A vector energy function approach for security analysis of AC/DC systems

The authors examine dynamic behavior in system models that reflect reasonably detailed third-order high-voltage DC (HVDC) dynamics along with AC system models that include reactive flows, and frequency and voltage-dependent load models. A vector Lyapunov function approach is used to define a system-wide energy function that can be used for general security analysis. They describe the derivation of individual component Lyapunov functions for simplified models of HVDC links connected to infinitely strong AC systems, along with a standard AC only system Lyapunov function. A novel method of obtaining weighting coefficients to sum these components for the overall system energy function is proposed. Use of the new energy function for transient stability and security analysis was illustrated in a test system