Steady-state analysis method and system for offshore wind farm

Abstract

The application provides a steady-state analysis method and system for an offshore wind farm. The method comprises the following steps: according to the steady-state working characteristics of full-power conversion wind turbine generators in the offshore wind farm, each wind turbine generator is equivalent to a constant current source, and the equivalent current phasor of each constant current source is calculated; based on the topology structure and line parameters of the power collection line of the offshore wind farm and the equivalent current phasor of each wind turbine generator under the same collection bus, each collection bus in the power collection line is equivalent to an equivalent model in parallel connection with an equivalent current source and an equivalent impedance; an equivalent calculation model of the offshore wind farm is generated according to the equivalent models corresponding to all the collection buses, and the steady-state analysis results of multiple parameters of the offshore wind farm are obtained through the power flow calculation of the equivalent calculation model. The method can be applied to the steady-state analysis calculation of large-scale offshore wind farms, and the accuracy of the steady-state analysis calculation is improved.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a steady-state analysis method and system for offshore wind farms. Background Technology

[0002] Currently, to reduce carbon emissions and alleviate energy pressure, the adoption rate of new energy power generation is gradually increasing, with wind power being one of the main new energy power generation technologies. In practical applications, to maintain the normal operation of wind farms and facilitate the analysis and calculation of large-scale power systems, steady-state analysis of wind farms is necessary. This steady-state analysis mainly refers to the power flow calculation of the wind farm within the power system. To reduce the scale of system modeling and solution during the analysis and calculation process, static equivalent models are used to replace the wind farm's turbines and collection systems.

[0003] In related technologies, when performing power flow calculations, wind turbines are typically treated as PQ nodes, taking into account the impedance of the turbine's output transformer and collector lines. Then, a static equivalent model of the wind farm is constructed using the principle of constant losses, treating each wind turbine as a single unit and the collector lines as equivalent impedances. This scheme assumes all wind turbines have the same power factor and ignores differences in terminal voltage between units.

[0004] However, in practical applications, due to the uneven wind speed distribution in wind farms and the significant differences between the topology of the collection system and the ideal assumptions, the calculation results of the above-mentioned PQ node-based equivalent modeling steady-state analysis scheme are prone to errors and are not applicable to large-scale wind farms. Furthermore, because the collection lines used in offshore wind turbines often differ significantly from those used in onshore wind power, the errors in the steady-state analysis calculation results of offshore wind farms using the aforementioned related technologies will be further amplified.

[0005] Therefore, obtaining accurate steady-state analysis results for the power systems of large-scale offshore wind farms has become an urgent problem to be solved. Summary of the Invention

[0006] This application aims to at least partially address one of the technical problems in the related art.

[0007] Therefore, the first objective of this application is to propose a steady-state analysis method for offshore wind farms. This method considers the influence of the topology and parameters of the collection lines of different offshore wind farms on the steady-state analysis, and is applicable to the steady-state analysis calculation of large-scale offshore wind farms, thereby improving the accuracy of the steady-state analysis calculation.

[0008] The second objective of this application is to propose a steady-state analysis system for offshore wind farms.

[0009] The third objective of this application is to provide a non-transitory computer-readable storage medium.

[0010] To achieve the above objectives, a first aspect of this application provides a steady-state analysis method for offshore wind farms, the method comprising the following steps:

[0011] Based on the steady-state operating characteristics of full-power conversion wind turbine units in offshore wind farms, each wind turbine unit is equivalent to a constant current source, and the equivalent current phasor of each constant current source is calculated.

[0012] Based on the topology and line parameters of the collection lines of the offshore wind farm, and the equivalent current phasor of each wind turbine under the same collection bus, each collection bus in the collection lines is equivalent to an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel.

[0013] An equivalent calculation model of the offshore wind farm is generated based on the equivalent models corresponding to all the busbars, and the power flow calculation of the power system is performed through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

[0014] Optionally, in one embodiment of this application, the topology of the collector line includes: a radial collector topology and a star collector topology. The step of equating each collecting bus in the collector line with an equivalent model consisting of an equivalent current source and an equivalent impedance in parallel includes: for an offshore wind farm with the radial collector topology, constructing an equivalent impedance model for each wind turbine corresponding to any collecting bus; and performing Norton equivalents on the equivalent impedance model for the first wind turbine corresponding to any collecting bus to obtain the first wind turbine. The corresponding initial Norton equivalent circuit is obtained, and the parameter values ​​of the initial Norton equivalent circuit are calculated based on the line parameters and the equivalent current phasor of the first wind turbine. Based on the initial Norton equivalent circuit, the remaining wind turbines in any busbar are sequentially Norton equivalents according to the order of each wind turbine in any busbar until the Norton equivalent circuit corresponding to the last wind turbine in any busbar is obtained. The Norton equivalent circuit corresponding to the last wind turbine is used as the equivalent model corresponding to any busbar.

[0015] Optionally, in one embodiment of this application, performing stepwise Norton equivalent averaging on the remaining wind turbines in any of the busbars includes: starting from the initial Norton equivalent circuit, combining the Norton equivalent circuit corresponding to the current wind turbine with the single-unit equivalent impedance model corresponding to the next adjacent wind turbine in the busbar to generate a composite equivalent impedance model corresponding to the next wind turbine; performing Norton equivalent averaging on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine, and calculating the parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine based on the parameter values ​​of the composite equivalent impedance model.

