T. Das

Rochester Institute of Technology, Rochester, NY, United States

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Publications (14)7.61 Total impact

  • Source
    T. Allag, T. Das
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    ABSTRACT: Mitigating fuel starvation and improving load-following capability of solid oxide fuel cells (SOFC) are conflicting control objectives. In this paper, we address this issue using a hybrid SOFC ultracapacitor configuration. Fuel starvation is prevented by regulating the fuel cell current using a steady-state invariant relationship involving fuel utilization, fuel flow, and current. Two comprehensive control strategies are developed. The first is a Lyapunov-based nonlinear control and the second is a standard H <sub>∞</sub> robust control. Both strategies additionally control the state of charge of the ultracapacitor that provides transient power compensation. A hardware-in-the-loop test stand is developed where the proposed control strategies are verified.
    IEEE Transactions on Control Systems Technology 02/2012; · 2.52 Impact Factor
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    Tahar Allag, Tuhin Das
    IEEE Trans. Contr. Sys. Techn. 01/2012; 20:1-10.
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    Tuhin Das, Steven Snyder
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    ABSTRACT: Solid oxide fuel cells (SOFCs) offer a number of advantages beyond those of most other fuel cells. However, like other fuel cells, rapid load following is difficult, and can lead to fuel starvation and consequently fuel cell damage. Mitigating fuel starvation and improving load following capabilities are conflicting control objectives. However, the issue can be addressed by the hybridization of the system with an energy storage device. A steady-state utilization property, combined with a current regulation strategy, is used to manage transient fuel utilization. Meanwhile, an overall system strategy is employed to manage energy sharing in the hybrid system for load following as well as for maintaining the state-of-charge of the energy storage device. This work presents an adaptive strategy which updates the controller based on current parameter estimates. The control design is validated on a hardware-in the-loop setup and experimental results are provided.
    American Control Conference (ACC), 2011; 08/2011
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    Tahar Allag, Tuhin Das
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    ABSTRACT: In this paper we design robust control strategies for a hybrid solid oxide fuel cell ultra-capacitor system. Fuel cell control is established by using an invariant property of fuel utilization within an input-shaping framework. Two control strategies are developed. The first design uses a nonlinear control approach for which we prove the stability of the closed-loop system in presence of system uncertainties. The second uses a standard H<sub>∞</sub> robust control approach. Both strategies enforce the control of State of Charge (SOC) of the ultra-capacitor to a desired level. A hardware-in-the-loop test-stand is developed and experimental results are provided.
    American Control Conference (ACC), 2010; 08/2010
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    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; · 2.57 Impact Factor
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    T. Das
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    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
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    T. Das, R. Weisman
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    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
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    T. Das, R. Mukherjee
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    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
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    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
    T. Das, R. Mukherjee
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    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
    T. Das, R. Mukherjee
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    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
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    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
  • T. Das, R. Mukherjee
    Journal of Applied Mechanics-transactions of The Asme - J APPL MECH. 01/2001; 68(1).

Publication Stats

43 Citations
7.61 Total Impact Points

Institutions

  • 2009–2012
    • Rochester Institute of Technology
      • • Department of Electrical and Microelectronic Engineering
      • • Department of Mechanical Engineering
      Rochester, NY, United States
  • 2011
    • University of Central Florida
      • Department of Mechanical and Aerospace Engineering
      Orlando, Florida, United States
  • 2002–2009
    • Michigan State University
      • Department of Mechanical Engineering
      East Lansing, MI, United States