Method and device for quantifying interaction in alternating current and direct current hybrid network

Abstract

The invention provides an interaction quantification method and device in an AC-DC hybrid network, and belongs to the technical field of wind power generation systems, and the method comprises the steps: building a small signal model of a fan-flexible DC power grid system under a DC voltage control scale; determining an alternating current state variable of a sending end based on the small signal model and a direct current state variable of a receiving end in the flexible direct current power grid system; establishing an equivalent transfer function model of the fan-flexible DC power grid system based on the AC state variable; any fan is taken as target equipment, the interaction in the fan-flexible direct current power grid system is quantified based on the alternating current state variable and the equivalent transfer function model, and a self-stabilization effect coefficient and a stabilization effect coefficient are obtained through calculation. The technical problem that interaction cannot be directly quantified in the prior art is effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of wind power generation systems, and in particular to a method and device for quantifying interaction in an AC / DC hybrid network. Background Art

[0002] The increasing share of wind power in electricity supply has led to a trend toward the coexistence of AC and DC networks. While AC transmission faces challenges such as capacitance losses in long-distance transmission, DC transmission offers advantages in large-capacity, long-distance transmission and adaptability to renewable energy sources, driving the development of hybrid AC / DC networks. However, the differing electrical characteristics of the two systems in these hybrid AC / DC networks present challenges in analyzing system stability and inter-system interactions. Currently, research on the interaction between wind turbines and flexible DC grid equipment in hybrid AC / DC networks is inadequate and requires further exploration. The dynamic stability of such systems is influenced by multiple factors, particularly the characteristics of the wind turbines themselves and the interactions between various components of the power system. This interaction encompasses not only the dynamic relationships between wind turbines but also their dynamic interactions with other transmission equipment.

[0003] At present, there are mainly the following methods to analyze the small signal stability of wind power systems: 1. Impedance Analysis: This method divides the wind power system into an open-loop subsystem and other open-loop subsystems. It then establishes a frequency-domain impedance model to obtain the impedance function. The Nyquist stability criterion is then used to assess system stability. This method effectively analyzes the system's frequency response characteristics.

[0004] 2. Open-Loop Mode Analysis: The core of this method is to divide a system connected to multiple terminals into two subsystems: one subsystem is the wind farm to be studied, and the remaining subsystem is the other. When the modes of the two subsystems are close to each other, modal resonance will occur, increasing the risk of system instability.

[0005] 3. Self-stabilization and stabilizing effect coefficient method: Based on the concepts of self-stabilization and stabilizing effects, a closed-loop model of the system is constructed. Feedback channels are set by calculating analytical expressions for the interactions between equipment. This method can clearly reveal the equipment or interaction paths that cause oscillations in the wind power system and clarify the impact of different controller parameters on system stability.

[0006] However, modal analysis, impedance analysis, and open-loop mode analysis cannot directly quantify the interaction between devices, and therefore cannot directly analyze the impact of the interaction on system stability. Summary of the Invention

[0007] In view of this, it is necessary to provide a method and device for quantifying the interaction in an AC / DC hybrid network to solve the technical problem that the existing technology cannot directly quantify the interaction between equipment.

[0008] In order to solve the above technical problems, in a first aspect, the present invention provides a method for quantifying interactions in an AC / DC hybrid network, comprising: Establish a small signal model of a wind turbine-flexible DC grid system under the DC voltage control scale, wherein the wind turbine-flexible DC grid system is composed of several wind turbines connected to the flexible DC grid system; Determining the AC state variables of the sending end by converting the DC state variables of the receiving end in the flexible DC power grid system based on the small signal model; Establishing an equivalent transfer function model of the wind turbine-flexible DC power grid system based on the AC state variables; Taking any wind turbine as the target device, the interaction between the wind turbine and the flexible DC power grid system is quantified based on the AC state variables and the equivalent transfer function model, and the self-stabilizing effect coefficient and the stabilizing effect coefficient are calculated.

[0009] In some embodiments of the present invention, the wind turbine-flexible DC grid system includes at least four wind turbines; The small signal model includes:

[0010] Indicates the output active power, Indicates the output active power in the AC network of the grid-side converter station of wind turbines 1 to 4; Indicates the output reactive power, Indicates the output reactive power in the AC network of the grid-side converter station of wind turbines 1 to 4; represents the internal potential phase, Indicates the internal potential phase in the AC network of the grid-side converter station of the 1st to 4th wind turbines; represents the internal potential amplitude, Indicates the internal potential amplitude in the AC network of the grid-side converter station of the 1st to 4th wind turbines.

[0011] In some embodiments of the present invention, the DC state variables and AC state variables include: relationship expressions between angular frequency, internal potential amplitude, and output active power and reactive power.

