3) is X. WTS* =95.

[0164] (4) Calculation of per-unit impedance of collector lines

[0165] Calculation of per-unit impedance of the collector line from the 35kV switchgear of substation A to the nearest local step-up transformer for wind power, photovoltaic, or energy storage.

[0166] Calculation formula:

[0167] in:

[0168] X Lmin* - Per-unit impedance of the collector line from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage.

[0169] x - Impedance per unit length of collector line (Ω / km)

[0170] L min-k - Length (km) from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, solar power, or energy storage.

[0171] S j - Baseline Capacity (MVA)

[0172] - Reference voltage, 37kV

[0173] The other symbols have been explained previously.

[0174] The result calculated according to formula (4) is X. Lmin-k* =0.0497.

[0175] Calculation of per-unit impedance of collector lines for Wind Farm B

[0176] Calculation formula:

[0177] in:

[0178] X L* - Per-unit impedance of wind farm collector lines

[0179] x - Impedance per unit length of collector line (Ω / km)

[0180] L - Average length of a single-circuit collector line (km)

[0181] S j - Baseline Capacity (MVA)

[0182] - Reference voltage, 37kV

[0183] The result calculated according to formula (5) is

[0184] The per-unit average reactance of the single-circuit collector line under the #1 main transformer is 1.4609.

[0185] The per-unit average reactance of the single-circuit collector line under the #2 main transformer is 1.4609.

[0186] The per-unit average reactance of the single-circuit collector line under the #3 main transformer is 1.4609.

[0187] The per-unit average reactance of the single-circuit collector line under the #4 main transformer is 1.4609.

[0188] Step S4: Calculate the short-circuit current provided by wind, solar, energy storage and the system based on the pseudo-current source method and the equivalent approximation method: The short-circuit current provided by wind, solar, energy storage and the system includes the three-phase short-circuit current provided by the wind turbine generator, the three-phase short-circuit current provided by the photovoltaic power generation unit, the three-phase short-circuit current provided by the energy storage unit, and the three-phase short-circuit current provided by the system.

[0189] (1) Three-phase short-circuit current provided by wind turbine generator set

[0190] Calculation formula:

[0191] Calculation formula:

[0192] in:

[0193] - The three-phase short-circuit current (kA) supplied by the wind turbine generator to the 500kV bus.

[0194] I j525 -500kV voltage level reference current (kA)

[0195] - Three-phase short-circuit current (kA) supplied by the wind turbine generator to the 37kV bus.

[0196] I j37 -37kV voltage level reference current (kA)

[0197] The other symbols have been explained previously.

[0198] The result calculated according to formula (6) is

[0199] #1 Short-circuit current (kA) supplied by a single wind turbine generator set under the main transformer to the 500kV side: 0.01133 #2 Short-circuit current (kA) supplied by a single wind turbine generator set under the main transformer to the 500kV side: 0.01133 #3 Short-circuit current (kA) supplied by a single wind turbine generator set under the main transformer to the 500kV side: 0.01133 #4 Short-circuit current (kA) supplied by a single wind turbine generator set under the main transformer to the 500kV side: 0.01133 Calculated according to formula (7)

[0200] #1 Short-circuit current (kA) supplied by a single wind turbine generator set to the 37kV side under the main transformer: 0.1607(2) Three-phase short-circuit current supplied by the photovoltaic power generation unit

[0201] Calculation formula:

[0202] in:

[0203] - Three-phase short-circuit current (kA) provided by the photovoltaic power generation unit

[0204] K2-Photovoltaic Inverter Overcurrent Ratio

[0205] S inv -Rated capacity of a single photovoltaic power generation unit (MW)

[0206] U e-2 - Voltage level of short-circuit current injection into the photovoltaic power generation unit (kV)

[0207] The result calculated according to formula (8) is

[0208] The short-circuit current (kA) supplied by a single photovoltaic power generation unit to the 500kV side: Short-circuit current (kA) supplied by a single photovoltaic power generation unit to the 37kV side:

