Abstract

     The modern active distribution systems necessitate integrating storage systems, thereby facilitating the large-scale proliferation of photovoltaic (PV) energy resources. This further calls for the optimal planning of energy storage systems, satisfying all the operational and economic constraints. This article describes an exhaustive storage integration method, deeming the life cycle of the battery energy storage, the uncertainty of load and PV output, and the islanded mode of operation of the system. A two-stage mixed-integer linear programming problem is formulated that determines the capacity and the number of discharge cycles of the batteries in the first stage. The lifetime of the battery based on the partial depth of discharge is analyzed in the second stage. Furthermore, the uncertainty and variability of PV and demand are taken into account through probabilistic analysis and time-period clustering. The method is validated on a standard 33-bus radial distribution network for the allocation of distributed lithium-ion batteries. Also, the method’s scalability is validated on a practical Indian distribution network and a 141-bus distribution network of metropolitan area of Caracas with distributed PV installations on various nodes.

Introduction

     S MART grid is a gratuity to the consumers and the stakeholders involved in the electric grid’s generation, transmission, and distribution sections. It includes the complete modernization of the power system with smart meters, automation devices, intelligent monitoring, demand-side management, and self-healing capability schemes. Along with these activities, generation units are set up in the distribution section, i.e., nearer to the consumer premises, to reduce the transmission losses. This shift of the electric grid from a passive network to a bidirectional active network is due to the small generators being set up in the distribution grid known as distributed/decentralized generation. These distributed generators (DGs) mainly generate energy using renewable energy resources, such as photovoltaic (PV), wind, biomass, tidal, etc., as they are clean sources of energy and promote sustainable development. However, the intermittent nature and excess penetration of these resources pose problems, such as reverse power flow, voltage fluctuations, increase in losses, harmonic distortion, and instantaneous matching of demand and supply [1], [2]. Although integrating storage systems in the distribution network can help alleviate the aforementioned problems if allocated optimally. Also, India’s target of 40-GW PV rooftop installations by the year 2022 and the declining cost of batteries will provide a fillip to the installation of energy storage systems (ESSs) [3]. Therefore, an ESS can be seen as a game changer in the ever-changing power system paradigm and can serve multiple ranges of benefits. To achieve these benefits, methods for optimal sizing, allocation, and operation of ESSs are required

Conclusion

     The integration of renewable energy resources necessitates the allocation of distributed energy storage to mitigate voltage deviation and defer distribution upgrades. This article illustrated a two-stage procedure for integrating lithium-ion batteries in a PVpenetrated active distribution network. The planning methodology considered an ac-OPF model with the uncertainty of PV and demand to determine the batteries’ accurate size. Moreover, the reverse power flow due to excess PV penetration was utilized and the voltage was within limits after the integration of batteries in the system. The battery’s life cycle was examined in the second stage with the partial cycle of discharge and complete discharge cycles. For lithium-ion batteries, partial cycle discharging was fine as there was no memory effect, and the battery does not need full discharges periodically. From the results, it was illustrated that with the partial cycle of discharge, the battery will last longer. Moreover, the method used here was the mathematical programming, which provides a robust solution, but may require significant computation time for large and complex problems. Also, the maximum discharging capacity of the battery gradually declined with its cycles, which can be kept as a future research direction. Furthermore, to enhance the stability and cost-effectiveness, a smart charging and discharging operation can be added to the problem. In addition, different types of DGs, such as wind, micro-turbines, and fuel cells, can be considered an extension to the OPF formulation.

Abstract

     With the emergence of battery-based electric vehicles, transportation systems gradually leave using fossil fuel-based combustion engines. Due to their reasonable performance, Lithium-ion batteries have become one of the major batteries used for electric vehicles. Although these batteries are being used in most companies, their high production cost, rare raw material, and short life cycle have raised important incentives for their recovery process. However, locating a recovery center for end-of-life Lithium-ion batteries is a multi-aspect decision making problem influenced by many criteria. For this purpose, a novel integrated decision-making model is developed based on Measuring Attractiveness by a Categorical Based Evaluation TecHnique (MACBETH) for calculating the criteria weights and Weight Aggregated Sum Product ASsessment (WASPAS) methods under the fuzzy environment with Dombi norms for evaluating the alternatives to address recovery center location selection problem considering technical as well as environmental, economic, and social aspects. To show the reliability and applicability of the developed method, a real-world case study in Istanbul is investigated. The developed method is used to evaluate six potential locations for the possible establishment of a recovery center. Results showed that Tuzla district is the most suitable location for opening a recovery center for end-of-life Lithium-ion batteries. Tuzla is in a very good position in terms of proximity to suppliers, transportation and location. To illustrate the robustness of the obtained results, extensive sensitivity analysis tests are performed.