[0012] In some embodiments of the present invention, the conversion of the AC state variables at the sending end based on the small signal model and the DC state variables at the receiving end in the flexible DC power grid system includes: The first AC network power flow matrix of the wind turbine-flexible DC power grid system is established based on the small signal model:

[0013] represents the active power output of the AC network, represents the reactive power output of the AC network, represents the internal potential phase in the AC network of the grid-side converter station of the i-th wind turbine, represents the internal potential amplitude in the AC network of the grid-side converter station of the i-th wind turbine; 、 、 and Represents the parameter matrix of the i-th wind turbine. The parameters in each parameter matrix include:

[0014]

[0015] in, N Indicates the number of fans; 、 Respectively represent the output voltage of the AC network of the grid-side converter station of the i-th or j-th wind turbine, Indicates fan To the fan The susceptance, subscript , Indicates the and A fan; The power flow matrix of the DC network in the wind turbine-flexible DC grid system is established based on the small signal model:

[0016] in, represents the active power of the input DC capacitors of the grid-side converter stations of the wind turbines, represents the DC voltage of the input DC capacitor of the grid-side converter station of the several wind turbines, A A topology matrix representing the DC network; Based on the DC network power flow matrix and the circuit topology of the wind turbine-flexible DC grid system, an active input power matrix is established:

[0017] in, s Indicates slip, It represents the active input power of the converter station at the receiving end of the flexible DC grid. Indicates the active input power of the converter station at the sending end of the flexible DC grid; represents inductance, represents resistance, represents the DC current in different paths in the DC network, represents the DC voltage of different paths in the DC network, ; represents the DC voltage of the input DC capacitor of the receiving-end converter station of the flexible DC grid, represents the DC voltage of the input DC capacitor of the sending-end converter station of the flexible DC grid; Represents the parameters in the DC network topology matrix; Based on the topology of the wind turbine-flexible DC grid system, the output active power calculation formula of the converter station at the sending end of the flexible DC grid is listed as follows:

[0018] It represents the output active power of the converter station at the sending end of the flexible DC grid. represents infinite supply voltage, represents the coordinate transformation angle, It represents the reactance between the converter station at the sending end of the flexible DC grid and the infinite power source; Based on the relationship between the output active power and the input active power in the flexible DC transmission converter station and the output active power calculation formula, the unbalanced active power calculation formula is obtained:

[0019]

[0020] Indicates unbalanced active power, represents capacitance, ; The active input power matrix is expanded row by row and the active power calculation formula and the unbalanced active power calculation formula are established in parallel to obtain the first relationship between the input active power and the DC voltage of the flexible DC grid receiving-end converter station:

[0021] represents the parameters of the DC grid topology matrix, i is the number of rows, j is the number of columns, Indicates DC voltage; And the transfer function between the DC voltage and angular frequency at the receiving-end converter station of the flexible DC grid is:

[0022] represents the transfer function; Substituting the first transfer function into the first relational expression, a second relational expression between the input active power and the angular frequency of the flexible DC grid receiving-end converter station is obtained:

[0023] Substituting the second relation into the unbalanced active power calculation formula, we can obtain the third relation between the output active power of the converter station at the receiving end of the flexible DC grid and the angular frequency:

[0024] Based on the small signal model, the fourth relationship between the internal potential phase of the flexible DC grid receiving-end converter station and the input active power and angular frequency is established:

[0025] represents the transfer function, represents the damping transfer function of the converter station; Substituting the second relational expression into the fourth relational expression, we obtain the fifth relational expression between the internal potential phase and angular frequency of the converter station at the receiving end of the flexible DC grid:

[0026] Substituting the third relational expression into the fifth relational expression, the sixth relational expression between the internal potential phase and the output active power of the converter station at the receiving end of the flexible DC grid is obtained: .

[0027] In some embodiments of the present invention, establishing an equivalent transfer function model of a wind turbine-flexible DC power grid system based on the AC state variables includes: Based on the AC state variables and the small signal model, a first transfer function relationship matrix between the internal potential phase and the angular frequency is established:

[0028] represents the internal potential phase, represents the angular frequency, s Indicates slip, represents the damping transfer function of the converter station, , 、 are transfer functions, represents the feedforward channel; And, the second transfer function matrix between the internal potential phase and the output active power:

[0029] represents the transfer function, represents the feedforward channel, Indicates output active power; And, the third transfer function matrix between internal potential amplitude and reactive power:

[0030] represents the internal potential amplitude, represents the transfer function, represents the feedforward channel, Indicates reactive power; Based on the matrix operation rules, the first transfer matrix, the second transfer matrix and the third transfer matrix, a fourth transfer function matrix is established between the angular frequency, the internal potential amplitude and the output active power and reactive power:

[0031] Substituting the first transfer function matrix into the first AC network power flow matrix, a second AC network power flow matrix is obtained:

[0032] The equivalent transfer function model is obtained by solving the relationship between the output active power and the angular frequency generated by the internal potential based on the second AC network power flow matrix:

[0033] 、 、 and represents the parameter matrix, Represents the feedback channel of the equivalent transfer function model.

