High accuracy lithium-ion electric vehicle battery monitoring system.
11
"I hereby declare that I have read through this report entitle "High Accuracy Lithium-ion Electric
Vehicle Battery Monitoring System" and found that it has comply the partial fulfillment for
awarding the degree of Bachelor of Electrical Engineering (Control, Instrumentation and
Automation)"
Signature
Supervisor name
En. Musa Yusup Lada
Date
Lvi
......t'Jo
:.l.......G/10
........................
.
111
HIGH ACCURACY LITHIUM-ION ELECTRIC VEHICLE BATTERY MONITORING
SYSTEM
CHAWPUILING
A report submitted in partial fulfillment of the requirements for the degree of Bachelor in
Electrical Engineering (Control, Instrumentations and Instrumentations)
Faculty of Electrical Engineering
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2014
IV
I declare that this report entitle "High Accuracy Lithium-ion Electric Vehicle Battery Monitoring
System" is the result of my own research except as cited in references. The report has not been
accepted for any degree and is not concurrently submitted in candidature of any other degree.
Signature
Name
Date
Chaw Pui Ling
t=t-(b [,-01\f
................... ······ ... ······ ...... .
v
Acknowledgement
First of all, I acknowledge with appreciation to my supervisor Prof Dr Ismadi Bugis and
En Musa Yusup Lada for his valuable guidance and advice throughout the final year project. He
inspired us greatly to work, commit in this final year project. His guidance helped me all the time
of research and writing of this thesis.
Furthermore, I would like to express my gratitude to all lecturers that had been taught me
before for their continuous guidance and encouragement throughout the final year project.
Last but not least, I would like to thank to my family and friends who always support me
when I face problem in my final year project.
Vl
Abstract
Battery that widely used in electric vehicle (EV) and hybrid electric vehicle (HEV) is
Lithium-ion (Li-ion) battery. This is because these battery has higher energy density and
rechargeable. The objective of this project is to design a Li-ion battery monitoring system for
Proton PGMC electric car. The system was designed to measure of thirteen series connected 8 V
Li-ion batteries. The performance of the series batteries requires a monitoring system to measure
the individual battery voltage and its charging status. Previously, there are several measurement
methods had been used for series battery packs which are resistive divider, relay measurement
system, localized data processing and voltage transfer circuit. Hence, voltage transfer circuit
measurement system is used for this project. It must be carefully designed such that it able to
withstand relatively high voltage with higher accuracy. Furthermore, the circuit is also enhanced
with battery temperature measurement, and all the measuring data can be transferred to another
device for further manipulation. Due to the nonlinearity voltage-charge characteristic of the LiIon battery, this monitoring system requires scanning of the individual battery voltage promptly.
The result of measurement of battery voltage needed at least in range of± 1 % accuracy. This
method provides a solution which is high accuracy and low cost.
l
Vll
Abstrak
Bateri yang digunakan secara meluas bagi kenderaan elektrik dan kenderaan hibrid
elektrik ialah bateri litium-ion. Ini disebabkan kedua-dua bateri mempunyai kepadatan tenaga
yang tinggi dan boleh dicas semula. Objektif projek ini adalah merekabentuk sistem pemantauan
bateri Li-ion untuk Proton PGMC kenderaan elektrik. Sistem ini direka untuk mengukur tiga
belas 8V bateri Li-ion dipasang secara sesiri. Prestasi bateri sesiri memerlukan sistem
pemantauan untuk mengukur voltan bateri individu dan status casnya. Sebelum ini, beberapa
kaedah pengukuran telah digunakan untuk bateri pek resiri seperti pembahagi rintangan, sistem
pengukuran relay, pemprosesan data setempat dan litar pindah voltan. Oleh itu, system
pengukuran litar pindah voltan digunakan untuk projek ini. Ia perlu direka secara berhati-hati
supaya ia dapat menahan voltan yang agak tinggi dengan ketepatan yang lebih tinggi. Tambahan
pula, litar juga dipertingkatkan dengan pengukuran suhu bateri, dan semua data pengukuran
boleh dipindahkan ke peranti lain untuk manipulasi data. System pemantauan memerlukan
pengimbasan voltan bateri individu segera dengan keputusan pengukuran voltan bateri yang
diperlukan sekurang-kurangnya dalam julat ± 1 % ketepatan. Teknik ini menyediakan
penyelesaian yang ketepatan yang tinggi dan kos rendah.
l.
Vlll
TABLE OF CONTENTS
CHAPTER
TITLE
TABLE OF CONTENTS
1
2
3
PAGE
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF APPENDICES
xiii
INTRODUCTION
1
I. I Project Background
I
I .2 Problem Statement
2
I .3 Objective
3
I.4 Scope
3
1. 5 Outlines
3
LITERATURE REVIEW
4
2.1 Basic Principle
4
2.2 Research Studies
6
2.2.1 Resistive Divider Voltage Measurement System
6
2.2.2 Relay Measurement System
8
2.2.3 Localized Data Processing Measurement System
10
2.2.4 Voltage Transfer Circuit Measurement System
11
2.2.5 Environment Factor that Affect the Petformance of the Battery
13
2.3 Summary of Review
14
METHODOLOGY
15
3.1 Flow Chart
15
3 .2 Gantt Chart
17
3.3 Block Diagram of Battery Monitoring System
18
3.4 Method Selection for Battery Monitoring System
18
3 .5 Simulation Approach
19
3.5.1 Proteus
19
ix
3.5.2 MicroC
4
23
3.6 Hardware Implementation
25
3.6.1 Component Selection
25
3.6.1.1 Resistor
25
3.6.1.2 Bipolar Junction Transistor (BJT)
26
3.6.1.3 Microcontroller
27
3.6.2 Printed Circuit Board (PCB)
28
3.6.3 Testing Proton Green Mobility Challenge (PGMC) Battery
30
RESULT AND DISCUSSION
31
4.1 Temperature Test
31
4.1.1
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 26 °C
4.1.2
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 28 °C
4.1.3
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 35 °C
4.1.4
Measurement Variation due to Temperature Effect at Voltage
Supply is 7.8 V
