Condition Based Reliability Evaluation and Maintenance Strategy for Battery Energy Storage System

Abstract: The electrical grid balances production capacity and demand in real-time. With an increased demand for renewable energy sources, challenges such as stability of the grid, the balance between generation and demand, and power quality occur. One way to deal with the variability is by introducing Battery Energy Storage System (BESS) to the electric grid. To ensure a stable connection, the BESS must be reliable, and much research has been carried out on the BESS reliability. However, the previous studies have mainly focused on the DC reliability of the system and little research has been conducted on the AC side of a BESS. This thesis aims to provide a reliability-based maintenance strategy for the AC-side of a BESS. First, the reliability index of each AC component is calculated with established models, and based on the results, the maintenance strategy is developed. It is shown that the load current and ambient temperature are the two main parameters that affect a BESS’s reliability. For longer periods of continuous operation, the reliability declines with time and the failure rate increases. The most suitable maintenance strategy is a combination of preventive and predictive. The frequency of the scheduled preventive maintenance differs between the AC components since the schedule is based on the results from individual reliability indices. The preventive maintenance uses the condition monitoring method to observe some key elements such as DC-bus neutral current and junction temperature.