Control method, device and system of T-connection direct-current transformer and storage medium

Abstract

The invention relates to a T-connection direct current transformer control method, device and system, a computer readable storage medium and a computer program product. The T-connection direct-current transformer comprises n-phase direct-current conversion modules, and n is larger than or equal to 4. Each phase of DC conversion module comprises a bridge arm formed by connecting a plurality of energy conversion sub-module cascade structures and an electric reactor in series, and two groups of switches, and a common connection end of the two groups of switches connected in series is connected with a first end of the bridge arm; the external connection end of the DC conversion module is used for connecting the high-voltage end, the low-voltage end and the grounding end, and comprises a first end, a second end, a common connection end and a second end of the bridge arm after the two groups of switches are connected in series. The method comprises the following steps: receiving a commutation instruction; in the commutation period, the conduction state of the switch is switched, so that at least an i-phase direct current conversion module is conducted with the low-voltage end at the same moment; 2 < = i < = n-2. By adopting the method, the magnitude of the current which needs to be tolerated by each device can be reduced, so that the T-connection type direct-current transformer meets the requirement of high-capacity application.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to a control method, apparatus, system, computer-readable storage medium, and computer program product for a T-connected DC transformer. Background Technology

[0002] In DC power grids, DC transformers play a crucial role. They are not only key equipment for power conversion but also an indispensable part of building efficient and reliable DC power grids. With the increasing demand for efficient energy transmission and distribution in power systems, the technological development and application of DC transformers have become particularly important. Among them, T-type DC transformers, as an important technological direction for realizing large-capacity applications, are receiving increasing attention.

[0003] However, with the increasing demand for DC transformer capacity, traditional T-connected DC transformers face the challenge of their components being unable to withstand the large transmission current under high-capacity applications, making it difficult for T-connected DC transformers to meet the needs of high-capacity applications. Summary of the Invention

[0004] Therefore, it is necessary to provide a control method, device, system, computer-readable storage medium, and computer program product for a T-connected DC transformer that can be applied to large-capacity applications, addressing the aforementioned technical problems.

[0005] In a first aspect, this application provides a control method for a T-connected DC transformer, the T-connected DC transformer comprising: an n-phase DC-DC converter module, where n is an integer greater than or equal to 4; each phase of the DC-DC converter module comprises:

[0006] The structure comprises a bridge arm consisting of multiple cascaded energy conversion submodules and a series reactor, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm.

[0007] The control method includes:

[0008] Receive commutation command;

[0009] During the commutation cycle, the conduction state of the switch is switched so that at least i-phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

[0010] In one embodiment, the method further includes:

[0011] During the process of switching the conduction state of the switch, at least k phase DC-DC converter modules are connected to the high-voltage side at the same time; where k is an integer and 1≤k≤ni-1; and the DC-DC converter modules are not connected to the low-voltage side and the high-voltage side at the same time.

[0012] In one embodiment, switching the conduction state of the switch during the commutation cycle includes:

[0013] During the commutation cycle, the conduction state of the switch is switched in a preset sequence.

[0014] In one embodiment, the commutation cycle includes multiple sub-cycles; switching the conduction state of the switch within the commutation cycle includes:

[0015] In each sub-cycle, the conduction state of the switch is switched so that in two adjacent sub-cycles, the conduction state of at least two phases of the DC-DC converter module and the low-voltage side changes, and at least one phase of the DC-DC converter module is connected to the low-voltage side in both adjacent sub-cycles.

[0016] In one embodiment, within two adjacent sub-cycles, the state change durations of at least two of the switches that change their conduction state are equal.

[0017] Secondly, this application also provides a control device for a T-connected DC transformer, the T-connected DC transformer comprising: an n-phase DC-DC converter module, where n is an integer greater than or equal to 4; each phase of the DC-DC converter module comprises: a bridge arm formed by a cascaded structure of multiple energy conversion sub-modules and a reactor connected in series, and two sets of switches; the common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm; the external terminals of the DC-DC converter module are used to connect a high-voltage terminal, a low-voltage terminal, and a ground terminal, and the external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm; the device comprises:

[0018] The instruction receiving module is used to receive commutation instructions;

[0019] The commutation control module is used to switch the conduction state of the switch during the commutation cycle so that at least i phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

[0020] Thirdly, this application also provides a T-connected DC transformer system, including a T-connected DC transformer and a control system; the T-connected DC transformer includes: a bridge arm formed by a cascaded structure of multiple energy conversion sub-modules and a reactor connected in series, and two sets of switches; the common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm; the external terminal of the DC conversion module is used to connect a high-voltage terminal, a low-voltage terminal and a ground terminal, and the external terminal of the DC conversion module includes three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches and the second end of the bridge arm;

[0021] The control system is used to connect the controlled terminals of each of the switches, and the control system is used to control the T-connected DC transformer according to the method described above.

[0022] In one embodiment, the external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm SM is used to connect to the ground terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the low-voltage terminal one-to-one.

[0023] In one embodiment, the external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm is used to connect to the low-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the ground terminal one-to-one.

[0024] In one embodiment, the external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm is used to connect to the high-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the low-voltage terminal and the ground terminal one-to-one.

[0025] In one embodiment, one set of the two sets of switches includes a first switching device and a second switching device, and the other set of switches includes a third switching device and a fourth switching device; the first switching device, the third switching device, the second switching device, and the fourth switching device are connected in series in sequence; wherein, the common connection terminal of the two sets of switches connected in series includes a first common connection terminal connecting the first switching device and the third switching device, a second common connection terminal connecting the third switching device and the second switching device, and a third common connection terminal connecting the second switching device and the fourth switching device;

[0026] The external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second common connection terminal; wherein, the second common connection terminal is used to connect to the low-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the ground terminal one-to-one.

