Viewing the Battery Management

System Through Many Lenses

Martin Klein

LG Chem Power, Inc.

2011 PHM Conference

Battery Management System Workshop

September 26, 2011

Many Perspectives

• Protect the cells

• Calculate SOx quickly, accurately

• Inform the driver

• Robust design

• Safety

• Low cost

• Delivered on time

• Small, lightweight

Battery Management System Key Functions

Battery Management System Environment

Battery Management System Environment

Battery Scientist: Protect the Cells!

Cells don’t like– Over-charge– Over-discharge– Over-current– High temps– Operating at Low Temps

– ��������� (power drain)

Functions of Interest• Monitoring: V, I, T• Power limits �, , ���• State of Health• Thermal management

– Fan, pump speed– Heaters– Chillers

• Cell balancing• Isolation detection

Controls Engineer

Multiple Loops In Play:

- Measurements / Monitoring / Reporting- Cell voltage, Battery current

- High Voltage Interrupt Loop

- High Voltage Isolation

- Coolant Temperatures (Inlet/Outlet, Cells)

- Circuit Board Temperatures

- External commands (e.g., contactor control, crash sense)

- Weld Checks, Breaking Element Detection

- Cell Balancing

- SOx-Related Algorithms

- State of charge, power, energy, health

- Diagnostics & Rationality

Commands:

- Contactor Open / Close

Other

- Off-line diagnostics, reflash, test mode

- BMS Power Up, Power Down Sequencing

Highly

synchronized

Accuracy, speed

requirements vary with

application (HEV, PHEV, EV)

SOCA Modeling and HIL ValidationDeep-Dive State-of-Charge Algorithm validation in progress

Exercising SOCA to limits of battery pack operation Considering all modes of operation

RTC

Data Initialization

Algorithm (state) InitializationSOC Estimation

Hysteresis

Filter States

ResistanceCapacity

Bias

SOC Estimation

Hysteresis

Filter StatesResistance

Capacity

Current Bias

Robustness to voltage sensors stuck at low, nominal, highRobustness to temperature sensors stuck at low, nominal, high

Robustness to current sensor stuck at low, nominal, high

SOC Estimation

Hysteresis

Filter StatesResistance

Capacity

Bias

SOC EstimationFilter States

HysteresisResistanceCapacity

Current BiasRobustness to SOC Initial Robustness to Cell BalancingRobustness to Temperature

Robustness to Cell Age

Startup mode

Normal operation

Fault mode

Shut-

down

8

Software TasksTop 3 (by HLF Requirements Count):

- Diagnostics: 22%

- Hardware Interface: 12%

- Cell & Pack Energy Mgmt: 12%

MEMO: Code releases

often proliferate to support

multiple vehicle builds!

Electronics Engineer• Electronics Design & Development

– Engineering Costs

– Part Count, Part Cost

– Change Management

– Hardware/Software Compatibility

– Component availability (wrt global shortages, Japan disaster)

– Package Space, connectors, enclosures

• Validation

– Environment• Temperature, Humidity, Vibration, Shock

• Electromagnetic Compatibility

• Electrical Overstress (e.g., ESD)

– Ability to test

Battery Energy

Control Module

(“Master”)

Battery Power

Slave Module

(“Slave”)

OEM Purchasing / Buyers

• The BMS is pure overhead:

– It does not store energy; yet

– It costs a lot of money,

– It takes us space, and

– It has mass

• “Just another piece of electronics”

Design & Development Strategy

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Move all but cell protection, battery monitoring to

vehicle-level controller + + + + + + +Repeating, common electronic circuits should be

book-shelved for re-use on multiple programs + + + +Next Generation ASICs to in increase circuit

integration (and reduce part count) + + + + + +

Highly modular SW - + +

Hardware-independent SW - +Make SOx only as complex as necessary for the

intended roles (i.e., HEV, PHEV, EV) + + + + +Make HILs an integrated part of the Validation

Process + + +

BMS Design Strategies for Satisfying Multiple Demands

Design Strategies for Satisfying Multiple Demands

Battery Architecture: Minimize BMS Responsibilities

• Keep – Cell-related functions with battery

• V,I,T monitoring

• SOx algorithms, power limits,

– Communications (e.g., CAN)

– Minimum diagnostics; e.g., HVIL, ∆V, ∆T

– Minimum data recording functions

• Move other functions to vehicle controller– Link-side voltage measurement

– Contactor Control / Breaking Element Detection

– Thermal Controls (Fans, Pumps, etc.)

…and Diagnostics will follow!

Design Strategies for Satisfying Multiple Demands

• Hardware Architectures

– Maximize circuit reuse; minimize or simplify pack-

specific circuits

– Seek to increase manufacturing volumes of

common PCBs; eliminate low-volume HW variants

– Off the shelf commercial ASICs

Design Strategies for Satisfying Multiple Demands

• Software Architecture

– Move cell-specific parameters into calibratable tables

– Core / Apps partition, with book-shelved SW modules

– SOx algorithms as complex as necessary, but no more

– Hardware-in-the-Loop should be fundamental element of validation

Challenges in BMS SW Testing + Development

• Simulating accurate cell voltages

• Automating diagnostics testing

• Next generation ASIC decisions

• Cell balancing and State of Health – what is the optimal cell balancing strategy?

• SOC accuracy @ cold temperatures(-20°C) – For example: Coulomb-counting alone at cold

ignores unreliably high OCV’s.)

• SOx and Power Management are critical BMS functions…but

not the only functions

• To make the BMS affordable and to reduce the time to

market, focus on the functions most critical to enhancing cell

performance and life

• Electronic hardware drives piece cost and a good part of

development costs

• Book-shelf and modularize to increase re-use of circuits and

SW to drive up volumes and drive down costs

• Many challenges remain to satisfying all users

Summary

Thank You