State switching simulation system and method of wind turbine generator

Abstract

The invention provides a state switching simulation system and method for a wind turbine generator, and relates to the field of analog simulation. The system comprises a main control module, a test module, a human-computer interaction interface and a shared address bus, the main control module is used for sending a starting instruction to the test module and entering a starting mode, and the test module responds to the starting instruction to simulate the starting process of the wind turbine generator and shares starting simulation parameters with the main control module in real time; the main control module is used for sending a grid-connected instruction to the test module and entering a grid-connected mode after monitoring that the starting simulation parameters meet grid-connected conditions, and the test module responds to the grid-connected instruction to simulate the grid-connected process of the wind turbine generator and shares grid-connected simulation parameters with the main control module in real time; the main control module is used for sending a shutdown instruction to the test module and entering a shutdown mode after monitoring that the grid-connected simulation parameters meet shutdown conditions, and the test module responds to the shutdown instruction to simulate the shutdown process of the wind turbine generator and shares shutdown simulation parameters with the main control module in real time.

Description

Technical Field

[0001] The present application relates to the field of wind power generation and simulation technology, and in particular to a state switching simulation system and method for a wind turbine generator set. Background Art

[0002] In the field of wind power generation, the state machine of the main control system of wind turbines plays a vital role, directly affecting the operating efficiency, reliability and stability of the units. With the continuous development of wind power generation technology, especially in the application of large-capacity and intelligent wind turbines, the performance requirements of the main control system are constantly increasing. The main control system of modern wind turbines not only needs to adapt to complex and changing environmental conditions, but also needs to handle interactions with smart grids and support more accurate fault diagnosis and prediction functions. Therefore, how to ensure the efficient and stable operation of the state machine of the main control system of wind turbines has become an important issue facing the industry. Summary of the invention

[0003] The present application aims to solve one of the technical problems in the related art at least to some extent.

[0004] To this end, one purpose of the present application is to propose a state switching simulation system for a wind turbine generator set, including a main control module, a test module, a human-computer interaction interface and a shared address bus, wherein: the main control module is used to send a start-up instruction to the test module and enter a start-up mode, the test module responds to the start-up instruction to simulate the start-up process of the wind turbine generator set, and shares the start-up simulation parameters with the main control module in real time; the main control module is used to send a grid-connected instruction to the test module and enter a grid-connected mode after monitoring that the start-up simulation parameters meet the grid-connected conditions, the test module responds to the grid-connected instruction to simulate the grid-connected process of the wind turbine generator set, and shares the start-up simulation parameters with the main control module in real time. Grid-connected simulation parameters; the main control module is used to send a shutdown command to the test module and enter the shutdown mode after monitoring that the grid-connected simulation parameters meet the shutdown conditions. The test module responds to the shutdown command to simulate the shutdown process of the wind turbine set, and shares the shutdown simulation parameters with the main control module in real time; wherein, the main control module and the test module communicate in real time through a shared address bus, the shared address bus allocates the variables required by the main control module to the shared address area, and the test module reads and feeds back the simulation parameter information in real time; the main control module and the test module receive instructions issued by the user through the human-computer interaction interface to update the simulation parameters.

[0005] The second objective of the present application is to provide a state switching simulation method for a wind turbine generator set.

[0006] The third objective of the present application is to provide an electronic device.

[0007] A fourth object of the present application is to provide a non-transitory computer-readable storage medium.

[0008] A fifth object of the present application is to provide a computer program product.

[0009] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a state switching simulation system for a wind turbine generator set, including a main control module, a test module, a human-computer interaction interface and a shared address bus, wherein: the main control module is used to send a startup instruction to the test module and enter a startup mode, the test module responds to the startup instruction to simulate the startup process of the wind turbine generator set, and shares the startup simulation parameters to the main control module in real time; the main control module is used to send a grid-connected instruction to the test module and enter a grid-connected mode after monitoring that the startup simulation parameters meet the grid-connected conditions, the test module responds to the grid-connected instruction to simulate the grid-connected process of the wind turbine generator set, and sends the startup simulation parameters to the main control module in real time Shared grid-connected simulation parameters; the main control module is used to send a shutdown command to the test module and enter the shutdown mode after monitoring that the grid-connected simulation parameters meet the shutdown conditions. The test module responds to the shutdown command to simulate the shutdown process of the wind turbine set, and shares the shutdown simulation parameters to the main control module in real time; wherein, the main control module and the test module communicate in real time through a shared address bus, the shared address bus allocates the variables required by the main control module to the shared address area, and the test module reads and feeds back the simulation parameter information in real time; the main control module and the test module receive instructions issued by the user through the human-computer interaction interface to update the simulation parameters.

