PCIM 2026 500 kW/l Power Density: New SiC Inverter from Fraunhofer IZM

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FAULHABER Drive Systems

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Fraunhofer IZM has developed an inverter for electric drives that processes 500 kilowatts of power in a volume of one liter—many times more than conventional alternatives. The inverter developed for Mitsubishi Heavy Industries (MHI) achieves an efficiency of 99 percent.

Inverters convert direct current from batteries into three-phase current for electric motors. However, as the available installation space is limited, particularly in electric vehicles, the inverter must have a compact design with high performance.

On behalf of Mitsubishi Heavy Industries (MHI), Fraunhofer IZM has developed an inverter that delivers 500 kilowatts (almost 680 hp) with a volume of one liter. This corresponds to a power density of 500 kW/l; higher than conventional alternatives. The efficiency is said to be 99 percent. The inverter will be presented at the Fraunhofer IZM stand in Hall 6 at PCIM Europe in Nuremberg from June 9 to 11, 2026, where it can be inspected live.

The technical data of the 3-phase drive inverter according to the manufacturer:

• Power density: 500 kVA per liter, 500 ARMS per phase at 800 V DC voltage
• Switching speed: 65 V/ns
• Effective inductance: approx. 1 nH
• Peak efficiency: >99%

Embedded SiC Modules with Low Inductance

The inverter uses one power module for each of the three phases. Each module in turn contains twelve silicon carbide MOSFETs from MHI, which are embedded directly into the circuit board using PCB technology. The result is extremely compact modules, which means that the parasitic inductances are very low. The effective inductance is one nanohenry. This is so low that the MOSFETs can be switched at 63 volts per nanosecond. The high switching speed helps to reduce switching losses, which in turn reduces the cooling requirement, as the engineers from Fraunhofer IZM explain.

A flat, extruded aluminum cooler sits beneath the three modules. Its low design saves space and enables a short thermal path from the semiconductor to the coolant. Over 40 thin, slightly corrugated ribs on the inside offer the coolant flowing through sufficient surface area for heat exchange. The heat sink is created in a single production step, saving not only space but also costs.

Laser Welding Instead of Screw Connections

Laser welding is used as the connection technology. "The contact points of the busbars are shaped in such a way that we can weld them directly onto the PCB using a laser. This eliminates the need for screw connections. Not only would they take up more space, they would also increase the inductance," says Wiljan Vermeer from Fraunhofer IZM. The vertical integration of the two input busbars positions them close enough to each other so that their fields almost cancel each other out. This further reduces the inductance.

In collaboration with the company Polycharge, Nanolam DC link capacitors were specially configured for this purpose. Six capacitors are arranged together with the busbars in such a way that the DC link has a total inductance of just two nanohenries despite its capacitance of 300 microfarads. The nanolam technology of the capacitors enables a high power density, but is associated with increased thermal losses. "The copper connections of the electrical contacts also serve to improve heat dissipation," explains Vermeer. "We designed them so that the electrical connections compensate for the poor heat conduction and distribute the heat evenly both horizontally and vertically." The condensers are designed for 150 °C (approx. 302 °F), but have been limited to 130 °C (approx. 266 °F) to increase reliability. The condenser unit is placed under the aluminum radiator and integrated within the housing, which further reduces the required space.

The project shows how much modern power electronics now depend on packaging, thermal management and system integration, and no longer just on the semiconductor. The combination of SiC MOSFETs, PCB embedding and extremely low parasitic inductances enables very high power densities with high efficiency. This is an important development path for applications such as electromobility, aviation or fast-charging systems. At the same time, industrial implementation remains challenging, for example with regard to EMC, reliability and production costs. (sb)