Alternating current voltage control method and device for common point of direct current transformer

Abstract

The invention provides an AC voltage control method and device for a common point of a DC transformer. And calculating an AC voltage design value of the common point according to the fundamental frequency voltage component and the triple frequency voltage component. And determining an AC voltage actual value of the common bridge arm according to the AC voltage design value of the common point. And controlling the AC voltage actual value of the common point according to the AC voltage actual value of the common bridge arm. The fundamental frequency voltage component and the triple frequency voltage component are combined, the modulation voltage amplitude of the bridge arm can be reduced, the number of sub-modules needed on the bridge arm is further reduced, the cost of the bridge arm is reduced, the cost of the direct current transformer is further reduced, and the direct current transformer is easy to widely apply. The number of the sub-modules is greatly reduced, the structure of the direct-current transformer is simplified, the manufacturing and assembling difficulty is reduced, later maintenance is facilitated, the efficiency of the bridge arms can be improved, and then the working efficiency of the whole direct-current transformer is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a method and device for controlling the AC voltage at a common point of a DC transformer. Background Art

[0002] With the rapid development of new energy technologies, power grids face numerous challenges. On the one hand, due to the intermittent and random nature of renewable energy generation, such as wind and solar power, the high penetration of renewable energy is increasingly impacting the safe operation of the power grid and power quality. On the other hand, with the development of large-scale offshore wind power and offshore renewable energy, AC and DC transmission technologies are struggling to meet these demands. Therefore, new technologies, equipment, and grid structures are essential to meet the profound changes in the future energy landscape. DC grid technology, with its advantages such as avoiding the inherent synchronization and stability issues of AC grids, virtually unlimited transmission distances, and the ability to regulate and control power flows over a wide range, is considered the most effective solution for centralized transmission of offshore wind farm clusters, integrating large-scale distributed renewable energy, and building new urban power grids.

[0003] DC transformers enable voltage conversion and power transmission, and are a core component in power grid applications. Related technologies offer control methods that design the AC voltage at the common point of the DC transformer as a sinusoidal wave. Because the bridge arm voltage amplitude is directly related to the number of submodules, high-voltage, high-capacity bridge arms require a large number of submodules connected in series, resulting in high DC transformer costs and hindering widespread application. Summary of the Invention

[0004] In order to solve the problem of high cost of DC transformers in the prior art, the present application provides a method and device for controlling the AC voltage at the common point of a DC transformer.

[0005] In a first aspect, the present application provides a method for controlling the AC voltage at a common point of a DC transformer, which may include:

[0006] The design value of the AC voltage at the common point is calculated based on the fundamental frequency voltage component and the triple frequency voltage component. The actual value of the AC voltage at the common bridge arm is determined based on the design value of the AC voltage at the common point. The actual value of the AC voltage at the common bridge arm is controlled based on the actual value of the AC voltage at the common point.

[0007] In some possible implementations, calculating the AC voltage design value at the common point based on the fundamental frequency voltage component and the tripled frequency voltage component includes:

[0008] Calculate the amplitude of the fundamental frequency voltage component based on the rated capacity of the DC transformer, and set its phase angle to zero. With the goal of minimizing the AC voltage amplitude at the common point, determine the amplitude of the tripled frequency voltage component, and determine its phase angle based on the fundamental frequency voltage component. Calculate the design AC voltage value at the common point based on the amplitudes and phase angles of the fundamental and tripled frequency voltage components.

[0009] Optionally, the amplitude of the fundamental frequency voltage component satisfies:

[0010]

[0011] Among them, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U1 indicates the DC voltage on the first side of the DC transformer, U2 indicates the DC voltage on the second side of the DC transformer, P indicates the rated capacity of the DC transformer, N indicates the number of poles of the DC transformer, M indicates the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the sub-module in the bridge arm.

[0012] Furthermore, determining the phase angle of the tripled frequency voltage component according to the fundamental frequency voltage component includes:

[0013] The peak of the fundamental frequency voltage component and the trough of the triple frequency voltage component are matched to obtain the phase angle of the triple frequency voltage component.

