Bill Diong

Dynamic output feedback variable structure control for system stabilization

Simplex type dynamic output feedback variable structure control for stabilizing multivariable linear time-invariant plants is analysed. Two types of controllers are considered; a compensator type and an observer type. It is shown that while the compensator-type controller stabilizes the plant only if the plant is minimum-phase, the observer-type controller does not face the same restriction. The design of low-order (less than the order of the plant) observer-type controllers is also considered.

Fuel cells : modeling, control, and applications

Introduction The Past, Present, and Future of Fuel Cells Typical Fuel Cell Power System Organization The Importance of Fuel Cell Dynamics Organization of This Book Fundamentals of Fuel Cells Introduction PEMFC Components The Balance-of-Plant Components Linear and Nonlinear Models of Fuel Cell Dynamics Introduction Nomenclature Nonlinear Models of PEMFC Dynamics State Space Dynamic Model of PEMFCs Electrochemical Circuit Model of PEMFCs Linear Model of PEMFC Dynamics Parametric Sensitivity of PEMFC Output Response Linear and Nonlinear Control Design for Fuel Cells Introduction Linear Control Design for Fuel Cells Nonlinear Control Design for Fuel Cells Nonlinear Control Design for Interface Analysis of Control Design Simulation of Nonlinear Control for PEMFC Simulink Implementation of Fuel Cell Models and Controllers Introduction Simulink Implementation of the Fuel Cell Models Simulink Implementation of the Fuel Cell Controllers Simulation Results Applications of Fuel Cells in Vehicles Introduction Fuel Cell Vehicle Components Hybrid Electric Vehicles and Fuel Cell System Design for Electric Vehicles Control of Hybrid Fuel Cell System for Electric Vehicles Fault Diagnosis of Hybrid Fuel Cell System Application of Fuel Cells in Utility Power Systems and Stand-Alone Systems Introduction Utility Power Systems and Residential Applications Stand-Alone Application Modeling Distributed Generators in Load Flow Analysis Control and Analysis of Hybrid Renewable Energy Systems Introduction Hybrid System Consisting of Wind and Fell Cell Sources Hybrid Renewable Energy System for Isolated Islands Power Management of a Stand-Alone Wind/Photovoltaic/Fuel Cell Energy System Hybrid Renewable Energy Systems in Load Flow Analysis Appendices Index References appear at the end of each chapter.

Nonlinear Control of PEM Fuel Cells by Exact Linearization

This paper presents a dynamic model of polymer electrolyte membrane fuel cells (PEM FC) for the purpose of constructing a nonlinear control strategy for PEM FC by using the exact linearization approach. By introducing additional states and outputs, the original multiple-input single-output (MISO) nonlinear model of PEM FC is transformed into a multiple-input multiple-output (MIMO) system so that the exact linearization approach can be directly utilized. Simulation results show that PEM fuel cells with nonlinear control have better transient and steady-state performances.

Harmonic Distortion Optimization of Cascaded H-Bridge Inverters Considering Device Voltage Drops and Noninteger DC Voltage Ratios

This paper considers achieving the minimum total harmonic distortion (THD) or frequency-weighted THD (WTHD) of the staircase-modulated output voltage of single-phase multilevel inverters, with or without elimination of the lowest order harmonics. The minimal THD values, together with the corresponding step angles and dc voltage source ratios, have been obtained for the 5-, 7-, 9-, 11-, and 13-level cases; accounting for the device voltage drops when the load is resistive or is moderately inductive is described. Similarly, the minimal WTHD values, together with the corresponding step angles and dc source voltage ratios, have been obtained for the five-, seven-, and nine-level waveform cases. The results show that requiring harmonic elimination leads to larger W/THD than the minimum W/THD that can be achieved without this requirement. Furthermore, a 13-level waveform is needed to attain a voltage THD less than 5%, and a nine-level waveform is needed to attain a WTHD less than 0.5%. Experimental measurements are presented as verification of the analytical results.

