Sensorless control of DFIGs based on active and reactive power computation for encoder fault tolerance

In this paper a new detection and isolation technique for encoder faults is presented for doubly-fed induction generators. This method compares the measured rotor position with an estimation from a new MRAS observer based on the computation of both active and reactive power transferred via the air gap. The difference between measured and estimated position is monitored by a CUSUM algorithm, while a second observer, based on an internal state-space model, detects anomalous changes in the measured position. A position fault is flagged when both algorithms react. The combination of sensorless algorithm and fault detection technique is tested experimentally on a 3 kW 4-pole DFIG for different working points. The starting performance of the MRAS observer and its behaviour in case of transients is tested during the synchronization process of the DFIG.