Energy Saving of Dual-Machine Systems in Speed-Addition and Torque-Addition Architectures

Multimachine systems are increasingly utilized in electrified vehicles, offering enhanced opportunities for system optimization. This article investigates the energy-saving potentials of two dual-machine systems designed for electric vehicles: one employing speed addition and the other torque addition. In the speed-addition system, two electrical machines are linked to the sun and the ring of a planetary geartrain. In the torque-addition system, both machines share the same shaft. To ensure a fair assessment, a unified co-design that involves sizing, design, modeling, control, and energy management is adopted. Each machine is designed using the finite element method (FEM), following optimal sizing specifications with uniform materials, topologies, and adherence to identical physical constraints. Comparative trip analyses employing optimal energy management strategies reveal distinct outcomes. The speed-addition system achieves an energy saving of up to 3% compared to a conventional single-drive vehicle. In contrast, the torque-addition system demonstrates a more substantial energy saving of up to 12%. The findings confirm that the dual-machine system using torque addition is notably more efficient and advantageous for automotive applications under the same constraints, outperforming the speed-addition configuration in terms of efficiency, cost, volume, mass, and complexity.