[0027] Fourthly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the following steps:

[0028] Receive commutation command;

[0029] During the commutation cycle, the conduction state of the switch is switched so that at least i-phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

[0030] Fifthly, this application also provides a computer program product, including a computer program that, when executed by a processor, performs the following steps:

[0031] Receive commutation command;

[0032] During the commutation cycle, the conduction state of the switch is switched so that at least i-phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

[0033] The aforementioned control method, apparatus, system, computer-readable storage medium, and computer program product for a T-connected DC transformer include an n-phase DC-DC converter module, where n is an integer greater than or equal to 4. Each phase DC-DC converter module includes a bridge arm consisting of multiple cascaded energy conversion sub-modules and a reactor connected in series, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect to the high-voltage end, the low-voltage end, and the ground end. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm. The control method for this T-connected DC transformer includes: receiving a commutation command; and switching the conduction state of the switches during the commutation cycle so that at least i-phase DC-DC converter modules are connected to the low-voltage end at any given time; where i is an integer, and 2 ≤ i ≤ n-2. Therefore, this T-connected DC transformer includes at least four-phase DC-DC converter modules, and during the commutation cycle, at least two phases of the DC-DC converter modules are connected to the low-voltage side. This allows the large transmission current on the low-voltage side in high-capacity scenarios to be jointly withstood by the components in at least two phases of the DC-DC converter modules. This reduces the current that each component in the DC-DC converter modules connected to the low-voltage side needs to withstand, enabling each component to operate stably in high-capacity scenarios. Consequently, the T-connected DC transformer can meet the requirements of high-capacity applications, improving its practicality. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a T-connected DC transformer system in one embodiment;

[0036] Figure 2a This is a schematic diagram of the structure of a half-bridge submodule in one embodiment;

[0037] Figure 2b This is a schematic diagram of the structure of a full-bridge submodule in one embodiment;

[0038] Figure 2c This is a schematic diagram of the switching device in one embodiment;

[0039] Figure 3 This is a schematic diagram of a T-connected DC transformer in one embodiment;

[0040] Figure 4This is a schematic diagram of the T-connected DC transformer in another embodiment;

[0041] Figure 5 This is a schematic diagram of the T-connected DC transformer in another embodiment;

[0042] Figure 6 This is a schematic diagram of the T-connected DC transformer in another embodiment;

[0043] Figure 7 This is a flowchart illustrating the control method for a T-connected DC transformer in one embodiment;

[0044] Figure 8 This is a schematic diagram of the T-connected DC transformer in another embodiment;

[0045] Figure 9 for Figure 8 A schematic diagram of the commutation control of the T-connected DC transformer in the embodiment;

[0046] Figure 10 for Figure 8 Another commutation control diagram of the T-connected DC transformer in the embodiment;

[0047] Figure 11 This is a schematic diagram of the commutation control of a T-connected DC transformer in one embodiment;

[0048] Figure 12 This is a structural block diagram of the control device for a T-connected DC transformer in one embodiment. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0051] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0052] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0053] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0054] The control method for a T-connected DC transformer provided in this application can be applied to a T-connected DC transformer system, such as... Figure 1 As shown, the T-connected DC transformer system includes a T-connected DC transformer 102 and a control system 104. In one embodiment, the T-connected DC transformer 102 includes an n-phase DC-DC converter module, where n is an integer greater than or equal to 4. That is, the T-connected DC transformer 102 includes at least a 4-phase DC-DC converter module.

[0055] Each phase DC-DC converter module includes a bridge arm consisting of multiple cascaded energy conversion sub-modules and a series reactor, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect the high-voltage terminal, the low-voltage terminal, and the ground terminal. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm.

[0056] The structure of the energy conversion submodule is not unique; it can be either a full-bridge submodule or a half-bridge submodule. Therefore, the bridge arm can be composed of a cascaded half-bridge submodule structure connected in series with a reactor, or a cascaded full-bridge submodule structure connected in series with a reactor. Please refer to [reference needed]. Figure 2a The half-bridge submodule consists of a series branch of fully controlled devices connected in parallel with a capacitor. Please refer to [reference needed]. Figure 2b The full-bridge submodule consists of an H-bridge connected in parallel with capacitors. Each arm of the H-bridge is composed of fully controlled devices, and each fully controlled device is connected in anti-parallel with a diode. The fully controlled devices can be IGBTs (Insulated Gate Bipolar Transistors) or GTOs (Gate-Turn-Off Thyristors), etc.

[0057] Each group of switches may include one switching device or multiple switching devices. Please refer to [link / reference]. Figure 2cSwitching devices consist of multiple power electronic devices connected in series. Power electronic devices include fully controlled devices (such as IGBTs or GTOs) and their anti-parallel diodes, semi-controlled devices (such as thyristors), or diodes.

[0058] The number of phases n of the DC-DC converter module 10 can be set comprehensively based on factors such as capacity requirements, voltage level, current withstand parameters of each device in the cascaded energy conversion submodule structure, and cost. This embodiment does not impose any limitations on this. The number of submodules in the cascaded energy conversion submodule structure is also not limited, and those skilled in the art can set it according to specific circumstances.

[0059] In this embodiment, the T-connected DC transformer 102 includes an n-phase DC-DC converter module, thereby forming an n-phase conversion structure. By controlling each set of switches, the DC-DC converter module can be switched between the high-voltage and low-voltage ends, thereby realizing energy transfer.

[0060] In practical implementation, the end of the cascaded structure of multiple energy conversion submodules that is not connected to the reactor serves as the first end of the bridge arm, and the end of the reactor that is not connected to the cascaded structure of energy conversion submodules serves as the second end of the bridge arm. Which three ends—the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common terminal of the two sets of switches connected in series, and the second end of the bridge arm—serve as the external terminals of the DC-DC converter module needs to be determined based on the actual situation.

[0061] Exemplarily, in one embodiment, please refer to Figure 3 The T-connected DC transformer 102 includes an n-phase DC-DC converter module 10. Each phase DC-DC converter module 10 includes a bridge arm SM formed by multiple energy conversion sub-modules 100 cascaded together and a reactor L connected in series, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm SM. The external terminals of the DC-DC converter module 10 are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal.

[0062] In this embodiment, the external terminals of the DC-DC converter module 10 include a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the ground terminal, and the first and second terminals of the two sets of switches connected in series are used to connect the high-voltage terminal and the low-voltage terminal one-to-one.

[0063] Taking the first-phase DC-DC converter module 10 as an example, the first-phase DC-DC converter module 10 includes a first set of switches, a second set of switches, and a bridge arm SM. The first set of switches includes switching device S1, and the second set of switches includes switching device S2. Switching device S1 and switching device S2 are connected in series, and the first end of the bridge arm SM is "T-connected" to switching device S1 and switching device S2. In power systems, a "T-connection" usually refers to connecting one line to another, forming a shape similar to the English letter "T". In this embodiment, the common terminal of the series-connected switching device S1 and switching device S2 is connected to the first end of the bridge arm SM, forming a connection structure similar to the English letter "T".

[0064] After switching devices S1 and S2 are connected in series, the end of switching device S1 not connected to switching device S2 and the end of switching device S2 not connected to switching device S1 serve as the first and second terminals of the two sets of switches connected in series, respectively. For example, the end of switching device S1 not connected to switching device S2 can be connected to the high-voltage terminal, and the end of switching device S2 not connected to switching device S1 can be connected to the low-voltage terminal. The end of reactor L in bridge arm SM not connected to the cascaded structure of energy conversion submodule 100 is used to connect to the ground terminal. The specific connection relationships of other phase DC-DC conversion modules 10 in this embodiment are not described in detail.

