# Dispatchable Substation for Operation and Control of Renewable Energy Resources
## 4 Conclusions  
A sizing method and control of the ESS in the substation were proposed in this study based on forecast errors. The substation proposed herein is a conceptual facility for the hierarchical control of renewable resources. Furthermore, the concept and operation of a dispatchable substation were proposed for renewable interconnection. In a hierarchical control structure, a TSO can expect a dispatchable substation to stabilize the local network's voltage and support the frequency response of the network, similar to a synchronous generator. As the dispatchable substation reports the renewable generation status and forecast values, the TSO calculates and orders the dispatch signal and reserve requirement back to each substation. The possible forecast mismatch or fluctuation that exceeds the DNE limit will be handled within the substation. To increase the utilization ratio of the transmission line, a medium voltage DC connection can be considered between each hub station. DC-based grid expansion planning would resolve line congestion for a future power system with collaborative operation with an ESS in the substation. To realize the concept of the proposed substation, mutual interference among mid-level substations should be investigated during active power control. Since the proposed concept requires ESS as a solution for renewable interconnection, it also should be economically attractive to both TSO and renewable generators. It also should be noted that the development of the weather forecast technology influence directly on assessment of facilities in dispatch-able substation. Thus, state-of-the-art forecast technology should be considered for validation of the proposed concept. When deployed in the network sufficiently, the proposed dispatchable substation can manage problems via the renewable integration of the power system in the future. Conceptualization, Y.Y., G.J., S.J. ; investigation, S.K., S.S., J.L., C.H. ; methodology, Y.Y., S.J. ; supervision, G.J. ; validation, Y.Y. ; visualization, Y.Y. and S.J. ; writing--original draft, Y.Y. ; writing--review and editing, Y.Y., G.J. All authors have read and agreed to the published version of the manuscript. This work was supported by Korea Institution of Energy Technology Evaluation and Planning (KETEP) under grant (20183010025440). The authors declare no conflict of interest. The following abbreviations are used in this manuscript: \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & \multicolumn{2}{c}{**ESS Capacity**} & \multicolumn{2}{c}{**80\% Chance Zone**} \\ \cline{2-5}  & **MW** & **MWh** & **Upper Range [MW]** & **Lower Range [MW]** \\ \hline
**Case 1** & 5.5 & 1.38 & 18.26 & 7.07 \\ \hline
**Case 2** & 4.3 & 1.08 & 14.71 & 7.31 \\ \hline
**Case 3** & 3.5 & 0.88 & 13.27 & 7.28 \\ \hline
**Case 4** & 4.1 & 1.03 & 16.18 & 8.51 \\ \hline
**Case 5** & 5.5 & 1.38 & 18.35 & 8.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: ESS capacity and operation parameters for dispatchable substation for each case in Table 1.  
* [PERSON] et al. (2019) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Optimal sizing of energy storage considering the spatial-temporal correlation of wind power forecast errors. _IET Renew. Power Gener._**2019**, _13_, 530-538. [CrossRef]
* [PERSON] et al. (2016) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Evaluating the spatial correlations of multi-area load forecasting errors. In Proceedings of the 2016 International Conference on Probabilistic Methods Applied to Power Systems (PMAPS), Beijing, China, 16-20 October 2016; pp. 1-6. * [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Modeling the temporal correlation of hourly day-ahead short-term wind power forecast error for optimal sizing energy storage system. _Int. J. Electr. Power Energy Syst._**2018**, _98_, 373-381. [CrossRef]
* [PERSON] and [PERSON] (2015) [PERSON]; [PERSON] Taming wind power with better forecasts. _IEEE Spectr._**2015**, _52_, 47-52. [CrossRef]
* [PERSON] et al.