Novel flexible DC power transmission converter module capable of realizing voltage reversal

Abstract

The invention relates to the technical field of flexible current converters of power systems, and discloses a novel flexible direct-current power transmission current converter module capable of realizing voltage reversal, which comprises a flexible direct-current power transmission current converter, and is characterized in that a plurality of'open-loop 'half-bridge modules are connected in a trapezoidal manner in a flexible current converter bridge arm; the change of the working state of each module can be realized through selective conduction of the positive switch and the negative switch, and positive voltage and negative voltage are output or no voltage is output through the module group, so that on the premise that the polarity of a module capacitor is not changed and a full-bridge sub-module is not introduced, the working state of the module is changed. Forward and reverse switching of output voltage of a bridge arm of the flexible converter is achieved, the technical defect that an existing flexible direct-current power transmission converter formed by a conventional half-bridge module can only output voltage in a single direction is overcome, and meanwhile system complexity caused by increase of the number of power devices in a full-bridge module scheme is avoided.

Description

Technical Field

[0001] This invention relates to the field of flexible converter technology for power systems, specifically a novel flexible DC transmission converter module capable of voltage reversal. Background Technology

[0002] With the continuous development of power systems, flexible converters have also evolved. Modern flexible converters represent an important direction for the development and application of new energy sources and are a crucial component of modern intelligent power transmission, distribution, and consumption networks. To improve the transmission efficiency of power systems, reduce losses, and ensure the safe, stable, and reliable operation of power systems, the design and control methods of high-performance flexible converters are of great significance.

[0003] Existing multilevel modular flexible converters are composed of half-bridge or full-bridge modules. Flexible converters constructed with conventional half-bridge or full-bridge modules share a common characteristic: each module is either bypassed and directly connected across the system, not supplying module voltage, and its capacitor is isolated from the system; or it is connected in series to the converter arm, supplying module voltage to the system. Due to the limitations of this connection method, flexible DC transmission converters constructed using conventional modules have the following drawbacks: 1. When using a half-bridge module, the resulting chain circuit can only output voltage in one direction.

[0004] 2. When using a full-bridge module, the resulting chain circuit can output voltages in both positive and negative directions. However, the number of switches required is twice that of a half-bridge module, making control more complex and resulting in greater losses.

[0005] Therefore, those skilled in the art provide a novel flexible DC-DC converter module capable of reverse voltage to solve the aforementioned problems. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a novel flexible DC-DC converter module capable of reverse voltage operation, thereby solving the problems mentioned in the background section.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: a novel flexible DC-DC converter module capable of voltage reversal, comprising a flexible DC-DC converter (10), wherein the flexible DC-DC converter (10) includes at least one flexible converter bridge arm (8), each flexible converter bridge arm (8) is composed of multiple 'open-loop' half-bridge modules (4) connected in a trapezoidal manner, each of the 'open-loop' half-bridge modules (4) includes a capacitor (3), a positive switch (1) connected to the positive terminal of the capacitor (3), and a switch connected to the positive terminal of the capacitor (3). 3) The negative switch (2) is connected to the negative terminal. The positive switch (1) and the negative switch (2) do not form an electrical closed loop. Their common connection point is in an electrical open loop state. Multiple open loop half-bridge modules (4) are cross-connected to the capacitor (3) ports of adjacent modules through the ports of their positive switches (1) and negative switches (2) to form a trapezoidal circuit (5) composed of open loop half-bridge modules. This enables the flexible converter bridge arm (8) to switch the output voltage in the forward and reverse directions without using full bridge sub-modules, for flexible DC power transmission converter.

[0008] Preferably, the 'open-loop' half-bridge module (4) is a four-port power module, including a capacitor positive port, a capacitor negative port, a positive switch port and a negative switch port, so as to realize the cascading and trapezoidal connection of the 'open-loop' half-bridge module (4) in the flexible converter arm (8).

[0009] Preferably, when the positive switch (1) is turned on, the 'open-loop' half-bridge module (4) is in a positive working state, and when the negative switch (2) is turned on, the 'open-loop' half-bridge module (4) is in a negative working state, so that the 'open-loop' half-bridge module has the condition to output positive or negative voltage to the outside.

