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Distributed maximum power point tracking (DMPPT) is one of the most promising solutions to overcome the drawbacks associated with mismatching phenomena in photovoltaic (PV) applications. DMPPT is based on the adoption of a dc/dc converter dedicated to each PV module. The design of the power stage of such a converter is a challenging task because of the very high efficiency requirements and of the continuous changes of the operating point during the day, depending on the sun irradiation conditions. In this paper the guidelines for the design of dc-dc converters for DMPPT applications are presented and discussed. [DOI: 10.1115/1.4001465]

The perturb and observe (P&O) best operation conditions are investigated in order to identify the edge efficiency performances of this most popular maximum power point tracking (MPPT) technique for photovoltaic (PV) applications. It is shown that P&O may guarantee top-level efficiency, provided that a proper predictive (by means of a parabolic interpolation of the last three operating points) and adaptive (based on the measure of the actual power) hill climbing strategy is adopted. The approach proposed is aimed at realizing, in addition to absolute best tracking performances, high robustness and promptness both in sunny and cloudy weather conditions. The power gain with respect to standard P&O technique is proved by means of simulation results and experimental measurements performed on a low power system. Besides the performance improvements, it is shown that the proposed approach allows possible reduction of hardware costs of analog-to-digital (A/D) converters used in the MPPT control circuitry.

The use of one-cycle control (OCC) for maximum power point tracking (MPPT) and power factor correction (PFC) in grid connected photovoltaic (PV) applications is discussed. Circuit and operating parameters of the one cycle-based controller of a cost-effective single-stage inverter are optimized in order to obtain the best performances of the system under different irradiance levels. Firstly, design constraints are formulated which allow to get a very efficient OCC operation in terms of power extracted from the PV array, stability, and PFC. Afterwards, such constraints are used to perform the parametric optimization of the one cycle controller by means of suitable heuristic approaches. Various selection criteria of the best parameters set under different conditions are discussed and applied. Finally, a customized perturb and observe (P&O) control is applied to the optimized one cycle controlled single-stage inverter in order to perform a real MPPT in presence of varying irradiance conditions. Subjects described here are covered by the Italian Patent Application SA2005A000014-13.07.2005 and PCT Application PCT/IT2005/000747-20.12.2005.

This paper introduces an evolutionary approach to worst case tolerance analysis of static field problems ruled by the Poisson equation, over suitable spatial domains and with given boundary conditions. The approach ensures a better estimation of the true worst case with respect to classical stochastic methods, especially if parameters are affected by large uncertainties and whenever the performance function of interest is nonlinear or, even worse, nonmonotonical with respect to parameters. Index Terms--Static fields, tolerance, worst case analysis.

In this paper, a new method for the large-signal time-domain analysis of switching converters is presented. It is based on a discrete-time transition model for the coefficients of time-domain spectral form of state variables describing the behavior of the converter between each pair of switching instants. The variables controlling the zero-current and zero-voltage switching instants are represented by finite-order approximating polynomials, whose zeros are determined by means of a fastly convergent interval analysis technique; the analysis of synchronous commutations is carried out by means of the compensation theorem. In order to illustrate the effectiveness and accuracy of the proposed method the example of a regulated dc-dc converter is given. Index Terms--Simulation, switched networks, Vandermonde matrices.

It is shown that the joint use of Monte Carlo techniques and Interval Analysis with Affine Arithmetic can be profitably exploited to carry out range analysis in electroquasistatic field linear problems. Stochastic and deterministic techniques can support each other in order to overcome the main limits of each method of analysis thus providing reliable inner and outer bounds for the True Worst Case solution. A benchmark 2-D linear problem has been used to show the main features of the proposed approach which can be applied to study all those physical phenomena ruled by Poisson's equation and characterized by some (eventually all) parameters ranging in specific intervals. Index Terms--Monte Carlo analysis, interval analysis, Affine arithmetic, electroquasistatic field linear problems, range analysis.

This paper illustrates a general method to formulate the equations for the analysis of commutations and of the effects caused by large step-wise perturbations, large change of parameters, and circuit failures in switching converters including transformers, feedback circuitry, and soft-switching cells. The matrix equations obtained by means of the modified nodal analysis--based method proposed in this work are useful for theoretical inspection of switching converters as well as for numerical simulations. The examples of applications concern the analysis and the synthesis of switching converters and show that the Compensation Theorem (CT)--based model may help in selecting circuit topologies valid for the circuit design.

