**5. Discussion**

The presented comparative reliability analysis has provided information on the differences of the two configurations for 1500 V PV systems in terms of reliability. This section discusses the possible reliability-affecting factors, as well as some opportunities that could be further explored for improving their reliability performance in practice.

From the case study, it is concluded that, as compared with the AC-coupled configuration, the DC-coupled configuration has a shorter lifetime period and lower reliability. This is in agreemen<sup>t</sup> with the hypothesis in Section 1, but this comparison result is different from the conclusion in [19]. A comparative reliability evaluation has been performed for residential PV-battery systems in [19], where it was shown that the DC-coupled configuration was more reliable. The main reason behind this difference is the increased DC voltage of the 1500 V PV system, which has a considerable impact on the lifetime and reliability of the battery converter for DC-coupling, as observed in the above analysis. In such a case, instead of using the bidirectional converter that is based on 1700-V half-bridge power modules, a three-level bidirectional converter might be a better option [35], which can be applied to this case with the series connection of two 1200-V half-bridge power modules. In all, it is indicated that the reliability performance is dependent on applications.

On the other hand, the reliability improvements could also be achieved through power devices advancements. For instance, the Silicon Carbide (SiC) devices offer superior features, like low switching losses, fast switching speed, high voltage blocking capability, and high allowable operating temperatures [36]. These features are very suitable for the power converters in both configurations. At the same time, when compared with the IGBT modules, the SiC modules with improved packaging technologies follow different failure mechanisms or modes. New lifetime models are needed to properly analyze their reliability [37].

It should be noted that the passive components (e.g., the DC-link capacitors) and gate drivers can also affect the lifetime and reliability of these power converters, which will be the future work.