[0014] In one example, the DC transformer adopts a two-phase parallel structure, and the AC voltage design value at the common point satisfies:

[0015] U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°)

[0016] Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0017] In another example, the DC transformer adopts a three-phase parallel structure, and the AC voltage design value at the common point satisfies:

[0018] U A =U AC1 cosωt+U AC3 cos(3ωt+180°)

[0019] U B=U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°)

[0020] U C =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°)

[0021] Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0022] In some other possible implementations, determining the actual value of the AC voltage of the common bridge arm according to the design value of the AC voltage at the common point includes:

[0023] The AC voltage design value of the common point is used as the AC voltage command value of the common point. The voltage difference between the AC voltage command value of the common point and the actual AC voltage value of the common point is subjected to proportional resonance control to obtain the actual AC voltage value of the common bridge arm.

[0024] In a second aspect, the present application provides an AC voltage control device for a common point of a DC transformer, which may include:

[0025] The calculation module is used to calculate the AC voltage design value of the common point according to the fundamental frequency voltage component and the triple frequency voltage component.

[0026] The determination module is used to determine the actual value of the AC voltage of the common bridge arm according to the design value of the AC voltage of the common point.

[0027] The control module is used to control the actual value of the AC voltage at the common point according to the actual value of the AC voltage of the common bridge arm.

[0028] In some possible implementations, the computing module is specifically configured to:

[0029] The amplitude of the fundamental frequency voltage component is calculated according to the rated capacity of the DC transformer, and the phase angle of the fundamental frequency voltage component is set to zero.

[0030] With the goal of minimizing the AC voltage amplitude at the common point, the amplitude of the triple frequency voltage component is determined, and the phase angle of the triple frequency voltage component is determined based on the fundamental frequency voltage component.

[0031] The design value of the AC voltage at the common point is calculated based on the amplitude and phase angle of the fundamental frequency voltage component and the triple frequency voltage component.

[0032] Optionally, the calculation module determines the amplitude of the fundamental frequency voltage component according to the following formula:

[0033]

[0034] Among them, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U1 indicates the DC voltage on the first side of the DC transformer, U2 indicates the DC voltage on the second side of the DC transformer, P indicates the rated capacity of the DC transformer, N indicates the number of poles of the DC transformer, M indicates the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the sub-module in the bridge arm.

[0035] Exemplarily, the calculation module is specifically used for:

[0036] The peak of the fundamental frequency voltage component and the trough of the triple frequency voltage component are matched to obtain the phase angle of the triple frequency voltage component.

[0037] In one example, the DC transformer adopts a two-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula:

[0038] U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°)

[0039] Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0040] In another example, the DC transformer adopts a three-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula:

[0041] U A =U AC1 cosωt+U AC3 cos(3ωt+180°)

[0042] U B =U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°)

[0043] UC =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°)

[0044] Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0045] In some other possible implementations, the determination module is specifically configured to:

[0046] The AC voltage design value of the common point is used as the AC voltage command value of the common point. The voltage difference between the AC voltage command value of the common point and the actual AC voltage value of the common point is subjected to proportional resonance control to obtain the actual AC voltage value of the common bridge arm.

[0047] On the other hand, the present application also provides a computer device, including: one or more processors.

[0048] A processor is used to execute one or more programs.

[0049] When one or more programs are executed by one or more processors, the control method described above is implemented.

[0050] In another aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed, the control method described above is implemented.

[0051] Compared with the prior art, the present invention has the following advantages:

[0052] In the AC voltage control method for the common point of a DC transformer provided in the present application, a design value of the AC voltage at the common point is calculated based on the fundamental frequency voltage component and the triple frequency voltage component. The actual value of the AC voltage at the common bridge arm is determined based on the design value of the AC voltage at the common point. The actual value of the AC voltage at the common point is controlled based on the actual value of the AC voltage at the common bridge arm. The present application combines the fundamental frequency voltage component and the triple frequency voltage component, which can reduce the modulation voltage amplitude of the bridge arm, thereby reducing the number of submodules required on the bridge arm, reducing the cost of the bridge arm, and thus reducing the cost of the DC transformer, and is easy to be widely used.

[0053] This application significantly reduces the number of sub-modules, which not only simplifies the structure of the DC transformer, reduces the difficulty of manufacturing and assembly, and facilitates later maintenance, but also improves the efficiency of the bridge arm, thereby improving the working efficiency of the entire DC transformer.

