Balanced performance preserving controller reduction

Two methods for controller reduction based on the closed-loop system performance-preserving criterion are proposed. They are the closed-loop block balanced and the closed-loop structurally balanced truncating methods. Reduced-order controllers are obtained directly by solving the closed-loop system reduction problem with performance-preserving weights.     

Large-scale, hot-filament-assisted synthesis of tungsten oxide and related transition metal oxide nanowires

A scalable and versatile method for the large-scale synthesis of tungsten trioxide nanowires and their arrays on a variety of substrates, including amorphous quartz and fluorinated tin oxide, is reported. The synthesis involves the chemical-vapor transport of metal oxide vapor-phase species using air or oxygen flow over hot filaments onto substrates kept at a distance. The results show that the density of the nanowires can be varied from 10(6)-10(10) cm(-2) by varying the substrate temperature. The diameter of the nanowires ranges from 100-20 nm. The results also show that variations in oxygen flow and substrate temperature affect the nanowire morphology from straight to bundled to branched nanowires. A thermodynamic model is proposed to show that the condensation of WO(2) species primarily accounts for the nucleation and subsequent growth of the nanowires, which supports the hypothesis that the nucleation of nanowires occurs through condensation of suboxide WO(2) vapor-phase species. This is in contrast to the expected WO(3) vapor-phase species condensation into WO(3) solid phase for nanoparticle formation. The as-synthesized nanowires are shown to form stable dispersions compared to nanoparticles in various organic and inorganic solvents.     

Novel Strategies for the Deposition of ?COOH Functionalized Conducting Copolymer Films and the Assembly of Inorganic Nanoparticles on Conducting Polymer Platforms

A method for the preparation of ? COOH functionalized conducting copolymer films; toward the ultimate goal of developing resistance‐based sensing platforms, is presented. The method involved vapor phase copolymerization of pyrrole with a monomer containing the ? COOH functionality, thiophene‐3‐acetic acid (TAA). This copolymerization strategy aided in avoiding the need to employ brittle poly(thiophene‐3‐acetic acid) (PTAA) films in sensing applications. In this strategy, variation in the gas phase feed ratio of pyrrole to TAA allowed for the variation of the composition of the copolymer film and further allowed for the variation of both the conductivity and the amount of ? COOH functionality in the films. Further, the effect of covalent attachment of silver on the conductivity of the copolymer films is performed and presented. This covalent attachment of silver served the dual purpose of verifying the presence of active ? COOH groups on the surface, and also allowed for the quantification of the change in conductivity as a result of such attachment. Use of the conjugated ring containing 4‐aminothiophenol as the linker material enhanced the conductivities of the films. In contrast, employing cysteamine to link silver nanoparticles to the copolymer films did not result in any enhancement in the conductivities. An enhancement in the conductivities, ranging from 2 to 1000 times, is observed on covalent attachment of silver nanoparticles to the copolymer films using 4‐aminothiophenol as the linker material. This increase depended on the amount of TAA in the films and increased with increasing concentrations of TAA in the films. These results clearly indicate the use of these copolymer films in resistance‐based sensing. Further, this covalent attachment could be used as a novel strategy to integrate other inorganic nanomaterials on conducting polymer platforms.     

A note on ‘improved results on frequency weighted balanced truncation and error bounds’

In this note, we provide a small correction to the paper ‘improved results on frequency weighted balanced truncation and error bounds’ and present an additional result. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of three-phase zero-voltage switching with synchronousstart

The analysis of three-phase zero-voltage switching circuits (star-connected load without neutral connection as well as line-controlled delta-connected load) with resistive load is presented. The system is started in the same way as a single-phase system with zero-voltage synchronous switching, and after 90° the system reverts to three-phase. Results show that, although there is a small DC component in the load voltages, their amplitudes decrease as the number of cycles in the time base is increased. It is also shown that the configurations discussed have approximately the same characteristics as the one-phase integral zero-voltage switching scheme for larger values of the time base. Experimental results obtained with a prototype unit are given to verify the analysis     

The generation of discrete-time q-Markov covers via inversesolution of the Lyapunov equation

A new method for generating q-Markov covers for SISO discrete-time systems is proposed. It is based on computing first the impulse-response Gramian from the Markov parameters and covariances, and then solving the Lyapunov equation inversely to get the system matrices in controllability canonical form. The conditions for existence of q-Markov covers are also derived. The method is illustrated by a numerical example and is shown to be computationally simple     

Digital compensation in IQ modulators using adaptive FIR filters

This paper discusses digital compensation for frequency-dependent transfer characteristics and implementation errors in digital PAM/continuous-phase frequency-shift keying (CPFSK) quadrature modulators. Recently, several methods have been proposed to digitally compensate for the shortcomings of the analog reconstruction filters in IQ modulators. While these methods have shown to be effective, they result in filters with long coefficients that are computationally demanding to implement on the DSP. Furthermore, the modulator needs to be taken offline while the precompensation filters are updated to reflect the changes in the I and Q channel characteristics. In this paper, a digital compensation method is proposed here using two adaptive finite-impulse response filters to compensate for the magnitude and phase characteristics of the analog reconstruction filters in the IQ modulator. The experimental results show that this technique is effective and lead to substantial improvement of the output envelope ripples.     

Discrete system reduction via impulse-response Gramians and itsrelation to q-Markov covers

A method for model reduction of linear discrete systems is proposed. It is based on the impulse-response Gramian proposed by the authors (1989) for discrete systems. This Gramian is an extension of the one proposed for linear continuous systems and contains information on the input-output behavior of the system. The rth-order reduced-order models are made to retain the first r Markov parameters and the first r×r elements of the impulse-response Gramian of the original system. The relation between this method and the q-Markov cover method is also discussed. The method is illustrated by a numerical example     

Optimal Model Reduction with a Frequency Weighted Extension

Inthis paper, a model reduction technique based on optimizationis presented. The objective function minimized is the impulseenergy of the overall system. An extension of the technique tothe frequency weighted case is also presented, where single-sidedor double-sided weightings can be incorporated in the reductionprocedure. The paper proposes an alternative to find an optimizationsolution by solving ordinary differential equations which aregradient flow associated with the objective function to be minimized.Two examples are presented to illustrate the effectiveness ofthe method.     

Robust H∞ control of norm bounded uncertain systems via Markovian approach

This paper presents a new approach to analyze and synthesize linear uncertain systems with time‐varying norm bounded uncertainty. Firstly, the uncertainty set is classified into several different subsets according to the maximum singular value of uncertainty. Then, based on the proposed classification, the original uncertain system is transformed into a Markovian jump system. By an uncertainty‐dependent Lyapunov function, new version of bounded real lemma is developed and two sufficient conditions for designing uncertainty‐dependent controllers are established. Finally, numerical examples and simulations are used to demonstrate the utility of the given methods. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society