Jorge Varela Barreras

Jorge Varela Barreras
Imperial College London | Imperial · Department of Mechanical Engineering

Doctor of Philosophy

About

45
Publications
56,140
Reads
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402
Citations
Introduction
I am a senior battery researcher in Imperial College London, and joint chair of the IEEE UK & Ireland education chapter. My current research focus is on novel electric vehicle concepts and Lithium-ion battery modeling, simulation, emulation, diagnosis, balancing and management systems. I was a Post Doc in battery management at Oxford University. I got my PhD in battery management systems at Aalborg University. Previously, I studied power electronics also at Aalborg, and electrical engineering at University of Vigo.
Additional affiliations
January 2019 - present
Imperial College London
Position
  • Senior Researcher
June 2016 - January 2019
University of Oxford
Position
  • PostDoc Position
July 2015 - May 2016
Aalborg University
Position
  • PhD. mentor

Publications

Publications (45)
Article
Full-text available
To ensure the safe and stable operation of lithium-ion batteries in battery energy storage systems (BESS), the power/current is de-rated to prevent the battery from going outside the safe operating range. Most derating strategies use static limits for battery current, voltage, temperature and state-of-charge, and do not account for the complexity o...
Preprint
Full-text available
This works deals with the design and validation of a control strategy for hybrid balancing systems, an emerging concept that joins battery equalization and hybridization with supercapacitors in the same system. To control this system, we propose a two-layer model predictive control (MPC) framework. The first layer determines the optimal state-of-ch...
Preprint
Full-text available
The ability to correctly predict the behavior of lithium ion batteries is critical for safety, performance, cost and lifetime. Particularly important for this purpose is the prediction of the internal temperature of cells, in order to reproduce the positive feedback between temperature generation and current distribution. In this work, a comprehens...
Article
Full-text available
The Lithium-ion battery (LIB) is an important technology for the present and future of energy storage, transport, and consumer electronics. However, many LIB types display a tendency to ignite or release gases. Although statistically rare, LIB fires pose hazards which are significantly different to other fire hazards in terms of initiation route, r...
Article
Developers and manufacturers of Battery Management Systems (BMSs) require extensive testing of controller HW and SW, such as analog front-end (AFE) and performance of generated control code. In comparison with tests conducted on real batteries, tests conducted on a state-of-the-art hardware-in-the-loop (HIL) simulator can be more cost and time effe...
Article
Full-text available
Islanded mini-grids with batteries are crucial to enable universal access to energy. However, batteries are still costly, and how to select and operate them in an optimal manner is often unclear. The combination of variable climates with simple and low-cost passive thermal management also poses a challenge. Many techno-economic sizing tools usually...
Article
Scenarios with rapid energy conversion for lithium-ion batteries are increasingly relevant, due to the desire for more powerful electric tools or faster charging electric vehicles. However, higher power means higher cooling requirements, affecting the battery temperature and its thermal gradients. In turn, temperature is a key quantity influencing...
Chapter
Future power systems bring new challenges that require innovative solutions. In that regard, stationary energy storage is expected to play a key role in our transition to clean energies, i.e., generation using technologies with lower carbon footprint. A variety of stationary energy storage technologies are available and commercially viable for mult...
Poster
Full-text available
In this work, an experimentally validated degradation model of a Li-ion battery is mapped offline to predetermine the degradation rates. The results are integrated into the current-derating algorithm using simple look-up tables. This framework can be adapted to any degradation model and allows flexible tuning. The method is evaluated in simulations...
Article
This work deals with the design and validation of a control strategy for hybrid balancing systems (HBSs), an emerging concept that joins battery equalization and hybridization with supercapacitors (SCs) in the same system. To control this system, we propose a two-layer model predictive control (MPC) framework. The first layer determines the optimal...
Article
Full-text available
Batteries stacks are made of cells in certain series-parallel arrangements. Unfortunately, cell performance degrades over time in terms of capacity, internal resistance, or self-discharge rate. In addition, degradation rates are heterogeneous, leading to cell-to-cell variations. Balancing systems can be used to equalize those differences. Dissipati...