[0016] Optionally, in one embodiment of this application, each collecting bus in the collecting line is equivalent to an equivalent model of an equivalent current source and an equivalent impedance connected in parallel. The method further includes: for the offshore wind farm with the star-shaped collecting topology, constructing an equivalent impedance model for each wind turbine in any collecting bus; performing Norton equivalent equivalence on each of the single-unit equivalent impedance models, equating the single-unit equivalent impedance model to an initial Norton circuit consisting of an initial current source and an initial impedance connected in parallel, and calculating the parameter values ​​of the initial Norton equivalent circuit corresponding to each wind turbine based on the line parameters and the equivalent current phasor of each wind turbine; equating all the parallel initial Norton equivalent circuits to the Norton equivalent circuit corresponding to any collecting bus, and calculating the parameter values ​​of the Norton equivalent circuit corresponding to any collecting bus based on the parameter values ​​of each of the initial Norton equivalent circuits.

[0017] Optionally, in one embodiment of this application, the equivalent impedance model of a single generator unit includes: the constant current source, the equivalent resistance of the generator terminal transformer, the equivalent reactance of the generator terminal transformer, the resistance of the target cable, the reactance of the target cable, and the susceptance to ground on both sides of the target cable. The first end of the constant current source is grounded, and the second end of the constant current source is connected to the first end of the equivalent resistance of the generator terminal transformer. The second end of the equivalent resistance of the generator terminal transformer is connected to the first end of the equivalent reactance of the generator terminal transformer. The second end of the equivalent reactance of the generator terminal transformer is connected to the first end of the left-side susceptance to ground and the first end of the resistance of the target cable. The second end of the left-side susceptance to ground of the target cable is grounded, and the second end of the resistance of the target cable is connected to the first end of the reactance of the target cable. The second end of the reactance of the target cable is connected to the first end of the right-side susceptance to ground of the target cable, and the second end of the right-side susceptance to ground of the target cable is grounded.

[0018] Optionally, in one embodiment of this application, the equivalent current phasor of each of the constant current sources is calculated using the following formula:

[0019]

[0020] Among them, I i I is the equivalent current phasor of the i-th wind turbine. d，i I is the active component of the i-th wind turbine. q，i I is the reactive component of the i-th wind turbine. max，i θ is the maximum current limit of the converter of the i-th wind turbine unit. i It is the power factor angle, and i represents any wind turbine in the offshore wind farm.

[0021] To achieve the above objectives, a second aspect of this application also proposes a steady-state analysis system for offshore wind farms, comprising the following modules:

[0022] The first equivalent module is used to convert each wind turbine into a constant current source based on the steady-state operating characteristics of the full-power conversion wind turbine in the offshore wind farm, and to calculate the equivalent current phasor of each constant current source.

[0023] The second equivalent module is used to, based on the topology and line parameters of the collection line of the offshore wind farm, and the equivalent current phasor of each wind turbine under the same collection bus, to convert each collection bus in the collection line into an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel.

[0024] The calculation module is used to generate an equivalent calculation model of the offshore wind farm based on the equivalent models corresponding to all the collecting buses, and to perform power flow calculation of the power system through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

[0025] Optionally, in one embodiment of this application, the second equivalent module is specifically used for: constructing an equivalent impedance model for each wind turbine in any collection bus for the offshore wind farm with the radial collector topology; performing Norton equivalent equivalence on the equivalent impedance model for the first wind turbine in any collection bus to obtain an initial Norton equivalent circuit for the first wind turbine, and calculating the parameter values ​​of the initial Norton equivalent circuit based on the line parameters and the equivalent current phasor of the first wind turbine; performing Norton equivalent equivalence step by step on the remaining wind turbines in any collection bus according to the order of each wind turbine in any collection bus, until obtaining the Norton equivalent circuit for the last wind turbine in any collection bus; and using the Norton equivalent circuit for the last wind turbine as the equivalent model for any collection bus.

[0026] Optionally, in one embodiment of this application, the second equivalent module is further configured to: starting from the initial Norton equivalent circuit, combine the Norton equivalent circuit corresponding to the current wind turbine with the single-unit equivalent impedance model corresponding to the next adjacent wind turbine in the bus to generate a composite equivalent impedance model corresponding to the next wind turbine; perform Norton equivalence on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine, and calculate the parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine based on the parameter values ​​of the composite equivalent impedance model.

[0027] To implement the above embodiments, a third aspect of this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steady-state analysis method for offshore wind farms in the above embodiments.

[0028] The technical solution provided by the embodiments of this application brings at least the following beneficial effects: First, this application equates each full-power conversion wind turbine to a constant current source and calculates the equivalent current phasor of each current source. Then, based on the topology and parameters of the offshore wind farm's collector lines, Norton's equivalent principle is applied to obtain the equivalent circuit at each collector bus. Finally, the equivalent model is substituted into the power system power flow calculation equation to conduct steady-state calculation analysis of the wind farm. This application is applicable to the steady-state analysis calculation of power systems containing large-scale offshore wind farms. The physical meaning of each component in the constructed equivalent model is clear, accurately reflecting the influence of different offshore wind farm collector line topologies and parameters on steady-state analysis. It can adapt to various output conditions of offshore wind farms, enriching the applicable scenarios for steady-state analysis and improving the accuracy and relevance of steady-state calculations for offshore wind farms.

