Charged EVs | Fraunhofer IZM’s novel SiC inverter hits 99% efficiency in a 1-liter package for 800 V EV drives

Fraunhofer IZM has developed a 500-kW inverter that fits in a volume of 1 liter—500 kVA per liter—with peak efficiency exceeding 99%. The unit was built for Mitsubishi Heavy Industries and is designed for 800 V DC drives, delivering 500 A RMS per phase with an effective inductance of approximately 1 nanohenry and switching speeds of 65 V/ns.

The design reaches those numbers through four interacting approaches. The power modules use a two-level half-bridge topology, one per phase, each with twelve silicon carbide MOSFETs embedded directly onto the PCB. Embedding the SiC switches eliminates component height and cuts parasitic inductance. An RC snubber between each module and the DC-link capacitor reduces oscillations and increases switching speed. The resulting 1 nH effective inductance allows the MOSFETs to switch at their physical limit—faster switching means lower losses, reducing cooling requirements.

The second approach is the cooler: a flat, extruded aluminum heat sink beneath the three modules with more than 40 thin, slightly corrugated channels giving coolant a large surface area for heat exchange. The entire heat sink is produced in a single extrusion step, minimizing both cost and form factor.

The third approach is the busbar connection. “The contacts of the busbars were formed just so that we could laser-weld them directly onto the circuit board,” said Wiljan Vermeer of Fraunhofer IZM’s Power Electronic Systems group. “That means we could get rid of screws that would not only eat up valuable space but increase inductance as well.” The two input busbars are arranged vertically and close enough that their magnetic fields partially cancel, further reducing inductance.

The fourth approach addresses the DC-link capacitors. Working with PolyCharge, the team used NanoLam capacitors specifically configured for the application and arranged alongside the busbars, achieving 2 nH total DC-link inductance at 300 microfarads of capacitance. NanoLam capacitors produce higher thermal losses than conventional types; the team used copper contacts for better heat dissipation and integrated the capacitor unit into the casing below the aluminum cooler, limiting operating temperature to 130 °C against a 150 °C maximum.

Fraunhofer says the resulting unit outperforms common inverter alternatives by five times on power density and beats current top systems by 2.5×. Vermeer will present the inverter at PCIM Europe in Nuremberg, June 9–11.

Source: Fraunhofer IZM