4.1.5
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 30 °C
4.1.7
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 3 5 °C
4.1.8
Measurement Variation due to Temperature Effect at Voltage
Supply is 8.0 V
4.1.9
34
35
36
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 26 °C
4.1.6
32
Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 26 °C
4.1.10 Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 30 °C
37
38
39
40
41
42
x
4.1.11 Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 35 °C
43
4.1.12 Measurement Variation due to Temperature Effect at Voltage
Supply is 7.8 V
4.2 Duration Test
4.2.1
46
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 35 °C
5
45
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 28 °C
4.2.3
45
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 26 °C
4.2.2
44
47
CONCLUSION AND RECOMMENDATION
48
5.1 Conclusion
48
5.2 Recommendation
49
REFERENCES
50
PUBLICATION
52
APPENDIX A
53
APPENDIXB
57
XI
LIST OF TABLES
TABLE TITLE
PAGE
2.1
Battery Voltage Measurement
9
2.2
Comparison of Battery Voltage
13
3.1
Components with Part Number
24
3.2
Features of PIC16F877A
27
4.1
Average Measured Voltage at Temperature 26°C
32
Accuracy of the BMS System when Voltage Supply is 7.8 V and
4.2
Temperature is 26°C
33
Accuracy of the BMS System when Voltage Supply is 7.8 Vand
4.3
Temperature is 28°C
34
Accuracy of the BMS System when Voltage Supply is 7.8 Vand
4.4
4.5
4.6
4.7
Temperature is 35°C
Measurement Variation due to Temperature Effect at Voltage Supply is 7.8 V
Temperature is 26°C
4.10
Measurement Variation due to Temperature Effect at Voltage Supply is 8.0 V
39
40
Accuracy of the BMS System when Voltage Supply is 8.2 Vand
Accuracy of the BMS System when Voltage Supply is 8.2 V and
Temperature is 30°C
4.12
38
Accuracy of the BMS System when Voltage Supply is 8.0 Vand
Temperature is 26°C
4.11
37
Accuracy of the BMS System when Voltage Supply is 8.0 V and
Temperature is 35°C
4.9
36
Accuracy of the BMS System when Voltage Supply is 8.0 V and
Temperature is 30°C
4.8
35
41
42
Accuracy of the BMS System when Voltage Supply is 8.2 Vand
Temperature is 35°C
43
4.13
Measurement Variation due to Temperature Effect at Voltage Supply is 8.2 V
44
4.14
Duration Test when Voltage Supply is 7.8 Vand Temperature is 26°C
45
Xll
LIST OF FIGURES
FIGURE
TITLE
PAGE
Typical Battery Voltage of a Li-ion Battery during Charging or
2.1
Discharging
4
2.2
Example of Resistive Divider Network
7
2.3
Relay Measurement System
8
2.4
Accuracy of the Relay Measurement System
10
2.5
Localized Data Processing Measurement System
10
2.6
Block Diagram of Transfer Circuit Measurement System
11
2.7
Transfer Circuit Measurement System
12
2.8
Accuracy of the Transfer Circuit Measurement System
12
2.9
Temperature Characteristic of Li-ion Battery
14
3.1
Flow Chart for the Process of Designing a Battery Monitoring System
16
3.2
Block Diagram of Voltage Transfer Circuit Monitoring System
18
3.3
Measurement Voltage Transfer Circuit
20
3.4
Measurement Voltage Transfer Circuit with Voltage Supply is 7.8 V
21
3.5
Measurement Voltage Transfer Circuit with Voltage Supply is 8.2 V
21
3.6
PCB Layout for Main Board of BMS
22
3.7
PCB Layout for PIC and LCD Display of BMS
22
3.8
Coding for Display the Battery Voltage
24
3.9
Sample of resistor(± 1 % tolerance)
26
3.10
Sample of BJT (part no: ZTX 758)
26
3.11
Flow Chart of Implement PCB Board
27
3.12
PCB Layout on Tracing Paper
29
3.13
Prototype of the BMS System
29
3.14
PGMC Battery
30
4.1
Comparison between Actual Voltage and Measured Voltage at
Temperature is 26°C
33
X111
Comparison between Actual Voltage and Measured Voltage at
4.2
Temperature is 28°C
34
Comparison between Actual Voltage and Measured Voltage at
4.3
4.4
Temperature is 35°C
Measurement Variation due to Temperature Effect
35
36
Comparison between Actual Voltage and Measured Voltage at
4.5
Temperature is 26°C
37
Comparison between Actual Voltage and Measured Voltage at
4.6
Temperature is 30°C
Comparison between Actual Voltage and Measured Voltage at
4.7
4.8
Temperature is 35°C
Measurement Variation due to Temperature Effect
38
39
40
Comparison between Actual Voltage and Measured Voltage at
4.9
4.10
4.11
Temperature is 26°C
41
Comparison between Actual Voltage and Measured Voltage at
Temperature is 30°C
Comparison between Actual Voltage and Measured Voltage at
Temperature is 35°C
42
43
4.12
Measurement Variation due to Temperature Effect
44
4.13
Duration Test at Temperature 26°C
46
4.14
Duration Test at Temperature 28°C
46
4.15
Duration Test at Temperature 35°C
47
XIV
LIST OF APPENDICES
APPENDIX
A
TITLE
Publication: High Accuracy Lithium-Ion Electric
PAGE
53
Vehicle Battery Monitoring System
B
Temperature Test
57
1
Chapter 1
IlNTRODUCTION
1.1 Project Background
Battery lifespan is one of the important factors for the EV to function properly.
Nowadays, the series battery packs are mostly used in automated application such as EV
which has to scan individual battery voltage from time to time[l]. Besides, the
performance of the series battery packs in EV is very important. For flexibility and
economic reasons, the batteries that are used in EV must be a rechargeable battery.
The primary requirement for the battery packs of EV is high power capability,
high energy density, long life, high charging efficiency and light weight. Li-ion battery
and lead acid battery consist of same properties which are high energy density and high
power. Both of them are secondary batteries which are rechargeable batteries. Li-ion
batteries are becoming more commonly used compared to lead acid batteries due to lead
plates and acid electrolyte is heavier than lithium or carbon anode and lithium iron
phosphate cathode. Li-ion batteries can provide the same voltage as lead-acid batteries. In
addition, Li-ion is a rechargeable battery types in which lithium ions move from the
anode to the cathode during discharge and back when charging therefore, currently Li-ion
battery is the most suitable choice for the EV battery[3].
