Control circuits for electrically driven vehicles

Claim 1

A control circuit for an electrically driven vehicle, comprising in combination a traction motor driving the vehicle, a thyristor chopper circuit controlling the speed of the traction motor, said chopper circuit including a main thyristor in series with the motor, and a commutating thyristor which when fired turns off the main thyristor, means controlling the instants of firing of the thyristors to regulate the mean current flow in the motor, said means including an operational amplifier having first and second states, the operational amplifier serving when it is driven from its first state to its second state to fire the main thyristor, and serving when it is driven from its second state to its first state to fire the commutating thyristor, means for sensing current flow through said motor and for driving said operational amplifier to said first state when a predetermined current level is sensed through said motor, the circuit further including delay means which operates when the main thyristor is fired and when the current through said current sensing means is below said predetermined level for driving said operational amplifier to its first state after a predetermined delay.