AC coupled dual active bridge (DAB) dc-dc converters typically use phase shifted square wave (PSSW) modulation to manage the power flow between two dc sources. With this scheme, the current flowing between the converter bridges injects high-magnitude current harmonics into each dc port at multiples of the primary switching frequency, which can excite resonances in the LC circuits created by parasitic second-order impedances such as wiring inductances in the dc-link connections. This can cause substantial dc bus voltage and current oscillations, particularly with the higher switching frequencies that are used with wide bandgap devices, leading to excessive electromagnetic interference, significant filter stress, and eventual component operational failure. Conventionally, a relatively large dc bus filter capacitor (or inductor) helps to suppress these dc bus harmonic dynamics. However, the use of adaptive three-level modulation for a single phase DAB provides a much greater solution space to achieve a desired power transfer condition, with the three PSSW control angles that are available. This paper now explores the additional use of these angles to selectively suppress particular dc bus current harmonics across the entire operating range of the converter and thus allow the size of the DAB dc bus bridge capacitors to be minimized. This new active harmonic suppression (AHS) strategy is validated by theory, simulation, and matching experimental results.