[0209] (3) Three-phase short-circuit current provided by the energy storage unit

[0210] Calculation formula:

[0211] in:

[0212] - Three-phase short-circuit current (kA) provided by the energy storage unit

[0213] K3-Energy Storage Converter Overcurrent Ratio

[0214] S CN -Rated capacity of a single energy storage unit (MW)

[0215] U e-3- Voltage level of short-circuit current injection into the energy storage unit (kV)

[0216] The result calculated according to formula (9) is

[0217] Short-circuit current (kA) supplied by a single energy storage unit to the 500kV side: Short-circuit current (kA) supplied by a single energy storage unit to the 37kV side: (4) The three-phase short-circuit current provided by the system

[0218] System A supplies three-phase short-circuit current to the 500kV bus.

[0219] Calculation formula:

[0220] in:

[0221] -The three-phase short-circuit current (kA) supplied by the system to the 500kV bus.

[0222] X S1* -500kV system positive sequence impedance per unit value

[0223] I j525 -500kV voltage level reference current (kA)

[0224] The result calculated according to formula (10) is

[0225] The three-phase short-circuit current (kA) supplied by the system to the 500kV bus is 25.3983B. The three-phase short-circuit current supplied by the system to the 37kV bus is...

[0226] Calculation formula:

[0227] in:

[0228] -The three-phase short-circuit current (kA) supplied by the system to the 37kV bus.

[0229] I j37 -37kV voltage level reference current (kA)

[0230] The other symbols have been explained previously.

[0231] The result calculated according to formula (11) is

[0232] The three-phase short-circuit current (kA) supplied by the system to the 37kV bus is 23.3496.

[0233] Step S5: Calculate the short-circuit current at each short-circuit point using the infinite calculation method. The short-circuit current at each short-circuit point includes the three-phase short-circuit current of the 500kV busbar of the substation, the three-phase short-circuit current of the 37kV busbar of the substation, the three-phase short-circuit current of the 37kV busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic, or energy storage local step-up transformer of the substation, the three-phase short-circuit current of the low-voltage side busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic, or energy storage local step-up transformer of the substation, the single-phase grounding short-circuit current of the 500kV busbar of the substation, and the short-circuit current flowing through the neutral point of the main transformer in the single-phase grounding fault.

[0234] (1) Three-phase short-circuit current of the 500kV busbar of the substation

[0235] Calculation formula:

[0236] in:

[0237] - Three-phase short-circuit current (kA) of the 500kV busbar at the substation

[0238] n1, n2, and n3 represent the number of main transformers connected to wind power, solar power, and energy storage, respectively.

[0239] N 1i N 2i N 3i - represents the number of units connected to the i-th main transformer, including wind power, photovoltaic power, and energy storage. - These represent the three-phase short-circuit currents (kA) supplied to the 500kV bus by the wind power, photovoltaic, and energy storage units under the i-th main transformer.

[0240] i-Main Transformer Number

[0241] The other symbols have been explained previously.

[0242] The result calculated according to formula (12) is

[0243] Three-phase short-circuit current (kA) of the 500kV busbar at the substation: 27.8697

[0244] (2) Three-phase short-circuit current of the 37kV busbar of the substation

[0245] Calculation formula:

[0246]

[0247] in:

[0248] - Three-phase short-circuit current (kA) of the 37kV busbar at the substation

[0249] - The three-phase short-circuit current (kA) supplied to the 500kV bus by the wind power, photovoltaic and energy storage units under the first main transformer.

[0250] N 11 N 21 N 31 - These represent the number of wind power, photovoltaic, and energy storage units connected to the first main transformer. The other symbols have been explained previously.

