An alternative synchronous machine model for Quasi-Steady-State simulations

The conventional system model for quasi-steady-state (QSS) simulation considers a current injection equilibrium model of the synchronous machine and a nodal admittance matrix model of the transmission system. An alternative representation of the system for QSS simulation, referred to as the ldquoreduced to the network modelrdquo has also been proposed, but has been considered less accurate or convenient than the conventional model. In this paper we present the basics and improvements to the synchronous machine model used in the ldquoreduced to the network modelrdquo with special attention to the accuracy of the results. Accuracy is tested by a direct comparison between QSS simulation results and the ones obtained by a transient stability program, on an IEEE test system, using detailed modeling of the synchronous machines and their controls. We review the performance of the synchronous machine model in the operating region in which machine variables are within their permissible operating limits. The proposed new synchronous machine model is represented by its Q-V characteristic, in a similar way to the Q-V characteristic of a SVC, but in this case the slope of the linear part varies with system operating conditions. According to the results of extensive simulations, considering the effect of different static load characteristics, this improved synchronous machine model can also achieve an excellent accuracy in long term time-domain simulations.