[0010] According to one embodiment of the present application, the main control module is also used for: in response to the main control module monitoring that the incoming flow simulated wind speed is greater than the wind speed threshold and the duration is greater than a preset duration, sending a start instruction to the test module, wherein the incoming flow simulated wind speed is simulated by the test module and shared with the main control module; or, in response to the main control module monitoring the start instruction sent by the host computer, sending a start instruction to the test module.

[0011] According to one embodiment of the present application, the test module includes a wind speed simulation unit, a pitch simulation unit, a speed simulation unit, and a grid-connected simulation unit, wherein: the wind speed simulation unit is used to generate an incoming simulated wind speed according to a set initial wind speed value; the pitch simulation unit is used to simulate and generate a pitch angle and a pitch speed of the unit based on a pitch instruction issued by a main control module, and the pitch instruction carries at least a pitch angle target value and a pitch angle target rate; the speed simulation unit is used to generate a generator simulated speed according to speed-related parameters, and simulate and control the speed to increase or decrease based on the generator simulated speed, and the speed-related parameters include at least the incoming simulated wind speed, the simulated pitch angle of the unit, and the unit power demand issued by the main control module; the grid-connected simulation unit is used to generate a grid-connected active power according to the generator simulated speed and the electromagnetic torque instruction issued by the main control module, and simulate the grid-connected process.

[0012] According to one embodiment of the present application, the test module simulates the shutdown process of the wind turbine generator set in response to a shutdown command, including: the test module simulates the shutdown process of the wind turbine generator set according to the shutdown command, and the simulated wind turbine generator set shutdown process includes simulating the blade retraction operation and simulating the deceleration operation until the generator set shuts down.

[0013] According to an embodiment of the present application, the main control module and the test module are controlled by the same simulation controller.

[0014] According to an embodiment of the present application, the main control module and the test module are respectively controlled by two independent simulation controllers.

[0015] To achieve the above-mentioned purpose, the second aspect of the present application proposes a state switching simulation method for a wind turbine group, including: in response to monitoring a state switching simulation instruction of the wind turbine group, executing a state switching simulation process of the wind turbine group based on the state switching simulation system of the above-mentioned wind turbine group.

[0016] To achieve the above-mentioned purpose, the third aspect embodiment of the present application proposes an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to implement the state switching simulation method of the wind turbine group as described in the second aspect embodiment of the present application.

[0017] To achieve the above-mentioned purpose, the fourth aspect embodiment of the present application proposes a non-transitory computer-readable storage medium storing computer instructions, wherein the computer instructions are used to implement the state switching simulation method of the wind turbine group as described in the second aspect embodiment of the present application.

[0018] To achieve the above-mentioned purpose, the fifth embodiment of the present application proposes a computer program product, including a computer program, which, when executed by a processor, implements the state switching simulation method of the wind turbine group as described in the second embodiment of the present application.

[0019] The present application achieves at least the following beneficial effects: the state switching simulation system of the wind turbine proposed in the present application can comprehensively test the performance of the main control system of the wind turbine by accurately simulating the startup, grid connection and shutdown process of the wind turbine, and can verify the stability and reliability of the wind turbine under various working conditions, providing important data support for the design and optimization of the wind turbine. In addition, through the control of the human-computer interaction interface, the simulation parameters can be adjusted in real time to improve the test efficiency and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0021] Figure 1 It is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in an embodiment of the present application.

[0022] Figure 2 It is a schematic diagram of a shared address bus shown in one embodiment of the present application.

[0023] Figure 3 It is a schematic diagram of a test module shown in an embodiment of the present application.

[0024] Figure 4 It is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in an embodiment of the present application.

[0025] Figure 5 It is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in an embodiment of the present application.

[0026] Figure 6 It is a schematic diagram of a state switching simulation method of a wind turbine set from the perspective of a main control module according to an embodiment of the present application.

[0027] Figure 7 It is a schematic diagram of an electronic device shown in one embodiment of the present application. DETAILED DESCRIPTION

[0028] Embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0029] Figure 1 is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in the present application, such as Figure 1 As shown, the state switching simulation system of the wind turbine generator set includes a main control module, a test module, a human-computer interaction interface and a shared address bus, wherein:

[0030] The main control module is used to send a startup instruction to the test module. At this time, the main control module enters the startup mode. The test module responds to the startup instruction to simulate the startup process of the wind turbine set and shares the startup simulation parameters with the main control module in real time.

