A Wide Speed Range Sensorless Control for Three-Phase PMSMs Based on a High-Dynamic Back EMF Observer

The current industry-proven back electromotive force (back EMF)-based sensorless control frequently fails at low speeds and is also laborious to use. Interestingly, in this study, these defects can be improved by developing a novel open-loop back EMF observer, where the sensorless drive could operate from 1% to 100% of the maximum speed, and it also enables the direct start-up from the standstill. This indicates one single sensorless control scheme is enough to fit the full speed range for some specific applications. The key technique behind this is a novel open-loop back EMF observer that features easy implementation and no additional filters; meanwhile, it necessitates only the phase resistance and q-axis inductance. An in-depth investigation of the proposed sensorless control from a complex-frequency notation, instead of the classical 2-by-2 matrix notation, is carried out, and an experiment is also conducted to reveal its superior performance over the industry-proven method.