[0251] The result calculated according to formula (13) is

[0252] Three-phase short-circuit current (kA) of the 37kV busbar of the substation: 32.0511

[0253] (3) Three-phase short-circuit current from the 35kV switchgear of the substation to the 37kV busbar of the nearest local step-up transformer for wind power, photovoltaic or energy storage in the substation

[0254] Calculation formula:

[0255]

[0256] in:

[0257] - Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the 37kV busbar of the nearest local step-up transformer for wind power, photovoltaic, or energy storage.

[0258] The other symbols have been explained previously.

[0259] The result calculated according to formula (14) is

[0260] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the 37kV busbar of the nearest local step-up transformer for wind power:

[0261] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the 37kV busbar of the nearest photovoltaic local step-up transformer:

[0262] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the 37kV busbar of the nearest energy storage local step-up transformer:

[0263] (4) Three-phase short-circuit current from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest local step-up transformer for wind power, photovoltaic or energy storage in the substation

[0264] Calculation formula:

[0265]

[0266] in:

[0267] - Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest local step-up transformer for wind power, photovoltaic, or energy storage.

[0268] I j-k - These represent the reference current (kA) on the low-voltage side of the local step-up transformer for wind power, photovoltaic, or energy storage.

[0269] K k - These represent the overcurrent multiples (kV) for wind power, photovoltaic, or energy storage units.

[0270] The other symbols have been explained previously.

[0271] The result calculated according to formula (15) is

[0272] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest local step-up transformer for wind power:

[0273] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest photovoltaic local step-up transformer in the substation:

[0274] Three-phase short-circuit current (kA) from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest energy storage local step-up transformer:

[0275] (5) Single-phase grounding short-circuit current of the 500kV busbar of the substation

[0276] Calculation formula:

[0277]

[0278] in:

[0279] -Single-phase ground fault current (kA) of the 500kV busbar at the substation

[0280] X S2* -500kV system negative sequence impedance per unit value

[0281] X S0* -500kV system zero-sequence impedance per unit value

[0282] X T0* - Per-unit value of zero-sequence impedance of main transformer

[0283] n - Number of main transformers with neutral point grounding

[0284] The other symbols have been explained previously.

[0285] The result calculated according to formula (16) is

[0286] Single-phase ground fault current (kA) of the 500kV busbar of the substation:

[0287] (6) During a single-phase ground fault, the total short-circuit current flows through the neutral point of the main transformer.

[0288] Calculation formula:

[0289]

[0290] in:

[0291] I n -Short-circuit current (kA) flowing through the neutral point of the main transformer

[0292] The other symbols have been explained previously.

[0293] The result calculated according to formula (17) is

[0294] Short-circuit current (kA) flowing through the neutral point of the main transformer: I n =6.4815.

[0295] This invention first analyzes and determines the grid connection characteristics of converter-type or asynchronous-type wind turbine generators, photovoltaic power sources, and energy storage systems. Specifically, the grid connection voltage of these three power sources must be established by the system before grid connection can occur. They supply current to the system, exhibiting voltage-controlled current source characteristics, but not true current source characteristics. Therefore, special equivalent processing is required for the calculation models of these three power sources in short-circuit current calculations. For short-circuit current calculations at the grid connection point, the invention proposes first calculating the short-circuit capacity provided at the grid connection point using the characteristics of a current source for each of the three converter-type power sources. Then, this short-circuit capacity is independently injected into the system's short-circuit capacity for equivalent merging. Finally, the equivalent merged system short-circuit capacity is obtained. Asynchronous-type wind turbine generators are calculated as infinite power sources. After this equivalent merging process, the infinite power source method can be used for short-circuit current calculations. When calculating the short-circuit current at a non-grid-connected point, it is proposed that the short-circuit capacity injected from the power source at the short-circuit point to the grid-connected point should be deducted from the equivalent system short-circuit capacity. The deducted short-circuit capacity is considered according to the calculation model of the current source characteristics. Therefore, the short-circuit current at the non-grid-connected point is equal to the sum of the short-circuit current provided by the equivalent system and the short-circuit current provided by the current source.

