Luigi Egiziano

A Galerkin model to study the field distribution in electrical components employing nonlinear stress grading materials

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.

Robust Design of Electromagnetic Systems Based on Interval Taylor Extension Applied to a Multiquadric Performance Function

A worst case robust design approach based on a suitable application of interval arithmetic (IA) is proposed. The use of IA leads to a definition of the interval extension of the Taylor series named interval Taylor extension (ITE). The width of the ITE (WITE) has been shown to be a valuable robustness index in the case of polynomial performance functions (PFs). In this paper, the method is extended to nonpolynomial PFs, as those ones obtained by multiquadric interpolation in computer assisted electromagnetic design (by FEM, BEM, etc.). In particular, it is shown that the ITE of a multiquadric function furnishes a rigorous overbounding of the PF and the WITE gives an overestimation of the PF range in presence of an assigned uncertainty of the design parameters, both in an analytical monodimensional case study and in the benchmark TEAM 22 optimization problem. Moreover, the most robust stationary solution can be achieved by looking at the minimum of WITE.

Photovoltaic inverters with Perturb&Observe MPPT technique and one-cycle control

This work presents a single-stage photovoltaic inverter which is based on one-cycle control. Such an inverter is characterized by two original features. The first one lies in a new formulation of the set of equations for the design of the one-cycle control circuitry of the inverter, such constraints are explained in L. Egiziano et al. (2006) and are here used to select the optimal solution. The second original characteristic of the proposed inverter lies in the development of a Perturb&Observe maximum power point tracking technique customized for a one cycle controlled single-stage inverter (patent pending) based on a sub set of the constraints reported in L. Egiziano et al. (2006). The results obtained show that the performances of the proposed system are top level and that the proposed solution represents the first true single stage photovoltaic inverter

Electrical properties of different composite materials for stress relief in HV cable accessories

In order to ensure optimal electrical performances of high voltage cable accessories an important aspect which determine both the steady-state long-term and impulse performances of the components, resides on the appropriate selection of the grading material. The use of a simple circuital approach, and significant control parameters, allow the evaluation of suitable limits for the values of the resistivity and permittivity of the adopted composite material which should guarantee a reliable operation of the components. In order to supply this significant information and compare the performances of thermosets and rubber based composites, typically adopted in these applications, the electrical properties of carbon black-loaded polyolefins and EPDM materials are analysed for a broad range of applied field and temperature.

Optimization of Perturb and Observe control of grid connected PEM Fuel Cells

In this paper the use of the Perturb and Observe (P&O) control strategy aimed at extracting the maximum allowable power from a Fuel Cell (FC) in a grid connected application is proposed. The values of the P&O operating parameters, namely the amplitude and frequency of the perturbations, are optimized by keeping into account their impact on the FC safety operation.

Experimental characterization of the photovoltaic generator for a hybrid solar vehicle

In this paper, the experimental characterization and the model identification of a photovoltaic generator for a hybrid solar vehicle are described and discussed. After a discussion about the decisions made during the design stage, the experimental results obtained by using a prototype of hybrid solar vehicle are presented and compared with those ones obtained by means of a non linear numerical model, both under uniform irradiance level as well as in mismatching conditions. The experimental test bed is described in detail and results of the measurements, in terms of power and energy produced during daylight, are used to sketch the future activities concerning the optimization of the prototype of hybrid solar vehicle.

Design and Optimization of a Maximum Power Point Tracking controller for a PV battery charger

In this paper the design criteria for a Maximun Power Point Tracking (MPPT) controller of a dc-dc converter for photovoltaic (PV) applications are presented. The switching converter matches a single panel with a battery and performs the maximum power point tracking at the batterys terminals instead that at the panels output. Comparisons among analytic results, simulations and experimental measurements on a laboratory prototype are presented and discussed.

Voltage distortion effects on insulation systems behaviour in ASD motors

Adopting PWM-like voltage waves, the insulation systems of stator windings of medium voltage motors have been characterized in presence and in absence of partial discharges. In addition, the dielectric losses increase for similar test samples, stressed both by a quasi square voltage and by a sinusoidal voltage, have been evaluated and reported.

Influence of circuit parameters on the electric discharge machining of the bearings of a PWM inverter driven motor

In inverter motor drives an increasing fraction of faults is associated to the bearings damages induced by circulating currents. In particular, the capacitive couplings between the stator and the rotor give rise to a shaft voltage which, in turn, may produce the breakdown of the lubricating film in the bearings and the associated electric discharge machining (EDM) currents. By using an accurate circuital model for an inverter-driven induction motor for traction applications such damaging mechanisms, the statistical occurrence of the discharges and the associated energy level are evaluated. In order to investigate the relations among the currents amplitude and frequency and the influencing parameters of the drive, such as the cable length, the geometrical and physical characteristics affecting the bearings impedance, the Response Surface Method is applied. The most influencing parameter, the sensitivity level and the mutual effects induced by the parameters variations are obtained. The resulting information can be used in the design phase. The same approach can be applied also for correlating different performances of the motor with further influencing parameters.

Partial discharges mechanisms under different voltage waveforms

A special experimental research project studied the different partial discharges (PD) degradation mechanisms in action when stressing two types of insulating objects by applying square wave voltages and different PWM voltages. The data output evidenced a sort of threshold in the increase of the PD aging processes.