Highly reliable and consistent starting is achieved by first initializing the rotor position, namely establishing the rotor in a known starting position. This is accomplished by gating on two pairs of SCRs in sequence and supplying current pulses through the gated SCRs to the stator of the motor to rotate...http://www.google.com/patents/US4565957?utm_source=gb-gplus-sharePatent US4565957 - Method and system for starting a motor-commutated SCR inverter
