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An active bypass structure is proposed to maximize the power production in photovoltaic modules under mismatched conditions. Its efficiency is compared with single and distributed maximum power point tracking solutions based on conventional DC/DC structures. The analysis and simulations performed under realistic assumptions demonstrate the benefits of the novel active bypass converter over solutions based on Boost, Buck or Buck-Boost converters. [ABSTRACT FROM AUTHOR]

This paper presents two different robust controllers for boost converters with two stages in a cascade. The first robust controller is monovariable; that is, the duty-cycle is the same for the two switches. The monovanable controller ensures that some prescribed constraints on pole placement and control effort are met, and optimizes the load disturbance rejection, while takes into account the uncertainty in certain parameters. The first controller is then compared with a multivariable robust controller; that is, with independent duty cycles in each switch. The multivariable controller takes into account the same uncertainty, constraints and optimization function. The comparison shows that the multivariable controller performs better at the expense of a slightly more complex implementation; that is, the multivanable controller provides a better rejection of the load disturbance. The paper also describes simulations and experimental results that are in perfect agreement with theoretical derivations. [ABSTRACT FROM AUTHOR]

In this paper, a polymer-electrolyte-membrane fuel-cell (FC) model that is useful for simulation and control purposes is presented. The model uses both electrical-circuit components and functional blocks to reproduce both static and dynamic FC behaviors. Its main feature is in the reproduction of the oxygen-excess-ratio behavior, but it is also able to interact with any electrical device connected at the FC terminals, e.g., a load or a switching converter. Consequently, the proposed model can be used to develop new control strategies aimed at avoiding the oxygen-starvation effect and/or minimizing the fuel consumption. The model has been customized for a Ballard Nexa 1.2-kW power system, and this has allowed an experimental validation by means of measurements performed on a real FC device. [ABSTRACT FROM AUTHOR]

Discusses a study which analyzed boost topologies in interleaved operation under sliding-mode control. Details on interleaved converters in open loop; Information on sliding-mode control; Results of the study.

Presents information on a study which focused on a family of low-ripple direct current to direct current switching converters based on current-mode control. Aspects of the interleaved converter based on current-mode control; Ripple calculations; Conclusions.

Describes analytical models for a bidirectional coupled-inductor Cuk converter operating in sliding mode. Use of Cuk converters in the design of high efficiency minimum weight power processing units; Nonlinear techniques of variable structure theory; Development of sliding mode control laws;.

Summary: Even with significant progresses in the maximum power point (MPP) research area, the necessity to improve the existing methods becomes mandatory to increase the energy conversion efficiency. Since the power–voltage (P‐V) characteristic curve of photovoltaic (PV) arrays has multiple peaks under partially shaded (PS) conditions, the conventional MPP tracking (MPPT) control methods have the difficult challenge of locate the global MPP (GMPP) among many local MPPs (LMPPs). In recent years, numerous research papers have been focused on techniques to efficiently track the GMPP and alleviate the partial shading effects. One of the most popular evolutionary search technique is particle swarm optimization (PSO) that provides high tracking speed and the ability operate under different environmental conditions. For solving some conventional PSO technique common weaknesses, several modifications and improvements have emerged in the past years. This paper provides a comparative and comprehensive review of some relevant PSO‐based methods taking into account the effects of important key issues such as particles initialization criteria, search space, convergence speed, initial parameters, performance with and without partial shading, and efficiency. The simulation results are validated under numerous test conditions using MATLAB code and Simulink package. [ABSTRACT FROM AUTHOR]

Solar photovoltaic (PV) energy sources are rapidly becoming more popular. The PV system output power relies on the applied current or voltage nonlinearity and there exist a unique point called the maximum power point (MPP). For effective energy extraction from the PV system, this paper presents a new controller design strategy to track the MPP of a PV system using a sliding mode control method of self-optimisation. The proposed controller design offers fast and accurate convergence to the MPP in steady state and during varying environmental conditions. A DC/DC boost converter is utilised as a control actuator for the MPP tracking using PWM control. Simulation and experimental results are provided to demonstrate the validity of the proposed controller design. [ABSTRACT FROM AUTHOR]

Subharmonic oscillation is widely studied in switching converters under current mode control (CMC). Its boundary of occurrence in the design parameter space is well known in the case of an infinite-bandwidth current sensor. However, in a practical implementation, either a limited-bandwidth current sensor or an additional filter is used. This could have an effect on the system dynamics particularly for relatively high switching frequencies. This paper discusses the effect of the additional dynamics due to the finite-bandwidth current sensor or the additional filter on the stability and subharmonic oscillation boundaries in switching converters under CMC. It is shown that a simplified model, taking into account the dynamics of the inductor current and the sensor/filter, is enough to obtain accurate results concerning the prediction of the occurrence of subharmonic instabilities in switched converters. Design-oriented equations describing the occurrence of subharmonic oscillations are used to show some problems related to the additional dynamics on the ramp compensator design in a single-switch dc–dc converter working in continuous conduction mode. Some proposed solutions are also discussed. Numerical simulations and experimental measurements corroborate the theoretical predictions. [ABSTRACT FROM PUBLISHER]

