T. Das

Rochester Institute of Technology, Rochester, New York, United States

Are you T. Das?

Claim your profile

Publications (20)17.36 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A novel wind machine is described in which an airfoil-like kite is tethered to a moving base; the non-conservative nature of the wind loads over a cycle of the kite allows energy to be extracted at the base. A dynamic model for the kite-tether system is derived which models the tether as a series of point masses connected by massless rods. The lift and drag characteristics of the kite are determined from airfoil calculations. The system has been found to be stable via simulation at several wind speeds of interest. A sample base motion which extracts energy from the oncoming wind is also presented.
    ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control; 01/2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The standard control problem of the pendubot refers to the task of stabilizing its equilibrium configuration with the highest potential energy. Linearization of the dynamics of the pendubot about this equilibrium results in a completely controllable system and allows a linear controller to be designed for local asymptotic stability. For the underactuated pendubot, the important task is, therefore, to design a controller that will swing up both links and bring the configuration variables of the system within the region of attraction of the desired equilibrium. This paper provides a new method for swing-up control based on a series of rest-to-rest maneuvers of the first link about its vertically upright configuration. The rest-to-rest maneuvers are designed such that each maneuver results in a net gain in energy of the second link. This results in swing-up of the second link and the pendubot configuration reaching the region of attraction of the desired equilibrium. A four-step algorithm is provided for swing-up control followed by stabilization. Simulation results are presented to demonstrate the efficacy of the approach.
    IEEE Transactions on Robotics 09/2009; · 2.65 Impact Factor
  • Source
    T. Das
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we present an observer design for species concentration estimation in recirculation based solid oxide fuel cell systems. The proposed strategy is useful for sensor reduction and control. In designing the observer, we attempt to reduce the number of required concentration sensors, that are often less reliable and also expensive, and instead use readily available voltage. We design a nonlinear adaptive observer based on voltage measurement that is an improvement upon our prior results. For this observer, we prove ultimate boundedness of state and parameter estimation errors with arbitrarily small error bounds.
    American Control Conference, 2009. ACC '09.; 07/2009
  • Source
    T. Das, R. Weisman
    [Show abstract] [Hide abstract]
    ABSTRACT: Solid oxide fuel cells are attractive energy conversion devices due to their fuel flexibility and high efficiency. Fuel utilization is a critical variable in SOFC systems that directly impacts efficiency and longevity. In this paper we propose a control strategy for mitigating drastic fluctuations in fuel utilization that arise during load transients. The strategy uses a feedback based dynamic input shaping approach. A preliminary control law derived from a model-based analysis forms the basis of this design. The strategy requires one fuel flow sensor upstream of the integrated fuel processor and admits convenient integration into a comprehensive hybrid fuel cell control algorithm.
    American Control Conference, 2009. ACC '09.; 07/2009
  • Tuhin Das, Ranjan Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: A global model structure is developed for parametrization and identification of a general class of Linear Parameter-Varying (LPV) systems. By using a fixed orthonormal basis function (OBF) structure, a linearly parametrized model structure follows for ...
    Automatica 06/2009; 45(6). · 3.13 Impact Factor
  • Source
    T. Das, R. Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: As an alternative to self-sensing, we propose the concept of shared-sensing for reversible transducers. In shared-sensing, reversible transducers are continuously switched between actuator and sensor modes. This results in a hybrid system, and, in this paper, we investigate stability properties of the equilibrium for linear systems and a class of nonlinear systems with a single shared-sensing transducer. Our theoretical results are validated through simulations and experiments with a dc servo motor.
    IEEE Transactions on Control Systems Technology 02/2009; · 2.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The standard control problem of the pendubot refers to the task of stabilizing its equilibrium configuration with the highest potential energy. Linearization of the dynamics of the pendubot about this equilibrium results in a completely controllable system and allows a linear controller to be designed for local asymptotic stability. For the under-actuated system, the important task is therefore to design a controller that will swing up both links and bring the configuration variables of the system within the region of attraction of the desired equilibrium. This paper provides a method for swing-up control based on a series of rest-to-rest maneuvers of the first link about its vertically upright configuration. The rest-to-rest maneuvers are designed such that each maneuver results in a net gain in energy of the second link. This results in swing-up of the second link and the pendubot configuration reaching the region of attraction of the desired equilibrium. A four-step algorithm is provided for swing-up control followed by stabilization. Simulation results are presented to demonstrate the efficacy of the approach.
    Intelligent Robots and Systems, 2008. IROS 2008. IEEE/RSJ International Conference on; 10/2008
  • Source
    Tuhin Das, Ranjan Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we address the problem of optimal switching for switched linear systems. The uniqueness of our approach lies in describing the switching action by multiple control inputs. This allows us to embed the switched system in a larger family of systems and apply Pontryagin’s Minimum Principle for solving the optimal control problem. This approach imposes no restriction on the switching sequence or the number of switchings. This is in contrast to search based algorithms where a fixed number of switchings is set a priori. In our approach, the optimal solution can be determined by solving the ensuing two-point boundary value problem. Results of numerical simulations are provided to support the proposed method.
    Automatica 05/2008; 5(5). · 3.13 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we propose the concept of shared-sensing for reversible transducers. In shared- sensing, the transducers switch between sensing and actuation modes, which is different from self-sensing where sensing and actuation are performed simultaneously. Both shared-sensing and self-sensing offer to reduce the number of transducers and provide collocation. However, our initial investigations indicate that shared-sensing has many advantages as compared to self-sensing. In this paper we develop observer based control design for systems with shared-sensing transducers. Through simulations and experimental results we demonstrate the simplicity and effectiveness with which shared-sensing and control can be implemented.
    American Control Conference, 2007. ACC '07; 08/2007
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The control problem of the pendubot refers to the task of stabilizing its equilibrium configuration with the highest poten-tial energy. Linearization of the dynamics of the pendubot about this equilibrium results in a completely controllable system and allows a linear controller to be designed for local asymptotic stability. Therefore, the real challenge is to design a control law for the underactuated system that will swing up both the links and brings the configuration variables of the system within the region of attraction of the equilibrium. This paper provides a method for swing-up control based on a series of start and stop maneuvers of the first link about its vertically upright configuration. The start and stop maneuvers are designed such that each maneuver results in a net gain in the energy of the second link. This results in swinging up of the second link and the pendubot configuration reaching the region of attraction of the desired equilibrium. A three step algorithm is provided for swing up control followed by stabilization. Simulation results are presented to demonstrate the efficacy of the approach.
    01/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we design an observer for online estimation of species concentrations in a steam reformer based Solid Ox-ide Fuel Cell (SOFC) system with anode recirculation and with methane as fuel. Since in SOFCs steam reforming occurs both in the reformer and in the fuel cell, a large number of concentra-tion sensors are necessary for accurate control of critical perfor-mance variables such as utilization and steam-to-carbon-ratio. The purpose of the observer is to reduce the number of sensors required for control. In contrast to existing observers which are either designed for chemical reactors or for fuel cells exclusively, our design considers the coupled dynamics of the reformer and the fuel cell. We design an adaptive observer where the rates of reforming reactions are treated as slowly varying unknown parameters. Using a few concentration sensors we show that all other species concentrations, molar flow rates, and reaction rates in the fuel path can be dynamically estimated. Simulation results are provided in support of the proposed design. NOMENCLATURE C p Specific heat at constant pressure (J/kg/K) C s Specific heat of solid volume (J/kg/K) C v Specific heat at constant volume (J/kg/K) E a , E b , E c Activation energy of reactions (a), (b), (c) in Eqns.(6) and (17) (J/mol) F Faraday's constant (= 96485.34 coulomb/mol) * Address all correspondence to this author.
    01/2007;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we perform transient analysis of a Solid Ox-ide Fuel Cell (SOFC) system. We consider a steam reformer based SOFC system with anode recirculation and with methane as fuel. For the analysis, we develop a control-oriented model that captures the details of heat and mass transfer, chemical ki-netics and electrochemistry of the SOFC system. The coupled dy-namics of the steam reformer and the fuel cell anode control vol-umes are extracted and through coordinate transformations we derive closed-form expressions characterizing the steady-state and transient behaviors of two critical performance variables of reformer-based SOFC systems, namely utilization and steam-to-carbon balance. Our analysis is supported by simulations. Using the results derived, we address steady-state fuel optimization by posing it as a problem in linear programming. Our results can be applied in predicting system response to step changes in cur-rent and will be useful in designing control strategies for SOFC based power plants. NOMENCLATURE C p Specific heat at constant pressure (J/kg/K) C s Specific heat of solid volume (J/kg/K) C v Specific heat at constant volume (J/kg/K) E a , E b , E c Activation energy of reactions (a), (b), (c) in Eqns.(6) and (17) (J/mol) F Faraday's constant (= 96485.34 coulomb/mol) * Address all correspondence to this author.
