I am reposting this from your support ticket:
The control strategy is a simplified implementation of the control approach given in 'Control of a Modular DC-DC Converter Dedicated to Energy Storage‘. We used only this reference to develop the demo model. We omitted the magnetizing current control loop for this demo since we assume an ideal transformation.
Maybe you can find additional hints in the papers referenced by the paper: https://ieeexplore.ieee.org/document/7309134/references#references
Some additional information on the control approach:
The goal is to control the current flowing between the battery (low voltage side) and the DC-bus (high voltage side).
Ideally, we would like to have equal current sharing among the two DABs. However, in reality balancing the voltages on the two input capacitors is not trivial, e.g. due to small differences in the passive elements. Without an appropriate control strategy, the two voltages would drift away.
In the demo model, this is prevented in the following way: The current is distributed among the two DABs in such a way that the two voltages equalise. Since we only use a simple proportional controller, there will be a small (uncritical) steady-state error.