Spanik, P., J. Sedo, P. Drgona, and M. Frivaldsky. “Real Time Harmonic Analysis of Recuperative Current through Utilization of Digital Measuring Equipment”. Elektronika Ir Elektrotechnika, vol. 19, no. 5, May 2013, pp. 33-38, doi:10.5755/j01.eee.19.5.4364.