Search

Lithium-ion battery is considered one of the most attractive energy storage systems for electric vehicles. However, one of its main drawbacks is the sensitivity to temperature. In a battery pack composed of lithium-ion batteries, during the charge/discharge operations, the temperature gradually increases, especially in the batteries positioned in the central part of the battery pack. This leads the central batteries to age faster and exposes them to the risk of a thermal runaway. In order to mitigate these problems, thermal management systems are needed. However, for the implementation of the control, it is important to know the temperature distribution inside the whole pack. In this paper, an integrated electro-thermal model capable of estimating the thermal behavior of each battery cell, composing the battery pack, only knowing the total current and ambient temperature, is proposed and analyzed. The proposed model was tuned and validated by means of experimental results. The circuital approach used in this model gives good results with a low degree of complexity.

Renewable energy sources, such as photovoltaic (PV) panels, are spreading day by day. Nevertheless, their intermittent and uncertain generation can be an issue for the connection in the electrical grid or for self-consumption. In order to face these problems, battery energy storage systems (BESSs) are used to store the energy in excess and deliver it when required. With and without the integration of BESSs, many solutions to interface PV panels to the grid are analyzed and proposed in the literature. Focusing on the PV power extraction, several maximum power point trackers have been analyzed, also facing the issue related to the partial shading conditions. In fact, the latter can cause inefficiency in maximizing the power extraction when many PV panels are subjected to different irradiations. Modular multilevel converters (MMCs) are recently used even in low voltage systems for their intrinsic advantages. In particular, PV panels and BESSs can be integrated into the MMC at either the submodule level or the dc-Iink of the MMC itself. Taking the advantages of both kinds of connection, in the present paper, a three-phase MMC with PV panels integrated into its submodules and a battery pack connected to its de-link is proposed and analyzed.

The presence and evolution of static power converters in electric grids are growing on a daily basis. Starting from the most used voltage source converter (VSC), passing through the use of multilevel converters, the most recent configuration is the so-called modular multilevel converter (MMC). Because of its intrinsic advantages, it is used not only in high-voltage systems but also in low- and medium-voltage ones to interface renewable energy sources such as photovoltaic (PV) panels. Several configurations and maximum power point tracker (MPPT) algorithms have been proposed and analyzed for MMC-PV-based systems. However, when using distributed MPPTs, partial shading conditions cause a problem. The PV panel can be directly connected to the MMC using its dc link or submodule. Based on this configuration, this paper proposes a novel control strategy that tracks both the ac grid current and ac circulating current for a single-phase low-voltage system to obtain the maximum power under any irradiance condition. The effectiveness of the proposed control strategy is demonstrated through time-domain simulation results.

The increasing integration of renewable energies reduces the inertia of power systems and thus adds stiffness to grid dynamics. For this reason, methods to obtain virtual inertia have been proposed to imitate mechanical behavior of rotating generators, but, usually, these methods rely on extra power reserves. In this paper, a novel ancillary service is proposed to alleviate frequency transients by smoothing the electromagnetic torque of synchronous generators due to change of active power consumed by loads. Being implemented by grid-tied inverters of renewables, the ancillary service regulates the reactive power flow in response to frequency transients, thereby demanding no additional power reserves and having little impact on renewables’ active power generation. Differently from the active power compensation by virtual inertia methods, it aims to low-pass filter the transients of the active power required to synchronous generators. The proposed ancillary service is firstly verified in simulation in comparison with the virtual inertia method, and afterwards tested on processor by controller-hardware-in-the-loop simulation, analysing practical issues and providing indications for making the algorithm suitable in real implementation. The ancillary service proves effective in damping frequency transients and appropriate to be used in grid with distributed power generators.

Power-like functions based on Tellegen’s theorem are important tools in the study of electrical networks. Networks containing power converters are nonlinear and/or time-variant. This fact continues to represent a challenge regarding both theoretical analysis and practical application. The topologies of existing converters are multiform and there is not one single general approach to them.In terms of circuit theory, a number of theorems regarding ideal switching can be derived. This paper proposes a novel power-like function to describe the switching phenomenon and thus contribute to principles underlying power converters. Specifically, it sets out theorems and describes certain empirical applications which clearly work in practice but for which no formal proof has yet been provided. It focuses in detail on hard commutation of switches and formulates a principle of correlation between active (i.e. externally fired) and passive hard switching. The paper concludes by presenting examples of applications in support of the theoretical results.