[0065] In one embodiment, please refer to Figure 4 The external terminals of the DC-DC converter module 10 include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the low-voltage end, and the first terminal and the second terminal formed by the two sets of switches connected in series are used to connect one-to-one to the high-voltage end and the ground end. For example, in the first phase DC-DC converter module 10, the end of switch device S1 not connected to switch device S2 may be used to connect to the high-voltage end, and the end of switch device S2 not connected to switch device S1 may be connected to the ground end. The end of reactor L in the bridge arm SM not connected to the cascaded structure of the energy conversion submodule 100 is used to connect to the low-voltage end. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment are not described in detail.

[0066] In one embodiment, please refer to Figure 5The external terminals of the DC-DC converter module 10 include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the high-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect to the low-voltage terminal and the ground terminal, respectively. For example, in the first phase DC-DC converter module 10, the end of switch device S1 not connected to switch device S2 may be used to connect to the low-voltage terminal, and the end of switch device S2 not connected to switch device S1 may be connected to the ground terminal. The end of reactor L in the bridge arm SM not connected to the cascaded structure of the energy conversion submodule 100 is used to connect to the high-voltage terminal. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment are not described in detail.

[0067] Regarding the energy transfer process, Figure 3 Taking the first-phase DC-DC converter module 10 of the illustrated embodiment as an example, during energy transfer, when switch S1 is turned on and switch S2 is turned off, the positive current of the high-voltage side enters the bridge arm SM through switch S1, and the voltage output by the bridge arm SM is the high-voltage side voltage, used to compensate for the voltage difference between the high-voltage side and ground. When switch S2 is turned on and switch S1 is turned off, the low-voltage side current is injected into the bridge arm SM through switch S2, and the voltage output by the bridge arm SM is the low-voltage side voltage, used to compensate for the voltage difference between the low-voltage side and ground. Thus, through the alternating operation between multiple phases, stable power conversion can be achieved.

[0068] In one embodiment, one set of switches includes a first switching device and a second switching device, and the other set of switches includes a third switching device and a fourth switching device. The first switching device, the third switching device, the second switching device, and the fourth switching device are connected in series in sequence. The common connection terminal of the two sets of switches connected in series includes a first common connection terminal connecting the first switching device and the third switching device, a second common connection terminal connecting the third switching device and the second switching device, and a third common connection terminal connecting the second switching device and the fourth switching device.

[0069] The external terminals of the DC-DC converter module include: a second common connection terminal, a first terminal formed by two sets of switches connected in series, and a second terminal formed by two sets of switches connected in series; wherein, the second common connection terminal is used to connect to the low voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high voltage terminal and the ground terminal one-to-one.

[0070] For easier understanding, please refer to Figure 6 For example, the two sets of switches include a first set of switches and a second set of switches. The first set of switches may include a first switching device S1 and a second switching device S1', and the second set of switches includes a third switching device S2' and a fourth switching device S2. The first switching device S1, the third switching device S2', the second switching device S1', and the fourth switching device S2 in the two sets of switches are connected in series in sequence.

[0071] It is understood that in this embodiment, the common connection terminals of the two sets of switches respectively include a first common connection terminal, a second common connection terminal, and a third common connection terminal. Specifically, the first common connection terminal is the common terminal connecting the first switching device S1 and the third switching device S2', the second common connection terminal is the common terminal connecting the second switching device S1' and the third switching device S2', and the third common connection terminal is the common terminal connecting the second switching device S1' and the fourth switching device S2.

[0072] The first end of the bridge arm SM is connected to the third common connection terminal, and the second end of the bridge arm SM is connected to the first common connection terminal. The external terminals of the DC-DC converter module 10 include: the first terminal of two sets of switches connected in series, the second terminal of two sets of switches connected in series, and the second common connection terminal of the two sets of switches.

[0073] For example, taking the first-phase DC-DC converter module 10 as an example, in the first-phase DC-DC converter module 10, the end of the first switching device S1 not connected to the third switching device S2' can be used to connect to the high-voltage end, the end of the fourth switching device S2 not connected to the second switching device S1' can be connected to the ground end, and the second common connection end can be used to connect to the low-voltage end. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment will not be described in detail.

[0074] In practical implementation, the switching devices in the first group of switches are controlled synchronously, and the switching devices in the second group of switches are controlled synchronously as well. For example, when switching devices S1 and S1' are on, switching devices S2 and S2' are off. The positive current at the high-voltage end flows through switching devices S1 and S1' into the bridge arm, and the output voltage of the bridge arm is the high-voltage end voltage minus the low-voltage end voltage, used to compensate for the voltage difference between the high-voltage and low-voltage ends. When switching devices S2 and S2' are on, switching devices S1 and S1' are off. The current difference between the low-voltage and high-voltage ends is injected into the bridge arm through switching devices S2 and S2', and the output voltage of the bridge arm is the low-voltage end voltage, used to compensate for the low-voltage end voltage difference to ground. Thus, through the alternating operation between multiple phases, stable power conversion can be achieved.

[0075] The control system 104 is used to connect the controlled terminals of each switch in each phase DC-DC converter module 10, and to receive commutation commands. During the commutation cycle, the control system switches the conduction state of the switches so that at least i phase DC-DC converter modules are connected to the low-voltage terminal at any given time; where i is an integer and 2≤i≤n-2. The structure of the control system 104 is not limited and can be configured by those skilled in the art according to specific circumstances.

[0076] In one exemplary embodiment, such as Figure 7 As shown, a control method for a T-connected DC transformer is provided, which is then applied to... Figure 1 The control system 104 in the diagram is used as an example for illustration, including steps 202 and 204. Wherein:

[0077] Step 202: Receive commutation command.

[0078] The commutation command can be input into the control system by the controller based on the actual situation, or it can be generated and transmitted to the control system by other devices capable of communicating with the control system; there is no specific limitation. After receiving the commutation command, the control system controls the T-connected DC transformer to begin the commutation operation.

[0079] Step 204: During the commutation cycle, switch the conduction state of the switch so that at least one i-phase DC-DC converter module is connected to the low-voltage side at any given time.

[0080] The duration of the commutation period is not limited. For example, the duration of the commutation period can be 1 second, 2 seconds, 100 milliseconds, etc.

[0081] Where i is an integer, and 2≤i≤n-2.

[0082] Switching the conduction state includes switching from the conduction state to the off state, and switching from the off state to the conduction state. When switching the conduction state of each switch, the switches can be switched in a certain order or randomly according to the conditions.

[0083] It is understood that when each group of switches includes one switching device, switching the conduction state of each switch includes switching the conduction state of the switching devices in each DC-DC converter module. When each group of switches includes at least two switching devices, the states of the switching devices in each group of switches are switched synchronously; switching the conduction state of each switch specifically includes: synchronously switching the conduction state of each switching device in each group of switches.