During operation, the battery must be charged and discharged for many times. The
battery will be damaged if there is mishandling over them. To handle battery perfectly,
one should know its condition accurately. Overcharging or over-discharging will reduce
battery lifespan[2]. Furthermore, Li-ion batteries easily to explode when overcharge
occur. Therefore, a battery monitoring system (BMS) is required to monitor and measure
the individual batteries in order to prevent damage and identify defective segments. The
battery monitoring system is designed to scan and measure the individual battery voltage
in a fast and accurate manner. Fast measurement is needed to minimize the voltage
2
measurement skew that occurs when large variation m battery before the scan 1s
completed.
Most BMS systems incorporate some form of communications between the
battery and test equipment. Some have links to other systems interfacing with the battery
for monitoring its condition or its history. Communications interfaces are also needed to
allow the user access to the battery for modifying the BMS control parameters or for
diagnostics and test.
1.2 Problem Statement
Reducing the impact of road transportation on the environment is a mandatory
task for the automotive industry all over the world. With no exhaust fumes, the EV is an
optimum solution for urban transportation. Currently, more and more electric car and
hybrid car can be seen on the road throughout the world. Most of the car implements Liion battery. Considering this, it is important to design a fast and accurate battery
monitoring system.
In this project, battery monitoring system is made to monitor the cells in 13 series
Li-ion battery. Li-ion battery has high power density and high energy density than other
types of battery. However, Li-ion battery cannot withstand overcharge. When overcharge
occur, it will have a high risk for explosion[3]. Besides, when over discharge occur, it
will shorten the battery life.
The voltage of the battery sometimes will be losing charge due to catastrophic
factors such as length of usage, length of storage and temperature[l]. However, repetition
of battery charging and discharging may cause variation battery voltages due to different
characteristics. The voltage life and storage capacity of the batteries will be affected by
the imbalance voltage. When the batteries have different voltage level, voltage will not
charge or discharged uniformly. Hence, some batteries may occur overcharged or
excessively discharged.
The battery monitoring system is required to scan and measure individual battery
with very fast and very accurate. This is because there may have large changes of battery
3
voltage occur during the scanning process. Hence, the accuracy of the BMS will be
directly affected also.
1.3 Objective
The main objectives of this project are:
1. To measure the voltage level of series connected Li-ion batteries with rapid and
high accuracy.
2. To design a voltage monitoring system for EV using Proteus 7.1.
1.4 Scope
This project will discuss on the performance of the serially connected Li-ion
batteries for EV. 13 stacks of 8 V battery connected in series are designed for battery
monitoring system with low cost, light weight and at least ± 1 % accuracy. The voltage
of individual Li-ion batteries that used in EV will be measured and compared. The battery
monitoring circuit is simulated by using software, Proteus. The hardware of the battery
monitoring system will be implemented and tested. The environmental factors that affect
the battery monitoring system will be examined.
1.5 Outlines
The design of battery monitoring system may be arbitrarily classified in the
following four categories which is operation of Li-ion battery monitoring system for EV,
measured the individual battery rapidly, accuracy of the battery monitoring system by
design the proper way of measurement and environment factors such as temperature that
affect the battery monitoring system.
4
Chapter 2
LITERATURE REVIEW
2.1 Basic Principles
As battery in EV facing a repetition charging and discharging, it can causes the
individual battery have variation voltage. The battery life will be reduced due to high or
low level of voltage. The range of the charging voltage limit (CVL) and discharging
voltage limit (DVL) for series connected battery packs shows in Figure 2.1 [4].
Small
Voltage
ｄｩｦ･ｾｮ｣＠
_J-t- - - - - -- - - - - - - - - - - - - - -
L, - - -__:.-:....:-:....::-::......::::-0---r--------ｾﾷ＠
L>tc ·L
ｬＧＭﾷＱｾ＠
---.---ｾ＠
Large difference of SOC
Figure 2.1: Typical Battery Voltage of a Li-ion Battery during Charging or Discharging
From the Figure 2.1, it can be seen that when there is a small voltage difference in
the charging process, it can cause a big difference of state of charge (SOC). There are
many factors that can affect the SOC such as temperature, battery capacitance and battery
internal resistance. During the charging process, as one of the terminal battery voltages
has exceeded the CVL limit, the process required to stop immediately. This is to prevent
5
Li-ion cell damage. It is also similar in the discharging process. As one of the terminal
battery voltages has exceeded the DVL limit. At this point, the process required to stop
immediately. Charging of the battery stack cannot be continued as one cell is completely
charged although others are not. When one the cell is totally empty, the process of
discharging of battery stack required to stop as well.
The SOC of a battery, which is used to describe its remaining capacity, is a very
important parameter for a control strategy. Battery SOC is an important parameter, which
reflects the battery performance and capacity. Hence accurate estimation of the SOC not
only protects battery, it also prevents over-discharge, and improves the battery life.
Besides that, it allows the application to make rational control strategies to save more
energy. The units of SOC are in percentage points which 0 % for empty and 100 % for
full respectively. An alternate form of the same measure is the depth of discharge (DOD),
which is vice versa of SOC. DOD is the percentage of energy withdrawn from a battery
compared to its fully charged capacity. The maximum percentage of total capacity that is
permitted to be withdrawn from a battery is called operational capacity of the battery.
For the large Lithium batteries, SOC is particularly important. This is because
Lithium is the most chemically reactive of all the common cell chemistries. Hence
Lithium batteries require electronic BMS to keep the battery within a safe operating
window and to ensure a long cycle life. The major function of the BMS is to control the
SOC. Furthermore, most of the automotive applications uses of large number of Lithium
batteries. Hence, it needs very precise control of the SOC for efficient and safe
management of the energy flows. In EV applications, the SOC is used to determine range
of battery capacity.
The performance of a battery stack with different single-cell capacities can
significantly be increased when the charge from the cells is equalized with an electronic
circuit. This technique called cell balancing. Cell balancing is a technique used to
maintain equal or near equal voltage-levels on all cells in a battery pack. This only can be
applied for that connected in series, as cells connected in parallel will be self-balancing.
The main reason for keeping cells in balance is to keep the batteries capacity as high as
6
possible throughout its lifespan. The battery monitoring system is a protocol for which a
battery system can communicate to human being. It can display the cell number and
voltage values of the highest and lowest cells.
