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BMS Firmware Platform Development

which have different requirements depending on the

customer; and (2) to ensure a high level of safety and

reliability when used with other Keihin’s products.

With regard to the first task above, we would define

the specifications of our battery system, presume the

required specification for each application in advance

and have corresponding functions ready-prepared.

This would enable us to respond well to trends in

the rapidly changing battery market. With regard to

the latter task, we would use the V-type development

process to achieve quality improvement at each step,

thus ensuring quality at the system level.

3. Eventual Goals of the BMS Firmware Platform Development

Eventual goals were set as follows: (1) to construct

a firmware platform so that more than 90% of

firmware functions belong to common applications

in Keihin’s BMS products; and (2) to establish and

implement a development process based on Automotive

SPICE Capability Level 2, corresponding to the tasks

mentioned above respectively (see Table 1).

Michiya OIDAIRA＊１ Takanori ATSUMI＊１

1. Background

Electric vehicles are becoming ever more popular

and common due to market environments such as

tougher regulations in response to global warming.

Hybrid electric vehicles (HEVs) and battery

electric vehicles (BEVs) are equipped with lithium-

ion batteries (LiBs), the most typical rechargeable

batteries, to drive traction motor(s) and accessories.

In China and Europe, reducing the cost of

batteries and increasing their energy density have

been trends of late in development, and expectations

for a variety of further advances in battery technology

have been growing in recent years.

On the other hand, in Japan, battery manufacturers

are bringing out batteries with superior qualities, such

as a high level of safety and high quality in cycle life,

output performance, low temperature operation, etc.

Keihin recognizes the electrification of automotive

power-train systems as an important strategic field,

and considers expansion of our business in this field

as an urgent task.

2. Purpose of the BMS Firmware Platform Development

The purpose of our project is to accelerate

development of firmware equipped in the battery

management system (BMS). The BMS firmware

platform development focuses on the following

tasks: (1) to realize parallel development for systems

Technical Digest

BMS Firmware Platform Development※

＊１BMSDevelopmentDepartment,R&DOperations

※Received31August2018

Table 1 Eventual Goals

Items Criteria Plan

Firmware reuse rate 90% 2018/12/E

Automotive SPICE Level 1 2019/4/E

Automotive SPICEcertification

Level 2 2020/4/E

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Keihin Technical Review Vol.7 (2018)

TechnicalDigests

4. BMS Product Outline

As a differentiated technology, the BMS unit

firmware uses Keihin’s original high-accuracy cell

voltage measurement technology for control and has

the features shown in Fig. 1.

Normally, the battery control system is composed

of the battery body known as the battery cell,

control circuits for controlling ten or more battery

cells, and a battery control board for the circuits.

Battery cells with control circuits are referred to

as battery modules and multiple battery modules

constitute a battery pack.

The functions of firmware mounted on the

battery control board are fault detection for the

battery cell and the control circuit, cell balancing

and ba t t e ry equa l i za t ion , and coopera t ion /

communication with the power control unit (PCU)

(e.g., indicating the amount of energy left in a

battery and maximum power output) (see Fig. 2).

Furthermore, the battery array varies depending

on system-usage. Figure 3 shows the bat tery

characteristics for BEVs (requiring a high capacity

but a lower power) and HEVs (requiring a high

power but a lower capacity).

For example, in the case of the BEV, the battery

is the sole source of power so that battery needs

to be controlled to deliver power on a continuous

basis. On the other hand, HEV uses power from an

internal combustion engine (ICE) and a relatively

small battery so that the battery must be capable

of delivering instantaneous high power. Thus, the

control algorithms and parameters of the firmware

are different depending on the battery array.

A BMS equ ipped wi th t he f i rmware was

developed for application to 3 products under

different customer specification requirements:

company A that had BEV type bat ter ies and

vehicles, company B and company C that have

HEV type batteries and vehicles.

Fig. 1 Features of Keihin’s BMS firmware

BMS platformMeasurement (V, I, T)

Reusable firmware design

SOPestimation

Extracting common / non-commonrequirements, creating an environment

to easily design and test whenspecification changes.