[0010] Preferably, the adjacent 'open-loop' half-bridge modules (4) are arranged in opposite directions in the flexible converter arm (8), and the ports of their positive switch (1) and negative switch (2) are cross-connected with the capacitor (3) ports of the adjacent modules, thereby forming a trapezoidal voltage superposition structure.

[0011] Preferably, the 'open-loop' half-bridge module (4) in the flexible converter arm (8) is divided into a module group according to two adjacent modules. Each module group serves as the minimum voltage synthesis unit for the output voltage of the flexible converter arm (8). The voltage output of the module group depends on the logical sum of the working states of the two modules in the module group: This results in the module group outputting twice the positive voltage of the capacitor; Positive or negative, or negative-positive, will cause the module group to not output voltage; The negative voltage causes the module group to output twice the negative voltage of the capacitor.

[0012] Preferably, the module group achieves three output states—positive voltage, zero voltage, and negative voltage—by combining the control of the conduction states of the positive switch (1) and the negative switch (2) in the two 'open-loop' half-bridge modules (4) within the group.

[0013] Preferably, within one working cycle of the same flexible converter arm (8), the voltage polarity of all modules involved in the output remains consistent, and the module group is only allowed to be in one of the positive voltage state, negative voltage state or zero voltage state.

[0014] Preferably, by selectively investing different module groups to participate in the voltage synthesis of the flexible converter bridge arm (8), and combining the voltage state of the capacitor (3) in each open-loop half-bridge module (4), the voltage required for the flexible converter bridge arm (8) to commutate the system output can be realized, and the balanced control of the capacitor voltage in the flexible converter bridge arm (8) can also be realized.

[0015] Preferably, the flexible converter bridge arm (8) formed by the trapezoidal circuit (5) composed of the open-loop half-bridge module is connected to the three-phase AC system (6) via the transformer (7) and connected to the DC system (9). In terms of control equivalence, it is equivalent to the full-bridge modular multilevel converter and is suitable for high-voltage DC transmission systems, flexible DC distribution systems or multi-terminal DC grids.

[0016] This invention provides a novel flexible DC-DC converter module capable of voltage reversal. It offers the following advantages: 1. This invention employs multiple open-loop half-bridge modules connected in a trapezoidal configuration within the flexible converter arm. Each module's operating state can be changed by selectively switching its positive and negative terminals. The module group enables the output of positive, negative, or no voltage. This achieves forward and reverse switching of the flexible converter arm's output voltage without altering the module capacitor polarity or introducing full-bridge sub-modules. This overcomes the technical limitation of existing flexible DC-DC converters using conventional half-bridge modules, which can only output voltage in one direction. It also avoids the system complexity resulting from the increased number of power devices in full-bridge module solutions.

[0017] 2. This invention can achieve positive voltage, zero voltage, and negative voltage output by combining the ladder connection relationship between modules and the switching state control within the module group. While ensuring the flexible adjustment capability of the bridge arm voltage polarity, it effectively reduces the number of power devices, reduces switching losses and conduction losses, and simplifies the control strategy, thereby improving system operating efficiency and reducing engineering implementation costs.

[0018] 3. This invention divides adjacent 'open-loop' half-bridge modules into module groups and selectively engages different module groups to participate in bridge arm voltage synthesis, thereby providing the voltage required for system output commutation. It can also achieve balanced control of capacitor voltage within the bridge arm by combining the voltage status of the module capacitors. Attached Figure Description

[0019] Figure 1 This is the wiring diagram for the 'open-loop' half-bridge module circuit. Figure 2 This is the wiring diagram for a ladder-type circuit composed of open-loop half-bridge modules. Figure 3 This is a schematic diagram of the DC transmission converter circuit for a flexible converter bridge arm constructed using a 'trapezoidal' circuit.

[0020] Legend: 1. Positive switch; 2. Negative switch; 3. Capacitor; 4. Open-loop half-bridge module; 5. Trapezoidal circuit constructed using open-loop half-bridge modules; 6. Three-phase AC system; 7. Transformer; 8. Flexible converter arm; 9. DC system; 10. Flexible DC transmission converter. Detailed Implementation

