Abstract:
Transient stability studies are required to be carried out for an efficient and secure operation of power systems. However, due to the limitations of computer memory and processing speed, handling a complete set of DAEs (differential-algebraic system of equations) that describe a large scale interconnected power system is difficult and uneconomical. Hence, the transient stability of large power system is generally studied by dividing the system into study and external areas, and the external areas are replaced with a dynamic equivalent circuit to reduce the calculation time. The research on dynamic equivalent circuit is still worth exploring. Therefore, this thesis attempts to propose an approach to obtain a dynamic equivalent circuit for the external system.
In the proposed method, a dynamic equivalent circuit is obtained by adding equivalent generators to boundary buses of a static equivalent circuit. The static equivalent circuit of the external system can be constructed utilizing the static network reduction features available in PSS/E. Coherent generator groups within the external system are identified using the non-linear time domain simulation combined with Prony analysis both available in PSS/E. If a complete set of dynamic parameters are available, the parameters of equivalent models are calculated by aggregation methods. If not, the optimization techniques based on minimizing the cost function are utilized to determine the model parameters of equivalent machines, where the cost function is defined as the sum of squares of the difference between equivalent system transient voltage results and the full system transient voltage results. The proposed method is validated with the New York and New England IEEE 68-bus system. The simulation has shown that the developed equivalent system is good at mimicking the dynamic features of the original system.