[0054] The reduction in the number of neutron modules in this application helps to reduce the volume of the entire DC transformer and reduce the weight of the DC transformer, thereby reducing the transportation and installation costs of the DC transformer, which is of great significance for application scenarios that are sensitive to space and weight, such as offshore wind power and mobile energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the technical solutions in the present application or 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 some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0056] Figure 1 This is a schematic structural diagram of a DC transformer in an embodiment of the present application;

[0057] Figure 2 This is a schematic flow chart of a method for controlling the AC voltage at the common point of a DC transformer in an embodiment of the present application;

[0058] Figure 3 A schematic waveform diagram of the AC voltage design value at the common point in the embodiment of the present application;

[0059] Figure 4 A schematic flow chart of determining the actual value of the AC voltage of the common bridge arm in an embodiment of the present application;

[0060] Figure 5 This is a schematic structural diagram of the AC voltage control device for the common point of the DC transformer in an embodiment of the present application. DETAILED DESCRIPTION

[0061] The technical solution in this application will be described below with reference to the accompanying drawings.

[0062] The terms "first," "second," and the like in the description, embodiments, claims, and drawings of this application are used solely for descriptive purposes and are not to be construed as indicating or implying relative importance or order. Furthermore, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions, such as, for example, inclusion of a series of steps or units. A method, system, product, or apparatus is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0063] It should be understood that in this application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the previous and next associated objects are in an "or" relationship. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0064] Example 1:

[0065] The embodiment of the present application provides a method for controlling the AC voltage at the common point of a DC transformer. DC transformers include face-to-face, auto-coupling, voltage-dividing, T-type, etc. Among them, the T-type DC transformer does not require an AC isolation transformer and a large Henry-level inductor, and adopts mature MMC technology, which has the best engineering application prospects. The embodiment of the present application is described by taking a T-type DC transformer as an example. Figure 1 As shown, a T-type DC transformer includes a positive portion 1 and a negative portion 2. The first port P1 of the positive portion 1 and the second port P2 of the negative portion constitute the first side of the T-type DC transformer, which can be either the high-voltage side or the low-voltage side. The third port P3 of the positive portion 1 and the fourth port P4 of the negative portion constitute the second side of the T-type DC transformer, which can be either the low-voltage side or the high-voltage side.

[0066] The positive portion 1 and the negative portion 2 are connected via a neutral point O. Both the positive portion 1 and the negative portion 2 include an A-phase bridge arm, a B-phase bridge arm, and a C-phase bridge arm. Each phase bridge arm includes a first bridge arm, a second bridge arm, and a common bridge arm. The first, second, and common bridge arms of the A-phase bridge arm are connected via a common point E. The first, second, and common bridge arms of the B-phase bridge arm are connected via a common point F. The first, second, and common bridge arms of the C-phase bridge arm are connected via a common point G.

[0067] In the positive portion 1, the first arms of the A-phase arm, the B-phase arm, and the C-phase arm are connected to form a first port P1, and the second arms of the A-phase arm, the B-phase arm, and the C-phase arm are connected to form a second port P2.

[0068] In the negative portion 2, the first arms of the A-phase arm, the B-phase arm, and the C-phase arm are connected to form a third port P3, and the second arms of the A-phase arm, the B-phase arm, and the C-phase arm are connected to form a fourth port P4.

[0069] In the embodiment of the present application, both the first bridge arm and the common bridge arm may include a plurality of half-bridge sub-modules HB connected in series, and the second bridge arm may include a plurality of full-bridge sub-modules FB connected in series.

[0070] like Figure 2 As shown, the control method 100 provided in the embodiment of the present application may include the following steps:

[0071] Step S1: Calculate the AC voltage design value at the common point based on the fundamental frequency voltage component and the triple frequency voltage component.

[0072] Step S2: determining the actual value of the AC voltage of the common bridge arm according to the design value of the AC voltage at the common point.

[0073] Step S3: controlling the actual value of the AC voltage at the common point according to the actual value of the AC voltage of the common bridge arm.

[0074] In some possible implementations, calculating the AC voltage design value at the common point based on the fundamental frequency voltage component and the tripled frequency voltage component in step S1 includes:

[0075] Calculate the amplitude of the fundamental frequency voltage component based on the rated capacity of the DC transformer, and set its phase angle to zero. With the goal of minimizing the AC voltage amplitude at the common point, determine the amplitude of the tripled frequency voltage component, and determine its phase angle based on the fundamental frequency voltage component. Calculate the design AC voltage value at the common point based on the amplitudes and phase angles of the fundamental and tripled frequency voltage components.

[0076] In the embodiment of the present application, the amplitude of the tripled frequency voltage component may be one sixth of the amplitude of the fundamental frequency voltage component.