Introduction

     Electric vehicles (EVs) are an appealing solution for the decarburization of the transportation sector (Romero-Ocaño et al., 2022, Zhang et al., 2020). It is estimated that more than 125 million EVs will be on the road worldwide by 2030 (Hua et al., 2020). Lithium-ion batteries (LiBs) have exponential growth and a key portion of industry investments (Chen et al., 2019, Cui et al., 2022). An automobile Lithium-ion battery (ALiB) is a major component of an EV (Pelletier et al., 2017, Ramoni and Zhang, 2013). ALiBs provide the required energy storage for EVs due to the superiority of high energy density, high output voltage, low self-discharge rate, and long cycling life (Tang et al., 2019, Wang et al., 2022). They are composed of a cathode, an anode, an electrolyte, and a separator (Olivetti, Ceder, Gaustad, & Fu, 2017). The useful lifetime of ALiBs is 120,000–240,000 km (Onat, Kucukvar, Tatari, & Zheng, 2016).

     Approximately 11 million ALiBs are expected to be sold worldwide by 2020 (Li et al., 2018; Alamerew & Brissaud, 2020). Due to the degradation in capacity and quality, the service life of these complex multiple material products, which belong to class 9 of dangerous goods, is 5–10 years (Li et al., 2018; Chen et al., 2019, Tang et al., 2019, Alamerew and Brissaud, 2020, Li et al., 2020). ALiB is replaced when the capacity has reached 70–80 % of its initial capacity (Alamerew and Brissaud, 2020, Hua et al., 2020, Ramoni and Zhang, 2013).

Conclusions

     The emergence of EVs has been a noticeable point for transportation systems to transform from fossil fuel-based vehicles to cleaner vehicles which require lower energy costs and also produce lower negative environmental, economic, and social impacts. The utilization of ALiBs is of great importance for EVs, but more and more valuable resources are being depleted without appropriate recovery. Therefore, countries should consider establishing recovery centers for ALiBs as soon as possible. However, locating a recovery center is a complex and multi-aspect decision-making problem. For this purpose, we developed a novel decision-making approach based on the MACBETH-D-WASPAS model under the fuzzy environment. The proposed integrated fuzzy decision-making approach empowers experts in the field of LiB management to enhance their decision-making capabilities and select the most suitable location for an EoL ALiB recovery center. Besides, the real-life case study of Istanbul is provided to show the feasibility and applicability of the developed methodology for solving the recovery center location selection problem. Results showed that Sariyer and Büyükçekmece are top first and second locations that a recovery center for an EoL ALiB recovery center. On the other hand, results pointed out that Ümraniye is the least preferred location for establishment of an EoL ALiB recovery center.

Abstract

Keywords

1. Introduction

2. Methodology

2.1. LIBs and system boundaries

2.2. The battery system of electric passenger cars

2.3. The phase of production

2.4. The phase of usage

2.5. The phase of recycling

3. Life cycle environmental impact assessment

4. Conclusions

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgments

Appendix.

