Modelling and Control of a Complementary Energy Recuperation System for MobileWorking Machines

The concept of hybrid technologies for mobile working machines has gained increased attention in recent years. This paper deals with a parallel hybrid system for energy recuperation based on a two-machine hydraulic transformer. The system can be connected hydraulically to an existing hydraulic circuit as a complementary add-on system. The linear analysis of the system visualises the control difficulties coming from a low inertia, slow control dynamics of the machines and the non-linear stick-slip friction during low speeds. A control strategy based on linear control methods is proposed and evaluated in a hardware test bench. It is shown that an acceptable performance can be achieved even with fairly simple models. Additionally, a start-up procedure is proposed to start the transformer from zero speed.