[0077] Optionally, the amplitude of the fundamental frequency voltage component satisfies:

[0078]

[0079] Among them, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U1 indicates the DC voltage on the first side of the DC transformer, U2 indicates the DC voltage on the second side of the DC transformer, P indicates the rated capacity of the DC transformer, N indicates the number of poles of the DC transformer, M indicates the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the sub-module in the bridge arm.

[0080] In the embodiment of the present application, P = 1000MW, N = 2, M = 3, U1 = 320kV, U2 100kV, I1 = 2.25kA. It can be obtained that I ACRMS=1.94kA, U AC1 =83.5kV.

[0081] Furthermore, the above-mentioned determination of the phase angle of the tripled frequency voltage component based on the fundamental frequency voltage component includes:

[0082] The peak of the fundamental frequency voltage component is matched with the trough of the triple frequency voltage component to obtain the phase angle of the triple frequency voltage component. In the embodiment of the present application, the phase angle of the triple frequency voltage component can be 180°.

[0083] In the embodiment of the present application, the amplitude of the tripled frequency voltage component can be 13.9 kV.

[0084] In one example, the DC transformer adopts a two-phase parallel structure, and the AC voltage design value at the common point satisfies:

[0085] U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°)

[0086] Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0087] In another example, the DC transformer adopts a three-phase parallel structure, and the AC voltage design value at the common point satisfies:

[0088] U A =U AC1 cosωt+U AC3 cos(3ωt+180°)

[0089] U B =U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°)

[0090] U C =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°)

[0091] Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0092] against Figure 1 The DC transformer shown in the figure has a common point AC voltage design value as shown in the figure. Figure 3 The red line in. Figure 3 In the figure, the blue line represents the fundamental frequency voltage component, and the green line represents the triple frequency voltage component. Figure 3 It can be seen that when the fundamental frequency voltage component is superimposed on the 1 / 6 triple frequency voltage component and the fundamental frequency peak is relative to the triple frequency trough, the amplitude of the AC voltage design value at the common point can be reduced by 13%.

[0093] In some other possible implementations, determining the actual value of the AC voltage of the common bridge arm according to the design value of the AC voltage at the common point in step S2 includes:

[0094] refer to Figure 4 , take the AC voltage design value of the common point as the AC voltage command value of the common point (you can use u _acref The AC voltage command value u for the common point _acref Actual value of AC voltage u at common point _ac The voltage difference (which can be expressed as Δu) is used for proportional resonance control (i.e. PR control) to obtain the actual value of the AC voltage of the common bridge arm (which can be expressed as u _arm express).

[0095] Example 2:

[0096] Based on the same inventive concept, the embodiment of the present application also provides an AC voltage control device for a common point of a DC transformer. Figure 1 As described above, the embodiments of the present application will not be described in detail here.

[0097] like Figure 5 As shown, the control device 200 includes:

[0098] The calculation module 201 is used to calculate the AC voltage design value of the common point according to the fundamental frequency voltage component and the triple frequency voltage component.

[0099] The determination module 202 is configured to determine the actual value of the AC voltage of the common bridge arm according to the design value of the AC voltage of the common point.

[0100] The control module 203 is configured to control the actual value of the AC voltage at the common point according to the actual value of the AC voltage at the common bridge arm.

[0101] In some possible implementations, the calculation module 201 is specifically configured to:

[0102] The amplitude of the fundamental frequency voltage component is calculated according to the rated capacity of the DC transformer, and the phase angle of the fundamental frequency voltage component is set to zero.

[0103] With the goal of minimizing the AC voltage amplitude at the common point, the amplitude of the triple frequency voltage component is determined, and the phase angle of the triple frequency voltage component is determined based on the fundamental frequency voltage component.

[0104] The design value of the AC voltage at the common point is calculated based on the amplitude and phase angle of the fundamental frequency voltage component and the triple frequency voltage component.

[0105] Optionally, the calculation module 201 determines the amplitude of the fundamental frequency voltage component according to the following formula:

[0106]

[0107] Among them, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U1 indicates the DC voltage on the first side of the DC transformer, U2 indicates the DC voltage on the second side of the DC transformer, P indicates the rated capacity of the DC transformer, N indicates the number of poles of the DC transformer, M indicates the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the sub-module in the bridge arm.