[0021] To enable those skilled in the art to understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0022] The present invention will now be described in detail with reference to the accompanying drawings: Please see the appendix Figures 1 to 3 This invention provides a novel flexible DC-DC converter module capable of reverse voltage switching, comprising a flexible DC-DC converter 10. The flexible DC-DC converter 10 includes at least one flexible converter arm 8. Each flexible converter arm 8 is composed of multiple open-loop half-bridge modules 4 connected in a trapezoidal configuration. Each open-loop half-bridge module 4 includes a capacitor 3, a positive switch 1 connected to the positive terminal of the capacitor 3, and a negative switch 2 connected to the negative terminal of the capacitor 3. The positive switch 1 and the negative switch 2 do not form an electrical closed loop; their common connection point is in an electrical open-loop state. Multiple open-loop half-bridge modules 4 are cross-connected to the capacitor 3 ports of adjacent modules through their positive and negative switch 1 and negative switch 2 ports, forming a trapezoidal circuit 5 composed of open-loop half-bridge modules. This allows the flexible converter arm 8 to achieve forward and reverse voltage switching of the output voltage without using full-bridge sub-modules, for flexible DC-DC converter switching.

[0023] Specifically, the flexible DC-DC converter includes at least one flexible converter arm consisting of multiple open-loop half-bridge modules connected in a trapezoidal configuration. Each open-loop half-bridge module connects its positive and negative switches to the positive and negative terminals of a capacitor, respectively, ensuring an electrical open-loop connection. The positive and negative switch ports between modules are then cross-connected to the capacitor ports of adjacent modules, forming a trapezoidal circuit structure. This allows the flexible converter arm to switch the output voltage in both forward and reverse directions using only the open-loop half-bridge module structure. Thus, without using full-bridge submodules, it achieves both bidirectional voltage regulation capability and a smaller number of power devices, reducing system losses and control complexity.

[0024] See appendix Figures 1 to 3 The 'open-loop' half-bridge module 4 is a four-port power module, including a capacitor positive port, a capacitor negative port, a positive switch port, and a negative switch port, so as to realize the cascading and ladder connection of the 'open-loop' half-bridge module 4 in the flexible converter arm 8.

[0025] Specifically, by cross-connecting each port with the ports of adjacent modules, the 'open-loop' half-bridge module 4 can achieve a cascaded and ladder-shaped connection structure in the flexible converter arm 8, thereby effectively constructing the arm voltage regulation path and realizing the bidirectional voltage switching function. This design simplifies the system structure, reduces the number of power devices, and improves the overall operating efficiency of the system.

[0026] See appendix Figures 1 to 3 When the positive switch 1 is turned on, the open-loop half-bridge module 4 operates in a positive state. When the negative switch 2 is turned on, the open-loop half-bridge module 4 operates in a negative state, enabling the open-loop half-bridge module to output either a positive or negative voltage.

[0027] Specifically, by controlling the conduction states of the positive switch 1 and the negative switch 2 in the 'open-loop' half-bridge module 4, the module operates in a positive state when the positive switch 1 is on and in a negative state when the negative switch 2 is on. This allows a single 'open-loop' module to have both positive and negative voltage output capabilities, providing a basis for the flexible switching of voltage polarity in the flexible converter bridge arm 8. At the same time, it avoids the problems of increased power device quantity and increased control complexity caused by using full-bridge sub-modules.

[0028] See appendix Figures 1 to 3 The adjacent 'open-loop' half-bridge modules 4 are arranged in opposite directions in the flexible converter arm 8, and their positive switch 1 and negative switch 2 ports are cross-connected with the capacitor 3 ports of the adjacent modules, thus forming a trapezoidal voltage superposition structure.

[0029] Specifically, the output voltages of each module can be superimposed step by step along the bridge arm direction, which is conducive to the smooth synthesis and polarity adjustment of the bridge arm voltage. At the same time, it ensures that the connection relationship between the modules is clear and the structure is compact, providing a structural basis for the flexible converter bridge arm 8 to achieve stable multi-level voltage output.

[0030] See appendix Figures 1 to 3 In the flexible converter arm 8, the 'open-loop' half-bridge module 4 is divided into a module group according to two adjacent modules. Each module group serves as the minimum voltage synthesis unit for the output voltage of the flexible converter arm 8. The voltage output of the module group depends on the logical sum of the operating states of the two modules in the module group: This results in the module group outputting twice the positive voltage of the capacitor; Positive or negative, or negative-positive, will cause the module group to not output voltage; The negative voltage causes the module group to output twice the negative voltage of the capacitor.