Article
The ability to correctly predict the behavior of lithium ion batteries is critical for safety, performance, cost and lifetime. Particularly important for this purpose is the prediction of the internal temperature of cells, because of the positive feedback between heat generation and current distribution. In this work, a comprehensive electro-therma...
Article
Full-text available
Hybridizing a lead–acid battery energy storage system (ESS) with supercapacitors is a promising solution to cope with the increased battery degradation in standalone microgrids that suffer from irregular electricity profiles. There are many studies in the literature on such hybrid energy storage systems (HESS), usually examining the various hybridi...
Presentation
Full-text available
Overview of the research career of Dr Jorge Varela Barreras, including: short bio and timeline, publications timeline, field of publication, publication record, selected awards, key contributions, Google scholar stats, ResearchGate stats, Publons record, and list of references.
Conference Paper
Full-text available
Derating is the operation of an electrical or electronic device at less than its rated maximum capability in order to ensure safety, extend lifetime or avoid system shutdown. Relatively simple derating approaches have been proven effective for lithium-ion batteries. They are typically based on limiting battery charging and discharging currents to p...
Conference Paper
Full-text available
Mini-grids are expected to play a key role in achieving universal access to electricity. The International Energy Agency estimates that 25% of people gaining access to electricity by 2030 will do so through a mini-grid. Generation is often paired with a battery, primarily lead acid or li-ion in this context. Battery storage can help to displace the...
Conference Paper
Full-text available
Mass production and usage of lithium-ion cells demand rapid screening methods to find manufacturing defects, problems, or monitor processes. In order to measure some parameters (capacities, energies, efficiencies…) a full charge and discharge cycle at moderate Crates is normally required. This means that the cost of screening tests can be relativel...
Poster
Full-text available
In this study, a full-cycle test is run on 208 new Li-ion cells. Then, using this data set, machine learning (ML) methods are investigated to predict discharge parameters from charge parameters (and vice versa). The goal is to ascertain whether is possible to replace the conventional full-cycle by a half-cycle, whilst still giving key dis/charge pa...
Article
Full-text available
Performance of series connected batteries is limited by the ‘weakest link’ effect, i.e. the cell or group of cells with the poorest performance in terms of temperature, power, or energy characteristics. To mitigate the ‘weakest link’ effect, this study deals with the design, modeling and experimental demonstration of a smart and hybrid balancing sy...
Article
Full-text available
The series connection of cells in a battery pack, like in any chain, means that performance is limited by the weakest cell. If the cells were identical, this would not be a problem. However, there are cell-to-cell variations, which increase over time, leading to limited pack capacity and power, and uneven temperature distributions. The automotive i...
Conference Paper
Full-text available
This paper presents and analyses results from simplified screening tests conducted on more than 200 large format Kokam NMC lithium-ion pouch cells at their beginning of life. Such data are not common in the literature. The cells were sandwiched between two large heat sinks for testing, which was conducted using an automated dis/charge test system a...
Poster
Full-text available
This poster presents results from simplified screening tests conducted on over 200 lithium-ion Kokam 53 Ah large pouch format Nickel Manganese Cobalt-Graphite (NMC/G) cells (Type SLPB 120216216) at their beginning of life. Such results are not common in the literature, especially for large cells. The screening test procedure consisted basically on...
Poster
Full-text available
A Li-ion battery electro-thermal model was developed in simulations, combining an electric equivalent circuit model and a thermal equivalent circuit model. Experimental data from a Kokam NMC 53 Ah pouch cell was used for parameterization. Diagnosis algorithms for state-of-charge (SoC), internal resistance, power capability and capacity estimation w...
Article
This paper presents a study of the combined influence of battery models and sizing strategy for hybrid and battery-based electric vehicles. In particular, the aim is to find the number of battery (and supercapacitor) cells to propel a light vehicle to run two different standard driving cycles. Three equivalent circuit models are considered to simul...
Thesis
Full-text available
This thesis presents, as a collection of papers, practical methods in Li-ion batteries for simplified modeling (Manuscript I and II), battery electric vehicle design (III), battery management system testing (IV and V) and balancing system control (VI and VII). Manuscript I tackles methodologies to parameterize electrical equivalent circuit models...
