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http://dx.doi.org/10.5370/KIEE.2015.64.8.1193

A Study of Circulating Current in MMC based HVDC System under an Unbalanced Grid Condition  

Do, Won-Seok (Dept. of Electrical Engineering Hanyang University)
Kim, Si-Hwan (Dept. of Electrical Engineering Hanyang University)
Kim, Tae-Jin (Living & Energy R&D Center, LG Electronics)
Kim, Rae-Young (Dept. of Electrical and Biomedical Engineering Hanyang University)
Publication Information
The Transactions of The Korean Institute of Electrical Engineers / v.64, no.8, 2015 , pp. 1193-1201 More about this Journal
Abstract
This paper presents a study of circulating current of modular multi-level converter (MMC) based a high voltage direct current (HVDC) system under unbalanced grid conditions. Due to the connection of a dependent DC source in each phase, the MMC system inherently generates the power ripple of double-line-frequency components in the AC-side and as a result, the additional sinusoidal current named circulating current flows through the each arm. Reliability improvement of HVDC system under an unbalanced grid condition is one of the important criteria. Generally, the modeling of the circulating current is based on the power relation between DC-side and AC-side. However, the method is not perfectly matched in the MMC system due to the difference of the structural characteristic. In this paper, improved modeling method of circulating current is proposed, which is based on the inner arm power. The proposed method is verified by several simulations to have good agreement of the circulating current components.
Keywords
Circulating current; Modular multi-level converter (MMC); High voltage direct current (HVDC);
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