An optimal configuration for a 6 kW DC to AC converter with ultrasonic AC link

The authors report on the development of an ultrasonic-frequency modular inverter system for application in track-side signaling houses of railway companies. The inverter is one of the components of an uninterruptible power supply system providing up to four hours standby for interlocking and track-side equipment. The small light-weight inverter incorporates an ultrasonic AC link, thus facilitating the use of a ferrite transformer for input-output isolation purposes and resulting in the practical implementation of the modularity principle, ZVS (zero voltage switching) is achieved by good circuit layout and controlled transformer capacitance. A novel integrated sensor in the transformer is used for flux balancing purposes and the associated airgap contributes to the ZVS process. Enhanced modulation depth is realized for inductive loads by allowing a large-frequency AC ripple on the DC bus