Optimal control method and system for bipolar AC-AC converter under three-phase inductance asymmetry

Abstract

The invention discloses an optimal control method and system for a bipolar AC-AC converter under three-phase inductance asymmetry. The bipolar AC-AC converter is of an ABC three-phase structure, each phase comprises an upper bridge arm and a lower bridge arm which are the same, each of the upper bridge arm and the lower bridge arm comprises n full-bridge sub-modules and a bridge arm inductor which are connected in series, and the three-phase bridge arm inductors are different. The control method provided by the invention comprises three parts: firstly, suppressing power frequency negative-sequence current to be 0 in a dq coordinate system on a power frequency side, secondly, suppressing low-frequency negative-sequence current to be 0 in the dq coordinate system on a low-frequency side, and thirdly, eliminating three-phase capacitor voltage difference to be 0 in an alpha-beta coordinate system. Through negative sequence control and capacitor voltage balance control strategies, optimal control of the bipolar AC-AC converter under the condition of asymmetric three-phase inductance parameters is realized, suppression of negative sequence current and balance of capacitor voltage are realized, the running consistency of three-phase bridge arms is effectively maintained, and the reliability of the three-phase bridge arms is improved. And the safe operation capability of the bipolar AC-AC converter is improved.

Description

Technical Field

[0001] The invention belongs to the field of multi-level power electronic converters, and in particular relates to a positive and negative bipolar multi-level AC-AC converter. Background Art

[0002] Compared to traditional industrial frequency AC transmission, low-frequency transmission offers greater line transmission capacity, lower reactive power compensation capacity, and reduced line losses. Consequently, it has garnered widespread attention from technical experts in fields such as offshore wind power grid integration and long-distance AC transmission. AC-AC converters, as key devices connecting low-frequency AC systems with industrial frequency AC systems, are a crucial component of frequency-divided transmission.

[0003] Currently, there are three mainstream AC-AC converter types: back-to-back MMC, M3C, and Hexverter. Back-to-back MMC converter technology is relatively mature, employing MMCs connected at both DC ends for frequency conversion and boasting a simple and easy-to-understand control algorithm. However, it uses 12 bridge arms and a large number of submodules, resulting in a large footprint and high costs.

[0004] In contrast, the M3C AC-AC converter uses 9 bridge arms, which reduces the number of bridge arms and reduces manufacturing costs. However, its circuit structure is complex, the coupling is strong, and there are many circulation paths, which increases the difficulty of manufacturing and control.

[0005] The Hexverter AC-AC converter uses only six bridge arms, significantly reducing the number of bridge arms and lowering manufacturing costs. However, its topology has poor scalability and requires strict reactive power conditions to operate normally. It also has poor control and structural flexibility, making it difficult to cope with changing industrial applications. Summary of the Invention

[0006] The technical problem to be solved by the present invention is as follows: In view of the shortcomings of the existing AC-AC converter, the present invention aims to provide an optimized control strategy for a bipolar AC-AC converter under three-phase inductance asymmetry, so as to realize the control problem when the three-phase bridge arm equivalent inductance is asymmetric due to the asymmetric leakage inductance of the three-phase transformer and the asymmetric bridge arm inductance inside the bipolar AC-AC converter.

[0007] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0008] The bipolar AC-AC converter disclosed in this invention has an ABC three-phase structure. Each phase comprises identical upper and lower bridge arms. Each upper and lower bridge arm comprises n full-bridge submodules connected in series and a bridge arm inductor. The bridge arm inductor parameters vary between the three phases. The power-frequency side of the converter is connected to the power-frequency grid at the junction of the upper and lower bridge arms, while the low-frequency side is connected to the low-frequency grid via a bipolar transformer.

[0009] In each bridge arm, the full-bridge sub-module includes the first to fourth IGBTs and the first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge sub-module; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge sub-module; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

[0010] The bipolar transformer includes two secondary windings W1 and W2, where W1 is the positive winding and adopts the Y0 connection method, and W2 is the negative winding and adopts the Y6 connection method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm.