[0296] This invention proposes a short-circuit current calculation method for wind-solar-storage power stations based on the pseudo-current source method and equivalent merging. This method is adapted to the equivalent calculation model for short-circuit current calculation under the special output conditions of wind power, photovoltaic, and energy storage power sources, enabling rapid and effective calculation of short-circuit currents at various voltage levels of wind farms, photovoltaic, energy storage, or combined wind-solar-storage power stations. Compared to existing calculation methods that treat single-source new energy sources as true current sources, this invention addresses the problems of its applicability to short-circuit current calculations in combined power stations with multiple energy systems, and the irrationality of treating photovoltaic and energy storage as true current sources. It has high application value in current large-scale new energy base projects involving combined wind, solar, and energy storage power stations.

Claims

1. A wind-solar-storage power station short-circuit current calculation method based on pseudo current source method equivalent merging, characterized in that: Includes the following steps: S1. Reference value selection: The reference values ​​include the reference capacity, reference voltage, and reference current; S2. Electrical Parameter Input: Electrical parameters include system parameters, main transformer parameters, wind power generation system parameters, photovoltaic power generation system parameters, energy storage system parameters, and collector line parameters; S3. Network parameter calculation: including the calculation of the per-unit impedance of the main transformer, the calculation of the per-unit impedance of the local step-up transformer, the conversion calculation of the per-unit impedance of the wind turbine + box transformer, and the calculation of the per-unit impedance of the collector line. S4. Calculate the short-circuit current provided by wind, solar, and energy storage power sources and systems based on the pseudo-current source method and equivalent approximation method: including the three-phase short-circuit current provided by wind turbine generators, photovoltaic power generation units, energy storage units, and systems respectively; S5. Calculate the short-circuit current at each short-circuit point using the infinite calculation method: including the three-phase short-circuit current of the 500kV busbar and 37kV busbar of the substation, the three-phase short-circuit current of the 37kV busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic or energy storage local step-up transformer of the substation, the three-phase short-circuit current of the low-voltage side busbar from the 35kV switchgear of the substation to the nearest wind power, photovoltaic or energy storage local step-up transformer of the substation, the single-phase grounding short-circuit current of the 500kV busbar of the substation, and the short-circuit current flowing through the neutral point of the main transformer in a single-phase grounding fault. The formula for calculating the three-phase short-circuit current of the 500kV busbar in the substation is as follows: ， in: Three-phase short-circuit current of the 500kV busbar of the substation , , These represent the number of main transformers connected to wind power, solar power, and energy storage, respectively. , , These represent the number of wind power, photovoltaic, and energy storage units connected to the i-th main transformer, respectively. , , The first The three-phase short-circuit current supplied to the 500kV busbar by the wind power, photovoltaic, and energy storage units under the main transformer. Main transformer number; The formula for calculating the three-phase short-circuit current of the 37kV busbar in the substation is as follows: wherein: the three-phase short-circuit current of the 37 kV bus of the step-up station, , , the three-phase short-circuit current provided by the wind power, photovoltaic and energy storage units under the 1st main transformer to the 500 kV bus, respectively, , , the number of units of wind power, photovoltaic and energy storage connected to the 1st main transformer, respectively; The formula for calculating the three-phase short-circuit current from the 35kV switchgear of the substation to the nearest 37kV busbar of the local step-up transformer for wind power, photovoltaic, or energy storage is as follows: ， wherein: The three-phase short-circuit current of the booster station 35kV switch cabinet to the nearest wind power, photovoltaic or energy storage local booster transformer 37kV bus bar; The formula for calculating the three-phase short-circuit current of the low-voltage side busbar from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage is as follows: ， in: The three-phase short-circuit current from the 35kV switchgear of the substation to the low-voltage side busbar of the nearest local step-up transformer for wind power, photovoltaic, or energy storage is measured. These are the reference currents for the low-voltage side of the local step-up transformer for wind power, photovoltaic, or energy storage, respectively. These are the overcurrent multiples for wind power, photovoltaic, or energy storage units, respectively. The formula for calculating the single-phase ground fault current of the 500kV busbar in the substation is as follows: ， in: Single-phase ground fault current of the 500kV busbar at the substation. Per-unit value of negative sequence impedance for a 500kV system. The per-unit value of zero-sequence impedance for a 500kV system. The per-unit value of the zero-sequence impedance of the main transformer. Number of main transformers with neutral point grounding; Formula for calculating the total short-circuit current flowing through the neutral point of the main transformer during a single-phase ground fault: ， in: Short-circuit current flows through the neutral point of the main transformer.

2. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for calculating the per-unit value of the main transformer impedance in step S3 is as follows: ， in: Per-unit value of short-circuit impedance of main transformer The short-circuit impedance of the main transformer Baseline capacity, Rated capacity of the main transformer.

3. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for calculating the per-unit value of the local step-up transformer impedance in step S3 is as follows: , in: Per-unit value of short-circuit impedance of local step-up transformer The short-circuit impedance of the main transformer Baseline capacity, Rated capacity of the main transformer.

4. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for converting the per-unit value of the equivalent impedance of the wind turbine and transformer in step S3 is as follows: ， in: Per-unit equivalent impedance of fan + transformer substation with a base capacity of 1000MVA. Wind turbine generator set - transformer equivalent impedance per unit value Baseline capacity, Rated capacity of wind turbine generator set, Power factor of wind turbine generator set.

5. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The per-unit value calculation steps for the collector line impedance in step S3 are as follows: Step a: Calculate the per-unit impedance of the collector line from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage. The calculation formula is as follows: ， in: The per-unit impedance of the collector line from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, photovoltaic, or energy storage. Impedance per unit length of collector line, The length from the 35kV switchgear of the substation to the nearest local step-up transformer for wind power, solar power, or energy storage. Baseline capacity, Reference voltage, 37kV; Step b: Calculate the per-unit impedance of the wind farm's collector lines. The calculation formula is as follows: ， in: Per-unit impedance of wind farm collector lines Impedance per unit length of collector line, Average length of a single-circuit collector line Baseline capacity, Reference voltage: 37kV.

6. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for calculating the three-phase short-circuit current provided by the wind turbine generator set in step S4 is as follows: ， ， in: The three-phase short-circuit current supplied by the wind turbine generator to the 500kV busbar 500kV voltage level reference current, The three-phase short-circuit current supplied by the wind turbine generator to the 37kV bus. 37kV voltage level reference current.

7. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for calculating the three-phase short-circuit current provided by the photovoltaic power generation unit in step S4 is as follows: ， in: The three-phase short-circuit current provided by the photovoltaic power generation unit, Photovoltaic inverter overcurrent factor Rated capacity of a single photovoltaic power generation unit The voltage level of short-circuit current injection into the photovoltaic power generation unit.

8. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The formula for calculating the three-phase short-circuit current provided by the energy storage unit in step S4 is as follows: ， in: The energy storage unit provides three-phase short-circuit current, Overcurrent multiple of energy storage converter Rated capacity of a single energy storage unit The voltage level of short-circuit current injection into the energy storage unit.

9. The method for calculating short-circuit current of wind-solar-storage power stations based on the pseudo-current source method and equivalent merging as described in claim 1, characterized in that: The three-phase short-circuit current provided by the system in step S4 includes the following: The formula for calculating the three-phase short-circuit current supplied by the system to the 500kV bus is as follows: ， in: The system supplies three-phase short-circuit current to the 500kV bus. The per-unit value of the positive sequence impedance of a 500kV system. 500kV voltage level reference current; The formula for calculating the three-phase short-circuit current supplied by the system to the 37kV bus is as follows: ， in: The system supplies three-phase short-circuit current to the 37kV bus. 37kV voltage level reference current.

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