On Full-Bridge Bipolar MMC-HVDC Control and Protection for Transient Fault and Interaction Studies

Bipolar high voltage direct current (HVdc) links present one reasonable solution to realize bulk power transmission schemes. Especially if full-bridge modular multilevel converter topologies (FB MMC) are utilized, a broad variety of operational advantages exists. To completely unveil intrinsic technological potentials, comprehensive control and protection concepts to discriminate and handle ac, dc, as well as internal converter faults are essential. The proposed scheme consists of a fast and selective multizonal fault detection paired with decoupled ac and dc current controls. As a result, actively controlled dc fault current interruption as well as ac fault reactive current injection are incorporated. It is demonstrated that internal converter quantities remain within feasible technical boundaries, interactions are limited or even fully mitigated, and protection thresholds can be chosen to enable selective tripping. To validate and evaluate the proposed concept, simulations for characteristic faults are performed in electromagnetic transients software.