[0011] For the above bipolar AC-AC converter structure, a bipolar AC-AC converter optimization control method under three-phase inductance asymmetry is proposed. The specific steps are as follows:

[0012] S1. On the power frequency side, suppress the power frequency negative sequence current to 0 in the dq coordinate system to obtain the three-phase power frequency negative sequence reference voltage;

[0013] S2. On the low-frequency side, suppress the low-frequency negative-sequence current to 0 in the dq coordinate system to obtain the three-phase low-frequency negative-sequence reference voltage;

[0014] S3. Eliminate the three-phase capacitor voltage difference to 0 in the αβ coordinate system to obtain the zero-sequence reference voltage;

[0015] S4. In each bridge arm of the three-phase structure of the bipolar AC-AC converter, the sum of the power frequency negative-sequence reference voltage, the low-frequency negative-sequence reference voltage, and the zero-sequence reference voltage is used as the reference voltage added to the upper bridge arm and the lower bridge arm, respectively, to achieve negative-sequence current suppression and capacitor voltage balance.

[0016] Furthermore, the specific steps of step S1 are:

[0017] S101, extract the negative sequence current on the power frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the power frequency side gd- and i gq- ;

[0018] S102, in the dq coordinate system, the dq component i of the negative sequence current on the power frequency side gd- and i gq- Suppressed to 0, and the dq component u of the power frequency negative sequence reference voltage is obtained through PI control diffd- and u diffq- :

[0019]

[0020] Among them, K p and K i is the control parameter of PI control, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side;

[0021] S103, u diffd- and u diffq- At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency negative sequence reference voltage u is obtained diffj- , j = a, b, c.

[0022] Furthermore, the specific steps of step S2 are:

[0023] S201, extract the negative sequence current on the low frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the low frequency side ld- and I lq- ;

[0024] S202, in the dq coordinate system, the dq component i of the negative sequence current on the low frequency side is ld- and i lq- Suppressed to 0, and the dq component u of the low-frequency negative sequence reference voltage is obtained through PI control comd- and u comq- :

[0025]

[0026] Among them, K p and K i is the control parameter of PI control, ω l is the low-frequency corner frequency, L L is the equivalent inductance on the low-frequency side;

[0027] S203. Will u comd- and u comq- At low angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency side negative sequence current u is obtained comj- , j = a, b, c.

[0028] Furthermore, in step S3, the step of eliminating the three-phase capacitor voltage difference to 0 in the αβ coordinate system is as follows:

[0029] S301, the average value of the three-phase capacitor voltage u ca_ave ,u cb_ave ,u cc_ave After the following conversion, it becomes the capacitor voltage difference u cα_ave and ucβ_ave :

[0030]

[0031] S302, u cα_ave and u cβ_ave Suppressed to 0, and the zero-sequence voltage reference value u is obtained through PI control diff0α and u diff0β :

[0032]

[0033] S3. Will u diff0α and u diff0β Converted to zero-sequence reference voltage u in polar coordinate system diff0 .

[0034] Furthermore, in each bridge arm of the three phases,

[0035] Reference voltage u added to the upper arm ju_ref For: u ju_ref =-u diffj- +u comj- +u diff0 ;

[0036] The reference voltage u added by the lower bridge arm jl_ref For: u jl_ref =u diffj- +u comj- +u diff0 .

[0037] Secondly, the present invention also proposes an electronic system, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed 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 steps of the present invention.

[0038] Finally, the present invention also provides a computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method steps of the present invention.

[0039] By adopting the above technical solution, compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0040] 1. The present invention proposes an optimized control strategy for a bipolar AC-AC converter under three-phase inductance asymmetry. By stably suppressing the negative sequence current on the power frequency side and the negative sequence current on the low frequency side, the strategy ensures the symmetry of the three-phase output current waveform on the power frequency side and the symmetry of the phase output current waveform on the low frequency side. This improves the control capability of the bipolar AC-AC converter when connected to the grid, which is beneficial to ensuring the normal power supply capacity of the low-frequency AC power grid.

