Online accurate estimation of supercapacitor state-of-health (SoH) and state-of-energy (SoE) is essential to achieve efficient energy management and real-time condition monitoring in electric vehicle (EV) applications. In this article, for the first time, unscented Kalman filter (UKF) is used for online parameter and state estimation of the supercapacitor. In the proposed method, a nonlinear state-space model of the supercapacitor is developed, which takes the capacitance variation and self-discharge effects into account. The observability of the considered model is analytically confirmed using a graphical approach. The SoH and SoE are then estimated based on the supercapacitor online identified model with the designed UKF. The proposed method provides better estimation accuracy over Kalman filter (KF) and extended KF algorithms since the linearization errors during the filtering process are avoided. The effectiveness of the proposed approach is demonstrated through several experiments on a laboratory testbed. An overall estimation error below 0.5% is achieved with the proposed method. In addition, hardware-in-the-loop experiments are conducted and real-time feasibility of the proposed method is guaranteed.

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Online Parameter Estimation for Supercapacitor State-of-Energy and State-of-Health Determination in Vehicular Applications

Evaluating the technological evolution of battery electric buses: China as a case

Energy storage systems (ESS) are becoming essential as a solution for troublesome industrial systems. This study focuses on the application of a type of ESS, a high-power technology known in the literature as supercapacitors or electric double layer capacitors (EDLC). This technology has had a huge impact during the last decade on research related to the electric traction drives, renewable sources and powergrids. Related to this aspect, this paper summarizes the most relevant scientific publications in the last five years that study the use of supercapacitor technology (SCs) in electric traction applications (drives for rail vehicles and drives for road vehicles), generation systems for renewable energy (wind, solar and wave energy), and connection systems to the electric grid (voltage and frequency regulation and microgrids). The technology based on EDLC and the practical aspects that must be taken into account in the op-eration of these systems in industrial applications are briefly described. For each of the aforementioned applications, it is described how the problems are solved by using the energy storage technology, drawing the solutions proposed by different authors. Special attention is paid to the control strategies when combining SCs with other technologies, such as batteries. As a summary, some conclusions are collected drawn from the publications analyzed, evaluating the aspects in which it is necessary to conduct further research in order to facilitate the integration of EDLC technology.

https://www.mdpi.com/1996-1073/14/11/3060/pdf

Present and Future of Supercapacitor Technology Applied to Powertrains, Renewable Generation and Grid Connection Applications

Pollution derived from transportation systems is a worldwide, timelier issue than ever. The abatement actions of harmful substances in the air are on the agenda and they are necessary today to safeguard our welfare and that of the planet. Environmental pollution in large cities is approximately 20% due to the transportation system. In addition, private traffic contributes greatly to city pollution. Further, “vehicle operating life” is most often exceeded and vehicle emissions do not comply with European antipollution standards. It becomes mandatory to find a solution that respects the environment and, realize an appropriate transportation service to the customers. New technologies related to hybrid–electric engines are making great strides in reducing emissions, and the funds allocated by public authorities should be addressed. In addition, the use (implementation) of new technologies is also convenient from an economic point of view. In fact, by implementing the use of hybrid vehicles, fuel consumption can be reduced. The different hybrid configurations presented refer to such a series architecture, developed by the researchers and Research and Development groups. Regarding energy flows, different strategy logic or vehicle management units have been illustrated. Various configurations and vehicles were studied by simulating different driving cycles, both European approval and homologation and customer ones (typically municipal and university). The simulations have provided guidance on the optimal proposed configuration and information on the component to be used.

https://www.mdpi.com/1996-1073/11/11/2924/pdf

Urban and Extra-Urban Hybrid Vehicles: A Technological Review

Urban mobility plays a key role in the ecosystems of complex smart cities. It is considered a key factor in enabling cities to become more intelligent, which highlights the importance of identifying the drivers that improve the intelligence of cities. In this study, we investigate the main drivers with the potential to increase urban mobility intelligence and assign them a priority. Following on from a systematic review of the literature, we conducted broad and detailed bibliographic research based on the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). We also surveyed 181 professionals working in the field concerned to confirm the importance of different drivers and assign them a level of priority. The results show that 27 drivers identified in the literature were considered important, of which seven, related to city governance and technical solutions, were considered the most important to increase urban mobility intelligence.