2.2 Research Studies
The general concept of voltage measurement for series battery pack is to measure
the voltage of individual battery. Each measurement from the battery packs requires
transfer circuit to transfer individual battery voltage to the ground reference such that the
measurement voltage safe to operational amplifier and multiplexer, and furthermore it can
be used by the data processing system and displays the battery voltage[2]. The actual
values of battery SOC can be predicted using voltage data combined with the voltagecharge characteristic. The measured values of the cell voltages can be obtained from the
battery monitoring system. The BMS is a protocol for which a battery system can
communicate to human being. It can display the cell number and voltage values of the
highest and lowest cells. There are several methods used in voltage measurement system
of series battery packs. The operation, advantage and disadvantage of each method will
be discussed as below. The environment factors such as temperature that affect the
performance of the battery monitoring system will be analyzed.
2.2.1 Resistive Divider Voltage Measurement System
The resistive divider voltage measurement system is the most common method
used to measures battery voltage. This system is the simplest way to scale down a voltage
and minimized the high impedances. The voltage of each cell can be measure at each
node by using voltage dividers as shown in Figure 2.2. The general formula for resister
divider concept is as shown 2.1.
VB(n+l)
V
= RnRcn+1)
+R (n+1) B(n)
(2.1)
7
YB4
\':BJ
,,,
,,,
YB2
R2
R.;
+
ＱｾＭ
+
-
R1
!
RI
l°Bl
nu
r·
+
Figure 2.2: Example of Resistive Divider Network
The disadvantage of this method is it must provide switches to prevent the
resistors from drawing current from the battery when not in use[l-2]. Besides that,
voltages near the top of stack require very accurate divider ratios. For example, consider
the top battery contains a stack of n VDC batteries. Then,
(2.2)
; where n = 1,2 ...
If the ideal values of Kn as defined in Figure 2 are
1
Kn=n
(2.3)
(2.4)
Tr _ nVnc _ nVnc _
vn -
Kn
-
n
1
-
n
Z1r
vvc
(2.5)
If the actual of Kn is in error by + 1 %, then it will affect the actual value of Vn by
increase + I %. Therefore, the accuracy of this system can be directly affected by the
divider ratios, Kn[l-2].
8
2.2.2 Relay Measurement System
In this system, small electromechanical relay is used to send the signal to the
isolation amplifier as shown in Figure 2.3. All the relays are grouped into rows, which in
tum divide the stack so that one battery voltage appears as the output of the last row. The
isolation amplifier is used to provide galvanic isolation between the batteries and data
processing circuitry[2].
Figure 2.3: Relay Measurement System
The disadvantage of the relay measurement system is high cost and slow response.
The signal that sent to the isolation amplifier takes longer time to transfer the battery
voltage level. This is due to it requires time to energize or de-energize the relay. When
the current flowing through the contactor coil, the electromagnet started to energize. Thus,
the contactor will closed causing short circuit for the power to load. Once, the
electromagnet de-energized, the contactor will opened. No current will flowing through
the load. Hence, delay occurs in this system. From the previous experiment result, Table
2.1 shows the accuracy of the relay measurement system[2].
9
Table 2.1: Battery Voltage Measurement
Battery
Measured Value (V)
Actual Value (V)
Accuracy (%)
Bl
12.62
12.59
76
B2
12.65
12.62
76
B3
12.56
12.60
68
B4
12.60
12.63
76
B5
12.58
12.61
76
B6
12.57
12.60
76
B7
12.56
12.60
68
B8
12.59
12.63
68
B9
12.60
12.63
76
BIO
12.59
12.62
76
Bll
12.57
12.61
68
B12
12.51
12.55
68
By using the Equation (2.6) and (2. 7), the accuracy of each cell can be calculated.
I
actual value-meausred value
I
error= - - -actual
- -value
----
(2.6)
Accuracy of each battery(%)= (1- error) x 100%
(2.7)
Figure 2.4 shows the accuracy of the relay measurement system. The accuracy of
the whole system is 72.67 % and it can be calculated by using Equation (2.8). Therefore,
the accuracy of this system is average.
Accuracy of whole system= l.Bn
n
(2.8)
10
Accuracy (%)
80
-+-Accuracy(%)
Bl
B2
B3
B4
BS
BG
B7
BB
B9
BlO
Bll
B12
Figure 2.4: Accuracy of the Relay Measurement System
2.2.3 Localized Data Processing Measurement System
For this system, it is an expensive system due to it is using one microcontroller for
one cell as shown in the Figure 2.5[1]. Besides that, it also consists of analog-to-digital
converter and a galvanic isolated serial port. Galvanic isolation is a principle of isolating
functional sections of electrical systems to prevent current flow; no direct conduction
path is permitted for example fibre optic. For the communication of microcontroller and
central processing unit (CPU), a serial data link is used in this system. All the commands
in the microcontroller will be recorded in the CPU[l].
AD
ｾ＠
ＱＭｾ
ｾｦｩ｣ｲｯｮｴｂ･＠
ＭｾＫ＠
Isolated
Serial Port
ＱＭｾ＠
Ylh
-=-G:s
Serial Data Link
Figure 2.5: Localized Data Processing Measurement System
r
!
11
2.2.4 Voltage Transfer Circuit Measurement System
Operational amplifier (Op-amps) and bipolar junction transistor (BJT) is used to
designed the voltage transfer circuit measurement system[l-2]. The block diagram of
voltage transfer circuit measurement system is shown in Figure 2.6.
. . - - - - - . 1 - - - - 1 ｉｾｯｬ｡ｴｩｮ＠
.___-1 .Multiplexer i - - - r - - 1 ,
+ , .....
_
:uup
lifilff
.oi
_
llkrocontroller
Figure 2.6: Block Diagram of Transfer Circuit Measurement System
The transfer circuit measurement system is shown in Figure 2.7. These circuits
require a lot of discrete components such as MOSFET, BJT, resistor, Op-amps, analogto-digital converter (ADC) and microcontroller. The function of the MOSFET and BJT is
to prevent current leakage when the system not in use[l-2]. Voltage signal will send to
the ADC, it can convert the analog signal to digital signal. The digital signal is then sent
to the microcontroller to process. Then the microcontroller will display all the voltage on
the PC monitor. To improve the system, sample and hold function can be added in the
transfer circuit. The function of sample and hold is to prevent voltage skew problem
caused by rapid variation in battery current[ 1-2]. It also acts as measurement scan. The
initial tolerance can be reduced to a very low level.
