M. Pagano

Experimental Performance of MPPT Algorithm for Photovoltaic Sources Subject to Inhomogeneous Insolation

Photovoltaic (PV) power system performance depends on local irradiance conditions. PV systems are sometimes subject to partial shading, which may produce a nonideal characteristic curve, presenting true and local power maxima in the P -I curve. Traditional maximum power point tracking (MPPT) algorithms can converge to local maximum, which is not the true MPP. In order to solve the problem, this paper investigates the effects of nonuniform solar irradiance distribution on a PV source. An MPPT algorithm that is able to optimize the source instantaneous operating power under nonuniform irradiance is proposed. The ability of the algorithm and its increased performance with respect to traditional algorithms are evaluated by means of experimental tests performed on a real PV power system.

Hybrid Electrochemical Power Sources for Onboard Applications

In this paper, the performance of a hybrid ultracapacitor and battery power source for onboard applications is examined. First, the behavior of the system is shown by means of a nonlinear analytical model, which is solved using a double time scale procedure; then, the performances of the source is experimentally validated through an 80-V prototype. In light of the interaction between the battery and ultracapacitor during the provision of a pulsing load, issues related to power peak, internal loss, and lifecycle are discussed. The aim of this paper is to define the design criteria for battery and ultracapacitor integration in compact and light systems.

Experimental results of on-board battery-ultracapacitor system for electric vehicle applications

Automotive drive systems, which use more than one type of energy source, are considered an important step towards low polluting emission and fuel economy. All over the world, the automotive industry is undertaking strategic initiatives to develop new technologies applied to these systems; high-efficiency, high-specific power electric motors., load-levelling devices, hydrogen and direct-methanol fuel cells. advanced batteries, direct injection Diesel and Otto cycle engines are carrying out tests to evaluate their ability to reduce emission and increase vehicular economy. The aim of these initiatives is to propose a framework for analysis, design and control of vehicles within different energy generators. The paper discusses electrochemical capacitors, called ultracapacitors, and tests one of these to evaluate its ability for automotive applications. The results of the tests, effected on an ANSALDOBREDA prototype, want to evidence device ability to store energy during braking operations and to boost on requirements, to limit battery intervention. Some considerations on ultracapacitors charge efficiency are also reported.

2

A 2×25-kV 50 Hz traction power system was analyzed and modeled in the time domain in order to simulate short-circuit conditions and to attain a practical method to identify the short circuit behavior of the traction system. In particular, due to the difficulty in assessing the track-line parameters which mainly depend on changing environmental conditions, the possibility of neglecting the capacitive parameters was analyzed. A complete model of the 2×25-kV 50 Hz traction power system was developed and validated through comparison with the results of referenced models and experimental tests performed on real systems. Simulations, addressed to reduce the short-circuit modeling complexity, demonstrate that neglecting the capacitive effects between conductors and to ground does not affect the calculation accuracy for standard analyses. The obtained results show that the proposed model can be remarkably useful for the traction system design as well as for investigating the effects of short-circuit conditions on other circuits, such as telecom circuits, power-supply equipment, and signaling track circuits.

\,\times\,

For customer satisfaction a reliable and stable supply is required. Electric loads characteristics often make it a necessity to adopt back-tip energy sources, which, coupled with the main one, are able to satisfy load requirements in terms of continuity and quality. For special applications, which require a high continuity source, it is necessary to combine the main electric energy source with UPS sources, which consist of a DC battery and a rotating electric generator, which supports the finite capacity of the battery pack. The research is actually devolved to study electric power systems, which, characterised by high reliability and low maintenance costs, present also low pollution and noise level: in particular, it is already carrying out tests to use UPS, which are equipped with fuel-cell systems. When the duration of power outage/requirement is uncertain, the fuel-cell system is an ideal power source, which keeps generating power required by the loads, as long as a sufficient quantity of hydrogen and oxygen is provided. In the paper, the design for a fuel-cell-based inverter system is discussed. The defined fuel-cell characteristics are, in particular, focused on the possibility of selecting between battery or ultracapacitor-based energy storage device with reference to their features in terms of electrical and reliability aspects.

