Small-Signal Analysis of Digitally Controlled DAB Converter Under Transient Dc-Bias Current Elimination Strategies

A discrete-time small-signal modelling strategy is developed for the dual active bridge converter operating under modulation strategies for transient dc-bias inductor current suppression. Most of these techniques consist on changing the phase-shift in a two-step manner, which is modelled by expanding the matrices that form the difference equation. The dynamics of two different current offset mitigation strategies are compared with the basic single-step single-side modulation. The obtained control-to- output voltage and input current transfer functions are validated in simulations, which demonstrate the model effectively accounts for the high frequency dynamics of the different modulation strategies. Finally, by integrating an averaging filter of the measured variables into the model, the additional delay caused by the two-step phase-shift transition is observed in the results, which causes a higher phase decay at high frequencies than in the case of the single-step modulation.