Isolated-type DC-DC converter based on MMCs and control method of isolated-type DC-DC converter

Abstract

The invention provides an isolated-type DC-DC converter based on MMCs and a control method of the isolated-type DC-DC converter. The isolated-type DC-DC converter comprises a high-frequency transformer, the first MMC and the second MMC; one side of the high-frequency transformer is connected with a high-voltage flexible direct-current transmission network VSC-HVDC based on a voltage source type converter through the first MMC; the other side of the high-frequency transformer is connected with a high-voltage direct-current transmission network LCC-HVDC based on a line commutated converter through the second MMC; sub-modules of all bridge arms in the first MMC are each of a half-bridge structure; and sub-modules of all bridge arms in the second MMC are each of a full-bridge structure. The topological structure combining the full-bridge MMC and the half-bridge MMC is adopted to realize reliable interconnection of LCC-HVDC and VSC-HVDC, safe and stable operation of a hybrid direct-currentinterconnection system is supported, and a foundation is laid for the situation that new energy sources adopt the hybrid direct-current interconnection system for outgoing on large scale.

Description

technical field [0001] The invention relates to the field of hybrid DC interconnection grids, in particular to an MMC-based isolated DC-DC converter and a control method. Background technique [0002] In recent years, new energy power generation has developed rapidly. As of the end of 2017, only China's installed capacity of wind power reached 164 million kilowatts, and the installed capacity of photovoltaic power generation reached 130 million kilowatts, ranking first in the world. However, due to the reverse distribution of new energy resources and loads in most cases, large-scale new energy long-distance transmission has become the main way for new energy to be delivered and consumed. The transmission of new energy with weak synchronous support or even without synchronous support has become a research hotspot. With the development of DC transmission technology, large-scale new energy has become a development trend through DC long-distance transmission. [0003] After de...

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Problems solved by technology

However, LCC-HVDC adopts thyristor device phase-controlled converter LCC, when the power flow reverses, the voltage polarity reverses and the current direction remains unchanged, and VSC-HVDC adopts a voltage source converter, and the voltage polarity does not change when the power flow reverses. Direction, VSC-HVDC and LCC-HVDC cannot be directly connected, how to connect VSC-HVDC and LCC-HVDC becomes an important research topic

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