[0041] 2. The present invention proposes an optimization control strategy for a bipolar AC-AC converter under three-phase inductance asymmetry, which balances the three-phase capacitor voltage, ensures that the three-phase bridge arms have the same capacitor voltage during operation, and maintains the same working state of the three phases of the bipolar AC-AC converter, which is beneficial to ensure the reliable operation of the bipolar AC-AC converter and has high industrial value.

[0042] 3. The present invention proposes an optimization control strategy for a bipolar AC-AC converter under three-phase inductance asymmetry, which takes into account the common three-phase leakage inductance asymmetry in three-phase transformer equipment in the power system and the asymmetry of the bridge arm inductance due to aging, etc. It can be applied in the steady-state operation and transient process of the bipolar AC-AC converter and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention 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, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0044] Figure 1 1 is a schematic diagram of the topological structure of a bipolar AC-AC converter according to an embodiment of the present invention.

[0045] Figure 2 It is a flow chart of the control method of the present invention. DETAILED DESCRIPTION

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

[0047] like Figure 1As shown, an optimization control strategy for a bipolar AC-AC converter under three-phase inductance asymmetry is provided. The controlled system consists of two main parts: the first part is a bipolar AC-AC converter with a three-phase structure, each phase including an upper bridge arm and a lower bridge arm with exactly the same structure, the upper and lower bridge arms respectively including n full-bridge sub-modules connected in series and a bridge arm inductor, wherein the bridge arm inductance parameters of the three phases are different; the second part is a three-phase three-winding bipolar transformer, the bipolar transformer includes two secondary windings W1 and W2, wherein W1 is a positive winding with a Y0 winding method, and W2 is a negative winding with a Y6 winding method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm. In the proposed bipolar multilevel AC-AC converter, the power frequency side of the bipolar AC-AC converter is connected to the power frequency grid at the connection point of the upper and lower bridge arms, and the low frequency side is connected to the low frequency grid via the primary winding W0 of the bipolar transformer.

[0048] The full-bridge submodule used in the AC-AC converter includes the first to fourth IGBTs and a first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge submodule; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge submodule; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

[0049] refer to Figure 2 As shown, for the above bipolar AC-AC converter structure, the present invention proposes a bipolar AC-AC converter optimization control method under three-phase inductance asymmetry, and the specific steps are as follows:

[0050] S1. On the power frequency side, suppress the power frequency negative sequence current to 0 in the dq coordinate system to obtain the three-phase power frequency negative sequence reference voltage;

[0051] S2. On the low-frequency side, suppress the low-frequency negative-sequence current to 0 in the dq coordinate system to obtain the three-phase low-frequency negative-sequence reference voltage;

[0052] S3. Eliminate the three-phase capacitor voltage difference to 0 in the αβ coordinate system to obtain the zero-sequence reference voltage;

[0053] S4. In each bridge arm of the three-phase structure of the bipolar AC-AC converter, the sum of the power frequency negative-sequence reference voltage, the low-frequency negative-sequence reference voltage, and the zero-sequence reference voltage is used as the reference voltage added to the upper bridge arm and the lower bridge arm, respectively, to achieve negative-sequence current suppression and capacitor voltage balance.

[0054] As an embodiment of the present invention, when implementing an optimized control strategy for a bipolar AC-AC converter with asymmetric three-phase inductance, the steps for suppressing the negative sequence current on the power frequency side are as follows:

[0055] S1. Extract the negative sequence current on the power frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the power frequency side gd- and i gq- .

[0056] S2. In the dq coordinate system, the dq component i of the negative sequence current on the power frequency side is gd- and i gq- Suppressed to 0, and the dq component u of the power frequency negative sequence reference voltage is obtained through proportional integral (PI) control diffd- and u diffq- :

[0057]

[0058] Among them, K p and K i is the control parameter of PI control, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side.

