Modelling of a Multi-Period Damped Resonant DC-DC Converter with Capacitive Isolation

A new step-down Multi-Period Damped Resonant (MPDR) DC-DC converter for Capacitive Power Transfer (CPT) is proposed in this article for a grid adapter. The proposed solution is based on a Series Resonant Converter that exploits multiple resonant periods for the power transfer. In this way, it is possible to reduce the size of the resonant passive components while operating at lower switching frequencies, to reduce the impact of the switching losses of the active devices. Compared to other CPT solutions, the converter exploits a unique inductor as compensation network, improving the power density and reducing the design complexity. The converter operation and its analytical modelling based on a first-harmonic approximation modified with time-domain corrections are illustrated. The article includes a generalized design procedure to size the resonant inductance and select the switching frequency in order to produce the desired output voltage, and simultaneously achieve the ZVS turn-ON of the input FETs. The proposed model is validated in simulation and experimentally, showing high accuracy in both the operating modes of the converter.