Synchronous and induction generators operating at variable speed in DC networks

Most of the turbine-generator groups using renewables as primary energy (small hydro plants or wind farms) do not optimally provide the electric power when they have to operate at constant speed in order to supply the electric energy at the rated frequency. In this paper a solution that enables such a generator to operate at highest possible efficiency, i.e. at variable speed, is presented. An ac-dc-ac interface is developed in order to facilitate the integration into distribution networks. For several generators case, the PCC is a DC bus bar which allows a more stable operation and an easier droop control, converting a typical MIMO system into a SISO one.