[0084] For example, such as Figure 8 As shown, in Figure 8 In the illustrated embodiment, the T-connected DC transformer includes a 4-phase DC-DC converter module. Each group of switches includes one switching device, and the switching devices connected to the low-voltage side are switching devices S2, S4, S6, and S8, respectively. Within one commutation cycle, the conduction sequence of the switches connected to the low-voltage side can be as follows: switching devices S2 and S4 conduct first, followed by switching the non-conducting switching device S6 or S8; switching devices S6 and S4 conduct first, followed by switching the non-conducting switching device S2 or S8; or any other sequence.

[0085] The conduction sequence of each switch connected to the low-voltage side can be the same or different in different commutation cycles, and can be set according to the specific circumstances.

[0086] By appropriately switching the switches, at least two phase DC-DC converter modules can be connected to the low-voltage side at any given time. Therefore, the transmission current at the low-voltage side can be jointly withstood by the devices in at least two phase DC-DC converter modules.

[0087] The control method for the aforementioned T-connected DC transformer includes: receiving a commutation command; and switching the conduction state of the switch during the commutation cycle so that at least i phase DC-DC converter modules are connected to the low-voltage side at any given time; where i is an integer and 2≤i≤n-2. Therefore, during the commutation cycle, at least two phase DC-DC converter modules are connected to the low-voltage side of the T-connected DC transformer, allowing the large transmission current on the low-voltage side in high-capacity scenarios to be jointly withstood by the devices in at least two phase DC-DC converter modules. This reduces the current that each device needs to withstand, enabling each device to operate stably in high-capacity scenarios, thus allowing the T-connected DC transformer to meet the needs of high-capacity applications and improving its practicality.

[0088] In one embodiment, the step of switching the conduction state of the switch during the commutation cycle includes: switching the conduction state of the switch in a preset sequence during the commutation cycle.

[0089] By switching the conduction state of the switches in a preset sequence during each commutation cycle, the state switching of each switch can be made more orderly, thereby improving the stability of the energy conversion process.

[0090] The preset order does not need to be specified. (Still using...) Figure 8 Taking the illustrated embodiment as an example, in each commutation cycle, the switching devices S2 and S4 can be turned on in turn, followed by the sequence of turning on the switching devices S4 and S6, turning on the switching devices S6 and S8, turning on the switching devices S8 and S2, and turning on the switching devices S2 and S4, or the sequence of turning on the switching devices S2 and S6, turning on the switching devices S6 and S8, turning on the switching devices S8 and S4, turning on the switching devices S4 and S2, and turning on the switching devices S2 and S6, or other sequences.

[0091] By sequentially rotating the conduction states of each switch in a preset order during each commutation cycle, it can be ensured that each DC-DC converter module can connect and disconnect from the low-voltage side in a predetermined sequence. This rotation method allows for a relatively balanced transmission current across each phase of the DC-DC converter module during operation, which helps improve the operational stability of the T-connected DC transformer. Furthermore, sequentially rotating the conduction states of the switches optimizes the distribution of energy among the DC-DC converter modules, thereby improving the energy conversion efficiency and stability of the entire system.

[0092] In one embodiment, the commutation period T includes multiple sub-cycles. Steps: During the commutation period, the switching state of the switch is changed, specifically including:

[0093] In each sub-cycle, the conduction state of the switching switch is changed so that in two adjacent sub-cycles, the conduction state of at least two DC-DC converter modules and the low-voltage side changes, and at least one DC-DC converter module is connected to the low-voltage side in both adjacent sub-cycles.

[0094] In this embodiment, the connection state of at least two DC-DC converter modules to the low-voltage terminal can be changed by controlling the switching states of at least two phase DC-DC converter modules. Assuming that in adjacent sub-cycles, the conduction state of at least two DC-DC converter modules to the low-voltage terminal is changed, it can be understood that in the previous sub-cycle, one phase of the DC-DC converter module whose conduction state to the low-voltage terminal is changed is conducting with the low-voltage terminal, while the other phase is not conducting with the low-voltage terminal. In the next sub-cycle, the phase conducting with the low-voltage terminal switches to a non-conducting state, and the phase not conducting with the low-voltage terminal switches to a conducting state.

[0095] By switching the conduction state of the DC-DC converter modules, different DC-DC converter modules can be switched between the high-voltage and low-voltage sides to achieve energy transfer.

[0096] By ensuring that at least one DC-DC converter module is connected to the low-voltage side in both adjacent sub-cycles, the continuity of power transmission can be improved.

[0097] For example, please refer to Figures 8-9 Taking the T-connected DC transformer including a 4-phase DC-DC converter module as an example, at the same time, at least 2 phase DC-DC converter modules are controlled to be connected to the low-voltage side, that is, at least two of the switching devices S2, S4, S6 and S8 are controlled to be connected to the low-voltage side.

[0098] The commutation period T includes four sub-cycles: sub-cycle t1, sub-cycle t2, sub-cycle t3, and sub-cycle t4. In sub-cycle t1, control switching device S8 and switching device S2 are simultaneously turned on.

[0099] During sub-cycle t2, control switching devices S2 and S4 are simultaneously turned on; thus, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase containing switching device S8 is switched from on to off, and at the same time, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase containing switching device S4 is switched from off to on.

[0100] During sub-cycle t3, control switching devices S4 and S6 are simultaneously turned on; thus, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase where switching device S2 is located can be switched from on to off, and at the same time, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase where switching device S6 is located can be switched from off to on.

[0101] During sub-cycle t4, control switching devices S6 and S8 are simultaneously turned on; thus, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase containing switching device S4 is switched from on to off, and at the same time, the conduction state of the DC-DC converter module and the low-voltage terminal in the phase containing switching device S8 is switched from off to on.

[0102] It is understandable that, in adjacent sub-cycles, the control system will also ensure that at least one phase of the DC-DC converter module that is not connected to the low-voltage side is connected to the high-voltage side. Thus, by switching the connection status of the DC-DC converter module between the low-voltage and high-voltage sides, different DC-DC converter modules can be switched between the high-voltage and low-voltage sides, achieving energy transfer.

[0103] During adjacent sub-cycles t1 and t2, controlling switch S2 to remain continuously on ensures that the DC-DC converter module in the phase containing switch S2 remains continuously connected to the low-voltage side, thus enabling the DC-DC converter module to continuously transmit electrical energy. During adjacent sub-cycles t2 and t3, controlling switch S4 to remain continuously on ensures that the DC-DC converter module in the phase containing switch S4 remains continuously connected to the low-voltage side, thus enabling the DC-DC converter module to continuously transmit electrical energy. During adjacent sub-cycles t3 and t4, controlling switch S6 to remain continuously on ensures that the DC-DC converter module in the phase containing switch S6 remains continuously connected to the low-voltage side, thus enabling the DC-DC converter module to continuously transmit electrical energy.

