This paper joins a series of papers dealing with high-speed power system emulators. It clarifies the last details about the system level of the AC emulation approach by analyzing and quantifying the systematic errors introduced during modeling. Thereby a new optimized generator model has been developed. Its main advantage is improved stability. The functionality of this optimized model is proven by behavioral simulation comparing its results to results of a numerical reference simulator and to the original generator model. © 2010 by Department of Microelectronics & Computer Science, Technical University of Lodz.