# Control Strategy of Multiple Battery Energy Storage Stations for Power Grid Peak Shaving
## 2 Methodology
### Performance of Variable-Power Charging and Discharging Control Strategy  
The BESS operates at a constant power of 10 MW during charging and discharging. After analyzing the data, the load peak-shaving and valley-filling variation curves under the variable-power strategy can be obtained, as shown in Figure 8. The power output of the BESS is shown in Figure 9, and the corresponding indicator changes are shown in Table 4. The final plan for energy storage participation in peak shaving is shown in Table 5. The peak and valley values represent the peak and valley values of the load curve under the variable-power strategy. Figure 8 shows that after adopting a multi-ESS coordinated variable-power strategy, the load curve is precisely constrained within the target band. Compared with Figure 6, significant improvements can be seen: during the midday off-peak period, three-stage charging continuously raises the valley value to 47.2 MW; during the evening peak period, time-of-use discharge stabilizes the peak value at 114.5 MW. This result demonstrates that equivalent continuous-power regulation can be achieved through a discrete constant-power BESS cluster, significantly reducing the standard deviation of the daily load. Figure 9 illustrates the operational strategy of multi-BESS coordination: two BESS units alternate operations to achieve equivalent variable power. During the charging phase, the power gradually transitions between \(-20\) MW (dual unit) and \(-10\) MW (single unit); during the discharging phase, the power stops between 10 MW and 20 MW. This dynamic scheduling achieves continuous changes in charging and discharging power through a \begin{table}
\begin{tabular}{c c c} \hline
**Output Stage** & **Charging Period** & **Discharging Period** \\ \hline Total duration & 3.75–4.25 h (0.5 h) & 10.75–11.75 h (1.0 h) \\ Stage 1 & Charging two BESS simultaneously (3.75 h) & Discharging only BESS1 (10.75 h) \\ Stage 2 & Charging only BESS2 (4.00 h) & Discharging two BESS simultaneously (11.00 h) \\ Stage 3 & Charging only BESS1 (4.25 h) & Discharging only BESS2 (11.50 h) \\ \hline \end{tabular}
\end{table} 
Table 4: Output status of the BESS. \begin{table}
\begin{tabular}{c c c c} \hline
**Indicator** & **Before Peak Shaving** & **After Peak Shaving** & **Change** \\ \hline Maximum load (MW) & 120.13 & 114.50 & 5.63 \\ Minimum load (MW) & 44.92 & 47.20 & 2.28 \\ \(\Delta P\) (MW) & 75.21 & 67.30 & 7.91 \\ \(\alpha\) & 0.3739 & 0.4122 & 0.0383 \\ \(\beta\) & 0.6261 & 0.5878 & 0.0383 \\ X & 22.8483 & 21.2826 & 1.5657 \\ \hline \end{tabular}
\end{table} 
Table 5: Summary of energy storage peak-shaving effects under variable-power strategy. Figure 9: Schematic diagram of BESS output under variaable-power strategy. combination of start-stop operations, increasing the total regulation duration to 2 hours, which is a 33% improvement over the constant-power strategy, thereby fundamentally enhancing operational efficiency. Table 4 quantifies the scheduling logic for multi-BESS phased coordination. Taking the discharge period as an example, Phase 1 involves only BESS1, Phase 2 involves dual-machine parallel operation, and Phase 3 switches to BESS2. This sequential combination of discrete devices is the key to achieving the smooth load curve shown in Figure 8, validating the idea of optimizing cluster behavior to precisely track the target band. The duration of each phase is \(\leq\)0.25 h (minimum scheduling interval), demonstrating the strategy's ability to respond to short-term fluctuations. Table 5 data indicates that the variable-power strategy has achieved a significant overall improvement in peak-shaving performance, with the peak-to-valley difference reduction increasing to 7.91 MW, reflecting better peak-shaving and valley-filling effects. Additionally, the standard deviation of load decreased by 1.57, representing a 60% improvement. This highlights the advantage of the variable-power strategy in enhancing the depth and precision of peak shaving and valley filling.