Method and device for determining control parameters based on wide-frequency stability region modeling of direct-drive wind turbines

Abstract

The present application provides a control parameter determination method and device based on broadband stability domain modeling of a direct-drive wind turbine, the method comprising calculating the conversion ratio based on the expression of the acquired system's weakest grid-connected strength and the first current inner loop frequency; calculating the current inner loop cutoff frequency based on the conversion ratio and the actual current inner loop cutoff frequency; substituting the current inner loop cutoff frequency into the expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient; the first current inner loop frequency and the second current inner loop frequency are determined based on the transfer function model of the current inner loop control; determining the current inner loop integral constant based on the current inner loop proportional coefficient; determining the voltage outer loop cutoff frequency; substituting the voltage outer loop cutoff frequency into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient; and determining the voltage outer loop integral constant based on the voltage outer loop proportional coefficient. This method improves the broadband stability characteristics of direct-drive wind turbines under different grid-connected conditions.

Description

Technical Field

[0001] The present application relates to the technical field of analysis and control technology for dynamic stability of power systems, and specifically to a method and device for determining control parameters based on broadband stability domain modeling of direct-drive wind turbines. Background Art

[0002] The proportion of installed renewable energy power generation capacity in my country (such as direct-drive wind turbines) is increasing year by year. However, a series of broadband oscillation problems have emerged in the process of large-scale renewable energy transmission, which greatly restricts the transmission capacity of renewable energy. Renewable energy generators are mostly connected to the grid through power electronic converters. Due to the interaction between power electronic converters and the grid, broadband oscillation problems may occur. At present, the parameter design of grid-connected wind power usually takes the strong AC system as the standard operating condition and the operating performance of the power frequency band as the main optimization target. As a result, the existing wind turbine control parameters are insufficiently adaptable to weak grid conditions. This is the fundamental reason why wind turbines show weak damping in the sub / supersynchronous frequency band under weak grid conditions, which in turn causes oscillations. In order to improve the grid-connected characteristics of wind turbines and enable them to have the ability to operate stably under weak AC systems, it is necessary to propose a parameter coordination design method under weak grid conditions.

[0003] To address this issue, the paper "Optimal Design of a Subsynchronous Damping Controller for Direct-Drive Wind Farms Transmitted via HVDC" proposes a method to suppress subsynchronous oscillations in direct-drive wind farms operating under weak grid conditions by adding a subsynchronous additional damping controller. By conducting eigenvalue analysis on the direct-drive wind farm transmission system and analyzing the dominant oscillation mode participation factors of the system oscillations, the optimal installation location of the subsynchronous additional damping controller was determined, and an optimized design for the additional damping control parameters was proposed. However, in actual operation, adding a subsynchronous additional damping controller requires hardware modifications to the wind turbine control devices, and due to investment constraints, this cannot be implemented for all devices in the wind farm. Summary of the Invention

[0004] In view of this, an embodiment of the present application provides a control parameter determination method and device based on broadband stability domain modeling of a direct-drive wind turbine, so as to overcome the problem in the prior art of being unable to perform hardware modifications on all equipment in a wind farm to add a synchronous additional damping controller, thereby solving the problem of oscillation of the direct-drive branch under a weak power grid.

[0005] In a first aspect, an embodiment of the present application provides a method for determining control parameters based on broadband stability domain modeling of a direct-drive wind turbine, wherein the direct-drive wind turbine is connected to the grid via a grid-side AC device, wherein the grid-side AC device includes a current inner loop control and a voltage outer loop control. The method includes:

[0006] Obtain the expressions of the system's weakest grid-connected strength and the first current inner loop frequency;

[0007] Calculating a conversion ratio according to an expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop;

[0008] Based on the dynamic response requirements of the current inner loop, select the actual current inner loop cutoff frequency;

[0009] Substituting the conversion ratio and the actual current inner loop cut-off frequency into an expression for the first current inner loop frequency to calculate the current inner loop cut-off frequency;

[0010] Substituting the current inner loop cutoff frequency into the expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient;

[0011] Determining a current inner loop integral constant according to the current inner loop proportional coefficient;

[0012] Determine the cutoff frequency of the voltage outer loop based on the dynamic response requirements of the voltage outer loop;

[0013] Substituting the voltage outer loop cutoff frequency into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient;

[0014] Determining a voltage outer loop integral constant according to the voltage outer loop proportional coefficient;

[0015] Among them, the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by grid connection; the expression of the second current inner loop frequency is the expression of the open-loop cross-frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

[0016] In a second aspect, an embodiment of the present application provides a control parameter determination device based on broadband stability domain modeling of a direct-drive wind turbine, wherein the direct-drive wind turbine is connected to the grid via a grid-side AC device, wherein the grid-side AC device includes a current inner loop control and a voltage outer loop control. The device includes:

[0017] An information acquisition module, used to obtain expressions of the system's weakest grid-connected strength and the first current inner loop frequency;

[0018] a conversion ratio calculation module, configured to calculate the conversion ratio according to an expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop;

[0019] A frequency selection module is used to select the actual current inner loop cutoff frequency based on the dynamic response requirements of the current inner loop;

[0020] a frequency calculation module, configured to substitute the conversion ratio and the actual current inner loop cut-off frequency into an expression of the first current inner loop frequency to calculate the current inner loop cut-off frequency;

[0021] an inner loop proportional coefficient calculation module, configured to substitute the current inner loop cutoff frequency into an expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient;

[0022] An inner loop integral constant determining module, configured to determine a current inner loop integral constant according to the current inner loop proportional coefficient;

[0023] A frequency determination module, used for determining a cutoff frequency of the voltage outer loop based on a dynamic response requirement of the voltage outer loop;

[0024] an outer loop proportional coefficient calculation module, configured to substitute the voltage outer loop cutoff frequency into an expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient;

[0025] An outer loop integral constant determining module, configured to determine a voltage outer loop integral constant according to the voltage outer loop proportional coefficient;

[0026] Among them, the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by grid connection; the expression of the second current inner loop frequency is the expression of the open-loop cross-frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

[0027] In a third aspect, an embodiment of the present application provides a terminal device comprising: a memory; one or more processors coupled to the memory; one or more applications, wherein the one or more applications are stored in the memory and configured to be executed by the one or more processors, and the one or more applications are configured to execute the control parameter determination method based on broadband stability domain modeling of direct-drive wind turbines provided in the first aspect above.

