Patent ID: 6967461

Claim:
A north-south discriminator for discriminating between the north and south poles of a rotor for a polyphase alternating current (AC) wound field synchronous machine that has a power frequency representative of rotor angular velocity and current representative of torque and is driven by a control system that comprises a carrier injection sensorless (CIS) position sensing system that uses a polyphase AC carrier signal that has a frequency substantially higher than the power frequency applied to a stator of the machine whilst leaving the rotor unexcited, the rotor being excited by power generated by an exciter through a rotating rectifier, comprising: a polyphase AC to two phase stationary transformation for transforming polyphase second harmonic components of the carrier frequency signal to a two phase stationary reference frame to produce carrier second harmonic positively rotating components and negatively rotating components; a positive sequence carrier second harmonic transformation for transforming the carrier second harmonic rotating components into a positive sequence reference frame for the second harmonic of the carrier frequency; and a low pass filter for low pass filtering the transformed second harmonic components to generate north-south determination signal components representative of the position of the north pole of the rotor.