"I hereby declare that I have read through this report entitle "High Accuracy Lithium-ion Electric
Vehicle Battery Monitoring System" and found that it has comply the partial fulfillment for
awarding the degree of Bachelor of Electrical Engineering (Control, Instrumentation and
Automation)"
Signature
Supervisor name
En. Musa Yusup Lada
Date
Lvi
......t'Jo
:.l.......G/10
........................
.
111
HIGH ACCURACY LITHIUM-ION ELECTRIC VEHICLE BATTERY MONITORING
SYSTEM
CHAWPUILING
A report submitted in partial fulfillment of the requirements for the degree of Bachelor in
Electrical Engineering (Control, Instrumentations and Instrumentations)
Faculty of Electrical Engineering
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2014
IV
I declare that this report entitle "High Accuracy Lithium-ion Electric Vehicle Battery Monitoring
System" is the result of my own research except as cited in references. The report has not been
accepted for any degree and is not concurrently submitted in candidature of any other degree.
Signature
Name
Date
Chaw Pui Ling
t=t-(b [,-01\f
................... ······ ... ······ ...... .
v
Acknowledgement
First of all, I acknowledge with appreciation to my supervisor Prof Dr Ismadi Bugis and
En Musa Yusup Lada for his valuable guidance and advice throughout the final year project. He
inspired us greatly to work, commit in this final year project. His guidance helped me all the time
of research and writing of this thesis.
Furthermore, I would like to express my gratitude to all lecturers that had been taught me
before for their continuous guidance and encouragement throughout the final year project.
Last but not least, I would like to thank to my family and friends who always support me
when I face problem in my final year project.
Vl
Abstract
Battery that widely used in electric vehicle (EV) and hybrid electric vehicle (HEV) is
Lithium-ion (Li-ion) battery. This is because these battery has higher energy density and
rechargeable. The objective of this project is to design a Li-ion battery monitoring system for
Proton PGMC electric car. The system was designed to measure of thirteen series connected 8 V
Li-ion batteries. The performance of the series batteries requires a monitoring system to measure
the individual battery voltage and its charging status. Previously, there are several measurement
methods had been used for series battery packs which are resistive divider, relay measurement
system, localized data processing and voltage transfer circuit. Hence, voltage transfer circuit
measurement system is used for this project. It must be carefully designed such that it able to
withstand relatively high voltage with higher accuracy. Furthermore, the circuit is also enhanced
with battery temperature measurement, and all the measuring data can be transferred to another
device for further manipulation. Due to the nonlinearity voltage-charge characteristic of the LiIon battery, this monitoring system requires scanning of the individual battery voltage promptly.
The result of measurement of battery voltage needed at least in range of± 1 % accuracy. This
method provides a solution which is high accuracy and low cost.
l
Vll
Abstrak
Bateri yang digunakan secara meluas bagi kenderaan elektrik dan kenderaan hibrid
elektrik ialah bateri litium-ion. Ini disebabkan kedua-dua bateri mempunyai kepadatan tenaga
yang tinggi dan boleh dicas semula. Objektif projek ini adalah merekabentuk sistem pemantauan
bateri Li-ion untuk Proton PGMC kenderaan elektrik. Sistem ini direka untuk mengukur tiga
belas 8V bateri Li-ion dipasang secara sesiri. Prestasi bateri sesiri memerlukan sistem
pemantauan untuk mengukur voltan bateri individu dan status casnya. Sebelum ini, beberapa
kaedah pengukuran telah digunakan untuk bateri pek resiri seperti pembahagi rintangan, sistem
pengukuran relay, pemprosesan data setempat dan litar pindah voltan. Oleh itu, system
pengukuran litar pindah voltan digunakan untuk projek ini. Ia perlu direka secara berhati-hati
supaya ia dapat menahan voltan yang agak tinggi dengan ketepatan yang lebih tinggi. Tambahan
pula, litar juga dipertingkatkan dengan pengukuran suhu bateri, dan semua data pengukuran
boleh dipindahkan ke peranti lain untuk manipulasi data. System pemantauan memerlukan
pengimbasan voltan bateri individu segera dengan keputusan pengukuran voltan bateri yang
diperlukan sekurang-kurangnya dalam julat ± 1 % ketepatan. Teknik ini menyediakan
penyelesaian yang ketepatan yang tinggi dan kos rendah.
l.
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TABLE OF CONTENTS
CHAPTER
TITLE
TABLE OF CONTENTS
1
2
3
PAGE
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF APPENDICES
xiii
INTRODUCTION
1
I. I Project Background
I
I .2 Problem Statement
2
I .3 Objective
3
I.4 Scope
3
1. 5 Outlines
3
LITERATURE REVIEW
4
2.1 Basic Principle
4
2.2 Research Studies
6
2.2.1 Resistive Divider Voltage Measurement System
6
2.2.2 Relay Measurement System
8
2.2.3 Localized Data Processing Measurement System
10
2.2.4 Voltage Transfer Circuit Measurement System
11
2.2.5 Environment Factor that Affect the Petformance of the Battery
13
2.3 Summary of Review
14
METHODOLOGY
15
3.1 Flow Chart
15
3 .2 Gantt Chart
17
3.3 Block Diagram of Battery Monitoring System
18
3.4 Method Selection for Battery Monitoring System
18
3 .5 Simulation Approach
19
3.5.1 Proteus
19
ix
3.5.2 MicroC
4
23
3.6 Hardware Implementation
25
3.6.1 Component Selection
25
3.6.1.1 Resistor
25
3.6.1.2 Bipolar Junction Transistor (BJT)
26
3.6.1.3 Microcontroller
27
3.6.2 Printed Circuit Board (PCB)
28
3.6.3 Testing Proton Green Mobility Challenge (PGMC) Battery
30
RESULT AND DISCUSSION
31
4.1 Temperature Test
31
4.1.1
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 26 °C
4.1.2
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 28 °C
4.1.3
Temperature Test when Supply Voltage, Vs is 7.8 Vat
Temperature 35 °C
4.1.4
Measurement Variation due to Temperature Effect at Voltage
Supply is 7.8 V
4.1.5
