Alessandro Giustiniani

Maximum Power Point Tracking in a One-Cycle-Controlled Single-Stage Photovoltaic Inverter

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.

Low-Frequency Current Oscillations and Maximum Power Point Tracking in Grid-Connected Fuel-Cell-Based Systems

The study of a double-stage single-phase inverter for fuel-cell-based applications is proposed in this paper. A novel control strategy aimed at reducing the low-frequency oscillations of the fuel-cell (FC) current in order to guarantee the FC safety operating conditions is proposed. The reduction of such oscillations increases the FC lifetime and avoids high mechanical stress of the membrane and unnecessary consumption of reactants. Furthermore, it allows one to design a strategy for extracting the maximum power from the FC stack with a total control of the concentration losses. Simulation and experimental results confirm the effectiveness of the proposed approach.

Experimental tests of a magnetostrictive energy harvesting device toward its modeling

This paper deals with a recently proposed device for energy harvesting from environmental vibrations, employing a magnetostrictive material. Even if most of the modeling efforts were focused on a linear approach, more complex and nontrivial phenomena are experimentally observed. A sample of such nontrivial behaviors, suggesting the definition of potentially more effective models, is described and discussed in this paper.

Capacitive Load Effects on a Magnetostrictive Fully Coupled Energy Harvesting Device

Vibration energy harvesting is a promising method to feed ultra-low power devices as wireless sensors, mems, etc. The accuracy of the design of the harvesting device, and then the harvested power, strongly depends on the modeling quality of the magnetostrictive relationships and on the device modeling in general. A further important issue is the optimization of the converted power with respect to the frequency of the vibration source, which is critical for low frequencies. The use of a capacitor in the electric circuit allows more harvested power at low frequencies and open the possibility of power optimizing stages. This analysis could be reliably carried out only in connection to a sufficiently realistic modeling of the employed material. Aim of the paper is therefore to study, by the definition of a simple nonlinear model, the effects of the capacitive load and of the mechanical source on the power conversion performances of the device. Several numerical examples are presented and discussed.

A Two-Port Nonlinear Model for Magnetoelastic Energy-Harvesting Devices

The aim of this paper is to present a two-port equivalent circuit that is able to describe the main features of an energy-harvesting device based on magnetoelastic materials. The magnetomechanical model behind the equivalent circuit is nonlinear and fully coupled. Therefore, the most part of the typical real-device behavior, without the limits of linear magnetomechanical modeling, is described. A preliminary validation of the model, by exploiting experimental data, is provided. Moreover, simulation tests and comparisons to the linear model are also carried out to underline the basic features of the proposed nonlinear approach. To this end, numerical results of the harvested power and peak voltage for the two devices in different working conditions are presented and discussed.

Numerical study of electrical behaviour in carbon nanotube composites

A structure aimed at modeling a polymeric nanocomposite loaded with carbon nanotubes (CNTs) is simulated by considering, in a three-dimensional space, a random distribution of impenetrable conducting cylinders inside an insulating cubic matrix. The variation of the electrical conductivity of the structure for different volume loadings of the conducting phase is estimated through a 3D resistor network. The tunneling effect between conducting clusters which is deemed responsible of the global conductivity is taken into account. By using a Monte Carlo method, the electrical conductivity and the percolation thresholds of the obtained structures are analyzed as a function of geometrical and physical influencing parameters.

Design and Test of a Stress-Dependent Compensator for Magnetostrictive Actuators

Magnetostrictive transducers are employed for several purposes where, often, the applied mechanical stress strongly affects the device hysteretic behavior. This issue complicates the design of controllers where such variable has to be considered as an additional input. Nevertheless, a compensation scheme with two input variables can be defined and fruitfully utilized in a suitable invertibility region. Aim of this paper is to present a novel compensation algorithm able to take into account the applied mechanical stress. Numerical results compared with experimental data, over a magnetostrictive actuator, show that the proposed approach leads to lower compensation errors with respect to stress-independent, classical, compensators.

Experimental properties of an efficient stress-dependent magnetostriction model

In this paper a generalization of a stress-dependent magnetostriction phenomenological model is presented. The model makes use of a classical Preisach operator and of a memoryless bivariate function and includes a pure elastic contribution. It is shown that, even if the structure of the model is simple, the operator state is still influenced by the applied stress. This property is important because the model is able to catch real magnetostrictive behavior in the presence of complex time evolutions of both the variables, current and stress. Experimental and numerical results confirm the effectiveness of the proposed approach.

Analysis of a magnetostrictive power harvesting device with hysteretic characteristics

A model for the description of the energy harvesting in magnetostriction devices is discussed. In particular, the effects of hysteresis, normally observed in these materials, are highlighted and compared to the predictions of the linear modeling. The coupling of the model to the circuit equations leads to a differential equation with hysteresis, which could provide an effective macroscopic description of the energy conversion mechanism taking place in these devices. Numerical tests are performed in order to show the effect of a magnetic field bias on the generated electric power.

Energy Harvesting Tests With Galfenol at Variable Magneto-Mechanical Conditions

This paper deals with the experimental characterization of Galfenol (iron-gallium alloy) and its energy harvesting capabilities. Two rods are considered, one with a stress annealing treatment. The impact on the harvesting performance of magnetic bias, mechanical prestress and termination resistor are considered. Moreover, the performed measurements allow to verify an important feature of the energy conversion of this magneto-mechanical material: the energy harvested loops, in the B-H plane, are confined within the magnetic characteristics at the extrema of the applied stress. This suggests the significance of the static characteristics in the energy conversion process.