RIFT: Residual-based Iterative Fault Tolerance Algorithm for Reconfigurable Cascaded Multilevel Converters in BESS Applications

Reconfigurable Cascaded Multilevel Converters (RCMC) in Battery Energy Storage Systems (BESS) are highly susceptible to Open Switch Faults (OSFs) due to their complex architecture and numerous switching devices. These faults, unlike short-circuit events, manifest as gradual degradations, leading to voltage imbalances and potential cascade failures. This paper introduces an advanced Residual-based Iterative Fault Tolerance (RIFT) algorithm designed to ensure the uninterrupted operation of RCMCs by effectively detecting, localizing, and mitigating OSFs. The RIFT algorithm leverages existing Battery Management System (BMS) cell voltage measurements and phase-voltage sensing, eliminating the need for additional hardware. Its core functionalities include an adaptive threshold monitoring mechanism for fault detection, an iterative hypothesis-testing procedure for precise fault localization across nine Reconfigurable Battery Modules (RBMs) per phase, and a dynamic cell reordering strategy coupled with proportional load redistribution for fault tolerance. The proposed method achieves rapid fault identification and seamless system reconfiguration within a single control cycle, thereby maintaining rated voltage output even with a 33% capacity loss per faulty submodule. This significantly enhances BESS reliability and operational continuity, offering a robust software-based solution to a critical hardware vulnerability. The implementation details, supported by MATLAB functions, demonstrate the practical applicability and effectiveness of the RIFT algorithm in real-world scenarios.