Reliability Modeling and Analysis of Lithium-Ion Battery Packs in Renewable Energy Systems

Renewable energy systems (RES) are emerging as clean power systems. Battery pack is one of the most critical components in RES. Since the power generation and load of RES is time-varying, it is essential to conduct credible reliability analysis of battery packs according to application scenarios. In this study, a belief reliability model for lithium-ion battery packs is developed based on the reliability science principles, taking into account functional requirements, battery degradation, and various sources of uncertainties. Firstly, the state of charge (SOC) of the battery pack is identified as the key performance indicator according to functional requirements. Next, an equivalent circuit model (ECM) is utilized and a cell-to-pack model is constructed to establish the performance margin model. Furthermore, the battery capacity loss over time is considered. Afterwards, the sources of uncertainties are analyzed and quantified with the help of probability theory. Ultimately, the reliability model is established. A case study of a battery pack in RES is introduced to show the effectiveness of the proposed model. The findings indicate that the proposed model can assess the reliability of the battery pack based on internal parameters and operating profiles, aligning closely with its functional requirements. Additionally, guidance can be provided for designers to achieve high reliability standards.