Analysis of a bidirecctional coupled-inductor Cuk converter operating in sliding mode

Analytic models for a bidirectional coupled-inductor Cuk converter operating in sliding mode are described. Using a linear combination of the converter four state variable errors as a general switching surface, the expression for the equivalent control is derived and the coordinates of the equilibrium point are obtained. Particular cases of the general switching surface are subsequently analyzed in detail: 1) surfaces for ideal line regulation, 2) surfaces for ideal load regulation, and 3) surfaces for hysteretic current control. Simulation results verifying the analytical predictions are presented.Peer Reviewe

HM/PWM Seamless Control of a Bidirectional Buck-Boost Converter for a Photovoltaic Application

The versatile buck-boost dc/dc converter is found suitable for a particular photovoltaic application that requires either a voltage step-up or a voltage step-down operation injecting the maximum available current into an intermediate-voltage battery. It is proposed to implement the converter control stage providing seamless changes between the step-up (boost) and step-down (buck) operating modes. Based on the sliding-mode control technique, a hysteretic-modulation-based (HM) controller is designed allowing the tuning of the switching frequency around either of the two possible operating points. The introduction of minor modifications into the HM implementation results in a pulse-width modulation (PWM) controller that preserves the seamless changing features between buck and boost working modes while providing a fixed switching frequency. Experimental results demonstrate that both solutions allow the converter input voltage control by showing a perfect tracking of 1-kHz square-type references, similar to those provided by a classical perturb-and-observe (P&O) MPPT algorithm but much faster

Control en modo deslizante aplicado a sistemas de acondicionamiento de potencia de satélites

El sistema de acondicionamiento de potencia es clave para el funcionamiento correcto del resto de sistemas eléctricos de un satélite. Los reguladores conmutados continua - continua son las piezas que enlazan los paneles solares y las baterías con el bus principal de alimentación. La estabilidad, precisión y robustez del sistema de control son fundamentales en el diseño de esos convertidores.Desde el punto de vista de los especialistas en control, los convertidores conmutados son sistemas de estructura variable, en los cuales se aplica de forma natural el control en modo deslizante. Sin embargo, no es fácil encontrar un ejemplo en el que se haya aplicado con éxito en los sistemas de alimentación de satélites. Con esta tesis se pretende cubrir el vacío existente entre la teoría de control en modo deslizante y la práctica de diseño de controles de convertidores conmutados continua - continua que tienen aplicación en los sistemas de alimentación de satélites.La tesis comienza introduciendo las características básicas del sistema de alimentación y presentando algunos reguladores cargadores y descargadores de batería que han sido utilizados en satélites concretos. El resto de la tesis es un estudio teórico con el fin de diseñar reguladores controlados en modo deslizante para esa aplicación.Se ha comenzado obteniendo un conjunto finito de convertidores básicos, a partir de los circuitos con dos interruptores, aplicando un método de síntesis basado en reglas topológicas y se han seleccionado los convertidores con estrés mínimo en los interruptores. Se han escogido, de entre estos, los convertidores con la corriente de salida continua, para utilizar como descargadores de batería, y los que tienen la corriente de entrada continua como cargadores de batería.Se ha encontrado que todos los convertidores seleccionados (tomando como salida del sistema el error de la corriente que se debe controlar) tienen grado relativo uno y su dinámica cero es asintóticamente estable, si se cumplen ciertas relaciones entre los parámetros que se han obtenido explícitamente para cada convertidor. En algunos casos es necesario acoplar magnéticamente los dos inductores o añadir una red R-C serie en paralelo con el condensador.Se han proporcionado criterios de diseño del lazo de corriente y del lazo de tensión, utilizando comparadores con histéresis para generar la señal de control en modo deslizante. Se han simulado varios de estos reguladores, encontrando que cumplen las especificaciones restrictivas de impedancia en el bus y al mismo tiempo tienen un comportamiento robusto frente a perturbaciones de gran señal cuando los parámetros toman sus valores extremos.Los reguladores encontrados pueden servir para mejorar las prestaciones y reducir el coste de los sistemas de alimentación de satélites y tienen muchas otras aplicaciones fuera de la industria aerospacial.Power conditioning system is key to correct operation of the rest of electrical systems of satellites. Dc-to-dc switching converters link solar panels and batteries with the main power bus. Control system stability, accuracy and robustness is basic in the design of those converters.Switching converters are variable structure systems from the point of view of control specialist. In those systems, sliding-mode control can be applied in a natural way. Nevertheless it is difficult to find a successful example in power conditioning systems of satellites. This thesis try to fill the gap between sliding-mode control theory and control design practice of dc-to-dc switching converters for power conditioning systems of satellites.Thesis begin introducing basic features of power conditioning system and some battery charge and discharge regulators which have been actually used in satellites. The rest of the thesis is a theoretical study with the purpose of design sliding-mode controlled regulators for that application.A finite set of basic converters has been obtained from two switch circuits, applying a synthesis method based on topological rules. Converters with minimum switch stress have been selected from that set. Among them, converters with continuous output current have been chosen for battery discharge regulators and converters with continuous input current for battery charge regulators.The analysis of selected converters show that all of them (taking as system output the error of current that must be controlled) have a relative degree of one and an asymptotically stable zero dynamics if certain conditions on the parameters are fulfilled. Those conditions have been found individually for each converter. In some cases, inductors must be coupled and a series R-C network must be added in parallel with a capacitor.A comparator with hysteresis is used to get sliding-mode control signal. Design criteria for the parameters of current and voltage loops are given. Some of those regulators have been simulated finding that they meet restrictive bus impedance specifications. In addition, they have a robust behavior in simulations of large signal perturbations where parameters take their extreme values.The found regulators can be used to improve performance and reduce cost of power conditioning systems of satellites. They also have a lot of others applications outside aerospace industry