[0028] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium, in which program code is stored. The program code can be called by a processor to execute the control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in the first aspect above.

[0029] The control parameter determination method and device based on broadband stability domain modeling of direct-drive wind turbines provided in the embodiment of the present application first obtain the expression of the system's weakest grid-connected strength and the first current inner loop frequency; wherein the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by the grid; the conversion ratio is calculated based on the expression of the system's weakest grid-connected strength and the first current inner loop frequency; based on the dynamic response requirements of the current inner loop, the actual current inner loop cutoff frequency is selected; according to the conversion ratio and the actual current inner loop cutoff frequency, the expression of the first current inner loop frequency is substituted to calculate the current inner loop cutoff frequency; and the current inner loop cutoff frequency is substituted into the expression of the second current inner loop frequency. The expression is used to calculate the current inner loop proportional coefficient; the expression of the second current inner loop frequency is the expression of the open-loop crossover frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the current inner loop integral constant is determined according to the current inner loop proportional coefficient; the voltage outer loop cutoff frequency is determined based on the dynamic response requirements of the voltage outer loop; the voltage outer loop cutoff frequency is substituted into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient; the voltage outer loop integral constant is determined according to the voltage outer loop proportional coefficient; wherein, the open-loop crossover frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

[0030] The control parameter determination method based on broadband stability domain modeling of direct-drive wind turbines provided in the embodiment of the present application carries out parameter coordination design for wind turbines adapted to weak grid conditions, which can reduce the need for hardware modification in wind farms and is more economical; and takes into account the influence of different grid connection strengths, thereby improving the broadband stability characteristics of direct-drive wind turbines under different grid connection conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0032] Figure 1 Schematic diagram of an application scenario of the control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in an embodiment of the present application;

[0033] Figure 2 A flow chart of a method for determining control parameters based on broadband stability domain modeling of a direct-drive wind turbine provided by one embodiment of the present application;

[0034] Figure 3 A schematic structural diagram of a direct-drive blower provided in one embodiment of the present application;

[0035] Figure 4 A topological diagram of a grid-side AC unit for a direct-drive wind turbine according to one embodiment of the present application;

[0036] Figure 5 A transfer function model diagram of a grid-side converter (controlling the d-axis) provided in one embodiment of the present application;

[0037] Figure 6 A diagram of the current inner loop integral time constant provided by one embodiment of the present application;

[0038] Figure 7 A diagram of the voltage outer loop integral time constant provided for one embodiment of the present application;

[0039] Figure 8 A diagram of a grid-side converter (controlling the d-axis) transfer function model considering network strength provided in one embodiment of the present application;

[0040] Figure 9 A simplified (d-axis) transfer function model diagram of a converter control considering network strength according to one embodiment of the present application;

[0041] Figure 10 This is a schematic structural diagram of a control parameter determination device based on broadband stability domain modeling of a direct-drive wind turbine provided in one embodiment of the present application;

[0042] Figure 11 This is a schematic diagram of the structure of a terminal device provided in one embodiment of the present application;

[0043] Figure 12 A schematic diagram of the structure of a computer-readable storage medium provided in one embodiment of the present application. DETAILED DESCRIPTION

[0044] The following is a clear and complete description of the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0045] In order to explain the present application in more detail, the following specifically describes a control parameter determination method, apparatus, terminal device and computer-readable storage medium based on broadband stability domain modeling of a direct-drive wind turbine provided by the present application in conjunction with the accompanying drawings.

[0046] Please refer to Figure 1 , Figure 1A schematic diagram of an application scenario of a control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in an embodiment of the present application is shown. The application scenario includes a terminal device 100 provided in an embodiment of the present application. The terminal device 100 can be various electronic devices with a display screen (such as the structural diagrams of 102, 104, 106 and 108), including but not limited to smart phones and computer devices, wherein the computer device can be at least one of a desktop computer, a portable computer, a laptop computer, a tablet computer, etc. The terminal device 100 can generally refer to one of a plurality of terminal devices. This embodiment is only illustrated by the terminal device 100. Those skilled in the art will appreciate that the number of the above-mentioned terminal devices can be more or less. For example, the above-mentioned terminal devices can be only a few, or the above-mentioned terminal devices can be dozens or hundreds, or more. The embodiment of the present application does not limit the number and type of terminal devices. The terminal device 100 can be used to execute a control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in an embodiment of the present application.

[0047] In an optional embodiment, the application scenario includes, in addition to the terminal device 100 provided in the embodiment of the present application, a server, wherein a network is provided between the server and the terminal device. The network is used as a medium for providing a communication link between the terminal device and the server. The network can include various connection types, such as wired or wireless communication links or fiber optic cables.

