A new hybrid multi-level voltage-source converter with DC fault blocking capability

Abstract

Voltage-Source Converters have brought numerous advantages to HVDC transmission. However, they suffer from high losses and are usually weak against faults on the DC-side. In this paper, a new topology which brings together some concepts from traditional Current Source Converters and multi-level converters, is presented. Two stacks of Hbridge cells alternate to construct the converter voltage using director switches made of IGBTs in series. The resulting converter generates AC current with low harmonic content and with low loss. Furthermore, the converter is still very responsive in case of a fault. This paper first explains the composition and the working of this converter, then detailed simulations at 20 MW illustrate the performances and low losses of this converter under normal conditions. The ability of this topology to deal with abnormal conditions is also demonstrated, especially its ability to keep control of the current despite the collapse of the DC bus voltage, e.g. a DCside fault.

Zero phase sequence voltage injection for the alternate arm converter

“…In [4] and [5] two methods to control the energy stored in the cells were presented. The energy exchanged by one of the methods, the overlap current, is proportional to the length of the overlap angle, as described in equations (6) and (7) from [5].…”

DC fault ride‐through capability and STATCOM operation of a HVDC hybrid voltage source converter

“…Under normal operating conditions the converter is controlled using a method presented in [14]. Using this method the six director switches, shown in Fig.…”

Assessment of DC/DC converters for use in DC nodes for offshore grids

“…The following subsections will examine different topologies for high-voltage, high-power DC/DC converters. There are several DCAC/DC converters proposed in [10], with the first one presented being a converter based upon the multi-level VSC topology from [6], the Alternate Arm Converter (AAC). The AAC is modular, providing low effective switching rates, redundancy and increased reliability.…”

“…The main restriction with realising a DC grid has been the lack of a commercially available DC circuit breaker [3], [4], although one has been proposed, and tested at 80 kV, [5]. There have also been VSC converters presented that have the ability to block DC faults [6], [7].…”