1,721,232 research outputs found
Impianti fotovoltaici non uniformemente irradiati: determinazione della condizione di funzionamento ottimale
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A lithium-ion capacitor model working on a wide temperature range
Full text linkEnergy storage systems are spreading both in stationary and transport applications. Among innovative storage devices, lithium ion capacitors (LiCs) are very interesting. They combine the advantages of both traditional electric double layer capacitors (EDLCs) and lithium ion batteries (LiBs). The behavior of this device is much more similar to ELDCs than to batteries. For this reason, several models developed for traditional ELDCs were extended to LiCs. Anyway, at low temperatures LiCs behavior is quite different from ELDCs and it is more similar to a LiB. Consequently, EDLC models works fine at room temperature but give worse results at low temperatures. This paper proposes a new electric model that, overcoming this issue, is a valid solution in a wide temperature range. Based on only five parameters, depending on polarization voltage and temperature, the proposed model is very simple to be implemented. Its accuracy is verified through experimental tests. From the reported results, it is also shown that, at very low temperatures, the dependence of the resistance from the current has to be taken into account
Electrical networks fed by fuel-cells for uninterruptible electrical supply
No full textCustomer satisfaction a reliable and stable supply requires. Electric loads characteristics often make it necessity to adopt back-up energy sources, which, coupled with the main one, are able to satisfy loads 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 [1]. 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. Defined fuel-cell characteristics, it is, 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
A control algorithm of power converters in smart-grids for providing uninterruptible ancillary services
No full textThis paper deals with the use of grid-connected photovoltaic (PV) power plants for supplying the ancillary service of reactive power compensation to the distribution grid. A control strategy has been developed for controlling both real and reactive power exchanged with the distribution network. The paper suggests how the real and reactive power references should be selected in order to maximize the electrical energy generated by PV arrays and to exploit the apparent power of the inverter close to its rated value. The choice suggested for reference signals allows reactive power compensation service also when the solar irradiation is negligible. The control strategy is then applied to a sample grid-connected PV unit, which has been simulated in Simulink environment. Numerical simulations show that, using an adaptive Perturb & Observe algorithm, the maximum power point tracking is achieved in about 2 seconds, both at starting and when the irradiation changes. The inverter is also capable of giving without interruptions the reactive power support to the grid, reducing grid currents and voltage drops along the line respect to the classical configuration where no reactive compensation is present
A control strategy for high-quality electric energy supply system equipped with fuel cells and ultracapacitors
No full textThe paper focuses on experimental and numerical
results of a research program addressed to study the possibility
of coupling fuel cell source with ultracapacitor storage
device. The paper, starting from the experimental tests done on
a fuel cell source, useful to set up subsystem analytical models,
examines the energy flow among the electrical sources. It is
defined a control strategy suitable to manage the power flow
for load variations. In particular, are considered the possibilities
that: i) the fuel cell is able to furnish power to the load and
the ultracapacitor device acts as active filter for stabilizing dc
bus voltage; ii) the fuel cell is not able to feed the whole power
demand and the ultracapacitor device compensates the difference
between maximum fuel cell power and load required
power
A Fast Charging Station for Electric Vehicles with 400-V/800-V Charging Ports and Second-Life Batteries
No full textDirect State-of-Charge Balancing Control for Modular Multilevel Converter Integrating Batteries
Full text linkThis article proposes a novel balancing control strategy for modular multilevel converters (MMCs) integrating a battery pack (BP) at the submodule (SM) level. During the converter operation, balancing the energy of the distributed resources within the converter is necessary to ensure the converter stability, avoid generating undesired current harmonic components, and increase the overall system efficiency. In particular, exploiting the MMC topology, ac and dc circulating currents are controlled to cope with unbalanced conditions. In this context, this article proposes a circulating current control strategy to equalize the state-of-charge (SOC) values of BPs by properly injecting ac and dc circulating currents. In addition, a dynamic saturation method for the circulating components was designed to reduce the SOC equalization time while continuously preventing the design converter limitations from being overcome. The proposed control algorithm was experimentally tested and compared with a state-of-the-art solution, which demonstrated its effectiveness in terms of overall efficiency and balancing time
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