Research and/or Engineering Questions/Objective In electric axle drive systems (e-drives), the inverter represents a linking element between battery and electric powertrain. Inverter requirements are strongly affected by the electric machine design. Moreover, the fulfilment of these inverter requirements does not necessarily lead to one unique solution as there are manifold design variants for appropriate inverter sub-components, each impacting efficiency, performance, cost and package. This high design variability of inverter component variants leads to a complex problem in the overall design process of electric axle drives. Methodology In this context, the present contribution introduces an inverter design optimization method. For given requirements imposed by the electric machine candidates, the inverter component design is optimized for each potential configuration of the solution space to handle efficiency, performance, cost and package in a multi-objective manner. A focus is put on the manifoldness regarding inverter package and their system integration. The power module and the DC link capacitor are identified as package-critical inverter sub-components that strongly vary with the requirements. Considering manifold possible design variants, a multi-objective optimization for the DC link design is introduced and combined with adequate power module selection for optimal integration on inverter level. The resulting set of inverter candidates is then combined on e drive system level to find the best e-drive system solution, considering electric machine, inverter and gearbox and the desired installation space. Results The approach enables a holistic discussion of e-drive system tradeoffs. In particular, it reveals the best tradeoffs between the package space for the electric machine and the inverter, which typically stand in conflict with each other. The result is displayed as Pareto front of e-drive system solutions, from which decision makers choose the best suitable tradeoff. The new approach is demonstrated on an actual design problem of a common inverter topology for state-of-the-art electric axle drives. It turns out that a small inverter design height is critical to achieve highest energy efficiency of the overall e-drive system. Limitations of this study The approach is demonstrated for the most common inverter topology, which is radially attached to the electric machine, although also other topologies might be of interest. As an outlook, also the EMI (electro-magnetic interference) filter design might be included to cover its influence on inverter package. What does the paper offer that is new in the field including in comparison to other work by the authors? An innovative method is presented for optimizing the inverter-internal component design in the context of holistic e-drive system development, specifically focusing on package integration. Contrary to that, state-of-the-art publications regarding e-drive system optimization do not consider the variability of the inverter package, especially in the initial development phases. Conclusions An innovative method is presented for optimizing the inverter-internal component design in the context of holistic e-drive system development. Key system objectives of efficiency, performance and cost are covered with a special focus on package integration. The method supports finding the best suitable system solution for specified vehicle powertrain requirements.
Dr. Martin Hofstetter, Project Manager, Graz University of Technology