Download Multi-Cell Lithium Ion Battery Management System

2011
Multi-Cell Lithium Ion Battery Management System
-For Electric Vehicles
Final Report
Iowa State University
Team: Sdmay11-04
Pramit Tamrakar
Jimmy Skadal
Matthew Schulte
Hao Wang
William Zimmerman
4/28/2011
Table of Contents
Definitions..................................................................................................................................................... 6
Executive Summary ...................................................................................................................................... 7
Acknowledgement ........................................................................................................................................ 8
Statement and Approach ............................................................................................................................... 8
Problem Statement .................................................................................................................................... 8
Solution Approach .................................................................................................................................... 8
Operating Environment ................................................................................................................................. 9
Intended Users and Intended Uses ................................................................................................................ 9
Intended Users .......................................................................................................................................... 9
Intended Uses ............................................................................................................................................ 9
Assumptions and Limitations ..................................................................................................................... 10
Assumptions............................................................................................................................................ 10
Limitations .............................................................................................................................................. 10
Expected End Product ................................................................................................................................. 10
System Design Approach ............................................................................................................................ 11
Functional Requirements ........................................................................................................................ 11
Non Functional Requirements ................................................................................................................ 11
Market Alternatives ................................................................................................................................ 12
Proposed Approach and statement of work ................................................................................................ 13
Proposed Approach ................................................................................................................................. 13
Constraints considerations .................................................................................................................. 13
Technology Consideration .................................................................................................................. 13
Comparison of two similar integrated circuits from Texas Instruments: ............................................ 16
Detailed Design ........................................................................................................................................... 17
Boost Converter .......................................................................................................................................... 17
Boost Converter Control ......................................................................................................................... 19
Implementation and Testing: Boost Converter ....................................................................................... 20
Testing of the Boost Converter ............................................................................................................... 21
Boost Converter Test Results.................................................................................................................. 22
Boost converter Usage ............................................................................................................................ 25
Battery Management System ...................................................................................................................... 26
Cell monitoring and regulating ............................................................................................................... 26
Page | 1
Technical Approach ................................................................................................................................ 26
Implementation and Testing for the BMS: bq76PL536EVM-3 ................................................................. 27
Implementation of multiple EVM Stacking ............................................................................................ 29
Testing of the bq76PL536EVM-3........................................................................................................... 30
DC Power Supply - EVM Test ........................................................................................................... 30
DC Power Supply – EVM Test Results .............................................................................................. 30
EVM Stack Testing ............................................................................................................................. 31
EVM Stacking Test Results ................................................................................................................ 31
Implementation and Testing of Complete System ...................................................................................... 32
Complete System Test – Charging Cycle ............................................................................................... 32
TI analog design contest ............................................................................................................................. 33
MSP430G2231........................................................................................................................................ 33
MSP430F5529 ........................................................................................................................................ 33
bq76PL536EVM-3 .................................................................................................................................. 33
UCC27322 MOSFET driver ................................................................................................................... 33
OPA335 .................................................................................................................................................. 33
Security Consideration ................................................................................................................................ 34
Safety Consideration ................................................................................................................................... 34
Intellectual Property Consideration ............................................................................................................ 34
Commercialization considerations .............................................................................................................. 34
Possible risks and risk management............................................................................................................ 35
Schedule ...................................................................................................................................................... 36
Hardware/Software Statement of work ....................................................................................................... 37
Resources .................................................................................................................................................... 38
