Observer techniques for estimating the state-of-charge and state-of-health of VRLABs for hybrid electric vehicles

The paper describes the application of observer-based state-estimation techniques for the real-time prediction of state-of-charge (SoC) and state-of-health (SoH) of lead-acid cells. Specifically, an approach based on the well-known Kalman filter, is employed, to estimate SoC, and the subsequent use of the EKF to accommodate model non-linearities to predict battery SoH. The underlying dynamic behaviour of each cell is based on a generic Randles' equivalent circuit comprising of two-capacitors (bulk and surface) and three resistors, (terminal, transfer and self-discharging). The presented techniques are shown to correct for offset, drift and long-term state divergence-an unfortunate feature of employing stand-alone models and more traditional coulomb-counting techniques. Measurements using real-time road data are used to compare the performance of conventional integration-based methods for estimating SoC, with those predicted from the presented state estimation schemes. Results show that the proposed methodologies are superior with SoC being estimated to be within 1% of measured. Moreover, by accounting for the nonlinearities present within the dynamic cell model, the application of an EKF is shown to provide verifiable indications of SoH of the cell pack

Safety of Lithium Nickel Cobalt Aluminum Oxide Battery Packs in Transit Bus Applications

The future of mass transportation is clearly moving toward the increased efficiency and greenhouse gas reduction of hybrid and electric vehicles. With the introduction of high-power/high-energy storage devices such as lithium ion battery systems serving as a key element in the system, valid safety and security concerns emerge. This is especially true when the attractive high-specific-energy and power-chemistry lithium nickel cobalt aluminum oxide (NCA) is used. This chemistry provides great performance but presents a safety and security risk when used in large quantities, such as for a large passenger bus. If triggered, the cell can completely fuel its own fire, and this triggering event occurs more easily than one may think. To assist engineers and technicians in this transfer from the use of primarily fossil fuels to battery energy storage on passenger buses, the Battery Application Technology Testing and Energy Research Laboratory (BATTERY) of the Thomas D. Larson Pennsylvania Transportation Institute (LTI) in the College of Engineering at The Pennsylvania State University partnered with advanced chemistry battery and material manufacturers to study the safety concerns of an NCA battery chemistry for use in transit buses. The research team ran various experiments on cells and modules, studying rarely considered thermal events or venting events. Special considerations were made to gather supporting information to help better understand what happens, and most importantly how to best mitigate these events and/or manage them when they occur on a passenger bus. The research team found that the greatest safety concern when using such a high-energy chemistry is ensuring passenger safety when a cell’s electrolyte boils and causes the ventilation of high-temperature toxic material. A cell-venting event can be triggered by a variety of scenarios with differing levels of likelihood. Also, though the duration of a venting event is relatively short, on the order of just a few seconds, the temperature of the venting material and cell is extremely high. During a venting event, the high-pressure, burning gases tend to burn holes in nearby packaging materials. Most interestingly, the team discovered that following a venting event the large-format cells tested immediately reached and remained at extremely high external skin temperatures for very long periods, on the order of hours. The majority of this report covers the testing designed to better understand how high-energy cells of this chemistry fail and what materials can be used to manage these failures in a way that increases passenger survivability

Possibilities and limitations of active battery management systems for lithium-ion batteries