[0029] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0030] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 A flowchart illustrating a steady-state analysis method for an offshore wind farm proposed in this application embodiment;

[0032] Figure 2 This is a schematic diagram of a radial collector topology offshore wind farm grid connection structure proposed in an embodiment of this application;

[0033] Figure 3 This is a schematic diagram of a star-shaped collector topology grid connection structure for an offshore wind farm proposed in an embodiment of this application;

[0034] Figure 4 A flowchart illustrating a method for constructing an equivalent model of a busbar according to an embodiment of this application;

[0035] Figure 5 This is a schematic diagram of the structure of an equivalent impedance model for a single generator unit proposed in an embodiment of this application;

[0036] Figure 6 This is a schematic diagram of the structure of a Norton equivalent circuit proposed in an embodiment of this application;

[0037] Figure 7 This is a schematic diagram of the structure of a composite equivalent impedance model proposed in an embodiment of this application;

[0038] Figure 8 A flowchart illustrating another method for constructing an equivalent model of a busbar according to an embodiment of this application;

[0039] Figure 9 This is a schematic diagram of the equivalent circuit of each unit in a busbar according to an embodiment of this application;

[0040] Figure 10 A flowchart illustrating a specific steady-state analysis method for an offshore wind farm proposed in this application embodiment;

[0041] Figure 11 This is a schematic diagram of the structure of a steady-state analysis system for an offshore wind farm proposed in an embodiment of this application. Detailed Implementation

[0042] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0043] It should be noted that for offshore wind farms, the offshore wind turbines are connected via medium-voltage submarine cables. Compared to the overhead lines commonly used for onshore wind turbines, submarine cables have higher ground capacitance, leading to significant differences in the terminal voltages of each turbine. This results in substantial errors when using equivalent methods in related technologies to calculate power flow in offshore wind farms, and the differences in turbine output further exacerbate the errors in steady-state calculations. Therefore, this application proposes a steady-state analysis method for offshore wind farms. This method can be applied to the steady-state analysis and calculation of power systems containing large-scale offshore wind farms, improving the accuracy of steady-state calculations.

[0044] The steady-state analysis method and system for offshore wind farms proposed in this application are described in detail below with reference to the accompanying drawings.

[0045] Figure 1 This is a flowchart of a steady-state analysis method for offshore wind farms proposed in an embodiment of this application, as shown below. Figure 1 As shown, the method includes the following steps:

[0046] Step S101: Based on the steady-state operating characteristics of the full-power conversion wind turbine units in the offshore wind farm, each wind turbine unit is equivalent to a constant current source, and the equivalent current phasor of each constant current source is calculated.

[0047] Specifically, since offshore wind farms typically use variable speed constant frequency full power conversion units, i.e. direct drive units, this application constructs an equivalent model and performs calculations based on the steady-state operating characteristics of offshore wind turbine units when conducting steady-state analysis of offshore wind farms.

[0048] Specifically, during steady-state operation, the offshore wind turbine adopts a maximum power point tracking (MPPT) control strategy, adjusting the converter output current based on the AC voltage at the turbine terminals. Based on the steady-state operating characteristics of the variable-speed constant-frequency full-power converter, this application treats each full-power converter wind turbine in the offshore wind farm as an equivalent constant current source, and calculates the equivalent current phasor of each wind turbine (which can also be regarded as an equivalent constant current source) in combination with the specific operating conditions of each wind turbine.

[0049] In one embodiment of this application, various operating condition information such as wind speed, turbine status, and power factor settings in the environment where different wind turbines are located can be combined to treat each wind turbine as an equivalent constant current source, and the terminal current phasor of each wind turbine (i.e., the equivalent current phasor of the constant current source) can be calculated using the following formula:

[0050]

[0051] Among them, I i I is the equivalent current phasor of the i-th wind turbine. d，i I is the active component of the i-th wind turbine. q，i I is the reactive component of the i-th wind turbine. max，i θ is the maximum current limit of the converter of the i-th wind turbine unit. i It is the power factor angle, and i represents any wind turbine in the offshore wind farm.

[0052] In this embodiment, the values ​​of each parameter in the above formula can be calculated based on the operating conditions information of the current scenario, such as wind speed, unit status, and power factor setting. This allows for steady-state analysis based on the current operating conditions of the unit, improving the real-time performance of the steady-state analysis.

[0053] Step S102: Based on the topology and line parameters of the collection line of the offshore wind farm, and the equivalent current phasor of each wind turbine under the same collection bus, each collection bus in the collection line is equivalent to an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel.

[0054] It should be noted that offshore wind farms typically consist of multiple full-power converter wind turbines. These turbines are connected to an offshore AC step-up substation via submarine cables of appropriate types; for example, a 35kV submarine cable might connect to a 220kV offshore AC step-up substation. Offshore wind farms can connect to the grid using various types of collection lines, meaning they may have multiple grid connection structures.

[0055] For example, the topology of a collector line may have two types of topologies: radial and star. Figure 2 The radial collector topology of the offshore wind farm grid connection structure and Figure 3 The diagram shows the grid connection structure of an offshore wind farm with a star-shaped collector topology. As shown in the figure, there are multiple collecting buses in the offshore wind farm (for simplicity, ...). Figure 2 and Figure 3 Only two busbars are labeled (namely, the first collecting busbar 11 and the first collecting busbar 12). Each collecting busbar connects multiple offshore wind turbines, as shown in the figure. Each busbar includes turbine 1, turbine 2, up to turbine n, where n is a positive integer determined according to actual needs. Each collecting busbar can also be connected to the 220kV power grid via subsequent reactance compensation busbars, etc.

[0056] Therefore, this application conducts steady-state analysis on different offshore wind farm collection structures so that the steady-state analysis method of this application can be applied to a variety of offshore wind farms in practical applications.

