Visit to Tesla Gigafactory, no lecture
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Battery Systems for Transportation and Grid Services
Visit to Tesla Gigafactory, no lecture
Battery pack design for transportation is a rapidly evolving and fascinating topic at the intersection of electrical, mechanical, and software engineering. We will discuss how to translate vehicle level requirements such as vehicle weight, speed, drag, range, and recharge time into battery pack specifications such as voltage, energy (kWh), and power (kW). We will then discuss the typical design of a lithium ion battery pack including cells, packaging, thermal management, battery management, and safety and look at a few examples from scooters, motorcycles, cars, and airplanes. Next we will look at lithium ion battery pack safety and various strategies to mitigate the failure modes. Finally, we will review the cutting edge of battery pack design and a few potentially breakthrough technologies.
The lecture will provide an overview of lessons learned when designing battery thermal management systems for advanced vehicles. We will start by understanding where the heat is generated in a cell, the efficiencies of power and energy cells, and what type of battery thermal management solutions are available in today's market. We will then investigate three different battery pack thermal management strategies employed by the OEMs – water cooling, air cooling and active (vapor compression) cooling- and outline the advantages and disadvantages of each technology. We will also delve into the Department of Energy's extreme fast charging program describing how the cell and module thermal design needs to be improved to meet the lifetime and safety expectations of the consumer. Finally, we will introduce the ultimate thermal challenge – cells entering into thermal runaway and what strategies are being employed to control or mitigate this phenomena. In the end, we hope to show that energy storage systems are varied, and each application requires a unique thermal solution to address today's technological barriers.
Safety incidents with lithium ion batteries have been the "elephant in the room" for several years now, with high profile incidents in consumer electronics, electric vehicles and stationary installations popping up periodically on the news with often dramatic consequence. All stored energy ultimately carries an inherent hazard. The hazards inherent to lithium ion batteries however are often less well understood than those of more conventional means of energy storage. Sandia National Laboratory's Battery Abuse Testing Laboratory looks to use destructive battery testing to better understand the hazards presented lithium ion batteries. This talk will look at the general consequences of catastrophic battery failure, including heat release, projectiles and fire/flammable components. Various battery chemistries have been observed to have different responses as well. Battery failure calorimetry has been used in the past to quantify this effect, with collected results discussed here. Ultimately, as progressively larger battery systems are explored the system level impact of a single cell battery failure becomes important as well. Sandia has explored techniques for cell to system thermal runaway propagation with examples of this testing shown.
TOPIC: Battery Modeling and Design
This lecture provides an overview of lithium-ion technology with a focus on modeling for design and simulation. Lithium-ion is dominant battery technology mainly because of high energy and power density, outstanding cycle and calendar life, and acceptable cost. The design of practical cells is a trade-off among competing requirements. The design options are determined by the components (active materials, separators, electrolytes, collectors, packages). The electrical and thermal behavior of lithium-ion cells depends on the rates of solid and liquid phase mass transfer in the cell. The electrothermal performance can be estimated by modeling and numerous commercial software programs are available. Simple circuit models have proven especially useful for simulation of automotive cells.
TOPIC: Power Electronics: Dc-dc and DC-AC converters
In this lecture, we will briefly describe the various topologies that are used in the design of dc-dc converters commonly used in battery-operated systems. We will also describe the basic modulations used in Dc-ac converters that are commonly used in electric motor drives.
In this lecture, we will introduce how power electronics components operate to deliver power from the grid to a dc source efficiently. We will also describe how to measure the distortion introduced by the converters as well as the allowable limits in distortion.
This lecture will discuss some of the foundations of health-conscious lithium-ion battery control. The lecture will motivate the need for health-conscious control, and discuss some of the models used for representing battery performance and degradation dynamics in the literature. Based on these foundations, examples of health-conscious control problem formulations, solution methods, and results will be presented for cell-, pack-, system-, and infrastructure-level applications. Connections between health-conscious control and more classical battery control challenges such as pack balancing will be discussed, motivating a broader perspective on those more traditional challenges.
Battery-management systems (BMS) comprise electronics and software designed to monitor the status of a battery pack, estimate its present operating state, and advise the battery load regarding the maximum amount of power that may be sourced or sunk by the load at every point in time while maintaining safety and acceptable battery-pack service life. This lecture will first discuss BMS sensing requirements imposed by these tasks. It will then give an introduction to state-of-art equivalent-circuit-model-based algorithms to estimate the battery pack's operating state: nonlinear Kalman filters for state-of-charge, recursive total-least-squares methods for state-of-health, direct computations for state-of-energy, and a bisection method for state-of-power.
Lithium-ion battery packs for transportation and grid services represent a large investment that must be continuously monitored to ensure safety, to maximize performance, and to extend life to the greatest degree possible. The best available battery-management methods are model based; that is, they depend on sets of equations ("models") that describe the behaviors of the lithium-ion cells in the battery pack in order to perform their management tasks. This lecture will first derive "equivalent-circuit" models, which are presently state-of-art. It will next introduce "physics-based" models, which have potential benefits for future battery-management systems. Physics-based models are computationally complex, so a method will be presented to develop highly accurate reduced-order models suitable for battery management. Finally, a high-level overview of mechanisms of cell degradation will be given to motivate power-limits computations to be discussed in the next lecture.