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 30 °C
4.1.7
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 3 5 °C
4.1.8
Measurement Variation due to Temperature Effect at Voltage
Supply is 8.0 V
4.1.9
34
35
36
Temperature Test when Supply Voltage, Vs is 8.0 Vat
Temperature 26 °C
4.1.6
32
Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 26 °C
4.1.10 Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 30 °C
37
38
39
40
41
42
x
4.1.11 Temperature Test when Supply Voltage, Vs is 8.2 Vat
Temperature 35 °C
43
4.1.12 Measurement Variation due to Temperature Effect at Voltage
Supply is 7.8 V
4.2 Duration Test
4.2.1
46
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 35 °C
5
45
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 28 °C
4.2.3
45
Duration Test when Voltage Supply, Vs is 7.8 Vat
Temperature 26 °C
4.2.2
44
47
CONCLUSION AND RECOMMENDATION
48
5.1 Conclusion
48
5.2 Recommendation
49
REFERENCES
50
PUBLICATION
52
APPENDIX A
53
APPENDIXB
57
XI
LIST OF TABLES
TABLE TITLE
PAGE
2.1
Battery Voltage Measurement
9
2.2
Comparison of Battery Voltage
13
3.1
Components with Part Number
24
3.2
Features of PIC16F877A
27
4.1
Average Measured Voltage at Temperature 26°C
32
Accuracy of the BMS System when Voltage Supply is 7.8 V and
4.2
Temperature is 26°C
33
Accuracy of the BMS System when Voltage Supply is 7.8 Vand
4.3
Temperature is 28°C
34
Accuracy of the BMS System when Voltage Supply is 7.8 Vand
4.4
4.5
4.6
4.7
Temperature is 35°C
Measurement Variation due to Temperature Effect at Voltage Supply is 7.8 V
Temperature is 26°C
4.10
Measurement Variation due to Temperature Effect at Voltage Supply is 8.0 V
39
40
Accuracy of the BMS System when Voltage Supply is 8.2 Vand
Accuracy of the BMS System when Voltage Supply is 8.2 V and
Temperature is 30°C
4.12
38
Accuracy of the BMS System when Voltage Supply is 8.0 Vand
Temperature is 26°C
4.11
37
Accuracy of the BMS System when Voltage Supply is 8.0 V and
Temperature is 35°C
4.9
36
Accuracy of the BMS System when Voltage Supply is 8.0 V and
Temperature is 30°C
4.8
35
41
42
Accuracy of the BMS System when Voltage Supply is 8.2 Vand
Temperature is 35°C
43
4.13
Measurement Variation due to Temperature Effect at Voltage Supply is 8.2 V
44
4.14
Duration Test when Voltage Supply is 7.8 Vand Temperature is 26°C
45
Xll
LIST OF FIGURES
FIGURE
TITLE
PAGE
Typical Battery Voltage of a Li-ion Battery during Charging or
2.1
Discharging
4
2.2
Example of Resistive Divider Network
7
2.3
Relay Measurement System
8
2.4
Accuracy of the Relay Measurement System
10
2.5
Localized Data Processing Measurement System
10
2.6
Block Diagram of Transfer Circuit Measurement System
11
2.7
Transfer Circuit Measurement System
12
2.8
Accuracy of the Transfer Circuit Measurement System
12
2.9
Temperature Characteristic of Li-ion Battery
14
3.1
Flow Chart for the Process of Designing a Battery Monitoring System
16
3.2
Block Diagram of Voltage Transfer Circuit Monitoring System
18
3.3
Measurement Voltage Transfer Circuit
20
3.4
Measurement Voltage Transfer Circuit with Voltage Supply is 7.8 V
21
3.5
Measurement Voltage Transfer Circuit with Voltage Supply is 8.2 V
21
3.6
PCB Layout for Main Board of BMS
22
3.7
PCB Layout for PIC and LCD Display of BMS
22
3.8
Coding for Display the Battery Voltage
24
3.9
Sample of resistor(± 1 % tolerance)
26
3.10
Sample of BJT (part no: ZTX 758)
26
3.11
Flow Chart of Implement PCB Board
27
3.12
PCB Layout on Tracing Paper
29
3.13
Prototype of the BMS System
29
3.14
PGMC Battery
30
4.1
Comparison between Actual Voltage and Measured Voltage at
Temperature is 26°C
33
X111
Comparison between Actual Voltage and Measured Voltage at
4.2
Temperature is 28°C
34
Comparison between Actual Voltage and Measured Voltage at
4.3
4.4
Temperature is 35°C
Measurement Variation due to Temperature Effect
35
36
Comparison between Actual Voltage and Measured Voltage at
4.5
Temperature is 26°C
37
Comparison between Actual Voltage and Measured Voltage at
4.6
Temperature is 30°C
Comparison between Actual Voltage and Measured Voltage at
4.7
4.8
Temperature is 35°C
Measurement Variation due to Temperature Effect
38
39
40
Comparison between Actual Voltage and Measured Voltage at
4.9
4.10
4.11
Temperature is 26°C
41
Comparison between Actual Voltage and Measured Voltage at
Temperature is 30°C
Comparison between Actual Voltage and Measured Voltage at
Temperature is 35°C
42
43
4.12
Measurement Variation due to Temperature Effect
44
4.13
Duration Test at Temperature 26°C
46
4.14
Duration Test at Temperature 28°C
46
4.15
Duration Test at Temperature 35°C
47
XIV
LIST OF APPENDICES
APPENDIX
A
TITLE
Publication: High Accuracy Lithium-Ion Electric
PAGE
53
Vehicle Battery Monitoring System
B
Temperature Test
57
1
Chapter 1
IlNTRODUCTION
1.1 Project Background
Battery lifespan is one of the important factors for the EV to function properly.
Nowadays, the series battery packs are mostly used in automated application such as EV
which has to scan individual battery voltage from time to time[l]. Besides, the
performance of the series battery packs in EV is very important. For flexibility and
economic reasons, the batteries that are used in EV must be a rechargeable battery.
The primary requirement for the battery packs of EV is high power capability,
high energy density, long life, high charging efficiency and light weight. Li-ion battery
and lead acid battery consist of same properties which are high energy density and high
power. Both of them are secondary batteries which are rechargeable batteries. Li-ion
batteries are becoming more commonly used compared to lead acid batteries due to lead
plates and acid electrolyte is heavier than lithium or carbon anode and lithium iron
phosphate cathode. Li-ion batteries can provide the same voltage as lead-acid batteries. In
addition, Li-ion is a rechargeable battery types in which lithium ions move from the
anode to the cathode during discharge and back when charging therefore, currently Li-ion
battery is the most suitable choice for the EV battery[3].
