## 7 Conclusions  
This paper describes the experimental validation and implementation of a methodology for inertia estimation of wind power plants. This methodology is based on the equation of oscillation, and it uses measurements of the angle bus, detection of the disturbance, peak value of the disturbance, and the knowledge of active power flow in the generation units.  
A comparison between the results obtained with two professional tools (RTDS and DlgSILENT PowerFactory) was carried out in order to demonstrate the accuracy, performance, and robustness of the methodology. RTDS is used for the validation of the methodology used, while DlgSILENT PowerFactory is used to calculate the inertia estimation of a large-scale power system.  
Furthermore, the results of the inertia estimation of the area of the Istmo of Tehuantepec, Mexico, were analyzed and presented. From the obtained results, it can be concluded that the methodology can be applied to wind power plants. The estimation of generator inertia is accurate when a generation trip occurs in the system. However, a disadvantage of this methodology is that the accuracy is reduced when small perturbations are applied to the system. This means that the inertia estimation also depends on measurements of the disturbances and their natures.  
From the results presented in this paper, it can be concluded that despite the differences between the case studies analyzed in terms of disturbances, network topology, controllers, professional tools, and modeling of the elements, the methodology presents a great robustness to obtain the inertia estimations, i.e., the results of the inertia estimation present a considerable accuracy with respect to the real inertia of the generation units.  
With this methodology, it is possible to estimate the inertia in generation units, such as wind power plants, and to set the references of the synthetic inertial controllers to improve frequency stability.  
Figure 11: Active power in p.u. at bus 2 (Chicoasen): load increment case.  
\begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Power Plants** & **Generation** & **\(H\) (Input)** & **\(H\) (Estimated)** & **Absolute Error \%** \\ \hline Angostura & Hydropower & 4 & 4.08 & 2.00 \\ Bombana & Hydropower & 4 & 4.03 & 0.75 \\ Chicoasen & Hydropower & 4.7 & 4.78 & 1.70 \\ Schpoina & Hydropower & 3.7 & 3.61 & 2.43 \\ Tapachula & Hydropower & 4 & 4.01 & 0.25 \\ Juchitan & Wind power & 0.00237 & 0.0023 & 2.95 \\ Ixtepec & Wind power & 0.00237 & 0.00228 & 3.80 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Inertia estimation results, load increment case.  
**Author Contributions:** Conceptualization, O.B., E.M. and D.W.; Methodology, O.B., R.P., J.S., E.M. and D.W.; Software, O.B. and A.E.; Validation, O.B. and A.E.; Formal Analysis, O.B., R.P. and J.S.; Investigation, O.B., R.P., J.S., E.M. and D.W.; Data Curation, O.B. and A.E.; Writing--Original Draft Preparation, O.B., R.P. and J.S.; Writing--Review and Editing, O.B., R.P., J.S., E.M. and D.W.; Supervision, R.P.  
**Funding:** This research received no external funding.  
**Acknowledgments:** The authors want to acknowledge the Universidad Autonoma de San Luis Potosi through the Facultad de Ingenieria, the University of Denver, and the National Renewable Energy Laboratory (NREL) for the facilities granted to carry out this investigation. [PERSON] wants to acknowledge the financial support received from CONACYT through a scholarship to carry out his Ph.D. studies. We also thank Schweitzer Engineering Laboratories (SEL) for donating the PMU devices used to develop the case studies in real time.  
**Conflicts of Interest:** The authors declare no conflict of interest.