In (5), Ac is the cross-sectional area of the core. B is the
flux density going through the core. V is piece-wise voltage
applied on the transformer and t is the corresponding time
duration for each V. According to the voltage and flux
density waveforms of DAB1 and DAB3 shown in Fig. 6 and
Fig. 7, single and three-phase transformer cross-sectional
areas can be calculated and summarized as in (6).