Electric vehicle traction motor control

Abstract From the Canadian patent

An electric vehicle traction motor control circuit includes a main thyristor in series with the motor armature. A second thyristor is connected in series with a commutating capacitor across the main thyristor which can be switched off by firing the second thyristor so that the motor current is diverted into the commutating capacitor. A third thyristor is connected in series with an inductor across the commutating capacitor and serves when fired to reverse the voltage re??ding on the commutating capacitor following commutating. The reversed voltage on the capacitor is detected and is used to control upper and lower current limit signals set by a driver operable control so that the capacitor …