[0034] In some embodiments of the present invention, taking any wind turbine as the target device, quantifying the interaction in the wind turbine-flexible DC power grid system based on the AC state variables and the equivalent transfer function model, and calculating the self-stabilizing effect coefficient and the stabilizing effect coefficient include: Based on the definitions of the self-stabilizing effect coefficient and the stabilizing effect coefficient, the following unbalanced active power expression is listed:

[0035] Indicates unbalanced active power, Indicates the unbalanced active power of the target device. Indicates the unbalanced active power of devices other than the target device. represents the angular frequency, is the self-stabilizing coefficient, is the stabilizing effect coefficient; By combining the AC state variables and the equivalent transfer function model, the seventh relationship between the unbalanced active power of the target device and the angular frequency corresponding to the internal potential is obtained:

[0036] Indicates the unbalanced active power of the target device. represents the feedback channel of the equivalent transfer function model, , represents the equivalent inertia matrix, represents the angular frequency corresponding to the internal potential; By combining the unbalanced active power expression and the seventh expression, the self-stabilizing action coefficients are obtained:

[0037] Represents the feedback channel of the equivalent transfer function model; And, the stabilization coefficient: .

[0038] In some embodiments of the present invention, the stabilizing effect coefficient includes: a single stabilizing effect coefficient of a single other device on a target device, a double stabilizing effect coefficient of two other devices acting together on the target device, and a triple stabilizing effect coefficient of three other devices acting together on the target device; Among them, The interactive effect of the typhoon on the target equipment is recorded as the single stabilizing effect coefficient:

[0039] Indicates the j The single stabilizing effect coefficient of the typhoon on the target equipment, represents the equivalent inertia of the converter station; And, 、 The interactive effects of typhoons on target equipment are recorded as pairwise stabilizing effect coefficients:

[0040] Indicates the j 、 k The pairwise stabilizing effect coefficient of the typhoon on the target equipment, Represents the parameters in the equivalent inertia matrix; And, the interactive effects of the other equipment from the second to the fifth on the target wind turbine are recorded as the three-three stabilizing effect coefficient:

[0041] represents the three-three stabilizing effect coefficient, .

[0042] In a second aspect, the present invention further provides a device, comprising: a memory for storing a program; A processor is coupled to the memory and is used to execute the program stored in the memory to implement the steps of the method for quantifying interaction in an AC / DC hybrid network described in any one of the above method items.

[0043] The beneficial effects of the present invention are as follows: the present invention provides a method for quantifying interactions in an AC / DC hybrid network, by establishing a small signal model of the AC / DC hybrid network and in parallel with the DC state variables of the receiving end of the flexible DC power grid system, and calculating the DC state variables of the sending end of the flexible DC power grid system, which can more accurately analyze the operating state and stability of the flexible DC system at the sending end, and can analyze the interaction brought by the flexible DC system to the AC system at the sending end; further, an equivalent transfer function model is established based on the AC state variables, and finally, based on the equivalent transfer function model, the interaction caused by the change of the state quantity of the target device itself on its own unbalanced power and the interaction caused by the change of the state quantity of other wind turbines other than the target device on the unbalanced power of the target device are quantified in the form of a transfer function, providing a technical idea of quantifying the interaction through transfer functions, thereby solving the technical problem that the existing technology cannot directly quantify the interaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0045] Figure 1 This is a structural diagram of the wind turbine-flexible DC power grid system provided by the present invention; Figure 2 A schematic flow chart of an embodiment of a method for quantifying interaction in an AC / DC hybrid network provided by the present invention; Figure 3 A schematic structural diagram of an embodiment of a small signal model provided by the present invention; Figure 4 A schematic structural diagram of an embodiment of an equivalent transfer function model provided by the present invention; Figure 5 This is a structural diagram of an embodiment of the device provided by the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0047] In the description of the embodiments of the present invention, unless otherwise specified, "plurality" means two or more. "And / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone.

[0048] The terms "first," "second," and so on, used in the embodiments of the present invention are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, technical features designated as "first" or "second" may explicitly or implicitly include at least one such feature.

[0049] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute a separate or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0050] Before presenting the embodiments, the following terms are explained.

[0051] A flexible DC grid system refers to a grid system built using flexible DC transmission technology. It interconnects AC networks and enables power transmission through two or more converter stations. Converters can independently control their output active and reactive power, effectively supporting and controlling the AC system.

