Tuhin Das

University of Central Florida, Orlando, Florida, United States

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Publications (33)26.06 Total impact

  • Energy 08/2015; DOI:10.1016/j.energy.2015.07.076 · 4.84 Impact Factor
  • Greg Semrau · Sigitas Rimkus · Tuhin Das
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    ABSTRACT: The key control problems associated with variable speed wind turbines are maximization of extracted energy when operating below the rated wind speed, and power and speed regulation when operating above the rated wind speed. In this paper, we develop a nonlinear systems framework to address these problems. The framework is used to visualize and analyze the equilibria of the wind turbine as its operating regimes and controllers change. For both below rated and above rated wind speeds, we adopt nonlinear controllers, analyze the stability property of the resulting equilibria, and establish the criterion for switching between control regimes. Further, the regions of attraction of the resulting equilibria are determined, and the existence of a common region of attraction, which allows stable switching between operating regimes, is shown. The control input maintains continuity at the point of switching. We next provide a method for blade pitch modulation to control rotor speed at high wind speeds. Through Lyapunov stability analysis, we prove stability of the equilibria in the presence of the two independently functioning torque-and pitch-control feedback loops. Simulation results are presented and the controller is compared with existing works from the literature.
    Journal of Dynamic Systems Measurement and Control 04/2015; 137(4). DOI:10.1115/1.4028775 · 1.04 Impact Factor
  • Omid Madani · Tuhin Das
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    ABSTRACT: Controlling the transient response of variables for which sensing or accurate estimation is not feasible, and a detailed plant model is also largely unavailable, poses significant challenges. It is a situation that is true in solid oxide fuel cells. In SOFCs, transient control is essential for fuel utilization, especially if the fuel cell is to be operated in a dynamic load-following mode at high fuel utilization. The objective is to design the control input(s) such that it isolates the output (fuel utilization in this case) from measurable disturbances, while the plant itself maybe largely unknown. The features assumed known are the output’s functional dependence on states which is essentially the output definition, and the steady-state equation relating the multiple inputs and the output of interest. Simulations have shown good disturbance rejection in fuel utilization through input shaping. This idea is abstracted to linear multi-variable systems to provide conditions when this approach is applicable. The analysis is carried out in time-domain as well as in frequency domain (through singular value analysis). The type of output variables that are amenable to transient control using this approach is derived through analysis. It is shown that the fuel utilization, although inherently nonlinear within the nonlinear dynamics of the fuel cell, has some similarities with the linear abstraction that leads to the observed transient control.
    ASME 2013 Dynamic Systems and Control Conference; 10/2013
  • Sigitas Rimkus · Tuhin Das
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    ABSTRACT: Auto-rotation or autogyro is a well-known phenomenon where a rotor in a wind field generates significant lift while the wind induces considerable aerodynamic torque on the rotor. The principle has been studied extensively for applications in aviation. However, with recent works indicating immense, persistent, and pervasive, available wind energy at high altitudes, the principle of autogyro could potentially be exploited for energy harvesting. In this paper, we carry out a preliminary investigation on the viability of using autogyros for energy extraction. We mainly focus on one of the earliest documented works on modeling of autogyro and extend its use to explore energy harvesting. The model is based on blade element theory. We provide simulation results of the concept. Although the results are encouraging, there are various practical aspects that need to be investigated to build confidence on this approach of energy harvesting. This work aims to build a framework upon which more comprehensive research can be conducted.
    ASME 2013 Dynamic Systems and Control Conference; 10/2013
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    ABSTRACT: The stability analysis of a tethered airfoil system is presented and conditions required for the existence of stable equilibrium points are derived. Two cases are investigated: a case where the tether is assumed to be straight; and a second, more general case, where the tether is assumed to take a catenary geometry. For each case, the relevant equations of motion are derived and simulation results are used to validate the mathematical models. Specifically, for the straight tether case, the analytical conditions for stability are derived and simulated. For the catenary case, simulations were performed to investigate how the equilibrium point moves as operating conditions are varied.
    American Control Conference (ACC), 2013; 06/2013
  • Omid Madani · Tuhin Das
