Generating isolated outputs in a multilevel modular capacitor clamped DC-DC converter (MMCCC) for hybrid electric and fuel cell vehicles

This paper presents a new technique to obtain isolated dc voltage outputs from a capacitor clamped dc-dc converter. The multilevel modular capacitor clamped converter (MMCCC) has several key features that make it possible to generate ac outputs (10 kHz) from a dc-dc converter circuit. Using those high frequency ac outputs, the MMCCC circuit can incorporate single or multiple high frequency transformers to generate isolated ac outputs. These isolated outputs can be rectified and filtered to obtain unidirectional or bi-directional dc outputs. Using another MMCCC converter stage or an active full bridge block, the ac port can be made bi-directional to transfer power in both directions. By adopting the MMCCC topology to achieve isolated outputs, it is possible to simultaneously integrate multiple dc sources in an isolated and non-isolated manner. This paper will investigate the origin of the ac outputs in the MMCCC circuit, and present an analytical approach to estimating the isolated dc output voltage. Finally, experimental results will be presented for further verification of the concept.