A method and system for configuring grid-type converter capacity based on short-circuit ratio margin

Abstract

A method and system for configuring grid-connected converter capacity based on short-circuit ratio margin, belonging to the field of new energy grid connection technology, is disclosed. The method includes: constructing a grid-connected converter system model and obtaining the critical short-circuit ratio of the power plant; calculating the current short-circuit ratio of the power plant based on the AC system short-circuit capacity and the grid-connected equipment capacity; setting a target short-circuit ratio margin for the power plant's grid-connected system, calculating the current short-circuit ratio margin and comparing it; if the current short-circuit ratio margin is not less than the target short-circuit ratio margin, it indicates that the stability requirements have been met; otherwise, based on the target short-circuit ratio margin, a corrected short-circuit ratio that satisfies the short-circuit ratio margin is calculated; based on the corrected short-circuit ratio, the required total capacity of the grid-connected converter is calculated. This invention solves the problem in the prior art of lacking quantitative capacity calculation for configuring grid-connected converters in grid-connected new energy power plants.

Description

Technical Field

[0001] This invention belongs to the field of small-disturbance stability analysis of new energy power generation, and specifically relates to a method and system for configuring the capacity of grid-type converters based on short-circuit ratio margin. Background Technology

[0002] Grid-connected renewable energy uses phase-locked synchronous grid connection, which carries the risk of subsynchronous oscillations when the power plant connects to a weak grid via long-distance lines and multiple transformers. In contrast, grid-connected renewable energy is based on power synchronization control grid connection, exhibiting stronger adaptability to weak grids. Therefore, configuring a certain capacity in traditional renewable energy power plants can be considered to improve subsynchronous stability under small disturbances. Current research on the quantitative configuration of grid-connected converters in traditional renewable energy power plants is limited.

[0003] The short-circuit ratio (SCR), calculated from the short-circuit capacity of the AC system and the capacity of grid-connected equipment, and its related indicators, reflect the relative strength of power electronic equipment such as converters connected to the grid in AC systems. It is currently used to assess the potential risks of subsynchronous oscillations caused by AC-DC interaction in weak AC systems. The SCR is strongly correlated with the grid connection impedance of the converter and the converter capacity. Increased grid connection impedance and converter capacity lead to a decreased SCR and an increased risk of subsynchronous oscillations.

[0004] Regarding the configuration of grid-type converters, the following existing studies exist:

[0005] 1. Patent application number CN202410010304.X discloses a method and system for optimizing the location and configuration of a grid-type energy storage power station, specifically including: setting constraints on conventional generating units and energy storage power stations; under the constraints, establishing a joint optimization model of conventional generating units and energy storage power stations, including an inner optimization model and an outer optimization model; solving the inner optimization model to obtain the optimal operating cost, substituting the optimal operating cost into the outer optimization model, and using a particle swarm optimization algorithm to solve the outer optimization model to obtain the optimized energy storage configuration capacity; setting a fixed number of iterations, when the current iteration number is less than the fixed number of iterations, feeding back the solution result of the outer optimization model to the inner optimization model to update the energy storage configuration capacity, until the current iteration number equals the fixed number of iterations, obtaining the optimal energy storage configuration capacity; calculating the standard deviation of the regional power grid inertia constant based on the optimal energy storage configuration capacity, and obtaining the optimal configuration location of the grid-type energy storage power station when the standard deviation is minimized. However, this invention mainly optimizes the configuration of grid-type energy storage capacity based on system operating costs. After obtaining the capacity optimization configuration result, it optimizes the site selection based on the regional inertia constant, ignoring the relationship between the size of the grid-type energy storage capacity and system stability. It cannot provide an optimized capacity configuration scheme for weak grid conditions.

[0006] 2. Patent application number CN202311736349.7 discloses a current limiting control system and method for a grid-type converter, including: Step S1, analyzing the voltage source characteristics of the grid-type converter based on the maximum singular value index of the impedance matrix, and establishing a voltage source-equivalent internal reactance circuit model of the grid-type converter; Step S2, using the generalized short-circuit ratio to quantify the small-disturbance stability of the grid-type and grid-connected converter hybrid power grid system, and obtaining the small-disturbance stability of the grid-type and grid-connected converter hybrid power grid system. Qualitative indicators; Step S3, based on the established voltage source-equivalent internal reactor circuit model, correct the small-disturbance stability indicators of the grid system with grid-connected and integrated converters, and obtain the analytical relationship between the capacity ratio of grid-connected and integrated converters and the generalized short-circuit ratio; Step S4, based on the analytical relationship between the capacity ratio of grid-connected and integrated converters and the generalized short-circuit ratio, obtain the estimation method for the capacity ratio of grid-connected and integrated converters, and the recommended values ​​for the capacity ratio of grid-connected and integrated converters in typical scenarios. However, this invention estimates the capacity ratio of integrated and grid-connected converters based on small-disturbance stability indicators, but lacks clear quantitative standards for the capacity configuration method of grid-connected converters, especially in the case of low grid strength, and lacks consideration for precise capacity configuration schemes. Summary of the Invention

