*6.1. Test System*

In order to validate the data-driven controller of a VSC-based STATCOM model, a two areas power system is employed. The test system is simulated in Matlab/Simulink software; it is comprised of a 2-area power system connected by two AC transmission lines and two machines in each area; these test systems are well-known, such as the Kundurs 2-area 4-machine power system. The complete details of the electrical grid can be found in [33]. The single-line diagram can be seen in Figure 4. The active power exchange between two areas is around 400 MW, going from area 1 to area 2, and the swing generator corresponds to machine 2, labeled as G2. The STATCOM model is connected to Bus 7 (B7) for controlling the AC bus voltage *Vac* and the power ratings of the STATCOM can be seen in Appendix A, particularly in Table A1, where a step-up transformer 195 kV/230 kV is employed to connect it to the grid.

**Figure 4.** Two-area power system [33].

The proposed data-driven control is assessed considering different operating conditions according to the established voltage profile as well as transient faults to analyze power oscillations just after the fault clearing time. All simulations are carried out using Matlab/Simulink software, and a time step *Ts* equal to 1 <sup>×</sup> <sup>10</sup>−<sup>4</sup> is used for the implementation of the data-driven controller. The data-driven controller can be set up from the historical data collected from the grid or even from another model-based closed-loop operation of the STATCOM connected to the grid. Therefore, the data-driven controller will guarantee the dynamic performance of the STATCOM according to the rated reactive power because this will be mainly designed to operate to their limits.

The main advantage of the data-driven controller is that it is completely model-free, while its stability and general dynamic performance are equally deterministic, as if it was based on the existence of a completely accurate model of the grid. To account for this fact, we proceed to make a comprehensible comparison between the two scenarios: model-based and model-free. Other advantages include the ability to bypass the issue arising from model uncertainties, which is the typical weakness of any model-based approach. Based on the described advantages, the proposed approach is validated analyzing the performance of a VSC-based STATCOM model, which is compared to the model-based control system under three different scenarios: (a) by using changes in AC reference voltage; (b) by analyzing the voltage recovery after a three-phase fault; (c) power oscillation damping after the fault clearing time. For either, data-driven and conventional models, an average model of the VSC is used. The PPL parameters and grid parameters are kept the same for both types of controllers.
