An integral function approach to the exponential stability of linear time-varying systems

This paper studies the exponential stability of linear time-varying (LTV) systems using the recent proposed integral function. By showing the properties of the integral function and applying the Bellman-Gronwall Lemma, a sufficient and necessary condition for the exponential stability of LTV systems is derived. Furthermore, the exponential decay rate of the system trajectories can be obtained by computing the radii of convergence of integral function. The algorithm for computing the integral function is also developed and two classical examples are given to illustrate the proposed approach.     

Composite nonlinear feedback control for linear systems with input saturation: theory and an application

We study in this paper the theory and applications of a nonlinear control technique, i.e., the so-called composite nonlinear feedback control, for a class of linear systems with actuator nonlinearities. It consists of a linear feedback law and a nonlinear feedback law without any switching element. The linear feedback part is designed to yield a closed-loop system with a small damping ratio for a quick response, while at the same time not exceeding the actuator limits for the desired command input levels. The nonlinear feedback law is used to increase the damping ratio of the closed-loop system as the system output approaches the target reference to reduce the overshoot caused by the linear part. It is shown that the proposed technique is capable of beating the well-known time-optimal control in the asymptotic tracking situations. The application of such a new technique to an actual hard disk drive servo system shows that it outperforms the conventional method by more than 30%. The technique can be applied to design servo systems that deal with "point-and-shoot" fast targeting.     

Source current harmonic analysis of adjustable speed drives under input voltage unbalance and sag conditions

Adjustable Speed Drives (ASDs) have become the primary choice for most new and retrofit precision motor-control applications, offering major improvements in system efficiency. The significant increase in the use of ASDs makes it important to understand the compatibility issues between ASDs and their electrical environment in order to appropriately design the electrical systems. Even though there have been numerous studies addressing ASD effects on power systems, models for predicting the effect of the source voltage sags or unbalance have been limited. This paper is devoted to the analysis of utility-side input current harmonics under input voltage unbalance and sag conditions and the effects of these harmonics on the distribution transformer K-factor for practical ASD systems. The relationships between the unbalanced input voltages, the resulting input current harmonics, the input inductance, and the required transformer K-factor are explored for 5 hp, 100 hp, and 600 hp power distribution systems with ASDs. The results can be used as a design guide for power distribution system design with ASDs. Theoretical derivations are accompanied by both simulations and experimental results to provide verification of key conclusions.     

A method to study the phase transition and desorption of self-assembled monolayers on planar gold surfaces

In-plane resistance of thin gold films (thickness approximately 1,000 A) after the formation of self-assembled monolayers has been measured as a function of temperature. We attribute the observed increase in the slope of the resistance vs temperature plot in the case of octadecanethiol and octanethiol monolayers at characteristic temperatures to phase transitions. The structural transition of 1,4-benzenedimethanethiol is also manifested similarly. Propanethiol does not show any phase transition, as expected. The observed changes in the alkanethiol monolayers are related to the decrease in the lifetime of the parallel vibrational motion of the adsorbate on the gold surface. The increase in slope is followed by a decrease which is attributed to the commencement of desorption of monolayers from the gold surface.     

Fast thermal profiling of power semiconductor devices using Fourier techniques

Accurate prediction of temperature variation of power semiconductor devices in power electronic circuits is important to obtain optimum designs and estimate reliability levels. Temperature estimation of power electronic devices has generally been performed using transient thermal equivalent circuits. In the presence of varying load cycles, it has been typical to resort to a time-domain electrical simulation tool such as P-Spice or SABER to obtain a time series of the temperature profiles. However, for complex and periodic load cycles, time-series simulation is time consuming. In this paper, a fast Fourier analysis-based approach is presented for obtaining temperature profiles for power semiconductors. The model can be implemented readily into a spreadsheet or simple mathematical algebraic calculation software. The technique can be used for predicting lifetime and reliability level of power circuits easily. Details of the analytical approach and illustrative examples are presented in this paper.     

An Acousto-Optic Vibrometer for Measurement of Vibration in Ultra-Precision Machine Tools

Measurement of vibration is a vital factor that limits the precision and accuracy of machining of micro and macro components. In this paper, a novel technique for measurement of vibration is proposed using an acousto-optic modulator, which highlights an improved approach in measuring vibration in the subnanometre range. An experimental comparison was made with a laser Doppler vibrometer. This novel concept is proposed for application to a precision machine tool to measure the vibration on the machine bed induced during the machining process and by the external environment, which can be compensated for by in-process techniques. This novel measurement technique can also be applied for the precision measurement of the stage movement in ultra-precision machines to a subnanometre resolution.     

Generation unit sizing and cost analysis for stand-alone wind,photovoltaic, and hybrid wind/PV systems

This paper presents the results of investigations on the application of wind, photovoltaic (PV), and hybrid wind/PV power generating systems for utilization as stand-alone systems. A simple numerical algorithm has been developed for generation unit sizing. It has been used to determine the optimum generation capacity and storage needed for a stand-alone, wind, PV, and hybrid wind/PV system for an experimental site in a remote area in Montana with a typical residential load. Generation and storage units for each system are properly sized in order to meet the annual load and minimize the total annual cost to the customer. In addition, an economic analysis has been performed for the above three scenarios and is used to justify the use of renewable energy versus constructing a line extension from the nearest existing power line to supply the load with conventional power. Annual average hourly values for load, wind speed, and insolation have been used     

Novel thin‐film reactor for photocatalytic degradation of pesticides in an aqueous solution

A thin‐film reactor was fabricated with immobilised TiO₂ and this reactor was used for photocatalytic mineralisation of common pesticides, 2,4‐dichlorophenoxyacetic acid (DPA) and monocrotophos (MCP), and their commercially formulated products in an aqueous solution. Zeolites HY and Hβ with different physico‐chemical properties were chosen as support material. The supported TiO₂ was used for the degradation and mineralisation studies. TiO₂/zeolite‐supported photocatalyst showed enhanced degradation efficiency compared with bare TiO₂ for both DPA and MCP. Formulated pesticides were mineralised at shorter irradiation times than technical grade pesticides. The results clearly demonstrated that the good adsorption capacity of the support, and the effective light utilisation by TiO₂, improved the photocatalytic activity of supported TiO₂. Reusability studies have also shown the stability of supported photocatalysts. Copyright © 2004 Society of Chemical Industry