Abstract: A motor control circuit includes a chopper circuit (11) including a main switching element (14) which is connected in series with the motor armature (12). The chopper is controlled by a Schmitt bistable circuit (34) which operates to switch the main switching element on when the actual motor current falls more than a set amount below a demanded level and off when the actual motor current rises more than a set amount above the demanded level, the demand level is determined by the driver's pedal controlled potentiometers (37, 38) but is required to be modified in accordance with the motor speed. Instead of using a mechanical speed transducer, the present invention includes a circuit (40) which is connected to the output of the bistable circuit (34) and produces a signal varying in accordance with the ratio of the on and off times of the main switching element.

Abstract: A d.c. motor control circuit includes an armature current chopper including a main thyristor, a commutating thyristor for turning off the main thyristor by diverting the armature current into a commutating capacitor and a third thyristor connected to reverse the voltage on the capacitor. There is a charging path for the capacitor to keep it charged up to the voltage it reaches on commutation and the firing circuits for the thyristors are arranged to ensure that the third thyristor is fired a fixed period before the commutating thyristor. This ensures that there is an adequate reverse voltage on the capacitor for correct commutation to occur.

Abstract: An electric vehicle traction motor control circuit includes separate armature and field current controls. The armature control includes a difference amplifier connected to compare a current demand signal with an actual current signal from a transducer and a switching circuit controlled by this difference amplifier. The field control includes a second difference amplifier which operates to weaken the field current in either of two eventualities. In motoring the second difference amplifier receives its input via a start up circuit which connects the output of the first difference amplifier to the input of the second difference amplifier when the switching means has been in a first state for more than a predetermined time. In this case the field is weakened in accordance with the short fall of the output of the first difference amplifier below a first reference level.

Abstract: An electric vehicle traction motor control circuit includes an armature current control and a separate field current control. The armature current control includes an armature current demand signal generator, a difference amplifier comparing the demand signal with a signal from an armature current transducer. This amplifier drives an armature current switching regulator including a Schmitt trigger. The field current control is arranged to provide a fixed field current normally, which is weakened when the actual armature current fails to reach its demand value.