Toroidal Inductor Design in Multilevel DC-DC Electric Vehicle Battery Charger Including High-Frequency Effects

Inductor filters, such as the ones implemented in DC-DC buck-boost converters for electric vehicle chargers, have a major impact on the converter weight, volume and cost. Thus, their design is key in order to obtain an optimal design of the whole converter. This paper proposes a design methodology for powder core toroidal inductors, which is based on a holistic approach of the design of the inductor, where losses due to high-frequency effects are computed by means of specific loss model for toroidal windings, and saturation, geometrical and thermal constraints are considered. The convenience of the design tool is shown through an analysis over a wide variation of parameters, including converter topology, parallelization, switching frequency and inductance. The analysis demonstrates the relevance of high-frequency effects on the inductor design, so certain misconceptions can be avoided, such as that the inductor volume monotonically decreases when the inductance value is decreased or that paralleling inductors always results in more compact designs. A design example is presented for a 15-kW, three-level electric vehicle battery charger. The algorithm is used to obtain an optimal design of the converter, including the inductors and SiC MOSFET devices. Finally, an easy method to obtain a commercial inductor design from the theoretical one provided by the algorithm is presented.