Walter Zamboni

Parameter identification of Li-Po batteries in electric vehicles: A comparative study

An effective management of the onboard energy storage system is a key point for the development of electric vehicles. This requires the accurate estimation of the battery state over time and in a wide range of operating conditions. The battery state is usually expressed as state-of-charge and state-of-health. Its estimation demands an accurate model to represent the static and dynamic behaviour of the battery. Developing such a model requires the online identification of the battery parameters. This paper aims at comparing the performance of two popular system identification techniques, i.e., the Extended Kalman Filter and the classic Least Squares method. A significant contribution of this work is the definition of a benchmark which is representative of the real use of the battery in an electric vehicle. Simulation results show the peculiarities of both methods and their effectiveness.

Stability Issues in Peak-Current-Controlled SEPIC

The aim of this paper is to discuss the impact of passive power components on peak-current-controlled single-ended primary inductance converter (PCC-SEPIC) current loop stability. Stability conditions are determined by means of a novel dynamic model of the PCC-SEPIC, taking into account the difference between the small-signal ac components of the voltage across coupling capacitor and of the input voltage. The analysis of dominant closed-loop poles allowed by the new model highlights the dependence of PCC-SEPIC stability on input and output inductors, coupling capacitor, and current modulator gain and losses. Inductive and capacitive damping approaches are discussed to achieve intrinsic stability of the current loop. In both cases, the damping of dominant poles is investigated by numerical resolution of the new model and design guidelines are provided about how the L-C parameters can be chosen in such a way that oscillations on the voltage across the coupling capacitor are adequately damped. Experimental verifications confirm the validity of predictions provided by the new model.

Comparing particle filter and extended kalman filter for battery State-Of-Charge estimation

The battery State-Of-Charge (SOC) and parameters estimation is one of the crucial points to be addressed in the development of innovative electric/hybrid electric vehicles. Extended Kalman Filter (EKF) and Particle Filters (PF) are two possible approaches to the problem. While EKF is attractive for its computational efficiency, it may not be accurate for the non-linearity and for the uncertainties involved in the battery modelling. PF is a promising alternative, even if it is computationally more demanding. In this paper, we compare the EKF and PF performance in the dual Bayesian estimation of battery state and parameters, with particular reference to lithium batteries, showing that PF is attractive, especially in the presence of inaccurate battery models.

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.

Experimental analysis of open-circuit voltage hysteresis in lithium-iron-phosphate batteries

This paper aims at investigating and modelling the hysteresis in the relationship between state-of-charge and open-circuit voltage of lithium-iron-phosphate batteries. A first-order charge relaxation equation was used to describe the hysteresis dynamics. This equation was translated into a voltage-controlled voltage source and included within an equivalent electric circuit of the battery used in online state-of-charge estimators. The effectiveness of the obtained battery model was verified comparing simulated and experimental data.

Stress-Induced Eddy Currents in Magnetostrictive Energy Harvesting Devices

The paper aims to provide a more accurate analysis of a magnetostrictive energy harvesting device by proposing a FEM model which, assuming a realistic nonlinear characteristic of the material, is able to describe the harvesting phenomena in presence of the eddy currents induced by the Villari effect. The study is focused on the investigation of the influence of those parameters, such as pre-stress and bias, on the field dynamics and, consequently, on the eddy currents loss phenomena which cannot be disregarded if a reliable prediction of the global performances of these devices is required. The numerical results are computed by considering a compressive stress-driven vibration source and show spatial profiles of the fields, losses, and recovered powers in different operating conditions. Comparisons with the linear model are also provided.

Hysteresis Modeling in Li-Ion Batteries

This paper investigates the applicability of the scalar Preisach model to describe the hysteresis in the state of charge versus open-circuit voltage plane of lithium-iron-phosphate batteries. The model is implemented using the Everett function, identified with experimental data related to first-order reversal hysteresis branches. To show the effectiveness of the approach and the predictive capabilities of the Preisach model in this peculiar application, numerical simulations of a major hysteresis loop and a set of minor loops are compared with the experimental data.

A Unified Practical Design Method for Capacitors of Switching Converters

This paper presents a practical algebraic unified design method for the selection of capacitors in dc-dc switching converters. The model adopted accounts for the correlation existing between the capacitance C and the equivalent series resistance (ESR) of capacitors and provides reliable design formulas for the choice of commercial components. The application of the method is illustrated for the design of capacitors complying with maximum acceptable steady-state ripple voltage. A piecewise-defined algebraic function is introduced, which expresses the boundary of the capacitor acceptability region in the C-ESR plane. Numerical and experimental validations, referred to the design of capacitors of a single-ended primary inductor converter (SEPIC), prove the effectiveness of the method.

Modeling Issues and Performance Analysis of High-Speed Interconnects Based on a Bundle of SWCNT

The effects of the uncertainties associated with the transverse pattern of carbon nanotubes (CNTs) of the conducting type in a semiglobal interconnect based on a densely packed CNT bundle are investigated. The effectiveness of the insertion of a variable number of repeaters along the interconnect and the influence of the contact resistances between CNTs and external circuitry are also studied. The numerical computations are performed by using a multiconductor transmission line model in which the per-unit length parameters are accurately derived from a macroscopic fluidlike description of the conduction phenomena in CNTs.

Fast Solution of a 3-D Integral Model for the Analysis of ITER Superconducting Coils

In this paper, we simulate the electromagnetic behavior of cable-in-conduit conductors (CICCs) and coils using a 3-D integral formulation of magneto-quasistatic Maxwells equations, where the superconductors are represented by a power-law. The integral equation is numerically formulated using edge-elements and the nonlinear problem is discretized with a quasi-Newton algorithm. The solution of each iteration step is achieved with an iterative GMRES solver, which benefits from an singular value decomposition of the full matrix representing the integral operator. The model is applied to study the electromagnetic behavior of international thermonuclear experimental reactor (ITER) CICC and coils.