25-kV 50 Hz High-Speed Traction Power System: Short-Circuit Modeling

The paper focused on the operating characteristics of a smart-grid scheme. The power system was equipped with Distributed Energy Resources (DER) consisting of storage-integrated photovoltaic (PV) power systems. A realistic simulation scheme aiming to evaluate the DER power system behaviour under varying grid requirements was implemented in ®Matlab. The operating performance were observed in steady state and transient conditions. The action of the storage buffer was pointed out, aiming to focus on the advantages offered to the grid interactive control by using storage integrated DER units. Some discussions about the behaviour of the components and system operating characteristics were reported.

Electrical networks fed by fuel-cells for uninterruptible electrical supply

In the paper, the problem of uncertain data in reliability analysis of complex systems is examined. The analysis is addressed to system reliability assessment with imprecise knowledge of component reliabilities, an item becoming more and more important for systems affected by considerable technological change. Starting from component uncertain data, a new method for the whole system reliability uncertainty description, based upon a Bayesian approach and not depending on the reliability model of each component, is proposed. The reliability value of each component is considered as a random variable described by a Negative Log‐Gamma distribution. The proposed methodology makes it possible to compute the features of system reliability uncertainty (i.e. reliability distribution, confidence intervals, etc.) as functions of component uncertain data, thus characterizing the propagation of uncertainty from the components to the system. Numerical applications, related to a test system, are presented to show the validity of the method and its “robustness”, i.e. it is shown that it yields satisfactory results also when component reliabilities are not Negative Log‐Gamma but Beta distributed.

Ultracapacitor-based distributed energy resources to support time-varying smart-grid power flows

The reliability of electrical energy storage systems, related to the various mobile applications, needs to be carefully measured. The Italian research centre ENEAs “Low Environmental Impact Vehicles” Laboratory has started experimental testing activities on storage systems, as illustrated here with reference to acid batteries reliability performances. In this paper, starting from the results of the campaign of laboratory tests, a probabilistic method for describing the distributions of battery lifetime is presented. The approach is based upon the Rakhmatov and Virudhula battery model. In the final part of the paper, numerical tests show that the battery expected lifetime can be well described by models, such as the Inverse Weibull or the Lognormal, with decreasing hazard rate for large mission times, a fact which has been sometimes observed in literature as a paradox. Some considerations with respect to parameter estimation of the reliability models close the paper.

Negative Log‐Gamma distribution for data uncertainty modelling in reliability analysis of complex systems ‐ Methodology and robustness

An optimal maintenance program for electrical power system components should be based on their reliability. Since, for components characterized by high reliability and cost such as HV circuit breakers, available statistical data are in limited number, a physical model for their ageing is opportune. In the paper a Predictive Maintenance Program (PMP), for determining when a HV circuit‐breaker should be rebuilt, is formalized; it is based upon an adequate stochastic model of electrical wear associated with breaking operations due to system faults. In the model, both fault times and amplitudes are described by means of random variables, in order to deduce a reliability function used as input data for a Bayesian discriminant analysis which dynamically estimates, also in the presence of observation errors, the state of the component, determining the optimal times to perform a maintenance action.

Experimental performances and life cycle estimation of hybrid electric storage systems

In the paper the uncertainty of the photovoltaic (PV) cell model, by properly deriving the probability density function of the interest parameters, is characterized. This issue is crucial for predicting the capability of the photovoltaic source in producing electrical energy, but also for the control aspects of designing an efficient Maximum Power Point Tracker (MPPT). The PV source is modeled by means of a five parameters model: Iph, I0, VT, Rs and Rsh. The probabilistic approach is based upon the knowledge of the cell datasheet. The shunt resistance Rsh, in absence of information, is characterized by a Gamma distribution. A statistical analysis, based upon Monte Carlo simulation, is performed for verify how the other parameters can be affected by the stochastic nature of the random variable. In the final part of the paper, the uncertainty of the datasheet values is also introduced. A case study is reported and the numerical results are discussed in detail.