Conventional ac to dc power conversion with galvanic isolation is done with two stages, one for ac-dc conversion and one for isolation. However, both stages can be combined into one single-stage ac-dc converter. Previous publications of such single-stage converters focus on unity power factor operation and can't transfer current during the zero crossing of the grid. A novel control approach for a single-stage ac-dc dual active bridge is presented in this work that allows for arbitrary reactive power flow at the grid terminals. This is achieved by utilizing multiple modulation schemes that enable efficient operation over the wide voltage range of the grid. These modulation schemes are implemented with an open-loop control concept which relies on analytic equations that describe the dual active bridge behavior. The concept is validated with a 3 kW prototype which features low disturbance sinusoidal output current (THD of 5.0 %) as well as a demonstrated peak efficiency of over 96.5 %.

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