Low-Loss Modular Multilevel DC Transformer with Fault Blocking Capability

Abstract

The present invention provides a low-loss modular multi-level DC transformer with fault blocking capability, which includes two subsystems and a three-phase power frequency transformer, each subsystem includes three phase units, and each phase unit is divided into upper and lower The lower bridge arm, each bridge arm includes several sub-modules connected in series, the sub-module topology consists of two half-bridge structures, four capacitors and two freewheeling diodes, in the half-bridge structure, the first half The bridge includes a first switch module and a second switch module, and the second half-bridge includes a third switch module and a fourth switch module; the negative pole of the first switch module is connected to the positive pole of the second switch module, and the first switch module The negative pole of the second switch module is connected to the positive pole of the third switch module, and the negative pole of the third switch module is connected to the positive pole of the fourth switch module. The present invention can realize the fault blocking of the short circuit of the DC side by controlling the switching of the switch module without increasing the loss at the same time.

Description

Technical field [0001] The present invention relates to the technical field of power system transmission and distribution, in particular to a low-loss modular multilevel DC transformer with fault blocking capability. Background technique [0002] With the increase of renewable energy power generation, the grid connection of renewable energy has become a very important research direction. [0003] Flexible DC transmission technology provides a solution for the grid connection of renewable energy and has strong technical advantages. Concepts such as multi-terminal DC and DC grid have also been proposed and have begun to be used in actual systems. [0004] In the DC power grid, there are often some DC-DC converters used to boost the DC voltage or reverse the voltage polarity. Where DC voltages on both sides need to be isolated. Usually an isolated DC transformer is used. [0005] The structure of the DC transformer is relatively diverse, among which there is a DC transformer that uses...

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Problems solved by technology

[0009] However, the above-mentioned patents have the following disadvantages: in the normal operating state, the driving signals for each thyristor must be kept at the same time, and the voltage equalization of each thyristor must be guaranteed during operation, which puts forward higher requirements for the driving circuit and voltage equalizing circuit

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