Hybrid Electric Vehicles, 2nd Edition

12Battery Modeling

12.1 Introduction

Chapter 11 contained quite a significant amount of discussion on energy sources, including batteries, ultracapacitors, and flywheels. It also gave details on items related to battery and other energy systems, state of charge, state of health, life cycle and other details with particular reference to lead acid battery. In that chapter, battery and other energy device modeling were also covered to some extent, so this chapter will not deal too much with those items and will directly focus on hybrid and electric vehicle batteries, particularly the nickel metal hydride and lithium based batteries especially with reference to modeling. Although the previous chapter pertained primarily to lead acid batteries, the methodologies and philosophies will remain more or less the same in other battery chemistries covered here.

In this chapter the main focus will be on modeling of batteries. Battery modeling is useful: (1) for calculation of SOC, (2) for calculation of SOH, (3) as part of an overall vehicle model and to study the steady state and dynamic system behavior of the hybrid or electric vehicle as affected by the presence of the battery. This means obtaining the performance characteristics of the overall system with the battery model incorporated.

As is well known, a battery is a highly nonlinear device which displays hysteresis – in other words, not just its present situation or state of the battery, but also how it came to that state or operating ...