## 5 Simulation Result Analysis and Discussion
### Simulation Results  
The LVRT performance of the system with the proposed control scheme is demonstrated under both symmetrical and asymmetrical fault conditions. To capture all the possible details, and for better representation, a uniform time span of 0-5 s used in the graph results. A zoomed-in portion is also provided inside all figures for better visualization. The simulation results are described in the subsequent sections.  
LVRT Enhancement by the Proposed Control Scheme under a Symmetrical Fault (3 LG)  
The effectiveness of the proposed control scheme in LVRT capability enhancement is investigated by applying a symmetrical fault (3 LG) at line 2, near the PCC point (Figure 7). The fault is created at t = 0.5 s and cleared after 0.15 s. The simulation time is 5 s, and the mode is discreet with a step time of 50 \(\upmu\)s. In this work, to verify the performance of the proposed control during the change in atmospheric conditions, irradiation and temperature varies from 250 w/m\({}^{2}\) to 1000 w/m\({}^{2}\) and 25 \({}^{\circ}\)C to 50 \({}^{\circ}\)C, respectively. Such parameter checks are another salient feature of this work, since most of the existing LVRT techniques require a constant irradiance and ambient temperature. The simulation results of the grid-connected SPV system without the proposed strategy (MPPT control) are shown in Figure 9. Figure 9a shows that, during the 3 LG fault, 100% voltage sag occurs on the PCC without the proposed control scheme. This fault type, as the worst one, causes a severe voltage sag in the PCC. Once the 3 LG fault occurs, the voltage at the PCC drops to zero. The DCL voltage is unstable with 1000 V overvoltage, which exceeds the limitation severely, as shown in Figure 9b. The IGBTs in the power converters may fail in this situation, and the SPV system cannot perform LVRT. It can be seen  
Figure 8: I-V and P-V characteristics of the solar Photovoltaic array model used in the simulation analysis.  
Figure 7: Power system simulation model. SG: Synchronous generator.  
in Figure 9c that the SPV system injects maximum active power at the same time that it injects less reactive power (Figure 9d),which is not acceptable under a 3 LG fault.  
The simulation results with the proposed control strategy are shown in Figure 10. As shown in Figure 10a, DCL voltage retains the maximum 600 V, which is below the DCL over-voltage limitation. Simultaneously, as shown in Figure 10b, the SPV system can inject an average amount of 500 kVAR reactive power (Qmax) into the grid to support grid recovery under 100% voltage sag conditions (Figure 10b). The SPV output active power (Figure 10c) is effectively reduced to zero, as mentioned in Algorithm 1, which enhances the LVRT capability of the system. Figure 10d shows that the PV inverter injects 1.01 pu reactive current (Iq) under 100% voltage sag, which meets the German E.ON grid code requirements. Since the input parameters of irradiance and temperature vary, the active and reactive power results show trivial oscillations in the pre-fault period. However, active and reactive power results in the post fault conditions reaching the steady state within the time limit mentioned in the E.ON grid code.  
Figure 9: _Cont._  
Figure 10: _Cont._  
Figure 9: Simulation results of MPPT control under a symmetrical (3 LG) fault. (**a**) Grid voltage (Vgrid), (b) DC-link voltage (DCL), (**c**) active power (P), (**d**) reactive power (Q).  
Figure 10: Simulation results of the proposed control under a symmetrical (3 LG) fault. **(a)** DC-link voltage (DCL), **(b)** active power (P), **(c)** reactive power (Q), **(d)** reactive current (I\({}_{\text{q}}\)).  
The reliability of the above results when compared with previous studies can be clearly seen by considering the results in [31]. These results address the excessive AC current and DC voltage using similar means to this study, but using different controls and additional devices, which increases the cost.