Licentiate seminar – Roberto Felicetti (HydroFlex PhD candidate, Uppsala University)

Roberto Felicetti is a PhD Candidate at the Division of Electricity of Uppsala University in Sweden. He has been Licentiate seminarconducting research under WP4 of HydroFlex.

His Licentiate seminar will be conducted on Friday 12th of March at 10:00(CET) entitled “Voltage Transients in the Field Winding of Salient Pole Wound Synchronous Machines – Implications from fast switching power electronics”. Opponent will be Dr. Jon Kjellin.
The seminar will be held online via Zoom:


Wound Field Synchronous Generators provide more than 95% of the electricity need world-wide. Their primacy in electricity production is due to ease of voltage regulation, performed by simply adjusting the direct current intensity in their rotor winding. Nevertheless, the rapid progress of power electronics devices enables new possibilities for alternating current add-ins in a more than a century long DC dominated technology. Damping the rotor oscillations with less energy loss than before, reducing the wear of the bearings by actively compensating for the mechanic unbalance of the rotating parts, speeding up the generator with no need for additional means, these are just few of the new applications which imply partial or total alternated current supplying of the rotor winding.

This thesis explores what happens in a winding traditionally designed for the direct current supply when an alternated current is injected into it by an inverter. The research focuses on wound field salient pole synchronous machines and investigates the changes in the field winding parameters under AC conditions. Particular attention is dedicated to the potentially harmful voltage surges and voltage gradients triggered by voltage-edges with large slew rate. For this study a wide frequency band simplified electromagnetic model of the field winding has been carried out, experimentally determined and validated. Within the specific application of the fast field current control, the research provides some references for the design of the rotor magnetic circuit and of the field winding. Finally the coordination between the power electronics and the field winding properties is addressed, when the current control is done by means of a long cable or busbars, in order to prevent or reduce the ringing.

Keywords: apparent resistance, cable modeling, current control, transmission line model, eddy currents, field winding, frequency analysis response, Fourier Transform, impedance mismatch, main inductance, over-voltage, parasitic capacitance, partial discharge, quality factor, ringing, slew rate, stray inductance, voltage gradient, winding resonance frequency.

The Thesis will be available for download from: