Analysis and Design of SQR-Based High-Voltage LLC Resonant DC-DC Converter

This paper presents the analysis and design of an isolated high-voltage LLC resonant dc-dc full-bridge converter based on symmetrical quadrupler rectifier (SQR). Unlike conventional Cockcroft-Walton and full-bridge diode rectifiers, the SQR circuit provides significant improvement in power density by reducing the transformer turns-ratio without much increase in the output impedance. Moreover, the LLC converter can provide additional voltage boost, if operated, below the series resonant frequency of the LLC tank. The operating region of the converter is chosen in such a way that the converter always operates in ZVS for all line and load conditions with additional voltage boost. A new method based on basic differential equation is proposed for the accurate analysis and design of the converter and subsequently, the key results are compared with a first harmonic approximation based analysis method. A 120 V dc input, 2 kV output, 200Wlaboratory prototype has been designed, built, and tested. Simulation and experimental results shown in this paper demonstrate the validity of the analysis and design of the presented converter.