Today's residential battery energy storage systems (BESSs) are off the shelf products used to increase the self-consumption of residential photovoltaic (PV) plants and to reduce the losses related to energy transfer in distribution grids. This work investigates the economic viability of adding a BESS to a residential grid-connected PV plant by using a methodology for optimising the size of the BESS. The identification of the optimal size which minimises the total cost of the system is not trivial; indeed, it is a trade-off between OPEX and CAPEX, which are mainly affected by the battery technology, usage profile, expected lifetime, and efficiency. Here, an analysis of the opportunity to install a storage system together with a grid-connected residential PV plant is performed. Three typical low-voltage prosumers (Italy, Switzerland, and the UK) are investigated in order to take into account the different legislative and tariff framework over Europe. Numerical results reported here show that present costs of storages are still too high to allow an economic convenience of the storage installation. Moreover, an indication of the necessary incentives to allow the spreading of these systems is given.

Electric vehicles range is limited by the available storage systems and it is influenced by many external factors such as ambient temperature, vehicle auxiliary systems and driving patterns. An accurate and reliable estimation of the remaining energy and, as a consequence, of the available travelling distance is one of the key factors that allows drivers to consciously take advantage of their electric vehicle (EV).The present paper describes the application of a previously-defined model for EVs batteries to estimate on line the available range. The effectiveness of the proposed methodology, which has been designed in order to use a reduced set of measurements, has been validated on a real Lithium-ion cell simulating three different EVs under two different temperatures and with two standard test driving cycles.

In the past, the diffusion of electric vehicles (EVs) has been hindered by energy storage limits. In fact, these are the reason for the limited EV range and the consequent range anxiety of their drivers. Thanks to constant improvements in storage system technologies over the years, in terms of both energy and power density, lithium-ion batteries (LiBs) now guarantee vehicle ranges higher than 150 km for small vehicles. Another important improvement has been achieved by the hybridisation of LiBs with other storage technologies such as electric double-layer capacitors or lithium-ion capacitors. By adding an additional storage unit (ASU) to the EV battery system, the overall efficiency increases, with a consequent gain in the vehicle's expected range. In a previous paper, an optimal sizing procedure was proposed, through which it is possible to calculate the optimal ASU mass that maximises the EV range for a given vehicle, ambient conditions, and driving cycle, which was considered to be known a priori. In the present work, a real-time implementation of the control strategy on which the optimal sizing procedure was based is proposed and analysed using the results of simulation tests.

In micro-grids, due to the heavy penetration of distributed energy resources (DERs), especially renewable energy sources (RESs), the characteristic inertia of the system has been decreasing with respect to the total power capacity. In a weak grid, a high step variation of the load leads to a hard transient of frequency. This could imply stability issues for the grid and specific problems for sensitive loads. In order to face this problem, in the technical literature, several algorithms introducing virtual inertia in the system have been proposed. Since, these algorithms are based on the assumption that an equivalent inertia has to be simulated, they need to exchange active power with the network. When this function is implemented in a PV system, a power reserve or an additional storage unit has to be used. In this paper, a technique to increase the transient stability of the generation system, based only on the exchange of reactive power, will be proposed. Its feasibility is demonstrated by means of numerical simulations.

Modular converters are of particular interest for high-power applications where the usage of a certain number of modules instead of a single converter allows to obtain better power quality and dynamic behavior, as well as higher reliability. In this paper a detailed analysis of harmonic distortion in modular three-phase converters is performed. Analytical expressions of voltage harmonics are provided and analyzed in terms of space vector and zero component. Commutation interleaving is also considered and its effects on space vector and zero component are studied in detail. A modular three-phase converter constituted by four modules with 2+2 redundancy is considered as case study. Analytical expressions and simulation results are presented and compared.

Pulse-width modulation is one of the most common modulation strategies. Nevertheless, some issues about the harmonic content of the output voltage and current are still debated. In the present paper, the space vector and zero component are used for harmonic analysis of the naturally sampled three-phase PWM. An overall analytical formulation of the Fourier series is derived, through which a detailed evaluation of the ripple shifting among the phases is carried out. Simulations support the consistency of the proposed analysis.

