An Online Multicapacitor Monitoring Scheme for the Modular Cascaded <i>LLC</i> Converter

Modular cascaded LLC converters are widely used in high-power scenarios of the DC power system with wide voltage gain, not limited by the voltage withstand level of existing equipment. However, the cascaded structure brings a larger number of capacitors and may increase the failure risk of the entire system if one of them fail. However, monitoring these capacitors require complex and multiple monitoring circuits if the conventional solutions are applied. Hence, a simple way to realize the health monitoring of all of them is preferred and is rarely discussed for the modular cascaded LLC converter. In this paper, an online monitoring scheme for multiple capacitors based on only one-time transient large-signal trajectory is proposed for an input-series-output-parallel type LLC cascade converter. Instead of adding additional dedicated sensors, the scheme utilizes the existing sensors and extracts the input capacitance, resonance capacitance and output capacitance from the large-signal trajectory simultaneously, without affecting the normal operation of converter. Finally, experiments are conducted to verify the effectiveness and accuracy of the method for capacitance monitoring in an LLC converter platform.