On Thermal and State-of-Charge Balancing using Cascaded Multi-level Converters

Faisal Altaf; Lars Johannesson; Bo Egardt

On Thermal and State-of-Charge Balancing using Cascaded Multi-level Converters

Faisal Altaf

Lars Johannesson

Bo Egardt

Vol. 13, No. 4, pp. 569-583, Jul. 2013

10.6113/JPE.2013.13.4.569

Hybrid electric vehicles

Multi-level Converter

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Abstract

In this study, the simultaneous use of a multi-level converter (MLC) as a DC-motor drive and as an active battery cell balancer is investigated. MLCs allow each battery cell in a battery pack to be independently switched on and off, thereby enabling the potential non-uniform use of battery cells. By exploiting this property and the brake regeneration phases in the drive cycle, MLCs can balance both the state of charge (SoC) and temperature differences between cells, which are two known causes of battery wear, even without reciprocating the coolant flow inside the pack. The optimal control policy (OP) that considers both battery pack temperature and SoC dynamics is studied in detail based on the assumption that information on the state of each cell, the schedule of reciprocating air flow and the future driving profile are perfectly known. Results show that OP provides significant reductions in temperature and in SoC deviations compared with the uniform use of all cells even with uni-directional coolant flow. Thus, reciprocating coolant flow is a redundant function for a MLC-based cell balancer. A specific contribution of this paper is the derivation of a state-space electro-thermal model of a battery submodule for both uni-directional and reciprocating coolant flows under the switching action of MLC, resulting in OP being derived by the solution of a convex optimization problem.

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Cite this article

[IEEE Style]

F. Altaf, L. Johannesson, B. Egardt, "On Thermal and State-of-Charge Balancing using Cascaded Multi-level Converters," Journal of Power Electronics, vol. 13, no. 4, pp. 569-583, 2013. DOI: 10.6113/JPE.2013.13.4.569.

[ACM Style]

Faisal Altaf, Lars Johannesson, and Bo Egardt. 2013. On Thermal and State-of-Charge Balancing using Cascaded Multi-level Converters. Journal of Power Electronics, 13, 4, (2013), 569-583. DOI: 10.6113/JPE.2013.13.4.569.