## 3 Simulation Results
### Case 5: SST Supplying Power to Instantly Shifted Different Loads  
In order to verify the stable performance of the proposed SST, simulation results were presented at various stages for different shifts of loads. The simulation was performed for 1.0 p.u three different test loads, which were resistive, inductive and capacitive in nature. Just like case 1, when the system was energized, it provided only the active power to the load. The test scenario was created such that at 0.7 s, the resistive load was disconnected and the pure inductive load was connected instantly. As simulation goes on, at 0.14 s, the pure inductive load was disconnected and the pure capacitive load was connected instantly. These shifts of loads where SST instantly shifted to provide lagging VARs and leading VARs to the load are depicted in Figure 25.  
When SST was energized with the resistive loading, this scenario was analogous to Case 1. When the resistive load was disconnected and the pure inductive load was connected at 0.7 s, the output current of the inverter to the load is displayed in Figure 26. At 0.7 s from Figure 26, a shift of 90 degrees in the output current can be seen clearly.  
Figure 26: SST output current to the load. The figure is displaying the shift in phase of the current from the resistive load to inductive load at 0.7 s.  
Figure 25: Filtered SST output voltage to resistive, inductive and capacitive load.  
As the load shifted at 0.7 s, output current increased for a cycle to fulfill the instant lagging reactive power demand of the load and then settled down. During and after this transition time, the SST input voltage (phase A) and current (phase A) at the grid side remained in phase, as shown in Figure 27, thus supplying power at the unity power factor just like the previous scenario. The three phase supply current to the SST at the grid side was still balanced and harmonic content was still low. These results are depicted in Figure 28.  
Figure 29 shows the output current of the SST at the instant when the pure inductive load was disconnected at 1.4 s, and pure capacitive load was connected instantly. Again from Figure 29, the phase shift in the output current could be visualized easily. As the load was instantly shifted to capacitive  
Figure 28: (**a**) SST input current at the grid side. (**b**) THD analysis of phase A input current.  
Figure 27: Result displaying that phase A voltage and current are in phase.  
nature, the instant leading reactive power demand caused the output current of the SST to be increased at 1.4 s. The current settled down when the transient period of one cycle elapsed.  
During and after the instant when SST shifted from delivering lagging VARs to the leading VARs, SST maintained its feature of operating at the unity power factor. Only for phase A, in-phase SST input voltage and input current are shown in Figure 30 while the same results were valid for the other phases as well.  
Figure 30: Result displaying that phase A voltage and current are in phase.  
Figure 29: SST output current to the load. The figure is displaying the shift in current from the inductive load to the capacitive load at 1.4 s.  
SST still maintained the balanced three phase current at the grid side with only 1.89% THD. These results are shown in Figure 31.  
When the load shifted to capacitive nature, the output current of the SST increased at 1.4 s as shown in Figure 29. Figure 31 displays yet another interesting result. Input current to the SST from the grid side also increased at 1.4 s, but the THD of the balanced input current was further decreased.