References

Abstract

The use of electric vehicles is for reducing carbon emissions, thereby reducing environmental pollution caused by transportation. However, the large-scale production and application of electric vehicle batteries have brought another notable issue, i.e., the production and application of these batteries also cause environmental pollution. Particularly, the precious metal materials used in the batteries are harmful to human health and the surrounding ecological system. Nowadays, many types of batteries are available. It is essential to understand which of them is most suitable for electric vehicles from the perspective of environmental protection. To answer this question, the life cycle environmental impact assessment of LiFePO 4 battery and Li(NiCoMn)O2 battery, which are being popularly used in pure electric passenger vehicles, are conducted in this paper. The research has shown that the two types of batteries show different environmental impact features in different phases. For example, LiFePO 4 batteries are more environmentally friendly in the phase of production, while Li(NiCoMn)O2 batteries are more eco-friendly in the application and transportation phases. Despite this, LiFePO 4 batteries are generally more environmentally friendly than Li(NiCoMn)O2 batteries from the perspective of the entire life cycle. In addition, the research results also suggest that due to the heavier mass, LiFePO 4 batteries can probably gain more benefit when used for energy storage.

1. Introduction

Electric vehicles (EVs) are considered to be carbon-free, which helps to slow climate change, improve public health, and reduce ecological damage. Coupled with the increasing pressure to achieve the net-zero target, the global EV market has taken a huge leap forward in the past decade (Du et al., 2017). In 2019, the number of light EVs globally reached 2,264,400 units, which is 9% higher than in 2018. Take the world’s largest EV market, China, as an example, only 5,000 EVs were sold in the Chinese market in 2011. In 2018, China sold 984,000 pure EVs, which was an increase of 50.8% over the previous year (China Association of Automobile Manufacture, 2019). In 2019, more than 1 million EVs were sold in China, and the stock of EVs reached 3.8 million (Sun et al., 2020). These data imply that there will be more and more EVs running on the road in the following years.

Since batteries are the only source of power for EVs, the globally booming EV market means that a huge number of Lithium-ion power batteries (LIBs) will be produced, used, and disposed of in the future (IEA, 2020). For example, the cumulative installed capacity of LIBs reached about 206 GWh in China by the end of 2019 (MIIT, 2019). Among these LIBs, LiFePO4 batteries and Li(NiCoMn)O2 batteries dominate the market, but their market shares changed over time. The market shares of LiFePO4 batteries, Li(NiCoMn)O2 batteries, and lithium titanate (LTO) batteries were respectively 28%, 18%, and 21% before 2016 (MIIT, 2019). Since 2016, the market share of Li(NiCoMn)O2 batteries increases rapidly. During the period from 2016 to 2018, more than 80% of electric passenger cars in China used Li(NiCoMn)O2 batteries. This situation changed again in 2019 when manufacturers favored using LiFePO4 batteries to power electric passenger cars.

Highlights

Abstract

Graphical abstract

Keywords

Nomenclature

1. Introduction

2. Why focusing on LIB risk management and safety issues?

2. Contextualising the relative levels of risk of electric vehicle LIBs

3. Potential failure mechanisms of LIBs

4. Origins and categorisation of risks associated with LIBs

5. End of Life LIB incidents

6. Safety measures, regulatory gaps and discussions

7. Conclusions

Credit author statement

Declaration of competing interest

Acknowledgments

References

Abstract

Lithium-ion Batteries (LIB) are an essential facilitator of the decarbonisation of the transport and energy system, and their high energy densities represent a major technological achievement and resource for humankind. In this research, it has been argued that LIBs have penetrated everyday life faster than our understanding of the risks and challenges associated with them. The current safety standards in the car industry have benefited from over 130 years of evolution and refinement, and Electric Vehicle (EV) and LIB are comparably in their infancy. This paper considers some of the issues of safety over the life cycle of batteries, including: the End of Life disposal of batteries, their potential reuse in a second-life application (e.g. in Battery Energy Storage Systems), recycling and unscheduled End of Life (i.e. accidents). The failure mechanism and reports from a range of global case studies, scenarios and incidents are described to infer potential safety issues and highlight lessons that can be learned. Therefore, the safety risks of LIBs were categorised, and the regularity requirements to create and inform a wider debate on the general safety of LIBs were discussed. From the analysis, a range of gaps in current approaches have been identified and the risk management systems was discussed. Ultimately, it is concluded that robust educational and legal processes are needed to understand and manage the risks for first responders and the public at large to ensure a safe and beneficial transition to low carbon transportation and energy system.

