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An efficiency-optimized modulation scheme and design method are developed for an existing hardware prototype of a bidirectional dual active bridge (DAB) dc/dc converter. The DAB being considered is used for an automotive application and is made up of a high-voltage port with port voltage V 1 , 240 V ≤ V 1 ≤ 450 V, and a low-voltage port with port voltage V 2 , 11 V ≤ V 2 ≤ 16 V; the rated output power is 2 kW. A much increased converter efficiency is achieved with the methods detailed in this paper: The average efficiency, calculated for different voltages V 1 and V 2 , different power levels, and both directions of power transfer, rises from 89.6% (conventional phase shift modulation) to 93.5% (proposed modulation scheme). Measured efficiency values, obtained from the DAB hardware prototype, are used to verify the theoretical results.Index Terms-Battery chargers, circuit optimization, dc-dc power conversion, design methodology, digital systems. NOMENCLATURE D 1Duty cycle used for the HV full bridge. D 2 Duty cycle used for the LV full bridge. ϕPhase angle between v T1 and v T2 . f S Switching frequency. i T1 Transformer current, HV side. i T2 Transformer current, LV side. I S1,sw,min Minimum HV MOSFET current needed to achieve low switching losses, HV side. I S2,sw,opt LV MOSFET current needed to achieve minimum switching losses on the LV side. L DAB converter inductance. n Transformer turns ratio. P 1 HV port power. P 2 LV port power. P out Converter output power. P out,d Designated output power (mod. scheme). P ,a,maxMaximum power of the modified triangular current mode modulation for V 2 ≤ V 2,lim .Maximum power of the modified triangular current mode modulation for V 2 ≥ V 2,lim . P ,V2 lim,max Maximum power of the modified triangular current mode modulation at V 2 = V 2,lim . P opt,a,min Minimum power of the high-power mod. scheme for V 2 ≤ V 2,lim (P opt,a,min > P ,a,max ).P opt,b,min Minimum power of the high-power mod. scheme for V 2 ≥ V 2,lim (P opt,b,min > P ,b,max ). P opt,a,hi Transition power level with D 1 = D 2 = 0.5 for V 2 ≤ V 2,lim (P opt,a,hi > P opt,a,min ). P max Maximum output power of the DAB. T S Switching period,Defines the boundary between different operating modes of the DAB. v T1 AC volt. generated by the HV full bridge. v T2 AC volt. generated by the LV full bridge.

An accurate power loss model for a high-efficiency dual active bridge converter, which provides a bidirectional electrical interface between a 12-V battery and a high-voltage (HV) dc bus in a fuel cell car, is derived. The nominal power is 2 kW, the HV dc bus varies between 240 and 450 V, and the battery voltage range is between 11 and 16 V. Consequently, battery currents of up to 200 A occur at nominal power. In automotive applications, high converter efficiency and high power densities are required. Thus, it is necessary to accurately predict the dissipated power for each power component in order to identify and to properly design the heavily loaded parts of the converter. In combination with measured efficiency values, it is shown that conventional converter analysis predicts substantially inaccurate efficiencies for the given converter. This paper describes the main reasons why the conventional method fails and documents the different steps required to predict the power losses more accurately. With the presented converter prototype, an efficiency of more than 92% is achieved at an output power of 2 kW in a wide input/output voltage range.Index Terms-Bridge circuits, dc-dc power conversion, modeling, switching transients.

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The main aim of this paper is to improve the performance of high current dual active bridge converters when operated over a wide voltage range. A typical application is for fuel cell vehicles where a bi-directional interface between a 12V battery and a high voltage DC bus is required. The battery side voltage ranges from 11V to 16V while the fuel cell is operated between 220V and 447V and the required power is typically 1kW. Careful analysis shows that the high currents on the battery side cause significant design issues in order to obtain a high efficiency. The standard phase shift modulation method can result in high conduction and switching losses. This paper proposes a combined triangular and trapezoidal modulation method to reduce losses over the wide operating range. Approximately, a 2% improvement in efficiency can be expected. An experimental system is used to verify the improved performance of the dual active bridge using the proposed advanced modulation method. I.