During operation, the battery must be charged and discharged for many times. The
battery will be damaged if there is mishandling over them. To handle battery perfectly,
one should know its condition accurately. Overcharging or over-discharging will reduce
battery lifespan[2]. Furthermore, Li-ion batteries easily to explode when overcharge
occur. Therefore, a battery monitoring system (BMS) is required to monitor and measure
the individual batteries in order to prevent damage and identify defective segments. The
battery monitoring system is designed to scan and measure the individual battery voltage
in a fast and accurate manner. Fast measurement is needed to minimize the voltage
2
measurement skew that occurs when large variation m battery before the scan 1s
completed.
Most BMS systems incorporate some form of communications between the
battery and test equipment. Some have links to other systems interfacing with the battery
for monitoring its condition or its history. Communications interfaces are also needed to
allow the user access to the battery for modifying the BMS control parameters or for
diagnostics and test.
1.2 Problem Statement
Reducing the impact of road transportation on the environment is a mandatory
task for the automotive industry all over the world. With no exhaust fumes, the EV is an
optimum solution for urban transportation. Currently, more and more electric car and
hybrid car can be seen on the road throughout the world. Most of the car implements Liion battery. Considering this, it is important to design a fast and accurate battery
monitoring system.
In this project, battery monitoring system is made to monitor the cells in 13 series
Li-ion battery. Li-ion battery has high power density and high energy density than other
types of battery. However, Li-ion battery cannot withstand overcharge. When overcharge
occur, it will have a high risk for explosion[3]. Besides, when over discharge occur, it
will shorten the battery life.
The voltage of the battery sometimes will be losing charge due to catastrophic
factors such as length of usage, length of storage and temperature[l]. However, repetition
of battery charging and discharging may cause variation battery voltages due to different
characteristics. The voltage life and storage capacity of the batteries will be affected by
the imbalance voltage. When the batteries have different voltage level, voltage will not
charge or discharged uniformly. Hence, some batteries may occur overcharged or
excessively discharged.
The battery monitoring system is required to scan and measure individual battery
with very fast and very accurate. This is because there may have large changes of battery
3
voltage occur during the scanning process. Hence, the accuracy of the BMS will be
directly affected also.
1.3 Objective
The main objectives of this project are:
1. To measure the voltage level of series connected Li-ion batteries with rapid and
high accuracy.
2. To design a voltage monitoring system for EV using Proteus 7.1.
1.4 Scope
This project will discuss on the performance of the serially connected Li-ion
batteries for EV. 13 stacks of 8 V battery connected in series are designed for battery
monitoring system with low cost, light weight and at least ± 1 % accuracy. The voltage
of individual Li-ion batteries that used in EV will be measured and compared. The battery
monitoring circuit is simulated by using software, Proteus. The hardware of the battery
monitoring system will be implemented and tested. The environmental factors that affect
the battery monitoring system will be examined.
1.5 Outlines
The design of battery monitoring system may be arbitrarily classified in the
following four categories which is operation of Li-ion battery monitoring system for EV,
measured the individual battery rapidly, accuracy of the battery monitoring system by
design the proper way of measurement and environment factors such as temperature that
affect the battery monitoring system.
4
Chapter 2
LITERATURE REVIEW
2.1 Basic Principles
As battery in EV facing a repetition charging and discharging, it can causes the
individual battery have variation voltage. The battery life will be reduced due to high or
low level of voltage. The range of the charging voltage limit (CVL) and discharging
voltage limit (DVL) for series connected battery packs shows in Figure 2.1 [4].
Small
Voltage
ｄｩｦ･ｾｮ｣＠
_J-t- - - - - -- - - - - - - - - - - - - - -
L, - - -__:.-:....:-:....::-::......::::-0---r--------ｾﾷ＠
L>tc ·L
ｬＧＭﾷＱｾ＠
---.---ｾ＠
Large difference of SOC
Figure 2.1: Typical Battery Voltage of a Li-ion Battery during Charging or Discharging
From the Figure 2.1, it can be seen that when there is a small voltage difference in
the charging process, it can cause a big difference of state of charge (SOC). There are
many factors that can affect the SOC such as temperature, battery capacitance and battery
internal resistance. During the charging process, as one of the terminal battery voltages
has exceeded the CVL limit, the process required to stop immediately. This is to prevent
5
Li-ion cell damage. It is also similar in the discharging process. As one of the terminal
battery voltages has exceeded the DVL limit. At this point, the process required to stop
immediately. Charging of the battery stack cannot be continued as one cell is completely
charged although others are not. When one the cell is totally empty, the process of
discharging of battery stack required to stop as well.
The SOC of a battery, which is used to describe its remaining capacity, is a very
important parameter for a control strategy. Battery SOC is an important parameter, which
reflects the battery performance and capacity. Hence accurate estimation of the SOC not
only protects battery, it also prevents over-discharge, and improves the battery life.
Besides that, it allows the application to make rational control strategies to save more
energy. The units of SOC are in percentage points which 0 % for empty and 100 % for
full respectively. An alternate form of the same measure is the depth of discharge (DOD),
which is vice versa of SOC. DOD is the percentage of energy withdrawn from a battery
compared to its fully charged capacity. The maximum percentage of total capacity that is
permitted to be withdrawn from a battery is called operational capacity of the battery.
For the large Lithium batteries, SOC is particularly important. This is because
Lithium is the most chemically reactive of all the common cell chemistries. Hence
Lithium batteries require electronic BMS to keep the battery within a safe operating
window and to ensure a long cycle life. The major function of the BMS is to control the
SOC. Furthermore, most of the automotive applications uses of large number of Lithium
batteries. Hence, it needs very precise control of the SOC for efficient and safe
management of the energy flows. In EV applications, the SOC is used to determine range
of battery capacity.
The performance of a battery stack with different single-cell capacities can
significantly be increased when the charge from the cells is equalized with an electronic
circuit. This technique called cell balancing. Cell balancing is a technique used to
maintain equal or near equal voltage-levels on all cells in a battery pack. This only can be
applied for that connected in series, as cells connected in parallel will be self-balancing.
The main reason for keeping cells in balance is to keep the batteries capacity as high as
6
possible throughout its lifespan. The battery monitoring system is a protocol for which a
battery system can communicate to human being. It can display the cell number and
voltage values of the highest and lowest cells.
