*2.1. Mission Profile*

A one-year mission profile that is provided in [21] is used in this paper, which was recorded in the year of 2019 in Denmark with a sampling rate of 1 min./sample. It should be mentioned that the mission profile sampling rate could affect the reliability prediction, as discussed in [22], where a high sampling rate (e.g., 1 s to 1 min. per sample) is recommended to obtain as much information as possible in the mission profile translation process. In contrast, a lower sampling rate (e.g., 5 min. per sample) may give rise to a certain degree of uncertainty in the lifetime results. The mission profile is shown in Figure 3. As it can be observed in Figure 3, the solar irradiance and ambient temperature both vary in a wide range. Moreover, the frequent presence of clouds will inevitably affect the PV output power, where a BESS is highly expected to smooth the power fluctuations and limit the power ramp rate. This is to guarantee the system security and stability.

**Figure 3.** One-year mission profile: (**a**) ambient temperature and (**b**) solar irradiance.

#### *2.2. PV Array and PV Inverter*

In this study, it is assumed that the PV-battery system is rated at 160 kW. The JKM380M-72-V solar panel is selected to assemble the 1500 V PV arrays [23]. In this case, 432 solar panels (27 panels per string, 16 strings) are used to achieve the rated power around 160 kW and the maximum open-circuit voltage up to 1500 V. Subsequently, a three-level I-type inverter is employed for interfacing the PV arrays to the AC grid, as shown in Figure 4, where the overall control algorithms are also illustrated. It should be pointed out that when integrating a DC-coupled BESS to this PV system, an appropriate coordinated control of the PV system and the BESS should be considered [14]. The system specifications are given in Table 1. Regarding the power semiconductor devices, three 1200 V/300 A IGBT modules from Semikron are adopted [24] and, correspondingly, their heatsink sizing is designed to guarantee the maximum junction temperature below 125 oC during the rated operation with the ambient temperature being 50 oC.

**Figure 4.** General configuration and control structure of the 1500 V PV system based on the three-level I-type topology: *<sup>P</sup>*pv—PV power, *<sup>V</sup>*pv—PV voltage, *<sup>I</sup>*pv—PV current, *<sup>P</sup>*<sup>∗</sup>pv—active power reference, *<sup>V</sup>*<sup>∗</sup>pv—DC-link voltage reference, *Q*∗—reactive power reference, *<sup>i</sup>*g—grid current, *<sup>v</sup>*g—grid voltage, *<sup>θ</sup>*g— phase angle of the grid voltage, *<sup>v</sup>*inv—output voltage of the inverter, *g*inv—gate signals, MPPT—maximum power point tracking, and SVPWM—space vector pulse width modulation.

**Table 1.** PV System Specifications.


1 Root Mean Square.
