Flexible DC power distribution network with coexistence of multiple types of converters and fault isolation method thereof

Abstract

The invention discloses a flexible DC power distribution network with coexistence of multiple types of converters and a fault isolation method thereof. The flexible DC power distribution network withthe coexisting multiple types of converters comprises a modular multilevel converter MMC, a voltage source converter VSC and a direct-current transformer DCT. The method aims at solving the problem offault isolation of a flexible direct-current power distribution network where MMC, VSC and DCT coexist, an improved ET-MMC topology is designed by adding an external thyristor parallel branch, a current-limiting reactor and an energy consumption module in the half-bridge MMC topology to realize self-clearing of a direct current fault, and the defect of uncontrolled rectification of the half-bridge MMC is overcome. For VSC and DCT, residual energy is absorbed by newly adding an on-state low-loss branch, a converter side energy absorption branch and a line energy absorption branch.

Description

technical field [0001] The invention belongs to the field of electric power technology, and in particular relates to a flexible direct current distribution network with coexistence of multiple types of converters and a fault isolation method thereof. Background technique [0002] In recent years, the proportion of distributed energy and DC loads in the power system has been increasing. Using DC grids to realize the consumption of distributed energy and the access of DC loads can save power electronic converter equipment and reduce investment costs. The converter technology to realize AC and DC conversion is one of the core technologies of the flexible DC grid. Among them, the two-level voltage source converter (Two-level Voltage Source Converter, Two-level VSC) has become the first choice of the initial converter because of its simple control method and good economical advantages. [0003] At present, there are three main types of fault isolation methods for flexible DC sys...

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Problems solved by technology

Most of the above-mentioned improved HB-SM schemes connect thyristors in parallel in the MMC sub-modules. When the number of sub-modules is large, the number of thyristors connected in parallel will increase significantly, which increases the investment cost.

[0005] In addition, in a multi-terminal flexible DC grid with distributed energy access, the types of converters include VSC and DC transformer (DCTransformer, DCT) in addition to MMC. After a DC fault occurs, distributed power may also pass through VSC or DCT Feed current to the fault point, and the above-mentioned literatures only improve the MMC topology, and most of them are aimed at the DC power grid at both ends, and there are few studies on the fault ride-through of VSC and DCT

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