Estimating in-/out-put density withhigh precision

SOHestimation

Estimating capacitydeterioration in

cycle/standby use

SOCestimation

Control to attain fulluse of battery

effective capacity

Chargingcontrol

Optimum batterycharging even atlow temperature

Safety

Protecting from fireor explosion in

harsh conditions

Calculation (SOC/SOH/SOP)Control (cell balance, contactor,

charger)Protection (over-charge/discharge,

high/low temperature)Diagnostics (duplication of cell

voltage protected)

CHARGER

CHARGERECU

BMS

LeakageLi-ion

Current sensorHeater

MotorVCU

PCUCell voltage sensorCell balancingState of batteryGround faultsensor

Cooling

Chargingmanagement

Leakagemanagement

Batterymanagement

Temperaturemanagement

Energymanagement

Distributionmanagement

Cell voltage

Temperature

Current

Fig. 2 BMS Firmware configuration diagram

BEV HEV

High capacity, low power- full use for longer driving distance

Low capacity, high power- instantaneous high-rate output

Fig. 3 Example of battery array for each system

5. Classification of Customer Specifications

We defined the specifications with reference

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BMS Firmware Platform Development

to universal speci fica t ion descr ib ing manner

(USDM) considering specification differences

a m o n g t h e c u s t o m e r s ( s e e Ta b l e 2 ) . M o r e

specifically, we extracted functional requirements

from four viewpoints, <hardware configuration>,

<battery control>, <applied standard>, and <OEM

characterist ics>, then formulated requirement

specifications. Then, we added a column to define

whether there is dependency or not to each usage.

Furthermore, a separate column was provided to

describe specifications for each usage.

Functional requirements were classified and

organized on the basis of following criteria. Their

configurations are shown in Table 3.

① F i r s t , c l a ss i fy requ i rements accord ing to

t he pu rpose o f a sys t em ins t ead o f each

measurement/ control object.

• Define requirements concerning measurement,

protection and control for each purpose.

• D e f i n e c o n s t r a i n t c o n d i t i o n s i n o r d e r

t o f o r m u l a t e n e c e s s a r y a n d s u f f i c i e n t

requirements specifications after clarifying

the purpose (see Table 4).

② Express various information / commands handled

by the system in a form that is not specific to

particular hardware or usage.

<Data / control command (common data)>

performed interconversion between

• a specialized form for hardware / usage, and

• a form not linked to specific hardware / usage

(see Fig. 4).

The main points of BMS control, i.e., <charging

/ discharging>, <fan control>, <charger control>,

and <ground fault detection>, were not tailored for

hardware and usage. In other words, BMS control

just considers <measurement>, <calculation>,

<diagnosis>, and <control> separately (see Table 5).

The BMS firmware consisted of common parts

(driver, protocol, data conversion, control logic) and

non-common parts (algorithms and parameters for

Table 2 Example of specification definition using USDM

Function block or signal Sub-itemsID

2-1 Voltage andtemperaturemeasurement

Battery protection

Current measurement Current measurement

Cell voltage Cell voltage

Battery pack current

End-of-charge warningEnd-of-discharge warning

Over-discharge protection

High-temperature warning

High-temperatureabnormality

Over-current abnormality(charging)Over-current abnormality(discharging)

Low-temperatureabnormalityBattery capacity lackwarning

Low-temperature warning

Over-charge protection

End-of-regenerationwarning

Voltage differenceabnormality

Cell voltage

Module temperature

Battery deterioration

Battery pack current

Total voltagemeasurement

Sum of cell voltage in series

Temperaturemeasurement

Module temperature

Ground fault (Insulation resistance measurement)

2-1

2-3

2-42-5Sample of management data for battery operation:3-13-2

3-3

3-43-5

3-6

3-73-8

3-9

3-10

3-11

3-12

3-13

Function blockSample of monitoring data acquired by BMS:

ItemsBatterymoduletemperature

Module temperature ishigher than 70.0°C.

Module temperature islower than -30.0°C.

The operatingtemperature range ofbattery module isbetween -30.0°C and70.0°C.

Temperatureabnormality- highTemperatureabnormality- low

Diagnosis Criteria Constraint specification

Table 3 Example of functional requirements definition

Table 4 Example of constraint specification definition

Common specification Customer-specificRequirements Calculate the maximum instantaneous discharge current (SOP).

Reason To maximize electrical energy utilization by controllingdischarge current.

Content The maximum discharge current is represented by [A]. The maximum possible dischargevalue in continuous 10 seconds isrepresented by [A].

Constraint Setting in consideration of SOC estimation error.Procedure Set measurement time to 0.1 second, calculate battery pack

current using following formulas, to obtain the maximuminstantaneous discharge current as a limit.

