Automotive Traction Inverter for Highest Power Density

The main drivers for the development of automotive traction inverters can be summarized to be cost, power density, specific power, efficiency and reliability [1], [2]. Nowadays, traction inverters are commonly assembled using individual building blocks serving the system as switch (power semiconductor module), energy storage (DC link capacitor), current distributor (copper bus bar structure) and cooling system (liquid cooled heat sink). In addition sensor functions (Hall elements, thermistors) and control circuits are integrated. In most cases this setup is supported by mechanical parts and protected by an enclosure. Engineers have the demanding task to combine these individual components in a way that enables highest power densities at lowest possible cost. This paper proposes an automotive traction power inverter design concept combining these building blocks into one integrated "mini stack". Electrical connection, thermal interface and mechanical fixing were developed to facilitate each other by using the same mechanical parts for different tasks at the same time. Thus, an optimum in performance is achieved at maximum power density and a minimum of individual parts. The combination of a compact and high performance direct water cooling system, with a laminated bus bar directly bonded to low loss film capacitors leads to highest power densities, while the demanding lifetime requirements of automotive traction applications can still be fulfilled by usage of latest bonding and joining technology [3]. Besides the compact design, this demonstrator is targeting operation with elevated coolant temperature. An approach investigated in this content is the combination of Si IGBT and with SiC diodes.