Single-Stage AC-DC Dual Active Bridge Converter With Reactive Power Capability

Conventional ac-to-dc power conversion with galvanic isolation is done in 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 (PF) operation and cannot 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 using multiple modulation schemes that enable efficient operation over a 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 [total harmonic distortion (THD) of 5.0%] and a demonstrated peak efficiency of over 96.5%.