Ride-through protection circuit for a voltage source inverter traction motor drive

Drive apparatus for an AC traction motor, comprising:

• source means including an engine driven machine for developing a DC supply voltage across a pair of DC supply terminals;
• inverter means for supplying alternating current to one or more windings of said traction motor from a pair of DC load terminals;
• means including a first thyristor for connecting said DC supply terminals to the DC load terminals of said inverter means, the first thyristor being adapted when supplied with a gate signal to enable said source means to supply load current to said inverter means;
• a commutation circuit including a second thyristor and commutation capacitor connected in series across said DC supply terminals, the second thyristor being adapted when supplied with a gate signal to divert said current supplied by said source means;
• and
• control means operative in response to a detected fault condition during the supply of load current to said inverter means for (1) interrupting the gate signal supplied to said first thyristor, (2) supplying a gate signal to said second thyristor, whereby said first thyristor is commutated to isolate said source means from said inverter means and inductive energy stored in said source means is transferred to said commutation capacitor.