Future Work ................................................................................................................................................ 39
Closing Summary........................................................................................................................................ 39
Project Team Information ........................................................................................................................... 40
Client’s Information ................................................................................................................................ 40
Faculty advisor Information .................................................................................................................... 40
Student Team Information ...................................................................................................................... 40
References ................................................................................................................................................... 41
Appendix A ................................................................................................................................................. 43
Appendix B ................................................................................................................................................. 44
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Appendix C ................................................................................................................................................. 57
Appendix D ................................................................................................................................................. 61
Appendix E ................................................................................................................................................. 63
Appendix F.................................................................................................................................................. 68
Appendix G ................................................................................................................................................. 70
Operational Manual by 491 Team .......................................................................................................... 70
Appendix F.................................................................................................................................................. 72
Constant current test code ....................................................................................................................... 72
Appendix G ................................................................................................................................................. 74
Constant voltage test code ...................................................................................................................... 74
Appendix H ................................................................................................................................................. 76
Full system code ..................................................................................................................................... 76
Appendix I .................................................................................................................................................. 81
3.3V Regulated source from 12V ........................................................................................................... 81
Page | 3
Table of Figures
Figure 1: The NLG503-light battery charger. 1.6 kW 200-540V, $2,145 (Brusa) ........................................ 12
Figure 2: Hardware Functional Block Diagram .......................................................................................... 14
Figure 3: Large scale system diagram ......................................................................................................... 14
Figure 4: Small Scale system diagram ......................................................................................................... 15
Figure 5: Software Functional Block Diagram ............................................................................................. 15
Figure 6: The series scalability of the bq76pl536 ........................................................................................ 16
Figure 7: Boost Converter Schematic .......................................................................................................... 17
Figure 8: Boost Converter Specification ...................................................................................................... 18
Figure 9: Boost Converter Bill of Materials ................................................................................................. 20
Figure 10: Boost Converter Test Stages ...................................................................................................... 21
Figure 11: 27 V Input for the Boost Converter ............................................................................................ 21
Figure 12: Boost Converter Test Setup ........................................................................................................ 22
Figure 13: Test 3 output at 61% duty cycle ................................................................................................. 22
Figure 14: Average efficiency over the range of inputs is 87% ................................................................... 23
Figure 15: Test 1 output voltage with various loads ................................................................................... 23
Figure 16: Output voltage vs. PWM duty cycle for Test 4 ........................................................................... 23
Figure 17: Schematic for current sense circuit ........................................................................................... 24
Figure 18: Output voltage from a Current Sense Circuit ............................................................................. 24
Figure 19: Output voltage from a voltage sense circuit.............................................................................. 25
Figure 20: Connection between Bq76PL536EVM-3, computer, cells and adaptor ..................................... 26
Figure 21: Main Window for the Evaluation software ................................................................................ 27
Figure 22: Plot View of Cell Information within Evaluation software ......................................................... 28
Figure 23: (a & b) The Stacked EVMs .......................................................................................................... 29
Figure 24: (a & b) Resistor changes for EVM Stacking ................................................................................ 29
Figure25(a): Bq76PL536EVM-3 DC Supply Testing setup with computer display ....................................... 30
Page | 4
Figure26(b): A closer view of the DC Supply connections ........................................................................... 30
Figure 27: A close up view of voltage information displayed for device 1 .................................................. 30
Figure 28: EVM Stacking Test setup while connected to Li-Ion cells ........................................................... 31
Figure 29 : EVM Stacking Test Results Display ............................................................................................ 31
Figure 30: Screen Print of a short full stack charge test ............................................................................. 32
Figure 31: Various components require a 3.3V source, and the LM317 voltage regulator is used from the
input 12V source ......................................................................................................................................... 81
Page | 5
Definitions
Terms
EV
DC
AC
Fuel gauge
Power Converter
Feedback
Overcharging
BMS
PWM
Constant Current
Constant Voltage
Thermal Runaway
Fast Charge
SPI
SMBus
Level 1 Charging
Definition
Electric Vehicle
Direct current
Alternating current
Device to measure overall status of the battery
A Device for stepping up or down the voltage
Used stabilize the signal of the output of the
device
Continuing to charge a fully charged battery
Warning! Overcharging could lead to
overheating which could cause explosion,
damage, or shortened life of the cell.
Battery Management System
Pulse Width Modulation
The current is held a specific value(C = 3A)
until a the adequate voltage is achieved
The voltage is held at specific value (3.6V)
until the cell is fully charged (current is 0.1C)
Overheating of cell in relation to overcharging
A condition where 10A is used to charge the
cell in 15 minutes
Serial Peripheral Interface - bus for device
communication
System Management Bus This is an industry standard Bus protocol
Ac energy to the vehicle’s onboard charger
from a typical 120V outlet. 120Vac; 16A
(1.8kW)
Page | 6
Executive Summary
Electric vehicles are one of the cleanest, most efficient, and most cost effective form of
transportation. The market demand for electric vehicles has increased ever since the
Toyota Prius was introduced as an alternative to traditional oil vehicles. (Wired) Other
vehicle manufacturers are now introducing full electric vehicles, including Tesla Motors,
Nissan, and Ford. A major complication in developing an electric vehicle is the battery
management system. This project’s goal is to find an efficient and safe way to charge
and monitor multi-cell series lithium ion batteries for an electric vehicle using AC to DC
converters and monitoring microcontrollers
The approach to accomplish this task is twofold: develop a charging system and develop
a battery management system. In order to focus more on the battery management system,
and to prevent from electric shock due to high voltage, we are scaling down the power
supply from using a 120V AC outlet to four series connected DC power supplies that will
output 65 VDC and up to 3 Amp for the system. This is an agreement with our faculty
advisor and the client. Therefore, when we have to bring the system to a large scale it will
be just the matter of building up from smaller abstract systems.
When planning for the high voltage, full scale system (90 Series cells in 18 parallel
packs) the most efficient way to transform the 120VAC from the wall outlet to the
needed 324VDC will be by using a line filter, full-wave rectifier, AC-DC power
Correction boost pre-regulator and a DC-DC boost converter.
With the full scale system needing high voltage poses some difficult roadblocks, the
focus will thus be directed at developing the battery management system for the small
scale system (18 series cells). This system will monitor the charge of each individual cell
in order to prevent the batteries from overheating, overcharging, or over discharging. The
result of over-heating, over-charging, or over-discharging can include loss of cell
functionality, fire, or even explosion. The approach used to handle this major problem is
to use a battery management system (bq76PL536EVM-3) to monitor the charge of the
batteries while monitoring the temperature of the cells. The system will keep track of
how much power is remaining in the batteries, sending the information to a PC for
displaying, and from there the PC will send needed information to the MSP430 to adjust
the voltage to the battery pack. The expected functionality of the design is to efficiently
and safely charge multi-cell lithium ion batteries. It will charge the 18 series lithium ion
batteries while checking for overcharging and overheating. The system will continue to
monitor cells and will automatically turn off supply voltage when charge is complete.
Page | 7
Acknowledgement
We would like to acknowledge the client for this project, Adan Cervantes, from Element
1 Systems. He will be giving us direction, feedback, and guidance throughout the process
of this project. He will also be contributing the vehicle to be tested, the bank of lithium
ion batteries, the engine controller, and the engine. Adan will also provide financial aid
for this project.
Secondly, we would like to acknowledge our faculty advisor, Professor Ayman Fayed for
giving valuable guidance and advice in order to achieve the goals of our project.
Statement and Approach
Problem Statement
To develop an efficient, safe and scalable system for charging and monitoring multi-cell
series battery pack for electric vehicles. The system will use switching mode power
supply and a battery management system. The initial scope of this project was to charge
the bank of lithium-ion batteries to 324 VDC supplied from a 120 VAC wall outlet. In
order to focus more on the battery management system of this project, we are scaling
down the power supply to 65 VDC, and developing a battery management system for 18
series cells that can later be scaled to 90 series cells.
Solution Approach
The first objective of this project is to develop the battery management system for a small
scale battery pack (18 series cells). Several integrated circuits are offered from Texas
Instruments to provide battery monitoring for battery packs with a large number of cells.
The bq76pl536 is used specifically to monitor the state of charge and battery status of
packs with many series cells. The information obtained from the bq76pl536 integrated
circuits is then used to control a switching mode power supply that follows the charging
algorithm necessary for safe and efficient lithium ion battery charging. The system will
keep track of remaining batteries power and send information to a PC where it will be
displayed while being sent to the MSP430 to adjust the voltage to the battery pack.