[0104] Therefore, by ensuring that at least one phase DC-DC converter module is connected to the low-voltage side in two adjacent sub-cycles, the continuity of power transmission can be improved, and the current fluctuations and instability caused by frequent switching of each phase module can be mitigated, thereby enhancing the stability of the T-connected DC transformer.

[0105] In one implementation, within two adjacent sub-cycles, the state change durations of at least two switches that change their conduction state are equal.

[0106] It can be understood that whether a switch switches from an on state to an off state or from an off state to an on state, it is a switch that changes its on state. The state change duration of a switch that changes its on state includes: the off time of the switch when switching from an on state to an off state, and the on time of the switch when switching from an off state to an on state.

[0107] By making the off-time of the switch transitioning from the on state to the off state equal to the on-time of the switch transitioning from the off state to the on state, energy fluctuations caused by inconsistent switch state change durations can be reduced, thereby improving the stability of the T-connected DC transformer.

[0108] For example, with Figure 8-9 Taking the illustrated embodiment as an example, at the first moment before the end of sub-cycle t1, switching device S8 begins to turn off, and switching device S4 begins to turn on. The first moment differs from the end of sub-cycle t1 by half the state change duration. At the second moment after the start of sub-cycle t2, switching device S8 is completely turned off, and switching device S4 is completely turned on. The second moment also differs from the start of sub-cycle t2 by half the state change duration.

[0109] This achieves synchronous state switching between switching devices S8 and S4, with the off-time of S8 being equal to the on-time of S4, both being state change durations. This makes the switching process between the DC-DC converter module containing switching devices S8 and S4 and the low-voltage side more stable, improving the stability of energy transfer during this switching process.

[0110] It should be noted that during the commutation process, the switching process of other switches in the synchronous commutation state is similar to that of switching devices S8 and S4, and will not be described in detail here. By controlling the state change duration of the switches that change their conduction state to be equal, the energy of the T-connected DC transformer can be stably transmitted during the commutation process.

[0111] In one embodiment, the control method for the T-connected DC transformer further includes:

[0112] At any given moment, at least one k-phase DC-DC converter module is connected to the high-voltage side.

[0113] Where k is an integer, and 1≤k≤ni-1; and the DC-DC converter module is not simultaneously connected to the low-voltage end and the high-voltage end.

[0114] In this embodiment, at least one phase DC-DC converter module is connected to the high-voltage side at the same time, which enables the high-voltage side to transmit energy to at least one phase DC-DC converter module at the same time.

[0115] It should be noted that when the capacity of the T-connected DC transformer is very large, the transmission current at the high-voltage end will be relatively small due to the high voltage level. Therefore, even if only one phase DC-DC converter module is connected to the high-voltage end, the transmission current at the high-voltage end will not exceed the maximum withstand value of each component in that one phase DC-DC converter module.

[0116] Regarding k≤ni-1, since at any given moment, at least i switches are turned on to connect the i-phase DC-DC converter module to the low-voltage side, and during the commutation process (within adjacent sub-cycles), at least i+1 phase DC-DC converter modules will be connected to the low-voltage side. Since the same phase DC-DC converter module does not simultaneously connect to the low-voltage and high-voltage sides, at most n-(i+1) phase DC-DC converter modules will be connected to the high-voltage side at any given moment.

[0117] Under the condition that 1 ≤ k ≤ ni-1, the number of phases of the DC-DC converter module connected to the high-voltage side needs to be set according to the specific circumstances during actual implementation. Assuming the T-connected DC transformer includes 4-phase DC-DC converter modules, then at least i=2 phases of the DC-DC converter module are connected to the low-voltage side at any given time. During commutation, 3 phases of the DC transformer are connected to the low-voltage side, so at any given time, k=1 phase of the DC-DC converter module is connected to the high-voltage side. Assuming the T-connected DC transformer includes 5-phase DC-DC converter modules, then at least i=2 phases of the DC-DC converter module can be connected to the low-voltage side at any given time. During commutation, 3 phases of the DC transformer are connected to the low-voltage side; therefore, at any given time, 1 or 2 phases of the DC-DC converter module can be connected to the high-voltage side.

[0118] Assuming the T-connected DC transformer includes 5-phase DC-DC converter modules, and at least 3 phase DC-DC converter modules are connected to the low-voltage side at any given time, then during the commutation process, there are 4 phase DC transformers connected to the low-voltage side; therefore, at any given time, there is 1 phase DC-DC converter module connected to the high-voltage side.

[0119] In this embodiment, by flexibly adjusting the number of phases of the DC-DC converter modules connected to the high-voltage and low-voltage ends, the energy transmission path can be optimized, thereby improving the overall efficiency.

[0120] To better understand the above embodiments, a detailed explanation will be provided below with reference to a specific embodiment.

[0121] First of all, still with Figure 8 Taking the illustrated embodiment as an example, assuming that at least one phase of the DC-DC converter is connected to the low-voltage side at any given time, the transmission current at the low-voltage side needs to be withstood by the components in that phase of the DC-DC converter connected to the low-voltage side. Assuming the T-connected DC transformer has a capacity of 8000MW and a voltage level of ±800kV / ±400kV, its low-voltage side transmission current will be 10kA. Please refer to... Figure 10This 10kA transmission current will be withstood by the devices in the DC-DC converter module of each phase where the switch connected to the low-voltage side is located (assuming the switching sequence of the switches connected to the low-voltage side is switch device S2--switch device S4--switch device S6--switch device S8). Those skilled in the art will understand that such a large current may very well exceed the maximum withstand capability of each device.

[0122] In this embodiment, please refer to Figures 8-9 Taking the T-connected DC transformer including a 4-phase DC-DC converter module as an example.

[0123] The commutation cycle T consists of four sub-cycles. In sub-cycle t1, control switches S8 and S2 are turned on, while switches S1 and S7 are turned off. During this stage, the DC-DC converter modules of the phases containing switches S8 and S2 are connected to the low-voltage side. Simultaneously, switch S5 can be turned on and switch S6 can be turned off to connect the DC-DC converter module of the phase containing switch S6 to the high-voltage side; alternatively, switch S3 can be turned on and switch S4 can be turned off to connect the DC-DC converter module of the phase containing switch S4 to the high-voltage side.

[0124] During sub-cycle t2, control switches S2 and S4 are turned on, while switches S1 and S3 are turned off. This switches the DC-DC converter module in the phase containing switch S8 from being on to being off, and switches the DC-DC converter module in the phase containing switch S4 from being off to being on. Simultaneously, control switch S5 is turned on and switch S6 is turned off, connecting the DC-DC converter module in the phase containing switch S6 to the high-voltage side.

