Parallel Hybrid Converter: Derived Topologies and Control

Abstract

Modular multilevel converter (MMC) has gained a huge research interest for high voltage direct current (HVDC) applications. Recently significant research has been carried out to develop hybrid MMC to address the technical constraints of the MMC. Parallel hybrid converter (PHC) is the most promising topology for high power applications due to its series connected chain-links on dc side and smaller sub-module capacitors. Moreover in PHC, the chain-link SMs are not in the main conduction path and the H-bridges are switched at fundamental frequency, which leads to lower semiconductor losses. However, the dc and ac side of the PHC are strongly coupled which lead to a fixed output voltage without using a dedicated control to tackle this issue. Moreover, PHC loses controls during dc fault. Various methods have been proposed in literature to decouple the dc and ac side of the converter and to make it tolerant to dc fault. In this paper, a review of these state of art control strategies are presented. This paper contributes in summarizing key benefits and limitations of various existing control methods through extensive analyses and simulation studies.