Fraunhofer Institute for Reliability and Microintegration IZM
Drive inverters for electric mobility control the energy flow between the high-voltage battery and the motor. They play a decisive role in determining efficiency and performance. The Power Electronic Systems Group at Fraunhofer IZM has once again set new standards in this field: Commissioned by Mitsubishi Heavy Industries (MHI), a cost-effective inverter was developed that delivers a full 500 kilowatts of power (just under 680 hp) with 99 percent efficiency, yet occupies a volume of only one liter. A combination of innovative power module, capacitor, and cooling concepts makes this sensational power density possible.
Three power modules, one per phase, each utilize 12 silicon carbide MOSFETs. They are embedded directly into the circuit board using PCB technology, which reduces parasitic inductance to approximately 1 nanohenry and also minimizes the size of the power module. This, in turn, enables high switching speeds with minimal losses and low cooling requirements. A compact aluminum heat sink with a low profile efficiently dissipates heat and shortens the
thermal path to the coolant. It stands out for its low material costs and cost-effective produc- tion via an extrusion process, which allows the heat sink to be manufactured in a single step. The busbars are laser-welded directly onto the printed circuit board. This eliminates the need for screw connections, saving space and minimizing inductance.
The vertical and close arrangement of the busbars causes their fields to nearly cancel each other out. This further reduces inductance. The DC link capacitors – six Polycharge NanoLam capacitors – are also designed to have low inductance. Furthermore, the capacitor terminals are used to dissipate heat and conduct it to the heat sink, which is integrated directly above the capacitor. This multifunctionality enables operation with high currents in a capacitor with a small volume.
The power density of 500 kW or 0.5 MW per liter exceeds standard solutions by a factor of five and state-of-the-art technology by a factor of two and a half. The efficiency of 99 % at moderate manufacturing costs also speaks for itself.
