Dissipativity-based adaptive and robust control of UPS

In this paper, we investigate the output voltage control for a three-phase uninterruptible power supply (UPS) using controllers based on ideas of dissipativity. To provide balanced sinusoidal output voltages, even in the presence of nonlinear and unbalanced loads, we first derive a dissipativity-based controller using a frequency-domain representation of system dynamics. Adaptive refinements have been added to the controller to cope with parametric uncertainties. Second, based on the first adaptive controller, we propose a controller which turns out to have the proportional-plus-integral-type structure on rotating-frame variables, but with a special design of gain matrices. A sufficient condition in terms of the design parameters is presented for this controller that guarantees stability of the desired equilibrium and robustness against parameter uncertainties. Finally, simulation and experimental results on a three-phase prototype show effectiveness and advantages of the proposed approach     

Space/spatial-frequency analysis based filtering

Space-invariant filtering of signals that overlap with noise in both space and frequency can be inefficient. However, the signal and noise may be well separated in the joint space/spatial-frequency domain. Then, it is possible to benefit from the application of space/spatial frequency approaches. Processing based on these approaches can outperform space or frequency invariant-based methods. To this aim the concept of nonstationary space-varying filtering is introduced in this paper as an extension of the time-varying filtering concept. The filtering definitions are based on statistical averages, although the filtering should commonly be applied knowing only a single noisy signal realization. The procedures that can produce good estimates of quantities crucial for efficient filtering, based on a single noisy signal realization, are considered. Special attention has been paid to the region of support estimation and cross-term effects removal. The efficiency of the proposed space/spatial-frequency filtering concept is tested on the signal forms inspired by the interferograms in optics, including real images as disturbances. Examples demonstrate the superiority of the proposed filtering over the space-invariant one for the considered type of signals and noise     

Investigation of sorbents synthesised by mechanical–chemical reaction for sorption of As(III) and As(V) from aqueous medium

Efficiency of Fe₂O₃ and mixture of Fe₂O₃ and MnO₂ nanoparticles synthesised by mechanical–chemical reaction for inorganic As(III) and As(V) sorption was examined. Sorbents (Fe₂O₃ and mixture Fe₂O₃:MnO₂ = 3:1) synthesised by mechanical–chemical treatment in planetary ball mile with different milling times were tested by batch experiments. Experimental data were fitted both to Freundlich and Langmuir adsorption models. Efficiency of sorption was in good correlation with the time of milling in case of pure oxide. There were small differences in sorption between As(III) and As(V). In the case of mixture of oxides results were different. The best results were obtained by 30 min of milling. With prolonged milling, the sorption decreased to 3 h and after that increased again. These results were explained by phase transition. Sorption kinetics, influence of pH and the presence of other anions were examined for mixture of oxides with highest sorption capacity. The bioavailability of sorbed arsen was tested using modified Tessier procedure.     

Effects of ACTH and cytokines on dehydroepiandrosterone sulfotransferase messenger RNA in human adrenal cells

Dehydroepiandrosterone sulfate (DS) is the major adrenal androgen produced in the fetal and adult human; its formation is dependent upon the action of dehydroepiandrosterone sulfotransferase (DST). Since the factors that regulate DST are poorly characterized, we investigated the effects of ACTH, which stimulates DS production, and the cytokines transforming growth factor-beta (TGF-beta), and tumor necrosis factor-alpha (TNF-alpha) , both of which are inhibitory to adrenal steroidogenesis, on cultured human fetal adrenal cells. Cellular levels of DST mRNA were increased in a dose dependent fashion in response to ACTH; DST mRNA was less responsive to ACTH stimulation than was 17 hydroxylase (CYP 17) mRNA. The stimulatory effects of ACTH on DST mRNA levels were blunted by both TGF-beta and TNF-alpha; the inhibitory effects of TNF-alpha on DST mRNA were more striking than were those on CYP 17 mRNA. These data suggest that DS production can be altered by several agents acting on the DST gene.     

An analysis of some time-frequency and time-scale distributions

This paper presents an analysis of the representation of instantaneous frequency and group delay using time-frequency transforms or distributions of energy density domain. The time-frequency distributions which ideally represent the instantaneous frequency or group delay (itfd) are defined. Closeness to the itfd is chosen as a criterion for comparison of various commonly used distributions. It is shown that the Wigner distribution is the best among them, with respect to this criterion. The wavelet and scaled forms of the Wigner distribution are defined and analyzed. In the second part of the paper we extended the analysis to the multicomponent signals and cross terms effects. On the basis of that analysis, an efficient method, derived from the analysis of the Wigner distribution defined in the frequency domain, is proposed. This method provides some substantial advantages over the Wigner distribution. The theory is illustrated on numerical examples.     

An application of interval analysis and optimization to electric energy markets

In this paper, we address the issue of quantifying model uncertainties in a deregulated power market. We are interested in a worst-case analysis of effects of network parameter uncertainties on optimization problems that are solved on the level of an independent system operator (ISO). The focus is on linear programming (LP) formulations because of their practical relevance. After briefly reviewing applications of different interval analysis tools (interval matrix inversion and various contractors and solvers for systems of interval equations), we propose two tailored algorithms. In the first (basic LP approach), we propose another solver for a system of linear interval equations, while in the second (power system-customized LP approach), we use features of the power system model to reduce the width of the interval solution. The interval-based results are compared with a deterministic robust noninterval matrix inversion-based solution of a model of the benchmark 68-node New England/New York interconnected power system. Presented analyzes demonstrate that even small parameter variations can have significant impact on optimization.     

Instantaneous frequency estimation using the Wigner distributionwith varying and data-driven window length

The estimation of the instantaneous frequency (IF) of a harmonic complex-valued signal with an additive noise using the Wigner distribution is considered. If the IF is a nonlinear function of time, the bias of the estimate depends on the window length. The optimal choice of the window length, based on the asymptotic formulae for the variance and bias, can be used in order to resolve the bias-variance tradeoff. However, the practical value of this solution is not significant because the optimal window length depends on the unknown smoothness of the IF. The goal of this paper is to develop an adaptive IF estimator with a time-varying and data-driven window length, which is able to provide quality close to what could be achieved if the smoothness of the IF were known in advance. The algorithm uses the asymptotic formula for the variance of the estimator only. Its value may be easily obtained in the case of white noise and relatively high sampling rate. Simulation shows good accuracy for the proposed adaptive algorithm     

Model abstraction and inclusion principle: a comparison

This paper discusses connections between the inclusion principle and model abstraction in large-scale hierarchical control systems. It also provides conditions for implementation of controllability and observability in linear continuous-time dynamic systems satisfying either aggregation or restriction conditions, as well as for observability implementation in linear continuous-time dynamic systems satisfying conditions for abstraction