Encoderless field-oriented control of a synchronous reluctance machine with a direct estimator

This paper presents a rotor position estimator for encoderless control of a synchronous reluctance machine (SynRM). Because of strong rotor saliency, the magnetic flux generated by the stator currents is deviated and induces an orthogonal position-dependent voltage at nonzero speed. Exploiting this effect, the mechanical angle is directly calculated based on a linearized model in stator coordinates, avoiding use of an asymptotic observer and initial position information. The influence of parametric uncertainties and of nonlinearities on position accuracy is analyzed. A stability proof is provided for closed-loop encoderless field-oriented current control with proportional controllers under uncertainties. Even through the model parameters are linearized in an arbitrary setpoint, the control scheme is stable in a wide operation range. Encoderless startup is possible. Experimental results are provided.