Mini-Workshop on
Cooperative Control
Jointly Organized
by
Division of Control and Instrumentation, EEE, NTU
IEEE Singapore Control Systems Chapter
Date: 18 April 2008 (Friday)
Time : 03:30 pm to 05:45 pm
Venue: Executive Seminar Room (S2.2-B2-53)
School of EEE
Nanyang Technological University
03:30 – 03:50pm
Exploring Hybrid Cooperative Control for Multi-robot Systems
Prof. Hai Lin, National University of Singapore
03:50 – 04:10pm
Formation Flying of Nanosatellites: A Model Predictive Control Approach
Prof. Yun Chung Chu, Nanyang Technological University
04:10 – 04:30pm
Decentralized Adaptive Control
Dr. Hongbin Ma, Temasek Lab, National University of Singapore
04:30 – 04:45pm
Tea Break
04:45 – 05:05pm
A Leader-Follower Formation Flight Control of UAV Helicopters
Mr. Yun Ben, Nantional University of Singapore
05:05 – 05:25pm
Asymptotically Unbiased Average Consensus Under Measurement Noises and Fixed Topologies
Mr. Tao Li, Nanyang Technological University
05:25 – 05:45pm
Nonlinear Optimization of Low-thrust Trajectory for Satellite Formation
Mr. Baolin Wu , Nanyang Technological University
Abstract and Biographies of Speakers
Exploring Hybrid Cooperative Control for Multi-robot Systems
Prof. Hai Lin, NUS
Abstract: Nowadays, it becomes possible to deploy hundreds and even thousands of small and
inexpensive ground, air, and under water robots. Although each individual robot could be very rudimentary
with very limited capabilities, however the large collection of these robots, as a whole, may exhibit
remarkable capabilities and display highly complex behaviors. Most of the exciting research activities so far
have been focused on understanding how global behavior is generated from local interactions among these
robots. However, a more important question is how to design these local interaction rules such that certain
desired global behaviors can be achieved. The control of such large scale complex systems poses several
new challenges that fall beyond the traditional methods and calls for new frameworks and approaches. This
talk aims to share some thoughts and viewpoints from the perspective of hybrid systems and symbolic
control. In particular, we will describe our research thrust in developing a formal design method for
distributed coordination and control of multi-robot systems. The stages of the research effort and
corresponding challenges are briefed. Then, the talk finishes with discussions on our current on-going
research activities along this direction.
Speaker: Dr. Lin Hai is currently an assistant professor in the National University of Singapore, Electrical
and Computer Engineering Department. He received the B.S. degree from University of Science and
Technology, Beijing, China in 1997, the M.Eng degree from Chinese Academy of Science, China in 2000,
and the Ph.D. degree from the University of Notre Dame, USA in 2005. His research interests are in the
multidisciplinary study of the problems at the intersection of control, communication, computation and life
sciences. He is particularly interested in hybrid systems theory, networked systems, and systems biology.
Formation Flying of Nanosatellites: A Model Predictive Control Approach
Prof. Yun Chung Chu, NTU
Abstract: In this talk, the formation keeping of nanosatellites in eccentric earth orbits is considered. The
overall control design follows a non-hierarchical control architecture based on the virtual structure approach.
For the local level control, the linear parameter varying model describing the relative motion of member
satellites is approximated by an uncertain model with polytopic uncertainties. An infinite-horizon robust MPC
is then used to handle the model uncertainties as well as the state and control constraints while minimizing
the fuel requirement. In addition, a scheme for switching on/off of the individual satellite controllers for
minimizing overall fuel consumption is explored. The performance of this control strategy is studied with an
extensive nonlinear satellite formation simulation. Simulation results show the effective performance of the
overall control strategy.
Speaker: Dr. Y. C. Chu received the B.Sc. degree with first class honours in Electronics and the M.Phil.
degree in Information Engineering from the Chinese University of Hong Kong, Hong Kong, in 1990 and 1992
respectively, and the Ph.D. degree in Control from the University of Cambridge, U.K., in 1996. He worked as
a Postdoctoral Fellow at the Chinese University of Hong Kong in 1996-97, a Research Associate at the
University of Cambridge in 1998-99, and is currently an Associate Professor in the School of Electrical and
Electronic Engineering, Nanyang Technological University, Singapore. His research interests are control
theory and artificial neural networks, with applications to spacecraft, nanoelectronics, optical sensing,
combustion oscillations and power systems.
Decentralized Adaptive Control
Dr Hongbin Ma, Temasek Lab@NUS
Abstract: In this talk, we shall briefly introduce some of our work on decentralized adaptive control,
including the motivations of our work, the theoretical problem framework, and two concrete examples that
we have studied. Some conceptual ideas will be demonstrated although only very basic issues are
discussed and many challenging issues are still left for consideration in the future.