2.2 Research Studies
The general concept of voltage measurement for series battery pack is to measure
the voltage of individual battery. Each measurement from the battery packs requires
transfer circuit to transfer individual battery voltage to the ground reference such that the
measurement voltage safe to operational amplifier and multiplexer, and furthermore it can
be used by the data processing system and displays the battery voltage[2]. The actual
values of battery SOC can be predicted using voltage data combined with the voltagecharge characteristic. The measured values of the cell voltages can be obtained from the
battery monitoring system. The BMS is a protocol for which a battery system can
communicate to human being. It can display the cell number and voltage values of the
highest and lowest cells. There are several methods used in voltage measurement system
of series battery packs. The operation, advantage and disadvantage of each method will
be discussed as below. The environment factors such as temperature that affect the
performance of the battery monitoring system will be analyzed.
2.2.1 Resistive Divider Voltage Measurement System
The resistive divider voltage measurement system is the most common method
used to measures battery voltage. This system is the simplest way to scale down a voltage
and minimized the high impedances. The voltage of each cell can be measure at each
node by using voltage dividers as shown in Figure 2.2. The general formula for resister
divider concept is as shown 2.1.
VB(n+l)
V
= RnRcn+1)
+R (n+1) B(n)
(2.1)
7
YB4
\':BJ
,,,
,,,
YB2
R2
R.;
+
ＱｾＭ
+
-
R1
!
RI
l°Bl
nu
r·
+
Figure 2.2: Example of Resistive Divider Network
The disadvantage of this method is it must provide switches to prevent the
resistors from drawing current from the battery when not in use[l-2]. Besides that,
voltages near the top of stack require very accurate divider ratios. For example, consider
the top battery contains a stack of n VDC batteries. Then,
(2.2)
; where n = 1,2 ...
If the ideal values of Kn as defined in Figure 2 are
1
Kn=n
(2.3)
(2.4)
Tr _ nVnc _ nVnc _
vn -
Kn
-
n
1
-
n
Z1r
vvc
(2.5)
If the actual of Kn is in error by + 1 %, then it will affect the actual value of Vn by
increase + I %. Therefore, the accuracy of this system can be directly affected by the
divider ratios, Kn[l-2].
8
2.2.2 Relay Measurement System
In this system, small electromechanical relay is used to send the signal to the
isolation amplifier as shown in Figure 2.3. All the relays are grouped into rows, which in
tum divide the stack so that one battery voltage appears as the output of the last row. The
isolation amplifier is used to provide galvanic isolation between the batteries and data
processing circuitry[2].
Figure 2.3: Relay Measurement System
The disadvantage of the relay measurement system is high cost and slow response.
The signal that sent to the isolation amplifier takes longer time to transfer the battery
voltage level. This is due to it requires time to energize or de-energize the relay. When
the current flowing through the contactor coil, the electromagnet started to energize. Thus,
the contactor will closed causing short circuit for the power to load. Once, the
electromagnet de-energized, the contactor will opened. No current will flowing through
the load. Hence, delay occurs in this system. From the previous experiment result, Table
2.1 shows the accuracy of the relay measurement system[2].
9
Table 2.1: Battery Voltage Measurement
Battery
Measured Value (V)
Actual Value (V)
Accuracy (%)
Bl
12.62
12.59
76
B2
12.65
12.62
76
B3
12.56
12.60
68
B4
12.60
12.63
76
B5
12.58
12.61
76
B6
12.57
12.60
76
B7
12.56
12.60
68
B8
12.59
12.63
68
B9
12.60
12.63
76
BIO
12.59
12.62
76
Bll
12.57
12.61
68
B12
12.51
12.55
68
By using the Equation (2.6) and (2. 7), the accuracy of each cell can be calculated.
I
actual value-meausred value
I
error= - - -actual
- -value
----
(2.6)
Accuracy of each battery(%)= (1- error) x 100%
(2.7)
Figure 2.4 shows the accuracy of the relay measurement system. The accuracy of
the whole system is 72.67 % and it can be calculated by using Equation (2.8). Therefore,
the accuracy of this system is average.
Accuracy of whole system= l.Bn
n
(2.8)
10
Accuracy (%)
80
-+-Accuracy(%)
Bl
B2
B3
B4
BS
BG
B7
BB
B9
BlO
Bll
B12
Figure 2.4: Accuracy of the Relay Measurement System
2.2.3 Localized Data Processing Measurement System
For this system, it is an expensive system due to it is using one microcontroller for
one cell as shown in the Figure 2.5[1]. Besides that, it also consists of analog-to-digital
converter and a galvanic isolated serial port. Galvanic isolation is a principle of isolating
functional sections of electrical systems to prevent current flow; no direct conduction
path is permitted for example fibre optic. For the communication of microcontroller and
central processing unit (CPU), a serial data link is used in this system. All the commands
in the microcontroller will be recorded in the CPU[l].
AD
ｾ＠
ＱＭｾ
ｾｦｩ｣ｲｯｮｴｂ･＠
ＭｾＫ＠
Isolated
Serial Port
ＱＭｾ＠
Ylh
-=-G:s
Serial Data Link
Figure 2.5: Localized Data Processing Measurement System
r
!
11
2.2.4 Voltage Transfer Circuit Measurement System
Operational amplifier (Op-amps) and bipolar junction transistor (BJT) is used to
designed the voltage transfer circuit measurement system[l-2]. The block diagram of
voltage transfer circuit measurement system is shown in Figure 2.6.
. . - - - - - . 1 - - - - 1 ｉｾｯｬ｡ｴｩｮ＠
.___-1 .Multiplexer i - - - r - - 1 ,
+ , .....
_
:uup
lifilff
.oi
_
llkrocontroller
Figure 2.6: Block Diagram of Transfer Circuit Measurement System
The transfer circuit measurement system is shown in Figure 2.7. These circuits
require a lot of discrete components such as MOSFET, BJT, resistor, Op-amps, analogto-digital converter (ADC) and microcontroller. The function of the MOSFET and BJT is
to prevent current leakage when the system not in use[l-2]. Voltage signal will send to
the ADC, it can convert the analog signal to digital signal. The digital signal is then sent
to the microcontroller to process. Then the microcontroller will display all the voltage on
the PC monitor. To improve the system, sample and hold function can be added in the
transfer circuit. The function of sample and hold is to prevent voltage skew problem
caused by rapid variation in battery current[ 1-2]. It also acts as measurement scan. The
initial tolerance can be reduced to a very low level.