# Control Strategy of Multiple Battery Energy Storage Stations for Power Grid Peak Shaving
## 2 Methodology
### Peak Load Shifting Control Strategies
#### 2.1.2 Control Strategy for Variable-Power Charging and Discharging Mode  
The aforementioned strategy primarily targets single-storage operation scenarios. However, when implementing peak shaving and valley filling at the power-grid level, the capacity, power, and flexibility of a single storage power station often fail to meet actual peak regulation requirements. Additionally, adopting a single variable-power strategy imposes high demands on equipment regulation performance. Therefore, a variable-power charge-discharge control strategy based on the coordinated operation of multiple BESSs is adopted for power grids.  
The core idea of this strategy is to utilize multiple BESS units configured with constant power charging and discharging control strategies. By coordinating the start/stop  
Figure 1: Constant power control strategy for BESS participating in peak shaving in power grids.  
Figure 2: Constant power control strategy flowchart.  
timing and charging/discharging states of each BESS unit, the strategy achieves an equivalent, dynamically varying charging and discharging power across the entire grid, thereby adapting to the continuous fluctuations in load. The objective is to constrain the strategy based on the power-grid load forecast curve and overall energy balance within a daily timeframe. By optimizing the cluster behavior of multiple constant-power BESS units, the strategy precisely tracks the peak-shaving and valley-filling curves, ultimately ensuring that the regulated load curve operates as smoothly as possible within the target range. This significantly enhances the depth, accuracy, and system flexibility of peak-shaving and valley-filling operations while reducing the dynamic regulation requirements on individual energy storage device inverters. The specific operational mode is illustrated in Figure 3.  
The implementation of this strategy relies on centralized coordination and control of multiple BESS units within the region. Each BESS operates independently with its own constant-power charging and discharging strategy, meaning that its charging/discharging power is fixed at its rated power, and its actions are triggered by the dispatch instructions it receives. Based on the total load forecast curve of the power grid and the overall peak-shaving and valley-filling objectives, commands are directly issued to dynamically adjust the output of each BESS participating in the cluster. Through this combination of operations of discrete constant-power BESS, a continuously varying charging/discharging power is effectively generated on the power-grid bus.  
The specific steps are formalized in Algorithm 1 (Section 2.4). firstly, obtain the load forecast curve of the power grid and determine the overall peak-shaving and valley-filling targets. Secondly, obtain the parameters of each BESS participating in the cluster (rated power, available capacity, initial SOC, etc.). Thirdly, compare the forecast load curve with the target band and calculate the total charging/discharging power demand of the power-grid bus required to maintain the load within the target band for each scheduling period. Then, based on the total demand, the current status of each BESS, and the constraints, determine the operation plan for each BESS. Finally, each BESS independently executes its constant-power charging/discharging operation based on the received instructions. Figure 4 shows the flowchart of the variable-power control strategy.  
Figure 3: Variable-power control strategy for multiple BESS participating in peak shaving in power grids.