Semi-analytical fault-on trajectory simulation and its application in direct methods

This paper proposes a time series based semi-analytical solution (SAS) which can approximately represent the solution of dynamical power system equations within a short period of time. All system parameters and initial conditions are represented by symbolic variables such that different system operating conditions and contingencies can be completely considered in the evaluation of any power system. The proposed SAS is accurate at the initial point while its error increases over time. It is observed that using the SAS for approximating the fault-on trajectory is fairly accurate. Since faults in a power system are cleared after a short period of time, i.e 5 or 6 cycles (.08 to .1 seconds), then the proposed SAS can be integrated with any direct methods to access the transient stability of the system. A decoupling based direct method is used in this paper along with the proposed SAS for demonstration purposes. Case studies performed on the IEEE 9-bus system and the simplified WECC 179-bus system show the accuracy of the proposed SAS and its application in transient stability analysis using direct methods.