1. Introduction

Lithium-ion batteries (LIBs) have penetrated deeply into society, finding a wide range of applications in personal electronic devices since their discovery and development in the 1980s and 90s, and more recently in larger energy systems for traction and energy storage. This is mainly owing to the unique characteristics of LIB technology, i.e. high energy densities, high voltage, good stability, low self-discharge rate, long-life cycle and availability of a wide range of chemistries with diverse electrode designs [1,2]. LIBs are incorporated into ever widening application areas and are to be found at scales as diverse as their usages. This is evidenced by the growth in the uptake of LIBs having increased eight fold between 2010 and 2018 to 160 GWh [3] and the steady increase in annual sales of LIBs which are predicted to be upwards of 4 TWh by 2040 [4]. In the UK, it is forecast that the number of LIBs reaching the end of their life from automotive applications would have reached approximately 75,000 units, or 28,000 t by 2025 [5]. The advent of lithium-ion technology and the paradigm shift in the energy and power density capabilities that it represents, are perceived as the enabling technology for an extremely broad range of energy storage applications. Accordingly, LIBs are increasingly recognised as essential and integral to enable the large-scale temporary storage of electrical energy from renewable energy sources.

Abstract

Keywords

References

Abstract

The number of electric vehicle batteries is expected to increase. Their integration into circular economy requires their recollection at end-of-life. Decision makers need tools to determine suitable locations of recollection centers, as the decision is not trivial. Lithium batteries are hazardous materials, which require a minimization of transport duration. Here, we develop a mathematical model for locating a number of battery recollection centers. We discuss the results on the case of Germany for the time period from 2020 to 2050. The aim is to identify the influence factors on the location choice and therefore enable a founded decision.

1. Introduction

In 2019, the size of the global electric vehicle fleet was 7.2 million. Ninety-two percent of vehicles were used in the People’s Republic of China, Europe, and the United States [1]. According to the International Energy Agency (IEA), in 2030 global electric vehicle sales will reach 25 million, while the stock will be 140 million units [1]. The electric vehicle market is in growth phase.

Batteries are crucial parts of electric vehicles and have become a hot topic in research and development [2]. Within the last decade the capacity density increased by 300% [3]. Global Battery Alliance predicts that total weight of endof-life (EOL) Lithium-Ion-Batteries (LIBs) will increase more than threefold between 2018 and 2025 [4]. We must prevent formation of battery landfills. Therefore, EOL vehicle batteries must become a part of a circular economy value chain.

Circularity demands for repurposing batteries to secondlife applications through remanufacturing and recycling. As an initial step, recollection is required. Locations for recollection must be determined appropriately.

The goal of this paper is to determine the locations of recollection centers by means of minimization of the transport duration.

The paper is organized as follows. In Section 2, we give an overview of the research about repurposing of vehicle batteries and the facility location related to EOL vehicle batteries. In Section 3, we define the problem for determination of recollection center locations, and, in Section 4, we present the mathematical model. In Section 5, we solve and discuss instances of the model based on information from Germany. In Section 6, we conclude and present further research activities.

1- INTRODUCTION

2- SYSTEM LAYOUT

3- CONTROL SCHEME

4- CONCLUSION

REFERENCES

Abstract

In this paper, we are proposing currentcontrolled hill-climbing strategy used in Maximum power point tracking (MPPT) of the solar photovoltaic array to Charge OFF Board Electric vehicle lithium-ion batteries within the safety limits and supported rating of batteries so that EV battery does not get damaged and can also increase the life of the battery. Here, a current sensor and potential difference sensor-based electric vehicle off-board battery charging by hill-climbing strategy is tested on MATLAB simulation. The satisfactory steady-state battery is charging within the rated charging limit, under variable solar irradiance.

INTRODUCTION

The transportation sector has seen a major shift towards electric vehicles as it not only stops our dependence on fossil fuels and stop pollution from these vehicles that vehicles release. Hence, we are moving towards cleaner sources of energy. Also, photovoltaic resources are increasing in demand as they are the source of clean energy and don’t emit carbon dioxide

Two types of charging method are there ON Board charging and OFF Board charging. ON Board charging is when Battery is kept in the Electric vehicle and charging circuit is not on the vehicle itself but near the charging station. And the battery is charged directly through the DC supply.

