Controlling a combined polymer fuel cell and directional battery system maintaining efficiency at the optimum pointYuriy Kozhubaev, Elena Ovchinnikova, Svetlana Krotova, Aleksei Ilin and Aref SabbganE3S Web of Conf., 389 (2023) 02014DOI: https://doi.org/10.1051/e3sconf/202338902014