Speaker: Hongbin Ma was born in 1978, in China. He received the B.Sc. degree in Mathematics from
Zhengzhou University, China, in 2001 and the Ph.D. degree in Control Theory and Operational Research
from Institute of Systems Science, Academy of Mathematics and Systems Science, Chinese Academy of
Sciences, in 2006. Currently he is a research scientist in Temasek Laboratories, National University of
Singapore. His research interests include dynamical games, pursuit and evasion, stochastic control
systems, adaptive estimation and control, hybrid systems and multi-agent dynamical systems.
A Leader-Follower Formation Flight Control of UAV Helicopters
Mr. Yun Ben, Nantional University of Singapore
Abstract: Cooperative control of unmanned vehicles has received significant interest due to a variety of
applications. Autonomous UAV is capable of accomplishing important missions while reducing risk to
personnel. The advantages of small-scale helicopters for UAV research include their agility and their vertical
takeoff and landing capability. Moreover, the ability to hover is useful in many applications. Along with these
advantages come several characteristics that make small-scale helicopters difficult to model and control.
Specifically, the dynamics are nonlinear, unstable, and subject to complex aerodynamic effects. In this talk,
through theoretical analysis and formula deduction, a simple formation dynamic model for the wing UAV in a
leader-follower formation flight scheme is developed. In the formation control algorithm, only the leader
periodically broadcasts its position and velocity (or velocity reference) to the other vehicles that are
commanded to maintain a fixed separation from the leader while following a prescribed trajectory. To avoid
collision between formation team members, we proposed a hybrid decision making scheme, which is
verified in simulation. An experiment with a virtual leader via wireless communication shows the overall
formation scheme yields a good performance.
Speaker: Mr. Yun Ben received his B.Sc and M.Sc. in Control Engineering from Harbin Institute of
Technology in 1997 and 2000, respectively. After graduation, he worked at Beijing Institute of Control
Engineering (BICE), Chinese Academy of Space and Technology (CAST). He is currently studying towards
his Ph.D. in Electrical and Computer Engineering at National University of Singapore. His current research
interests include sensor fusion, formation flight control of multiple unmanned aerial vehicles. He is a student
member of IEEE.
Asymptotically Unbiased Average Consensus Under Measurement Noises and Fixed Topologies
Mr Tao Li, EEE, NTU
Abstract: This work is concerned with average-consensus control under directed topologies and random
measurement noises. To attenuate the measurement noises, time-varying consensus gains are introduced
in the protocol. It is shown that under the protocol designed, all agents' states converge to a common
Gaussian random variable, whose mathematical expectation is just the average of the initial states, and the
mean square static error vanishes as the number of agents increases to infinity under certain topologies. In
addition, for the noise-free case, necessary and sufficient conditions are given on the network topology and
consensus gains to achieve average-consensus; and for the noisy measurement case, by combining
algebraic graph theory and stochastic analysis, necessary and sufficient conditions are given on the
consensus gains to achieve
asymptotically unbiased mean square average-consensus.
Speaker: Tao Li was born in Tianjin, China, in 1981. He received the B.S. degree in Automation from
Nankai University, Tianjin, China, in 2004. Now he is a Ph.D. candidate of Academy of Mathematics and
Systems Science, Chinese Academy of Sciences, Beijing, China. His current research interests are system
modeling, stochastic systems and multi-agent systems.
Nonlinear Optimization of Low-thrust Trajectory for Satellite Formation
Mr. Baolin Wu , Nanyang Technological University
Abstract: In this talk, we focus on the design of fuel-optimal maneuver strategy to reconfigure
satellite formation using low thrust propulsion system. We cast it as an optimization problem with a
desired final satellite formation configuration subject to collision avoidance constraints on the paths
of the chief and all deputy satellites. The satellite terminal orbit states corresponding to this desired
satellite formation are ensured by including energy-matching condition and final geometry
configuration constraints in the problem formulation. In addition, we adopt our recently developed
relative satellite kinematics model to accurately describe relative satellite orbit geometry in the
presence of J2 effects. The resulting nonlinear optimal control problem is converted into a nonlinear
programming problem by application of Legendre pseudospectral method and is solved using a
sparse nonlinear optimization algorithm named SNOPT. Simulation results demonstrate the
efficiency of our method in designing fuel-optimal satellite maneuvers for several formation
reconfiguration problems.
Speaker: Baolin Wu received the BS and the MS degrees from the Harbin Institute of Technology,
Harbin, People’s Republic of China, in 2003 and 2005, respectively. He is now completing the PhD
degree in the Aerospace Electronics Lab, School of Electrical and Electronics Engineering,
Nanyang Technological University, Singapore. His current research interests are in the area of
optimal control, and satellite formation control.