Modified dual active bridge bidirectional DC-DC converter with optimal efficiency

In this paper a modified dual active bridge (DAB) topology with a new modulation technique is proposed for bidirectional dc-dc conversion that not only improves the soft switching range of the converter but also highly reduces the large current ripples at low voltage side. Phase shift and duty cycles of active bridges on two sides, (d₁, d₂, θ), are used to control the converter in order to extend the soft switching range against wide range of operating voltages on both ports and also to maximize the efficiency. The converter operation is analyzed and the soft switching conditions are extracted. For an aero space application it is shown that with a proper converter design the soft switching zones in control space can cover full power range against the wide voltage range required by standards. The extraction of optimal trajectories of control parameter values (d_1opt, d_2opt, θ_opt), for maximum efficiency are also discusses and an implementation method for the controller is proposed. Precise simulated model of the converter is developed to verify the analytic results and fine tune the design. A 2KW, 250 KHz prototype is also implemented to verify the results in practice.