Determination of DC link harmonics in dual active bridge DC-DC converters using frequency domain analysis

Dual Active Bridge (DAB) converters offer an unmatched capability to transfer energy in either direction between two DC sources. However, an unrecognised problem with these converters is their potential for parasitic DC link inductances to cause substantial DC bus ringing, filter stress and consequent operational failure when excited by modulated current harmonics. This paper explores this problem by using frequency domain analysis to determine the DC link harmonics of a DAB. It then shows how particular DC link current harmonics can be eliminated using adaptive 3-level modulation. The analysis strategy is validated by matching experimental results.