Professor Daniel Liberzon, from the Department of Electrical and Computer Engineering at the University of Illinois Urbana-Champaign, USA, has visited CDSL. His main research area includes switched system, networked system, and nonlinear control theory. Especially, he has conducted multiple collaborative works such as nonlinear observer design with prof. Shim. He delivered the following three lectures during his visit.
The title of the first lecture was “Nonlinear control with limited information”. Prof. Liberzon introduced a framework over the limited flow of information between the plant and the controller in the context of nonlinear control. Specifically, prof. Liberzon focused on the cases where the limitations arise from time-delay, external disturbance, and quantization error. He analyzed the effects of such limitations using control theoretic tools such as input-to-state stability, Lyapunov functions, and hybrid systems theory. As a result, he captured the interplay between control and communication by building such theoretical framework.
In the second lecture, prof. Liberzon introduced an iterative algorithm which estimates the state of a contiuous-time nonlinear system with quantized and sampled state measurements. Prof. Liberzon proposed a novel notion called ‘estimation entropy’ and used this to show that the algorithm converges to the actual state at a desired exponential rate with the lowest bit rate possible. He also mentioned that his team is now working on extending the algorithm to switched systems.
Lastly, prof. Liberzon delivered the lecture under the title “Nonlinear observers robust to measurement errors and their applications in control and synchronization”. The concept of quasi-Disturbance-to-Error Stable (qDES) observer is presented with the relation to an asymptotic ratio characterization of input-to-state stability, which is one of the collaborative works with prof. Shim. Prof. Liberzon also introduced some applications of qDES observer, to control problems such as output feedback control design and synchronization of electric power generators in the presence of measurement errors.
Overall, it was a great honor to share three lectures with prof. Liberzon. We hope that CDSL students and other seminar attendees are motivated by these creative ideas and develop further ideas on nonlinear system and control. Also, we are looking forward to the future collaborative research of prof. Liberzon and prof. Shim!
