An Edge-Based Condition Monitoring Scheme for the AC and DC Capacitors in LLC Converter

LLC converters are widely used in high-power, high-power-density scenarios due to their ability to achieve high-frequency operation and galvanic isolation. However, the ac resonant capacitor and output dc capacitor are prone to aging and failure under high-frequency charging and discharging conditions. This article proposes an online condition monitoring scheme for the multicapacitors in the LLC converter based on an active control transient. The motivation behind the active control is to create a ms-level discharge processes during the converter operation while maintaining the output voltage fluctuations within an acceptable level. During this discharging transient, the output voltage, output current, and resonant current of the converter are recorded only. Subsequently, a capacitance estimation algorithm based on a back propagation neural network is proposed and embedded in the microcontroller. Finally, experiments verify the effectiveness of the method for capacitance monitoring in the field, and its estimation error is less than 3% for the resonant capacitor and less than 1.5% for the output capacitor.