Internal converter- and DC-fault handling for a single point grounded bipolar MMC-HVDC system

In order to address challenges caused by an increasing need for power transmission, embedded bipolar HVDC links utilizing Modular Multilevel Converter (MMC-HVDC) technology present a preferred solution as several operational and dynamic advantages compared to conventional ac grid enforcement are provided. In this paper, an approach to quickly detect and handle internal as well as dc-side faults in a full-bridge bipolar MMC-HVDC link is presented. Due to non-technical reasons and environmental constraints, the system is comprised of mixed overheadline-cable (OHL-cable) transmission and single point solid grounding with dedicated metallic return (DMR). To validate and evaluate the proposed concept, detailed electromagnetic transient (EMT) simulations are provided. These highlight effects of mixed transmission system design on transient voltage and current stresses as well as on converter-internal quantities.