Up to few years ago, one of the main problems in the optimal design of a battery energy storage system (BESS) was the availability of both the generation (e.g. renewable sources) and load power profiles of the considered plant. This paradigm has limited the potential of BESSs to drive down overall energy costs and reduce carbon emissions. Nowadays, the exponential growth of data available on the industrial plants has opened the way to new possibilities and opportunities. In addition, BESSs are a viable opportunity to start transforming existing plants with an incremental hybridization of the plant topology. In light of the above, this work develops a commissioning tool that, starting from the data collected on the field, provides the final users the optimal dimensioning of any BESS - according to the taraet performances required bv the specific application.

Nowadays, electric vehicles (EVs) are of great interest over the world. In the past, the diffusion of EVs was impeded because of the limits of energy storage units, which reflect in vehicle range limited extension. In recent years, a significant progress was made in terms of power and energy density thanks to the lithium based batteries that can guarantee vehicle ranges higher than 100 km. Another further step can be done by coupling more than one storage technology and leading to an increased efficiency and extension of the vehicle range. In this paper, the effectiveness of adding another storage unit to a lithium ion battery is investigated for different EVs and driving cycles. Furthermore, a methodology procedure, based on the knowledge of the test driving cycle, and parameters of the EV, is proposed to find the optimal size of the auxiliary storage, that maximizes the EV range.

Nowadays, energy storage systems are playing an important role in several electrical applications. The modeling of these devices is very important, in particular, for electric vehicles, in order to understand and predict their behavior under different working conditions. Recently, the lithium-ion based solutions, and, in particular, lithium-ion capacitors (LiCs), are gaining a predominant position, as they display both high power and high energy densities. In the literature, different past works have modelled the LiCs using the electro-chemical impedance spectroscopy, a frequency domain technique. These models are able to represent the dynamic behavior of the LiC in a wide range of frequencies, currents and temperatures. On the other hand, they use a high number of parameters to be estimated, resulting quite complex to manage them. In the present paper, a novel current dependent LiC model, with only four unknown parameters characterized using a simple time domain technique, is presented.

In modern electric vehicles (EVs), the storage system is usually composed only of lithium ion batteries (LiBs), which are characterized by a high energy density but medium power density. In order to increase also the power density, a hybrid energy storage system (HESS) that combines LiBs with supercapacitors (SCs) could be produced. In particular, at very low temperatures SCs can be very helpful because, unlike LiBs, they maintain good performances. In the literature, it is possible to find three different ways to combine LiBs and SCs: passive, semi-active, and fully active HESSs. Despite the passive solution seems to have been abandoned, this paper analyses the direct parallelizing of LiBs and SCs focusing on the advantages that this simple solution can involve at very low temperatures. Indeed, LiBs fail at those temperatures, which could make it impossible to start the EV unless to use a pre-heating system for the batteries that can take up to several minutes. Based on the results of experimental tests, this paper shows that, at low temperatures, adding a relatively small SC unit to the battery pack makes it possible to start immediately the EV without waiting for the pre-heating of batteries, greatly increase the EV range, and thus use the vehicle under very harsh conditions.

Energy 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.

Nowadays, battery storage systems are very important in both stationary and mobile applications. In particular, lithium ion batteries are a good and promising solution because of their high power and energy densities. The modeling of these devices is very crucial to correctly predict their state of charge (SoC) and state of health (SoH). The literature shows that numerous battery models and parameters estimation techniques have been developed and proposed. Moreover, surveys on their electric, thermal, and aging modeling are also reported. This paper presents a more complete overview of the different proposed battery models and estimation techniques. In particular, a method for classifying the proposed models based on their approaches is proposed. For this classification, the models are divided in three categories: mathematical models, physical models, and circuit models.

This paper shows that the space-vector approach is an eminent and powerful tool in three-phase analysis. It is able to manage in a unitary way the sinusoidal, distorted and transient conditions. Its complex Fourier series implements a formal unification between unbalance and distortion; such unification is conceptually significant and leads to simplification of principle, as well as powerful analytical processing. Examples illustrate the effectiveness of the complex Fourier series as analytical tool in different application areas.

