Mirko Marracci

High power Lithium Batteries usage in hybrid vehicles

Hybrid vehicles require an energy storage device capable of delivering or absorbing high specific powers (powers per unit of the device size), and still, in some cases, adequate levels of specific energy.

Single PEM Fuel Cell Analysis for the Evaluation of Current Ripple Effects

In this paper, the results of an experimental analysis performed on a polymer electrolyte membrane fuel cell (FC) for the evaluation of the current ripple effects are reported. The polarization curve (PC) and the impedance spectrum measured for a single FC with a Nafion membrane are presented discussing some advantages and disadvantages of the two adopted techniques from the measurement point of view. The ohmic and activation resistance values provided by the PC are compared to the frequency limits of the equivalent resistance estimated by the spectroscopic analysis to evaluate the additional losses and the system efficiency reduction introduced by the current ripple. The presence of a voltage–current hysteretic behavior is discussed throughout the paper, and some comments on how such a relationship can impact on the identification of the indicated parameters are included.

Characterization of the Accommodation Effect in Soft Hysteretic Materials Via Sensorless Measurement Technique

The well-known voltamperometric method has only been used so far in the identification of symmetric hysteresis cycles for reasons that are explained in the main text. This paper extends the sensorless measurement method to the characterization of asymmetric loops, without losing the main advantage of this technique, i.e., the low-cost setup and the simplicity of the procedure. The current through-and the induced voltage on-the primary and secondary coils, which are wound around a magnetic core, are the measurands. Moreover, by carefully choosing the input signals, so that a series of major loops is defined along the whole B - H measured path, a way is suggested to avoid the problems caused by the dc offset of the instrumentation chain and to reduce the uncertainty in the determination of the initial state of magnetization. Both the offset and the initial magnetization state are necessary for a correct reconstruction of the induction field. A complete analysis of the capabilities and critical aspects of the proposed measurement procedure is carried out through a theoretical discussion supported by simulation and experimental results. The measurement of nonsymmetric cycles and their accommodation are shown and discussed as the final objective of the proposed approach.

Ultracapacitor Degradation State Diagnosis via Electrochemical Impedance Spectroscopy

In this paper, we propose the use of the electrochemical impedance spectroscopy technique for state diagnosis of electric double-layer ultracapacitors. Ultracapacitors under investigation are Maxwell BCAP 0350 and they were stressed in several ways for our study. The analyzed stress conditions include accelerated aging tests, overvoltage, and over temperature tests. Chemical and physical effects on supercapacitor materials are pointed out through a morphologic analysis implemented by means of an environmental scanning electron microscope and a chemical composition analysis obtained by means of an energy dispersive spectrometer. Consequent degradation effects are described in terms of frequency behavior of equivalent circuital parameters.

Characterization of Inductance Gradient and Current Distribution in Electromagnetic Launchers

We reapproach the characterization of the inductance gradient and the current distribution in electromagnetic rail launchers with multiple brush armatures. A measurement procedure based on the use of a loop system mutually coupled with the launcher is illustrated for the case of a two-brush armature. We show how to estimate the current distribution between the brushes following the basic rules of the partial-inductance method. To test the proposed procedure, we performed an experimental analysis on a rail launcher prototype supplied by a high-voltage high-power capacitor bank. Experimental results were obtained under the static condition of the armature, and they are in agreement with theoretical calculations.

Characterization of a system for measurements on soft ferrites

This paper deals with the characterization of a system for measurements on soft ferrites through a volt-amperometric method. The accurate control of the driving input field is discussed as a critical aspect for the definition of the correct operating conditions on the magnetic sample. A custom-built transimpedance amplifier is characterized in terms of total harmonic distortion and signal-to-noise and distortion ratio of the primary current and shown as a valid configuration for the required purposes. As a main contribution, the uncertainty analyses of the major loop measurement and of the magnetic accommodation measurement of minor asymmetric loops are provided.

Analytical Study of Impulse Current Measuring Shunts With Cage Configuration

In this paper, an analytical study of high-impulse current measuring shunts with cage configuration is presented. Through the use of the partial mutual inductance method, an equivalent first-order model is developed, and a discussion of the minimization of the time constant taking into account physical constraints for two different materials is presented. The transfer function of the measuring circuit is provided, and the possibility of compensating the inductance via the use of rectangular loops formed by the sensing wires and placed inside the cage is shown. The derived model is tested on a homemade shunt prototype with application to an electromagnetic rail launcher. The experimental results confirm the validity of the model and its robustness with respect to the geometrical parameter uncertainty.

Uncertainty Analysis of Local and Integral Methods for Current Distribution Measurements

This paper provides an uncertainty analysis for current distribution measurements based on local magnetic field measurements (e.g., via Hall probes) or on magnetic flux measurements using large pick-up loops. The fundamental difference between the two approaches is first pointed out in the ideal case of an infinite straight wire. Then, a more complex geometry composed by parallel identical conductors connected between two bars is considered. The mathematical models employed for the current reconstruction according to the two approaches are derived, and their uncertainties are evaluated. An experimental validation of the model for pick-up loops is presented with application to an actual rail launcher prototype. From this analysis, the critical aspects of the two methods are highlighted, showing the different effect that the uncertainty of the sensor position has on the reconstructed current uncertainty. Finally, a case study aimed at evaluating the current distribution uncertainty under simplified hypotheses is described.

Analysis of ultracapacitors ageing in automotive application

Abstract Ultracapacitors are characterized by a high specific power and long life cycle, thus they are a very interesting design solution for on-board energy applications such as hybrid-electric vehicles. In this paper the analysis of ultracapacitors ageing in automotive application is discussed to investigate the optimal performances during the whole vehicle lifetime. To study the ageing effects on the ultracapacitors, calendar life tests and power cycling tests have been carried out. The degradation of the performance of the ultracapacitors was analyzed by means of impedance spectroscopy technique.

Classification and analysis of failures of ultracapacitors in rail launchers applications

This paper deals with the classification and analysis of failures of ultracapacitors to be used in rail launchers applications with the aim of investigating the influence of strong impulsive electromagnetic fields on their performance. Considering the very harsh environment present in rail launchers applications, a reliability analysis of components of the launch mass is very important to assess the failure modes and the relevant effects. To this purpose, we introduced a Failure Modes and Effects analysis methodology (FMEA) to ensure an optimal design and material choice as well as to evaluate the impact of all possible failure mechanisms and causes on the ultracapacitors. This approach allows to reduce or possibly eliminate the effects of potential failure modes before the launch mass design completion and before failures occur during the launch.