[0048] It should be understood that the number of terminal devices, networks and servers is only schematic. Depending on the implementation needs, there can be any number of terminal devices, networks and servers. For example, the server can be a server cluster composed of multiple servers, etc. The terminal device interacts with the server through the network to receive or send messages, etc. The server can be a server that provides various services. The server can be used to execute the steps of a control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in an embodiment of the present application. In addition, when the terminal device executes a control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine provided in an embodiment of the present application, part of the steps can be executed on the terminal device and part of the steps can be executed on the server, which is not limited here.

[0049] Based on this, the embodiment of the present application provides a method for determining control parameters based on broadband stability domain modeling of a direct-drive wind turbine. Figure 2 , Figure 2 A flow chart of a method for determining control parameters based on broadband stability domain modeling of a direct-drive wind turbine provided by an embodiment of the present application is shown. Figure 1 Taking the terminal equipment in the example as an example, the direct-drive wind turbine is connected to the grid through the grid-side AC device. The grid-side AC device includes current inner loop control and voltage outer loop control, including the following steps:

[0050] Step S110 , obtaining expressions of the system's weakest grid-connected strength and the first current inner loop frequency.

[0051] The expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency affected by grid connection, and the first current inner loop frequency is determined according to a transfer function model of the current inner loop control.

[0052] Step S120 , calculating the conversion ratio according to the expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop.

[0053] Step S130 : selecting an actual cutoff frequency of the current inner loop based on the dynamic response requirement of the current inner loop.

[0054] Step S140 , substituting the conversion ratio and the actual current inner loop cut-off frequency into the expression of the first current inner loop frequency to calculate the current inner loop cut-off frequency.

[0055] In one embodiment, the expression of the first current inner loop frequency is:

[0056]

[0057] where f' ci It indicates the cut-off frequency of the inner current loop after being affected by the grid impedance, and also indicates the actual cut-off frequency of the inner current loop; f ci Indicates the cut-off frequency of the current inner loop, L g is the grid-side converter filter inductor; L s is the equivalent inductance of the grid-connected system; K f is the conversion ratio.

[0058] Step S150 , substituting the current inner loop cutoff frequency into the expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient.

[0059] The expression of the second current inner loop frequency is the expression of the open-loop crossover frequency of the current inner loop; the second current inner loop frequency is determined according to the transfer function model of the current inner loop control.

[0060] In one embodiment, the expression of the second current inner loop frequency is:

[0061]

[0062] Where, Kcon represents the voltage gain of the grid-side converter output, k mi Indicates the proportional coefficient of the current sampling link, K iP Represents the proportional coefficient of the current inner loop PI controller.

[0063] Step S160 , determining the current inner loop integral constant according to the current inner loop proportional coefficient.

[0064] In one embodiment, determining the current inner loop integral constant according to the current inner loop proportional coefficient includes: calculating the current inner loop integral constant using the following formula:

[0065]

[0066] in, T iI represents the current inner loop integral constant, The phase margin required for the open loop of the current inner loop, T mi Represents the transmission delay of the current sampling link, T con Indicates the delay time constant of the grid-side converter output.

[0067] Step S170 : determining the cutoff frequency of the voltage outer loop based on the dynamic response requirement of the voltage outer loop.

[0068] In step S180 , the voltage outer loop cutoff frequency is substituted into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient.

[0069] The open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

[0070] In one embodiment, the open-loop crossover frequency of the voltage outer loop is expressed as:

[0071]

[0072] Among them, f cu Indicates the open-loop cross-frequency of the voltage outer loop, K uP Indicates the voltage outer loop proportional coefficient, k mu It represents the proportional coefficient of the DC voltage sampling link, and C represents the DC link capacitance.

[0073] In one embodiment, the transfer function model of the current inner loop control and the transfer function model of the voltage outer loop control are established by the following method:

[0074] S1: According to the structure of the direct-drive wind turbine and the structure of the grid-side converter, determine the DC voltage equation and the output voltage equation of the grid-side converter input; S2: Perform Laplace transform on the DC voltage equation and the output voltage equation to obtain the control transfer functions of the voltage outer loop and the current inner loop; S3: Perform first-order transfer function equivalence on the control transfer functions of the voltage outer loop and the current inner loop respectively to obtain the transfer function model of the direct-drive wind turbine grid-side converter; S4: According to the transfer function model of the direct-drive wind turbine grid-side converter, obtain the transfer function model of the current inner loop control and the transfer function model of the voltage outer loop control.

[0075] Step S170 , determining the voltage outer loop integral constant according to the voltage outer loop proportional coefficient.

[0076] In one embodiment, determining the voltage outer loop integral constant according to the voltage outer loop proportional coefficient includes: calculating the voltage outer loop integral constant using the following formula:

[0077]

[0078] Among them, T uI Represents the voltage outer loop integral constant, T mu represents the transmission delay of the DC voltage sampling link, It represents the phase margin required for the open loop of the voltage outer loop.

[0079] Specifically, please refer to Figure 3 As shown in the figure, a direct-drive wind turbine (PMSG) consists of a wind turbine, a permanent magnet synchronous generator (PMSG), a full-power converter (FPC), and a filter inductor. The FPC includes a generator-side converter and a grid-side converter. A direct-drive wind turbine primarily connects to the grid via the grid-side converter, so its grid-connected characteristics are primarily related to the grid-side converter. Figure 4 The topological structure diagram of the grid-side converter of the direct-drive wind turbine is shown in Figure 2. Figure 4 The broadband stability domain modeling of the direct-drive wind turbine shown in FIG. 1 is to perform transfer function modeling on each link of the grid-side converter of the direct-drive wind turbine.

[0080] Furthermore, the specific process of transfer function modeling for each link of the direct-drive wind turbine grid-side converter is as follows:

[0081] 1) Establish the DC voltage equation of the grid-side converter input. The specific expression is:

[0082]

[0083] Where U dc is the DC voltage; i o is the input current of the AC converter on the machine side; i dc It is the DC current input to the grid-side converter.