[0057] Specifically, this application first constructs an equivalent model of each collecting bus in the wind farm based on the current wind farm's collector line topology, the line parameters of each collecting bus in the collector line (such as cable resistance and reactance), and the equivalent current phasor of each wind turbine calculated in step S101, so as to subsequently generate an equivalent model of the entire wind farm. The following section addresses... Figure 2 and Figure 3 The process of constructing equivalent models of offshore wind farms with the two collector topologies shown is explained in detail.

[0058] To more clearly illustrate the specific implementation process of establishing an equivalent model of the collecting bus in an offshore wind farm with a radial collecting topology, the following is an exemplary description of a method for constructing an equivalent model of the collecting bus proposed in one embodiment of this application. Figure 4This is a flowchart illustrating a method for constructing an equivalent model of a busbar according to an embodiment of this application, as shown below. Figure 4 As shown, the method includes the following steps:

[0059] Step S401: For an offshore wind farm with a radial collector topology, construct an equivalent impedance model for each wind turbine unit in any collector bus.

[0060] It should be noted that when constructing the equivalent model of the wind farm, this application retains the model of the medium-voltage bus (i.e., the collection bus) and above voltage levels in the wind farm, and performs equivalent calculations on the wind turbines under each medium-voltage bus.

[0061] Specifically, since the equivalent process of wind turbines under each collection bus in an offshore wind farm is the same, this embodiment arbitrarily selects one bus from multiple collection buses for illustrative purposes. For example, it selects... Figure 2 The first collecting bus 11 in the process will be used as an example for explanation. First, the characteristics of the variable speed constant frequency full power converter are analyzed, and a corresponding single unit equivalent impedance model is constructed for each wind turbine in the selected collecting bus.

[0062] As an example, the equivalent impedance model of a single wind turbine unit constructed for the first wind turbine unit in the busbar is as follows: Figure 5 As shown, the model includes: a constant current source I1 and the equivalent resistance R of the terminal transformer. T1 Equivalent reactance X of the generator terminal transformer T1 The resistance R1 of the target cable, the reactance X1 of the target cable, and the susceptance to ground on both sides of the target cable. and

[0063] Among them, the first terminal of the constant current source I1 is grounded, and the second terminal of the constant current source is connected to the equivalent resistance R of the terminal transformer. T1 The first terminal is connected; the equivalent resistance R of the transformer at the generator terminal. T1 The equivalent reactance X of the second terminal and the generator terminal transformer T1 The first terminal is connected, and the equivalent reactance X of the transformer at the generator terminal is... T1 The second end, with the left side of the target cable to ground susceptance. The first end is connected to the first end of the resistor R1 of the target cable; the left side of the target cable has a susceptance to ground. The second terminal is grounded, and the second terminal of the resistor R1 of the target cable is connected to the first terminal of the reactance X1 of the target cable; the second terminal X1 of the reactance of the target cable is connected to the right side of the target cable relative to ground. The first end is connected, and the right side of the target cable has a ground susceptance. The second end is grounded.

[0064] For radial collector topology offshore wind farms, the target cable is the cable between the current wind turbine and the next adjacent turbine on the busbar, for example, Figure 2 The submarine cable between Unit 1 and Unit 2 in the first busbar. and Both are ground susceptances represented by the PI-type equivalent circuit of this section of cable. The two values ​​are equal and are only used to distinguish different components.

[0065] It should be noted that the structure of the equivalent impedance model for each wind turbine unit in this busbar is as follows: Figure 5 As shown, due to the differences in line parameters at different units and the equivalent current phasors of each unit, the parameter values ​​of each component in the equivalent impedance model of a single wind turbine unit may be different.

[0066] Step S402: Perform Norton equivalent model on the equivalent impedance model of the first wind turbine in any busbar to obtain the initial Norton equivalent circuit corresponding to the first wind turbine, and calculate the parameter values ​​of the initial Norton equivalent circuit based on the line parameters and the equivalent current phasor of the first wind turbine.

[0067] Specifically, the first offshore wind turbine in the selected busbar is first evaluated using equivalent values. Figure 2 The radial collector topology shown has the first wind turbine at the end of the feeder. This offshore wind turbine is treated as a constant current source. The calculated current phasor of this constant current source is obtained, and the following calculations are performed: Figure 5 After obtaining the parameter values ​​of each component in the equivalent impedance model of a single wind turbine unit, Norton equivalent circuits are performed on the equivalent impedance model to obtain the Norton equivalent circuit corresponding to the wind turbine unit.

[0068] Specifically, from Figure 5 The port on the right side of the equivalent impedance model shown is equivalent to the impedance of the port shown. Figure 5 The model shown is equivalent to, for example: Figure 6 As shown, a current source I eq A reactor in parallel Z eq The Norton equivalent circuit is formed.

[0069] Furthermore, based on Norton's equivalence principle, the values ​​of the current and equivalent impedance of the equivalent current source at the port are derived. The current of the equivalent current source can be calculated using the following first formula:

[0070]

[0071] Among them, I eq1 It is the current of the equivalent current source in the Norton equivalent circuit of the first unit. Z1 = R1 + jX1, ZT1 =R T1 +jX T1 The meanings of the parameters in the formula are as described above.

[0072] The equivalent impedance can be calculated using the following second formula:

[0073]

[0074] Among them, Z eq1 It is the impedance value of the Norton equivalent circuit of the first unit, and the meaning of each parameter in the formula is as described above.

[0075] Step S403: Based on the initial Norton equivalent circuit, the remaining wind turbines in any busbar are subjected to Norton equivalent circuits in sequence according to the order of each wind turbine in any busbar, until the Norton equivalent circuit corresponding to the last wind turbine in any busbar is obtained.

