Combined Control and Design Optimization of a Parallel Electric–Hydraulic Hybrid Wheel Loader to Prolong Battery Lifetime

Electric off-road vehicles provide an opportunity for reductions in noise pollution and tailpipe emissions along with increased fuel economy, productivity, and reliability. However, the complex duty cycles, high power requirements, and long operational hours present difficulties toward electrification. Hybridizing the powertrain with the addition of a hydraulic accumulator as a secondary power source increases the battery life and can reduce energy consumption with appropriate control. The complex interactions between powertrain component sizing and optimal operation are key to enhancing the overall system operation. Co-design or combined control and design optimization creates an optimal solution that considers this coupling, superior to the traditional sequential design approach. This work formulates and solves the control co-design problem for a wheel loader with a parallel electric-hydraulic hybrid powertrain. A verified digital-twin wheel loader model that captures the bucket rigid-body dynamics, lifting mechanism, and soil particle mechanics is used to generate diverse working cycles. Our co-design methodology minimizes the total operational cost by emphasizing battery life requirements and accounting for powertrain component and energy usage costs. The optimal result decreases the total cost compared to a purely electric wheel loader. Comparison of specified sequences demonstrates that the optimization is robust to material changes and showcases a strong correlation between cycle speed and powertrain component sizes.