Article
In this paper a novel battery electric vehicle (BEV) concept based on a small fixed and a big swappable Li-ion battery pack is proposed in order to achieve: longer range, lower initial purchase price and lower energy consumption at short ranges. For short ranges the BEV is only powered by the relatively small fixed battery pack, without the large s...
Article
Typically, the unique objective pursued in either active or passive balancing is equalization of single cell charge. However, a balancing circuit may offer more control features, like virtual equalization of single cell internal resistance or thermal balancing. Such control features for balancing systems are evaluated in this paper by means of conv...
Conference Paper
Full-text available
In comparison with tests conducted on real Li-ion batteries, Battery Management System (BMS) tests conducted on a Hardware-In-the-Loop (HIL) battery simulator may be more cost and time effective, more flexible and traceable, easier to reproduce and safer beyond the normal range of operation. This is particularly the case of tests at early stages in...
Conference Paper
Full-text available
During many years, battery models have been proposed with different levels of accuracy and complexity. In some cases, simple low-order aggregated battery pack models may be more appropriate and feasible than complex physic-chemical or high-order multi-cell battery pack models. For example: in early stages of the system design process, in non-focuse...
Conference Paper
Full-text available
In this paper a novel battery electric vehicle (BEV) concept based on a small fixed and a big swappable li-ion battery pack is proposed in order to achieve: longer range, lower initial purchase price and lower energy consumption at short ranges. For short ranges the BEV is only powered by the relatively small fixed battery pack, without the large s...
Conference Paper
Full-text available
Developers and manufacturers of Battery Management Systems (BMSs) require extensive testing of controller HW and SW, such as analog front-end (AFE) and performance of generated control code. In comparison with tests conducted on real batteries, tests conducted on hardware-in-the-loop (HIL) simulator may be more cost ant time effective, easier to re...
Conference Paper
Full-text available
While a great number of battery balancing circuit topologies have been proposed, the unique control objective typically pursued is equalization of single cell charge. However, a balancing circuit could offer potentially more control features, especially with topologies able to provide bidirectional power flow control. This has not been explored yet...
Conference Paper
Full-text available
This paper presents a comparative study of the influence of different aggregated electrical circuit battery models in the sizing process of a hybrid energy storage system (ESS), composed by Li-ion batteries and supercapacitors (SCs). The aim is to find the number of cells required to propel a certain vehicle over a predefined driving cycle. During...
Chapter
Full-text available
One of the common phenomena for most of the battery cell chemistries is hysteresis. Since an open circuit voltage (OCV) path is not identical for the charge and discharge of the battery cell at different states of charge (SoC) level, the battery cell show the hysteresis effect. Usually, the OCV i.e. voltage with zero current after previous charge i...
Conference Paper
Full-text available
The 54-meter-high Tvindkraft windmill was built by a group of volunteers during 1975-1978, as an argument for renewable energy sources as well as an argument against nuclear power. At that time it was the world's biggest windmill. So far, Tvindkraft has been running for 35 years, proving that a well-constructed wind turbine is a sustainable approac...
Conference Paper
Full-text available
Researchers and developers use battery models in order to predict the performance of batteries depending on external and internal conditions, such as temperature, C-rate, Depth-of-Discharge (DoD) or State-of-Health (SoH). Most battery models proposed in the literature require specific laboratory test for parameterization, therefore a great majority...

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Projects

Projects (3)
Archived project
Improving state of charge and state of health prediction by better modelling and improved understanding of parameter estimation and observability
Project
The University of Oxford Department of Engineering Science partners WMG (Warwick Manufacturing Group), at the University of Warwick, which will lead a £14 million consortium to create a new automotive battery pack manufacturing research centre. The project will help develop the next generation of traction batteries for electric and hybrid vehicles. It will combine the best human and automated assembly methods to manufacture battery packs and lay the foundations of a new UK automotive supply chain based around this technology.