[0125] During sub-cycle t3, control switches S4 and S6 are turned on, while switches S3 and S5 are turned off. This switches the DC-DC converter module in the phase containing switch S2 from being on to being off, and the DC-DC converter module in the phase containing switch S6 from being off to being on. Simultaneously, control switch S7 is turned on and switch S8 is turned off, connecting the DC-DC converter module in the phase containing switch S8 to the high-voltage side.

[0126] During sub-cycle t4, control switches S6 and S8 are turned on, while switches S5 and S7 are turned off. This switches the DC-DC converter module in the phase containing switch S4 from being on to being off, and the DC-DC converter module in the phase containing switch S8 from being off to being on. Simultaneously, control switch S1 is turned on and switch S2 is turned off, connecting the DC-DC converter module in the phase containing switch S2 to the high-voltage side.

[0127] By switching the conduction state of each switch in the DC-DC converter module, different DC-DC converter modules can be switched between the high-voltage and low-voltage sides to achieve energy transfer.

[0128] During adjacent sub-cycles t1 and t2, control switch S2 is continuously turned on; during adjacent sub-cycles t2 and t3, control switch S4 is continuously turned on; during adjacent sub-cycles t3 and t4, control switch S6 is continuously turned on. Thus, by ensuring that at least one phase DC-DC converter module is turned on to the low-voltage side during two adjacent sub-cycles, the continuity of power transmission can be improved, and the current fluctuations and instability caused by frequent switching of phase modules can be mitigated, thereby improving the stability of the T-connected DC transformer.

[0129] Please continue to refer to Figure 9 In this embodiment, the conduction time of a single switch is adjusted from one-quarter of the commutation cycle to one-half of the commutation cycle. At the same time, at least two devices in the DC-DC converter module connected to the low-voltage side share the transmission current of the low-voltage side, reducing the current that each device needs to withstand by at least half.

[0130] The T-connected DC transformer includes a 5-phase DC-DC converter module; please refer to [link / reference]. Figure 11 Assuming the switches that switch the five-phase DC-DC converters between their on and off states are S2, S4, S6, S8, and S10, at least three switches are on simultaneously. This increases the on-time of a single switch to three-fifths of the commutation period T, meaning at least three phases of the DC-DC converter module simultaneously bear the transmission current at the low-voltage side. The peak current that each phase's DC-DC converter module needs to handle is only one-third of the transmission current at the low-voltage side.

[0131] It is understandable that when a T-connected DC transformer includes more phases of DC-DC converter modules, more DC-DC converter modules can be simultaneously turned on to the low-voltage side, thereby reducing the current that devices that need to withstand transmission current need to withstand, thus improving the reliability of each device.

[0132] When increasing the capacity of a T-connected DC transformer, the number of phases in the DC-DC converter module can be increased. This allows more DC-DC converter modules to be simultaneously connected to the low-voltage side, ensuring that the current that devices requiring transmission current withstand do not exceed their maximum withstand value. Therefore, the T-connected DC transformer can meet the needs of high-capacity applications, improving its practicality.

[0133] The control method for the aforementioned T-connected DC transformer achieves a breakthrough in control strategy by leveraging the flexibility and freedom of energy distribution within the transformer. By enabling free combination of multiple bridge arms through commutation, the withstand current of the devices is "extended," significantly reducing the peak current that the devices need to withstand, thereby lowering the device's withstand stress and reducing the difficulty of engineering implementation.

[0134] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0135] Based on the same inventive concept, this application also provides a control device for a T-connected DC transformer to implement the control method for the T-connected DC transformer described above. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the control device for a T-connected DC transformer provided below can be found in the limitations of the control method for the T-connected DC transformer described above, and will not be repeated here.

[0136] In one exemplary embodiment, such as Figure 12 As shown, a control device for a T-connected DC transformer is provided. The T-connected DC transformer includes: an n-phase DC-DC converter module, where n is an integer greater than or equal to 4; each phase DC-DC converter module includes: a bridge arm formed by multiple energy conversion sub-modules cascaded together and a reactor connected in series, and two sets of switches; the common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm; the external terminals of the DC-DC converter module are used to connect to the high-voltage end, the low-voltage end, and the ground end, and the external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm. The control device for the T-connected DC transformer includes: a command receiving module 302 and a commutation control module 304, wherein:

[0137] The instruction receiving module 302 is used to receive commutation instructions.

[0138] The commutation control module 304 is used to switch the conduction state of the switch during the commutation cycle so that at least i phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

[0139] In one embodiment, during the switching process of the phase control module 304, at least k phase DC-DC converter modules are connected to the high-voltage side at the same time; where k is an integer and 1≤k≤ni-1; and the DC-DC converter modules are not connected to the low-voltage side and the high-voltage side at the same time.

[0140] In one embodiment, the commutation control module 304 is further configured to switch the conduction state of the switch in a preset sequence during the commutation cycle.

[0141] In one embodiment, the commutation control module 304 is further configured to switch the conduction state of the switch in each sub-cycle, so that in two adjacent sub-cycles, the conduction state of at least two phases of the DC-DC converter module changes with the low-voltage end, and at least one phase of the DC-DC converter module is connected to the low-voltage end in both adjacent sub-cycles.

[0142] In one embodiment, the commutation control module 304 is further configured to ensure that the state change duration of at least two switches changing their conduction state is equal in two adjacent sub-cycles.

[0143] The various modules in the control device for the aforementioned T-connected DC transformer can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0144] In one exemplary embodiment, a T-connected DC transformer system is provided; please refer again to... Figure 1 The T-connected DC transformer system includes a T-connected DC transformer 102 and a control system 104. In one embodiment, the T-connected DC transformer 102 includes an n-phase DC-DC converter module, where n is an integer greater than or equal to 4. That is, the T-connected DC transformer 102 includes at least a 4-phase DC-DC converter module.

[0145] Each phase DC-DC converter module includes a bridge arm consisting of multiple cascaded energy conversion sub-modules and a series reactor, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect the high-voltage terminal, the low-voltage terminal, and the ground terminal. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm.

[0146] The structure of the energy conversion submodule is not unique; it can be either a full-bridge submodule or a half-bridge submodule. Therefore, the bridge arm can be composed of a cascaded half-bridge submodule structure connected in series with a reactor, or a cascaded full-bridge submodule structure connected in series with a reactor. Please refer to [reference needed]. Figure 2a The half-bridge submodule consists of a series branch of fully controlled devices connected in parallel with a capacitor. Please refer to [reference needed]. Figure 2b The full-bridge submodule consists of an H-bridge connected in parallel with capacitors. Each arm of the H-bridge is composed of fully controlled devices, and each fully controlled device is connected in anti-parallel with a diode. The fully controlled devices can be IGBTs (Insulated Gate Bipolar Transistors) or GTOs (Gate-Turn-Off Thyristors), etc.