[0059] S3. Will u diffd- and u diffq- At the angular frequency ω g Down-converted to the power frequency negative sequence reference voltage u in the abc three-phase coordinate system diffj- .

[0060] As an embodiment of the present invention, when implementing an optimized control strategy for a bipolar AC-AC converter with three-phase inductance asymmetry, the steps for suppressing the negative sequence current on the low-frequency side are as follows:

[0061] S1. Extract the negative sequence current on the low frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the low frequency side ld- and I lq- .

[0062] S2. In the dq coordinate system, the dq component i of the negative sequence current on the low frequency side is ld- and i lq- Suppressed to 0, and the dq component u of the low-frequency negative sequence reference voltage is obtained through proportional integral (PI) control comd- and u comq- :

[0063]

[0064] Among them, ω l is the low-frequency corner frequency, L L is the equivalent inductance on the low-frequency side.

[0065] S3. Will u comd- and u comq- At the angular frequency ω l Down-converted to the low-frequency negative sequence reference voltage u in the abc three-phase coordinate system comj- .

[0066] As an embodiment of the present invention, when implementing an optimized control strategy for a bipolar AC-AC converter with asymmetric three-phase inductance, the steps for suppressing the three-phase capacitor voltage difference are as follows:

[0067] S1, the average value of the three-phase capacitor voltage u ca_ave ,u cb_ave ,u cc_ave After the following conversion, it becomes the capacitor voltage difference u cα_ave and u cβ_ave :

[0068]

[0069] S2, u cα_ave and u cβ_ave Suppressed to 0, and the zero-sequence voltage reference value u is obtained through proportional integral (PI) control diff0α and u diff0β :

[0070]

[0071] S3. Will u diff0α and u diff0β Converted to zero-sequence reference voltage u in polar coordinate system diff0 .

[0072] As an embodiment of the present invention, when the optimization control strategy is implemented for a bipolar AC-AC converter under three-phase inductance asymmetry, the reference voltage u added to the upper bridge arm is ju_ref for:

[0073] u ju_ref =-u diffj- +u comj- +u diff0 ,

[0074] The reference voltage u added by the lower bridge arm jl_ref for:

[0075] u jl_ref =u diffj- +u comj- +u diff0 .

[0076] Compared with the existing bipolar AC-AC converter control method, the control method proposed in the present invention eliminates the negative sequence current on the power frequency side and the negative sequence current on the low frequency side introduced by the asymmetry of the three-phase inductance parameters, while ensuring the balance of the three-phase capacitor voltage. The provided method can not only improve the output power quality, but also effectively ensure the operating balance of the internal modules of the bipolar AC-AC converter, thereby improving the reliability of the bipolar AC-AC converter.

[0077] Example 2:

[0078] This embodiment proposes an electronic system, 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 enable the at least one processor to perform the method steps described in the present invention.

[0079] Example 3:

[0080] This embodiment provides a computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method steps described in the present invention.

