6.3.1. Transient Fault on Bus 7

Figure 9 shows the dynamic response during a transient fault simulated at Bus 7. Notice that both controllers present small differences in the voltage control. However, a better performance can be observed when the data-driven controller is employed. From Figure 9, one can notice that the proposed control presents a higher voltage overshoot than

the model-based control; however, once the fault is cleaned up, the data-driven controller reaches the steady-state faster than the conventional controller. In addition, during any transient fault, the STATCOM will act to maintain the voltage profile according to the AC voltage reference and depending on the fault severity, where sometimes the controller can be saturated. This will be defined by the reactive power requirements during the pre-fault condition, where a larger AC voltage reference will be demanding more reactive power. A fault may also produce a higher overshoot during the transient response, and the controller may be saturated because this has physical limits.

**Figure 9.** Voltage control during transient fault at Bus 7.

Figure 10 confirms the robustness of the proposed approach because the power flows between the interconnected areas, active and reactive powers, present smaller power oscillations than the generated with the conventional control. For instance, Figure 10a shows significant differences during the transient behavior of the active power, while Figure 10b displays the results of the reactive power.

**Figure 10.** Power flow during a fault at Bus 7: (**a**) active power, and (**b**) reactive power.

On the other hand, a STATCOM not only offers the capability to improve the power system efficiency due to its fast dynamic response of voltage control but can also help to mitigate low-frequency power oscillations [38]. For example, Figure 11 displays the difference between two rotor angles corresponding to Generator 1 and Generator 2 (defined

as slack generator). The results show low-frequency oscillations between both generators when a PSS is used for every generator, except for Generator 4. For all analyzed scenarios, the machine speed deviation is used as an input signal to each PSS. According to the results shown in Figure 11, notice that the proposed controller helps to reduce the power oscillations due to the fast dynamic response to recover the AC voltage at the PCC. In addition, the differences shown in Figure 11 not only depend on the STATCOM but are also due to other generators. This is the main reason that both responses do not match very well during the transient period. However, notice that after some seconds both controllers have the same behavior; this means that the power system has reached the new steady-state.

**Figure 11.** Rotor angles during a fault at Bus 7.

## 6.3.2. Fault along the Transmission Line

In this case, a transient fault is analyzed, which is cleaned up by opening the circuitbreakers of the faulted transmission line. The dynamic response corresponding to voltage at the PCC is depicted in Figure 12, where significant differences occur between the proposed control scheme and the model-based control. In addition, Figure 13 shows the power flow changes after the fault clearing time. The power flow measurements are taken from the non-faulted transmission line. The power transmission losses are increased due to the presence of only one transmission line. The damping capability is highly noticeable in Figure 14, which shows the rotor angle difference after the clearing time and due to the change of topology caused by the opening of one transmission line. Figures 11 and 14 help to confirm the dynamic performance of the data-driven controller in comparison with the conventional model-based controller. Notice that a better performance is exhibited when the STATCOM is controlled by the data-driven approach. Finally, the described results help to confirm the dynamic performance of the data-driven controller in comparison with the model-based controller, where significant differences appear during the transient period. Table 2 summarizes the controller performance during transient faults after evaluating different time steps; voltage recovery after the fault clearing time. Finally, considering all analyzed variables, the results showed that the data-driven controller offers better performance during transient events because the resulting power oscillations are smaller in magnitude for all analyzed scenarios.

**Table 2.** Controller performance during transient faults using different time steps.


**Figure 13.** Power flows during transient fault and topology change: (**a**) active power, and (**b**) reactive power.

**Figure 14.** Rotor angles during transient fault and topology change.