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    ABSTRACT: This paper addresses decentralized control of a simple hybrid power system consisting of a single fuel cell and an ultra-capacitor. This work develops separate controllers for the fuel cell and the ultra-capacitor, rather than a centralized controller. With a goal developing a control paradigm that is scalable to many energy resources connected to a network, the controllers are designed primarily to use locally sensed information. Explicit communication between controllers, such as exchange of locally sensed information, is absent. An energy conservation based approach, combined with a current regulation method developed by the authors in their earlier work [1], is used for transient control of the fuel cell. The control of state-of-charge of the ultra-capacitor is also principally governed by energy conservation, but implemented using two different approaches. One is based on dissipation, and the other is based on voltage modulation. The former is a conservative approach, while the latter is potentially more energy efficient. Simulation results are presented to demonstrate these concepts. Further research is ongoing to develop a detailed analytical base for this work.
    American Control Conference (ACC), 2013; 06/2013
  • T. Das · W. Nowak
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    ABSTRACT: Solid oxide fuel cells (SOFCs) offer many benefits over various other fuel cells as a result of their high operating temperatures. Our prior work has addressed the conflicting goals of preventing fuel starvation and improving load-following in SOFCs through a combination of current regulation and hybridization with an ultra-capacitor. The associated controllers are largely model independent, excepting certain generalized assumptions that were made about the unknown and nonlinear dynamics of the SOFC's fuel supply system (FSS). In this paper we formulate a generalized structure of the control problem and controller from our earlier work, and relax the conditions imposed on the FSS. Thereafter, we analytically determine conditions of instability. We obtain inequality conditions that impose restrictions on the controller gains and the unknown nonlinearity. The conditions are helpful in predicting the limits of performance of the controller. The results are verified through simulations and through hardware-in-the-loop tests.
    American Control Conference (ACC), 2012; 06/2012
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    Tahar Allag · Tuhin 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; 20(1-20):1 - 10. DOI:10.1109/TCST.2010.2098478 · 2.52 Impact Factor
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    Tahar Allag · Tuhin Das
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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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    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
  • Tuhin Das · Greg Semrau · Sigitas Rimkus
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    ABSTRACT: One of the key control problems associated with variable speed wind turbine systems is maximization of energy extraction when operating below the rated wind speed and power regulation when operating above the rated wind speed. In this paper, we approach these problems from a nonlinear systems perspective. For below rated wind speeds we adopt existing work appearing in the literature and provide further insight into the characteristics of the resulting equilibrium points of the closed-loop system. For above rated wind speeds, we propose a nonlinear controller and analyze the stability property of the resulting equilibria. We also propose a method for switching between the two operating regimes that ensures continuity of control input at the transition point. The control laws are verified using a wind turbine model with a standard turbulent wind speed profile that spans both operating regimes.
    ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control; 01/2011
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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
  • Journal of Fuel Cell Science and Technology 01/2010; 7(1):011022. DOI:10.1115/1.3120269 · 0.79 Impact Factor
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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; 25(4-25):975 - 982. DOI:10.1109/TRO.2009.2022427 · 2.65 Impact Factor
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    Tuhin 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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    Tuhin Das · Ryan 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
  • Tuhin Das · Ranjan Mukherjee
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    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). DOI:10.1016/j.automatica.2009.02.007 · 3.13 Impact Factor
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    Tuhin Das · Ranjan 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; 17(1-17):242 - 248. DOI:10.1109/TCST.2008.924570 · 2.52 Impact Factor
  • Source
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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 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

Publication Stats

146 Citations
26.06 Total Impact Points

Institutions

  • 2011–2013
    • University of Central Florida
      • Department of Mechanical and Aerospace Engineering
      Orlando, Florida, United States
  • 2001–2013
    • Michigan State University
      • Department of Mechanical Engineering
      Ист-Лансинг, Michigan, United States
  • 2008–2012
    • Rochester Institute of Technology
      • Department of Mechanical Engineering
      Rochester, New York, United States
  • 2006
    • Plymouth State University
      Плимут, New Hampshire, United States