[0084] 2) Determine the output voltage equation of the grid-side converter (i.e., in the dq rotating coordinate system). The specific expression is:

[0085]

[0086] Where u gcd ,u gcq are the dq components of the grid-side converter output voltage respectively; u gd ,u gq ,i gd ,igq are the dq components of the voltage and current at the PCC point; L g ,R g Where PCC is the point of common connection, which is the connection point between the grid-side converter and the grid, and is the busbar between Lg and Ls.

[0087] 3) Perform Laplace transform on equations (1) and (2) respectively, and then obtain the control transfer functions of the voltage outer loop and the current inner loop:

[0088]

[0089]

[0090] Then the (PI) control transfer function of the voltage outer loop of the grid-side converter is G uPI (s) and the (PI) control transfer function of the current inner loop is G iUI (s):

[0091]

[0092]

[0093] where K uP ,T uI are the proportional coefficient and integral time constant of the voltage outer loop control, K iP ,T iI They are the proportional coefficient and integral time constant of the current inner loop control respectively.

[0094] 4) The process from the converter modulation signal to the converter output voltage can be expressed as a simple first-order transfer function:

[0095]

[0096] Where T con Indicates the delay time constant of the converter output, usually half of the switching time; K con Represents the voltage gain of the converter output.

[0097] Similarly, for the current sampling and DC voltage sampling process of the grid-side AC device, there are two processes that can be equivalent to a first-order DC voltage sampling link H. mu (s) and current sampling link H mi (s):

[0098]

[0099]

[0100] where k mi ,T mi are the proportional coefficient and transmission delay of the current sampling link, k mu ,T mu are the proportional coefficient and transmission delay of the DC voltage sampling link respectively.

[0101] 5) The transfer function model of the grid-side converter of the direct-drive wind turbine on the d-axis is derived. Please refer to Figure 5 As shown, the transfer function model for the q-axis is similar to that for the d-axis and will not be described in detail herein. The transfer function model may include a transfer function model for current inner loop control and a transfer function model for voltage outer loop control.

[0102] 6) According to the transfer function model, the loop gain Ti(s) in the inner current loop can be expressed as:

[0103]

[0104] In order to ensure the stability of the current inner loop, the following stability criterion is used for the loop gain of the current inner loop:

[0105]

[0106] where f ci is the open-loop crossover frequency of the current inner loop (i.e., the second current inner loop frequency); is the required phase margin.

[0107] At the same time, due to the integral link 1 / T iI s is higher than the current inner loop turning frequency f iL The system amplitude-frequency characteristics of the frequency band are slightly affected. Usually, the current internal transition frequency is set lower than the open-loop crossover frequency f of the current inner loop. ci , so in the analysis above f ci When the current loop amplitude-frequency characteristics of the frequency band are iPI (s) can be approximated by K iP Instead. Similar current G in the inner loop con (s) and H mi (s) link can also be approximately equivalent to K con and k mi Two gains.

[0108] 7) The amplitude equation in formula (11) can be rewritten as:

[0109]

[0110] Therefore, the expression of the open-loop crossover frequency of the current inner loop can be derived as:

[0111]

[0112] From formula (13), we can know that the crossover frequency f of the inner current loop is ci Mainly by K iP , K con 、k mi and L g In general, for a certain system, its parameter K con 、k mi and L g Therefore, the K of the inner current loop is iP The larger the current loop crossover frequency f ci The higher the crossover frequency, the higher the gain. According to the theory of automatic control, the crossover frequency of the loop gain is approximately equal to the cutoff frequency of the closed-loop transfer function, so the crossover frequency f ci The higher it is, the higher the bandwidth of the inner current loop.

[0113] 8) Substituting equations (13) and (10) into equation (11), we can obtain the phase equation of the current loop:

[0114]

[0115] Taking the tangent of both sides of equation (14), we can get the current inner loop integral time constant T iI As the open loop crossover frequency f ci and phase margin The stable domain range of the value will also change with the change of . The specific expression is:

[0116]

[0117] in:

[0118]

[0119] According to formula (15), the current inner loop integral time constant T is plotted. iI As the crossover frequency changes, the stable value range, such as Figure 6 As shown. Figure 6 It can be seen that as the open loop crossover frequency f of the current inner loop ci The increase of T iI The lower limit of the value of first decreases and then increases, and when the system requires the phase margin to change, T iI The lower limit of the value is also changing.

[0120] 9) From the above analysis, we can see that the required cutoff frequency of the inner current loop is first determined by the dynamic response characteristics of the circuit inner loop, generally selected to be within 1 / 10 of the equivalent switching frequency. Due to the high-frequency response characteristics of the switching process, the current inner loop frequency is selected to be 1 / 10 of the switching process. The main purpose is to keep the cutoff frequency at least one order of magnitude higher than the switching frequency, so that the response characteristics of the inner current loop are not affected by the switching frequency band. However, too low a cutoff frequency will affect the dynamic response speed, so keeping it within the same order of magnitude is sufficient.

[0121] The corresponding open-loop crossover frequency f can be further determined ci The proportional coefficient K of the current inner loop PI controller can be selected and calculated according to formula (13). iP At the same time, according to the requirements of meeting the system phase margin, determine the appropriate PI controller integral time constant T iI , according to formula (15) and Figure 6 The stability range in takes an appropriate value.