[0031] The main control module is used to send a grid-connected instruction to the test module after monitoring that the startup simulation parameters meet the grid-connected conditions. At this time, the main control module enters the grid-connected mode, and the test module responds to the grid-connected instruction to simulate the grid-connected process of the wind turbine set and shares the grid-connected simulation parameters with the main control module in real time.

[0032] The main control module is used to send a shutdown command to the test module after monitoring that the grid-connected simulation parameters meet the shutdown conditions. At this time, the main control module enters the shutdown mode, and the test module responds to the shutdown command to simulate the shutdown process of the wind turbine (the test module simulates the shutdown process of the wind turbine according to the shutdown command, and the simulated wind turbine shutdown process includes simulated propeller retraction operation and simulated deceleration operation until the unit shuts down), and shares the shutdown simulation parameters to the main control module in real time.

[0033] The main control module and the test module communicate in real time through a shared address bus. Figure 2 is a schematic diagram of a shared address bus shown in this application, such as Figure 2 As shown, the shared address bus allocates the variables required by the main control module to the shared address area, and the test module reads and feeds back the simulation parameter information in real time;

[0034] The main control module and the test module receive instructions issued by the user through the human-computer interaction interface to update the simulation parameters. For example, the user can issue a start instruction based on the human-computer interaction interface, or issue parameters such as the pitch angle target value, pitch angle target rate, and unit power demand.

[0035] Before the main control module sends a start command to the test module, it needs to determine whether the start condition is met. There are two judgment methods:

[0036] 1. When the main control module is in the unit standby mode, it continuously receives the incoming flow simulated wind speed simulated by the test module. In response to the main control module monitoring that the incoming flow simulated wind speed is greater than the wind speed threshold for a duration greater than a preset duration, it sends a start instruction to the test module, wherein the incoming flow simulated wind speed is simulated by the test module and shared with the main control module.

[0037] 2. In response to the main control module detecting the start-up instruction sent by the host computer, the main control module sends a start-up instruction to the test module.

[0038] in, Figure 3 is a schematic diagram of a test module shown in this application, such as Figure 3 As shown, the test module includes a wind speed simulation unit, a pitch simulation unit, a speed simulation unit and a grid-connected simulation unit. When the test module receives a control instruction from the main control module, each unit of the test module can generate unit operation status information according to the corresponding instruction signal and feed it back to the main control module. Among them:

[0039] 1. The wind speed simulation unit is used to generate the incoming flow simulation wind speed according to the set initial wind speed value, and share the incoming flow simulation wind speed to the main control module in real time, so that the main control module can judge whether the unit start-up conditions are met.

[0040] Specifically, the wind speed simulation unit calculates the wind speed according to the initial wind speed value V set inside it. 0Or according to the initial wind speed value V set by the user through the human-computer interaction interface 0 , generate the simulated wind speed v of the incoming flow with natural fluctuations, where:

[0041] v=f(V 0 )

[0042] 2. The pitch simulation unit is used to simulate and generate the pitch angle and pitch speed of the unit based on the pitch command issued by the main control module, and share it to the main control module in real time. The pitch command carries at least the pitch angle target value and the pitch angle target rate. Among them, the pitch command and the start command can be combined into one command, that is, it can be understood that when the main control module issues a start command to the test module, the start command carries the pitch angle target value and the pitch angle target rate.

[0043] Specifically, according to the set initial pitch angle β 0 , given the pitch angle target value β ref , given the pitch angle target rate ω ref The actual pitch angle β of the unit is simulated and generated; according to the given pitch angle target value β ref and a given pitch angle target rate ω ref The simulation generates the variable pitch speed ω of the unit.

[0044] β=f(ω ref ,β 0 ,β ref )

[0045] ω=f(ω ref ,β ref )

[0046] 3. The speed simulation unit is used to generate a simulated generator speed according to speed-related parameters, and share it to the main control module in real time, and simulate and control the speed to increase or decrease based on the simulated generator speed. The speed-related parameters include at least the simulated wind speed of the incoming flow, the pitch angle of the unit generated by the variable pitch simulation unit, and the power demand of the unit issued by the main control module.

[0047] Specifically, after the unit is started, according to the simulated wind speed v, the simulated pitch angle β of the unit, and the unit power P ref And the working mode generates the generator speed n gen , and control the speed to increase or decrease.

[0048] n gen =f(v,β,P ref )

[0049] 4. The grid-connected simulation unit is used to generate grid-connected active power according to the simulated generator speed and the electromagnetic torque command issued by the main control module, simulate the grid-connected process, and share it with the main control module in real time. Specifically, after the unit simulates entering the grid, according to the generator speed n gen , the electromagnetic torque command Te generates the unit’s grid-connected active power P.

