Switch Open-Circuit Fault Detection and Compensation System for LLC Resonant Converters in LDC Applications of Electric Vehicles

Abstract

Low-voltage DC–DC converters (LDCs) require high availability to prevent critical vehicle accidents caused by abrupt voltage drops resulting from switch faults. Therefore, rapid fault detection and technologies that ensure safe operation during fault conditions are essential. This paper proposes a fault-leg identification algorithm and a compensation control strategy to rapidly detect switch open-circuit faults (OCFs) in an LLC resonant converter while ensuring continuous system operation. The proposed fault diagnosis method analyzes the current conduction patterns of the primary-side full bridge using a single current sensor, enabling the identification of the fault location without requiring additional sensing hardware. Immediately after fault detection, the system transitions to a half-bridge operation mode to prevent cascading device failures caused by voltage spikes. To compensate for the sudden reduction in the resonant tank input voltage during this transition, a hardware compensation technique is applied by coupling a compensation capacitor, which physically doubles the voltage gain of the resonant tank. In addition, the switching frequency is reconfigured and the PI controller gains are optimized according to the modified resonant parameters, allowing the output voltage to rapidly recover to its reference value. The performance of the proposed algorithm is validated through hardware-in-the-loop simulation (HILS) experiments on an automotive LDC system. The results demonstrate rapid fault identification within tens of microseconds and stable output voltage recovery under all switch fault conditions.