Department of Electrical & Computer Engineering
|1515 St. Catherine W., EV12.111|
Montréal, Québec, Canada H3G 2W1
|Tel.: (514) 8482424 Ext.3135|
Fax.: (514) 8482802
Email: luisrod at encs.concordia.ca
All of these research interests fit into my three primary focus areas within the theory and practice of automatic control systems: (1) the development and validation of mathematical models of complex dynamic systems; (2) the analysis of the stability and performance properties of these systems and (3) the synthesis and the validation of automatic controllers that can improve stability and performance of these systems. My main research interest, besides increasing knowledge and understanding, is the development of technology leading to novel automatic controllers that can be used in industry to enhance performance of engineering systems while saving energy and being sustainable. To synthesize such novel controllers, it is essential to understand the physical principles behind the particular engineering system to be controlled to be able to develop an accurate mathematical model that can then be used for controller design. Knowledge of optimization techniques is important so that energy can be minimized for such systems making them more sustainable.
My research group is working on novel switching controller design methods that can be cast as optimization problems that can then be solved numerically.
The focus is on a particular class of switched controllers with a special switching structure, called piecewise-affine controllers. The final objective is the development of modeling and synthesis
algorithms that can be easily programmed into available computer-aided design software such as, for example, Matlab/Simulink (a trademark of The Mathworks Inc.) or Maple (a trademark of Maplesoft) and then interfaced with
a real-time operating system for implementation in engineering systems. The advantages of considering switched controllers in engineering applications is twofold:
My research group has been working on synthesis of optimal flight management systems, energy-efficient autopilots with applications to commercial jets and Uninhabited Air Vehicles (UAVs).
One of the main difficulties in controlling these vehicles is the fact that their dynamics are highly nonlinear and, as one scales down to the micro scale (considered to be around 15 cm wingspan or even less),
aerodynamics at small Reynolds numbers must be considered instead of the more conventional large Reynolds number condition.
On top of this, the communication between vehicles in formation and the associated delays and possible packet dropouts of the wireless network add complexity to the task of controller design.
The computer-aided design methodology we are developing, approximates the nonlinear terms by piecewise-affine terms and then designs a
piecewise-affine controller for this approximate model that is guaranteed to stabilize the original system for small enough modeling errors.
The research of our group has focused so far on the following aerospace applications:
Switched controller synthesis has also being investigated in my research group for automotive applications, mostly in active suspension systems, ABS and engine valves. In suspension systems, magneto-rheological actuators exhibit a characteristic behavior that can be described accurately by a piecewise-affine function. The dynamic models are thus naturally in the framework of piecewise-affine systems for which the computer-aided design methodology being developed in my group is the appropriate tool to be used. In ABS systems, the variation of the coefficient of adhesion to the road versus slip coefficient can be accurately approximated by a piecewise-affine characteristic with only three sectors. The methodology being developed in my research group can then be applied to design controllers that guarantee a working point close to the maximum coefficient of adhesion to the road. Finally, the unthrottled control of engine valves has the potential to be made possible using voice coil actuators controlled by a Pulse Width Modulation (PWM) controller that switches between two voltage levels: one for good performance in the transient period and another for good performance in steady state. The analysis and synthesis of such controller falls under the framework of switched control and the tools developed in our group are also applicable (past collaboration with Dr. Hong).
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Speech signals are nonstationary signals. However, for speech frames of very small periods of time (typically on the order of miliseconds), the speech signal can be assumed to be stationary. For articulatory models (models of the mechanical articulators, such as lips, tong and teeth) of speech frames of this duration, a linear model can be accurate enough. Therefore, switched linear systems are adequate articulatory speech models for speech frames having minutes to hours of speech. The research in this area, in a past collaboration with Dr. Kroeker from Eliza Corporation has focused on the modeling of speech production systems and the study of properties such as controllability and state transfer, as well as the energy of speech. In the future, controller synthesis for speech production and speech recognition will be targeted.top of page
The model of inventory in production systems leads naturally to a constrained switched system. The switching variable is the stock level. When the stock level is positive, the produced parts are being stored. When the stock level is negative it leads to backorders, which means that orders for production of parts are coming in and there are no stocked parts to immediately meet the demand. These two situations correspond to different models that are switched based on the sign of the stock level. A state feedback controller that forces the stock level to be kept close to zero (sometimes called a just-in-time policy), even when there are fluctuations in the demand, can be designed using piecewise-linear H-infinity control theory. The synthesis of the state feedback controller that quadratically stabilizes the production dynamics and at the same time rejects the external demand fluctuation (treated as a disturbance) can be cast as a set of linear matrix inequalities (LMIs) and solved numerically in a efficient way, given that the resulting optimization problem is convex. Future work will concentrate on the study of interconnected production systems in supply chains (this work started as a past collaboration with Dr. E.-K. Boukas from Ecole Polytechnique).
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If you are a student with a background on either electrical or mechanical and aerospace engineering, and you are interested in one of these topics, here is what I am looking for in the background of students:
I am the founder of the HYbrid CONtrol Systems (HYCONS) Lab and the leader of the
Flight Simulation and Control Laboratory at Concordia University.
Aerospace Control Theory and Applications
Control and Art
From left to right: Behzad Samadi, KyungJae Baik, Scott Casselman, Luis Rodrigues, Shaun DiSalvo, Xiaoxi Huang, Giancarlo Luglio
Past Collaborations with Postdoctoral Fellows:
The following students have worked in my lab and have already graduated: