# RMS Modeling and Control of a Grid-Forming E-STATCOM for Power System Stability in Isolated Grids
## 5 Results and Discussion
### Short Circuit in the Grid  
This subsection analyses the system response when connecting either a SynCon (case study 2) or an E-STATCOM (case study 3) during a direct three-phase short circuit at La Oliva bus at 66 kV (see Figure 12). The results are presented in Figure 14.  
Figure 14a shows the frequency measured at the Punta Grande bus for the two studied scenarios. It can be observed that in the initial moments during the short circuit, the frequency response exhibits almost identical behavior in both cases. However, once the fault is cleared, the dynamic response when connecting the SynCon stabilizes the system frequency earlier, not reaching such low-frequency oscillations.  
Figure 14b presents the voltage magnitude at the Macher bus, where the compensation devices are connected. The voltage recovery is better with the SynCon because it provides short-circuit current and does not have the current limitations of the E-STATCOM. Figure 14c and Figure 14d show the current components delivered by the SynCon and the E-STATCOM, respectively. Notice in Figure 14d how the quadrature component of the current from the E-STATCOM is constrained by the control system to prevent damage to the power converter, while the current from the SynCon reaches a value close to 5 p.u. Even though the E-STATCOM provides an initial boost due to its rapid response capabilities, its effectiveness is curtailed by built-in current limitations designed to protect its power electronics. This results in a less robust recovery compared to the SynCon. This protective regulation is critical for ensuring the integrity and reliability of the E-STATCOM, but it imposes limitations on its immediate power delivery capabilities during short circuits.  
The performance of the E-STATCOM during short-circuit events is inherently limited by its power electronic converters. Unlike the SynCon, which can deliver high short-circuit currents due to its electromechanical nature, the E-STATCOM is constrained by its current-limiting control mechanisms, designed to protect the converters. Figure 14d shows how the quadrature current component of the E-STATCOM is regulated to prevent excessive current flow, whereas the SynCon can inject up to 5 p.u. of current. This protective mechanism ensures the reliability of the E-STATCOM but simultaneously reduces its effectiveness in providing fault ride-through capability. Consequently, the system's voltage recovery is more robust with the SynCon, as shown in Figure 14b, since it can sustain high fault currents without restrictions. While the E-STATCOM offers advantages in frequency stabilization  
Figure 14: Response to a direct three-phase short circuit at La Oliva bus. (**a**) Frequency at Punta Grande bus. (**b**) Voltage at Mácher bus. (**c**) d-axis current: synchronous condenser and E-STATCOM. (**d**) q-axis current: synchronous condenser and E-STATCOM.  
and fast dynamic response, its ability to support the grid during severe fault conditions is limited compared to the SynCon, requiring supplementary grid-support measures.  
In summary, while both the SynCon and E-STATCOM play pivotal roles in frequency and voltage stabilization, their operational characteristics and limitations must be carefully considered when designing power system solutions. The SynCon's ability to provide short-circuit current allows for robust support during direct short circuits, whereas the E-STATCOM's rapid response and energy storage capacity provide quick frequency stabilization, albeit with constraints that must be managed to protect its internal components.