(English) Lithium-Ion Batteries (LIBs) are being used in more and more areas of application. At the same time, their chemical composition and their designs are constantly evolving. Major developments are also taking place in the field of Battery Management Systems (BMSs), which are essential for the safe operation of LIBs. The focus is on intelligent charge redistribution between individual cells, called Active Balancing (AB). This thesis deals with the possibilities and limitations of AB. An empirical long-term experiment provides new insights into the ageing behaviour of batteries that are actively balanced during their entire service life. The main objective of this work is to to demonstrate influences on the ageing behaviour of batteries that are still unknown at present. A literature study shows that previous work in this area is often based on theoretical approaches and rarely has a functional proof through measurement results. Most significant statements from literature are examined. These include the increase in discharge capacity, energy efficiency and service life associated with AB, as well as lower parameter variation of the individual cells installed in the battery. Before starting the empirical experiment, the current state of the art is captured and a universal AB topology is selected from a large number of known systems. The operating behaviour as well as the balancing algorithms are explained in detail in order to be able to understand the influences occurring during the ageing of the batteries. The ageing experiment itself is a comparison test between commercial Passive Balancing (PB) and the novel AB. Two identical battery packs are aged under uniform conditions, but with the two different BMSs mentioned above. At the end of the ageing process, the battery packs are disassembled and the parameters of all individual cells are determined for further investigation. The main contribution of this work is the proof of effects through AB, especially with large battery loads. Both the increase in discharge capacity and the service life are demonstrated. The work shows how parameter variation of individual cells can be made visible during operation. It also presents diagnosis and calculation methods. The energetic efficiency of the batteries cannot be increased, since the self-consumption of the power electronics of the AB system is always higher than with PB. However, the overall efficiency of the battery increases due to an increase in capacity and an extension of the service life. The thesis also shows that with lower battery loads, the use of AB is not beneficial any more or may lead to negative effects. In such applications conventional PB is sufficient. The results obtained during pack ageing are additionally substantiated and extended by the measurement results of the individual cells. At the end of the thesis, all results and contributions are summarised. Suggestions for optimisation as well as further research ideas are presented as a possible starting point for further scientific studies.(Català) Les bateries d’ions de liti (Lithium Ion Batteries, en anglès) s’usen en més aplicacions. Al mateix temps, la seva composició química i dissenys estan en evolució constant. Els sistemes de gestió del bateries (Battery Management Systems, en anglès), que són essencials per l’operació de les LIB, també estan en constant evolució. El focus principal està en la distribució intel·ligent de càrrega elèctrica entre cel·les individuals, l’anomenat balanceig actiu (Active Balancing, en anglès). Un assaig empíric, de llarga durada, com el dut a terme en aquest treball, dona molt informació en el procés d’envelliment de les cel·les durant tota la seva vida. El principal objectiu d’aquest treball és demostrar les influències encara desconegudes en el procés d’envelliment de les cel·les. L’estudi de la literatura mostra que el treball previ en aquesta àrea està sovint basat en aproximacions teòriques i estranyament ensenya resultats empírics que ho corroborin. En aquest treball s’examinen la majoria de presumpcions que es poden trobar a la literatura. Aquestes inclouen l’increment en la capacitat, l’eficiència energètica i la vida útil associada a un balanceig actiu de les cel·les, així com la reducció de la variació dels paràmetres de cada cel·la en una bateria. Abans de procedir amb l’experiment empíric, es revisa l’estat de l’art en els aspectes fonamentals per aquest estudi. També se selecciona una tipologia de sistema de balanceig actiu per tal de realitzar l’experiment. El treball detalla el procediment d’operació així com l’algoritme de balanceig actiu implementat per tal d’entendre els fenòmens que influencien la degradació de les cel·les durant la seva vida. L’experiment d’envelliment és una comparació entre un sistema de balanceig passiu (Passive Balancing, en anglès) i un de balanceig actiu. Per això s’escullen dues bateries idèntiques, però gestionades diferentment per dos sistemes de gestió diferents. Al final de l’assaig, les bateries es desmunten i s’analitza cada cel·la de forma individual per tal de determinar-ne els seus paràmetres i el seu envelliment. La principal contribució d’aquest treball es el demostrar els efectes del balanceig actiu , sobretot en bateries amb una càrrega elevada. El treball demostra que el balanceig actiu millor gla capacitat de la bateria i la vida útil. El treball també mostra com la variació dels paràmetres de les cel·les es pot fer visible durant la seva operació. També presenta nous mètodes de diagnosi i càlcul d’aquests paràmetres. L’eficiència energètica de les bateries no es pot augmentar degut al consum propi i les pèrdues del sistema de balanceig actiu basat en electrònica de potencia. Si que augmenta l’eficiència global de la bateria, ja que augmenta la seva capacitat i la vida útil. El treball també mostra que en bateries sotmeses a baixa càrrega, el balanceig actiu no aporta cap avantatge respecte el balanceig passiu. Fins i tot en algunes situacions, els efectes del balanceig actiu són negatius. En aquestes aplicacions, es recomana l’ús d’un sistema de balanceig passiu. Els resultats obtinguts durant l’assaig de la bateria queden reforçats quan es fa l’anàlisi de cada cel·la de forma individual. Al final del treball, es resumeixen tots els resultats a més de proporcionar suggereixes per la optimització així com possibles línies de futures investigacionsPostprint (published version

Passive and Active Battery Balancing Methods Implemented on Second Use Lithium-ion Batteries

As the number of electric vehicles (EVs) increases, the number of used battery packs that require disposal increases; however, many of these packs still have useful capacity and can be repurposed. When using repurposed large lithium-ion battery packs, deviations between cells within a pack become problematic. These deviations result in a pack that is unbalanced, affecting performance and proving potentially hazardous when charging. Consequently, a battery management system (BMS) is needed. To provide safety, the BMS in this paper monitors and controls the operation of the battery pack. In addition, it controls the redistribution of charge between the cells within the pack, providing battery balancing and performance benefits. Two designs are prototyped and tested using repurposed battery packs

