Fail-Safe System Design Method for LLC Resonant Converters of Electric Vehicle LDC

This paper proposes a fail-safe compensation circuit design method that allows an LLC resonant converter for mobility applications to maintain normal operation for a certain period even in the event of a switch Failure. In the proposed fail-safe system, when a switch fault occurs during full-bridge operation, the converter transitions to half-bridge operation to suppress unwanted voltage spikes caused by pole voltages. To compensate for the voltage drop resulting from the halved resonant tank input voltage, an additional fail-safe capacitor is connected in parallel with the existing resonant capacitor, and a semiconductor switch is used to form the parallel circuit upon switch Failure. As a result, the resonant tank voltage gain can be adjusted through the modified resonant tank parameters. This study also presents a capacitance determination method for fail-safe operation and verifies its effectiveness through PSIM simulations.