PLL-based Rotor Flux Estimation Method for Sensorless Vector Controlled Squirrel-Cage Induction Generators

This paper presents a new rotor flux estimation method for sensorless vector controlled squirrel-cage induction generators used in wind power applications. The proposed method is based on a phase-locked loop (PLL) and the orthogonality between the rotor flux space vector and its back electromotive force (EMF) space vector. Rotor flux is estimated using stator voltage equations without integrating the back EMF components in the stationary reference frame and the well-known difficulties with the implementation of pure integrators are thus avoided. Moreover, the proposed method ensures successful magnetization of a speed-sensorless squirrel-cage induction generator at nonzero speeds which makes it suitable for wind power applications. Experimental results on a 560 kW squirrel-cage induction generator are presented to confirm the effectiveness and the feasibility of the proposed method.