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The design of fourth-order dc-dc converters is discussed in this paper. The Principal Components Analysis is applied to find the set of passive components which allows to avoid double resonance in the control-to-output transfer function. The design of a synchronous SEPIC converter has been studied as an application of the proposed design methodology by using a database of real passive components. The performances of the SEPIC converter designed with the proposed methodology are verified through both time domain and frequency domain simulations and they are compared with those ones achieved by standard ripple-based design procedures. Index Terms--Fourth-order converters, power stage design, principal components analysis, SEPIC converter.

In this paper, the design of the one-cycle controller of a single-stage inverter for photovoltaic applications is carried out by means of a multiobjective strategy to optimize inverter performance at both high and low insolation levels. Design constraints that account for different weather conditions are adopted. The optimization algorithm also provides useful information concerning the system sensitivity with respect to each of the controller parameters. This allows the design of a maximum power point tracking perturb and observe controller that significantly improves inverter performance. Experimental measurements confirm the predictions of theoretical and simulation results. Index Terms--Maximum power point tracking (MPPT) techniques, one-cycle control (OCC), photovoltaic (PV) inverter.

One of the major drawbacks of photovoltaic (PV) systems is represented by the effect of module mismatching and of partial shading of the PV field. Distributed maximum power point tracking (DMPPT) is a very promising technique that allows the increase of efficiency and reliability of such systems. Modeling and designing a PV system with DMPPT is remarkably more complex than implementing a standard MPPT technique. In this paper, a DMPPT system for PV arrays is proposed and analyzed. A dc and small-signal ac model is derived to analyze steady-state behavior, as well as dynamics and stability, of the whole system. Finally, simulation results are reported and discussed. Index Terms--Distributed generation, maximum power point tracking (MPPT) techniques, photovoltaic (PV) systems.

Power processing systems will be a key factor of future photovoltaic (PV) applications. They will play a central role in transferring, to the load and/or to the grid, the electric power produced by the high-efficiency PV cells of the next generation. In order to come up the expectations related to the use of solar energy for producing electrical energy, such systems must ensure high efficiency, modularity, and, particularly, high reliability. The goal of this paper is to provide an overview of the open problems related to PV power processing systems and to focus the attention of researchers and industries on present and future challenges in this field. Index Terms--Inverters, maximum power point tracking (MPPT), photovoltaic (PV) systems, power electronics, power processing, solar energy.

Maximum power point tracking (MPPT) techniques are used in photovoltaic (PV) systems to maximize the PV array output power by tracking continuously the maximum power point (MPP) which depends on panels temperature and on irradiance conditions. The issue of MPPT has been addressed in different ways in the literature but, especially for low-cost implementations, the perturb and observe (P&O) maximum power point tracking algorithm is the most commonly used method due to its ease of implementation. A drawback of P&O is that, at steady state, the operating point oscillates around the MPP giving rise to the waste of some amount of available energy; moreover, it is well known that the P&O algorithm can be confused during those time intervals characterized by rapidly changing atmospheric conditions. In this paper it is shown that, in order to limit the negative effects associated to the above drawbacks, the P&O MPPT parameters must be customized to the dynamic behavior of the specific converter adopted. A theoretical analysis allowing the optimal choice of such parameters is also carried out. Results of experimental measurements are in agreement with the predictions of theoretical analysis. Index Terms--Maximum power point (MPP), maximum power point tracking (MPPT), perturb and observe (P&O), photovoltaic (PV).

An evolutionary approach to worst case tolerance design is introduced here, with a focus on feedback compensation networks for dc-dc switching converters. Assumed that varying parameters values are uniformly distributed and uncorrelated, as provided by the worst case approach, the proposed algorithm, of general applicability, seeks for the set of nominal values and tolerances of the circuit parameters ensuring that the design constraints are met and that a user-defined circuit performance index assumes its optimal value. Design constraints are fixed in the frequency domain, in terms of acceptability ranges of loop gain crossover frequency and phase margin, to guarantee closed loop stability and the desired dynamic performance. Resistive and capacitive compensation network's parameters values are chosen within a suitable database of couples nominal value/tolerance available on the market, while the nominal values and tolerances of the parameters of the power stage are fixed. Referring to a buck dc-dc switching regulator, two widely used different compensation network topologies are compared in terms of reliability, robustness, and cast of components. Simulation results show the wide usefulness of the proposed method in supporting designer decisions.