Reactivation System for Proton-Exchange Membrane Fuel-Cells

DOI: 10.3390/en5072404 URL: http://www.mdpi.com/1996-1073/5/7/2404 Filiació URV: SI Inclòs a la memòria: SIIn recent years, Proton-Exchange Membrane Fuel Cells (PEMFCs) have been the focus of very intensive researches. Manufacturers of these alternative power sources propose a rejuvenation sequence after the FC has been operating at high power for a certain period of time. These rejuvenation methods could be not appropriate for the reactivation of the FC when it has been out of operation for a long period of time or after it has been repaired. Since the developed reactivation system monitors temperature, current, and the cell voltages of the stack, it could be also useful for the diagnostic and repairing processes. The limited number of published contributions suggests that systems developing reactivation techniques are an open research field. In this paper, an automated system for reactivating PEMFCs and results of experimental testing are presented

Asymmetrical Interleaved DC/DC Switching Converters for Photovoltaic and Fuel Cell Applications-Part 1: Circuit Generation, Analysis and Design

DOI: 10.3390/en5114590 URL: http://www.mdpi.com/1996-1073/5/11/4590 Filiació URV: SI Inclòs a la memòria: SIA novel asymmetrical interleaved dc/dc switching converters family intended for photovoltaic and fuel cell applications is presented in this paper. The main requirements on such applications are small ripples in the generator and load, as well as high voltage conversion ratio. Therefore, interleaved structures and voltage multiplier cells have been asymmetrically combined to generate new converters, which inherently operate indiscontinuous conduction mode. The novel family is derived from boost, buck-boost and flyback-based structures. This converter family is analyzed to obtain the design equations and synthesize a design process based on the typical requirements of photovoltaic and fuel cell applications. Finally, the experimental results validate the characteristics and usefulness of the asymmetrical interleaved converter family

Static and Dynamic Current-Voltage Modeling of a Proton Exchange Membrane Fuel Cell Using an Input-Output Diffusive Approach

