**5. Conclusions**

In this article, the modeling of a WHIM has been presented, with detailed models for the HT, the penstock, the WT and DL, along with its associated controls. The Pelton type HT was chosen for its small *qnl* and good efficiency. The WHIM has been simulated using the MATLAB-Simulink environment.

In WO mode, both the DL-PID and the HT-PID work but because the DL-PID is around 24 times faster than the HT-PID, the final result is that the frequency regulation is achieved by the DL and its associated PID.

In WO mode to WH mode transition, the simulation has shown that the KS/no-KS frequency minimum values are 0.968/0.958 and the setup times are 26.487/32.844, so the KS case results in a much better transient. Therefore, the KS system has a fundamental role in the WO to WH transition. It is also seen in Section 4.4 the importance of using a HT with a small *qnl* in order to speed up the transient. In WH mode, the simulation shows that the isochronous HT-PID regulates the frequency while the HTG accommodates its power to the net consumed load.

**Author Contributions:** Conceptualization, R.S.; methodology, R.S.; software, A.N.; validation, R.S. and A.N.; formal analysis, R.S.; investigation, R.S. and A.N.; resources, R.S.; writing—original draft preparation, R.S.; writing—review and editing, A.N.; visualization, R.S.; supervision, A.N. All authors have read and agreed to the published version of the manuscript.

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

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