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Chen P.-C.,Kao Yuan University
International Journal of Hydrogen Energy | Year: 2011

This paper is on the dynamics analysis and controller design for the PEM fuel cell under the flowrate constraints of the supplied hydrogen and oxygen. By linearization around the equilibrium trajectories defined by the quantities of hydrogen and oxygen input flowrate, the nonlinear dynamics of the PEM fuel cell can be expressed as a linear parameter varying system with the output current and temperature as the system parameters. The state-feedback controller design is performed based on the linear time-invariant model obtained from the derived linear parameter varying system evaluated at the half load operation condition. The control objective is to achieve a maximized relative stability or equivalently the maximum decay rate under the specified magnitude constraints on the input flowrate of hydrogen and oxygen. The convex linear matrix inequality algorithm is utilized for numerical construction of the state-feedback control law. Under the fixed load resistance corresponding to the half load condition, the time response simulations are conducted for both the cases of initial condition regulation and external command tracking. For the simulation of regulation, the initial deviation of state variables diminishes quickly that agrees with the obtained large delay rate during controller design. In the case of command tracking for the same amount of state variables, the controlled system can follow the issued command in the right direction but leave large tracking error, which is due to the weak controllability of the gas flowrates on the activation overvoltage for the PEM fuel cell system dynamics. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Chen P.-C.,Kao Yuan University
International Journal of Hydrogen Energy | Year: 2011

An output-feedback voltage control system for nonlinear PEM fuel cells is presented. For voltage tracking around equilibrium operating points, the controller design minimizes the energy ratio between tracking error and normalized command while hydrogen and oxygen flowrates satisfy specified magnitude constraints and closed-loop poles meet desired placement constraints. Time response simulations based on Ballard 5 kW PEM fuel cell system parameters verify the design. Simulated controllers constructed numerically via the linear matrix inequality algorithm elaborate relationships between designed input flowrate and voltage tracking error. With controller design based on the same nominal input flowrate constraints, the achieved voltage tracking capability is comparable to our published state-feedback design study. To reduce voltage tracking error under fixed external resistance, gas flowrate magnitude constraints must be relaxed, requiring more fuel energy to manipulate the system variables for operation away from equilibrium conditions. Whereas state-feedback designs depend on internal state variables which are not always measurable, output-feedback control using only voltage tracking error as measurement simplifies practical implementation. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Wu C.-S.,Kao Yuan University
Carbohydrate Polymers | Year: 2012

The biodegradability, morphology, mechanical, and thermal properties of composite materials composed of maleic anhydride-grafted poly(butylene adipate-co-terephthalate) (PBAT) and cellulose acetate (CA) were evaluated. Composites containing maleic anhydride-grafted PBAT (PBAT-g-MA/CA) exhibited noticeably superior mechanical properties due to greater compatibility between the two components. The dispersion of CA in the PBAT-g-MA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules between the anhydride carboxyl groups of PBAT-g-MA and hydroxyl groups in CA. Each composite was buried in soil and monitored to assess biodegradability. Both the PBAT and the PBAT-g-MA/CA composite films were eventually completely degraded, and severe disruption of film structure was observed after 60-100 days of incubation. Although the degree of weight loss after burial indicated that both materials were biodegradable, even with high levels of CA, the higher water resistance of PBAT-g-MA/CA films indicated that they were more biodegradable than those made of PBAT. © 2011 Elsevier Ltd. All rights reserved.

In this paper, an efficient method is proposed to design fuzzy wavelet neural network (FWNN) for function learning and identification by tuning fuzzy membership functions and wavelet neural networks. The structure of FWNN is based on the basis of fuzzy rules including wavelet functions in the consequent parts of rules. In order to improve the function approximation accuracy and general capability of the FWNN system, an efficient genetic algorithm (GA) approach is used to adjust the parameters of dilation, translation, weights, and membership functions. By minimizing a quadratic measure of the error derived from the output of the system, the design problem can be characterized by the proposed GA formulation. Moreover, the solution is directly obtained without any need for complicated computations. The performance of our approximation is superior to that of existing methods. Several numerical design examples are likewise presented to demonstrate the design flexibility and usefulness of this presented approach. © 2010 Elsevier B.V. All rights reserved.

The biodegradability, morphology, and mechanical properties of composite materials made from maleic anhydride-grafted poly(hydroxyalkanoate) (PHA-g-MA) and treated (crosslinked) tea plant fibre (t-TPF) were evaluated. Composites containing PHA-g-MA (PHA-g-MA/t-TPF) had noticeably superior mechanical properties compared with those of PHA/TPF because of greater compatibility with TPF. The dispersion of t-TPF in the PHA-g-MA matrix was more homogeneous because of ester formation and the consequent creation of branched and crosslinked macromolecules between the anhydride carboxyl groups of PHA-g-MA and hydroxyl groups in t-TPF. Additionally, the PHA-g-MA/t-TPF composites were more easily processed because of their lower melt viscosities. The water resistance of PHA-g-MA/t-TPF was higher than that of PHA/TPF, although the weight loss of composites buried in soil compost indicated that both were biodegradable, especially at high levels of TPF substitution. The PHA/TPF and PHA-g-MA/t-TPF composites were more biodegradable than pure PHA, which implied a strong connection between TPF content and biodegradability. © 2013 Elsevier Ltd. All rights reserved.

