The research objective of this award is to investigate control methods for cancelling external disturbances for nonminimum-phase systems. Performance of feedback controller is limited for nonminimum-phase systems due to the special structure of the system dynamics. Recent developed non-causal feedforward techniques can only be effective when sufficient preview information of the disturbance is available. This research will investigate feedforward-based control for nonminimum phase systems when the disturbance is not known in advance. The theoretical developments will be for general nonminimum phase systems, and can be applied in diverse applications. The research issues to be addressed are: (i) Stability, since loss of stability can arise with multiple output transitions due to an outer-loop closure; (ii) Performance, e.g. maintaining system output within the desired region under multiple transitions triggered by aggressive disturbances, and (iii) Computation effort. It is important to keep the computational effort at an acceptable level, e.g., approximating the feedforward for output transitions from a set of pre-computed trajectories. Deliverables include tools to design controllers for nonminimum phase systems, conditions for guaranteed stability and performance, documentation of research results, and engineering student education.
This research will impact a variety of applications (with nonminimum phase dynamics), such as, (i) precision control of probe-sample forces to avoid sample damage during high-speed operation of Atomic Force Microscopes; (ii) wind turbines in the presence of wind-gust disturbances that are challenging to measure a-priori; and (iii) flight control of small unmanned aerial vehicles (UAVs), which are more sensitive to wind disturbances. Graduate and undergraduate engineering students will benefit through classroom instruction and involvement in the research. In addition to dissemination to students and other academics through classes, seminars, publications, and conference presentations, the results will be presented to high-school students and the community through exhibits in annual open houses.
