**2. System Modeling**

In this paper, a single-stage 1500 V PV system is considered, as shown in Figure 1, where a BESS is deployed under the DC- or AC-coupled configuration for power smoothing. The reliability analysis that is given in this paper focuses on the power semiconductor devices. The power flow of the system can then be modeled, as shown in Figure 2, where *T*a and *SI* are mission profile parameters, i.e., the ambient temperature and the solar irradiance, respectively; *<sup>P</sup>*pv and *<sup>V</sup>*pv respectively denote the power and voltage of the PV arrays; *P*inv−in and *P*inv−out represent the input and output power of the PV inverters; *P*bat−dc and *P*bat−ac are the input power of the battery converter and the battery inverter; *<sup>V</sup>*g, *V*bat−dc, and *V*bat−ac represent the grid voltage, the battery voltage for the DC coupling, and the battery voltage for the AC coupling, correspondingly; and, *T*j is the junction temperature of the power devices. The overall inputs are the mission profiles of the installation site that represent the system operating conditions [20] and the outputs are the thermal stress profiles of the power semiconductors in PV/battery converters for the next reliability analysis, as it can be observed in Figure 2. A description of each model for this mission profile translation is given in the following sections.

**Figure 2.** Schematic of the system modeling for the DC- and AC- coupling 1500 V PV systems.