This paper proposes the self-reconfigurable batteries topology without DC-DC converter, which is similar to selfreconfigurable batteries, but it can guarantee that the voltage of the battery pack is within the set range when the SOC (state of charge) is from 0 to 100%, even if the voltage will drop with the SOC or some cells will be bypassed. Simply put, when the battery pack is discharged, the batteries whose SOC is high and their voltages satisfy the demand are discharged, and the cell with lower SOC is continuously replaced, and the consistency of the battery pack is ensured while stabilizing the voltage. The topological and control strategy are analyzed in detail. The proposed topology is verified by the battery pack composed of 9 cells in series, the experiment result shows that this topology not only retains the advantages of good equalization of self-reconfiguration batteries but also maintains low voltage fluctuations even without DC-DC converters, besides, without the DC-DC converter, the capacity utilization rate of the battery pack reaches 99.8%, demonstrating the superior performance of the proposed topology.

Introduction

Lithium-ion batteries are widely used in a variety of applications, including electric vehicles, energy storage systems, due to their high energy density, long cycle life and low self-discharge rate [1]. A number of battery cells are usually connected in series in order to supply higher voltage and higher power to the load in a wide range of applications, while significant efforts are made by designers to select the battery cells such that they are as identical/matched as possible, the battery cells will still have mismatches in practice due to manufacturing tolerances, different self-discharge rates, uneven operating temperature across the battery cells, and nonuniform aging process, among others [2]. Such inevitable differences within battery cells will drift apart through cycling and could potentially lead to overcharging or over discharging, it is clear that such non-uniformity limits the battery capacity and may even cause safety issues [3]. Therefore, to properly maintain all cells balanced is of significant importance for enhancing battery life [4–6]. While the passive balancing dissipates the excess energy through resistors in the form of heat, the active balancing equalizes the battery cells by transferring the excess energy between battery cells [7].

Owing to the low cost, abundance and high working voltage, graphite cathodes have attracted tremendous attention in rechargeable batteries, especially in aluminum ion batteries (AIBs) and dual-ion batteries (DIBs). In this review, firstly, a general introduction is given to distinguish the working mechanism of graphite from the conventional metal oxide used as cathode in batteries. Secondly, the characterization methods of anion intercalated compounds, theoretical simulation of anion intercalation behavior into the graphitic cathode and the kinetic study of anion diffusion in graphite are discussed. Then, progresses and challenges of AIBs with different types of graphite cathode materials are presented. Next, typical DIBs systems with graphite cathode, a variety of anodes and electrolytes are introduced in detail. Finally, a conclusion for battery systems with anion intercalation graphite cathodes is draw, and a perspective is outlined to address the existing technical barriers that need to be overcome in future research direction.

Introduction

Background

A rechargeable battery is an electrochemical device that can store electrical energy as chemical energy in its anode and cathode during the charging process, and releases the energy as electrical output during the discharging process [1-3]. An ideal rechargeable battery is expected to have high energy density, high power density, long cycle life, excellent environmental compatibility and low cost [4-15]. Metal ion batteries (MIBs), including lithium ion batteries (LIBs), sodium ion batteries (SIBs) and potassium ion batteries (PIBs) et al. are typical rechargeable batteries, which rely on the metal ions shuttling between the anode and cathode to realize charging and discharging. Among them, LIBs, which possess the merits of long cycle life, high energy and power density and no memory effect, have dominated the battery market of portable electronics and electric vehicles for around two decades and are as well widely used in grid-scale energy storage [5, 16-20]. Despite currently enormous successes in portable electronics and electric vehicles (EVs), LIBs are limited in meeting the growing demand for higher energy and power densities [21-40]. In another aspect, LIBs are plagued by the shortage and high cost of resource metals (Li, Co, Ni etc.) needed in the battery manufacture, and the corresponding environmental pollution of abandoned batteries [17, 41, 42]. Therefore, searching for novel electrode materials, especially cathode materials that of resource-abundant and easily recyclable properties, is in great demand [1]. Graphite is a unique layered structure composed of graphene layers stacked together by the van der Waals force. Since its interlayer space are highly tunable, graphite can accommodate a variety of ions and molecules to form graphite intercalation compounds (GICs), which display applications in electrical, electrochemical and chemical industries because of their unique physicochemical properties. For instance, the reversible intercalation/de-intercalation of metal ions (Li+ , Na+ and K+ et al.) into/from the graphite makes it widely used as anodes for MIBs. Although comparatively less developed, graphite, which have also exhibited the reversible intercalation and de-intercalation of anions such as hexafluorophosphate anion (PF6 – ), bis(trifluoromethanesulfonyl)imide anion (TFSI- ) [43-48], is becoming a promising cathode materials in dual-ion batteries (DIBs), hybrid electrochemical capacitors (ECs) [49, 50] and aluminum ion batteries (AIBs). Among these, DIBs and AIBs are gaining more attention since they have obvious advantages over conventional MIBs: 1) lower cost and resource abundance compared to conventional metal oxide cathode in MIBs; 2) higher voltage, which benefits for a higher energy density [51, 52].

