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Subbarao Varigonda

Subbarao Varigonda
Carrier Corporation · Systems Model Based Engineering

PhD

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33
Publications
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805
Citations

Publications

Publications (33)
Article
Full-text available
From the design space explored for series architecture plug-in hybrid electric vehicle transit buses by the authors, one powertrain and control design is selected to provide maximum benefit to investment ratio. Sensitivity analysis is performed for this powertrain configuration. Vehicle parameters (including vehicle mass, coefficient of drag, coeff...
Article
This article performs a novel comparison of the life-cycle costs of the series and parallel architectures for plug-in hybrid electric vehicles. Economic viability is defined as having a payback period less than 2 years and number of battery replacements less than or equal to three over a vehicle life of 12 years along-with drivability and gradabili...
Article
Prior design optimization efforts do not capture the impact of battery degradation and replacement on the total cost of ownership, even though the battery is the most expensive and least robust powertrain component. A novel, comprehensive framework is presented for model-based parametric optimization of hybrid electric vehicle powertrains, while ac...
Article
Within electrified vehicle powertrains, lithium-ion battery performance degrades with aging and usage, resulting in a loss in both energy and power capacity. As a result, models used for system design and control algorithm development would ideally capture the impact of those efforts on battery capacity degradation, be computationally efficient, an...
Article
The light-duty vehicle market has seen some adoption of hybrid electric vehicles that is not reflected in the heavy-duty market. The major challenges associated with the heavy-duty segment are: (i) greater emphasis on economic viability, (ii) reluctance to take on risk associated with new technologies, and (iii) numerous diverse applications that p...
Conference Paper
Full-text available
Within electrified vehicle powertrains, lithium-ion battery performance degrades with aging and usage, resulting in a loss in both energy and power capacity. As a result, models used for system design and control algorithm development would ideally capture the impact of those efforts on battery capacity degradation, be computationally efficient, an...
Conference Paper
Full-text available
Physically-based Li-ion electrochemical cell models have been shown capable of predicting cell performance and degradation, but are computationally expensive for optimization-oriented design applications. Faster empirical models have been developed from experimental data, but are not generalizable to operating conditions outside of the range establ...
Article
Physically-based Li-ion electrochemical cell models have been shown capable of predicting cell performance and degradation, but are computationally expensive for optimization-oriented design applications. Faster empirical models have been developed from experimental data, but are not generalizable to operating conditions outside of the range establ...
Article
Full-text available
The optimal design of hybrid electric vehicle powertrains from a systems perspective is critical to realize the maximum benefits of hybridization for a given application, especially in the heavy-duty vehicle space due to the large number of unique applications. This paper proposes a novel framework that enables parametric design optimization of hyb...
Conference Paper
In recent years, commercially available wide bandgap (WBG) devices and modules have sparked significant interest among several industries to develop power electronics using WBG technology. The commercial viability and benefits of developing such WBG power electronics are visibly increasing. However, there exists a great deal of information disconne...
Article
Design and experimental results of a scalable and modular aircooled power inverter using commercial SiC power MOSFETs are reported. Compared to the well-established silicon IGBT power inverter, the new SiC power MOSFET inverter offers 40% more output power and 4% higher efficiency for a 10kW, 20kHz aircooled design. A detailed design and performanc...
Conference Paper
Solid Oxide Fuel Cell (SOFC) power systems are under active development for a range of applications. Tight thermo-chemical operating constraints together with strong thermal coupling in SOFC systems present significant challenges for system and control design. To facilitate model-based system design addressing steady state and transient performance...
Article
Administration of certain drugs at a steady rate results in deterioration of drug effect, also known as drug tolerance. Periodic delivery is an attractive option for minimizing tolerance and maximizing the desired effect of such drugs. In this paper, periodic drug infusion strategies for maximizing a time-averaged measure of drug effect are investi...
Article
Fuel cell power systems have witnessed intense development in the recent years as they offer a clean and efficient alternative for power generation in stationary and transportation applications. In this paper, we present an overview of recent work on dynamic modeling and control design for stationary and transportation fuel cell systems including t...
Conference Paper
Control of fuel cell power plants is very challenging due to the transient nature of the loads and the preference towards simpler, integrated system design necessitated by cost reduction. We study here, the problem of coordinating the fuel and air flows into the fuel processor of a stationary PEMFC power plant based on the load requirement while en...
Article
A control-oriented dynamic model of a catalytic partial oxidation-based fuel processor is developed using physics-based principles. The fuel processor system (FPS) converts a hydrocarbon fuel to a hydrogen (H2)-rich mixture that is directly feed to the proton exchange membrane fuel cell stack (PEM-FCS). Cost and performance requirements of the tota...
Article
