**6. Conclusions**

The aim of this paper is to experimentally evaluate the performance of a novel adaptive full-order observer in order to assess the accuracy of rotor position estimation by means of a Field Oriented Control (FOC) scheme for a Doubly Fed Induction generator (DFIG).

In particular, the work demonstrates that the rotor position evaluated by the observer estimated flux can be affected by significant errors due to parameter inaccuracies. The novelty of the proposed approach is linked to the fact that the rotor position estimation error is considered as an additional machine parameter. Thus, an adaptive law based on the Lyapunov theory was proposed for the tracking of the rotor position estimation error and, additionally, a current injection strategy was developed in order to ensure the necessary tracking sensitivity around zero rotor voltages. The roughly evaluated rotor position was corrected by means of the tracked rotor position estimation error so that the corrected rotor position was sent to the FOC for the necessary rotating coordinate transformation.

The proposed technique was tested experimentally on an 11 kW DFIG prototype moved by a 27 kW DC machine acting as the prime motor. The experimental results testify to the quality of the sensorless control, which is able to effectively track the real system speed with a negligible error (< 0.5%) in the range of 60–130% of the rated speed value. Moreover, the proposed adaptive law clearly improved observer performance by significantly reducing the rotor position estimation error from 17–20 degrees to 3 degrees in the best case.

Future work will focus on the analytical analysis of the stability of the conceived adaptive observer and on its robustness with respect to parameter variations and electric grid and mechanical perturbances, such as negative voltage sequences or rotor eccentricity.

**Author Contributions:** G.B. formalized the control algorithm and wrote the relevant section, I.S. implemented the control algorithm on the real time controller and wrote the relevant section, A.D. supervised the experimental tests, wrote the other sections and edited the whole manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
