| This thesis work focuses on the development, analysis, simulation, and implementation of a hybrid control methodology and its applications to physical systems such as an active vibration isolation system with electrohydraulic actuation.; Individual controllers suffer from the basic trade-off between performance and robustness. A hybrid control methodology switching between an adaptive controller and a robust controller is thus developed to lessen the fundamental trade-off for single controllers, and achieve high performance and robustness in one control system. The stability analysis of the hybrid control methodology is based on a new coordinated dwell-time approach, an improved version of traditional dwell-time approaches frequently used to guarantee the stability of hybrid systems. Simulation and implementation results demonstrate the effectiveness of the proposed methodology in reducing the fundamental trade-off between performance and robustness for single controllers, as well as combining the advantages of individual controllers.; Another major contribution of this thesis work is the development of new approaches to achieve broad-band active vibration isolation with electrohydraulic actuation. Two new methods, the velocity-tracking approach and the position-tracking approach, are proposed and implemented in a custom-built multiple degree-of-freedom active vibration isolation testbed. These approaches circumvent the fundamental bandwidth limitations associated with traditional force-control approaches, and significantly improve vibration isolation performance achievable by force-control approaches. The effectiveness of the position-tracking approach to selectively isolate different vibration modes in multiple dimensional systems is also demonstrated through simulation studies. |