[0007] To address the shortcomings of existing research, the present invention aims to provide a method and system for configuring the capacity of grid-connected converters based on the critical short-circuit ratio. This method can significantly improve the subsynchronous stability of new energy power plants under weak grid conditions and solves the problem of lacking quantitative capacity calculation for configuring grid-connected converters in existing technologies for grid-connected new energy power plants.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] To achieve the above objectives, a first aspect of the present invention proposes a network configuration variation based on short-circuit ratio margin, comprising the following:

[0010] Construct a grid-type converter system model and obtain the critical short-circuit ratio (CSCR) of the power station;

[0011] Calculate the current short-circuit ratio (SCR) of the power station based on the short-circuit capacity of the AC system and the capacity of the grid-connected equipment.

[0012] Set the target short-circuit ratio margin β0% for the power station grid connection system, calculate the current short-circuit ratio margin β% and compare it. If the current short-circuit ratio margin β% is not less than the target short-circuit ratio margin β0%, it indicates that the stability requirement has been met; otherwise, calculate the corrected short-circuit ratio SCR′ based on the target short-circuit ratio margin β0%.

[0013] Calculate the required total capacity of the grid-type converter based on the corrected short-circuit ratio SCR′.

[0014] Preferably, the control strategy of the grid-type converter in the system model is power outer loop control, and the voltage amplitude and phase angle are generated by the power outer loop.

[0015] Preferably, the control parameters of the grid-type converter are obtained, and the critical short-circuit ratio (CSCR) is obtained through analysis or black-box testing.

[0016] Preferably, the current short-circuit ratio (SCR) is calculated from the AC system short-circuit capacity and the grid-connected equipment capacity. The formula for calculating the SCR of a single grid-connected device is as follows:

[0017]

[0018] The SCR calculation formula for multi-equipment field grid connection is:

[0019]

[0020] Among them, S PCC To compensate for the short-circuit capacity at the AC grid connection point, U g Z is the system's rated voltage. g S is the sum of the transformer impedance and tie line impedance of the converter connected to the power grid. GFL n represents the capacity of a single grid-connected converter, and n represents the number of grid-connected converters connected to the system.

[0021] Preferably, the current system short-circuit ratio margin can be calculated from the relative relationship between the current short-circuit ratio (SCR) and the critical short-circuit ratio (CSCR), as shown in the formula:

[0022]

[0023] Where β% is the current system short-circuit ratio margin, SCR is the current short-circuit ratio, and CSCR is the critical short-circuit ratio.

[0024] Preferably, the target short-circuit ratio margin β0% is set to 20%.

[0025] Preferably, the step of calculating the corrected short-circuit ratio based on the target short-circuit ratio margin specifically involves:

[0026]

[0027] Where β0% is the target short-circuit ratio margin, SCR′ is the corrected short-circuit ratio, and CSCR is the critical short-circuit ratio.

[0028] Preferably, the step of calculating the required total capacity of the grid-type converter based on the corrected short-circuit ratio specifically involves:

[0029] The number of grid-type converters N in the connected system is calculated based on the corrected short-circuit ratio. The total capacity of the required grid-type converters is then calculated using the following formula:

[0030]

[0031] Among them, S GFM For the capacity of a single grid-connected converter in a system, This represents the total capacity of the required grid-type converter.

[0032] Preferably, the calculation of the number N of grid-type converters connected to the system based on the corrected short-circuit ratio specifically refers to:

[0033] The formula for calculating the short-circuit ratio when multiple grid-connected converters are connected is as follows:

[0034]

[0035] The formula for calculating the number N of grid-type converters in the connected system is:

[0036]

[0037] Where SCR′ is the corrected short-circuit ratio, Zn is the grid-side line impedance, Un is the main grid-side voltage, and Z GFM S represents the transient reactance of a grid-connected converter under overcurrent constraints for a single grid-connected converter, where n is the number of grid-connected converters connected to the system; and S represents the transient reactance of the grid-connected converter. GFM The capacity of a single grid-connected converter.

