Optimal supercapacitor energy storage system sizing for traction substationsSirmelis, Ugis; Zakis, Janis; Grigans, Linards2015 IEEE 5th International Conference on Power Engineering, Energy and Electrical Drives (POWERENG) : proceedings : May 11-13, 2015, Riga, Latvia2015 / p. 592-595 : ill http://dx.doi.org/10.1109/PowerEng.2015.7266383