**5. Conclusions**

In Spain, the Spanish Grid Code has developed a specific operation procedure, PO 12.3, which sets out the response that wind power plant installations must have under voltage dips. It also developed the so-called procedure for verification, validation and certification (PVVC), a set of guidelines that establish the steps to follow to comply with PO 12.3. Thus, in order to fulfill the requirements of PO 12.3, voltage dips were applied on actual machines using specialized equipment, and field measurements were compared to the responses of their corresponding detailed simulation models when subjected to those specific voltage dip measurements. Subsequently, errors were calculated.

Based on the concepts mentioned above, since IEC models are precisely intended to represent the wide range of actual WTs available in the market, this research work aimed to extend the functionality of international standard IEC 61400-27-1 by analyzing the compliance of these generic models with national grid code requirements such as the Spanish PO 12.3 for fault ride-through capability. In this way, field measurements from an actual Gamesa G52 WT, in addition to the dynamic responses of its corresponding detailed simulation model, were compared to the responses provided by a generic IEC 61400-27-1 Type 3 WT when they were all subjected to the same voltage dip. The PVVC was applied, and the generic WT's active and reactive power responses were analyzed.

The results obtained are of grea<sup>t</sup> interest to network operators as well as other stakeholders concerned with wind power integration. When the WT is operating at full load conditions, if the PVVC is applied at the testing point, the IEC model fails to comply with PO 12.3 in both active and reactive power. This is mainly due to transient periods of the actual WT not being well represented by the generic model as a result of the simplifications introduced in the standard. To improve its electrical behavior, it is proposed that the PI control of the IEC-developed generator system be defined based on the DQ system. It would also be necessary to distinguish between the parameters defining the active and reactive power controllers, since the Standard considers them of equal value. Moreover, regarding specifically the reactive power response, it is also observed that the generic model is unable to represent the fundamental component of the transformer inrush current, unlike in the case of the WT simulation model described. This is better reflected in the reactive power response of the WT at the low voltage side, when the transformer is no longer considered in the validation calculations and hence there is no influence of the inrush current. Indeed, reactive power response does comply with the PVVC in this second case. Concerning the detailed model, its active and reactive power behavior is already validated upstream the transformer, thus broadly complying with PO 12.3. Finally, the IEC WT model operating at partial load conditions only fails to comply with the Spanish grid code in the reactive power response when the validation criteria are applied to the high voltage side. This may be mainly attributed, as in the case of nominal load conditions, to the inability of the WT model to represent the fundamental component of the transformer inrush current.

Wind power is indisputably changing the way electricity networks operate, and this will change even more in the coming years. There is uncertainty about wind lead transmission and distribution system operators thoroughly planning grid activities to ensure power supply. Thus, time-domain analyses such as the ones carried out in the present work can contribute to improving the forecasts required to guarantee proper wind power integration in actual networks. In contrast to other works on this topic, based solely on the study of the certification process of actual WPPs and WTs according to the Spanish grid code, this study analyses the generic Type 3 WT simulation model with the objective of extending the use of Standard IEC 61400-27-1, since the model is subjected for the first time to national grid code validation criteria: Spanish operation procedure PO 12.3. The results show that some modifications should be carried out in the original dynamic sub-models within the generic Type 3 in order to improve its behavior and therefore comply with PO 12.3, thus enhancing the scope of the application of standard IEC 61400-27-1.

**Author Contributions:** Conceptualization, F.J.-B. and E.G.-L.; Investigation, R.V.-R. and F.J.-B.; Methodology, R.V.-R., F.J.-B. and A.H.-E.; Project administration, E.G.-L.; Supervision, F.J.-B., A.H.-E., Á.M.-G. and E.G.-L.; Writing—original draft, R.V.-R.

**Funding:** This research was funded by the Spanish Ministry of Economy and Competitiveness and European Union FEDER, gran<sup>t</sup> number ENE2016-78214-C2-1-R, as well as the Agreement signed between the UCLM and the Council of Albacete to foster Research in the Campus of Albacete.

**Acknowledgments:** The authors would also like to express their gratitude to the wind turbine manufacturer Siemens Gamesa Renewable Energy for the technical support received. Furthermore, the authors would like to thank the TC 88/WG 27 Committee "Wind turbines—Electrical simulation models for wind power generation", to his Convenor, Poul Sørensen, and to the 16 participating countries.

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