[0052] Converter station (VSC): refers to the voltage source converter, which is the core equipment of the flexible direct current grid system. It is composed of multiple power electronic devices such as thyristors or IGBTs, and can achieve fast and accurate conversion between AC and DC.

[0053] The present invention provides a method and device for quantifying interactions in an AC / DC hybrid network, which are described below.

[0054] like Figure 1As shown, in a specific embodiment, four direct-drive wind turbines are connected to a flexible DC grid system via converter stations VSC1-4 to form a wind turbine-flexible DC grid system, wherein the flexible DC grid side includes a receiving end and a sending end, and a converter station VSC5 is also provided on the sending end, and a converter station VSC6 is provided on the receiving end, and the receiving end is also connected to an infinite power source.

[0055] Figure 2 A schematic diagram of an embodiment of the method for quantifying interaction in an AC / DC hybrid network provided by the present invention is shown in FIG. Figure 2 As shown in Figure 2, the methods for quantifying interactions in AC / DC hybrid networks include: In a first aspect, the present invention provides a method for quantifying interactions in an AC / DC hybrid network, comprising: S201. Establish a small signal model of the wind turbine-flexible DC grid system under the DC voltage control scale; Among them, the wind turbine-flexible DC grid system consists of several wind turbines electrically connected to the flexible DC grid system.

[0056] In some embodiments of the present invention, the small signal model includes:

[0057] Indicates the output active power, Indicates the output active power in the AC network of the grid-side converter station of wind turbines 1 to 4; Indicates the output reactive power, Indicates the output reactive power in the AC network of the grid-side converter station of wind turbines 1 to 4; represents the internal potential phase, Indicates the internal potential phase in the AC network of the grid-side converter station of the 1st to 4th wind turbines; represents the internal potential amplitude, Indicates the internal potential amplitude in the AC network of the grid-side converter station of the 1st to 4th wind turbines.

[0058] Furthermore, if Figure 3 As shown, the present invention also provides Figure 1 Small signal model topology of the wind turbine-flexible DC grid system under the DC voltage control time scale.

[0059] Back to Figure 2 The method for quantifying interaction in an AC / DC hybrid network provided by the present invention further includes: S202: Determine the AC state variables at the sending end based on the small signal model and the DC state variables at the receiving end in the flexible DC power grid system.

[0060] In some embodiments of the present invention, the DC state variables and the AC state variables include: a relationship between angular frequency, internal potential amplitude, and output active power and reactive power.

[0061] In some embodiments of the present invention, step S202 includes: The first AC network power flow matrix of the wind turbine-flexible DC grid system is established based on the small signal model: (2) represents the active power output of the AC network, represents the reactive power output of the AC network, represents the internal potential phase in the AC network of the grid-side converter station of the i-th wind turbine, represents the internal potential amplitude in the AC network of the grid-side converter station of the i-th wind turbine; 、 、 and Represents the parameter matrix of the i-th wind turbine. The parameters in each parameter matrix include: (3)

[0062] in, N Indicates the number of fans; 、 Respectively represent the output voltage of the AC network of the grid-side converter station of the i-th or j-th wind turbine, Indicates fan To the fan The susceptance, subscript , Indicates the and A fan; The power flow matrix of the DC network in the wind turbine-flexible DC grid system is established based on the small signal model:

[0063] in, represents the active power of the input DC capacitors of the grid-side converter stations of the wind turbines, Indicates the DC voltage of the input DC capacitor of several wind turbine grid-side converter stations, A Represents the topological matrix of the DC network; The active input power matrix is established based on the DC network power flow matrix and the circuit topology of the wind turbine-flexible DC grid system: (4) in, s Indicates slip, It represents the active input power of the converter station at the receiving end of the flexible DC grid. Indicates the active input power of the converter station at the sending end of the flexible DC grid; represents inductance, represents resistance, represents the DC current in different paths in the DC network, represents the DC voltage of different paths in the DC network, ; represents the DC voltage of the input DC capacitor of the receiving-end converter station of the flexible DC grid, Indicates the DC voltage of the input DC capacitor of the converter station at the sending end of the flexible DC grid; Represents the parameters in the DC network topology matrix; Based on the topology of the wind turbine-flexible DC grid system, the output active power calculation formula of the converter station at the sending end of the flexible DC grid is listed as follows: (5) It represents the output active power of the converter station at the sending end of the flexible DC grid. represents infinite supply voltage, represents the coordinate transformation angle, It represents the reactance between the converter station at the sending end of the flexible DC grid and the infinite power source; Based on the relationship between the output active power and the input active power in the flexible DC transmission converter station and the output active power calculation formula, the unbalanced active power calculation formula is obtained: (6)

