A Parallel Connected Unfolding Bridge (PCUB) Multilevel Converter for HVDC Applications

Abstract

Hybrid Voltage Source Converters (VSC), that combine the conventional three-level VSCs and Modular Multilevel Chain-Links (CLs), offer a promising solution for future HVDC stations, achieving reduced footprint with respect to the MMC while maintaining high power quality and low loss. This paper introduces a new hybrid solution named 'Parallel Connected Unfolding Bridge Modular Multilevel Converter' (PCUB) which uses a parallel connection of phases on the DC side and comprises of wave shaping Chain-Links and unfolding H-bridges. This paper presents the operating principle and basic mathematical model of the PCUB and also details an optimisation of the transformers turn ratio for the minimisation of the energy requirements in the CLs. PLECS simulation results for the proposed topology operating at 20kV DC -11kV AC and 20MW are also presented to demonstrate its performance.

Beyond the MMC: Extended Modular Multilevel Converter Topologies and Applications

“…The PCUB has the potential to handle dc faults due to the introduction of FBSMs. During the operation of the PCUB, the energy of both, the HBSM and FBSM arms, need to be balanced leading to a complicated controller design [43].…”