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Title: Battery management systems with active loading and decentralised control
Author: Frost, Damien
ISNI:       0000 0004 6500 749X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2017
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This thesis presents novel battery pack designs and control methods to be used with battery packs enhanced with power electronics. There are two areas of focus: 1) intelligent battery packs that are constructed out of many hot swappable modules and 2) smart cells that form the foundation of a completely decentralised battery management system (BMS). In both areas, the concept of active loading/charging is introduced. Active loading/charging balances the cells in a battery pack by loading each cell in proportion to its capacity. In this way, the state of charge of all cells in a series string remain synchronized at all times and all of the energy storage potential from every cell is utilized, despite any differences in capacity there may be. Experimental results from the intelligent battery show how the capacity of a pack of variably degraded cells can be increased by 46% from 97 Wh to 142 Wh using active loading/charging. Engineering design challenges of building a practical intelligent battery pack are addressed. Start up and shut down procedures, and their respective circuits, were carefully designed to ensure zero current draw from the battery cells in the off state, yet also provide a simple mechanism for turning on. Intra-pack communication was designed to provide adequate information flow and precise control. Thus, two intra-pack networks were designed: a real time communication network, and a data communication network. The decentralised control algorithms of the smart cell use a small filtering inductor as a multi-purpose sensor. By analysing the voltage across this filtering inductor, the switching actions of a string of smart cells can be optimised. Experimental results show that the optimised switching actions reduce the output voltage ripple by 83% and they synchronize the terminal voltages of the smart cells, and by extension, their states of charge. This forms the basis of a decentralised BMS that does not require any communication between cells or with a centralised controller, but can still achieve cell balancing through active loading/charging.
Supervisor: Howey, David Sponsor: Jesus College Oxford ; N4L Limited ; Natural Sciences and Engineering Research Council ; Oxford Sciences Innovation
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Battery management systems ; Power electronics ; Electrical engineering ; MMC ; Battery management system ; BMS ; MOSFET