[0064] Indicates unbalanced active power, represents capacitance, ; Expand the active input power matrix row by row and establish the active power calculation formula and the unbalanced active power calculation formula in parallel to obtain the first relationship between the input active power and DC voltage of the converter station at the receiving end of the flexible DC grid: (7) represents the parameters of the DC grid topology matrix, i is the number of rows, j is the number of columns, Indicates DC voltage; And the transfer function between the DC voltage and angular frequency at the receiving-end converter station of the flexible DC grid is: (8) represents the transfer function between DC voltage and angular frequency; Substituting the first transfer function into the first relational expression, the second relational expression between the input active power and the angular frequency of the flexible DC grid receiving-end converter station is obtained: (9) Substituting the second relation into the unbalanced active power calculation formula, we can obtain the third relation between the output active power of the converter station at the receiving end of the flexible DC grid and the angular frequency: (10) Based on the small signal model, the fourth relationship between the internal potential phase of the flexible DC grid receiving-end converter station and the input active power and angular frequency is established: (11) represents the transfer function between the internal potential phase and the input active power, represents the damping transfer function of the converter station; Substituting the second relational expression into the fourth relational expression, we obtain the fifth relational expression between the internal potential phase and angular frequency of the converter station at the receiving end of the flexible DC grid: (12) Substituting the third relational expression into the fifth relational expression, the sixth relational expression between the internal potential phase and the output active power of the converter station at the receiving end of the flexible DC grid is obtained: (13) So far, all DC state variables involved in the receiving-end VSC6 have been converted to the sending-end VSC5, and the DC part of the flexible DC grid has been equivalent to the AC part.

[0065] It's important to note that converting the DC state variables at the flexible DC receiving end to the sending end (equating the DC component to the AC component) allows for a more precise analysis of the flexible DC system's operating state and stability at the sending end, as well as its impact on the AC system at the sending end. Furthermore, based on the calculated self-stabilizing and stabilizing action coefficients, a corresponding control strategy can be developed, thereby enhancing the self-stabilizing capability of the flexible DC system and achieving coordinated control between the flexible DC and AC systems.

[0066] S203. Establish an equivalent transfer function model of the wind turbine-flexible DC grid system based on the AC state variables.

[0067] It should be noted that the fundamental purpose of step S203 is to generate an equivalent transfer function matrix model based on the relationship between the obtained transfer function matrix of the output active power and the angular frequency generated by the internal potential.

[0068] Therefore, in some embodiments of the present invention, combined with Figure 4The equivalent transfer function model for interaction analysis between the wind turbine and the flexible DC grid equipment is shown, and step S203 specifically includes: Based on the AC state variables and the small signal model, the first transfer function relationship matrix between the internal potential phase and the angular frequency is established: (14) represents the internal potential phase, represents the angular frequency, s Indicates slip, represents the damping transfer function of the converter station, , 、 are transfer functions, represents the feedforward channel; And, the second transfer function matrix between the internal potential phase and the output active power: (15) represents the transfer function, represents the feedforward channel, Indicates output active power; And, the third transfer function matrix between internal potential amplitude and reactive power: (16) represents the internal potential amplitude, represents the transfer function, represents the feedforward channel, Indicates reactive power; Based on the matrix operation rules, the first transfer matrix, the second transfer matrix and the third transfer matrix, the fourth transfer function matrix between the angular frequency, the internal potential amplitude and the output active power and reactive power is established: (17) It should be noted that, taking formula (15) as an example, according to the rules of matrix operations, we can further directly obtain .

[0069] Substituting the first transfer function matrix into the first AC network power flow matrix, the second AC network power flow matrix is obtained: (18) Based on the second AC network power flow matrix, the relationship between the output active power and the angular frequency generated by the internal potential is solved to obtain the equivalent transfer function model: (19) 、 、 and represents the parameter matrix, Represents the feedback channel of the equivalent transfer function model.

[0070] It should be noted that after the above calculation process, according to the relationship between the transfer function matrix between the output active power and the angular frequency generated by the internal potential, Figure 4 The equivalent model in (a) is further transformed into Figure 4 (b) Transfer function matrix model shown.

[0071] S204, taking any wind turbine as the target device, quantifying the interaction between the wind turbine and the flexible DC grid system based on the AC state variables and the equivalent transfer function model, and calculating the self-stabilizing effect coefficient and the stabilizing effect coefficient; The self-stabilizing effect coefficient is the transfer function of the interaction between the change of the state quantity of the target device and its own unbalanced power, and the stabilizing effect coefficient is the transfer function of the interaction between the change of the state quantity of other wind turbines except the target device and its own unbalanced power.

