## 5 Case Study
### Analysis of Optimization Scheduling Indicators for Different Types of Pumped Storage  
3.1 Analysis of Net Load Curve Standard Deviation and Wind Power Curtailment Rate under Different Pumped Storage Configuration Schemes  
As depicted in Figure 8, the standard deviation of the net load curve in schemes 3 to 5 is lower than that in scheme 2, while schemes 6 to 8 is lower than that in schemes 3 to 5. Among them, the standard deviation of the net load curve decreases from 144.59 MW in scheme 2 to 141.66 MW in scheme 5, and further to 120.49 MW in scheme 8. The correlation between wind power curtailment rates and the standard deviation of the net load curve is  
Figure 7: The distribution of pumped storage output under different configuration schemes.  
evident across pumped storage configuration schemes. Among them, the wind curtailment rate of scheme 8 is the smallest, and the wind curtailment rate of scheme 2 is the largest. This is because the upper-level model optimizes scheduling on the premise of fully utilizing wind power. When the pumped storage has strong regulatory capabilities, the volatility of the net load curve after upper-level optimization is not significant, and thus, the thermal power adjustment in the lower-level model is smoother. In this case, the actual output power of the wind power will be closer to the forecasted power, resulting in a lower wind power curtailment rate.  
3.2 Analysis of Pump Electricity and Thermal Power Electricity under Different Pumped Storage Configuration Schemes  
In terms of pumping electricity, as shown in Figure 9, the pumping electricity of schemes 3, 4, and 5 is less than that of scheme 2, with 3069 MW-h in scheme 2 and approximately 2950 MW-h in schemes 3, 4, and 5, indicating that the pumping electric energy of pure FS-PS is higher than that of those with VS-PSUs. This is because FS-PSUs can only pump at maximum power, while VS-PSUs can adjust within a range near to the maximum pumping power, thus having more opportunities to pump according to actual demand, which results in less pumping energy.  
The pumping electric energy of schemes 6, 7, and 8 is higher than that of scheme 2. Among them, the pumped electricity of schemes 6, 7, and 8 is as high as 3307.2 MW-h, 3367.2 MW-h, and 3429 MW-h, respectively. This is because T-PSUs also pump at a maximum power of 99 MW during pumping conditions and generate electricity simultaneously, allowing them to pump across the full power range according to actual demand, which can be seen from Figures 4 and 6. However, in scheme 2 (all PSUs are fixed-speed), when the actual pumping demand (e.g., 110 MW) is less than an integer multiple of the maximum pumping power of 99 MW, opening an additional unit could lead to increased thermal power output and affect the total system cost. In such cases, pure FS-PS may abandon the excess 11 MW. Therefore, the pumping energy of scheme 2 is less than that of schemes 6, 7, and 8. Similarly, the increase in pumping energy from schemes 6 to 8 can be explained by  
Figure 8: The net load curve standard deviation and wind power curtailment rate under different pumped storage configuration schemes.  
Figure 9: The pump electricity and thermal electricity under different pumped storage configuration schemes.  
the growing proportion of T-PSUs, which enhance the flexibility and accuracy of pumped storage in satisfying actual demand.  
As for thermal power electricity, there is a downward trend in thermal power output from schemes 2 to 8 in Figure 9. Among them, the thermal power electricity of scheme 8 is the smallest, and the thermal power electricity of scheme 2 is the largest. Combined with Figure 8, this is because the wind power curtailment rate is also decreasing, meaning that the actual wind power electricity is increasing. With the total load demand remaining constant, the thermal power electricity will continue to decrease.