An investigation is described into the optimization of multi-phase, high power, bi-directional DC-DC interleaved converters suitable for Electric Vehicle (EV) applications. Two dual-interleaved topologies were considered initially for the optimization, the main difference being the magnetic devices: either discrete inductors (DI) or an Interphase Transformer (IPT). The comparison used a comprehensive multi-objective design optimization procedure for an 80 kW case study. High performance inductors comprising a split-core structure and dual-foil windings to reduce losses, and a 180 C core, enabled the DI to be competitive with IPT in terms of power density and efficiency. The optimized designs are validated experimentally with an 80 kW bi-directional SiC DC-DC converter, achieving a power density of 31.4 kW/L and specific power of 15.7 kW/kg. The study is then extended to 100-kW three and four-phase interleaved topologies.
To capitalize fully on modern component technologies such as nanocrystalline cores and wide-bandgap devices, multi-objective converter design optimization is essential, requiring simple, accurate component models. In this work, a lumped parameter thermal model is presented for nanocrystalline inductors with ceramic heat spreaders. The key challenge is the non-uniform loss distribution in gapped, tape-wound cores, particularly the high loss densities adjacent to the gaps. However, uneven loss distributions are not handled easily by lumped-parameter techniques. It is shown that by treating the ceramic heat spreaders as 'passive' heat sources, a simple thermal model of the inductor can be derived to estimate the hot spot temperature of the core. The model is validated through comparison with 3-D finite element analysis (FEA) and experimental measurements on a 60 kW DC-DC converter. The proposed model offers a comparable level of accuracy to FEA with a fraction of the running time, executing in 99 µs in MATLAB.
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