Smart Mobility: The Main Drivers for Increasing the Intelligence of Urban Mobility

As electric mobility becomes more important every day, scientific research brings us new solutions that increase performance, reduce financial and economic impacts and increase the market share of electric vehicles. Therefore, there is a necessity to compare technical and economic aspects of different technologies for each transport application. This article presents a comparison of three bus prototypes in terms of dynamic performance. The analysis is based on the collection of real data (acceleration, maximum speed and energy consumption) under different settings. Each developed prototype uses the same bus chassis but relies on different energy storage systems. Results show that the dynamic bus performance is independent on the three energy storage technologies, whereas technologies affect the management costs, charging time and available range. An extensive experimental analysis reveals that the bus equipped with a hybrid storage (lithium-ion batteries and supercapacitors) had the most favorable net present value, in comparison with storage composed of only lead–acid or lithium-ion batteries. This result is due to the greater life of lithium-ion batteries and to the capability of supercapacitors, which reduce both batteries depth of discharge and discharge rate.

Experimental Data Comparison of an Electric Minibus Equipped with Different Energy Storage Systems

Advantages of retrofitting old electric buses and minibuses

The lead-acid battery of an electric minibus has been replaced with a smaller size lithium-ion battery system consisting of standard 12 V modules and a hierarchical battery management system. The minibus has experimentally been tested to show that the reduced battery capacity, which also cuts costs, does not affect the daily operational mission. This is assuming that the driving phases are alternated with fast charging periods. Experiments show that fast charging of 8 min guarantees up to 1 h of operation.

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Experimental analysis of an electric minibus with small battery and fast charge policy

Bio-methane as fuel in a natural gas engine is a viable solution to reduce greenhouse gas emissions. The present paper illustrates the results of the first set of measurements carried out in the BiomethER project (EULIFE). BiomethER aimed to design and build two innovative bio-methane production plants, located in Emilia Romagna region (Italy), fed by different feedstock: the first one with sewage sludge and the other with landfill waste. Biogas extracted by the anaerobic digester was cleaned and upgraded to biomethane for road vehicles application. To verify the compatibility of biomethane in conventional compressed natural gas engine (CNG) vehicles, three passenger cars have been tested with two gases: conventional natural gas and bio-methane coming by BiomethER sewage sludge plant. Test concerned dynamic performances and exhaust emissions and was operated on the chassis dynamometer facility, in ENEA Casaccia Research Centre. Preliminary results showed no appreciable deviation was noticeable for fuel consumption and CO2 emissions between the two fuels, acceleration and maximum power were almost the same for the three vehicles tested. The WTW evaluation of GHG emissions for the biomethane resulted in up to 79% lower in comparison with natural gas provided by the Italian pipeline.

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Performance and Emissions Comparison between Biomethane and Natural Gas Fuel in Passenger Vehicles

Cost and reliability of energy storage systems are key factors for the electrification of road vehicles such as buses. In this work, authors propose a hybrid storage system in which a relatively small electrochemical battery is coupled with an array of super-capacitors. Super-capacitors are sized in order to store the energy needed to perform the travel between two bus stops. Each bus stop is equipped with a fast recharge system able to completely recharge super-capacitors in about thirty-sixty seconds. In this way on board batteries are used only as a backup source to compensate some unavoidable tolerances in the design of the system and to assure a residual autonomy that should allow a robust behaviour of the system respect to real perturbed mission profiles.

Fabio Cignini

Papers

Experimental Data Comparison of an Electric Minibus Equipped with Different Energy Storage Systems

Advantages of retrofitting old electric buses and minibuses

Experimental analysis of an electric minibus with small battery and fast charge policy

Performance and Emissions Comparison between Biomethane and Natural Gas Fuel in Passenger Vehicles

Design of a Hybrid Storage for Road Public Transportation Systems