The Extended Overlap Alternate Arm Converter: A Voltage-Source Converter With DC Fault Ride-Through Capability and a Compact Design
Merlin, Michael Marc Claude
Imperial College London
Judge, Paul Daniel
Imperial College London
Chaffey, Geraint
Imperial College London
Clemow, Philip
Imperial College London
Green, Tim C.
Imperial College London
Trainer, David R.
GEs Grid Solut
Dyke, Kevin J.
GEs Grid Solut
Journal
IEEE Transactions on Power Electronics
ISSN
0885-8993
1941-0107
Open Access
hybrid
Volume
33
Start page
3898
End page
3910
The alternate arm converter (AAC) was one of the first modular converter topologies to feature dc-side fault ride-through capability with only a small penalty in power efficiency. However, the simple alternation of its arm conduction periods (with an additional short overlap period) resulted in 1) substantial six-pulse ripples in the dc current waveform, 2) large dc-side filter requirements, and 3) limited operating area close to an energy sweet spot. This paper presents a new mode of operation called extended overlap (EO) based on the extension of the overlap period to 60 degrees, which facilitates a fundamental redefinition of the working principles of the AAC. The EO-AAC has its dc current path decoupled from the ac current paths, a fact allowing 1) smooth dc current waveforms, 2) elimination of dc filters, and 3) restriction lifting on the feasible operating point. Analysis of this new mode and EO-AAC design criteria are presented and subsequently verified with tests on an experimental prototype. Finally, a comparison with other modular converters demonstrates that the EO-AAC is at least as power efficient as a hybrid modular multilevel converter (MMC) (i.e., a dc fault ride-through-capable MMC), while offering a smaller converter footprint because of a reduced requirement for energy storage in the submodules and a reduced inductor volume.