Analytical Modeling and Design of an Active Clamp Forward Converter Applied as a Single-Stage On-Board DC-DC Converter for EVs

In an electric vehicle (EV), two major voltage levels have to be coupled by an on-board DC-DC-converter - the high voltage traction battery of about 400 V and the auxiliary battery of 12 V. Due to the varying state of charge (SOC) of the batteries, the converter has to cover very wide input and output voltage ranges. Considering recent developments in semiconductors, the active clamp forward converter is an interesting topology since only a very small energy is required in the series inductance for soft turn-on of the main switch. In the design process, however, common methods are not suitable because the clamp capacitor voltage cannot be calculated accurately. This paper presents a novel analytical model, which can be used for accurate calculation of the shape parameters. Results show a maximum deviation of 1.8 % from detailed numerical simulations, which proves that the proposed model is an excellent basis for the converter design procedure. A component stress analysis built on this model demonstrates the potential of this topology for the described application.