A drive system and a method of driving a vehicle in which the drive system includes a combustion engine, a brake device for braking the vehicle, an electric machine, an energy storage connected to the electric machine, at least one electric assembly operated by electric energy and a planetary gear including a sun wheel, a ring wheel and a planet wheel holder. A control unit is adapted to, when the vehicle is in motion, a driving moment is demanded and a coupling member is in a first position, based on a comparison between the demanded driving moment and a necessary moment required for operation of the electric assembly, control at least one of the combustion engine, the brake device and the electric machine such that desired electric energy is provided for operation of the electric assembly.