Inverter Design Optimization Method Focusing on Electric Powertrain Package Integration

In electric axle drive systems (e-drives), the inverter represents a linking element between battery and electric powertrain. The 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 subcomponents, each impacting efficiency, package, and cost. This high design variability of inverter component variants leads to a complex problem in the overall design process of e-drives. 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, package, and cost 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 subcomponents that strongly vary with the requirements. Taking possible manifold design variants into consideration, a multi-objective optimization for the DC link capacitor 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 an e-drive system level to find the best e-drive system solution allowing for the electric machine, inverter, gearbox, and the desired installation space. This approach enables a holistic discussion of e-drive system tradeoffs. In particular, it reveals the best tradeoffs between the package space for electric machine and 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 a design problem of a common inverter topology for state-of-the-art e-drives. It turns out that a small inverter design height is critical to achieve highest energy efficiency of the overall e-drive system. In conclusion, 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 and cost are covered with a special focus on package integration. The method supports finding the best suitable system solution for individual electric powertrain requirements and priorities.