Estimation of stability region for an interconnected AC/multi-terminal DC grid

This paper introduces a problem on large-signal stability of an interconnection of AC and MTDC (Multi-Terminal DC) grids. We formulate the problem as an estimation of stability region (or basin of attraction) of an asymptotically stable equilibrium point that is exhibited by coupled nonlinear differential-algebraic equations. A candidate of Lyapunov function is introduced for the interconnected AC/MTDC grid in terms of composite dynamical systems. We visualize several slices of the stability region of the interconnected grid under a practical setting of the grid's parameters. The preliminary visualization shows that the stability region can be estimated with the candidate of composite Lyapunov function.