[0072] In some embodiments of the present invention, step S204 includes: Based on the definitions of the self-stabilizing effect coefficient and the stabilizing effect coefficient, the following unbalanced active power expression is listed: (20) Indicates unbalanced active power, Indicates the unbalanced active power of the target device. Indicates the unbalanced active power of devices other than the target device. represents the angular frequency, is the self-stabilizing coefficient, is the stabilizing effect coefficient.

[0073] It should be noted that in Figure 1 In the scenario, the process of the target device’s own state quantity change affecting its own unbalanced power is defined as the self-stabilizing effect, while the process of the change of other equipment’s state quantity affecting the target device’s unbalanced power is called the stabilizing effect. Therefore, it is easy to know that the self-stabilizing effect coefficient is defined as and The transfer function between ; The stabilization coefficient is defined as and The transfer function between .

[0074] Furthermore, based on the definition of self-stabilization and stabilization, and Figure 2From the equivalent diagram of the small signal model, we can still draw the conclusion that the self-stabilizing and stabilizing effect coefficients are related to the transfer function between the angular frequency and the unbalanced active power.

[0075] Combine Figure 4 As well as formula (19), after the system is equivalent, the self-stabilizing effect coefficient and the corresponding stabilizing effect coefficient under different paths are calculated for the weak AC system of four direct-drive wind turbines connected to the flexible DC grid. The target equipment is set as the first wind turbine. Through the simultaneous equations and the substitution relationship between the state quantities in the system, the mathematical relationship between the unbalanced active power of the target wind turbine and the angular frequency corresponding to its internal potential is obtained: By combining the AC state variables and the equivalent transfer function model, we can obtain the seventh relationship between the unbalanced active power of the target device and the angular frequency corresponding to the internal potential: (twenty one) Indicates the unbalanced active power of the target device. represents the feedback channel of the equivalent transfer function model, , represents the equivalent inertia matrix, represents the angular frequency corresponding to the internal potential; By combining the unbalanced active power expression and the seventh expression, the self-stabilizing action coefficients are obtained: (twenty two) Represents the feedback channel of the equivalent transfer function model; And, the stabilization coefficient: (twenty three) It should be noted that the above-mentioned stabilizing effect coefficient is the sum of the interactions caused by other devices on the target device on different paths. Therefore, it is necessary to further decompose these interactions from the total stabilizing effect coefficient, which is conducive to a more intuitive study of the stability of the wind turbine-flexible direct current grid system.

[0076] In some embodiments of the present invention, the stabilizing effect coefficient includes: a single stabilizing effect coefficient of a single other device on a target device, a double stabilizing effect coefficient of two other devices acting together on the target device, and a triple stabilizing effect coefficient of three other devices acting together on the target device; Among them, The interactive effect of the typhoon on the target equipment is recorded as the single stabilizing effect coefficient: (twenty four) Indicates the j The single stabilizing effect coefficient of the typhoon on the target equipment, represents the equivalent inertia of the converter station; And, 、 The interactive effects of typhoons on target equipment are recorded as pairwise stabilizing effect coefficients: (25) Indicates the j 、 k The pairwise stabilizing effect coefficient of the typhoon on the target equipment, Represents the parameters in the equivalent inertia matrix; And, the interactive effects of the other equipment from the second to the fifth on the target wind turbine are recorded as the three-three stabilizing effect coefficient: (26) represents the three-three stabilizing effect coefficient, .

[0077] Compared with the prior art, the present invention provides a method for quantifying interactions in an AC / DC hybrid network. The present invention provides a method for quantifying interactions in an AC / DC hybrid network. By establishing a small signal model of the AC / DC hybrid network and in parallel with the DC state variables of the receiving end of the flexible DC power grid system, the DC state variables of the sending end of the flexible DC power grid system are calculated. This method can more accurately analyze the operating state and stability of the flexible DC system at the sending end, and can analyze the interaction brought by the flexible DC system to the AC system at the sending end; further, an equivalent transfer function model is established based on the AC state variables, and finally, based on the equivalent transfer function model, the interaction caused by the change of the state quantity of the target device itself on its own unbalanced power and the interaction caused by the change of the state quantity of other wind turbines other than the target device on the unbalanced power of the target device are quantified in the form of a transfer function, providing a technical idea of quantifying interactions through transfer functions, thereby solving the technical problem that the prior art cannot directly quantify interactions.

[0078] like Figure 5 ,In a second aspect, the present invention further provides a device 50 , comprising: a memory 510 for storing a program; The processor 520 is coupled to the memory 510 and is configured to execute the program stored in the memory 510 to implement the steps of the method for quantifying interaction in an AC / DC hybrid network described in any one of the above methods.