The digital implementation of all the control loops of a versatile buck-boost (VBB) dc–dc converter used in a stand-alone photovoltaic application is proposed in this paper to improve existing digital-analog sliding-mode-based implementations. All three control loops: maximum power point tracking (MPPT), fast input voltage regulation, and inner high-bandwidth current control, have been programmed in the same digital signal controller (DSC). A Model Predictive Control (MPC) based algorithm has satisfactorily solved the challenge of implementing the nominal 100 kHz switching frequency current loop. The MPC cost function is distributed throughout the algorithm to achieve three specific goals: the tracking of the reference current (G1), a quasi-constant steady-state switching frequency (G2), and the assurance that the duration of an interval is larger than the time required to calculate it (G3). The third goal requires the current control to toggle between peak- and valley-modes depending on the operating point. The correct fulfillment of these control objectives on the proposed MPC-based algorithm has been validated through simulations and experimental tests performed on a purpose built-prototype. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) grid-connected applications use an adaption stage to extract the maximum power from the PV module matching its optimal operating point with the load operation. This paper presents a sliding mode control based on the admittance of the PV module to follow a reference provided by an external maximum power point tracking (MPPT) algorithm, and at the same time, to mitigate the perturbations generated by the load. The sliding mode controller is mathematically analyzed, and a design process is proposed to ensure the desired performance in all the operation range. Finally, simulations and experimental results are used to demonstrate the efficiency of the proposed solution in the presence of both changes in the irradiance level and load perturbations. [ABSTRACT FROM AUTHOR]

In many grid-connected applications, a dc/dc switching converter is usually connected between the PV modules and the inverter. This paper presents an improved procedure to design a sliding controller for the PV system, which drives the PV voltage to follow a reference provided by an external MPPT algorithm and mitigates the perturbations caused by the irradiance changes and oscillations in the bulk voltage. By considering that the switching surface is the linear combination of the input capacitor current and the PV voltage error, the proposed design exhibits advantages in comparison with existing solutions that rely in the linearization of inner current loop dynamics. The proposed integral procedure, by taking also into account the effects in the closed-loop system dynamics of a reference filter, ensures a stable sliding regime in all the desired operation range of the system, while the settling time and overshoot of the PV voltage required by an MPPT algorithm are provided. Differently from a previous similar but less rigorous approach, the switching function and reference filter parameters are obtained by numerically solving a set of nonlinear equations. Simulations and experiments were used to demonstrate the efficiency of the proposed solution in presence of environmental and load perturbations. [ABSTRACT FROM PUBLISHER]

This paper introduces a novel maximum power point tracking (MPPT) technique aimed at maximizing the power produced by photovoltaic (PV) systems. The largest part of the MPPT approaches presented in the literature are based on the sensing of the PV generator voltage. On the contrary, in this paper, a current-based technique is proposed: the sensing of the current in the capacitor placed in parallel with the PV source is one of the innovative aspects of the proposal. A dual control technique based on an inner current loop plus an outer voltage loop allows to take profit of the fast current tracking capability of the inner current loop while the voltage loop benefits from the logarithmic dependency of the PV voltage on the irradiation level. The features of the proposed algorithm, particularly in terms of tracking of irradiation variations and disturbance rejection, are supported by theoretical analysis, simulations, and experimental results. The technique described in this paper is patent pending. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper a current controller is used to reject the 100-Hz oscillation of the voltage of the photovoltaic field taking place in any grid connected system. With respect to the classical linear voltage control the current-based sliding-mode approach ensures a wider regulation band but, unfortunately, in presence of a fast irradiance variation the sliding conditions might be violated, so that the operating point, which should be the maximum power point, might not be the expected one. In order to prevent such a drawback, an appropriate voltage compensation loop is used to interface the current-based sliding mode with the Maximum Power Point Tracking algorithm. Simulation and experimental results confirm the goodness of the proposed algorithm. [Copyright &y& Elsevier]

Fourth-order converters with both input and output filters are analyzed in self-oscillating sliding mode. The boost converter with output filter and the Cuk converter are shown to have stable dynamics and an equilibrium point with transformer characteristics. The analytical predictions are verified by experimental results. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]

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 pulsewidth modulation 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. [ABSTRACT FROM AUTHOR]