[0076] Specifically, the initial Norton equivalent circuit corresponding to the first wind turbine is used to perform Norton equivalent on the next adjacent wind turbine, and so on, to perform step-by-step equivalent on each turbine in the selected busbar until the Norton equivalent circuit corresponding to the last wind turbine in the busbar is obtained.

[0077] In one embodiment of this application, the remaining wind turbines in the selected busbar, excluding the first wind turbine, are subjected to step-by-step Norton equivalent equivalence, including the following steps: First, starting from the initial Norton equivalent circuit, the Norton equivalent circuit corresponding to the current wind turbine is combined with the single-unit equivalent impedance model corresponding to the next adjacent wind turbine in the busbar to generate a composite equivalent impedance model corresponding to the next wind turbine; then, Norton equivalent equivalence is performed on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine, and the parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine are calculated based on the parameter values ​​of the composite equivalent impedance model.

[0078] For example, for Figure 2 When performing equivalent circuitry for Unit 2 in the first busbar, the initial Norton equivalent circuit of Unit 1 and the single-unit equivalent impedance model of Unit 2 are combined to obtain the following: Figure 7 The composite equivalent impedance model shown is analyzed from the connection port between unit 2 and unit 3, resulting in the circuits of unit 1 and unit 2 as follows. Figure 7 As shown.

[0079] Where I2 is the current phasor of the equivalent current source of Unit 2, R T2 X is the equivalent resistance of the transformer at the second generator terminal. T2R2 is the equivalent reactance of the transformer at the generator terminal of Unit 2; R2 is the resistance of the submarine cable between Unit 2 and Unit 3; X2 is the reactance of this section of cable. This refers to the susceptance to ground on the left side of this cable segment. This refers to the susceptance to ground on the right side of this cable segment.

[0080] Furthermore, regarding Figure 7 The circuit shown is further equivalently represented using Norton's equivalence principle, yielding the same result. Figure 6 The Norton equivalent circuit in the form shown is used to derive the parameter values ​​of the Norton equivalent circuit based on the parameter values ​​of the initial Norton equivalent circuit in the composite equivalent impedance model and the parameter values ​​of the single unit equivalent impedance model of Unit 2.

[0081] Specifically, the current of the equivalent current source in the Norton equivalent circuit of Computer Group 2 can be obtained through the following third formula:

[0082]

[0083] Among them, I eq2 It is the current of the equivalent current source in the Norton equivalent circuit of Unit 2. Z2 = R2 + jX2, Z T2 =R T2 +jX T2 The meanings of each parameter are as described above.

[0084] The equivalent impedance value of the Norton equivalent circuit in Computer Group 2 can also be obtained using the following fourth formula:

[0085]

[0086] Among them, Z eq2 This is the impedance value of the equivalent impedance in the Norton equivalent circuit of Unit 2, and the meaning of each parameter is as described above.

[0087] Furthermore, following the above principle, the equivalent circuits for units 3 to n at the end of the selected bus are performed step by step, ultimately yielding the Norton equivalent circuit for unit n. The structure of this circuit is similar to... Figure 6 The same applies. Furthermore, by recursively applying the third and fourth formulas, the parameter values ​​of the Norton equivalent circuit for unit n can be obtained, as shown in the following formula:

[0088]

[0089]

[0090] Among them, Z eq,n-1 Let be the Norton equivalent impedance of the n-1 units before the feeder. Z n =Rn +jX n Z T,n =R T,n +jX T,n I n R is the current of the equivalent current source of unit n. T,n X is the equivalent resistance of the transformer at the nth terminal of the generator unit. T,n R is the equivalent reactance of the transformer at the n-end of the unit; n X is the resistance of the submarine cable from unit n to the first collecting bus. n The reactance of this section of cable. This is the susceptance to ground of this section of cable.

[0091] Step S404: Use the Norton equivalent circuit corresponding to the last wind turbine as the equivalent model corresponding to any busbar.

[0092] Thus, the equivalent model corresponding to any selected collection bus is obtained. Furthermore, following the steps in the above method, the equivalent model of each collection bus in the radial collection topology offshore wind farm can be obtained.

[0093] To more clearly illustrate the specific implementation process of establishing an equivalent model for the bus in a star-shaped collector topology offshore wind farm, the following is an exemplary description of another method for constructing an equivalent model for the bus proposed in one embodiment of this application. Figure 8 This is a flowchart illustrating another method for constructing an equivalent model of a busbar according to an embodiment of this application, as shown below. Figure 8 As shown, the method includes the following steps:

[0094] Step S801: For offshore wind farms with a star-shaped collector topology, construct the equivalent impedance model of each wind turbine unit in any collector bus.

[0095] Specifically, since the equivalent processes of wind turbines under each collecting bus in a star-shaped offshore wind farm are identical, this embodiment arbitrarily selects one bus from the multiple collecting buses of the star-shaped wind farm for illustrative purposes. For example, it selects... Figure 3 The first collecting bus 11 in the above example will be used for explanation. First, a corresponding single-unit equivalent impedance model is constructed for each wind turbine in the selected collecting bus. In this embodiment, the single-unit equivalent impedance model constructed for each turbine is consistent with that in the above embodiment of radial collecting topology, and will not be repeated here.

[0096] Step S802: Perform Norton equivalent transformation on the equivalent impedance model of each single unit, and transform the equivalent impedance model of a single unit into an initial Norton value circuit consisting of an initial current source and an initial impedance connected in parallel. Based on the line parameters and the equivalent current phasor of each wind turbine, calculate the parameter values ​​of the initial Norton equivalent circuit corresponding to each wind turbine.