[0122] 10) Same basis Figure 5 The transfer function model of the voltage outer loop can be obtained by using the transfer function model, in which the current inner loop is equivalent to a transfer function, and the loop gain of the voltage outer loop is derived as T u (s), whose expression is:

[0123]

[0124] Among them, G I (s) is the transfer function of the inner current loop:

[0125]

[0126] 11) Similar to the current loop, to ensure the stability of the voltage outer loop, the loop gain of the voltage outer loop must meet the following stability criteria:

[0127]

[0128] where f cu is the open-loop cross-frequency of the voltage outer loop; is the phase margin required for the open loop of the voltage outer loop. Similarly, substituting the expression of the voltage outer loop gain into the stability criterion, the module value equation of the voltage outer loop can be obtained as follows:

[0129]

[0130] 12) Since the dynamic response of the voltage link is much slower than that of the current link, the turning frequency f of the voltage outer loop uL Compared with the turning frequency f of the inner current loop iLIt is an order of magnitude smaller. Therefore, when analyzing the voltage loop crossover frequency f cu When the amplitude-frequency characteristics of the frequency band are iPI (s) can be approximated by K iP At the same time, due to the time constant T in the converter transfer function con and T in the transfer function of the sampling link mi ,T mu are very small, similar to the previous analysis, and can be equivalent to K con and k mi ,k mu Several buffs.

[0131] 13) Then at the voltage loop crossing frequency f cu Ignore the filter resistor R g , we can get:

[0132]

[0133] By simplifying the derivation, the expression of the open-loop cross-frequency of the voltage outer loop can be obtained as follows:

[0134]

[0135] 14) According to the analysis, the cross-over frequency f of the voltage outer loop is cu Mainly by K uP 、k mu 、k mi and C together, generally speaking, a parameter k that determines the system mu 、k mi and C are also determined. Therefore, K of the voltage outer loop uP The larger the voltage is, the open loop crossover frequency f of the voltage outer loop will be. cu The higher it is, the higher the bandwidth of the voltage outer loop will be.

[0136] 15) Substituting the open-loop crossover frequency expression of the voltage outer loop in equation (22) into the stability criterion equation, the phase equation of the voltage loop can be obtained:

[0137]

[0138] Since the current inner loop cutoff frequency f ci Much larger than the voltage outer loop cutoff frequency f cu , so the current inner loop transfer function G I The phase shift caused by (s) at the cutoff frequency of the voltage outer loop is close to zero and can be ignored.

[0139] 16) Taking the tangent of both sides, we can get the voltage outer loop integral time constant T uI As the voltage outer loop cut-off frequency f cu and phase margin P MuThe stable domain range of the value of the change:

[0140]

[0141] After analysis, the voltage outer loop time constant T can be drawn uI As the cutoff frequency changes, the stable value range is as follows: Figure 7 As shown in the figure, as the voltage loop cutoff frequency f cu The increase of T uI The lower limit of the value of first decreases and then increases, and when the system requires the phase margin to change, T uI The lower limit of the value is also changing.

[0142] 17) Since the control parameter design of most new energy devices currently uses a strong AC system as the standard operating condition, and since most new energy power generation devices currently operate in weak AC grid-connected systems, the stability range of the grid-side converter control parameters also varies under different AC network strength conditions. Further consideration is needed for system parameter optimization design methods that take into account different network strength conditions.

[0143] Considering the influence of network strength, we can obtain Figure 8 The control block diagram shown in the figure. s (s) is the equivalent impedance of the infinite system, Z s (s)=R s +sL s , R s is the equivalent resistance of the infinite system, L s is the infinite system equivalent inductance. Simplify the above equation and ignore the influence of the infinite grid voltage d-axis component. We can get Figure 9 The control block diagram shown in Figure 1 shows that network strength (SCR) will affect converter control characteristics. The SCR (Short Circuit Ratio) is the short-circuit capacity, which characterizes system strength, divided by the equipment capacity. The SCR was originally developed as a practical metric to measure the impact of electrical equipment on the voltage at the access point. A high SCR indicates good system performance; conversely, a low SCR indicates potential system vulnerabilities. Currently, the relationship between DC power transmission and AC system strength is often simply analyzed based on the SCR and effective SCR. The SCR represents the system short-circuit capacity divided by the DC power. When the system's SCR is low, auxiliary control devices or specialized control techniques are required to achieve satisfactory system dynamic characteristics.

[0144] 18) From formula (22), we can see that after considering the influence of system strength SCR, when the converter control parameters remain unchanged, the cutoff frequency f of the current inner loop is ci The expression is:

[0145]

[0146] The cut-off frequency f of the current inner loop ci From the expression, we can know that when the system becomes weaker, that is, when the equivalent inductance of the infinite system increases, the cut-off frequency f of the current inner loop ci is decreasing. According to T iI The stable value range of the current inner loop cutoff frequency f ci After the change, the stability margin also changes, and the adaptability of the changed stability margin needs to be analyzed.

[0147] At the same time, as the system short-circuit ratio decreases, the current inner loop cut-off frequency f ci Continuously approaching the voltage outer loop cutoff frequency f cu , the phase shift frequency of the closed-loop transfer function of the inner current loop is decreasing, which in turn has a certain impact on the phase margin of the outer voltage loop.

[0148] 19) When the current inner loop cutoff frequency f ci Continuously approaching the voltage outer loop cutoff frequency f cu When , the cutoff frequency of the voltage outer loop will be affected by the current inner loop. According to the loop gain expression of the voltage outer loop, the cutoff frequency expression of the voltage outer loop can be further derived as:

[0149]

[0150]

[0151] Through analysis, we know that when the open loop cross frequency f ci Greater than the open-loop cross-frequency f of the voltage outer loop cu When the magnitude is one, K m Approximately equal to 1, the cross-frequency of the voltage outer loop depends approximately on the voltage open-loop proportional coefficient K uP When considering the influence of the system short circuit ratio, when the system short circuit ratio SCR decreases, the current inner loop crossover frequency f ci Reduce, and then K m The corresponding cut-off frequency f of the voltage outer loop is cu In decreasing.

