Lightning Surge Analysis for DC Direct-Mounted Battery Energy Storage System in MMC-HVDC System

–Lightning surge overvoltages in a DC direct-mounted battery energy storage system (DCDM-BESS) integrated into a ±500 kV MMC-HVDC link are investigated. An electromagnetic transient (EMT) time-domain model with high-frequency representations of the DCDM-BESS and station equipment is developed to analyze three representative lightning strike scenarios, including tower-strike-initiated metallic return wire (MRW) flashover, direct strikes to the overhead pole wire (OPW) and direct strikes to the MRW. The resulting stress distribution at key measurement points (MPs), including energy storage submodule (ESSM) enclosure-to-ground potentials and the longitudinal voltage across the smoothing reactor (SR), is quantified under different operating modes and MRW installation configurations, and the impact of lightning surge arrester (LSA) arrangements is evaluated. Based on the computed overvoltages, a coordinated protection scheme is proposed, and the required lightning impulse withstand voltages (RLIWV) for ESSM post insulators are derived following an insulation coordination procedure.