1,721,103 research outputs found
Effect of current on cycle aging of lithium ion batteries
Full text linkNowadays, lithium ion batteries are increasingly spreading in different areas and therefore, it is very important to understand their aging behavior. According to the technical literature, battery aging can be dissociated in calendar aging and cycle aging. Calendar aging, in particular, depends on the temperature and state of charge (SoC). In addition to the previous factors, cycle aging also depends on the current rate, and charge/discharge cut-off voltages. In the literature, only a few papers have considered battery aging as a function of the charge/discharge current rate, but they agree that a higher current rate leads to faster battery aging. In any case, all of the tests have been conducted in a climactic chamber with a constant room temperature. However, even if the room temperature is controlled, for high current rates, the temperature of the battery cell increases, which makes it impossible to distinguish the aging due to the current from that due to the temperature. For this reason, in the present work, the authors focused on the lithium ion battery aging due to the current rate while maintaining a constant battery temperature using opportunely controlled Peltier cells. In this way, an interesting results was obtained, i.e. the cycle aging is not dependent on the current rate
Short-Circuit Protection Schemes for LVDC Microgrids Based on the Combination of Hybrid Circuit Breakers and Mechanical Breakers
Full text linkIn recent years, low-voltage direct current (LVDC) microgrids are becoming more attractive because they represent a solution to integrate renewable sources, storage, and electronic loads bringing some advantages in comparison with traditional AC grids. However, the protection of such a network involves many challenges, especially in the case of LVDC microgrids with more than one feeder and multiple energy sources. Indeed, the traditional protection breakers used for an AC grid cannot isolate the faults and protect the components of a DC grid, while the use of solid-state circuit breakers increases energy losses. This paper deals with the analysis and design of the protection schemes for LVDC microgrids through the combination of mechanical circuit breakers and hybrid circuit breakers. This solution has the advantage of energy loss reduction but introduces further issues due to the slow transition times of the mechanical circuit breakers. Thus, a completely decentralized control system capable of overcoming the fast fault-clearing time, cost-effectiveness, and selectivity issues is designed to protect from pole-to-pole faults. The proposed control strategy is compared with a centralized protection scheme available in the literature through numerical simulation. The two algorithms show similar performances, with a mean voltage dip duration of less than 30 ms and a maximum voltage dip duration of about 100 ms in the most severe fault condition, but the proposed solution is more reliable and flexible since it does not depend on the communication system
Battery aging due to 100 Hz current ripple of power converters
No full textLithium ion batteries (LIBs) represent one of the most important and used storage systems in different applications. In particular, the issue of the intermittence in power generation of renewable energy sources make it necessary their implementation in such plants. It is very important to take into account the aging phenomena of LIBs to optimize their usage and extend their lifetime. The aging is usually decomposed into calendar aging and cycle aging. In general, the factors that affect it are the temperature, the state of charge, the voltage limits, and the current rate. Several works analysed also the effect of the current ripple on the battery aging. Nevertheless, a rigorous analysis of the effect of the current frequency seems to be missing. Indeed, almost all the aging analyses relating current ripple do not take into account the higher temperatures due to the current ripple losses. Therefore, the effects of increased temperature and current ripple are never separated. Moreover, different frequency components in the same current ripple may lead to different aging. In this paper, a method to separate the temperature by the current frequency effect is proposed and the analysis of the aging LIBs due to the 100 Hz current harmonic is carried out
Design and Implementation of LVDC Hybrid Circuit Breaker
Full text linkIn recent years, dc distribution grids have become increasingly popular because of the interest in the diffusion of distributed renewable energy. In this scenario, dc distribution grids are also favored because of the increased use of batteries and power electronic loads. The main limit to the spread of dc grids is their protection devices, which still present several problems. At present, protection devices are represented by traditional mechanical breakers or static electronic components. The first, which interrupt dc currents, have good reliability but need maintenance and have long intervention periods. In contrast, electronic switches are fast and reliable, but they reduce the efficiency because of their voltage drop. In this scenario, some hybrid breakers have been proposed to obtain the advantages of both devices. The previous solutions of hybrid breakers still suffer several critical issues and, usually, are not capable of protecting a system from short circuits without significantly reducing their lifetime. In this paper, a new low-voltage hybrid circuit breaker topology is proposed. The procedure to dimension all of the active and passive components in the device is analyzed, and the effectiveness of the proposed solution is proven by means of experimental results obtained using a prototype
Integrated electro-thermal model for pouch lithium ion batteries
No full textLithium ion batteries are being used in an increasing number of applications. However, one of their major weaknesses is their sensitivity to temperature. Indeed, their safety and aging strongly depend on their temperature. In order to control cell temperatures, each cell in a battery pack is usually equipped with a thermal sensor. This paper proposes an integrated electro-thermal model that is capable of predicting the thermal behavior of a battery cell based only on its current and ambient conditions. The proposed model was tuned and validated by means of experimental results. The obtained precision is sufficient to predict the temperature of a battery with an acceptable accuracy considering the low complexity of the proposed model
Harmonic distortion reduction in modular multilevel converters by novel mixed harmonic injection
Full text linkThis paper proposes a novel modulation scheme to reduce the harmonic content of voltages and currents caused by modular multilevel converters with embedded battery cell when employed for application in battery energy storage systems in the grid. The reduction in total harmonic distortion (THD) is obtained by injecting selected harmonics in modulating wave for phase disposition sinusoidal pulse width modulation. The main innovation is in the frequency of these injected harmonics, most of which are kept considerably higher than the carrier frequency. The injection has further been improved using closed-loop control for optimum reduction in the harmonic content of output. The simulations are performed and tested on MATLAB-SIMULINK and demonstrate a satisfactory reduction in both voltage and current THD without any counter effect
Integration of stationary batteries for fast charge EV charging stations
Full text linkOne of the biggest issues preventing the spread of electric vehicles is the difficulty in supporting distributed fast charging stations by actual distribution grids. Indeed, a significant amount of power is required for fast charging, especially if multiple vehicles must be supplied simultaneously. A possible solution to mitigate this problem is the installation of auxiliary batteries in the charging station to support the grid during high peak power demands. Nevertheless, the integration of high-voltage batteries with significant power is not a trivial task. This paper proposes the configuration and control of a converter to integrate batteries in a fast charging station. The proposed configuration makes it possible to decouple the grid power from the vehicle power using several auxiliary battery modules. At the same time, the converter makes it possible to draw different amounts of power from the battery modules, allowing the use of second life batteries performing in different ways. This paper discusses the design, control, and operation of the converter. Moreover, the effectiveness of the proposed control is shown by means of numerical results
Simple control strategy for a PV-battery system
No full textNowadays, energy storage systems, such as batteries, are spreading in many applications. Among the kinds of batteries, the lithium-ion technology is one of the most promising solutions. Considering the photovoltaic (PV) plants, it is very important to perform a correct sizing of the battery pack to both maximise the self-consumption and minimise the total costs. In general, PV plants need a dc-dc converter to maximise the electric power that can be extracted from PV panels and a dc-ac converter to connect them to the ac grid. The battery pack can be connected in three different ways: dc coupled and ac coupled using a dedicated converter or through a direct connection on the dc-link between the dc-dc and dc-ac converters. In the present study, the last solution, without any dedicated converters, is used and a simple control strategy to both maximise the power extracted from the PV panel and regulate the charging/discharging of the battery is proposed
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