Phase Control using Network Node Voltage Feedback for Capacitor-Coupled Dual Active Bridge DC-DC Converters

Dual active bridge converters are widely applied to bidirectional power conversion systems. However, the volume and the losses of the high-frequency transformer are responsible for a considerable share of the total volume and losses of the converter system. Transformer-less capacitor-coupled dual active bridge converters that replace the transformer with series-connected capacitors have been introduced to mitigate this problem. For both the transformer-coupled and capacitor-coupled dual active bridge converters, digital isolators are used to transmit the high-frequency gating signals for the primary or secondary full-bridge circuit. However, the digital isolators bring in the issue of system reliability, manufacturing cost, and propagation delay. In this paper, a phase control using a network node voltage feedback for the capacitor-coupled dual active bridge has been proposed. The proposed method implements the phase-locked-loop on the opposite side phase information directly extracted from the node voltage of the capacitor-coupling network. The proposed method eliminates the digital isolator or any other communication methods for capacitor-coupled dual active bridge control. The proposed method is experimentally verified with a 2.2 kW capacitor-coupled dual active bridge DC-DC converter prototype with a peak efficiency of 98.6%.