Kinetic modeling of pentachlorophenol adsorption from aqueous solution on activated carbon fibers

The adsorption equilibrium data of pentachlorophenol (PCP) onto activated carbon fiber (ACF) in felt form were obtained in a batch adsorber at T = 25 °C and pH 12 and the Langmuir isotherm fitted reasonably well with the experimental data. The rate of adsorption of PCP on ACF was investigated in this work and the experimental concentration decay data were obtained in a differential column batch adsorber. The overall rate of adsorption of PCP was interpreted by a diffusional model that takes into account the external mass transport and intrafiber diffusion. The experimental concentration decay can be described quite well with the diffusional model if the overall rate of adsorption is mainly controlled by intrafiber diffusion and the external mass transport is not important to the overall rate of adsorption. Moreover, intrafiber diffusion was significantly affected by restricted diffusion since the molecular diameter of the PCP was closed to 55% of the average pore diameter. The effect of restricted diffusion was estimated using correlations reported in the literature. The molecules of PCP adsorbed on the surface of the pore also hindered the diffusion of PCP molecules inside the pores.     

A design criteria for the current gain in current-programmedregulators

The design of the inner loop for current-programmed regulators is discussed in this paper. The effect that current gain has on the quality factor Q of the LC filter is shown. A methodology is derived to reduce this value that, in most cases, can be very high. A high quality factor can produce drastic changes with undesirable effects on regulator stability. A low quality factor will produce two real poles with a consequent reduction in the current response. After the proper selection of the current gain is done, the design procedure for the proportional integral controller of the outer loop can be continued. The design-oriented analysis is applicable to the three basic switch-mode pulsewidth modulation converters, i.e. buck, boost and buck-boost. At the end, the procedure is applied to a 280 W boost regulator that shows the simplicity of this approach     

An asymptotic modal observer for linear autonomous time lag systems

A full state vector observer is derived for a class of linear autonomous time lag systems represented by differential equations. The major features of the approach are: (1) an observer is constructed just for the set of unstable or poorly damped modes of the delayed system once they have been determined, and (2) the design is accomplished by using a partial-fraction expansion separating the unstable part from the system and then applying well-known finite dimensional state vector techniques. A procedure for the construction is given along with some numerical results to illustrate the simplicity of the observer     

Multiloop controller design for a quadratic boost converter

A controller design methodology is given for a quadratic boost converter with a single switch using current-programmed control. Nonlinear and linear models are developed, the later exhibits fourth-order characteristic dynamics with complex right-half plane zeros. The proposed control scheme is based on sensing the current of the switch and using it for feedback purposes. When the current loop is introduced, the fourth-order dynamics of the converter are changed to a dominant first order, which simplifies substantially the controller design of the outer loop. For this loop, a conventional controller is designed. The design-oriented analytic results allow the designer to easily pinpoint the control circuit parameters that optimise the converter's performance. At the end, experimental results are given for a 23 W quadratic boost converter where open loop and closed-loop response are compared     

Passivity-based control for a DC/DC high-gain transformerless boost converter

In this work, an adaptive passivity-based controller for a DC-DC high-gain transformerlessdouble-inductor boost converter is fully detailed. The proposed current-mode control scheme results in two feedback loops, a current controller for tracking the inductor current considering damping injection and energy shaping, and a voltage loop composed by a proportional-integral action to guarantee output voltage regulation. Furthermore, a parametric uncertainty estimator using immersion-invariance approach is designed to improve the robustness of the current loop. As a result, a multi-loop adaptive nonlinear energy-based controller, which ensures regional asymptotic stability via Lyapunov analysis is accomplished. In addition, considering practical conditions, real-time numerical simulations, using a 1 kW case-study converter, are carried out in order to assess the effectiveness of the proposed control scheme. Results for output voltage regulation, current tracking, and parametric uncertainty estimation under input voltage and load step changes are shown.     

Matrix partial-fraction expansion method

A method for partial-fraction expansion of m × p transfer functions H(s) is presented, and a general formula is given. The procedure does not require derivatives for the case of repeated roots and it is suitable for digital computer applications.     

Diffusion in liquid-filled pores of activated carbon. I. Pore volume diffusion

The adsorption isotherms on activated carbon were measured for the following six systems: benzaldehyde, phenol, and potassium chloride in water; benzene, isopropylbenzene, and phenol in cyclohexane. The systems isopropylbenzene and benzene each in cyclohexane and potassium chloride in water proved to be slightly adsorbing systems, whereas the benzaldehyde and phenol each in water were highly adsorbing systems. The rate of diffusion of the slightly adsorbing solutes was interpreted by assuming that the intraparticle diffusion was due to pore volume diffusion. The results indicated that the tortuosity factor for activated carbon is 3.5. The effective pore volume diffusivity and the tortuosity factor were not affected by the concentration of the solute, solute molecular size and the particle diameter. The external mass transfer resistance was negligible when pore volume diffusion was the controlling intraparticle diffusion mechanism.     

Robust stability analysis for current-programmed regulators

Uncertainty models for the three basic switch-mode converters: buck, boost, and buck-boost are given in this paper. The resulting models are represented by linear fractional transformations with structured dynamic uncertainties. Uncertainties are assumed for the load resistance R=R/sub O/(1+/spl delta//sub R/), inductance L=L/sub O/(1+/spl delta//sub L/), and capacitance C=C/sub O/(1+/spl delta//sub C/). The interest in these models is clearly motivated by the need to have models for switch-mode DC-DC converters that are compatible with robust control analysis, which require a model structure consisting of a nominal model and a norm-bounded modeling uncertainty. Therefore, robust stability analysis can be realized using standard /spl mu/-tools. At the end of the paper, an illustrative example is given which shows the simplicity of the procedure.