Synthesis of a MIMO QFT controller for hydraulic hybrid swing system of excavators

In swing system of excavators, energy recuperation and hybrid actuation is desirable to improve energy efficiency because of its characteristic large inertial load and cyclic operation. Numerous studies have focused on optimisation of hybrid structures and power management strategies, whereas only a little attention has been paid to the control performance of hybrid swing drives. This paper investigates the control problem of the secondary controlled hybrid swing drive and employs multi-input multi-output quantitative feedback theory (MIMO QFT) for controller synthesis. Considering parametric uncertainties in load variation, viscous friction and bulk modulus, a two-input two-output QFT control scheme is constructed according to specifications given by robust margin, sensitivity reduction and tracking performance. Through simulation evaluation, the MIMO QFT controller shows excellent tracking performance over the defined range of uncertain parameters and much better robustness as compared to a well-tuned PI controller. The synthesis process is visualised, which is practical and promising for its further use in industrial settings.