[0097] Specifically, Norton equivalence is performed simultaneously on each wind turbine in the selected busbar, constructing a model for each turbine. Figure 6 The Norton equivalent circuit is shown. Then, referring to the first and second formulas in the above embodiments, the current of the equivalent current source and the resistance of the equivalent impedance in each Norton equivalent circuit are calculated respectively. Thus, we obtain... Figure 9 The equivalent circuits of each unit in the selected bus are shown.

[0098] Step S803: Equivalent all the initial Norton equivalent circuits connected in parallel to the Norton equivalent circuit corresponding to any bus, and calculate the parameter value of the Norton equivalent circuit corresponding to any bus based on the parameter value of each initial Norton equivalent circuit.

[0099] Specifically, such as Figure 9 As shown, based on the parallel connection relationship of the Norton equivalent circuits corresponding to each unit under the selected busbar, the Norton equivalent circuit at the same busbar in a star topology can be obtained. The structure of this Norton equivalent circuit is similar to... Figure 6 The same applies. Furthermore, based on the parameter values ​​of the initial Norton equivalent circuit corresponding to each unit, the parameter values ​​of the Norton equivalent circuit corresponding to the selected busbar are calculated. The specific calculation formula is as follows:

[0100]

[0101] Z eq =Z eq,1 / / Z eq,2 … / / Z eq,n

[0102] Among them, I eq It is the current value of the equivalent current source of the Norton equivalent circuit corresponding to the busbar, Z. eq It is the resistance value of the equivalent impedance of the Norton equivalent circuit corresponding to the busbar, I. eq，i Z is the current value of the equivalent current source of the Norton equivalent circuit corresponding to the i-th unit. eq，i This is the resistance value of the equivalent impedance of the Norton equivalent circuit corresponding to the i-th unit, for example, Figure 9 The first unit shown corresponds to I eq1 and Z eq1 And the I corresponding to the second unit eq2 and Z eq2 wait.

[0103] Therefore, this application can calculate the equivalent model corresponding to each collecting bus in the collector line for different collector line topologies.

[0104] Step S103: Generate an equivalent calculation model of the offshore wind farm based on the equivalent models corresponding to all the collecting buses, and perform power flow calculation of the power system through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

[0105] Among them, several parameters, including grid connection point voltage and power of the offshore wind farm, can represent the steady-state operating parameters of various parts of the offshore wind farm, such as the power distribution and power loss of each branch, and the voltage amplitude of each bus node.

[0106] Specifically, after constructing equivalent models for all busbars in the offshore wind farm, an equivalent calculation model for the offshore wind farm is obtained. In this equivalent calculation model, each node of the busbars in the offshore wind farm is considered an Iθ node, where the current amplitude I and phase θ of the node are known, and the steady-state operating parameters of the node are calculated. Then, each Iθ node is substituted into the power flow calculation equations of the power system to perform calculations and analyses on the grid connection voltage and power of the offshore wind farm.

[0107] It should be noted that power flow calculation is the process of calculating various steady-state operating parameters, such as the distribution of active power, reactive power, and voltage in the power grid, given the power system network topology, component parameters, and generation parameters. The process of power flow calculation using an equivalent calculation model of an offshore wind farm in this application can be referenced from the process of power flow calculation based on a static equivalent model in related technologies, and will not be elaborated here.

[0108] In summary, the steady-state analysis method for offshore wind farms in this application first treats each full-power conversion wind turbine as an equivalent constant current source and calculates the equivalent current phasor of each current source. Then, based on the topology and parameters of the offshore wind farm's collector lines, Norton's equivalent principle is applied to obtain the equivalent circuit at each collector bus. Finally, the equivalent model is substituted into the power system's power flow calculation equations to conduct steady-state calculation and analysis of the wind farm. This method is applicable to the steady-state analysis and calculation of power systems containing large-scale offshore wind farms. The physical meaning of each component in the constructed equivalent model is clear, accurately reflecting the influence of different collector line topologies and parameters of offshore wind farms on steady-state analysis. It can adapt to various output conditions of offshore wind farms, enriching the applicable scenarios for steady-state analysis and improving the accuracy and relevance of steady-state calculations for offshore wind farms.

[0109] To more clearly illustrate the implementation process of the steady-state analysis method for offshore wind farms in this application, a specific method embodiment will be described in detail below. Figure 10 A flowchart illustrating a specific steady-state analysis method for offshore wind farms proposed in this application is shown below. Figure 10 As shown, the fault diagnosis method of this embodiment includes the following steps:

[0110] Step S1: Equivalently treat each full-power converter wind turbine as a constant current source and calculate the equivalent current phasor.

[0111] Step S2: Applying Norton's equivalent principle, based on the topology and parameters of the offshore wind farm's collector lines, each wind turbine on the same collector bus is equivalent to a circuit with current sources and impedances connected in parallel.

[0112] Step S3: Complete the equivalent modeling of all the busbars of the offshore wind farm, and input the equivalent model into the power flow calculation equation of the power system to carry out the steady-state calculation analysis of the wind farm.

[0113] It should be noted that the specific implementation of each step in this embodiment can be referred to the relevant description in the above embodiments, and will not be repeated here.

[0114] To achieve the above embodiments, this application also proposes a steady-state analysis system for offshore wind farms. Figure 11 This is a schematic diagram of the structure of a steady-state analysis system for an offshore wind farm proposed in an embodiment of this application, as shown below. Figure 11 As shown, the system includes a first equivalent module 100, a second equivalent module 200, and a calculation module 300.

[0115] The first equivalent module 100 is used to convert each wind turbine into a constant current source based on the steady-state operating characteristics of the full-power conversion wind turbine in the offshore wind farm, and to calculate the equivalent current phasor of each constant current source.

