Nonlinear Control of Multi-Actuator Electrohydraulic Systems Based on Feedback Linearization with Application to Road Simulators

Open Access
Ayalew, Beshahwired
Graduate Program:
Mechanical Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
June 24, 2005
Committee Members:
  • Barbara E Kulakowski, Committee Chair
  • Moustafa El Gindy, Committee Member
  • Heath Hofmann, Committee Member
  • Kathryn Weed Jablokow, Committee Member
  • Christopher Rahn, Committee Member
  • actuator interaction
  • sliding mode control
  • input-output linearization
  • feedback linearization
  • electrohydraulic acutator
  • road simulators
Electrohydraulic actuators exhibit significant nonlinearities in their dynamics that are better handled by the use of more elaborate control techniques than the ubiquitous PID controllers. In this work, physical models are developed for a single actuator system including the major onlinearities and the dynamics of supply and return line components. A new result obtained from modal approximation of distributed transmission line dynamics is detailed. The experimentally validated interconnected system model is then used to derive nonlinear pressure/force and position controllers based on feedback linearization (Near input-output (IO)linearization) and sliding mode control to handle the nonlinearities. It is shown that the Near IO linearizing position controller is equivalent to a cascade controller implementing the Near IO linearizing pressure/force controller as an inner-loop to a feedback plus feed forward outer-loop position controller. A consequence of the equivalence is that a simple procedure for the design of the Near IO linearizing position controller is revealed. Furthermore, the cascade form allows one to view the robustness issues for position control from a Lyapunov backstepping perspective. The performance of the nonlinear controllers is compared against standard PID and linear state feedback with integral controllers using experiments and simulations of the nonlinear system model. It is shown that the nonlinear controllers have better tracking performance than the linear controllers. The linear (PID+ delta p) and nonlinear (Near IO linearizing) position controllers are considered further in a multi-actuator application in road simulation with a nonlinear full-bus model of a transit bus as the test vehicle. It turns out that there is little interaction between either of the linear or the nonlinear decentralized position controllers. However, a second cascaded decentralized control structure considered for tracking a remote parameter like spindle vertical acceleration response faces significant and persistent interactions. Finally, for a typical rough road profile, it is shown that the decentralized Near IO linearizing controllers give a more than 60% performance improvement in the tracking error metric across all four actuators and a more than 50% improvement in response matching of the sprung mass acceleration power spectral density over the decentralized linear controllers.