Energy management control strategies for hybrid construction equipment: Load sharing between diesel and electric prime movers in parallel hybrid excavators

Abstract

This study involves the development and evaluation of energy management strategies for hybrid excavators. A simulation-based framework was established in MATLAB and Simulink to model a parallel-hybrid powertrain with a diesel engine and electric motors driving the central hydraulic pump of an excavator. The load power from the pump was split between the prime movers by controllers programmed to follow certain strategies. Dynamic Programming (DP), Equivalent Consumption Minimi sation Strategy (ECMS), and a rule-based approach were formulated and assessed under varying operating conditions. The evaluation was conducted on a 50-tonne excavator using drive cycles with high, medium, and low power demands, subject to the operational constraints of using a smaller engine, maintaining the battery state of charge (SoC) balance over each drive cycle, and maintaining constant hydraulic pump speed under load. Results indicate that a carefully designed rules-based strategy can achieve perfor mance comparable to ECMS and the globally optimal solution indicated by the DP, while requiring substantially lower computational requirements than the other two, thereby enhancing its suitability for real-time implementation. Fuel consumption reductions were observed across all cycles, with more pronounced improvements in medium- and low-power scenarios. Combined fuel savings across all drive cycles for the 50-tonne machine were measured at 6-8%. These learnings were further applied to a high-power cycle of a 75-tonne excavator, with similar results. The study thus demonstrates that a hybrid configuration comprising a smaller internal combustion engine, supplemented by electric machines, can deliver operational capability equiv alent to that of a larger combustion engine. This enables increased flexibility in powertrain design, allowing manufacturers to expand machine capacity with their existing engines. An assessment of the total cost of ownership (TCO) was also conducted for the 50-tonne hybrid, incorporating both fuel savings and machine cost increases com pared to the conventional machine. For this, an estimate of the required battery size was also made. Overall, the results demonstrate that hybridisation, combined with effective energy management strategies, can significantly enhance the efficiency, adaptability, and economic feasibility of construction machinery.