Method for controlling a power plant comprising at least one drive system (6, 6'), said drive system (6, 6') comprising a source (7, 7') of electric energy and a motor device (60, 60') electrically connected to said source (7, 7') of electric energy, said source (7, 7') comprising an electric generator (70, 70') and an electric energy storage system (75, 75') electrically arranged parallel to said electric generator (70, 70'), said electric generator (70, 70') being provided with at least one fuel cell (71, 71'), said electric energy storage system (75, 75') being provided with at least one rechargeable electric energy storage device (76, 76') and a reversible electric converter (78, 78'), said method comprising the following steps of: - transmitting a first electric current by means of said electric generator (70, 70'); - measuring a first electric voltage relating to said first electric current to electric terminals of said electric generator (70, 70') using a measuring device; - comparing the first electric voltage with an electric voltage threshold using a management device (10, 10') of said power plant; and - transmitting a second electric current with a second electric voltage by means of said electric energy storage system (75, 75') when said first electric voltage is below said electric voltage threshold; characterised in that, during said step of transmitting a first electric current by means of said electric generator, said at least one fuel cell (71, 71') operates alternately in several operating modes respectively associated with predetermined operating points of said at least one fuel cell (71, 71'), with said electric voltage threshold corresponding to said predetermined operating point for each operating mode, such that: - either in a first operating mode associated with a first predetermined operating point, a heat dissipation of said at least one fuel cell (71, 71') is reduced; or - either in a second operating mode associated with a second predetermined operating point, a maximum power is provided by said at least one fuel cell (71, 71'); or - either in a third operating mode associated with a third predetermined operating point, a fuel consumption of said at least one fuel cell (71, 71') is limited. said method comprising the following steps of: - transmitting a first electric current by means of said electric generator (70, 70'); - measuring a first electric voltage relating to said first electric current to electric terminals of said electric generator (70, 70') using a measuring device; - comparing the first electric voltage with an electric voltage threshold using a management device (10, 10') of said power plant; and - transmitting a second electric current with a second electric voltage by means of said electric energy storage system (75, 75') when said first electric voltage is below said electric voltage threshold; - transmitting a first electric current by means of said electric generator (70, 70'); - measuring a first electric voltage relating to said first electric current to electric terminals of said electric generator (70, 70') using a measuring device; - comparing the first electric voltage with an electric voltage threshold using a management device (10, 10') of said power plant; and - transmitting a second electric current with a second electric voltage by means of said electric energy storage system (75, 75') when said first electric voltage is below said electric voltage threshold; characterised in that, during said step of transmitting a first electric current by means of said electric generator, said at least one fuel cell (71, 71') operates alternately in several operating modes respectively associated with predetermined operating points of said at least one fuel cell (71, 71'), with said electric voltage threshold corresponding to said predetermined operating point for each operating mode, such that: - either in a first operating mode associated with a first predetermined operating point, a heat dissipation of said at least one fuel cell (71, 71') is reduced; or - either in a second operating mode associated with a second predetermined operating point, a maximum power is provided by said at least one fuel cell (71, 71'); or - either in a third operating mode associated with a third predetermined operating point, a fuel consumption of said at least one fuel cell (71, 71') is limited. - either in a first operating mode associated with a first predetermined operating point, a heat dissipation of said at least one fuel cell (71, 71') is reduced; or - either in a second operating mode associated with a second predetermined operating point, a maximum power is provided by said at least one fuel cell (71, 71'); or - either in a third operating mode associated with a third predetermined operating point, a fuel consumption of said at least one fuel cell (71, 71') is limited.