Multi-kw dc power distribution system study program

The first phase of the Multi-kw dc Power Distribution Technology Program is reported and involves the test and evaluation of a technology breadboard in a specifically designed test facility according to design concepts developed in a previous study on space vehicle electrical power processing, distribution, and control. The static and dynamic performance, fault isolation, reliability, electromagnetic interference characterisitics, and operability factors of high distribution systems were studied in order to gain a technology base for the use of high voltage dc systems in future aerospace vehicles. Detailed technical descriptions are presented and include data for the following: (1) dynamic interactions due to operation of solid state and electromechanical switchgear; (2) multiplexed and computer controlled supervision and checkout methods; (3) pulse width modulator design; and (4) cable design factors

Aviation Propulsive Lithium-Ion Battery Packs State-of-Charge and State-of-Health Estimations and Propulsive Battery System Weight Analysis

Aviation propulsive battery pack research is in high demand with the development of electric and hybrid aircraft. Accurate inflight state-of-charge and state-of-health estimations of aviation battery packs still remain challenging. This thesis puts efforts on estimating the state-of-charge, state-of-health, and remaining energy of a lithium- ion propulsive battery pack with a recursive least squares based adaptive estimator. By reading the system measurements (discharging currents and terminal voltages) with persistent excitation, the proposed estimator can determine the present internal parameters of the battery cells and further interpolate them into state-of-charge, state-of-health, and the remaining energy information. The validation results indicate that the recursive least squares based estimator achieves convergence within a very short time period (_ 1 second) with desirable estimation accuracy (normally under 1%). To validate the recursive least squares based estimator, a lithium-ion single cell simulation model is developed to simulate a NCR18650GA single cell\u27s performance during discharge at 25oC. Validations of the single cell simulation model with both constant discharging current and HK-36 flight mission profile show simulation errors less than 1.3%. This thesis also empirically analyzes the propulsive battery system weight and weight fractions based on the HK-36 electric airplane propulsive battery system designing experiences. As a result, the entire HK-36 propulsive battery system takes approximately 27% of the aircraft gross weight. 58% of the battery system weight is the cells\u27 weight, and 42% is the auxiliary components weight. Taking the weight fraction into consideration, NCR18650GA cells\u27 effective specific energy reduces from 0.16 HP-hr/lb (259 W-hr/kg) to 0.09 HP-hr/lb (150 W-hr/kg)

ANALYSIS AND OPTIMIZATION OF ELECTRICAL SYSTEMS IN A SOLAR CAR WITH APPLICATIONS TO GATO DEL SOL III-IV

Gato del Sol III, was powered by a solar array of 480 Silicon mono-crystalline photovoltaic cells. Maximum Power Point trackers efficiently made use of these cells and tracked the optimal load. The cells were mounted on a fiber glass and foam core composite shell. The shell rides on a lightweight aluminum space frame chassis, which is powered by a 95% efficient brushless DC motor. Gato del Sol IV was the University of Kentucky Solar Car Team’s (UKSCT) entry into the American Solar Car Challenge (ASC) 2010 event. The car makes use of 310 high density lithium-polymer batteries to account for a 5 kWh pack, enough to travel over 75 miles at 40 mph without power generated by the array. An in-house battery protection system and charge balancing system ensure safe and efficient use of the batteries. Various electrical sub-systems on the car communicate among each other via Controller Area Network (CAN). This real time data is then transmitted to an external computer via RF communication for data collection

Autonomous Multi-Chemistry Secondary-Use Battery Energy Storage

Battery energy storage is poised to play an increasingly important role in the modern electric grid. Not only does it provide the ability to change the time-of-day and magnitude of energy produced by renewable resources like wind and solar, it can also provide a host of other 3ancillary grid-stabilizing services. Cost remains a limiting factor in deploying energy storage systems large enough to provide these services on the scale required by an electric utility provider. Secondary-use electric vehicle batteries are a source of inexpensive energy storage materials that are not yet ready for the landfill but cannot operate in vehicles any longer. However, the wide range of manufacturers using different battery chemistries and configurations mean that integrating these batteries into a large-format system can be difficult. This work demonstrates methods for the autonomous integration and operation of a wide range of stationary energy storage battery chemistries. A fully autonomous battery characterization is paired with a novel system architecture and transactive optimization to create a system which can provide utility-scale energy services using a multitude of battery chemistries in the same system. These claims are verified using a combination of in-situ testing and a computer modelling testbed. Results are presented which demonstrate the ability of the system to combine a wide range of batteries into an effective single system