## 3 Analysis of Power Source and Load Coordination Mechanism
### Power Source Capacity Planning Strategy Considering Source-Load Coordination
BESS will then be charged if energy still remains, i.e., \(\Delta E_{i}\)-\((E_{\text{SC-max}}\)-\(E_{\text{SC-available-}i})>0\) (Figure 5a). 2. Discharging process  
For a certain time interval \(t_{i}\), if \(\Delta E_{i}<0\), ES devices will discharge to supplement the energy shortage of load. The time intervals are classified into three categories:  
For \(t_{i}<t_{\text{B-switch}}\), SC is utilized for supplementary and the available capacity of SC is used for supplying all level 1 load and a part of level 2 and level 3 load. For \(t_{\text{B-switch}}<t_{i}<t_{\text{D-switch}}\), SC and BESS will both be utilized. SC will be switched in immediately and discharge until \(t_{\text{B-switch}}\), when BESS is ready to switch in, then BESS is used for supplying all level 1 and level 2 load as well as a part of level 3 load. For \(t_{i}>t_{\text{D-switch}}\), SC will be switched in immediately and discharge until \(t_{\text{B-switch}}\), when BESS is ready to switch in. Then the batteries will discharge until \(t_{\text{D-switch}}\), when diesel generators are ready to be switched in, then a diesel generator is used for supplying all level 1, level 2 and level 3 load (Figure 5b). Figure 4: Principle of source-load coordination. ES, energy storage. A flowchart of the proposed strategy is illustrated in Figure 6.  
Figure 5: Operation status and coordination strategy of power sources in different conditions. (**a**) Illustration of charging process; (**b**) Illustration of discharging process. SC, super capacitor. Figure 6: Flowchart of the planning strategy. Further explanation on discharge strategy is illustrated in Figure 7. For each time interval, the energy shortage is divided into three stages distributed along the time axis in Figure 7a. Each stage of energy shortage consists of forced-compensated part, optional compensated part and abandoned part, as illustrated in Figure 7b. Forced-compensated part is the part of energy shortage which must be supplied by energy storage (ES) considering the supply requirement in Table 2. On this basis, additionally compensated energy shortage, which is an optional compensated part for ES, helps to increase the supply reliability. The uncompensated part of energy shortage is considered the abandoned part. Herein, an index named \"additional compensation ratio\" (\(ACR\)) is proposed for balancing economic efficiency and reliability. It represents the ratio of optional compensated part for each stage of energy shortage. Optimal \(ACR\) is obtained through calculation of energy shortage compensation cost \(C_{1}\). \[C_{1\!-\!i}=(1-ACR)\cdot E_{a}\cdot c_{1}+E_{1\!-\!b}\cdot c_{2} \tag{11}\]  
\[E_{a}=E_{n}-E_{b},n=1,2,3 \tag{12}\]  
where \(E_{n}\) represents each stage of energy shortage in a time interval; \(E_{b}\) is the forced-compensated part of \(E_{n}\) and shall be compensated at all costs. Uncompensated energy \(E_{1\!-\!b}\) in this part will be punished with \(c_{2}\), which has an extremely high value. The abandoned part of energy shortage is considered and calculated with \(c_{1}\), which is relatively small. The components of each part of energy shortage stages are illustrated in Figure 3:0