CN-116345935-B - Mixed MMC flexible direct current conversion structure based on shared bridge arm

CN116345935BCN 116345935 BCN116345935 BCN 116345935BCN-116345935-B

Abstract

The application discloses a mixed MMC flexible direct current conversion structure based on a shared bridge arm, which comprises three-phase main circuits, wherein each phase of main circuit respectively comprises an upper bridge arm direct current switch group, a lower bridge arm direct current switch group, an upper bridge arm alternating current switch group, a lower bridge arm alternating current switch group and a shared bridge arm formed by cascading a plurality of full bridge submodules, one end of each shared bridge arm in any phase of main circuit is respectively connected with a first end of the upper bridge arm direct current switch group and a first end of the upper bridge arm alternating current switch group, the other end of each shared bridge arm is respectively connected with a first end of the lower bridge arm direct current switch group and a second end of the lower bridge arm alternating current switch group, the second ends of the upper bridge arm direct current switch group and the lower bridge arm direct current switch group are used as direct current ports for connecting direct current buses, and the upper bridge arm alternating current switch group is connected with the second end of the lower bridge arm alternating current switch group to form alternating current ports of each phase of the main circuit. The application can greatly reduce the number of submodules required by the system and can realize the lightweight operation of the converter valve.

Inventors

HUANG MING
LI WEILIN
LI JIANHUA
KANG ZHEN

Assignees

西北工业大学

Dates

Publication Date: 20260505
Application Date: 20230301

Claims (7)

1. The mixed MMC flexible direct current conversion structure based on the shared bridge arm is characterized by comprising a three-phase main circuit, a three-phase converter transformer and a compensation capacitor, wherein each phase main circuit comprises an upper bridge arm direct current switch group, a lower bridge arm direct current switch group, an upper bridge arm alternating current switch group, a lower bridge arm alternating current switch group and a shared bridge arm formed by cascading a plurality of full-bridge submodules; One end of the shared bridge arm in any phase main circuit is respectively connected with the first ends of the upper bridge arm direct current switch group and the upper bridge arm alternating current switch group, and the other end of the shared bridge arm is respectively connected with the first ends of the lower bridge arm direct current switch group and the lower bridge arm alternating current switch group; the primary winding of the three-phase converter transformer is connected with an alternating current port of each phase of main circuit, and the primary winding adopts a Y-shaped structure; One end of the compensation capacitor is connected with a neutral line point of a Y-shaped structure of the three-phase converter transformer, the other end of the compensation capacitor is connected with a voltage neutral point of a direct current bus, and the capacitance of the compensation capacitor is designed as follows: Wherein L 1 represents leakage inductance of primary winding of three-phase converter transformer, L 2 represents leakage inductance of secondary winding of three-phase converter transformer, k represents transformation ratio of three-phase converter transformer, Which represents the angular frequency of the ac voltage.
2. The hybrid MMC flexible DC converter structure of claim 1, wherein each phase of main circuit further comprises an AC side inductor, one end of the AC side inductor is connected with the AC port, and the other end of the AC side inductor is connected with a corresponding phase of a primary winding of the three-phase converter transformer.
3. The hybrid MMC flexible dc converter structure of claim 1 or 2, characterized in that the line voltage of ac ports of each phase main circuit is phase difference Is a three-phase voltage of (a).
4. The hybrid MMC flexible dc converter structure of claim 1 or 2, wherein the upper bridge arm dc switch group and the lower bridge arm dc switch group are each formed by connecting a plurality of power switching tubes connected in the same direction in series.
5. The hybrid MMC flexible dc converter structure of claim 1 or 2, wherein the upper bridge arm ac switch group and the lower bridge arm ac switch group are respectively formed by connecting a plurality of power switching tubes connected in the same direction in series with a plurality of power switching tubes connected in opposite directions.
6. The hybrid MMC flexible dc converter structure of claim 4 or 5, wherein the power switching tube employs an IGBT with a reverse diode.
7. A flexible direct current transmission system, characterized by comprising the hybrid MMC flexible direct current converter structure of any one of claims 1-6.

Description

Mixed MMC flexible direct current conversion structure based on shared bridge arm Technical Field The application relates to the technical field of power electronics, in particular to a hybrid MMC flexible direct current conversion structure based on a shared bridge arm. Background The flexible direct current converter valve is key equipment of a high-voltage direct current transmission system, and a modularized multi-level converter (Modular Multilevel Converter, MMC) is mainly used as a topology. The MMC has the characteristics of high modularization, easy expansion, good output voltage waveform and the like, can rapidly realize independent decoupling control of active power and reactive power, is free from communication, is easy to realize a multi-terminal system, and is particularly suitable for medium-high voltage high-power application occasions. However, with the increase of voltage class and system capacity, the weight, volume and cost of the converter valve are all increased sharply, and the popularization and application of the flexible direct current transmission technology are limited. The upper bridge arm and the lower bridge arm of the traditional MMC converter valve are provided with the same number of sub-modules, parameters are required to be set by referring to the voltage of the direct current bus, the number of the required sub-modules is large, the sub-modules are one of the main reasons of huge volume and weight of the converter valve, the equivalent capacitance of the sub-modules of the upper bridge arm and the lower bridge arm presents topological property of split capacitance relative to an alternating current side, the capacitor voltage of the sub-modules of the upper bridge arm and the lower bridge arm presents power frequency pulsation in a differential mode form, a large capacitance is required to meet ripple standards, in addition, each bridge arm current of the converter valve contains a direct current component, and a direct current reactor with heavy volume is required to be provided. The key technology for lightening the converter valve is researched, so that the size and weight of the valve body, the load of hardware fitting and the construction cost of an offshore platform can be effectively reduced, the engineering feasibility of the high-pressure high-capacity converter valve is improved, the development requirements of the intelligent power grid and global energy interconnection in the future are met, the technical economy of a new energy access system can be improved, and the low-carbon environment-friendly energy society of a framework can be quickened. Disclosure of Invention Aiming at least one defect or improvement requirement of the prior art, the invention provides a mixed MMC flexible direct current converter structure based on a shared bridge arm, and the number of submodules required by a system can be greatly reduced by designing and configuring a compensation capacitor with a proper capacitance value through the shared bridge arm structure, so that the lightweight operation of a converter valve can be realized. In order to achieve the above object, according to a first aspect of the present invention, there is provided a hybrid MMC flexible dc converter structure based on a shared bridge arm, which includes three-phase main circuits, wherein each phase main circuit includes an upper bridge arm dc switch group, a lower bridge arm dc switch group, an upper bridge arm ac switch group, a lower bridge arm ac switch group, and a shared bridge arm formed by cascading a plurality of full bridge sub-modules; One end of the shared bridge arm in any phase main circuit is respectively connected with the first ends of the upper bridge arm direct current switch group and the upper bridge arm alternating current switch group, the other end of the shared bridge arm is respectively connected with the first ends of the lower bridge arm direct current switch group and the lower bridge arm alternating current switch group, the second ends of the upper bridge arm direct current switch group and the lower bridge arm direct current switch group are used as direct current ports for connecting direct current buses, and the second ends of the upper bridge arm alternating current switch group and the lower bridge arm alternating current switch group are connected to form alternating current ports of each phase main circuit. According to the flexible direct current conversion structure provided by the invention, the switching states of the direct current switch group and the alternating current switch group are controlled, so that the shared bridge arm respectively works in the positive half cycle and the negative half cycle of the output voltage, the functions are equivalent to the upper bridge arm and the lower bridge arm of the traditional full-bridge sub-module MMC, and the topology structure sharing function of the shared bridge arm is realized. Further, the mixed MMC flexible di