    01/2007;
  • Source
    T. Das, R. Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we address the problem of optimal switching for switched linear systems. The uniqueness of our approach lies in casting the switching action as multiple control inputs. This allows us to apply the concept of Pontryagin's minimum principle in solving the optimal control problem. There is no restriction on the switching sequence or the number of switchings although the later is bound by the sampling interval. This is in contrast to search based algorithms where a fixed number of switchings is set a priori. We solve the optimization problem using an iterative scheme where a two point boundary value problem is solved. Simulation results are provided to support the proposed method
    American Control Conference, 2006; 07/2006
  • Source
    Tuhin Das, Ranjan Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: The task of complete reconfiguration of a rolling sphere is recast as a problem in planar geometry. Based on our specific choice of coordinate system, two control points are defined that equivalently represent the configuration of the sphere. Under the applied control inputs, the trajectories of these control points are shown to form an evolute-involute pair. The objective of complete reconfiguration is then captured within integral conditions over the path of the control points. A class of solution to the geometric problem is derived and a three step algorithm for complete reconfiguration is proposed. The solution is computationally in-expensive and is confirmed by simulation results.
    Journal of Applied Mechanics 01/2006; 73(4). · 1.40 Impact Factor
  • Source
    Tuhin Das, Ranjan Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we present a non-smooth controller for exponential stabilization of the sphere. This has remained an open problem despite significant progress in nonholonomic systems. Our control design is based on inputs in a rotating coordinate frame that individually produce primitive motions of the sphere along straight lines and circular arcs. The rotating coordinate frame is chosen in concert with Euler angle description of orientation and placement of the desired configuration at the singularity of the representation. In our paper, we separately establish global stability of the desired configuration and exponential convergence. Our theoretical claims are validated through numerical simulations.
    Automatica 11/2004; · 3.13 Impact Factor
  • Source
    T. Das, R. Mukherjee
    [Show abstract] [Hide abstract]
    ABSTRACT: In an earlier paper, we addressed the problem of stabilization of the rolling sphere about any desired configuration. For the controller proposed, we establish in this paper global stability of the desired configuration and exponential convergence of trajectories to this configuration from a large and well defined set in the configuration space. For configurations that lie outside the set, we define simple maneuvers to move them within the set in finite time such that the sphere can be exponentially converged to the desired configuration thereafter. Our theoretical claims are validated using simulations.
    Decision and Control, 2003. Proceedings. 42nd IEEE Conference on; 01/2004
  • R. Mukherjee, T. Das
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we discuss the problem of reconfiguring a sphere, rolling without slipping on a flat surface, from an arbitrary initial configuration to a desired final configuration. We propose a control algorithm that utilizes two control actions that are applied alternately. The individual control actions cause trajectories that are circular arcs and straight line segments. Through judicious choice of the sequence of individual control actions based on state feedback, we construct a control strategy that stabilizes the sphere to its desired configuration. Simulation results are presented to demonstrate the efficacy of the strategy.
    Intelligent Robots and Systems, 2002. IEEE/RSJ International Conference on; 02/2002
  • 40th AIAA Aerospace Sciences Meeting & Exhibit; 01/2002
  • [Show abstract] [Hide abstract]
    ABSTRACT: The design problems in the development of a spherical mobile robot are discussed in this paper. These problems include dynamics and design of the propulsion mechanism, motion planning and control problems, actuator selection and sensor placement, design and fabrication of the exo-skeleton, and other issues related to power management and computing. Each of the problems are discussed in brief and presented in relation to the spherical mobile robot currently under development at Michigan State University.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2001; · 0.20 Impact Factor
  • T. Das, R. Mukherjee
    Journal of Applied Mechanics 01/2001; 68(1). · 1.40 Impact Factor