This paper introduces a new control strategy to realize a virtual synchronous generator. The proposed control strategy is based on virtual impedance and band-pass damping algorithms to achieve the electro-mechanical characteristics of synchronous generator for the grid converter. Differences between new and traditional method on impedance emulation, and differences between traditional pure proportional damping algorithm and new band-pass damping algorithm are discussed as well. Additionally, detailed analysis of the components of synchronous generator is given, also the roles of the various parts of synchronous generator in the power system stability control are explained. The behavior of designed control strategy is validated by both simulations and experiments made on a 2kW grid-connected inverter.

Lithium-ion capacitors (LiCs) are novel storage devices with a high power density and high energy density compared to conventional supercapacitors (SCs). This paper proposes a method to validate the previously developed characterization and modeling methods, which are the same as those used for a conventional SC with double-layer-activated carbon technology. This paper presents two relevant contributions. First, a full frequency range model and the experimental parameter identification of two kinds of LiC cells are presented. In order to extend the LiC cell parameter identification to a module composed of several series-connected cells, an aggregate model of the LiC module was investigated and validated. The results of experiments and numerical simulations demonstrate the value and effectiveness of the proposed model when the cells operate at room temperature.

The use of storage systems is increasing in many applications. At the same time, new technologies for realizing storage devices are being proposed every year. Lithium-ion capacitor (LiC) cells can be included in these innovative technologies. In this study, extensive experimental research was carried out to determine the performance characteristics of LiC cells for practical applications. This study assessed the preliminary results of characterization tests to evaluate the performance of LiC cells over wide temperature and frequency ranges. In order to characterize the cells at different frequencies, galvano-electrochemical impedance spectroscopy (EIS) was performed at different temperatures and polarization voltages. Tests were performed on both laminated and prismatic cells in order to compare their behaviors. Finally, the experimental results were analyzed in order to assess the potential applications of this storage technology.

A reliable and accurate estimation of the parameters of batteries equivalent models is of paramount importance in many applications. This paper is focused on electric vehicle framework. A simplified method for estimating these parameters is presented and validated. The proposed methodology introduces the concept of apparent state of discharge (ASOD), i.e., the traditional state of discharge adjusted in order to take into account the effects of current and temperature. This ASOD is, then, used to estimate the open circuit voltage and, consequently, the output voltage of the battery cells. The effectiveness of this method has been experimentally tested on a real Lithium-ion cell in order to estimate the expected range of an electric vehicle.

Electrochemical storage devices are spreading in many applications. Nevertheless, the data given by the manufacturers are often few and not homogenous. Using these data a correct sizing for a given application results very difficult and usually the designers makes a rough design in which the expected lifetime is not known and the costs are not optimized. This situation depends, mainly, on the lack of knowledge in modeling and studying electrochemical storage devices. In this paper, the authors underline the necessity of an integrated model for the definition of the nominal data of a storage device. Moreover, starting always from the solution of an integrated model, they propose a methodology for a correct sizing of a storage unit for a given application.

Lithium-ion batteries are a key technology for current and future energy storage, whether they are used for mobile or stationary application. In particular, they play an important role for the electrification of mobility due to their high power and energy density and therefore their battery lifetime prediction is a fundamental aspect for successful market introduction. The ageing data provided by the battery manufacturers result from standard ageing tests. For this reason, it is very important to link, in the way as simple as possible, the effect of driving cycles (urban, extra-urban, combined) with the ageing of the batteries. The aim of this work is to investigate on the effect of driving cycles on the batteries lifetime through tests performed on different cells for different kinds of cycle. Afterwards, simulation tests are made in order to estimate the battery lifetime for different driving cycles of the electric vehicle.

In this paper, an analytical study of three-phase matrix converter behaviour under unbalanced and/or distorted operating conditions is presented. Because of the lack of any considerable storage device, matrix converter operations are significantly influenced by distorted conditions. Even if adequate control strategies are able to ensure a sinusoidal balanced output voltage, under input voltage and/or output load distortion or unbalance, unwanted harmonics are generated in the input currents. The analytical results proposed in this paper make it possible to predict both the frequencies and amplitude of the harmonic components in the input current once the input voltage and output current disturbances, expressed in terms of the frequency spectrum, are known. The proposed analysis is formalized using the space-vector concept, allowing a precise and general approach, which can be applied to any operating condition. Numerical and analytical results have been found and compared with the ones discussed by other authors and confirm the proposed approach.