[0147] Each group of switches may include one switching device or multiple switching devices. Please refer to [link / reference]. Figure 2c Switching devices consist of multiple power electronic devices connected in series. Power electronic devices include fully controlled devices (such as IGBTs or GTOs) and their anti-parallel diodes, semi-controlled devices (such as thyristors), or diodes.

[0148] The number of phases n of the DC-DC converter module 10 can be set comprehensively based on factors such as capacity requirements, voltage level, current withstand parameters of each device in the cascaded energy conversion submodule structure, and cost. This embodiment does not impose any limitations on this. The number of submodules in the cascaded energy conversion submodule structure is also not limited, and those skilled in the art can set it according to specific circumstances.

[0149] In this embodiment, the T-connected DC transformer 102 includes an n-phase DC-DC converter module, thereby forming an n-phase conversion structure. By controlling each set of switches, the DC-DC converter module can be switched between the high-voltage and low-voltage ends, thereby realizing energy transfer.

[0150] In this embodiment, the T-connected DC transformer 102 includes an n-phase DC-DC converter module, thereby forming an n-phase conversion structure. The control system 104 is used to control the T-connected DC transformer 102 based on the control methods of the T-connected DC transformers in the above embodiments. Thus, by controlling each set of switches, the n-phase DC-DC converter module can be switched between the high-voltage and low-voltage ends, thereby realizing energy transfer. The structure of the control system 104 is not limited, and those skilled in the art can set it according to specific circumstances.

[0151] In practical implementation, the end of the cascaded structure of multiple energy conversion submodules that is not connected to the reactor serves as the first end of the bridge arm, and the end of the reactor that is not connected to the cascaded structure of energy conversion submodules serves as the second end of the bridge arm. Which three ends—the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common terminal of the two sets of switches connected in series, and the second end of the bridge arm—serve as the external terminals of the DC-DC converter module needs to be determined based on the actual situation.

[0152] Exemplarily, in one embodiment, please refer to Figure 3 The T-connected DC transformer 102 includes an n-phase DC-DC converter module 10. Each phase DC-DC converter module 10 includes a bridge arm SM formed by multiple energy conversion sub-modules 100 cascaded together and a reactor L connected in series, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm SM. The external terminals of the DC-DC converter module 10 are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal.

[0153] In this embodiment, the external terminals of the DC-DC converter module 10 include a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the ground terminal, and the first and second terminals of the two sets of switches connected in series are used to connect the high-voltage terminal and the low-voltage terminal one-to-one.

[0154] Taking the first-phase DC-DC converter module 10 as an example, the first-phase DC-DC converter module 10 includes a first set of switches, a second set of switches, and a bridge arm SM. The first set of switches includes switching device S1, and the second set of switches includes switching device S2. Switching device S1 and switching device S2 are connected in series, and the first end of the bridge arm SM is "T-connected" to switching device S1 and switching device S2. In power systems, a "T-connection" usually refers to connecting one line to another, forming a shape similar to the English letter "T". In this embodiment, the common terminal of the series-connected switching device S1 and switching device S2 is connected to the first end of the bridge arm SM, forming a connection structure similar to the English letter "T".

[0155] After switching devices S1 and S2 are connected in series, the end of switching device S1 not connected to switching device S2 and the end of switching device S2 not connected to switching device S1 serve as the first and second terminals of the two sets of switches connected in series, respectively. For example, the end of switching device S1 not connected to switching device S2 can be connected to the high-voltage terminal, and the end of switching device S2 not connected to switching device S1 can be connected to the low-voltage terminal. The end of reactor L in bridge arm SM not connected to the cascaded structure of energy conversion submodule 100 is used to connect to the ground terminal. The specific connection relationships of other phase DC-DC conversion modules 10 in this embodiment are not described in detail.

[0156] In one embodiment, please refer to Figure 4The external terminals of the DC-DC converter module 10 include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the low-voltage end, and the first terminal and the second terminal formed by the two sets of switches connected in series are used to connect one-to-one to the high-voltage end and the ground end. For example, in the first phase DC-DC converter module 10, the end of switch device S1 not connected to switch device S2 may be used to connect to the high-voltage end, and the end of switch device S2 not connected to switch device S1 may be connected to the ground end. The end of reactor L in the bridge arm SM not connected to the cascaded structure of the energy conversion submodule 100 is used to connect to the low-voltage end. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment are not described in detail.

[0157] In one embodiment, please refer to Figure 5 The external terminals of the DC-DC converter module 10 include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm SM. The end of the bridge arm SM not connected to a switch is used to connect to the high-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect to the low-voltage terminal and the ground terminal, respectively. For example, in the first phase DC-DC converter module 10, the end of switch device S1 not connected to switch device S2 may be used to connect to the low-voltage terminal, and the end of switch device S2 not connected to switch device S1 may be connected to the ground terminal. The end of reactor L in the bridge arm SM not connected to the cascaded structure of the energy conversion submodule 100 is used to connect to the high-voltage terminal. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment are not described in detail.

[0158] Regarding the energy transfer process, Figure 3 Taking the first-phase DC-DC converter module 10 of the illustrated embodiment as an example, during energy transfer, when switch S1 is turned on and switch S2 is turned off, the positive current of the high-voltage side enters the bridge arm SM through switch S1, and the voltage output by the bridge arm SM is the high-voltage side voltage, used to compensate for the voltage difference between the high-voltage side and ground. When switch S2 is turned on and switch S1 is turned off, the low-voltage side current is injected into the bridge arm SM through switch S2, and the voltage output by the bridge arm SM is the low-voltage side voltage, used to compensate for the voltage difference between the low-voltage side and ground. Thus, through the alternating operation between multiple phases, stable power conversion can be achieved.

[0159] In one embodiment, one set of switches includes a first switching device and a second switching device, and the other set of switches includes a third switching device and a fourth switching device. The first switching device, the third switching device, the second switching device, and the fourth switching device are connected in series in sequence. The common connection terminal of the two sets of switches connected in series includes a first common connection terminal connecting the first switching device and the third switching device, a second common connection terminal connecting the third switching device and the second switching device, and a third common connection terminal connecting the second switching device and the fourth switching device.

[0160] The external terminals of the DC-DC converter module include: a second common connection terminal, a first terminal formed by two sets of switches connected in series, and a second terminal formed by two sets of switches connected in series; wherein, the second common connection terminal is used to connect to the low voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high voltage terminal and the ground terminal one-to-one.