[0152] According to T uI The stable value range of the current inner loop cutoff frequency f cu After the change, the stability margin also changes, and the adaptability of the changed stability margin needs to be analyzed.

[0153] From the above analysis, it can be seen that changes in network strength will affect some of the converter's internal control characteristics, such as reducing the cutoff frequency of the inner current loop and affecting the phase margin and stability of the outer voltage loop. Therefore, during the converter parameter design process, it is necessary to consider the network strength in which the converter will operate and provide a certain stability margin during the parameter design process to ensure stable operation under different grid strength conditions.

[0154] 20) Define f′ ci is the cut-off frequency of the current inner loop after being affected by the grid impedance, and its expression is:

[0155]

[0156] Where L g is the filter inductance of the grid-side converter; L s is the equivalent inductance of the grid-connected system; K f is the conversion ratio.

[0157] Therefore, when selecting the cutoff frequency of the current inner loop, the actual cutoff frequency f′ of the current inner loop determined by the dynamic response requirements and stability requirements of the current inner loop must be considered. ci Converted into the theoretical current inner loop cutoff frequency f of parameter optimization design ci , and then calculate and determine the stable range of other parameters of the current inner loop to take appropriate values. After the current inner loop parameters are optimized, the parameters of the voltage outer loop are optimized and designed.

[0158] It should be noted that the control parameters for modeling the wide-band stability domain of direct-drive wind turbines include the current inner loop cutoff frequency, the current inner loop proportional coefficient, the current inner loop integral constant, the voltage outer loop cutoff frequency, the voltage outer loop proportional coefficient, and the voltage outer loop integral constant. The current inner loop cutoff frequency can also be called the open-loop cross-frequency of the current inner loop, and the voltage outer loop cutoff frequency can also be called the open-loop cross-frequency of the voltage outer loop.

[0159] The specific steps for determining the control parameters under different grid-connected operation conditions are as follows: Calculate the maximum conversion ratio K according to formula (28) based on the system's weakest grid-connected strength SCR f， Determine the dynamic response requirements of the required current inner loop and select the appropriate actual current inner loop cutoff frequency f ci ; According to the conversion ratio K f Calculate the current inner loop cutoff frequency f ci ; According to formula (13), select the appropriate current inner loop proportional coefficient K iP ; According to formula (16), select the appropriate current inner loop integral constant T iI ; Determine the dynamic response requirements of the required voltage outer loop and select the appropriate voltage outer loop cutoff frequency f cu ; According to formula (22), select the appropriate current inner loop proportional coefficient KuP ; According to formula (24), select the appropriate current inner loop integral constant T uI .

[0160] The control parameter determination method based on broadband stability domain modeling of direct-drive wind turbines provided in the embodiment of the present application carries out parameter coordination design for wind turbines adapted to weak grid conditions, which can reduce the need for hardware modification in wind farms and is more economical; and takes into account the influence of different grid connection strengths, thereby improving the broadband stability characteristics of direct-drive wind turbines under different grid connection conditions.

[0161] It should be understood that although Figure 2 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Figure 2 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0162] The above-mentioned embodiments disclosed in this application describe in detail a method for determining control parameters based on broadband stability domain modeling of a direct-drive wind turbine. The above-mentioned method disclosed in this application can be implemented using various forms of equipment. Therefore, this application also discloses a control parameter determination device based on broadband stability domain modeling of a direct-drive wind turbine corresponding to the above-mentioned method. Specific embodiments are given below for detailed explanation.

[0163] See also Figure 10 , disclosed in an embodiment of the present application, is a control parameter determination device based on broadband stability domain modeling for a direct-drive wind turbine. The direct-drive wind turbine is connected to the grid via a grid-side AC converter. The grid-side AC converter includes a current inner loop control and a voltage outer loop control. The device mainly includes:

[0164] An information acquisition module 210 is used to obtain an expression for the system's weakest grid-connected strength and the first current inner loop frequency;

[0165] The conversion ratio calculation module 220 is used to calculate the conversion ratio according to the expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop;

[0166] The frequency selection module 230 is used to select the actual current inner loop cutoff frequency based on the dynamic response requirements of the current inner loop;

[0167] A frequency calculation module 240 is configured to substitute the conversion ratio and the actual current inner loop cutoff frequency into an expression of the first current inner loop frequency to calculate the current inner loop cutoff frequency;

[0168] An inner loop proportional coefficient calculation module 250 is used to substitute the current inner loop cutoff frequency into the expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient;

[0169] An inner loop integral constant determining module 260, configured to determine a current inner loop integral constant according to a current inner loop proportional coefficient;

[0170] A frequency determination module 270 is configured to determine a cutoff frequency of the voltage outer loop based on a dynamic response requirement of the voltage outer loop;

[0171] The outer loop proportional coefficient calculation module 280 is used to substitute the voltage outer loop cutoff frequency into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient;

[0172] An outer loop integral constant determining module 290 is configured to determine a voltage outer loop integral constant according to a voltage outer loop proportional coefficient;

[0173] Among them, the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by the grid connection; the expression of the second current inner loop frequency is the expression of the open-loop cross-frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

[0174] In one embodiment, the expression of the first current inner loop frequency is:

[0175]

[0176] where f' ci It indicates the cut-off frequency of the inner current loop after being affected by the grid impedance, and also indicates the actual cut-off frequency of the inner current loop; f ci Indicates the cut-off frequency of the current inner loop, L g is the grid-side converter filter inductor; L s is the equivalent inductance of the grid-connected system; K f is the conversion ratio.