DOI: 10.1109/TIE.2015.2480383 URL: http://ieeexplore.ieee.org/document/7273869/ Filiació URV: SI Inclòs a la memòria: SI Informació addicional: Article number 7273869This paper deepens in the study of the recently described diffusive proton exchange membrane fuel cell (FC) model. This model has demonstrated a close agreement to the experimental data provided by a real FC. The diffusive model is approximated by a finite-dimensional model that allows formulating an optimization problem of least square error type to estimate the model distribution. The diffusive model is identified by means of experimental measurements of current (input) and voltage (output) in the FC. It is well known that the FC static current-voltage characteristic has three operation regions, with only the ohmic region being strictly linear, so that it is very difficult to approximate the whole operation range with a linear model. Therefore, a new method is presented in this paper extending the diffusive approach by means of a linear parameter-varying model with the aim to overcome the limitations of linear time-invariant models. In addition, discrete-time expressions for the new diffusive model approach are derived. The obtained model is simple and can be used in systems that require real-time emulators or complex long-time simulations. Experimental results using the Ballard Nexa 1.2-kW FC illustrate the advantages of the new diffusive model approach with respect to previous reports

Hysteretic transition method for avoiding the dead-zone effect and subharmonics in a noninverting buck-boost converter

DOI: 10.1109/TPEL.2014.2333736 URL: http://ieeexplore.ieee.org/document/6845333/ Filiació URV: SI Inclòs a la memòria: SI Informació addicional: Article number 6845333A new hysteresis window method is proposed as a solution for avoiding the operational dead zone that exists at the transition between buck and boost operating modes in all noninverting buck-boost converters. In addition, this method also eliminates the discontinuities in the converter's steady-state output voltage transfer characteristic, which is a function of the duty cycle. The converter's output voltage function is surjective and, therefore, smooth mode transitions are achieved. The negative effects of operating within the dead zone are shown by the presence of subharmonics in the output voltage, increased output voltage ripple, poor regulation, and the instability of the converter during the transition between buck and boost operating modes. The dead-zone avoidance technique proposed in this paper eliminates all these issues while at the same time ensures highly efficient operation of the converter. An additional advantage of the technique is its simplicity, which allows for implementation into low-cost digital signal controllers, as well as into analog control circuits. The advantageous features of the proposed approach were evaluated on the basis of comparisons with three other dead-zone avoidance approaches and the initial case, which does not utilize any dead-zone avoidance technique. All the experiments were carried out on a purpose-built prototype of a noninverting buck-boost converter with magnetically coupled inductors

Design of Current Programmed Switching Converters Using Sliding-Mode Control Theory

Open AccessThis paper presents a comprehensive approach to analyze and design the voltage and current loops of switching DC-DC converters by using sliding-mode control theory. The approach is interchangeably applied to switching converters under current-programmed control with both fixed and variable frequency modulation. An ideal sliding-mode dynamics model is then obtained together with its circuit schematic representation that can be used for designing the output voltage compensator, as well as to predict the large signal behavior such as during start-up and under large disturbances. Simulations and experimental measurements illustrate the theoretical approach for two different examples of switching converters

Analysis of a bidirecctional coupled-inductor Cuk converter operating in sliding mode

Analytic models for a bidirectional coupled-inductor Cuk converter operating in sliding mode are described. Using a linear combination of the converter four state variable errors as a general switching surface, the expression for the equivalent control is derived and the coordinates of the equilibrium point are obtained. Particular cases of the general switching surface are subsequently analyzed in detail: 1) surfaces for ideal line regulation, 2) surfaces for ideal load regulation, and 3) surfaces for hysteretic current control. Simulation results verifying the analytical predictions are presented.Peer Reviewe

Energy Management of a Fuel-Cell Serial Parallel Hybrid System

In this paper, a serial-parallel hybrid (SPH) power system formed by a fuel cell (FC), an auxiliary storage device (ASD), and the current-controlled dc-dc converters responsible for the power management are realized by using the digital signal controller (DSC) TMS32F28335. The main energy management goal is to transfer energy from the sources (FC or ASD) to the load while ensuring dc bus voltage regulation and high power conversion efficiency. In addition, a safe and reliable operation of the system has to be achieved. The selected converter and its controller features are noninverting voltage step up and step down, high efficiency, regulation of input and output currents and low ripple values, and the ability to change from input to output current regulation loop, suddenly and smoothly, and vice versa. All these features allow it to be positioned in different FC system localizations and simplify the design of the master control. Simulation and experimental results have been validated on a 48-V 1200-W dc bus