This paper introduces a maximum power point tracking (MPPT) method based on a power (P) versus static conductance (G) curve of a photovoltaic (PV) array. The maximum power point (MPP) is tracked by comparing the PV array instantaneous power to a varying power reference generated by the MPPT algorithm. The comparison error is used to reduce or increase the conductance at which the PV array is forced to operate until the MPP is reached. Simultaneously, the error is used to change the power reference until the trajectory of this reference in the P–G curve enters a limit cycle around the MPP. The P–G curve is derived from a piecewise linear approximation of the current versus voltage (I–V) curve, which facilitates the analytical description of the tracking operation. The technique reported can also be implemented by means of simple analog or digital circuitry and requires two sensors to measure the instantaneous PV array current and voltage. It uses only four tuning parameters, which are selected depending on the maximum value of the derivative of the power with respect to the conductance. The theoretical predictions are verified with simulations and experimental results. The latter shows that the procedure performs well enough to be favorably compared with the most efficient MPPT methods. [ABSTRACT FROM AUTHOR]

This paper extends the use of the versatile buck–boost converter to power manage a parallel hybrid system topology as an alternative to the well-known serial hybrid (SH) topology and the most recent series–parallel hybrid (SPH) topology. These systems utilize a proton exchange membrane fuel cell as the primary source in combination with an auxiliary storage device (ASD), and the selected converter is in charge of the power management between the sources (fuel cell or ASD) and the load. Therefore, the converter has a very important role in the system since it is responsible of ensuring a dc-bus voltage regulation with a safe and reliable operation of the entire system while also guarantee a high power conversion efficiency. Hence, this is the third topology, where the coupled-inductor dc–dc buck–boost converter is studied to demonstrate and exploit its advantages such as 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. In order to determine which topology (SH, PH, or SPH) exhibits the highest power conversion efficiency under a certain load profile, it is important to ensure a fair efficiency comparison that will only reflect the properties of the topology and not its individual components. Therefore, the same design criteria, the same control, and the same components were used for all the studied topologies. Simulation and experimental results have been validated on a 48-V 1200-W dc bus. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

A 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 non-inverting 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 deadzone avoidance technique. All the experiments were carried out on a purpose-built prototype of a noninverting buck-boost converter with magnetically coupled inductors. [ABSTRACT FROM AUTHOR]

The oxygen starvation phenomenon is a dangerous operating condition that reduces the lifetime of PEM fuel cells. The detection and prevention of this undesired phenomenon require estimation of the oxygen excess ratio \lambdaO2. The mathematical complexities of the reported methods for obtaining \lambdaO2 complicate its real-time calculation and require high-performance computational devices, which significantly increase the costs of the system. In this paper, a mutual information approach is used in obtaining a simplified mathematical model for the calculation of \lambdaO2. The usage of such a simplified model requires much less computational power for real-time monitoring of the variable \lambdaO2, while it provides comparable results to those obtained by using the complex model. Therefore, it represents a cost-effective solution, suitable for usage within applications that require high sampling frequencies, like emulators, converter and air compressor control loops, simulations, etc. In order to validate the accuracy of this simplified \lambdaO2 calculation model, a real-time monitoring system was built and experimentally tested using both the simplified and complex models. The matching experimental results validate the proposed simplification and justify the use of this simplified model within real-time monitoring applications. [ABSTRACT FROM AUTHOR]

A previous article has presented the members of the asymmetrical interleaved dc/dc switching converters family as very appropriate candidates to interface between photovoltaic or fuel cell generators and their loads because of their reduced ripple and increased current processing capabilities. After a review of the main modeling methods suitable for high-order converters operating, as the asymmetrical interleaved converters (AIC) ones, in discontinuous current conduction mode a full-order averaged model has been adapted and improved to describe the dynamic behavior of AIC. The excellent agreement between the mathematical model predictions, the switched simulations and the experimental results has allowed for satisfactory design of a linear-quadratic regulator (LQR) in a fuel-cell application example, which demonstrates the usefulness of the improved control-oriented modeling approach when the switching converters operate in discontinuous conduction mode. [ABSTRACT FROM AUTHOR]

An already published current control strategy for the coupled-inductor buck–boost converter is able to change its aim from controlling the input current to controlling the output current, and vice versa, depending on the instantaneous operation point and the applied current references. The main drawback of the two PI-based control implementation is its slow response when the control aim is changed from one current to the other. Due to the magnetic coupling, the converter’s control-to-input and control-to-output current small signal transfer functions exhibit similar first-order characteristics. Therefore, it is possible to transform the previous control scheme to a PI-based one that exhibits faster and, in certain cases, much faster transitions between input and output current control operation. The presented experiments also show that the steady-state behavior of the converter is unaffected by the new control implementation. [ABSTRACT FROM AUTHOR]

