Turn-on behavior of automotive multi-phase converters with coupled inductors

Multi-phase converters with coupled inductors achieve high power density and high efficiency and are therefore very suitable for automotive applications. A disadvantage of coupled inductors in comparison to uncoupled inductors is the increased sensitivity to rapid changes of the volt-time product across the windings. These conditions occur at converter turn-on if the converter links two energy nets with constant voltages. In this paper an analysis has been performed to calculate the magnetic flux in the core of coupled inductors during the turn-on of the converter. Results of the analysis show that the peak flux obtained is much higher than the flux under steady-state conditions. To prevent core saturation an optimized start-up switching pattern has been developed for multi-phase converters with coupled inductors and arbitrary number of phases. Measurements with a full-size prototype converter have been carried out that confirm theoretical predictions.