A Robust Multi-Input Multi-Output Control Strategy for the Secondary Controlled Hydraulic Hybrid Swing of a Compact Excavator With Variable Accumulator Pressure

Over the last decade, a number of hybrid architectures have been proposed with the main goal of minimizing energy consumption of excavator swing drives. One of the most notorious architectures is the secondary controlled hydraulic swing drive. One of the advantages of this system is that, through the installation of a hydraulic accumulator, energy which otherwise would be wasted can be stored and reutilized on demand. However, the fact that the hydraulic motor in this architecture operates under a constant high pressure at all times diminishes the overall system efficiency significantly. Therefore, to investigate machine power management strategies, it is imperative to formulate a controller that overcomes this weakness. In this paper, a robust multi-input multi-output controller is synthesized for the control of the hybrid swing velocity and for first time the control of the accumulator state of charge. The simplified plant is tested using a high fidelity nonlinear model developed in the Simulink-Matlab environment. The proposed controller is then tested and compared against a PI controller using the optimal accumulator pressure obtained from dynamic programming and the desired cab velocity. Results show satisfactory tracking of the swing drive velocity and pressure. In addition, a study of the nominal stability, robust stability and robust performance of the controlled system reveals the advantages of the H∞ controller.