Heavy-Duty Electric Vehicles

Heavy-Duty Electric Vehicles

From Concept to Reality
2021, Pages 173-203
Heavy-Duty Electric Vehicles

Chapter 8 - Battery Management System: Charge Balancing and Temperature Control

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Abstract

Throughput of the state-of-the-art individual Li-ion cells is not enough to support an “electric powertrain.” Therefore battery packs are needed. However, intercellular variations exist and get amplified as the pack is used owing to internal and external factors such as impedance difference, different charging and discharge rates, and temperature gradient. This has a negative effect on normal battery pack operation. A battery management system (BMS) is used to monitor these irregularities and control battery cell and pack performance in a close range.

This chapter provides a comprehensive discussion on key functionalities of BMS, which include charge balance, temperature regulation, and data storage. BMS architecture is described. The charge equalization process is elaborated in the context of various equalization strategies and circuits. Ability to record battery signals and store cycle life history data is a crucial requirement for BMS. However, a large number of signals that is typical of a battery pack from heavy-duty EVs and a limited on-board memory compromises this ability. To that end, the multifrequency recording method is introduced as a suitable data storage method.

In the end, temperature regulation methods suitable for modular battery packs are discussed. Estimation of heat generation from battery cells is necessary for sizing the thermal management system correctly. Basics of estimating heat generated by batteries through the application of calorimetry principles are explained. Another technique of approximating heat generation from battery polarization equation is also presented.

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