[0116] The second equivalent module 200 is used to convert each collecting bus in the collecting line into an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel, based on the topology and line parameters of the collecting line of the offshore wind farm, as well as the equivalent current phasor of each wind turbine under the same collecting bus.

[0117] The calculation module 300 is used to generate an equivalent calculation model of the offshore wind farm based on the equivalent models corresponding to all the busbars, and to perform power flow calculation of the power system through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

[0118] Optionally, in one embodiment of this application, the second equivalent module 200 is specifically used for: constructing an equivalent impedance model for each wind turbine in any collection bus for an offshore wind farm with a radial collector topology; performing Norton equivalent equivalence on the equivalent impedance model for the first wind turbine in any collection bus to obtain an initial Norton equivalent circuit for the first wind turbine, and calculating the parameter values ​​of the initial Norton equivalent circuit based on the line parameters and the equivalent current phasor of the first wind turbine; based on the initial Norton equivalent circuit, performing Norton equivalent equivalence step by step on the remaining wind turbines in any collection bus according to the order of each wind turbine in any collection bus, until obtaining the Norton equivalent circuit for the last wind turbine in any collection bus; and using the Norton equivalent circuit for the last wind turbine as the equivalent model for any collection bus.

[0119] Optionally, in one embodiment of this application, the second equivalent module 200 is specifically used to: starting from the initial Norton equivalent circuit, combine the Norton equivalent circuit corresponding to the current wind turbine with the single-unit equivalent impedance model corresponding to the next adjacent wind turbine in the bus to generate a composite equivalent impedance model corresponding to the next wind turbine; perform Norton equivalence on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine, and calculate the parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine based on the parameter values ​​of the composite equivalent impedance model.

[0120] Optionally, in one embodiment of this application, the second equivalent module 200 is further configured to: construct an equivalent impedance model for each wind turbine in any collection bus for an offshore wind farm with a star-shaped collector topology; perform Norton equivalent equivalence on each equivalent impedance model, converting the equivalent impedance model of a single turbine into an initial Norton circuit consisting of an initial current source and an initial impedance connected in parallel, and calculating the parameter values ​​of the initial Norton equivalent circuit corresponding to each wind turbine based on the line parameters and the equivalent current phasor of each wind turbine; convert all the parallel initial Norton equivalent circuits into an equivalent Norton circuit corresponding to any collection bus, and calculate the parameter values ​​of the Norton equivalent circuit corresponding to any collection bus based on the parameter values ​​of each initial Norton equivalent circuit.

[0121] Optionally, in one embodiment of this application, the first equivalent module 100 is specifically used to calculate the equivalent current phasor of each constant current source using the following formula:

[0122]

[0123] Among them, I i I is the equivalent current phasor of the i-th wind turbine. d，i I is the active component of the i-th wind turbine. q，iI is the reactive component of the i-th wind turbine. max，i θ is the maximum current limit of the converter of the i-th wind turbine unit. i It is the power factor angle, and i represents any wind turbine in the offshore wind farm.

[0124] It should be noted that the explanation of the aforementioned embodiment of the steady-state analysis method for offshore wind farms also applies to the system in this embodiment, and will not be repeated here.

[0125] In summary, the steady-state analysis system for offshore wind farms in this application first treats each full-power conversion wind turbine as an equivalent constant current source and calculates the equivalent current phasor of each current source. Then, based on the topology and parameters of the offshore wind farm's collector lines, Norton's equivalent principle is applied to obtain the equivalent circuit at each collector bus. Finally, the equivalent model is substituted into the power system's power flow calculation equations to conduct steady-state calculation and analysis of the wind farm. This system is applicable to the steady-state analysis and calculation of power systems containing large-scale offshore wind farms. The physical meaning of each component in the constructed equivalent model is clear, accurately reflecting the impact of different collector line topologies and parameters of offshore wind farms on steady-state analysis. It can adapt to various output conditions of offshore wind farms, enriching the applicable scenarios for steady-state analysis and improving the accuracy and relevance of steady-state calculations for offshore wind farms.

[0126] To implement the above embodiments, this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steady-state analysis method for offshore wind farms as described in any of the above embodiments.

