Equal‐area criterion and analytical model for transient stability assessment of hybrid AC–DC transmission system using voltage sourced converter

Abstract An analytical model for transient stability assessment of hybrid AC–DC transmission systems is formulated, implemented, and validated. The equal‐area criterion, as known from the transient stability analysis of AC power systems, is redeveloped for AC–DC power systems using high‐voltage direct current (HVDC) transmission based on the voltage sourced converter and in particular the modular multilevel converter (MMC). Through the proposed analytical solution, the critical clearing angle and the critical clearing time are obtained through symbolic calculations for the most severe DC and AC short‐circuit faults. The assumptions made to enable the formulation of the analytical solution are conservative with respect to the assessment of transient stability. Since the analytical solution is a function of main system parameters and prefault active power flows, it offers an answer to an entire set of problems. It so yields a direct method of transient stability assessment that provides an in‐depth and educational insight into the parameters influencing transient stability. As an illustrative application, the impact of scheduled power flows on DC versus AC lines on the transient stability is analysed. In the performed validation involving the comparison with a computationally more expensive numerical solution, the assumptions underlying the analytic solution were justified