Accurate Power Loss Model Derivation of a High-Current Dual Active Bridge Converter for an Automotive Application

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.