[0177] In one embodiment, the expression of the second current inner loop frequency is:

[0178]

[0179] Where, Kcon represents the voltage gain of the grid-side converter output, k mi Indicates the proportional coefficient of the current sampling link, K iPRepresents the proportional coefficient of the current inner loop PI controller.

[0180] In one embodiment, determining the current inner loop integral constant according to the current inner loop proportional coefficient includes: calculating the current inner loop integral constant using the following formula:

[0181]

[0182] in, T iI represents the current inner loop integral constant, The phase margin required for the open loop of the current inner loop, T mi Represents the transmission delay of the current sampling link, T con Indicates the delay time constant of the grid-side converter output.

[0183] In one embodiment, the open-loop crossover frequency of the voltage outer loop is expressed as:

[0184]

[0185] Among them, f cu Indicates the open-loop cross-frequency of the voltage outer loop, K uP Indicates the voltage outer loop proportional coefficient, k mu It represents the proportional coefficient of the DC voltage sampling link, and C represents the DC link capacitance.

[0186] In one embodiment, determining the voltage outer loop integral constant according to the voltage outer loop proportional coefficient includes: calculating the voltage outer loop integral constant using the following formula:

[0187]

[0188] Among them, T uI Represents the voltage outer loop integral constant, T mu represents the transmission delay of the DC voltage sampling link, It represents the phase margin required for the open loop of the voltage outer loop.

[0189] In one embodiment, the device also includes: a transfer function model establishment module, which is used to determine the DC voltage equation and output voltage equation of the grid-side converter input according to the structure of the direct-drive wind turbine and the structure of the grid-side converter; perform Laplace transform on the DC voltage equation and the output voltage equation to obtain the control transfer functions of the voltage outer loop and the current inner loop; perform first-order transfer function equivalence on the control transfer functions of the voltage outer loop and the current inner loop respectively to obtain the transfer function model of the direct-drive wind turbine grid-side converter; obtain the transfer function model of the current inner loop control and the transfer function model of the voltage outer loop control according to the transfer function model of the direct-drive wind turbine grid-side converter.

[0190] Regarding the specific definition of the control parameter determination device based on broadband stability domain modeling of direct-drive wind turbines, please refer to the definition of the method above and will not be repeated here. Each module in the above device can be implemented in whole or in part by software, hardware, and a combination thereof. Each of the above modules can be embedded in or independent of the processor in the terminal device in hardware form, or can be stored in the memory of the terminal device in software form, so that the processor can call and execute the operations corresponding to each of the above modules.

[0191] Please refer to Figure 11 , Figure 11 It shows a structural block diagram of a terminal device provided in an embodiment of the present application. The terminal device 110 can be a computer device. The terminal device 110 in the present application can include one or more of the following components: a processor 112, a memory 114, and one or more application programs, wherein the one or more application programs can be stored in the memory 114 and configured to be executed by the one or more processors 112, and the one or more application programs are configured to execute the method described in the embodiment of the control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine.

[0192] The processor 112 may include one or more processing cores. The processor 112 utilizes various interfaces and circuits to connect various components within the terminal device 110. It executes instructions, programs, code sets, or instruction sets stored in the memory 114, and accesses data stored in the memory 114 to perform various functions and process data within the terminal device 110. Optionally, the processor 112 may be implemented using at least one of the following hardware forms: a digital signal processing (DSP), a field-programmable gate array (FPGA), or a programmable logic array (PLA). The processor 112 may integrate one or a combination of a central processing unit (CPU), a graphics processing unit (GPU), and a modem. The CPU primarily processes the operating system, user interface, and application programs; the GPU is responsible for rendering and drawing display content; and the modem handles wireless communications. It is understood that the modem may not be integrated into the processor 112 and may be implemented separately via a communication chip.

[0193] The memory 114 may include a random access memory (RAM) or a read-only memory (ROM). The memory 114 may be used to store instructions, programs, codes, code sets, or instruction sets. The memory 114 may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for implementing at least one function (such as a touch function, a sound playback function, an image playback function, etc.), instructions for implementing the following various method embodiments, etc. The data storage area may also store data created by the terminal device 110 during use.

[0194] Those skilled in the art will understand that Figure 11 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the terminal device to which the solution of the present application is applied. The specific terminal device may include more or fewer components than shown in the figure, or combine certain components, or have a different component arrangement.

[0195] In summary, the terminal device provided in the embodiment of the present application is used to implement the corresponding control parameter determination method based on broadband stability domain modeling of direct-drive wind turbines in the aforementioned method embodiment, and has the beneficial effects of the corresponding method embodiment, which will not be repeated here.

[0196] See also Figure 12 , which shows a block diagram of a computer-readable storage medium provided in an embodiment of the present application. The computer-readable storage medium 120 stores program code that can be invoked by a processor to execute the method described in the embodiment of the control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine.

[0197] The computer-readable storage medium 120 can be an electronic memory such as a flash memory, an EEPROM (Electrically Erasable Programmable Read-Only Memory), an EPROM, a hard disk, or a ROM. Alternatively, the computer-readable storage medium 120 includes a non-transitory computer-readable storage medium. The computer-readable storage medium 120 has storage space for program code 122 for executing any of the method steps described above. This program code can be read from or written to one or more computer program products. The program code 122 can be compressed, for example, in a suitable form.