Formula 1:[Predicted current of battery pack1] > = ([Lower limitvoltage of battery pack] - [Open circuit voltage of batterypack 1]) / [Internal resistance of battery pack 1]Formula 2:[Predicted current of battery pack 2] > = ([Lower limitvoltage of battery pack] - [Open circuit voltage of batterypack 2]) / [Internal resistance of battery pack 2]Formula 3:[remaining capacity of battery pack 1] > = 0Formula 4:[remaining capacity of battery pack 2] > = 0Formula 5:[Open circuit voltage of battery pack 1] > = [Lower limitvoltage of battery pack]Formula 6:[Open circuit voltage of battery pack 2] > = [Lower limitvoltage of battery pack]

a particular application). All parts were made into

modules, and the necessary algorithms and parameter

setting were configured according to the usage and

customers (see Fig. 5).

In t he modu la r a r ch i t ec tu re , we adop ted

the structured design proposed by Yourdon and

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Keihin Technical Review Vol.7 (2018)

TechnicalDigests

Constantine (Structured Design: Fundamentals of a

Discipline of Computer Program and System Design,

1979). This is a technique for balancing optimization

of cohesion and coupling (C&C) to so that changes

are localized and algorithms can be transported easily.

Table 5 BMS control status definition

Fig. 4 Information / command handled by system

Application

KeihinIntegration

Protocol

Dependency to customer usage

Charger Breaker diagnosis Batterycooling

Charging/Discharging

Data/command conversion

UDS CCP CAN I2C SPI I/O

HardwareContactor Microcomputer, IC Cooling fan

Fig. 5 Configuration diagram for the purpose of reuse

Items

MeasurementTo represent the state of measuringobject by numerical value (voltage, current, temperature, etc.)

To detect the status of the object, andrepresent the degree of risk level if fault,e.g., major fault, minor fault, warning.

From calculation and diagnosis results,the controlled variable, timing/time,target value for actuator control to berepresented by numerical value.

Using measurement value as inputs,results (SOC, SOP, etc.) are calculatedfrom formulas and expressed in

Calculation

Diagnosis

Control

Definition

Algorithms and parameters configured according to usage

Control algorithms

Data / information interconversion

Protocol

Real-time OS

Device driver

Hardware

Framework

Non

-com

mon

par

tsC

omm

on p

arts

Con

figu

ratio

n fo

r pu

rpos

e of

reu

se

Batteryconstruction

relatedparameters

Charger

Data / control command

CCPEvent dispatch

Interrupt State transition

Timer

Memory-managementUDS OBD

CAN SPI I2C I/O

Diagnosis Contractor control Cooling Security

Batterycontrol

algorithms

Laws andregulations

relatedparameters

Diagnosticalgorithms

6. Achieving High Quality in Upstream Process

The standard process of Automotive SPICE from

European Automobile Manufacturers is applied in

BMS firmware platform development.

Figure 6 shows the W-model process applied

to this development. In this process, a test strategy

/ plan and a test design were performed in the

upstream process, thus reducing the load of test in

the downstream process.

In each step, the following measures were put in

place to achieve high quality.

• Improve development speed by partial application

of model inspection, etc.

• Improve implementation quality by source code

analysis

• Improve test quality by working out test plans and

test strategies in the upstream process

Fig. 6 W-model development process

RequirementsElicitation

System RequirementsAnalysis

SystemQualification Test

System ArchitecturalDesign

Software RequirementsAnalysis

Software ArchitecturalDesign

Integrationtest results

Software Integrationand Integration Test

Software UnitVerification

Unit testresults

Unit testspecification

Coding

Software Detailed Designand Unit Construction

Integrationtest specification

Qualificationtest specification

Qualificationtest results

SoftwareQualification Test

System Integration andIntegration Test

Modelinspection

Source codeanalysis

7. Summary

The BMS fi rmware p la t form development

enabled us to accommodate differences in customer

specifications in a very efficient way, while also

main ta in ing h igh qua l i ty. Wi th an enhanced

development efficiency and shorter customer delivery

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BMS Firmware Platform Development

Author

M. OIDAIRA

The number of BMS players in the market

has been increasing year by year, intensifying the

competition.

To achieve high goals, we will continue our

efforts to further the technological evolution of the

BMS, and contribute to business expansion.

Finally, I would like to express my deepest

gratitude to everyone who has cooperated in this

development. Thank you very much! (OIDAIRA)

time, this process will improve customer satisfaction

and contribute to the electrification of the automotive

power-train.