[0108] Exemplarily, the calculation module is specifically used for:

[0109] The peak of the fundamental frequency voltage component and the trough of the triple frequency voltage component are matched to obtain the phase angle of the triple frequency voltage component.

[0110] In one example, the DC transformer adopts a two-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula:

[0111] U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°)

[0112] Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0113] In another example, the DC transformer adopts a three-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula:

[0114] U A =U AC1 cosωt+UAC3 cos(3ωt+180°)

[0115] U B =U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°)

[0116] U C =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°)

[0117] Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1 Indicates the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

[0118] against Figure 1 The DC transformer shown in the figure has a common point AC voltage design value as shown in the figure. Figure 3 The red line in. Figure 3 In the figure, the blue line represents the fundamental frequency voltage component, and the green line represents the triple frequency voltage component.

[0119] In some other possible implementations, the determining module 202 is specifically configured to:

[0120] The AC voltage design value of the common point is used as the AC voltage command value of the common point. The voltage difference between the AC voltage command value of the common point and the actual AC voltage value of the common point is subjected to proportional resonance control to obtain the actual AC voltage value of the common bridge arm.

[0121] Example 3:

[0122] Based on the same inventive concept, an embodiment of the present application further provides a computer device, comprising a processor and a memory, the memory being used to store a computer program, the computer program comprising program instructions, and the processor being used to execute the program instructions stored in the computer storage medium. The processor may be a central processing unit (CPU), or may be other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions in the computer storage medium to implement the corresponding method flow or corresponding functions, so as to implement the steps of the control method provided in the above embodiment.

[0123] Example 4:

[0124] Based on the same inventive concept, an embodiment of the present application further provides a computer-readable storage medium, specifically a computer-readable storage medium (Memory), which is a memory device in a computer device for storing programs and data. It is understandable that the computer-readable storage medium herein may include both a built-in storage medium in a computer device and, of course, an extended storage medium supported by the computer device. The computer-readable storage medium provides a storage space that stores the operating system of the terminal. In addition, one or more instructions suitable for being loaded and executed by a processor are also stored in the storage space. These instructions may be one or more computer programs (including program codes). It should be noted that the computer-readable storage medium herein may be a high-speed RAM memory or a non-volatile memory, such as at least one disk memory. The processor may load and execute one or more instructions stored in the computer-readable storage medium to implement the steps of the control method provided in the above embodiment.

[0125] Those skilled in the art will appreciate that embodiments of the application may be provided as methods, systems, or computer program products. Thus, the application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0126] The application is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as a combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0127] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0128] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0129] The above are merely embodiments of the application and are not intended to limit the application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the application are included in the scope of the claims of the pending application.

Claims

1. A method for controlling the AC voltage at the common point of a DC transformer, characterized in that: include: Calculate the design value of the AC voltage at the common point based on the fundamental frequency voltage component and the triple frequency voltage component; Determine the actual value of the AC voltage of the common bridge arm according to the AC voltage design value of the common point; The actual value of the AC voltage at the common point is controlled according to the actual value of the AC voltage at the common bridge arm.

2. The control method according to claim 1, characterized in that: The calculation of the AC voltage design value at the common point based on the fundamental frequency voltage component and the triple frequency voltage component includes: Calculating the amplitude of the fundamental frequency voltage component according to the rated capacity of the DC transformer, and setting the phase angle of the fundamental frequency voltage component to zero; With the goal of minimizing the AC voltage amplitude at the common point, determining the amplitude of the tripled frequency voltage component, and determining the phase angle of the tripled frequency voltage component based on the fundamental frequency voltage component; The AC voltage design value of the common point is calculated based on the respective amplitudes and phase angles of the fundamental frequency voltage component and the tripled frequency voltage component.

3. The control method according to claim 2, characterized in that: The amplitude of the fundamental frequency voltage component satisfies: Among them, U AC1 represents the amplitude of the fundamental frequency voltage component, U1 represents the DC voltage on the first side of the DC transformer, U2 represents the DC voltage on the second side of the DC transformer, P represents the rated capacity of the DC transformer, N represents the number of poles of the DC transformer, M represents the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the submodule in the bridge arm.

4. The control method according to claim 2, characterized in that: Determining the phase angle of the tripled frequency voltage component according to the fundamental frequency voltage component includes: The peak of the fundamental frequency voltage component and the trough of the triple frequency voltage component are matched to obtain the phase angle of the triple frequency voltage component.

