Transient Stability Analysis of Multi-Machine AC/DC Power Systems Via Energy-Function Method

In this paper, the direct method of stability analysis using energy functions is applied for single and multi-machine AC/DC power systems. The system loads including the terminal characteristics of the DC link are represented as constant current type loads, and their effects on the generators at the internal nodes are obtained as additional bus power injections using the method of distribution factors, thus avoiding transfer conductance terms. Using the center of angle formulation, a modified form of the energy-function method is used for the swing equations and the DC link dynamical equations to compute the critical clearing time for a given fault. Numerical results of critical clearing time for a single and multi-machine system using the energy-function method agree well with the step-by-step method.