[0127] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0128] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0129] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0130] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0131] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0132] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0133] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0134] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A steady-state analysis method for offshore wind farms, characterized in that, Includes the following steps: Based on the steady-state operating characteristics of full-power conversion wind turbine units in offshore wind farms, each wind turbine unit is equivalent to a constant current source, and the equivalent current phasor of each constant current source is calculated. Based on the topology and line parameters of the collector lines of the offshore wind farm, and the equivalent current phasor of each wind turbine unit under the same collector bus, each collector bus in the collector lines is equivalent to an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel. The topology of the collector lines includes radial collector topology and star collector topology. The equivalent model of each collector bus in the collector lines consisting of equivalent current sources and equivalent impedances connected in parallel includes: for the offshore wind farm with radial collector topology, constructing an equivalent impedance model for each wind turbine unit corresponding to any collector bus; for any collector bus... Norton equivalent modeling is performed on the equivalent impedance model of the first wind turbine in the busbar to obtain the initial Norton equivalent circuit corresponding to the first wind turbine. The parameter values ​​of the initial Norton equivalent circuit are calculated based on the line parameters and the equivalent current phasor of the first wind turbine. Based on the initial Norton equivalent circuit, Norton equivalent modeling is performed on the remaining wind turbines in any busbar in the order of their respective wind turbines until the Norton equivalent circuit corresponding to the last wind turbine in any busbar is obtained. The Norton equivalent circuit corresponding to the last wind turbine is then used as the equivalent circuit corresponding to any busbar. Model; For the offshore wind farm with the star-shaped collector topology, construct an equivalent impedance model for each wind turbine in any collector bus; perform Norton equivalence on each of the single-unit equivalent impedance models, equating the single-unit equivalent impedance model to an initial Norton equivalent circuit consisting of an initial current source and an initial impedance in parallel, and calculate the parameter values ​​of the initial Norton equivalent circuit corresponding to each wind turbine based on the line parameters and the equivalent current phasor of each wind turbine; equat all the parallel initial Norton equivalent circuits to the Norton equivalent circuit corresponding to any collector bus, and calculate the parameter values ​​of any collector bus based on the parameter values ​​of each initial Norton equivalent circuit. The parameter values ​​of the Norton equivalent circuit corresponding to a busbar, wherein the step of performing Norton equivalent equivalence on the remaining wind turbines in any busbar includes: starting from the initial Norton equivalent circuit, combining the Norton equivalent circuit corresponding to the current wind turbine with the single-unit equivalent impedance model corresponding to the next adjacent wind turbine in the busbar to generate a composite equivalent impedance model corresponding to the next wind turbine; performing Norton equivalent equivalence on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine, and calculating the parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine based on the parameter values ​​of the composite equivalent impedance model; An equivalent calculation model of the offshore wind farm is generated based on the equivalent models corresponding to all the busbars, and the power flow calculation of the power system is performed through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

2. The steady-state analysis method for offshore wind farms according to claim 1, characterized in that, The equivalent impedance model for a single generating unit includes: the constant current source, the equivalent resistance of the generator terminal transformer, the equivalent reactance of the generator terminal transformer, the resistance of the target cable, the reactance of the target cable, and the susceptance to ground on both sides of the target cable, wherein... The first terminal of the constant current source is grounded, and the second terminal of the constant current source is connected to the first terminal of the equivalent resistance of the machine terminal transformer. The second end of the equivalent resistance of the generator-end transformer is connected to the first end of the equivalent reactance of the generator-end transformer. The second end of the equivalent reactance of the generator-end transformer is connected to the first end of the left side ground susceptance of the target cable and the first end of the resistance of the target cable. The second end of the left side of the target cable is grounded, and the second end of the resistor of the target cable is connected to the first end of the reactance of the target cable. The second end of the reactance of the target cable is connected to the first end of the right-side ground susceptance of the target cable, and the second end of the right-side ground susceptance of the target cable is grounded.

3. The steady-state analysis method for offshore wind farms according to claim 1, characterized in that, The equivalent current phasor of each of the constant current sources is calculated using the following formula: in, I i It is the first i Equivalent current phasors of typhoon generators I d，i It is the first i Active power components of typhoon generators I q，i It is the first i The reactive power component of typhoon generators. I max，i It is the first i Maximum current limit for typhoon generator converters. θ i It is the power factor angle. i This refers to any wind turbine unit in an offshore wind farm.

4. A steady-state analysis system for offshore wind farms, characterized in that, A steady-state analysis method for offshore wind farms according to any one of claims 1 to 3, the system comprising the following modules: The first equivalent module is used to convert each wind turbine into a constant current source based on the steady-state operating characteristics of the full-power conversion wind turbine in the offshore wind farm, and to calculate the equivalent current phasor of each constant current source. The second equivalent module is used to, based on the topology and line parameters of the collection line of the offshore wind farm, and the equivalent current phasor of each wind turbine under the same collection bus, to convert each collection bus in the collection line into an equivalent model consisting of equivalent current sources and equivalent impedances connected in parallel. The calculation module is used to generate an equivalent calculation model of the offshore wind farm based on the equivalent models corresponding to all the collecting buses, and to perform power flow calculation of the power system through the equivalent calculation model to obtain the steady-state analysis results of multiple parameters of the offshore wind farm.

5. The steady-state analysis system for offshore wind farms according to claim 4, characterized in that, The second equivalent module is specifically used for: For the offshore wind farm with the radial collector topology, construct the equivalent impedance model of a single wind turbine unit corresponding to each wind turbine unit in any collector bus. Norton equivalent model of the single unit equivalent impedance model corresponding to the first wind turbine in any of the busbars is performed to obtain the initial Norton equivalent circuit corresponding to the first wind turbine. The parameter values ​​of the initial Norton equivalent circuit are calculated based on the line parameters and the equivalent current phasor of the first wind turbine. Based on the initial Norton equivalent circuit, the remaining wind turbines in any of the busbars are successively Norton equivalents according to the order of each wind turbine in any of the busbars until the Norton equivalent circuit corresponding to the last wind turbine in any of the busbars is obtained. The Norton equivalent circuit corresponding to the last wind turbine is used as the equivalent model corresponding to any of the busbars.

6. The steady-state analysis system for offshore wind farms according to claim 5, characterized in that, The second equivalent module is also used for: Starting from the initial Norton equivalent circuit, the Norton equivalent circuit corresponding to the current wind turbine is combined with the single equivalent impedance model of the next adjacent wind turbine in the bus to generate the composite equivalent impedance model corresponding to the next wind turbine. Norton equivalents are performed on the composite equivalent impedance model to generate the Norton equivalent circuit corresponding to the next wind turbine. The parameter values ​​of the Norton equivalent circuit corresponding to the next wind turbine are calculated based on the parameter values ​​of the composite equivalent impedance model.

7. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steady-state analysis method for offshore wind farms as described in any one of claims 1-3.

Images