5. The control method according to claim 1, characterized in that: The DC transformer adopts a two-phase parallel structure, and the AC voltage design value of the common point satisfies: U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°) Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 represents the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

6. The control method according to claim 1, characterized in that: The DC transformer adopts a three-phase parallel structure, and the AC voltage design value of the common point satisfies: U A =U AC1 cosωt+U AC3 cos(3ωt+180°) U B =U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°) U C =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°) Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1 represents the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

7. The control method according to claim 1, characterized in that: The determining the actual value of the AC voltage of the common bridge arm according to the AC voltage design value of the common point includes: Using the AC voltage design value of the common point as the AC voltage command value of the common point; Proportional resonance control is performed on the voltage difference between the AC voltage command value of the common point and the actual value of the AC voltage of the common point to obtain the actual value of the AC voltage of the common bridge arm.

8. An AC voltage control device for a common point of a DC transformer, characterized in that: include: A calculation module, used for calculating the AC voltage design value of the common point based on the fundamental frequency voltage component and the triple frequency voltage component; A determination module, configured to determine an actual value of the AC voltage of the common bridge arm according to a design value of the AC voltage of the common point; A control module is used to control the actual value of the AC voltage at the common point according to the actual value of the AC voltage of the common bridge arm.

9. The control device according to claim 1, characterized in that The calculation module is specifically used for: Calculating the amplitude of the fundamental frequency voltage component according to the rated capacity of the DC transformer, and setting the phase angle of the fundamental frequency voltage component to zero; With the goal of minimizing the AC voltage amplitude at the common point, determining the amplitude of the tripled frequency voltage component, and determining the phase angle of the tripled frequency voltage component based on the fundamental frequency voltage component; The AC voltage design value of the common point is calculated based on the respective amplitudes and phase angles of the fundamental frequency voltage component and the tripled frequency voltage component.

10. The control device according to claim 9, characterized in that: The calculation module determines the amplitude of the fundamental frequency voltage component according to the following formula: Among them, U AC1 represents the amplitude of the fundamental frequency voltage component, U1 represents the DC voltage on the first side of the DC transformer, U2 represents the DC voltage on the second side of the DC transformer, P represents the rated capacity of the DC transformer, N represents the number of poles of the DC transformer, M represents the number of phases of the DC transformer, and I ACRMS Represents the effective value of the AC current in the bridge arm of the DC transformer, satisfying I1 represents the maximum available current of the power devices of the submodule in the bridge arm.

11. The control device according to claim 9, characterized in that The calculation module is specifically used for: The peak of the fundamental frequency voltage component and the trough of the triple frequency voltage component are matched to obtain the phase angle of the triple frequency voltage component.

12. The control device according to claim 8, characterized in that The DC transformer adopts a two-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula: U AB =2U AC1 cosωt+2U AC3 cos(3ωt+180°) Among them, U AB Indicates the design value of the AC voltage at the common point, U AC1 represents the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

13. The control device according to claim 8, characterized in that The DC transformer adopts a three-phase parallel structure, and the calculation module calculates the AC voltage design value of the common point according to the following formula: U A =U AC1 cosωt+U AC3 cos(3ωt+180°) U B =U AC1 cos(ωt-120°)+U AC3 cos(3ωt+180°) U C =U AC1 cos(ωt+120°)+U AC3 cos(3ωt+180°) Among them, U A Indicates the design value of the AC voltage at the common point of phase A, U B Indicates the design value of the AC voltage at the common point of phase B, U C Indicates the design value of the AC voltage at the common point of phase C, U AC1 represents the amplitude of the fundamental frequency voltage component, U AC3 represents the amplitude of the tripled frequency voltage component, ω represents the angular frequency of the AC voltage at the common point, and t represents time.

14. The control device according to claim 8, characterized in that The determining module is specifically configured to: Using the AC voltage design value of the common point as the AC voltage command value of the common point; Proportional resonance control is performed on the voltage difference between the AC voltage command value of the common point and the actual value of the AC voltage of the common point to obtain the actual value of the AC voltage of the common bridge arm.

15. A computer device, characterized in that: include: one or more processors; The processor is configured to store one or more programs; When the one or more programs are executed by the one or more processors, the control method according to any one of claims 1 to 7 is implemented.

16. A computer-readable storage medium, characterized in that A computer program is stored thereon, and when the computer program is executed, the control method according to any one of claims 1 to 7 is implemented.

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