Abstract The process is used in a vehicle having a heat engine (11) which drives a three-phase generator (12) which supplies a two wire DC system (2) through an AC/DC convertor (13). A propulsion unit (3) consisting of an invertor (14) and motor (16) drives road wheels (4). Optional units such as battery (6), power absorber (7) and air-conditioning (8) may also be installed. An electronic control unit (20) receives driver signals for traction or braking (21,22), motor speed (V) and equipment state (X) data, also a supply voltage signal Uo. One of the power systems (3,6,7,8) is defined as the balancing unit and the supply voltage (Uo) is regulated to a preset value (Uoc).