Switch Open-Circuit Fault Diagnosis Method Using Bridge Arm Midpoint Voltage Integral for LLC Resonant Converter

The LLC resonant converter offers several advantages, including compact size, low losses, and high efficiency. These attributes make it an ideal choice for use in seafloor observation networks where space is limited and efficient heat dissipation is crucial. However, the reliability of the LLC converter is compromised due to the susceptibility of the primary switch to failure. In response to this issue, this article proposes a precise open-circuit fault diagnosis (OCFD) method for phase-shifted LLC resonant converters using the integral of the bridge arm midpoint voltage, aiming to identify the fault location and facilitate maintenance. First, the characteristics of the primary-side switch fault in the LLC resonant converter are analyzed in detail, and the characteristic quantity required for fault diagnosis is selected. Subsequently, the OCFD method is introduced, which exclusively depends on the integral value of the voltage at the midpoint of the primary-side switching bridge arm. Following this, a diagnostic circuit is designed to process the bridge-arm midpoint voltage and precisely pinpoint the faulty switch. Finally, the experimental verification is performed on the LLC resonant converter prototype. The results demonstrate that the proposed method can swiftly detect and locate faults within two switching cycles when the LLC converter operates at 100 kHz.