A first aspect of the present invention is concerned with a series hybrid drive train for a vehicle comprising a traction motor, an electric generator, a three-position clutch (20) and a controller. The three-position clutch allows the generator to be connected to an internal combustion engine (12) of the vehicle, to the traction motor or to remain freewheeling. In a second aspect of the present invention, a four-position clutch is used to further allow the internal combustion engine to be connected directly to the wheels to thereby yield a series/parallel drive train. A third aspect of the present invention is concerned with a method of operating such a hybrid drive train.