The Delta-Configured Modular Multilevel Converter

Abstract

The modular multilevel converter (MMC) has become an attractive option for dc/ac conversion in many power system applications, in particular for HVDC transmission. Due to its parallel arrangement of phase legs the MMC is known to be a wye configured architecture. In this paper, the equivalent delta formulation of the conventional wye architecture is introduced. The delta configured MMC, enabled by series-stacking phase legs, is an alternative realization to the wye configured MMC and has significantly different operating characteristics. Introduction of the delta MMC enables greater flexibility in converter voltage/current scaling for a given set of submodules, and may be an appealing option for dc/ac applications requiring a power tap-off from a high-voltage dc rail. The single-ended and differential delta topologies are derived, with the latter seen as the preferred topology due to its reduced energy storage requirements. The principle of operation of the differential delta configured MMC is described in detail. A dynamic controller is developed that regulates grid power injections while suppressing unwanted circulating ac currents. Comprehensive simulation results validate the differential delta MMC operation and proposed control scheme.

Recent contributions and future prospects of the modular multilevel converters: A comprehensive review

“…Delta‐configured MMC topology is proposed by Kish et al as an alternative of traditional wye‐configured MMC for DC/AC power conversion applications. Proposed topology has different operating performance as well as control stage.…”