[0198] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0199] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control parameter determination method based on broadband stability domain modeling of a direct-drive wind turbine, wherein the direct-drive wind turbine is connected to the grid via a grid-side AC converter, wherein the grid-side AC converter includes a current inner loop control and a voltage outer loop control, characterized in that: The method comprises: Obtain the expressions of the system's weakest grid-connected strength and the first current inner loop frequency; Calculating a conversion ratio according to an expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop; Based on the dynamic response requirements of the current inner loop, select the actual current inner loop cutoff frequency; Substituting the conversion ratio and the actual current inner loop cut-off frequency into an expression for the first current inner loop frequency to calculate the current inner loop cut-off frequency; Substituting the current inner loop cutoff frequency into the expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient; Determining a current inner loop integral constant according to the current inner loop proportional coefficient; Determine the cutoff frequency of the voltage outer loop based on the dynamic response requirements of the voltage outer loop; Substituting the voltage outer loop cutoff frequency into the expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient; Determining a voltage outer loop integral constant according to the voltage outer loop proportional coefficient; Among them, the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by grid connection; the expression of the second current inner loop frequency is the expression of the open-loop cross-frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

2. The method according to claim 1, characterized in that The expression of the first current inner loop frequency is: where f' ci It indicates the cut-off frequency of the inner current loop after being affected by the grid impedance, and also indicates the actual cut-off frequency of the inner current loop; f ci Indicates the cut-off frequency of the current inner loop, L g is the grid-side converter filter inductor; L s is the equivalent inductance of the grid-connected system; K f is the conversion ratio.

3. The method according to claim 2, characterized in that The expression of the second current inner loop frequency is: Where, Kcon represents the voltage gain of the grid-side converter output, k mi Indicates the proportional coefficient of the current sampling link, K iP Represents the proportional coefficient of the current inner loop PI controller.

4. The method according to claim 3, characterized in that Determining the current inner loop integral constant according to the current inner loop proportional coefficient includes: The current inner loop integral constant is calculated using the following formula: in, T iI represents the current inner loop integral constant, The phase margin required for the open loop of the current inner loop, T mi Represents the transmission delay of the current sampling link, T con Indicates the delay time constant of the grid-side converter output.

5. The method according to claim 4, characterized in that The expression of the open-loop cross-frequency of the voltage outer loop is: Among them, f cu Indicates the open-loop cross-frequency of the voltage outer loop, K uP Indicates the voltage outer loop proportional coefficient, k mu It represents the proportional coefficient of the DC voltage sampling link, and C represents the DC link capacitance.

6. The method according to claim 5, characterized in that Determining the voltage outer loop integral constant according to the voltage outer loop proportional coefficient includes: The voltage outer loop integral constant is calculated using the following formula: Among them, T uI Represents the voltage outer loop integral constant, T mu represents the transmission delay of the DC voltage sampling link, Expressed as the required phase margin for the open loop of the voltage outer loop.

7. The method according to claim 6, characterized in that The transfer function model of the current inner loop control and the transfer function model of the voltage outer loop control are established by the following method: According to the structure of the direct-drive wind turbine and the structure of the grid-side converter, determine the DC voltage equation of the grid-side converter input and the output voltage equation; Performing Laplace transform on the DC voltage equation and the output voltage equation to obtain control transfer functions of a voltage outer loop and a current inner loop; The control transfer functions of the voltage outer loop and the current inner loop are respectively equivalent to the first-order transfer function to obtain the transfer function model of the grid-side converter of the direct-drive wind turbine. According to the transfer function model of the grid-side converter of the direct-drive wind turbine, the transfer function model of the current inner loop control and the transfer function model of the voltage outer loop control are obtained.

8. A control parameter determination device based on broadband stability domain modeling for a direct-drive wind turbine, wherein the direct-drive wind turbine is connected to the grid via a grid-side AC converter, wherein the grid-side AC converter includes a current inner loop control and a voltage outer loop control, characterized in that: The device method comprises: An information acquisition module, used to obtain expressions of the system's weakest grid-connected strength and the first current inner loop frequency; a conversion ratio calculation module, configured to calculate the conversion ratio according to an expression of the weakest grid-connected strength of the system and the frequency of the first current inner loop; A frequency selection module is used to select the actual current inner loop cutoff frequency based on the dynamic response requirements of the current inner loop; a frequency calculation module, configured to substitute the conversion ratio and the actual current inner loop cut-off frequency into an expression of the first current inner loop frequency to calculate the current inner loop cut-off frequency; an inner loop proportional coefficient calculation module, configured to substitute the current inner loop cutoff frequency into an expression of the second current inner loop frequency to calculate the current inner loop proportional coefficient; An inner loop integral constant determining module, configured to determine a current inner loop integral constant according to the current inner loop proportional coefficient; A frequency determination module, used for determining a cutoff frequency of the voltage outer loop based on a dynamic response requirement of the voltage outer loop; an outer loop proportional coefficient calculation module, configured to substitute the voltage outer loop cutoff frequency into an expression of the open-loop crossover frequency of the voltage outer loop to calculate the voltage outer loop proportional coefficient; An outer loop integral constant determining module, configured to determine a voltage outer loop integral constant according to the voltage outer loop proportional coefficient; Among them, the expression of the first current inner loop frequency is the expression of the current inner loop cutoff frequency after being affected by grid connection; the expression of the second current inner loop frequency is the expression of the open-loop cross-frequency of the current inner loop; the first current inner loop frequency and the second current inner loop frequency are determined according to the transfer function model of the current inner loop control; the open-loop cross-frequency of the voltage outer loop is determined according to the transfer function model of the voltage outer loop control.

9. A terminal device, characterized in that: include: Memory; one or more processors coupled to the memory; One or more applications, wherein the one or more applications are stored in a memory and configured to be executed by one or more processors, and the one or more applications are configured to execute the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that The computer-readable storage medium stores program code, which can be called by a processor to execute the method according to any one of claims 1 to 7.

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