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusion

References

Abstract

A new cathode material, K2V3O8, is reported reports as a new active material for potassium storage. The K2V3O8 is stabilized into tetragonal structure with P4bm space group, and we verify the unique crystal structure that is coordinated with four hendecahedra of KO11, VO5, and VO4, in which one VO5 shares its four oxygens with four VO4 tetrahedra to produce four penta-shaped voids that allows insertion and extraction of potassium ions. The K2V3O8 modified with carbon exhibits a reversible capacity of 75 mAh (g-oxide)−1, and its electrochemical activity originates from the reversible de-/intercalation of potassium ions into/out of the hendecahedrally coordinated K2V3O8–carbon composite cathode, accompanied by a reversible V5+/4+ redox pair, which is retained for 200 cycles with 80% retention of its initial capacity.

Introduction

Various potassium insertion materials have been introduced and evaluated for their electrochemical performance as cathodes in potassium-ion batteries (KIBs) [1–4]. K-deficient P2- and P3-type KxMO2 (x � 0.7, M ¼ transition metal) layered oxides have been extensively investigated as analogues of sodium-ion batteries (SIBs) [5–12]. They exhibit good electrode performances in terms of specific capacities, although they suffer from detrimental phase transitions resulting from the insertion (and extraction) of the large Kþ ions (1.38 Å) into (and out of) the crystal structure, which, in turn, limit their cycling stability. Vanadium vanadates including oxides have been extensively investigated as cathode materials for rechargeable batteries activated by monovalent and divalent charge carriers (Li, Na, K and Zn ions) because of their diverse structures and outstanding electrochemical activities resulting from the multiple valence states of vanadium [13–16]. Recently, Lu et al. introduced K2V3O8 as an anode material for KIBs [17], presumably activated by conversion process. This unique K2V3O8 structure, arranged with alternating K–O layers and V–O layers along the c-axis, inspires us to adopt it as a cathode material for KIBs. It is thought that de-/intercalation of potassium ions into/out of this crystal structure is possible because hendecahedrally coordinated Kþ-ion layers are located between the edge-sharing VO5 and VO4 assemblies along the c-axis. In this study, we firstly introduce the physical and electrochemical properties of K2V3O8. Due to its poor electrical conductivity, the active material, K2V3O8, is modified by electro-conducting carbon (K2V3O8/C) (Fig. 1a). As per designated, this treatment increases the resulting electrical conductivity to 10 4 S cm 1 at 25 �C, which enables the present K2V3O8 active for Kþ extraction and insertion for 200 cycles, delivering a reversible capacity of 75 mAh (goxide) 1 .

The intermittent characteristics of microgrids (MGs) have motivated the development of energy management systems (EMSs) in order to optimize the use of distributed energy resources. In current studies, the implementation of an EMS followed by experimental-based analyses for both grid-tied and stand-alone MG operation modes is often neglected. Additionally, the design of a management strategy that is capable of preserving the storage device lifetime in battery-based MGs using a power gradient approach is hardly seen in the literature. In this context, this work presents the application of an EMS for battery-based MGs which is suitable for both grid-tied and stand-alone operation modes. The proposed EMS is formulated as an optimal power flow (OPF) problem using the -constraint method which is responsible for computing the current references used by the EMS to control the MG sources. In the optimization problem, the total generation cost is minimized such that the active power losses are kept within pre-established boundaries, and a battery management strategy based on power gradient limitation is included. Finally, the effectiveness of the proposed EMS is evaluated by two scenarios which enable detailed analyses and validation. The first considers a dispatchable and a non-dispatchable source, whereas the second a dispatchable source and a storage device. The experimental results showed that the proposed EMS is efficient in both operation modes and is also capable of smoothing the state of charge (SoC) behavior of the storage device.