In control theory, an observer is a numerical algorithm which estimates unmeasured physical variables from those that are measured with the help of dynamical models that correlate them. This paper presents nonlinear observer designs for the catalytic partial oxidation (CPO), water gas shift (WGS) and preferential oxidation (PROX) reactors in fuel c...
Article
Full-text available
A fuel processor that reforms natural gas to hydrogen-rich mixture to feed the anode field of fuel cell stack is considered. The first reactor that generates the majority of the hydrogen in the fuel processor is based on catalytic partial oxidation of the methane in the natural gas. We present a model-based control analysis and design for a fuel pr...
Conference Paper
Efficient propagation of probability distributions in feedback systems is central to a decomposition based approach for uncertainty propagation in complex, interconnected systems. In this note, we propose an iterative method for static feedback systems to obtain the probability density of the output from that of the input. We prove the convergence...
Conference Paper
Full-text available
Uncertainty propagation in complex, interconnected dynamical systems can be performed more efficiently by decomposing the network based on the hierarchy and/or the strength of coupling. In this paper, we first present a structural decomposition method that identifies the hierarchy of subsystems. We briefly review the notion of horizontal-vertical d...
Article
Administration of certain drugs at a steady rate results in a deterioration of the drug effect due to a phenomenon known as tolerance. Periodic drug delivery is an attractive option for maximizing the effect of drugs exhibiting tolerance. In this paper, periodic drug infusion strategies for maximizing an averaged measure of the drug effect are inve...
Article
A control-oriented dynamic model of a catalytic partial oxidation-based fuel processor is developed using physics-based principles. The fuel processor converts a hydrocarbon fuel to a hydrogen (H2) rich mixture that is directly feed to the PEM-FC. Cost and performance requirements of the total powertrain typically lead to highly integrated designs...
Article
Full-text available
Optimal periodic control (OPC) is of interest in many engineering applications. In practice, the numerical solution of the OPC problem has been found to be quite challenging. In this note, we present a method which uses differential flatness for the solution of OPC problems. The OPC problem is reformulated using the flatness of the underlying dynam...
Article
Full-text available
We present an observer design to estimate the partial pressure of hydrogen in the anode channel of a fuel cell. A precise knowledge of this pressure is of importance to ensure reliable and efficient operation of the fuel cell power system. Our design makes use of a monotonic nonlinear growth property of the voltage output on hydrogen partial pressu...
Conference Paper
Full-text available
The water gas shift (WGS) reactor is an essential component of the fuel processor in fuel cell power plants. The WGS reactor combines CO and H/sub 2/O in the reformate stream to produce H/sub 2/ and CO/sub 2/ in a mildly exothermic, equilibrium limited reaction. Proper regulation of the steam-to-carbon ratio and the operating temperature is critica...
Conference Paper
Full-text available
This work presents nonlinear observer designs for the catalytic partial oxidation (CPO) and the water gas shift (WGS) reactors in fuel cell power systems. The observers make use of available temperature and total pressure measurements and estimate the mole fractions of each species in the reactors. Estimation of H/sub 2/ and CO fractions is particu...
Conference Paper
We present an observer design to estimate the partial pressure of hydrogen in the anode channel of a fuel cell. Our design makes use of a monotonic nonlinear growth property of the voltage output on hydrogen partial pressures at the inlet and at the exit of the channel. By treating the slowly-varying inlet partial pressure as an unknown parameter,...
Conference Paper
Relaxation oscillators typically consist of a hysteresis element and a dynamic feedback. The robustness of oscillations in such an interconnection is of interest in many applications. In particular, we seek the robustness margin on the component perturbations in the gap metric so that oscillatory behavior of the closed loop is preserved. A new dist...
Article
Full-text available
Relaxation oscillators can usually be represented as a feedback system with hysteresis. The relay relaxation oscillator consists of relay hysteresis and a linear system in feedback. The objective of this work is to study the existence of periodic orbits and the dynamics of coupled relay oscillators. In particular, we give a complete analysis for th...
Conference Paper
We present an algorithm for the efficient solution of optimal periodic control (OPC) problems using a differential flatness approach. Existing methods for OPC problems involve repeated integration of an ODE system to satisfy periodicy and have severe stability and/or accuracy problems. However, when the underlying dynamics is differentially flat, t...
Conference Paper
We provide a sufficient condition for the global stability of a periodic orbit using the contraction mapping theorem. The condition is obtained by identifying an invariant set of the system dynamics in which the Poincare map is continuous and contractive. An upper bound on the norm of the derivative of the map is obtained by exploiting its geometri...
Conference Paper
We study the dynamics of a feedback system with hysteresis. The identification of switching surfaces in state space naturally gives rise to a Poincare map whose fixed points represent the periodic orbits of the system. For linear systems in feedback with a relay hysteresis nonlinearity, necessary and sufficient conditions for the existence of unimo...
Article
Full-text available
Fuel cell power plants with an integrated fuel processing system for hydrogen generation are an attractive option for stationary, distributed power generation. We consider a PEM fuel cell power plant with CPO based fuel processor for generating hydrogen from natural gas. During load transients, the temperatures at various points of the fuel process...

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