Grid connection method of MMC-type light direct-current power transmission system

Abstract

The invention discloses a grid connection method of an MMC-type light direct-current power transmission system. A virtual synchronization control method is combined with an MMC so that switching of operation modes of the MMC-type light direct-current power transmission system can be carried out, a special synchronization control circuit is needless, the system can be automatically synchronized with a power grid before grid connection, pre-synchronization time is short, the system can accurately follow frequency of the power grid after grid connection, and friendly grid connection is achieved.

Description

technical field [0001] The invention relates to the field of power electronics, in particular to a method for grid connection of an MMC (modular multilevel converter) type light direct current transmission system (HVDC-Light). Background technique [0002] In recent years, with the aggravation of energy and environmental problems, the penetration rate of renewable energy such as solar energy and wind energy in the power system has been increasing. With the improvement of distributed power capacity and voltage level, especially the development of offshore wind power, light direct current transmission has emerged as the times require. As the main circuit of the light DC transmission system, MMC can effectively reduce the harmonic content of the output voltage and realize high-voltage and high-power operation. Distributed power generation has the characteristics of being dispersed and close to the load. If it can realize smooth switching between grid-connected and island-conne...

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Problems solved by technology

[0003] 1. Operation mode switching control adopts dual-mode control technology. PQ current control method is adopted for grid-connected operation, and V / f control method is adopted for island operation. The dual-mode control technology meets the needs of micro-grid operation, but there is a gap between voltage control and current control. Switching is difficult, there is a risk of switching failure, and it is necessary to detect island information to determine whether switching control strategies are required

[0004] 2. The general droop control is adopted, and its control strategy remains unchanged in grid-connected operation and islanded operation mode, which conforms to the characteristics of plug and play, but does not consider the adaptability of droop control to grid-connected operation, and may There is a large inrush current

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