## 5 Simulation and Verification of Hybrid Reactive Power Compensation Program
### Transient Voltage Stability Simulation Verification  
In this section, the characteristics related to the transient voltage stability of the power grid in the Hami region of Xinjiang are further analyzed and studied by the time-domain simulation method. Based on the previous section, it can be known that the static voltage stability of the power grid near the Santanghu wind area in the Hami region is lower compared to the other two wind areas, and is the weak point of the voltage in the whole Hami region. Thus, the Santanghu wind area is the focus of this section, and the model built is shown in Figure 11.  
Figure 11: Schematic diagram of the power grid structure of the wind farm group near Santanghu. By improving the particle swarm algorithm, as discussed in Section 4 of this paper, when the fixed compensation capacity of the parallel capacitor is set to 10 MVar, the best compensation effect should be obtained when the SVG compensation capacity is 9.2 MVar. Program 1: The program of the reactive power compensation device, SVC, and a combination of SVC and parallel capacitors are used. The system has a three-phase short-circuit fault in the middle part of the transmission line between the busbar and the grid-connected busbar at 2.5 s, and the fault is eliminated after 0.3 s resection. Program 2: The reactive power compensation device, SVG, SVG, and shunt capacitor combination program are adopted, and other conditions are the same as program 1. Program 3: The combination of SVC and the shunt capacitor as well as the combination of SVG and the shunt capacitor are adopted, and other conditions are the same as program 1. The three programs are shown in Figures 12-14 below. Program 1: When there is no reactive power compensation device in the system, the voltage drops to 0.102 P.U. at the time of the fault. At only 1.6 s after the fault, the wind farm outlet voltage bus finally reaches a new stabilization curve, though the voltage value at the moment of stabilization is only 0.937 P.U., which is much smaller than the normal voltage value. However, after adding the dynamic reactive power compensation device SVC to the system, although the fall position was basically the same as above without the reactive power compensation device, the short circuit fault was removed. This further enabled the bus to recover stability quickly, with the voltage at the controlled bus returning to 1.001 P.U. within 1.4 s after the fault was removed. When the combined SVC and shunt capacitor reactive power compensation program is added, it is obvious that the bus voltage drops to 0.132 P.U., which shows some improvement compared with the first two methods, and the bus voltage is restored to 1.00 P.U. by 0.7 s after the fault removal. Program 2: When the dynamic reactive power compensation device SVG is added, the voltage dip is only 0.134 P.U. when the fault voltage dip occurs in the system. This is nearly 0.032 P.U. higher than without the reactive power compensation device, and the bus voltage recovery speed after the fault is removed is also much faster than without the reactive power compensation device. The bus voltage recovered to 1.001 P.U. within 0.76 s after the fault. However, when SVG is used for reactive power compensation, the tracking of bus voltage oscillation occurs, which directly causes the corresponding bus voltage to oscillate to a large extent. When the proposed combined reactive power compensation program of SVG and the shunt capacitor is used, it is similar to the dynamic reactive power compensation device SVG alone in terms of suppressing voltage dips, but after fault removal, especially in the process of bus voltage stabilization, it is obvious that the oscillation voltage is much smaller when the combined reactive power compensation program is used than when the SVG alone is used. The oscillation voltage is obviously much smaller than that of SVG alone.