Introduction

The connection of distributed generators (DGs) to electrical power systems and the renewable energy sources intermittent characteristics have motivated the study of energy management strategies to optimize microgrids (MGs) operations, therefore improving DGs performance in an intelligent, safe, reliable and coordinated way [1]. The control concepts applied to MGs are established hierarchically through the primary, secondary and tertiary levels. The energy management is executed at the tertiary level by solving an optimal power flow (OPF) problem which optimizes the energy resources usage [2]. This is performed based on an objective function differentiation. Typically, the OPF considers power balance constraints, emission of pollutants, fuel cost, performance, security boundaries, power sharing and stability [1], [3]–[9]. Basically, an energy management system (EMS) is addressed following either a decentralized or a centralized architecture. In the former, the management strategy runs locally with slow communication links. In the latter, on the other hand, it operates on the highest control layer and fast communication links are required [10]. The advantage of the centralized approach is that the EMS configuration provides broad observability of the MGs, which promotes optimal overall operation in terms of voltage and current (amplitude and phase) minimal requirements to run an optimization algorithm which computes each operating point that will be sent to the DGs.

This paper presents an efficient fuzzy logic control system for charging and discharging of the battery energy storage system in microgrid applications. Energy storage system can store energy during the off-peak hour and supply energy during peak hours in order to maintain the energy balance between the storage and microgrid. However, the integration of battery storage system with microgrid requires a flexible control of charging-discharging technique due to the variable load conditions. Therefore, a comparative evaluation of the developed model is analyzed by considering controllers with fuzzy only and optimized fuzzy algorithms. In this paper, backtracking search algorithm based fuzzy optimization is introduced to evaluate the state of charge of the battery by optimizing the input and output fuzzy membership functions of rate of change of the state of charge and power balance. Backtracking search algorithm is chosen due to its high convergence speed, and it is good for searching and exploration process with exploiting capabilities. To validate the performance of the developed controller, the obtained results are compared to the results obtained with the particle swarm optimization based fuzzy and fuzzy only controllers, respectively. Results show that the backtracking search algorithm based fuzzy optimization outperforms the other control methods in terms of effectively manage the charging-discharging of the battery storage to ensure the desired outcome and reliable microgrid operation.

Introduction

Fossil fuel-based conventional energy sources such as coal, oil, natural gas have strong negative impact on the environment. Moreover, the availability of these fossil fuels is decreasing day by day. Hence, extracting energy from renewable sources such as solar, wind, biomass etc. and their storage systems are becoming the new paradigm to overcome the shortcomings of energy development [1]. These renewable energy technologies have long term benefit of clean and sustainable energy production. Energy Storage Systems (ESS) manages the decent power balance during the power crisis, thus has a significant impact to stabilize the overall power system by mitigating the intermittent nature of renewable generation. ESS can store energy during off-peak hours and release them in peak hours. This trend of integrating renewable sources with ESS and loads is utilizing in microgrid applications. A simplified conceptual framework of this interconnected system is shown in Fig. 1 [2]. Here, the distributed sources, loads and storage are connected to the main grid with point of common coupling (PCC). Microgrid (MG) is capable of operating in both gridconnected and islanded mode. In grid-tied system, power balance between MG and main grid protect the system from frequency instability. However, in islanded mode MG operates with off-grid network, hence primary frequency control becomes crucial.

1- Introduction

2- Experimental

3- Results and discussion

4- Conclusions

References

ABSTRACT

Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity, structure versatility and environmental benignity. However, the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs. A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework. The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction. As a result, the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g−1 at 1 C (175 mA·g−1 ), remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate), and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C. Last but not least, a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode, showing a discharge capacity exceeding 300 mAh·g−1 at a current of 175 mA·g−1 .

