**5. Conclusions**

This study investigates the optimal control triggering of EDOC in AC systems. Optimal control triggering approaches are classified into direct and indirect approaches based on the used triggering indicator. In the direct SCOP-based EDOC, two events have been defined to capture both the transient and cumulative SCOP deviations, which maintains the SCOP at the ideal level in a closed-loop manner. Simulated case studies sugges<sup>t</sup> that direct SCOP-based EDOC achieved a higher energy saving than indirect PLR-based EDOC in all the typical load scenarios. The main reason is due to a more direct performance indicator, i.e., SCOP, that can reflect the system performance precisely and timely. However, the development of an accurate ideal SCOP model requires su fficient operation data and extensive work, which could restrict its implementation [8]. The robustness issues caused by the uncertainty of SCOP should also be paid attention to. Thus, in terms of actual applications, the SCOP-based EDOC can be recommended when the ideal SCOP model is available with a properly-handled uncertainty issue. However, the PLR-based EDOC could still be a more practical option to replace traditional TDOC, which features an easy development process, better robustness and acceptable energy performance.

**Author Contributions:** Conceptualization, J.W.; Data curation, R.L. and L.Z.; Formal analysis, H.S.A. and E.M.; Funding acquisition, J.W.; Investigation, R.L.; Methodology, J.W.; Resources, L.Z.; Supervision, J.W.; Validation, H.S.A. and E.M.

**Funding:** This research was funded by Natural Science Foundation of Jiangsu Province (BK20190942), Suzhou University of Science and Technology Research projects funding for the introducing talents (331911204), Comprehensive curriculum reform program (2018KJZG-09), and Suzhou science and technology plan projects (SNG2017052).

**Acknowledgments:** The authors would acknowledge to the Sta ffs of City University of Hong Kong for their supports.

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