Fraunhofer Institute for Reliability and Microintegration IZMPFC inductor for an on-board charger used in e-mobility
The conversion of automobiles from conventional combustion engines to electric drives represents an enormous challenge for the automotive industry. In addition to high efficiency and low weight, costs are of particular importance in high unit volumes.
In an on-board charger for electromobility, besides a DC-DC converter that provides galvanic isolation from the HV vehicle grid, there is a so-called power factor correction converter (PFC) used as the interface to the public supply grid. It ensures purely sinusoidal fundamental currents (50/60Hz) on the input side.
A particularly bulky and cost-intensive component here is the PFC inductor, which has to absorb the voltage difference between the voltage in the supply network (230V/50Hz) and the DC voltage in the DC link (800VDC) and at the same time carry the full load current (32A for 3-phase 22kW units).
A new type of inductor for this purpose is being developed as part of the European "HiEFFICIENT" project. Due to the special design with four magnetically coupled windings each on a separate winding leg and the high switching frequency of 140kHz, the windings can be manufactured in a standard PCB process. A low-cost ferrite core with very low core losses can be used as the magnetic core, which can also be produced by machine in large quantities.
This enables the component to be fabricated in a reproducible and completely automated manner. It is therefore very cost-effective and at the same time meets all technical requirements, such as insulation strength and continuous load capability. Due to its very flat design, the thermal path for its heat dissipation is very short. It is therefore not operated at its thermal limit, which increases its reliability.
Along with accurate loss modeling, a particular design challenge is to ensure uniform current distribution of the load current in all sub-windings. Moreover, the four sub-windings must be wired as short as possible without causing additional losses.
The designed component has a size of approximately 100mm x 88mm x 14mm. The efficiency of the converter is reduced by approx. 0.5% due to its losses (approx. 35W).