[0079] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0080] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0081] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0082] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 Finally, it should be noted that: the above is a detailed introduction to the method and device for quantifying the interaction in the AC / DC hybrid network provided by the present invention. This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core idea of the present invention. At the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for quantifying interactions in an AC / DC hybrid network, characterized in that: include: Establishing a small signal model of a wind turbine-flexible DC grid system under a DC voltage control scale, wherein the wind turbine-flexible DC grid system is composed of several wind turbines electrically connected to the flexible DC grid system; Determining the AC state variables of the sending end based on the small signal model and the DC state variables of the receiving end in the flexible DC power grid system; Establishing an equivalent transfer function model of the wind turbine-flexible DC power grid system based on the AC state variables; Taking any wind turbine as the target device, the interaction in the wind turbine-flexible DC power grid system is quantified based on the AC state variables and the equivalent transfer function model, and the self-stabilizing effect coefficient and the stabilizing effect coefficient are calculated, wherein the self-stabilizing effect coefficient is the transfer function of the interaction between the change of the state quantity of the target device itself and its own unbalanced power, and the stabilizing effect coefficient is the transfer function of the interaction between the change of the state quantity of other wind turbines except the target device and the unbalanced power of the target device.

2. The method for quantifying interaction in an AC / DC hybrid network according to claim 1, characterized in that: The wind turbine-flexible DC power grid system includes at least four wind turbines; The small signal model includes: Indicates the output active power, Indicates the output active power in the AC network of the grid-side converter station of wind turbines 1 to 4; Indicates the output reactive power, Indicates the output reactive power in the AC network of the grid-side converter station of wind turbines 1 to 4; represents the internal potential phase, Indicates the internal potential phase in the AC network of the grid-side converter station of the 1st to 4th wind turbines; represents the internal potential amplitude, Indicates the internal potential amplitude in the AC network of the grid-side converter station of the 1st to 4th wind turbines.

3. The method for quantifying interaction in an AC / DC hybrid network according to claim 1, characterized in that: The DC state variables and AC state variables include: relationship formulas among angular frequency, internal potential amplitude, output active power, and reactive power.

4. The method for quantifying interaction in an AC / DC hybrid network according to claim 3, characterized in that: The method of converting the DC state variables of the receiving end to determine the AC state variables of the sending end based on the small signal model and the flexible DC power grid system includes: The first AC network power flow matrix of the wind turbine-flexible DC power grid system is established based on the small signal model: represents the active power output of the AC network, represents the reactive power output of the AC network, represents the internal potential phase in the AC network of the grid-side converter station of the i-th wind turbine, represents the internal potential amplitude in the AC network of the grid-side converter station of the i-th wind turbine; 、 、 and Represents the parameter matrix of the i-th wind turbine. The parameters in each parameter matrix include: in, N Indicates the number of fans; 、 Respectively represent the output voltage of the AC network of the grid-side converter station of the i-th or j-th wind turbine, Indicates fan To the fan The susceptance, subscript , Indicates the and A fan; The power flow matrix of the DC network in the wind turbine-flexible DC grid system is established based on the small signal model: in, represents the active power of the input DC capacitors of the grid-side converter stations of the wind turbines, represents the DC voltage of the input DC capacitor of the grid-side converter station of the several wind turbines, A A topology matrix representing the DC network; Based on the DC network power flow matrix and the circuit topology of the wind turbine-flexible DC grid system, an active input power matrix is established: in, s Indicates slip, It represents the active input power of the converter station at the receiving end of the flexible DC grid. Indicates the active input power of the converter station at the sending end of the flexible DC grid; represents inductance, represents resistance, represents the DC current in different paths in the DC network, represents the DC voltage of different paths in the DC network, ; represents the DC voltage of the input DC capacitor of the receiving-end converter station of the flexible DC grid, represents the DC voltage of the input DC capacitor of the sending-end converter station of the flexible DC grid; Represents the parameters in the DC network topology matrix; Based on the topology of the wind turbine-flexible DC grid system, the output active power calculation formula of the converter station at the sending end of the flexible DC grid is listed as follows: It represents the output active power of the converter station at the sending end of the flexible DC grid. represents infinite supply voltage, represents the coordinate transformation angle, It represents the reactance between the converter station at the sending end of the flexible DC grid and the infinite power source; Based on the relationship between the output active power and the input active power in the flexible DC transmission converter station and the output active power calculation formula, the unbalanced active power calculation formula is obtained: Indicates unbalanced active power, represents capacitance, ; The active input power matrix is expanded row by row and the active power calculation formula and the unbalanced active power calculation formula are established in parallel to obtain the first relationship between the input active power and the DC voltage of the flexible DC grid receiving-end converter station: represents the parameters of the DC grid topology matrix, i is the number of rows, j is the number of columns, Indicates DC voltage; And the transfer function between the DC voltage and angular frequency at the receiving-end converter station of the flexible DC grid is: represents the transfer function; Substituting the first transfer function into the first relational expression, a second relational expression between the input active power and the angular frequency of the flexible DC grid receiving-end converter station is obtained: Substituting the second relation into the unbalanced active power calculation formula, the third relation between the output active power of the converter station at the receiving end of the flexible DC grid and the angular frequency is obtained: Based on the small signal model, the fourth relationship between the internal potential phase of the flexible DC grid receiving-end converter station and the input active power and angular frequency is established: represents the transfer function, represents the damping transfer function of the converter station; Substituting the second relational expression into the fourth relational expression, we obtain the fifth relational expression between the internal potential phase and angular frequency of the converter station at the receiving end of the flexible DC grid: Substituting the third relational expression into the fifth relational expression, the sixth relational expression between the internal potential phase and the output active power of the converter station at the receiving end of the flexible DC grid is obtained: 。 5. The method for quantifying interaction in an AC / DC hybrid network according to claim 4, characterized in that: The establishing of an equivalent transfer function model of a wind turbine-flexible DC power grid system based on the AC state variables includes: Based on the AC state variables and the small signal model, a first transfer function relationship matrix between the internal potential phase and the angular frequency is established: represents the internal potential phase, represents the angular frequency, s Indicates slip, represents the damping transfer function of the converter station, , 、 are transfer functions, represents the feedforward channel; And, the second transfer function matrix between the internal potential phase and the output active power: represents the transfer function, represents the feedforward channel, Indicates output active power; And, the third transfer function matrix between internal potential amplitude and reactive power: represents the internal potential amplitude, represents the transfer function, represents the feedforward channel, Indicates reactive power; Based on the matrix operation rules, the first transfer matrix, the second transfer matrix and the third transfer matrix, a fourth transfer function matrix is established between the angular frequency, the internal potential amplitude and the output active power and reactive power: Substituting the first transfer function matrix into the first AC network power flow matrix, a second AC network power flow matrix is obtained: The equivalent transfer function model is obtained by solving the relationship between the output active power and the angular frequency generated by the internal potential based on the second AC network power flow matrix: 、 、 and represents the parameter matrix, Represents the feedback channel of the equivalent transfer function model.

