**Acknowledgements**

This work was supported in part by the National Scientific and Technical Research Council (CONICET) and the Agency for Promotion of Science & Technology (ANPCyT), Argentina. The financial support of the German Academic Exchange Service (DAAD) is also gratefully acknowledged. The authors also thank the support of the colleagues at the Institute of Power Systems and Power Economics (IAEW), RWTH Aachen, Germany, especially Univ.-Prof. Dr.- Ing. Albert Moser as well as colleagues at Institute of Electrical Energy (IEE), National University of San Juan, Argentina.