Introduction

Lithium-ion batteries (LIBs) have played an essential role on energy storage for portable electronic devices in recent decades. However, the ever-growing energy storage demands, especially those driven by electrical vehicles and grid-scale storage of renewable electricity, have generated a great concern not only over the energy density and power density, but also the safety, cost, and sustainability of LIBs [1, 2]. Considering the elaborate preparation process, limited resource and environmental and safety issues of the conventional inorganic battery electrode materials, organic materials are intriguing alternatives for sustainable batteries [3, 4] because of the potentially low-cost, high safety, recyclablility, design diversity of molecular structures, and high theoretical capacities due to low formula weight and capability of multiple electron transfer [5–8]. The development of organic compounds as electrode material actually started as early as that of the inorganic materials [9], but the progress is lagging behind due to the tremendous success of inorganic intercalation compounds in the late 1980’s [10]. The main problem of most organic materials is their electronic insulating nature. This means that a large amount of conductive carbon (usually more than 30 wt.%) is normally required for the preparation of an organic electrode using the typical slurry coating method [11]. When the mass of the conductive carbon, the polymer binder and the Al current collector is considered, the practical energy density of organic electrodes is quite low [7]. Besides, uniform distribution and good physical contact of organic active materials and the conductive additive in the electrode is often difficult to achieve with the slurry coating method, resulting in low utilization of the active material and poor rate performance [12]. Polyimide (PI), an important engineering plastic with excellent mechanical strength and outstanding thermal stability, belongs to the category of organic carbonyl compounds, which bear high theoretical capacity for storage of lithium ion [13, 14]. Li ions reversibly that absorb or desorb on oxygen atoms as the carbonyl groups are reduced or oxidized [15]. This process is also known as enolation [15, 16]. Theoretically, PI polymers with 1 mole of repeating units can react to 4 moles of Li ions, resulting in a theoretical capacity of ~ 400 mAh·g−1. However, redox processes beyond two-electron transfer reaction have not been reported for PI electrodes in LIBs. It was predicated that four-electron redox process is nearly impossible to be realized reversibly because deep enolation would damage the molecular structure of PI materials [12, 15]. Furthermore, reaction kinetics of PI electrodes needs to be improved for practical considerations [17].

Accurate state-of-charge (SoC) estimation is remarkably difficult due to nonlinear characteristics of batteries and complex application environment in electric vehicles (EVs), particularly low temperature and low SoC. In this paper, an improved battery model is first built using a feedforward neural network (FFNN) by introducing newly defined inputs. Based on the FFNN model and the extended Kalman filter algorithm, a FFNN-based SoC estimation method is designed, and its robustness is verified and discussed using the experimental data obtained at different temperatures. Finally, a hardware-in-loop test bench is built to further evaluate the real-time and generalization of the designed FFNN model. The results show that the SoC estimation can converge to the reference value at erroneous settings of an initial SoC error and an initial capacity error, and the SoC estimation errors can be stabilized within 2% after convergence, which applies to all the cases discussed in this paper, including low temperature and low SoC. This indicates that the FFNN-based method is an effective method to estimate SoC accurately in complex EV application environment.

Introduction

With the improvement of performance requirements for electric vehicles (EVs), such as longer driving range and faster speed, more powerful energy sources are needed. At present, lithium ion batteries are the most commonly used energy sources in EVs due to their advantage of higher energy density and longer lifetime than other batteries with different chemistries (Subburaj et al., 2015), but they still cannot provide sufficient energy to drive EVs as far as fossil fuels in traditional vehicles. Under these circumstances, it is crucial to fully utilize the energy stored in batteries for EVs through battery management systems (BMSs). Battery state-of-charge (SoC) estimation is one of the main tasks of BMSs and its accuracy influences performances of other functions in BMSs, including charging control (Di Yin et al., 2016), balancing control (Ma et al., 2018), thermal management (Zhu et al., 2015), and safety management (Xiong et al., 2019a). Due to nonlinear characteristics and complex operation environments of batteries in EVs, it is very difficult to obtain accurate SoC, so a welldesigned SoC estimation method is necessary for any BMSs.