[0050] P = f(n gen ,Te)

[0051] In some implementations, the main control module and the test module are controlled by the same simulation controller, which can simplify the system architecture. Figure 4 is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in the present application, such as Figure 4 As shown, the main control module and the test module are controlled by the same simulation controller, which corresponds to a human-computer interaction interface.

[0052] In some implementations, the main control module and the test module are controlled by two independent analog controllers respectively, which ensures decoupling between the modules and facilitates expansion and flexible adjustment. Figure 5 is a schematic diagram of a state switching simulation system of a wind turbine generator set shown in the present application, such as Figure 5 As shown, the main control module and the test module are controlled by two independent simulation controllers, and the two controllers correspond to a human-computer interaction interface respectively.

[0053] The state switching simulation system of the wind turbine proposed in this application can comprehensively test the performance of the wind turbine main control system by accurately simulating the start-up, grid connection and shutdown process of the wind turbine, and can verify the stability and reliability of the wind turbine under various working conditions, providing important data support for the design and optimization of the wind turbine. In addition, through the control of the human-computer interaction interface, the simulation parameters can be adjusted in real time to improve the test efficiency and flexibility.

[0054] After designing the state switching simulation system of the wind turbine set as above, the present application also proposes a state switching simulation method of the wind turbine set, including: in response to monitoring the state switching simulation instruction of the wind turbine set, executing the state switching simulation process of the wind turbine set based on the state switching simulation system of the wind turbine set as above. Figure 6 This is a schematic diagram of a state switching simulation method of a wind turbine generator set from the perspective of a main control module, which includes the following steps:

[0055] 1. The main control module is used to send a startup instruction to the test module. At this time, the main control module enters the startup mode. The test module responds to the startup instruction to simulate the startup process of the wind turbine and shares the startup simulation parameters with the main control module in real time.

[0056] 2. After the main control module detects that the startup simulation parameters meet the grid-connected conditions, it sends a grid-connected instruction to the test module. At this time, the main control module enters the grid-connected mode. The test module responds to the grid-connected instruction to simulate the grid-connected process of the wind turbine and shares the grid-connected simulation parameters with the main control module in real time.

[0057] 3. After monitoring that the grid-connected simulation parameters meet the shutdown conditions, the main control module sends a shutdown command to the test module. At this time, the main control module enters the shutdown mode, and the test module responds to the shutdown command to simulate the shutdown process of the wind turbine (the test module simulates the shutdown process of the wind turbine according to the shutdown command, and the simulated wind turbine shutdown process includes simulated propeller retraction operation and simulated deceleration operation until the unit shuts down), and shares the shutdown simulation parameters to the main control module in real time.

[0058] If the state switching simulation method of the wind turbine is introduced in detail from both sides, the steps are as follows:

[0059] When the simulated wind turbine is in standby mode, the main control module needs to determine whether the incoming simulated wind speed generated by the wind speed simulation unit has been continuously greater than the preset time and is higher than the start wind speed threshold, or whether a start command from the host computer has been received. If the main control module detects that the incoming simulated wind speed is greater than the wind speed threshold for a duration greater than the preset time, or the host computer issues a start command, the main control module sends a start command to the test module, and the main control module enters the start mode.

[0060] In the startup mode, the main control module sends the given pitch angle target value β corresponding to the start of the wind turbine to the test module. ref and a given pitch angle target rate ω ref The test module simulates and generates the actual pitch angle, pitch speed and generator simulation speed of the unit according to these control instructions, and controls the speed to gradually increase to the grid-connected speed.

[0061] The main control module monitors the grid-connected conditions in real time to ensure that all parameters meet the grid-connected requirements and then enter the grid-connected mode.

[0062] In the grid-connected mode, the main control module sends an electromagnetic torque command to the test module. The test module calculates the generator speed based on the incoming simulated wind speed, the pitch angle of the unit simulated by the variable pitch simulation unit, and the unit power demand issued by the main control module, and controls the output power of the generator by adjusting the speed. The test module further calculates the active power of the unit and other grid-related variables based on the generator speed and electromagnetic torque command.

[0063] When the main control module detects that the shutdown conditions are met, it switches to shutdown mode. In shutdown mode, the test module performs the blade retraction operation according to the pitch angle target value and pitch angle target rate corresponding to the wind turbine shutdown issued by the main control module, and calculates the generator speed based on the real-time pitch angle, wind speed and other parameters of the simulated unit, and gradually reduces the speed until it is completely shut down.

