Energy supply unit with series connected step-up converter

The unit (2) has a direct current-direct current converter (8) i.e. bidirectional voltage converter, comprising a primary port (15) connected to a direct-current power source i.e. battery (6). A secondary port (19) of the converter supplies power to a direct current intermediate circuit (27). A low potential output (22) of the secondary port is short-circuited with a high potential-input (16) of the primary port. An inverter (10) generates alternating voltage for a three-phase electric motor (4), where a primary side of the converter is equipped with serially connected switching bridges.