Starting requirements of a range extender for electric vehicles: Based on a small size 4-stroke engine

It is convenient to use the generator of a range extender also for starting the engine. The torque needed by the engine at the early stage of engine cranking has been modeled. The sum of the torques developed by the starter/generator and the rotational inertia including the flywheel, have to be sufficiently large in order to overcome the compression torque so as to ensure a successful start of the engine. In order to minimize the torque required from the electric motor, the concept of flywheel effect can be used. This brings the possibility to downsize the converter. By reducing the torque demand from the motor, one can limit the current drawn from the source, thereby giving reliability to the switching devices.