1. On the nature of unstable equilibrium points in power systems;Berggren;Power Systems, IEEE Transactions on,1993
2. BMU (2013) Renewable energy sources in figures – national and international development. URL www.erneuerbare-energien.de/files/english/pdf/application/pdf/broschuere_ee_zahlen_en_bf.pdf.
3. Borsche, T., Ulbig, A., Koller, M., and Andersson, G. (2013) Power and Energy Capacity Requirements of Storages Providing Frequency Control Reserves. In IEEE PES General Meeting. Vancouver.
4. Chiang, H.D., Wu, F.F., and Varaiya, P.P. (1987) Foundations of Direct Methods for Power System Transient Stability Analysis. IEEE Transactions on Circuits and Systems. ENTSO-E (2009). Operation Handbook. URL www.entsoe.eu/resources/publications/entso-e/operation-handbook/.
5. Chaotic motions in the two-degree-of-freedom swing equations;Kopell;IEEE Transactions on Circuits and Systems,1982