Stability Analysis of Two Renewable Systems Fed to Two Power Grids through a Four-Terminal HVDC Link based on a Modular Multilevel Converter

This paper analyzes the stability of a multi-terminal high-voltage direct current (MTHVDC) link based on a modular multilevel converter (MMC) to integrate an offshore wind farm (OWF) and an ocean thermal energy conversion system (OTECS) into two power grids. The results of small-signal stability of the studied system under different operational conditions are first examined. The damping controllers for the MMC to damp low-frequency oscillations of the studied system are designed using modal control theory. Dynamic responses of a nonlinear system model subject to a disturbance finally evaluate the damping controllers' performance. The simulation results show that the designed damping controller for the MMC of the MTHVDC can improve the stability of the studied system subject to different operating conditions and disturbances. © 2025 IEEE.