A class of flux observers for doubly-fed induction generators used in small power wind generation systems

This paper investigates a family of stator and rotor flux observers for sensorless operation of doubly-fed induction generators (DFIG). Four stator flux observer topologies are described and compared. All proposed schemes use the voltage and current models connected in parallel or in series. For each scheme, a proportional-integral (PI) compensator is used to form a feedback correction loop that encloses one or both models. The estimation errors of either the stator current, rotor current, stator flux, or rotor flux are used as inputs for the PI blocks. The speed estimation is based on a model reference adaptive system and a PLL observer. The reference quantity is the measured rotor current, the adaptive model is a current estimator, and the adaptive quantity is the rotor position. Comparative experimental results with all observers on a 7.5 kW DFIG system are presented and discussed in the paper. It is concluded that the observers are able to produce accurate results and are suitable for practical applications.