The numerical evaluation of the electrical stress in the line-end coil of the stator winding of a medium voltage motor fed by a pulsed width modulated (PWM) inverter seems to be indispensable for a rational design of the machine. In order to fulfil such a task, the system, composed of a feeder cable and a stator winding, is modelled and simulated by using multi-conductor transmission line theory. The model can take into account the main phenomena occurring along the lines, i.e. the propagation and the reflection, together with the time dispersion introduced by the losses, eventually dependent on the frequency. The multi-conductor transmission line is solved in the time domain by adopting a technique based on the perturbation theory of the spectrum of symmetric matrices, which sensibly decreases the computational effort with respect to the analysis in the frequency domain. Furthermore, an accurate calculation of the characteristic matrices, which contain the cross-sectional information of the line, is performed by means of a FEM package, so taking into account the effective field distribution in the region of interest. The influence of the accurate evaluation of the capacitance and inductance matrices is considered by comparing the numerical results of the proposed model with those obtained by a simple equivalent circuit, frequently adopted in the literature. In order to validate the proposed model, the simulated results are compared with experimental data.

Corona is initiated in high field regions. To suppress corona or to increase the corona inception voltage in HV insulators or bushings, suitable semiconductor coatings, able to relieve high electric fields, are commonly used. The choice of appropriate materials to be used for the most effective corona suppression is typically made on the basis of expensive and time consuming trial and error tests or on the basis of approximate theoretical analysis. In this paper a guideline, based on the adoption of a suitable numerical method, is provided in order to lead to the optimal choice of the electrical characteristics of semiconductor materials for the most effective corona suppression.

An effective model is presented for the evaluation of the electric field dynamics inside electrical components, using nonlinear stress grading materials. The model, implemented in a numerical procedure, permits the solution of the Laplace equation and the diffusion equation by adopting the Galerkin method. Two-dimensional domains, even of very complex shapes and the finite thickness of the grading materials are properly taken into account, allowing an accurate evaluation of the electric field distribution and a sound understanding of the influence of the different types of nonlinearities on the stress grading efficiency. The proposed technique has been applied to study the field distributions inside a cable termination equipped with a stress control tube and in a suspension cap-and-pin glass insulator covered with an anti-corona layer. Numerical results for sinusoidal power frequency and standard impulse voltages elucidate the different role of resistive and capacitive contributions in determining the overall potential maps.

A new model for the evaluation of the electric field in a cable termination realized through a nonlinear stress control tube (SCT), is presented in this paper. It is based on the electro-quasistatic approximation of the Maxwell equations: the Laplace equation describes the field in the nonconducting regions whereas a diffusion-like equation gives the field dynamics in the stress control tube. A numerical model is devised by solving the Laplace equation by finite difference and diffusion equations by the Galerkin method. It is shown that even the well-known RC transmission line model can be derived from this general approach. The underlying approximations leading to the circuital model are discussed in detail. The proposed model, in contrast with the circuital one, allows us to take into account properly the nonlinear SCT characteristics and the actual boundary conditions: in this way both spatial and temporal effects of the nonlinearity are considered. The numerical results obtained by considering the general field approach and by using the transmission line model are compared.

The appearance of dry bands on polluted insulator surfaces may cause the ignition of electrical arcs, which in turn give rise to tracking and erosion, or may elongate until they bridge the electrodes causing flashover. Efficient models able to predict the occurrence of such a severe problem is of paramount importance for the engineer involved in the design of power lines insulation. The present paper concerns the evaluation of the temperature distribution along the surface of an outdoor insulator subjected to pollution of different severity in order to predict dry band formation. The proposed numerical procedure, based on the joint solution of Maxwell equations in their quasi-static formulation and thermal equations, has been applied to study the case of a suspension cap-and-pin glass insulator, covered with pollution layers of different conductivity and thickness. The dependence of the conductivity of the layer on the temperature has been taken into account properly. The influence of uniform and nonuniform pollution distribution on the temperature profile is discussed for an applied sinusoidal power frequency voltage.

The production technology of carbon-black loaded polyolefins adopted for stress grading purposes in ac cable terminations may impart, in addition to the nonlinear electrical properties, an anisotropic behavior to the material. In this paper a numerical study is presented in order to study the influence of both anisotropy and nonlinearity on the electrical field dynamics inside cable terminations adopting stress grading carbon-black loaded composites. The nonlinear anisotropic conductivity is properly taken into account in the model, allowing a sound understanding of the influence of such property on the stress grading performances of the considered accessory. The numerical results for sinusoidal power frequency and standard impulse voltages demonstrate the role of the different conduction mechanisms on stress grading efficiency and give useful indications for an effective material characterization.

A description of the experimental and theoretical investigations, carried out for the realization of a cryogenic cable termination, is presented. Identification and classification of the partial discharge (PD) patterns obtained on an HV vacuum bushing and on two types of cable model insulation was attempted. It is shown how a methodological and proper interpretation of experimental data can provide information on the design of cryogenic devices as well as indications on their optimal operating conditions.