[0031] Specifically, the regulation of the bridge arm voltage is upgraded from the single module level to the module group level, which helps to simplify the control logic while ensuring the accuracy of voltage synthesis, and provides a clear structural basis for realizing multiple output states such as positive voltage, zero voltage and negative voltage, thereby improving the stability and controllability of voltage synthesis and regulation of the flexible converter bridge arm 8.

[0032] See appendix Figures 1 to 3 The module group achieves three output states—positive voltage, zero voltage, and negative voltage—by combining the conduction states of the positive switch 1 and the negative switch 2 in the two 'open-loop' half-bridge modules 4 within the group.

[0033] Specifically, this control method simplifies the adjustment logic of the bridge arm voltage and can ensure the accuracy and stability of voltage synthesis under different output states, thereby improving the system's flexibility and operating efficiency.

[0034] See appendix Figures 1 to 3 During one working cycle of the same flexible converter arm 8, the voltage polarity of all modules involved in the output remains consistent, and the module group is only allowed to be in one of the following states: positive voltage, negative voltage, or zero voltage.

[0035] Specifically, by uniformly constraining the output polarity of the module group, the control complexity and voltage fluctuations caused by frequent switching of voltage polarity between different module groups within the bridge arm are avoided. This is conducive to achieving stable synthesis and orderly adjustment of the bridge arm output voltage, thereby improving the operational stability and control reliability of the flexible converter bridge arm 8.

[0036] See appendix Figures 1 to 3By selectively investing different module groups to participate in the voltage synthesis of the flexible converter bridge arm 8, and combining the voltage state of the capacitor 3 in each open-loop half-bridge module 4, the voltage required for the system output switching of the flexible converter bridge arm 8 can be realized, and the balanced control of the capacitor voltage within the flexible converter bridge arm 8 can also be realized.

[0037] Specifically, this method can achieve voltage balance control without additional voltage equalization circuits, which helps to reduce the complexity of the system structure and improve the stability and reliability of the flexible converter arm 8 during long-term operation.

[0038] See appendix Figures 1 to 3 The flexible converter bridge arm 8, formed by the trapezoidal circuit 5 composed of the open-loop half-bridge module, is connected to the three-phase AC system 6 via the transformer 7 and to the DC system 9. In terms of control equivalence, it is equivalent to the full-bridge modular multilevel converter and is suitable for high-voltage DC transmission systems, flexible DC distribution systems or multi-terminal DC grids.

[0039] Specifically, the above structure reduces the number of power devices and structural complexity while maintaining the operating characteristics of a full-bridge converter. This makes the flexible converter arm suitable for applications such as high-voltage direct current transmission systems, flexible direct current distribution systems, or multi-terminal direct current grids, thereby improving the system's engineering adaptability and practical value.

[0040] Working principle: In use, each flexible converter bridge arm 8 is composed of multiple 'open-loop' half-bridge modules 4 cascaded in a trapezoidal manner. Each 'open-loop' half-bridge module 4 includes a capacitor 3, a positive switch 1, and a negative switch 2. The positive switch 1 and the negative switch 2 do not form an electrical closed loop. Their common connection point is in an electrical open-loop state. Adjacent modules are arranged vertically and in opposite directions in the bridge arm. Their positive switch ports and negative switch ports are cross-connected with the capacitor ports of the adjacent modules to form a 'trapezoidal' circuit structure. This allows a single module to change its working state when the positive or negative switch is turned on, and outputs positive or negative voltage through the module group. Thus, the forward and reverse switching of the bridge arm output voltage can be achieved without using full-bridge sub-modules. Based on the above structure, the multiple 'open-loop' half-bridge modules 4 in the flexible converter arm 8 are divided into a module group according to two adjacent modules. Each module group serves as the minimum voltage synthesis unit for the output voltage of the bridge arm. By controlling the combined conduction states of the positive switch 1 and the negative switch 2 in the two 'open-loop' half-bridge modules 4 within the module group, the module group can achieve three output states: positive voltage, zero voltage, and negative voltage within one working cycle. Within the same working cycle, the voltage polarity of all module groups participating in the output remains consistent. Thus, by superimposing the output states of multiple module groups, the stable synthesis of multi-level voltages in the flexible converter arm 8 is achieved. During operation, by selectively engaging different module groups to participate in arm voltage synthesis, the voltage required for system output conversion can be obtained. It can also be coordinated and controlled in conjunction with the voltage state of capacitors 3 in each 'open-loop' half-bridge module 4 to achieve balanced regulation of capacitor voltage within the arm. The flexible converter arm 8, composed of 'open-loop' half-bridge modules, is connected to the three-phase AC system 6 via transformer 7 and to the DC system 9. In terms of control equivalence, it has the same voltage synthesis and polarity regulation capability as the full-bridge modular multilevel converter arm, and is suitable for high-voltage DC transmission systems, flexible DC distribution systems, or multi-terminal DC grids.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel flexible DC-DC converter module capable of voltage reversal, comprising a flexible DC-DC converter (10), characterized in that, The flexible DC-DC converter (10) includes at least one flexible converter arm (8). Each flexible converter arm (8) is composed of multiple open-loop half-bridge modules (4) connected in a trapezoidal manner. Each open-loop half-bridge module (4) includes a capacitor (3), a positive switch (1) connected to the positive terminal of the capacitor (3), and a negative switch (2) connected to the negative terminal of the capacitor (3). The positive switch (1) and the negative switch (2) do not form an electrical closed loop, and their common connection point is in an electrical open-loop state. Multiple open-loop half-bridge modules (4) are cross-connected to the capacitor (3) ports of adjacent modules through the ports of their positive switches (1) and negative switches (2) to form a trapezoidal circuit (5) composed of open-loop half-bridge modules. This allows the flexible converter arm (8) to switch the output voltage in the forward and reverse directions without using full-bridge sub-modules, for flexible DC-DC converter.

2. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, The 'open-loop' half-bridge module (4) is a four-port power module, including a capacitor positive port, a capacitor negative port, a positive switch port and a negative switch port, so as to realize the cascading and trapezoidal connection of the 'open-loop' half-bridge module (4) in the flexible converter arm (8).

3. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, When the positive switch (1) is turned on, the open-loop half-bridge module (4) is in a positive working state. When the negative switch (2) is turned on, the open-loop half-bridge module (4) is in a negative working state, so that the open-loop half-bridge module has the condition to output positive or negative voltage.

4. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, The adjacent 'open-loop' half-bridge modules (4) are arranged in opposite directions in the flexible converter arm (8), and the ports of their positive switch (1) and negative switch (2) are cross-connected with the capacitor (3) ports of the adjacent modules, thereby forming a trapezoidal voltage superposition structure.

5. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, The 'open-loop' half-bridge module (4) in the flexible converter arm (8) is divided into a module group according to two adjacent modules. Each module group serves as the minimum voltage synthesis unit for the output voltage of the flexible converter arm (8). The voltage output of the module group depends on the logical sum of the working states of the two modules in the module group: This results in the module group outputting twice the positive voltage of the capacitor; Positive or negative, or negative-positive, will cause the module group to not output voltage; The negative voltage causes the module group to output twice the negative voltage of the capacitor.

6. A novel flexible DC-DC converter module capable of voltage reversal according to claim 5, characterized in that, The module group achieves three output states: positive voltage, zero voltage, and negative voltage by combining the control of the conduction states of the positive switch (1) and the negative switch (2) in the two 'open-loop' half-bridge modules (4) within the group.

7. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, During one working cycle of the same flexible converter arm (8), the voltage polarity of all modules involved in the output remains consistent, and the module group is only allowed to be in one of the positive voltage state, negative voltage state or zero voltage state.

8. A novel flexible DC-DC converter module capable of voltage reversal according to claim 5, characterized in that, By selectively investing different module groups to participate in the voltage synthesis of the flexible converter bridge arm (8), and combining the voltage state of the capacitor (3) in each open-loop half-bridge module (4), the voltage required for the flexible converter bridge arm (8) to commutate the system output can be realized, and the balanced control of the capacitor voltage in the flexible converter bridge arm (8) can also be realized.

9. A novel flexible DC-DC converter module capable of voltage reversal according to claim 1, characterized in that, The flexible converter bridge arm (8) formed by the trapezoidal circuit (5) composed of the open-loop half-bridge module is connected to the three-phase AC system (6) via the transformer (7) and connected to the DC system (9). In terms of control equivalence, it is equivalent to the full-bridge modular multilevel converter and is suitable for high-voltage DC transmission systems, flexible DC distribution systems or multi-terminal DC grids.

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