[0081] It should be noted that the processing flow of Examples 2 to 3 corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not fully described in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0082] The program code for implementing the methods of the present application can be written in any combination of one or more programming languages. Such program code can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the program code is executed by the processor or controller, the functions / operations specified in the flow charts and / or block diagrams are implemented. The program code can be executed entirely on the machine, partially on the machine, as a stand-alone software package, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0083] In the context of the present application, a machine-readable medium can be a tangible medium that can contain or store a program for use by an instruction execution system, device or equipment or used in combination with an instruction execution system, device or equipment. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium can include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0084] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0085] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for optimizing and controlling a bipolar AC-AC converter with three-phase inductance asymmetry, wherein the bipolar AC-AC converter has a three-phase structure, wherein each phase comprises an upper bridge arm and a lower bridge arm of identical structure, wherein each upper bridge arm and the lower bridge arm each comprise n full-bridge submodules connected in series and a bridge arm inductor, wherein the bridge arm inductance parameters of the three phases are different; wherein the power frequency side is connected to the power frequency grid at the connection point of the upper and lower bridge arms, and the low frequency side is connected to the low frequency grid via a bipolar transformer, characterized in that: Specifically: S1. On the power frequency side, suppress the power frequency negative sequence current to 0 in the dq coordinate system to obtain the three-phase power frequency negative sequence reference voltage; S2. On the low-frequency side, suppress the low-frequency negative-sequence current to 0 in the dq coordinate system to obtain the three-phase low-frequency negative-sequence reference voltage; S3. Eliminate the three-phase capacitor voltage difference to 0 in the αβ coordinate system to obtain the zero-sequence reference voltage; S4. In each bridge arm of the three-phase structure of the bipolar AC-AC converter, the sum of the power frequency negative-sequence reference voltage, the low-frequency negative-sequence reference voltage, and the zero-sequence reference voltage is used as the reference voltage added to the upper bridge arm and the lower bridge arm, respectively, to achieve negative-sequence current suppression and capacitor voltage balance.

2. The method according to claim 1, wherein: The specific steps of step S1 are: S101, extract the negative sequence current on the power frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the power frequency side gd- and i gq- ; S102, in the dq coordinate system, the dq component i of the negative sequence current on the power frequency side gd- and i gq- Suppressed to 0, and the dq component u of the power frequency negative sequence reference voltage is obtained through PI control diffd- and u diffq- : Among them, K p and K i is the control parameter of PI control, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side; S103, u diffd- and u diffq- At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency negative sequence reference voltage u is obtained diffj- , j = a, b, c.

3. The method according to claim 1, wherein: The specific steps of step S2 are: S201, extract the negative sequence current on the low frequency side and convert it to the dq coordinate system to obtain the dq component i of the negative sequence current on the low frequency side ld- and I lq- ; S202, in the dq coordinate system, the dq component i of the negative sequence current on the low frequency side is ld- and i lq- Suppressed to 0, and the dq component u of the low-frequency negative sequence reference voltage is obtained through PI control comd- and u comq- : Among them, K p and K i is the control parameter of PI control, ω l is the low-frequency corner frequency, L L is the equivalent inductance on the low-frequency side; S203. Will u comd- and u comq- At low angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency side negative sequence current u is obtained comj- , j = a, b, c.

4. The method according to claim 1, wherein: In step S3, the steps of eliminating the three-phase capacitor voltage difference to 0 in the αβ coordinate system are as follows: S301, the average value of the three-phase capacitor voltage u ca_ave ,u cb_ave ,u cc_ave After the following conversion, it becomes the capacitor voltage difference u cα_ave and u cβ_ave : S302, u cα_ave and u cβ_ave Suppressed to 0, and through P I Control to obtain the zero sequence voltage reference value u diff0α and u diff0β : S303, u diff0α and u diff0β Converted to zero-sequence reference voltage u in polar coordinate system diff0 .

5. The method according to claim 1, wherein: In each bridge arm of the three phases, Reference voltage u added to the upper arm ju_ref for: in ju_ref =-in diffj- +in comj- +in diff0 , The reference voltage u added by the lower bridge arm jl_ref for: in jl_ref =in diffj- +in comj- +in diff0 。 6. The method according to claim 1, wherein: The bipolar transformer includes two secondary windings W1 and W2, where W1 is the positive winding and adopts Y0 winding method, and W2 is the negative winding and adopts Y6 winding method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm.

7. The method according to claim 1, wherein: The full-bridge submodule includes the first to fourth IGBTs and a first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge submodule; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge submodule; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

8. An electronic system 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, characterized in that the instructions are executed by the at least one processor so that the at least one processor can execute the method described in any one of claims 1-7.

9. A computer-readable storage medium storing computer instructions, characterized in that: The computer instructions are used to enable the computer to execute the method according to any one of claims 1 to 7.

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