Application of Phase-Locked Loop in Sensorless SynRM Drives

Phase-locked loop (PLL) algorithms can be found in a broad spectrum of applications due to their precision, reliability, low complexity and low computational burden. Their application extends from the grid-connected-converters to sensorless AC motor drives. Since the estimation of the flux position is necessary for the control algorithm operation, PLL is often used as a rotor speed and position estimator. In this paper application of PLL in synchronous reluctance machines (SynRM) drive is presented in more details. The model of the PLL based flux estimator is given and sensorless control of the SynRM is briefly discussed. Special attention is given to the harmonic distortion inherent to the back-electromotive-force (BEMF), especially in a low speed range, and its influence on the PLL results. Finally, experimental results on 1kW sensorless SynRM drive at different speeds are given.