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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 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]

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]

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]

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]