Multi-objective optimization and comparative evaluation of Si soft-switched and SiC hard-switched automotive DC-DC converters

The application of soft-switching concepts or silicon carbide (SiC) devices are two enabling technologies to further push the efficiency, power density or specific weight of power electronics converters. For an automotive application, such as a DC-DC converter that interconnects the high voltage battery or ultra-capacitor in a hybrid electrical vehicle (HEV) or a fuel cell vehicle (FCV) to the DC-link, costs and failure rate are likewise of importance. Due to increasing requirements on multiple of these converter characteristics the comprehensive multi-objective optimization of the entire converter system gains importance. Thereto, this paper proposes an optimization method to explore the limits of power density as a function of the switching frequency and the number of phases of non-isolated bi-directional multi-phase DC-DC converters operated with soft-switching and silicon devices and hard-switched converters that take advantage of SiC devices. In addition, the optimization includes an algorithm to determine the chip size required for the semiconductor devices under consideration of the thermal characteristics and efficiency requirements. Based on detailed analytical volume, loss and cost models of the converter components as well as on measurements demonstrative results on the optimum converter designs are provided and evaluated comparatively for the different converter concepts.