**6. Conclusions**

This study conducted simulations for cases wherein none of the four kinds of conditional equations (i.e., conditional equations for peak control, power use flattening, power demand response and operation of net zero Energy) or at least one of them had been applied to compare them and evaluate the effectiveness of each equation. The result showed that the conditional equations were found to be effective when attempting to optimize the microgrid's performance efficiently.

The peak-control conditional equation was found to be effective in the simulation as system power usage was decreased below the peak level set at 15 kW. ESS was charged during the daytime when the power cost was low and discharged in the time zones when peak control was implemented.

In the simulation applied with the conditional equation for flattening power use, this equation was found to be effective as the difference between the maximum and minimum system power usages was decreased from 38.68 kW to 9.8 kW. ESS charging was carried out during the daytime when the power cost was low, whereas discharging was performed in the time zones when it was high.

In the simulation applied with the conditional equation for power demand-response, the equation was found to be effective as the power set to be discharged (10 kW) in a fixed time zone was achieved successfully. In this case, ESS was charged during the daytime when the power cost was low.

In the simulation applied with the conditional equation for net zero energy operation, the equation was found to be effective as the system power usage became 0 in a designated time zone, despite the fact that the power cost in that time zone (daytime) was low. As for the rest of the time zones, ESS charging was performed during the daytime, but discharging was carried out in the time zones when the power cost was high.

The results above showed that all the equations were effective in every case and it can be confirmed that all the ESS operating schedules, except net zero energy operation, had been adjusted in such a way that power is charged during the daytime and discharged or sold when the power cost was highest.

**Author Contributions:** Conceptualization, S.J.; Data curation, S.J.; Formal analysis, S.J.; Funding acquisition, J.-H.H.; Methodology, S.J. and Y.T.Y.; Project administration, S.J., Y.T.Y. and J.-H.H.; Resources, Y.T.Y. and J.-H.H.; Software, S.J.; Supervision, Y.T.Y. and J.-H.H.; Visualization, S.J. and Y.T.Y.; Writing—original draft, S.J. and J.-H.H.; Writing—review & editing, Y.T.Y. and J.-H.H. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the National Research Foundation of Korea (NRF) Grant funded by the Korean Government (MSIT) (No.2017R1C1B5077157). Also, this research was supported by the Energy Cloud R&D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT (NRF-2019M3F2A1073385).

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