Page | 8
Operating Environment
The final product must operate in various conditions. It needs to handle dusty conditions,
due to sitting in garages or driving down a gravel road. It will also need to be able to
withstand typical summer and winter temperatures. The batteries and controllers will be
shielded from the rain and wet conditions to prevent short circuits. The circuits and
batteries will never be thrown or dropped since they will be semi-permanently fixed in
the vehicle, but they will have to withstand shocks from the road.
However, the scaled down version is just a proof of concept. It only must operate in
optimal laboratory conditions. The system will have to be made more rugged after
further development.
Intended Users and Intended Uses
Intended Users
The users of the final design will be the vehicle owners, family members, friends, etc.
They could range anywhere between 14 to 100 years old and could be of any sex. As long
as they can pick up an extension cord and plug it into the outlet and to the vehicle,
anyone could use this project. However, since this project is only a scaled down version
of the prototype the intended user is the client, Element 1 Systems.
However, the final user of the scaled down version will be the team that works to further
develop the project. It will be assumed that the next team will also work in optimal
laboratory conditions.
Intended Uses
The intended use of the project is to charge a bank of lithium ion batteries and manage
their charge and discharge cycles. The high voltage supply is designed to operate as a
constant-current constant-voltage lithium ion battery supply, and only for the specified
A123 battery chemistry.
Page | 9
Assumptions and Limitations
Assumptions
 The user has access to a suitable 200W DC power supply, or will build one in the future.
 The batteries are provided by the client and suitable analogs for the larger batteries that
will be used in the final implementation.
 The components in the design are expandable to handle more than rated power.
 This is only a small scale prototype. The client, or a future team, is responsible for
integration into the final system.
Limitations
 High voltage control.
 A suitable 200W DC power supply.
 Safety: In order to develop a scalable abstract system, only 18 cells in series will be used
in our design, rather than all 90 in series and 18 in parallel. The developed solution will
be scalable in order to handle more series cells in the future.
 Parts availability.
Expected End Product
The expected finished product will consist of the scaled down version of the original
project, with the associated documentation, design, construction plans, and software
necessary to complete the finalized product. The completed product will be delivered to
Adan Cervantes from Element 1 Systems in May 2011.
Page | 10
System Design Approach
Functional Requirements
The project goal is for the charger module to charge a battery bank with 16 parallel
branches, with each branch having 90 series cells. Our initial design will be limited to
18 series cells to ensure system functionality and scalability. A switching mode power
supply will convert the input wall outlet power from 120Vac up to 324dc (or three
phase DC power supply with 27 V input up to a 65 VDC output for the scaled down
version). The charging and discharging of these cells will be monitored with a battery
management system to prevent overcharge, over discharge, and over temperature
situations. With proper implementation of the charging cycle, the cells should be able to
reach full charge in about 45 minutes. The goal for this project is to provide a system
that is capable of charging a stack of cells within this amount of time. See the
Constraint Consideration section for details on charging time for large scale system.
The main areas that this system will be focusing on are the following:
 Constant-Current Constant-Voltage charging procedure
 Battery Gauging
 Temperature Monitoring
 Overcharge Protection
Non Functional Requirements
 The scaled down prototype should be usable by our client during the development of the
scaled up version.
 The system should be reliable, even in the condition of a fault.
 System maintenance should be straightforward.
 Price should be as low as possible to ensure the product is a competitive market
alternative.
 The system should be robust and long-lasting.
 Total weight should be kept to a minimum.
 The system should be using the most efficient methods available.
 The end product should be designed to ensure safety and prevent the user from coming
into contact with high voltages and currents.
Page | 11
Market Alternatives
Since only a handful of electric vehicles have been successfully implemented on a large
scale, there are few existing commercial solutions. As for the switching mode power
supply the only commercially available solution designed specifically for electric
vehicles is offered by Brusa. The NLG5 is a battery charger that provides a high voltage
power source from a 120V or 240V wall outlet. The only problem with using a Brusa
battery charger is cost; their simplest charger costs over $2,000. (Brusa)
Figure 1: The NLG503-light battery charger. 1.6 kW 200-540V, $2,145 (Brusa)
As for battery management systems, even Brusa is still developing a commercial
solution. Thus, there are no market alternatives to building a custom BMS. (Brusa)
Page | 12
Proposed Approach and statement of work
Proposed Approach
Constraints considerations
Lithium ion batteries require a protection system to maintain safe voltage and current
levels. They may suffer thermal runaway and cell rupture if overheated or
overcharged. Furthermore, over-discharge can irreversibly damage a battery. To
reduce these risks, we have to design a circuit that shuts down when the lithium ion
cells vary outside the safe range of 2V – 3.6 V.
