Filter Optimization for multi-phase DC-DC converter in automotive energy backup system

Cascaded filters offer a possibility to minimize the size of the filter components due to their increased attenuation at high frequencies. A cost optimized design of a cascaded filter of a multi-phase converter for an automotive energy backup system will be shown, that results in small values of the inductances. However, the decreasing inductance values results in increasing current ripples in the first filter stage. The implementation of coupled inductors helps to reduce the current ripples of the single phase currents significantly and achieves a cost optimized design with increased converter efficiency. The influence of tolerances on the ripple cancellation phenomenon in multi-phase converters and coupled inductors on the cascaded filter design will be analyzed. The theoretical predictions are in good correlation with the experimental results obtained from a full-size prototype converter.