# Fault ride-Through Control Strategy for Variable Speed Pumped Storage Unit with Full-Size Converter
## 5 Simulation Verification
### Verification of the HVRT Strategy  
This section verifies that the proposed combination of the HVRT strategies can meet the fault ride-through requirements mentioned in Section 4.1. The system voltage signal command is shown in Figure 19.  
Figure 16: Simulation results of deep voltage drop in power grid (fast power mode with LVRT strategy). (**a**) Rotor side power. (**b**) Grid side power. (**c**) Unit speed. (**d**) DC voltage. Figure 17: Simulation results of deep voltage drop in power grid (pumping condition). (**a**) Rotor side active power. (**b**) DC voltage. Figure 18: Simulation results of deep voltage drop in power grid (pumping condition with low power protection). (**a**) Rotor side active power. (**b**) DC voltage. Figure 20 shows the simulation curve of the fast speed mode under power generation conditions before and after the HVRT measures are applied. In this case, the rotor energy storage, reactive power compensation, and power reversal strategies are applied, while the crowbar circuit is not adopted. During the overvoltage period of the system, there is a significant drop in active power on the grid side, and the active power on the rotor side also decreases. The maximum DC voltage reaches 1.2 pu. With the HVRT strategy, the rotor speed increases to store the unit energy to reduce the rotor-side active power and the power imbalance. The GSC outputs reactive current to avoid overmodulation. The DC voltage decreased from 1.2 pu to 1.1 pu and immediately stabilized at 1.03 pu. Figure 21 shows the simulation curve of the fast power mode under power generation conditions before and after the HVRT measures are applied. In this case, the rotor energy storage, reactive power compensation, and fast power drop strategies are applied. The crowbar circuit is not adopted. Figure 19: Grid voltage during the HVRT. Figure 20: Simulation results of the HVRT (fast speed mode of the generation state). (**a**) Rotor side active power. (**b**) Rotor side reactive power. (**c**) Grid side active power. (**d**) Grid side reactive power. (**e**) Unit speed. (**f**) DC voltage. Without control strategy, the active and reactive power on the rotor side remain almost unchanged, and the unit speed does not change. The active power on the grid side decreases significantly during the overvoltage period, and the transient voltage of the DC bus rises to a maximum of 1.17 pu. With the proposed HVRT strategy, the GSC outputs inductive reactive current to maintain the grid voltage. Due to the power speed reduction strategy, the active power on the rotor side decreases to 0.87 pu during the fault period, and the maximum DC voltage drops from 1.17 pu to 1.1 pu. Figure 22 shows the simulation curve of the pumping condition before and after the HVRT measures are applied. In this case, the rotor speed increases, and reactive power compensation strategies are applied. The crowbar circuit is not adopted. During the fault period, the active power on both rotor and grid side increased significantly, the unit speed fluctuated greatly, and the changes in water head and flow rate are relatively small. The maximum DC bus voltage rises to 1.2 pu. With the proposed HVRT strategy applied, the rotor is precisely accelerated, increasing the active power consumption on the rotor side and reducing the unbalanced power stored in the DC capacitor. Combined with reactive power compensation of the inverter, the DC voltage decreases from 1.2 pu to 1.1 pu. The water head of the unit increases to 1.024 pu, and the pumping flow rate increases to 1.045 pu. The above simulation results verify the correctness of the fault analysis during the high voltage period, as well as the effectiveness of the proposed HVRT combination strategy. However, it should be further noted that although the DC overvoltage decreased to 1.1 pu after implementing control measures, it is still recommended to configure a crowbar circuit in engineering to ensure the unit's safe operation. Figure 21: Simulation results of the HVRT (fast power mode of the generation state).