Open-Circuit Fault Detection Algorithm for Switches in Full Bridge LLC Resonant Converters Based on Resonant Capacitor Voltage

This study proposes a two-step open-circuit fault (OCF) detection and localization method for full-bridge LLC resonant converters. If a primary-side switch fault occurs, then the full-bridge LLC converter may transition into the half-bridge mode to maintain continuous operation without interruption. Under these conditions, a robust fault detection and localization method is critical. The proposed method uses only a single voltage sensor to monitor the resonant capacitor voltage (RCV). The method first detects OCFs in primary-side switches by analyzing the slope of the integral of the measured RCV signal. Then, a phase-shift modulation is applied to induce additional slope variations for the precise localization of faulty switches. The effectiveness of the proposed method is experimentally validated on a 125 W/24 V LLC converter.