Drive system of a battery-operated vehicle with a frequency converter fed permanently excited synchronous machine

The drive system has a permanent magnet synchronous machine (10) whose the stator-side ports (U,V,W) are electrically connected with alternating current (AC)-side terminals (R,S,T) of a self-commutated converter (8) respectively. Three thyristors (44) of a short circuit controlling device (26) are electrically connected in delta connection and are electrically connected with the stator-side port of the permanent magnet synchronous machine.