Short-Circuit Fault Diagnosis and Post-Fault Control with Adaptive PLL-Based Synchronization for a Multi-Phase Quasi-Square-Wave DC-DC Converter

Fault-tolerant power management units have regained attention due to the rapid development of autonomous vehicles. This paper presents: 1) a fast short-circuit fault diagnosis method, which prevents turning on into a short-circuit, and 2) an adaptive post-fault control for a multi-phase variable-frequency Quasi-Square-Wave (QSW) synchronous buck converter with more than two phases. The converter employs GaN device as the primary switch due to its better figure-of-merit, while using Si device as protection switch due to superior short-circuit immunity. In this paper, the QSW operation mode and a multi-phase structure are combined to achieve enhanced efficiency and fault tolerance. The switching-node voltage during the dead-time intervals is used as the short-circuit fault signature. The adaptive post-fault control utilizes a PLL-based synchronization method in a closed daisy-chain arrangement to: 1) guarantee QSW operation mode regardless of the variable switching frequency due to the inductance value tolerance, and 2) automatically adjust the interleaving phase shifts between phases following a fault detection. The effectiveness of the proposed methods is evaluated and verified in a 75-W four-phase system.