Key Research Areas

As part of the European project "HiEFFICIENT," the use of novel and high-performance semiconductors, known as wide-bandgap semiconductors, is being investigated for the next generation of electric vehicles. The project aims to develop an efficient integrated charging unit for electric vehicles with a power of 22 kW.

For on-board chargers in electric vehicles, galvanic isolation between the power supply network and the vehicle battery is required. By using gallium nitride semiconductors (GaN), switching frequencies in the megahertz range can be achieved, allowing for a reduction in volume through smaller magnetic components. For galvanic isolation and voltage transfer, a Sine-Amplitude-Converter (SAC) is used, which has an LLC topology in terms of circuitry.

To obtain a highly efficient and power density-optimized system, special attention must be paid to a compensated transformer design that is necessary to keep losses low. Due to its low installation height, the transformer was designed with conventional PCB technology. The low profile creates a very short thermal path to the heat sink. PCB technology enables cost-effective and reproducible manufacturing with very high quantities.

A symmetric current distribution within the layers requires special care in the design of the layer structure and the connection of the transformer to the half-bridges and the local DC link. Optimization regarding current displacement effects was carried out using a 3D field simulator.

The result of the optimization was a transformer for a power of 11 kW with a total height of less than 13 mm, achieving a power density of 56 kW/l (without heat sink) with a maximum total efficiency of 98 percent.