Efficient management of lead-acid batteries for Micro Hybrid Vehicles

September 15, 2011 // By Michael Hutterer, Antonio Leone
More than half of the vehicle breakdowns that are caused by the electrical system can be traced back to the lead-acid battery and could have been avoided by knowledge of the battery state. A battery management system (BMS) provides the necessary information by fast and reliable detection of the State-of-Charge (SoC), State-of-Health (SoH) and State-of-Function (SoF) in terms of cranking capability.

In today‟s vehicles, the rising number of electrical loads presents a challenge to the battery. More than half of the vehicle breakdowns that are caused by the electrical system can be traced back to the lead-acid battery and could have been avoided by knowledge of the battery state. Additionally, new functions of micro hybrid vehicles like start-stop or intelligent alternator control require exact knowledge of the battery state.

A battery management system (BMS) provides the necessary information by fast and reliable detection of the State-of-Charge (SoC), State-of-Health (SoH) and State-of-Function (SoF) in terms of cranking capability. So, the BMS is able to minimize the number of vehicle breakdowns due to unforeseen battery failure, to maximize lifetime and efficiency of the battery and to enable CO2 saving functions. The key element of the BMS is an Intelligent Battery Sensor (IBS), which measures battery terminal voltage, -current and -temperature and calculates the battery state.
This paper describes the implementation of a BMS using state-of-the-art algorithms for calculation of SoC, SoH and SoF and the efficient implementation of these on Freescale‟s IBS for lead-acid batteries.

1) Introduction

Traditionally the charge level of a car battery has been an unknown factor, which in many cases resulted in vehicle breakdowns. Dependent on the vehicle life cycle, battery related failure rates could climb up to 10000 ppm [1].
Additional challenges to the already critical situation of the car battery are created by the increasing demand of electrical energy and power while CO2 emissions need to be reduced at the same time.
As electronics enable a large part of car innovation, increasing energy supply is required to account for growing functionality in comfort, electrification of safety relevant functions, hybridization of vehicles, driver assistance and infotainment.
On the other side more and more regulations call for reduced CO2 emissions and reduction of fuel consumption.
An advanced energy management system is required in order to manage those opposing requirements.

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