[0161] For easier understanding, please refer to Figure 6 For example, the two sets of switches include a first set of switches and a second set of switches. The first set of switches may include a first switching device S1 and a second switching device S1', and the second set of switches includes a third switching device S2' and a fourth switching device S2. The first switching device S1, the third switching device S2', the second switching device S1', and the fourth switching device S2 in the two sets of switches are connected in series in sequence.

[0162] It is understood that in this embodiment, the common connection terminals of the two sets of switches respectively include a first common connection terminal, a second common connection terminal, and a third common connection terminal. Specifically, the first common connection terminal is the common terminal connecting the first switching device S1 and the third switching device S2', the second common connection terminal is the common terminal connecting the second switching device S1' and the third switching device S2', and the third common connection terminal is the common terminal connecting the second switching device S1' and the fourth switching device S2.

[0163] The first end of the bridge arm SM is connected to the third common connection terminal, and the second end of the bridge arm SM is connected to the first common connection terminal. The external terminals of the DC-DC converter module 10 include: the first terminal of two sets of switches connected in series, the second terminal of two sets of switches connected in series, and the second common connection terminal of the two sets of switches.

[0164] For example, taking the first-phase DC-DC converter module 10 as an example, in the first-phase DC-DC converter module 10, the end of the first switching device S1 not connected to the third switching device S2' can be used to connect to the high-voltage end, the end of the fourth switching device S2 not connected to the second switching device S1' can be connected to the ground end, and the second common connection end can be used to connect to the low-voltage end. The specific connection relationships of the other phase DC-DC converter modules 10 in this embodiment will not be described in detail.

[0165] In practical implementation, the switching devices in the first group of switches are controlled synchronously, and the switching devices in the second group of switches are controlled synchronously as well. For example, when switching devices S1 and S1' are on, switching devices S2 and S2' are off. The positive current at the high-voltage end flows through switching devices S1 and S1' into the bridge arm, and the output voltage of the bridge arm is the high-voltage end voltage minus the low-voltage end voltage, used to compensate for the voltage difference between the high-voltage and low-voltage ends. When switching devices S2 and S2' are on, switching devices S1 and S1' are off. The current difference between the low-voltage and high-voltage ends is injected into the bridge arm through switching devices S2 and S2', and the output voltage of the bridge arm is the low-voltage end voltage, used to compensate for the low-voltage end voltage difference to ground. Thus, through the alternating operation between multiple phases, stable power conversion can be achieved.

[0166] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0167] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0168] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments of the above methods. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0169] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0170] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A control method for a T-connected DC transformer, characterized in that, The T-connected DC transformer includes: an n-phase DC-DC converter module, where n is an integer greater than or equal to 4; each phase of the DC-DC converter module includes: The structure comprises a bridge arm consisting of multiple cascaded energy conversion submodules and a series reactor, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm. The control method includes: Receive commutation command; During the commutation cycle, the conduction state of the switch is switched so that at least i-phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

2. The method according to claim 1, characterized in that, The method further includes: During the switching of the conduction state of the switch, at least k phase DC-DC converter modules are connected to the high-voltage side at the same time; where k is an integer and 1≤k≤ni-1; and the DC-DC converter modules are not connected to the low-voltage side and the high-voltage side at the same time.

3. The method according to claim 1 or 2, characterized in that, The step of switching the conduction state of the switch during the commutation cycle includes: During the commutation cycle, the conduction state of the switch is switched in a preset sequence.

4. The method according to claim 3, characterized in that, The commutation cycle includes multiple sub-cycles; switching the conduction state of the switch within the commutation cycle includes: In each sub-cycle, the conduction state of the switch is switched so that in two adjacent sub-cycles, the conduction state of at least two phases of the DC-DC converter module and the low-voltage side changes, and at least one phase of the DC-DC converter module is connected to the low-voltage side in both adjacent sub-cycles.

5. The method according to claim 4, characterized in that, Within two adjacent sub-cycles, the state change duration of at least two of the switches that change their conduction state is equal.

6. A control device for a T-connected DC transformer, characterized in that, The T-connected DC transformer includes: an n-phase DC-DC converter module, where n is an integer greater than or equal to 4; each phase of the DC-DC converter module includes: a bridge arm formed by multiple energy conversion sub-modules cascaded together and a reactor connected in series, and two sets of switches; the common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm; the external terminals of the DC-DC converter module are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal, and the external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm; the device includes: The instruction receiving module is used to receive commutation instructions; The commutation control module is used to switch the conduction state of the switch during the commutation cycle so that at least i phase DC-DC converter modules are connected to the low-voltage side at the same time; where i is an integer and 2≤i≤n-2.

7. A T-connected DC transformer system, characterized in that, The system includes a T-connected DC transformer and a control system. The T-connected DC transformer includes an n-phase DC-DC converter module, where n is an integer greater than or equal to 4. Each phase of the DC-DC converter module includes a bridge arm consisting of a cascaded structure of multiple energy conversion sub-modules and a series connection of a reactor, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The external terminals of the DC-DC converter module are used to connect to the high-voltage terminal, the low-voltage terminal, and the ground terminal. The external terminals of the DC-DC converter module include three of the following: the first end of the two sets of switches connected in series, the second end of the two sets of switches connected in series, the common connection terminal of the two sets of switches, and the second end of the bridge arm. The control system is used to connect the controlled terminals of each of the switches, and the control system is used to control the T-connected DC transformer according to any one of claims 1 to 5.

8. The T-connected DC transformer system according to claim 7, characterized in that, The external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm is used to connect to the ground terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the low-voltage terminal one-to-one.

9. The T-connected DC transformer system according to claim 7, characterized in that, The external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm is used to connect to the low-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the ground terminal one-to-one.

10. The T-connected DC transformer system according to claim 7, characterized in that, The external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second terminal of the bridge arm; wherein, the second terminal of the bridge arm is used to connect to the high-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the low-voltage terminal and the ground terminal one-to-one.

11. The T-connected DC transformer system according to claim 7, characterized in that, One set of the two sets of switches includes a first switching device and a second switching device, and the other set of the switches includes a third switching device and a fourth switching device; the first switching device, the third switching device, the second switching device, and the fourth switching device are connected in series in sequence; wherein, the common connection terminal of the two sets of switches connected in series includes a first common connection terminal connecting the first switching device and the third switching device, a second common connection terminal connecting the third switching device and the second switching device, and a third common connection terminal connecting the second switching device and the fourth switching device; The external terminals of the DC-DC converter module include: a first terminal formed by two sets of switches connected in series, a second terminal formed by two sets of switches connected in series, and a second common connection terminal; wherein, the second common connection terminal is used to connect to the low-voltage terminal, and the first and second terminals formed by the two sets of switches connected in series are used to connect the high-voltage terminal and the ground terminal one-to-one.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

13. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 5.

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