Dynamic operation of carrier-signal-injection-based sensorless direct field-oriented AC drives

This paper analyzes the dynamic operation of carrier-signal-based sensorless field-oriented AC motor drives. The effects of the harmonics introduced by the fundamental current transients at frequencies near the carrier-signal frequency are first analyzed, then compensation based on a fundamental current observer is proposed. The utilization of such a fundamental current observer provides the possibility of modifying the analog-to-digital conversion process to increase the number of bits effectively containing spatial information and thereby substantially increasing the accuracy of the estimated rotor position or flux angle.