[0038] A second aspect of the present invention provides a grid-type converter capacity configuration system based on short-circuit ratio margin using the method described in the first aspect of the present invention, comprising: a critical short-circuit ratio acquisition module, which obtains the critical short-circuit ratio of the site through analytical calculation of specific control parameters provided by the equipment manufacturer or by performing black-box testing, characterized in that:

[0039] The actual short-circuit ratio calculation module calculates the actual short-circuit ratio by comparing the short-circuit capacity of the AC system with the capacity of grid-connected equipment.

[0040] The actual stability margin compliance judgment module selects an appropriate short-circuit ratio margin, calculates the current short-circuit ratio margin, and compares it to determine whether the actual stability margin meets the standard.

[0041] If the actual stability margin compliance judgment module determines that the actual short-circuit ratio is not met, the actual short-circuit ratio correction module calculates the required corrected actual short-circuit ratio.

[0042] The grid capacity calculation module calculates the required total grid capacity based on the corrected actual short-circuit ratio.

[0043] A third aspect of the present invention provides an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program, when loaded onto the processor, implements the grid-type converter capacity configuration method based on short-circuit ratio margin as described in the first aspect of the present invention.

[0044] A fourth aspect of the present invention provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the grid-type converter capacity configuration method based on short-circuit ratio margin as described in the first aspect of the present invention.

[0045] The present invention has the following beneficial effects:

[0046] 1. This invention proposes a method and system for configuring grid-type converter capacity based on short-circuit ratio margin. By selecting an appropriate short-circuit ratio margin to correct the actual short-circuit ratio, the grid-type capacity is quantitatively calculated, solving the problem of quantitatively configuring the capacity of grid-type converters in new energy power plants in the prior art. Based on the proposed capacity calculation process, the grid-type configuration capacity that meets the required short-circuit ratio margin can be obtained, improving the stability margin of the power plant grid-connected system in the subsynchronous frequency band.

[0047] 2. Compared with other grid-type converter configuration methods, by selecting the target short-circuit ratio margin through the selection of set selection rules, the stability margin of the station can be improved more effectively and quantitatively, and the risk of subsynchronous oscillation can be reduced. Attached Figure Description

[0048] Figure 1 This is the main circuit topology of a grid-connected photovoltaic power station;

[0049] Figure 2 The time-domain simulation waveform of the grid connection point of a grid-connected photovoltaic power station;

[0050] Figure 3 To configure the main circuit topology after the grid-type converter;

[0051] Figure 4 Time-domain simulation waveforms after quantitative configuration of the grid-type converter;

[0052] Figure 5 Diagram of the grid-connected main circuit and control structure of a grid-type converter;

[0053] Figure 6 This is a flowchart of the present invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0056] Embodiment 1 of this invention proposes a capacity configuration method for grid-connected converters based on short-circuit ratio margin. Referring to a photovoltaic power station in Tibet, a total of 32 grid-connected converters with a rated capacity of 1260kW are installed. These converters are connected to a 110kV step-up substation via three 35kV collector lines through a 1250kW box-type transformer, and then transmitted to the 110kV substation via one overhead line. The total installed capacity is 40MW. The station topology is as follows: Figure 1 As shown. The line impedance Zg is 0.01mH. The simulation time is set to 3s, the simulation step size is 1 / 32000s, the initial state is 10% rated power output, and it switches to rated power output after 3s. The three-phase voltage V at the substation grid connection point is... abc Simulation waveforms of active power P and reactive power Q are shown below. Figure 2 Under the current grid strength, grid-connected converter stations cannot transmit rated power under the constraint of small disturbance subsynchronous oscillations, resulting in insufficient transmission capacity and power loss. Therefore, a quantitative configuration of grid-connected converters is required. The station topology after configuring grid-connected converters is as follows: Figure 1 As shown, Figure 6 The following content is shown:

[0057] A grid-type converter system model was constructed, and the critical short-circuit ratio (CSCR) of the power station was obtained.

[0058] Preferably, such as Figure 5 As shown, the control strategy of the grid-type converter in the system model is power outer loop control, and the voltage amplitude and phase angle are generated by the power outer loop.

[0059] Preferably, the control parameters of the grid-type converter are obtained, and the critical short-circuit ratio (CSCR) is obtained through analysis or black-box testing.

[0060] Specifically, in this embodiment, the critical short-circuit ratio (CSCR) of the power station was measured to be 1.417.