An improved small-signal model of the dynamic behavior of PEM fuel cells

The dynamic behavior of a fuel cell is integral to the overall stability and performance of the power system formed by the fuel cell source, power conditioner and electrical load. Present-day fuel cells have transient (dynamic) responses that are much slower than the dynamic responses of the typical power conditioner and load to which they are attached. As such, the fuel cells inability to change its electrical output (current) as quickly as the electrical load changes has significant implications on the overall power system design. In particular, some form of energy storage with quick charge/discharge capability is needed to function as firm power backup during electrical load increases if the fuel flow to the fuel cell is not being kept constant at its maximum level (which is wasteful and inefficient). The slower the fuel cells response, the larger the amount of energy storage that is needed with the attendant increases in its size, weight and cost; it also reduces the number of suitable energy storage options (ultracapacitor, flywheel, battery, etc). Hence, this paper describes an effort to model a PEM fuel cells dynamic behavior as an initial step to prescribe internal design modifications and/or external controller designs to improve its transient behavior. Simulation results obtained from this model are presented along with corresponding test results, which show generally good agreement with each other.

Nonlinear control of PEM fuel cells by exact linearization

This paper presents a dynamic model of polymer electrolyte membrane fuel cells (PEM FC) for the purpose of constructing a nonlinear control strategy for PEM FC by using the exact linearization approach. By introducing additional states and outputs, the original multiple-input single-output (MISO) nonlinear model of PEM FC is transformed into a multiple-input multiple-output (MIMO) system so that the exact linearization approach can be directly utilized. Simulation results show that PEM fuel cells with nonlinear control have better transient and steady-state performances.

Multilevel inverters with equal or unequal sources for dual-frequency induction heating

Most existing power supplies for induction heating equipment produce voltage at a single (adjustable) frequency. Recently, however, induction heating power supplies that produce voltage at two (adjustable) frequencies have been researched and even commercialized. Dual-frequency power supplies are a significant development for heat-treating workpieces with uneven geometries, such as gears, since different portions of such workpieces are heated dissimilarly at a single frequency and so require a two step process using a single-frequency power supply. On the other hand, a dual-frequency power supply can achieve the desired result for such workpieces in a one step process. This paper proposes the use of multilevel converters for providing induction heating power at two frequencies simultaneously, which may achieve higher efficiency, improved control, reduced electromagnetic interference and greater reliability than existing dual-frequency power supplies. It also describes how the stepping angles for the desired output from such converters can be determined for both the equal and unequal source cases. Furthermore, experimental results are presented as a verification of the analysis.

Can asthma in children be detected by the estimated parameter values of the augmented RIC model

This paper describes the estimation of the parameter values for the recently introduced augmented RIC respiratory system model from impulse oscillometry data obtained from both asthmatic and normal children. An analysis of these values has indicated that one of the capacitance parameters of the model provides good discrimination between these two groups of children; moreover, this finding corresponds well with current medical understanding of the pathology of asthma

WTHD-optimal staircase modulation of single-phase multilevel inverters

This paper considers the problem of achieving the minimum frequency-weighted THD of the output voltage of multilevel inverters, when staircase modulation is utilized. Since the single-phase AC case is being addressed, the triplen harmonics need to be included in the analysis. The results show that using unequal, non-integer ratio, DC source voltages is significantly better than using equal ones, as expected. They also indicate that imposing the requirement of eliminating the lowest harmonics leads to slightly worse distortion than the minimum that is achievable

A Comparison of Various Respiratory System Models Based on Parameter Estimates From Impulse Oscillometry Data

Impulse oscillometry offers an advantage over spirometry when conducting pulmonary function tests. Not only does it require minimal patient cooperation, it provides useful data in a form amenable to engineering methods. In particular, the data can be used to obtain parameter estimates for electric circuit-based models of the respiratory system, which can in turn aid the detection and diagnosis of various diseases/pathologies. Of the six models analyzed during this study, the DuBois model and a newly proposed extended RIC model seem to provide the most robust parameter estimates for our entire data set of 106 subjects with various respiratory ailments such as asthma and chronic obstructive pulmonary disease. Such a diagnostic approach, relying on estimated parameter values, may require additional measures to ensure proper identification of diseases/pathologies but the preliminary results are promising.