[0064] In order to implement the above embodiment, the present application embodiment also proposes an electronic device 700, such as Figure 7 As shown, the electronic device 700 includes: a processor 701 and a memory 702 communicatively connected to the processor, the memory 702 stores instructions executable by at least one processor, and the instructions are executed by at least one processor 701 to implement the state switching simulation method of the wind turbine group as shown in the above embodiment.

[0065] In order to implement the above embodiment, the embodiment of the present application further proposes a non-transitory computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable a computer to implement the state switching simulation method of a wind turbine set as shown in the above embodiment.

[0066] In order to implement the above embodiment, the embodiment of the present application further proposes a computer program product, including a computer program, which implements the state switching simulation method of the wind turbine generator set as shown in the above embodiment when executed by a processor.

[0067] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0068] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0069] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. 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 may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0070] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A state switching simulation system for a wind turbine generator set, characterized in that: It includes a main control module, a test module, a human-computer interaction interface and a shared address bus, among which: The main control module is used to send a startup instruction to the test module and enter a startup mode. The test module responds to the startup instruction to simulate the startup process of the wind turbine generator set and shares startup simulation parameters with the main control module in real time. The main control module is used to send a grid connection instruction to the test module and enter the grid connection mode after monitoring that the startup simulation parameters meet the grid connection conditions. The test module simulates the grid connection process of the wind turbine in response to the grid connection instruction and shares the grid connection simulation parameters with the main control module in real time; The main control module is used to send a shutdown command to the test module and enter a shutdown mode after monitoring that the grid-connected simulation parameters meet the shutdown conditions. The test module simulates the shutdown process of the wind turbine in response to the shutdown command and shares the shutdown simulation parameters with the main control module in real time; The main control module and the test module communicate in real time via the shared address bus, the shared address bus allocates the variables required by the main control module to the shared address area, and the test module reads and feeds back the simulation parameter information in real time; The main control module and the test module receive instructions sent by the user through the human-computer interaction interface to update simulation parameters.

2. The system according to claim 1, characterized in that The main control module is also used for: In response to the main control module detecting that the duration of the incoming flow simulation wind speed being greater than the wind speed threshold is greater than a preset duration, a start instruction is sent to the test module, wherein the incoming flow simulation wind speed is simulated by the test module and shared with the main control module; or In response to the main control module monitoring the start instruction sent by the host computer, the start instruction is sent to the test module.

3. The system according to claim 2, characterized in that The test module includes a wind speed simulation unit, a pitch simulation unit, a rotation speed simulation unit, and a grid connection simulation unit, wherein: The wind speed simulation unit is used to generate the incoming flow simulation wind speed according to the set wind speed initial value; The pitch simulation unit is used to simulate and generate the pitch angle and pitch speed of the unit based on the pitch instruction issued by the main control module, and the pitch instruction carries at least a pitch angle target value and a pitch angle target rate; The speed simulation unit is used to generate a simulated speed of the generator according to speed-related parameters, and simulate and control the speed to increase or decrease based on the simulated speed of the generator, wherein the speed-related parameters at least include the simulated wind speed of the incoming flow, the pitch angle of the unit generated by simulation, and the power demand of the unit issued by the main control module; The grid-connected simulation unit is used to generate grid-connected active power according to the simulated rotation speed of the generator and the electromagnetic torque instruction issued by the main control module, and simulate the grid-connected process.

4. The system according to claim 3, characterized in that The test module simulates the shutdown process of the wind turbine in response to the shutdown instruction, including: The test module simulates a shutdown process of the wind turbine generator set according to the shutdown instruction, wherein the simulated shutdown process of the wind turbine generator set includes a simulated blade retracting operation and a simulated deceleration operation until the generator set shuts down.

5. The system according to claim 4, characterized in that The main control module and the test module are controlled by the same simulation controller.

6. The system according to claim 4, characterized in that The main control module and the test module are respectively controlled by two independent simulation controllers.

7. A method for simulating state switching of a wind turbine generator set, characterized in that: include: In response to monitoring a state switching simulation instruction of a wind turbine generator set, a state switching simulation system for a wind turbine generator set according to any one of claims 1 to 6 executes a state switching simulation process for the wind turbine generator set.

8. An electronic device comprising: at least one processor; as well as, a memory communicatively connected to the at least one processor; wherein, The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method of claim 7.

9. A non-transitory computer-readable storage medium storing computer instructions, wherein: The computer instructions are used to cause the computer to execute the method according to claim 7.

10. A computer program product comprising a computer program which, when executed by a processor, implements the steps of the method according to claim 7.

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