High-order switched DC-DC converters, such as SEPIC, Ćuk and Zeta, are classic energy processing elements, which can be used in a wide variety of applications due to their capacity to step-up and/or step-down voltage characteristic. In this paper, a novel methodology for analyzing the previous converters operating in discontinuous conduction mode (DCM) is applied to obtain full-order dynamic models. The analysis is based on the fact that inductor currents have three differentiated operating sub-intervals characterized by a third one in which both currents become equal, which implies that the current flowing through the diode is zero (DCM). Under a small voltage ripple hypothesis, the currents of all three converters have similar current piecewise linear shapes that allow us to use a graphical method based on the triangular shape of the diode current to obtain the respective non-linear average models. The models' linearization around their steady-state operating points yields full-order small-signal models that reproduce accurately the dynamic behavior of the corresponding switched model. The proposed methodology is applicable to the proposed converters and has also been extended to more complex topologies with magnetic coupling between inductors and/or an R C damping network in parallel with the intermediate capacitor. Several tests were carried out using simulation, hardware-in-the-loop, and using an experimental prototype. All the results validate the theoretical models. [ABSTRACT FROM AUTHOR]

A 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 in discontinuous 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. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

A novel dc–dc switching converter consisting of a boost stage cascaded with a buck converter with their coils magnetically coupled is presented. The disclosed converter has the same step-up or step-down voltage conversion properties than the single inductor noninverting buck–boost converter but exhibits nonpulsating I/O currents. The converter control-to-output transfer function is continuous between operation modes if a particular magnetic coupling is selected. The addition of a damping network improves the dynamics and results in a control-to-output transfer function that has, even in boost mode, two dominant complex poles without right-half-plane zeros. An example shows that an output voltage controller can be designed with the same well-known techniques usually applied to the second-order buck regulator. Details of a prototype and experimental results including efficiency, frequency, and time domain responses are presented. The experimental results validate the theoretical expected advantages of the converter, namely, good efficiency, wide bandwidth, and simplicity of control design. [ABSTRACT FROM AUTHOR]

Many electronic power distribution systems have strong needs for highly efficient AC-DC conversion that can be satisfied by using a buck-boost converter at the core of the power factor correction (PFC) stage. These converters can regulate the input voltage in a wide range with reduced efforts compared to other solutions. As a result, buck-boost converters could potentially improve the efficiency in applications requiring DC voltages lower than the peak grid voltage. This paper compares SEPIC, noninverting, and versatile buck-boost converters as PFC single-phase rectifiers. The converters are designed for an output voltage of 200 V and an rms input voltage of 220 V at 3.2 kW. The PFC uses an inner discrete-time predictive current control loop with an output voltage regulator based on a sensorless strategy. A PLECS thermal simulation is performed to obtain the power conversion efficiency results for the buck-boost converters considered. Thermal simulations show that the versatile buck-boost (VBB) converter, currently unexplored for this application, can provide higher power conversion efficiency than SEPIC and non-inverting buck-boost converters. Finally, a hardware-in-the-loop (HIL) real-time simulation for the VBB converter is performed using a PLECS RT Box 1 device. At the same time, the proposed controller is built and then flashed to a low-cost digital signal controller (DSC), which corresponds to the Texas Instruments LAUNCHXL-F28069M evaluation board. The HIL real-time results verify the correctness of the theoretical analysis and the effectiveness of the proposed architecture to operate with high power conversion efficiency and to regulate the DC output voltage without sensing it while the sinusoidal input current is perfectly in-phase with the grid voltage. [ABSTRACT FROM AUTHOR]

Focuses on a study which presented a method based on a circuit-oriented approach for large signal stability analysis of the boost regulator. Review of equivalent circuit of a boost converter; Linear control laws for large-signal stability; Control implementation for large signal stability.

This paper presents the analysis and design of a PWM nonlinear digital control of a buck converter based on input-output linearization. The control employs a discrete-time bilinear model of the power converter for continuous conduction mode operation (CCM) to create an internal current control loop wherein the inductor current error with respect to its reference decreases to zero in geometric progression. This internal loop is as a constant frequency discrete-time sliding mode control loop with a parameter that allows adjusting how fast the error is driven to zero. Subsequently, an outer voltage loop designed by linear techniques provides the reference of the inner current loop to regulate the converter output voltage. The two-loop control offers a fast transient response and a high regulation degree of the output voltage in front of reference changes and disturbances in the input voltage and output load. The experimental results are in good agreement with both theoretical predictions and PSIM simulations. [ABSTRACT FROM AUTHOR]