## 3 Proposed System for Improving the LVRT Capability of a PV Power Plant  
The proposed hybrid protection system block of the 250 kW PVPP based on the ML approach is given in Figure 4. Modelling and control of 250 kW PVPP has been performed. The PVPP system is connected to the grid via a T-type inverter. The T-type inverter converts the DC voltage produced by the PV panel to AC voltage. A capacitor is placed between this inverter and the PV panel. The SPWM method controls the switching signals of the DA/AC inverter. MOSFET is used as the switching element in the DA/AC inverter. Using a DC-DC converter in the system has several disadvantages. First, the DC-DC converter causes switching and conduction losses. Second, the DC-DC converter complicates the system architecture. Third, the DC-DC converter increases both the implementation costs and maintenance complexity. Therefore, in this study, the series connection of seven PV modules was chosen instead of a front-end DC-DC converter. Moreover, a direct series-connected PV array provides faster dynamic response compared to a system with a DC-DC converter during LVRT events. Voltage regulation is frequently delayed when using a DC-DC converter. T-type inverters have become more advantageous than two-level converters, producing a better output signal. The semiconductor switches in the high-level inverter operate more efficiently because they perform at lower voltages. The THD value decreases when the number of levels increases. In other words, the output voltage's THD value is zero when there are infinite levels. However, as the number of levels increases, the control of the inverter becomes more difficult, and an imbalance is observed in the output voltage. In this study, the simulation circuit of the three-phase T-type inverter in the Matlab 2022b/Simulink program is given in Figure 5. The operating conditions of the designed three-phase T-type inverter are examined. Switching signals are generated using the sinusoidal pulse width modulation (SPWM) technique. The SPWM technique is a technique widely used for industrial inverters. The SPWM technique is one of the frequently used techniques that minimizes harmonics in square wave signals. The intersection points for switching times are determined by comparing the reference and carrier waves. The reference signal is a sine wave with peak differences and frequency. A triangular waveform is usually used as the carrier signal. The output voltage values of the single-phase three-level converter are illustrated in Table 2, according to the switching status. The switches are in conduction when they are in the 1 position. The switches are in the cut-off position when they are in the 0 position. As can be seen from Table 2, the \(V_{an}\) voltage takes three different values. To control the PVPP system, mathematical equations must be known. This mathematical model facilitates learning the transient and steady-state characteristics of the PV panel. The Clarke and Park transforms are a transformation used to simplify the analysis of three-phase circuits. The Clarke transform transforms the three-phase system (\(abc\)) into a fixed two-phase reference system (\(\alpha\beta\)) and the Park transform transforms the fixed two-phase reference system (\(\alpha\beta\)) into a direct quadrature (\(d\)) system. The fixed two-phase reference frame obtained via the Clarke transform is used when performing the Park transform. Figure 4: The proposed hybrid protection system block of the 250 kW PVPP based on the ML approach. The current of the three-phase system measured in the network is converted to the _dq_ system using the Clark and Park transformations. The control unit of the PVPP system consists of \(i_{d}\) and \(i_{q}\) axes. The input of the Id axis is the \(V_{dc}\) voltage. Then, 481 V is selected as the \(V_{dc}\) reference value. The \(V_{dc}\) voltage is always measured and compared with the \(V_{dc}\) reference voltage value. As a result of this comparison, the error \(V_{dc}\) voltage is obtained.