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 work, 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 startup 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.