[0061] The current short-circuit ratio (SCR) of the power station is calculated based on the short-circuit capacity of the AC system and the capacity of the grid-connected equipment. Preferably, the SCR is calculated from the short-circuit capacity of the AC system and the capacity of the grid-connected equipment. The formula for calculating the SCR of a single grid-connected device is as follows:

[0062]

[0063] The SCR calculation formula for multi-equipment field grid connection is:

[0064]

[0065] Among them, S PCC To compensate for the short-circuit capacity at the AC grid connection point, U g Z is the system's rated voltage. g S is the sum of the transformer impedance and tie line impedance of the converter connected to the power grid. GFL n represents the capacity of a single grid-connected converter, and n represents the number of grid-connected converters connected to the system.

[0066] Specifically, the short-circuit ratio (SCR) of the power station calculated in this embodiment is 1.19.

[0067] Preferably, the current system short-circuit ratio margin can be calculated from the relative relationship between the current short-circuit ratio (SCR) and the critical short-circuit ratio (CSCR), as shown in the formula:

[0068]

[0069] Where β% is the current system short-circuit ratio margin, SCR is the current short-circuit ratio, and CSCR is the critical short-circuit ratio.

[0070] Specifically, the β% calculated in this embodiment is -19%.

[0071] Set the target short-circuit ratio margin β0% for the substation grid-connected system, calculate the current short-circuit ratio margin β% and compare them. If the current short-circuit ratio margin β% is not less than the target short-circuit ratio margin β0%, it indicates that the stability requirements have been met; otherwise, calculate the corrected short-circuit ratio SCR′ based on the target short-circuit ratio margin β0%.

[0072] Preferably, the target short-circuit ratio margin β0% is set to 20%.

[0073] Preferably, the step of calculating the corrected short-circuit ratio based on the target short-circuit ratio margin specifically involves:

[0074]

[0075] Where β0% is the target short-circuit ratio margin, SCR′ is the corrected short-circuit ratio, and CSCR is the critical short-circuit ratio.

[0076] Specifically, the calculated short-circuit ratio SCR′ after network access correction should be 1.77.

[0077] Calculate the required total capacity of the grid-type converter based on the corrected short-circuit ratio SCR′.

[0078] Preferably, the step of calculating the required total capacity of the grid-type converter based on the corrected short-circuit ratio specifically involves:

[0079] The number of grid-type converters N in the connected system is calculated based on the corrected short-circuit ratio. The total capacity of the required grid-type converters is then calculated using the following formula:

[0080]

[0081] Among them, S GFM For the capacity of a single grid-connected converter in a system, This represents the total capacity of the required grid-type converter.

[0082] Preferably, the calculation of the number N of grid-type converters connected to the system based on the corrected short-circuit ratio specifically refers to:

[0083] The formula for calculating the short-circuit ratio when multiple grid-connected converters are connected is as follows:

[0084]

[0085] The formula for calculating the number N of grid-type converters in the connected system is:

[0086]

[0087] Where SCR′ is the corrected short-circuit ratio, Zn is the grid-side line impedance, Un is the main grid-side voltage, and Z GFM S represents the transient reactance of a grid-connected converter under overcurrent constraints for a single grid-connected converter, where n is the number of grid-connected converters connected to the system; and S represents the transient reactance of the grid-connected converter. GFM The capacity of a single grid-connected converter.

[0088] Specifically, in this embodiment, the capacity of a single grid-connected converter is 1.25MW. Figure 3 As shown. The equivalent output impedance under short-circuit fault conditions was measured to be 0.16mH. After calculation and rounding, the required capacity is 1.25MW, requiring 8 grid-connected converters. The corrected calculated short-circuit ratio is 1.78, which meets the requirements. At this point, the grid-connected converters account for 20% of the station's capacity. Time-domain simulation was performed, and the simulation waveforms are shown below. Figure 4 This verifies the effectiveness of capacity configuration. Embodiment 2 of the present invention proposes a grid-type converter capacity configuration system based on short-circuit ratio margin using the method described in Embodiment 1 of the present invention, comprising: a critical short-circuit ratio acquisition module, which obtains the critical short-circuit ratio of the site through analytical calculation of specific control parameters provided by the equipment manufacturer or by performing black-box testing, characterized in that;

[0089] The actual short-circuit ratio calculation module calculates the actual short-circuit ratio by comparing the short-circuit capacity of the AC system with the capacity of grid-connected equipment.

[0090] The actual stability margin compliance judgment module selects an appropriate short-circuit ratio margin, calculates the current short-circuit ratio margin, and compares it to determine whether the actual stability margin meets the standard.

[0091] If the actual stability margin compliance judgment module determines that the actual short-circuit ratio is not met, the actual short-circuit ratio correction module calculates the required corrected actual short-circuit ratio.

[0092] The grid capacity calculation module calculates the required total grid capacity based on the corrected actual short-circuit ratio.

