H∞ control of load-sensing electro-hydraulic servo system

Robust control design for load-sensing electro-hydraulic servo system for power steering of mobile machines is presented. Systematic approach is taken, where first a precise mathematical model is fitted to the experimental data obtained during an identification experiment using the prediction error methods and state space structure. Then H∞ controller is designed using the identified model by selecting appropriate manipulated signals and performance indicators together with respective weighting filters. Selection of the filters is achieved by observing the requirements for load disturbance attenuation in the low frequency band and acceptable controller gain in the high frequency band associated with the sensor noise amplification in the actuators. The H∞synthesis is carried by selecting an upper bound for the H∞ norm of the closed-loop interconnection between external disturbances and the performance indicators for a parametrized controller family. Selection of the upper bound is done with the bisection algorithm. The designed controller guarantees the internal stability of the closed-loop system which is verified with spectral stability criteria. Also the performance of the closed-loop system is verified in simulation by applying realistic reference signal. The controller is tested on a test rig with installed PLC over the CAN. Such real-time interconnection can be described as a HIL simulation which is a vital step in the modern embedded system development process.