This paper introduces an evolutionary approach to the variability analysis of nonlinear systems. The algorithm shows some advantages with respect to classical stochastic approaches and, in particular, with respect to Monte Carlo-based methods. First, it allows a significant reduction of the underestimation error that affects any nondeterministic approach; in other words, it guarantees a considerable saving of simulation time. Moreover, the technique ensures a higher reliability in pursuing the true range of variation of the system performance of interest. The method has been applied to a practical problem of great interest: the variability analysis of a stress control tube made of a composite material used for electric stress relief in cable accessories. The cable termination has been modeled by means of a lumped nonlinear circuit. The proposed technique also provides reliable results whenever large parameter variations need to be taken into account and/or nonlinear functions of varying parameters are considered. Simulation results prove it to be of great support for the designer in cable termination dimensioning and in composite material selection. Index Terms--Cable accessories, composite materials, variability analysis.

This paper presents an evolutionary approach to worst case tolerance design of magnetic devices. The algorithm improves on the classical nominal design, accounting for parameter variations and tolerances, so that the system performance does not exceed upper and lower specifications imposed in advance by the designer. The evolutionary algorithm adjusts central values and tolerances of parameters so that a user-defined objective function is optimized and the design constraints are met. The feasibility of the candidate sets of design parameters and tolerances is estimated by means of vertex analysis. The algorithm ensures that the optimized design set of parameters and tolerances is 100% feasible in a large number of practical eases. This paper gives an example of the design of a magnetic device and discusses the salient features and limitations of the approach. Index Terms--Genetic algorithms, tolerance analysis, tolerance design.

In this paper, a unified method for steady-state analysis of hard-switching and soft-switching dc-to-dc converters is presented. The power stage and the feedback control circuit forming the regulator are modeled separately and analyzed as two interconnected blocks. The intersection of the open loop dc steady-state characteristics of these cascaded blocks provides the initial condition for a guess candidate steady-state solution (CS). The CS is validated as true steady-state solution (TS) if the bias conditions of switching devices are fulfilled everywhere in the switching period, otherwise the CS is changed according to the conditions violated. The CS approaches the TS through an iterative process of validation. The basic tools adopted to ensure a reliable computation of the CS are interval analysis (IA), for the identification of the commutation instants (CI), and the compensation theorem (CT), for the analysis of commutations. Some examples of applications to hard-switching and soft-switching dc-dc regulators are presented. Index Terms--Steady-state analysis, switching regulators.

A new method for steady-state analysis of pulsewidth modulation (PWM) hard-switching dc-to-dc regulators is presented. The power stage and the feedback control circuit are analyzed as two interconnected blocks. The intersection of their open-loop dc steady-state characteristics with the ramp voltage provides a guess candidate steady-state solution (CS). An iterative process is used to validate it as true steady-state solution (TS) when the bias conditions of switching devices (SDs) are fulfilled everywhere in the switching period.

The analysis of synchronous commutations in switching converters is discussed in this paper. The Compensation Theorem (CT) is applied in order to define two matrices, called respectively zero-order and first-order master-slave connection matrix (Z-MSCM, F-MSCM), which allow a unified analysis of both hard and soft synchronous commutations in switching converters. The Z-MSCM and F-MSCM provide the analytical basis for studying the interactions among switching devices in any type of switching converter. The method is presented in its general formulation, valid for the analysis of switching converters including feedback circuitry and soft-switching cells. The examples presented show that the CT-based analysis of commutations is a useful and efficient tool for the comprehension of the mechanisms of synchronous commutations in switching converters and for numerical simulations. Index Terms--Compensation theorem, switching converters, synchronous commutations.

