Design Aspects of Resonant and Non-Resonant Capacitive-Coupled DC/DC Converters

A common method of achieving galvanic isolation in isolated dc/dc converters is through a transformer. However, capacitors by means of capacitive coupling can also provide galvanic isolation and is a promising alternative to the traditional inductive/magnetic coupling approach. Capacitive coupling increases the converter’s power density and offers better repeatability of the reactive network by eliminating one magnetic element and reducing its inherent parametric variation. In this context, capacitors are the key element in the capacitive-coupled dc/dc converter, such that resonant topologies can be seen as inherent capacitive-coupled dc/dc converters in terms of operation principle, as the capacitor is already an essential component to ensure resonant behavior. On the other hand, capacitors are hardly considered in non-resonant topologies and therefore such converters require a minimum capacitance value to ensure the operation principle and at the same time provide the capacitive coupling. Therefore, taking into account the operation principle of the well-known transformer-based dc/dc converters, the paper clusters the main topologies (in particular DAB and CLLC converters) into two groups (resonant and non-resonant) to define the main design aspects of capacitive-coupled converters: capacitance values, resonant tank arrangement, "magnetizing" inductance, and safe operating region. Finally, analysis and experimental results considering different switching frequencies support the concept and design aspects.