Chang Y.,Kao Yuan University
IEEE Transactions on Automatic Control | Year: 2011

Based on the Lyapunov stability theorem, a methodology of designing the block backstepping controller for a class of multi-input multi-output (MIMO) systems is proposed to solve the tracking problem. Some adaptive mechanisms are embedded both in the virtual input controller and in the backstepping controllers so that not only are the perturbations suppressed, but also some knowledge of the upper bound of perturbations is not required. Finally, an example of controlling a two-axis piezoelectric microposition is used to demonstrate the feasibility of the proposed methodology. © 2011 IEEE.

Chen P.-C.,Kao Yuan University
Energy Conversion and Management | Year: 2013

This paper presents a robust control approach for proton exchange membrane (PEM) fuel cell systems. In a linear parameter varying system representation of the nonlinear PEM fuel cell dynamics, the system matrices are dependent on the system varying parameters, the output current and the stack temperature. To obtain guaranteed design performance, system uncertainties caused by the variational system parameters are addressed during controller design. The voltage tracking performance is expressed in terms of H∞ optimization of the ratio of the tracking error to the issued command. The controller is constructed numerically in terms of the convex tractable linear matrix inequalities. Due to the parameter-dependent system matrices of the PEM fuel cells, the formulated matrix inequalities in denoting various design specifications are also dependent on the system varying parameters. Using the affinely dependent property of these matrix inequalities, design performance can be established by evaluating only the matrix inequalities in the extremes of the varying parameters. Both nominal and robust controller designs are verified through time response simulation for both nominal PEM fuel cell and nonlinear PEM fuel cell dynamics. © 2012 Elsevier Ltd. All rights reserved.

The biodegradability, morphology, and mechanical properties of composite materials consisting of acrylic acid-grafted poly(butylene succinate adipate) (PBSA-g-AA) and agricultural residues (rice husk, RH) were evaluated. Composites containing acrylic acid-grafted PBSA (PBSA-g-AA/RH) exhibited noticeably superior mechanical properties compared with those of PBSA/RH due to greater compatibility with RH. The dispersion of RH in the PBSA-g-AA matrix was highly homogeneous as a result of ester formation, and the consequent creation of branched and cross-linked macromolecules, between the carboxyl groups of PBSA-g-AA and hydroxyl groups in RH. Each composite was subject to biodegradation tests in an Azospirillum brasilense BCRC 12270 liquid culture medium. The bacterium completely degraded both the PBSA and the PBSA-g-AA/RH composite films. Morphological observations indicated severe disruption of the film structure after 20-40 days of incubation. The PBSA-g-AA/RH (20 wt%) films were not only more biodegradable than those made of PBSA but also exhibited lower molecular weight and intrinsic viscosity, implying a strong connection between these characteristics and biodegradability. © 2011 Published by Elsevier Ltd.

Chang T.-H.,Kao Yuan University
Information Sciences | Year: 2014

This study proposes a framework based on the concept of fuzzy sets theory and the VIKOR method to provide a rational, scientific and systematic process for evaluating the hospital service quality under a fuzzy environment where the uncertainty, subjectivity and vagueness are addressed with linguistic variables parameterized by triangular fuzzy numbers. This study applies the fuzzy multi-criteria decision making approach to determine the importance weights of evaluation criteria and the VIKOR method is taken to consolidate the service quality performance ratings of the feasible alternatives. An empirical case involving 33 evaluation criteria, 2 public and 3 private medical centres in Taiwan assessed by 18 evaluators from various fields of medical industry is solicited to demonstrate the proposed approach. The analysis result reveals that the service quality of private hospitals is better than public hospitals because the private hospitals are rarely subsidized by governmental agencies. These private hospitals have to fend themselves to retain existing patients or attract new patients to ensue sustainable survival. © 2014 Elsevier Inc. All rights reserved.

The present invention is a high-sensitivity insulation resistance detection method and circuit for an ungrounded DC power supply systems. When the ratio of the voltage of the positive bus to that of the negative bus exceeds a preset range, the DC current is injected into the ungrounded DC power supply systems. DC power supply systems have essentially some grounded stray and external capacitors, so some of the injected DC current will flow into the grounded capacitor, increasing the voltage of the fault bus and the leakage current. The proposed method increases the leakage current by the injection of DC current, so the current sensor can detect the leakage current from which the insulation resistance can be calculated. The DC current injection method can significantly improve the detection of ground insulation faults in ungrounded DC power supply systems.

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