Initial Rotor Polarity Detection and Sensorless Control of PM Synchronous Machines

Sensorless control of a PM synchronous machine at low and zero speed is based on the injection of an oscillating high-frequency carrier signal. A particular demodulation technique serves to eliminate the estimation error introduced by the nonlinear characteristics of the inverter. The initial rotor position and the magnet polarity is detected before the drive is started. The initialization is performed by injecting an ac carrier and two short current pulses in a sequence