Multi-terminal multi vendor HVDC grid design studies - Part II: dynamic study

Multi-Terminal (MT) HVDC networks have been studied for over a decade, with recent efforts increasingly focusing on enabling multi-vendor interoperability to support a competitive and scalable deployment framework. Concurrently, protection selectivity is receiving renewed attention in the context of large-scale offshore connections based on 2 GW bipolar building blocks, where the maximum loss of infeed has become a critical planning constraint. This three-part series addresses early-stage system-level studies of MT HVDC grids using generic models, which are essential to support primary design. As part of the InterOPERA project, involving HVDC vendors traditionally responsible for DC-side design in point-to-point schemes, a methodology is proposed to refine, and eventually instantiate, project-specific technical requirements at the DC point of connection of AC/DC converters. This second part focuses on dynamic studies, quantifying maximum DC voltage excursions resulting from single and bipole outages, as well as temporary loss of power caused by converter blocking and grid-side AC faults. The variability of these excursions is examined as a function of two key design parameters: AC/DC converter reactor sizing and control settings. Time-domain simulations reveal that relatively higher stresses observed at one location are caused by large oscillations triggered by a specific blocking event. Frequency-domain assessment provides further insight into the underlying resonance phenomena.