[0093] Embodiment 3 of the present invention proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the computer program is loaded onto the processor, it implements the grid-type converter capacity configuration method based on short-circuit ratio margin described in Embodiment 1 of the present invention.

[0094] Embodiment 4 of the present invention proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the grid-type converter capacity configuration method based on short-circuit ratio margin described in Embodiment 1 of the present invention.

[0095] The above description is only a part of the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the protection scope of the present invention.

Claims

1. A method for configuring the capacity of a grid-type converter based on short-circuit ratio margin, characterized in that, Includes the following: Construct a grid-type converter system model and obtain the critical short-circuit ratio of the power station. CSCR ; Calculate the current short-circuit ratio (SCR) of the power station based on the short-circuit capacity of the AC system and the capacity of the grid-connected equipment. Set the target short-circuit ratio margin for the power station grid connection system Calculate the current short-circuit ratio margin β And compare them, if the current short-circuit ratio margin is... β % not less than the target short-circuit ratio margin If the target short-circuit ratio is met, it indicates that the stable requirements have been met; otherwise, it is based on the target short-circuit ratio margin. Calculate the corrected short-circuit ratio to satisfy the short-circuit ratio margin. ; Based on the corrected short-circuit ratio Calculate the required total capacity of the grid-type converter as follows: : in, For the capacity of a single grid-connected converter in a system, The total capacity of the required grid-type converter, To calculate the number of grid-type converters in the connected system based on the corrected short-circuit ratio; Based on the corrected short-circuit ratio The calculation formula is: The formula for calculating the number N of grid-type converters connected to the system is: in, This is the corrected short-circuit ratio. Zn For the network-side line impedance, Un Main grid side voltage, Z GFM The transient reactance of a grid-connected converter under overcurrent constraints for a single grid-connected converter. n The number of grid-connected converters connected to the system; among which, S GFL The capacity of a single grid-connected converter.

2. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 1, characterized in that: In the system model, the control strategy for the grid-type converter is power outer loop control, where the voltage amplitude and phase angle are generated by the power outer loop.

3. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 1, characterized in that: Obtain the control parameters of the grid-type converter, and determine the critical short-circuit ratio through analysis or black-box testing. CSCR .

4. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 3, characterized in that: The current short-circuit ratio (SCR) is calculated from the short-circuit capacity of the AC system and the capacity of the grid-connected equipment, and is the grid-connected short-circuit ratio of a single device. SCR The calculation formula is: The SCR calculation formula for multi-equipment field grid connection is: in, S PCC To improve the short-circuit capacity at the AC grid connection point, U g The system's rated voltage. Z g This is the sum of the transformer impedance and tie line impedance of the converter connected to the power grid. S GFL For the capacity of a single grid-connected converter, n The number of grid-connected converters connected to the system.

5. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 4, characterized in that: The current system short-circuit ratio margin can be determined by the current short-circuit ratio. SCR Compared with critical short-circuit ratio CSCR The relative relationship is calculated using the following formula: in, β % represents the current system short-circuit ratio margin, SCR represents the current short-circuit ratio, and CSCR represents the critical short-circuit ratio.

6. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 1, characterized in that: The target short-circuit ratio margin Set to 20%.

7. The grid-type converter capacity configuration method based on short-circuit ratio margin according to claim 6, characterized in that: The calculation of the corrected short-circuit ratio based on the target short-circuit ratio margin is as follows: in, For the target short-circuit ratio margin, The corrected short-circuit ratio is CSCR, which is the critical short-circuit ratio.

8. A grid-type converter capacity configuration system based on short-circuit ratio margin using the method of any one of claims 1-7, comprising: The critical short-circuit ratio acquisition module obtains the critical short-circuit ratio of the station through analytical calculation of specific control parameters provided by the equipment manufacturer or by conducting black-box testing. Its key feature is: The actual short-circuit ratio calculation module calculates the actual short-circuit ratio based on the short-circuit capacity of the AC system and the capacity of the grid-connected equipment. The actual stability margin compliance judgment module selects an appropriate short-circuit ratio margin, calculates the current short-circuit ratio margin, and compares it to determine whether the actual stability margin meets the standard. If the actual stability margin compliance judgment module determines that the actual short-circuit ratio is not met, the actual short-circuit ratio correction module calculates the required corrected actual short-circuit ratio. The grid capacity calculation module calculates the required total grid capacity based on the corrected actual short-circuit ratio.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is loaded into the processor, it implements the grid-type converter capacity configuration method based on short-circuit ratio margin according to any one of claims 1-7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the grid-type converter capacity configuration method based on short-circuit ratio margin according to any one of claims 1-7.

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