Three-Level Switched Capacitor Resonant Converter-based DCX

Isolated dc transformer (DCX) applications typically require a large turns ratio to step the voltage down from a medium- or high-voltage grid. This causes challenges in the design and operation of the converter transformer. This work proposes an improved resonant converter designed to operate as a high frequency isolated DCX with reduced turns ratio. It employs a three-level half-bridge leg and a series connected blocking capacitor that is ideally charged with half of the total high voltage (HV) bus. This is shown to reduce the applied transformer HV-side voltage and, thus, the required turns ratio. The overall volume and losses are reduced as a consequence. The resonant tank is placed at the low voltage side (LV), where it operates with reduced voltage efforts. Additionally, due to the resonant nature and an appropriate modulation scheme, it can realize soft switching at all power devices in the entire operating range. Therefore, due to its unique characteristic, the proposed converter is an attractive solution where high efficiency isolated dc-dc conversion is mandatory.