Passivity-Based Sensitivity Analysis regarding Control Structures in Grid-Following MMC-HVdc Applications

This contribution focuses on high voltage dc current transmission systems comprising modular multilevel converters and conducts a passivity-based stability assessment with respect to the overall impact of inner control structures. The investigation is motivated by previous research, where it was found that the implementation of inner control structures plays an important role in terms of damping and passivity properties over a broad frequency range.Within this contribution, the inner control's impact is investigated under consideration of outer loop dynamics. Here, a thorough analysis of the converter input-admittance is carried out in order to determine challenges related to control design. The analysis especially focuses on operation point sensitivity as well as on the impact of inner control design and structure at low harmonic orders.