Low-loss modular multilevel direct-current transformer with fault blocking capability

Abstract

The invention provides a low-loss modular multilevel direct-current transformer with a fault blocking capability. The system comprises two subsystems and a three-phase industrial frequency transformer, wherein each subsystem comprises three phase units; each phase unit is divided into an upper bridge arm and a lower bridge arm; wherein each bridge arm comprises a plurality of sub-modules which areconnected in series, each sub-module topology is composed of two half-bridge structures, four capacitors and two fly-wheel diodes, in each half-bridge structure, a first half bridge comprises a firstswitch module and a second switch module, and a second half bridge comprises a third switch module and a fourth switch module; the negative electrode of the first switch module is connected with thepositive electrode of the second switch module, the negative electrode of the second switch module is connected with the positive electrode of the third switch module, and the negative electrode of the third switch module is connected with the positive electrode of the fourth switch module. Fault blocking of direct-current side short circuit can be achieved by controlling on-off of the switch module, and meanwhile losses are not increased.

Description

technical field [0001] The 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 integration of renewable energy into the grid has become a very important research direction at present. [0003] The flexible direct current transmission technology provides a solution to solve the grid connection of renewable energy, and has strong technical advantages. Concepts such as multi-terminal direct current and direct current power grid have also been proposed and started to be applied to practical systems. [0004] In the DC power grid, there are often some DC-DC converters for boosting the DC voltage or reversing the polarity of the voltage. In the case where the DC voltage on both sides needs to be isolated. Typically an isolated DC transformer is used. [0005] T...

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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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