6. The method for quantifying interaction in an AC / DC hybrid network according to claim 5, characterized in that: The method takes any wind turbine as the target device, quantifies the interaction between the wind turbine and the flexible DC power grid system based on the AC state variables and the equivalent transfer function model, and calculates the self-stabilizing effect coefficient and the stabilizing effect coefficient, including: Based on the definitions of the self-stabilizing effect coefficient and the stabilizing effect coefficient, the following unbalanced active power expression is listed: Indicates unbalanced active power, Indicates the unbalanced active power of the target device. Indicates the unbalanced active power of devices other than the target device. represents the angular frequency, is the self-stabilizing coefficient, is the stabilizing effect coefficient; By combining the AC state variables and the equivalent transfer function model, the seventh relationship between the unbalanced active power of the target device and the angular frequency corresponding to the internal potential is obtained: Indicates the unbalanced active power of the target device. represents the feedback channel of the equivalent transfer function model, , represents the equivalent inertia matrix, represents the angular frequency corresponding to the internal potential; By combining the unbalanced active power expression and the seventh expression, the self-stabilizing action coefficients are obtained: Represents the feedback channel of the equivalent transfer function model; And, the stabilization coefficient: 。 7. The method for quantifying interaction in an AC / DC hybrid network according to claim 6, characterized in that: The stabilizing effect coefficients include: a single stabilizing effect coefficient of a single other device on a target device, a double stabilizing effect coefficient of two other devices acting together on a target device, and a triple stabilizing effect coefficient of three other devices acting together on a target device; Among them, The interactive effect of the typhoon on the target equipment is recorded as the single stabilizing effect coefficient: Indicates the j The single stabilizing effect coefficient of the typhoon on the target equipment, represents the equivalent inertia of the converter station; And, 、 The interactive effects of typhoons on target equipment are recorded as pairwise stabilizing effect coefficients: Indicates the j 、 k The pairwise stabilizing effect coefficient of the typhoon on the target equipment, Represents the parameters in the equivalent inertia matrix; And, the interactive effects of the other equipment from the second to the fifth on the target wind turbine are recorded as the three-three stabilizing effect coefficient: represents the three-three stabilizing effect coefficient, .

8. A device, characterized in that include: Memory, used to store programs; A processor is coupled to the memory and is configured to execute the program stored in the memory to implement the steps of the method for quantifying interaction in an AC / DC hybrid network as described in any one of claims 1 to 7.

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