Steady-state analysis of soft-switching converters is discussed in this paper. Finding the steady-state solution of soft-switching converters by means of start-up transient simulation may involve onerous computations and convergence failure, because of the mix of fast and slow natural frequencies determined respectively by the presence of soft-switching Lr-Cr cells elements and bulky L-C filter elements. The numerical method proposed in this paper shows high reliability and fast convergence, thanks to the adoption of an interval analysis based technique for the detection of commutations and of a compensation theorem based technique for the analysis of commutations. Some examples of steady-state analysis of two dc-dc converters, an inverter and a power factor corrector are presented to highlight the good performances of the simulation algorithm. Index Terms--Compensation theorem, interval analysis, soft-switching converters, steady-state analysis.

The state-space modeling and related order reduction problems of switching dc-dc converters operating in discontinuous (D) mode are treated in this paper. A unified discrete-time full-order model is proposed assuming the discontinuous current and voltage mode (DCVM) as a general operation mode from which the discontinuous current mode (DCM), the discontinuous voltage mode (DVM), and continuous mode (CM) derive as special cases. Such model permits a straightforward study of the control-to-output response, in each operation mode. The order reduction of the transfer function is carried out by means of the principal component analysis considering the joint controllability and observability properties of the circuit. It is shown that a proper order reduction can be gained not only in DC mode, as expected, but also in DV and DCV modes. A substantial difference between DC and DV modes is also evidenced in terms of controllability. The frequency analysis and state-space model order reduction for a Cuk converter are proposed to show that the method is free of the limitations affecting other methods of analysis and that its predictions fit experimental measurements.

The nine papers in this special section focus on photovoltaic module and sub-module level power electronics. Grid connected photovoltaic energy systems have experienced an explosive growth over the last decade, with a cumulative installed capacity surpassing the 400 GW milestone as of 2017. Among PV system configurations, distributed module-level converter architectures can lead to a higher energy yield by mitigating partial shading, persistent shading (soiling, snow, bird droppings, and fallen leaves), mismatch, and aging, through a higher maximum power point tracking (MPPT) efficiency. Also, distributed electronics might be the key for implementing diagnostic and prognostic actions at a module level. Among these configurations, microinverters (also known as ac-module inverter), which connect a single PV module to the grid, and PV power optimizers, which are dc–dc converters performing the MPPT function at a module level, have attracted the academic and industrial interest in the last decade. So much so, that both microinverters and dc–dc power optimizers are commercialized by tens of companies around the world, with a great variety of circuit topologies, which comprise combinations of one or more power stages, interleaved converters, resonant converters, topologies with and without isolation, etc. [ABSTRACT FROM AUTHOR]

In this paper, a new approach to the calculation of the true worst case in circuit tolerance analysis (TWC-CTA) with parameters characterized by large uncertainties is presented. It is based on the joint use of genetic algorithms (GAs) and affine arithmetic (AA). The GAs are used to minimize the underestimation error which affects stochastic methods while the AA is applied to minimize the overestimation error which affects interval arithmetic methods in TWC-CTA problems. The joint GA-AA approach presented in this paper ensures a reliable TWC evaluation. Index Terms--Affine arithmetic, circuit tolerance analysis, genetic algorithms, interval arithmetic.

A new approach for improving the efficiency and accuracy of interval arithmetic (IA) based worst case (WC) circuit tolerance analysis (TA) is presented in this paper. The partitioning of the parameters' tolerance/uncertainty ranges, which is necessary to increase the accuracy of IA-based computations, is optimized by means of a genetic algorithm (GA). It is shown that the IA-GA approach permits us to solve problems of small-change (SC) as well as large-change (LC) WC circuit TA, accurately and reliably. Several applications to the analysis of circuits with uncertain parameters are presented and discussed. Index Terms--Circuit tolerance analysis, genetic algorithms, interval arithmetic.

In this paper, an efficient method for the online identification of the photovoltaic single-diode model parameters is proposed. The combination of a genetic algorithm with explicit equations allows obtaining precise results without the direct measurement of short circuit current and open circuit voltage that is typically used in offline identification methods. Since the proposed method requires only voltage and current values close to the maximum power point, it can be easily integrated into any photovoltaic system, and it operates online without compromising the power production. The proposed approach has been implemented and tested on an embedded system, and it exhibits a good performance for monitoring/diagnosis applications. [ABSTRACT FROM AUTHOR]