Inverter Building Block

Project Targets

New generation of automotive power modules with innovative electric/thermal interfaces and joining technologies.

Short Description

A new design for power modules for the use in hybrid and electric vehicles was developed. Many of the weak-points of today’s solutions regarding interfaces, constraints for the overall system design, the assembly effort and reliability could be eliminated. The result was the realization and testing of a modular ‘Inverter Building Block’.

State-of-the-art inverter designs have for example an interface between the power-modules and the DC-link capacitor. Constructional constraints regarding the component placement can lead to a high impedance of the commutation cell, especially for integrated drive solutions. The placement of the DC link foil capacitor in the ‘Inverter Building Block’ leads to a high switching performance of the module, independent from the overall 3D-inverter design. This provides also improvements in the fields of robustness (overvoltage margin), EMC behavior and energy efficiency (reduction of switching losses). Also, the gate driver and the current sensor are integrated in the module. An LTCC device with integrated gate resistors and the power stage of the gate driver is directly soldered on the well cooled DAB substrate (Direct Aluminum Bonding). This reduces parasitic effects and typical thermal hot spots.

Integrating power electronic components in mechanical drives leads to a higher level of thermal and mechanical stress compared to stand-alone solutions. To reduce the thermo-mechanical stress within the module, an all-aluminum material concept was used. Also the material weight and costs as well as the susceptibility to corrosion are minimized by the consequent use of aluminum based materials. Innovative joining technologies, like laser welding of the aluminum terminals with the DAB substrate and double-sided nanosilver sintering of the semiconductor devices, were investigated. Power cycling and passive temperature cycling tests have shown a significant improvement of the number of cycles before failure compared to standard technology.

The design of the ‘Inverter Building Block’ allows the modular use in a variety of drive and motor configurations (e.g. in single or double motor setups). A first test of the design was carried out in an axle drive system that was developed in the same project.

Project Partners

The research work for the power module was done in cooperation with other Fraunhofer institutes, for example IFAM, IKTS, ILT, IMS, IZM and ISIT.

Project Duration

2009 - 2011


M. Hofmann, A. Schletz, K. Domes, M. März, L. Frey: Modular Inverter Power Electronic for Intelligent e‑Drives. IEEE-proceedings of Electric Drives Production Conference (EDPC) 2012, Nuremberg, 16/17 October 2012.