The amount of power a typical 120V wall outlet in the United States can provide is
limited to about 1.8 kW, which is defined to be level 1 charging. (Electric) This will
constrain our charging time, as the battery will typically only be able to draw 1.8 kW.
Since our battery pack holds about 11 kW-hr, the minimum charging time will be
about 6 hours.
Technology Consideration
An MSP430 will be used to control the charging process in three stages;
As demonstrated in Appendix A:
 Slow charge: Pre- charging stage using current of 0.1C (where C is 3A).
 Constant-current charging stage: Using current of 1C.
 Constant voltage charging stage: Maintaining the nominal max battery voltage
until the minimum current is supplied, which is 0.1C
As shown in Figure 2, on the next page, the microcontroller is used to control the
boost converter by increasing or decreasing the voltage to maintain the current during
the slow charge and constant current charging stages. It will then maintain a constant
voltage during the constant voltage charging stage.
Page | 13
Figure 2: Hardware Functional Block Diagram
Figure 3: Large scale system diagram
Page | 14
Figure 4: Small Scale system diagram
The microcontroller software will be implemented according to the software functional diagram
in Figure 5 using either C language.
Figure 5: Software Functional Block Diagram
Page | 15
Comparison of two similar integrated circuits from Texas Instruments:
 bq78PL114
According to the TI data sheet slua495 for the bq78PL114 “The minimum number of
parallel cells is 1. The maximum number of parallel cells is limited by the system
capacity which is a16-bit unsigned integer.” This data sheet only refers to parallel
configurations of the bq78PL114. Nowhere does it talk about an implementation of a
series configuration. The bq78PL114 with the bq76PL102 allow for charging 12 series
cells alone. The ability to charge more than 12 cells with this design may be possible, but
very difficult to achieve. With no SMBus built into this IC, a series configuration of more
than 12 cells may be very difficult to implement. Also TI would have to write a custom
TMAP file for each bq78PL114 to assign an address for SMBus compatibility. The
bq78PL114 requires communication with a computer using the .Net communication
protocol, which we would we have to use to simulate the bq78PL114 API on a
microcontroller. With these many requirement and setbacks, we looked to find a more
suitable IC that would supply features more suitable for the design. (BQ78PL114)
 bq76PL536
After running into many issues with the bq78PL114 design we decided on the
bq76PL536 to give us the needed features that the previous configuration did not.
According to the TI data sheet, “The bq76PL536 can be stacked vertically to monitor up
to 192 cells without additional isolation components between ICs. A high-speed serial
peripheral interface (SPI) bus operates between each bq76PL536 to provide reliable
communications through a high-voltage battery cell stack.”
This device can run at a continuous 36 V Peak with respect to the voltage of the bottom
most cells in the series. Charging 6 cells at 3.6 V the voltage required is 21.6 V, and so
the bq76PL536 can handle the capacity of our supplied cells. With the ability to connect
up to 192 cells in series, the bq76PL536 is the perfect choice for this project. Also
another advantage to using the bq76PL536 is that there is already a SMBus built in to this
IC which will allow easy communication of series configurations. With the bq76PL536
hooked up in series one Host interface is required to communicate with the system which
is a lot easier than the previous design. (Battery)
Figure 6: The series scalability of the bq76pl536
Page | 16
Detailed Design
Boost Converter
The battery pack must be charged from a lower 120V source to 324V. This requires a step-up
voltage converter, and our design uses a boost converter switching mode power supply. A
switching mode power supply is a high frequency device capable of controlling charge through
ideally lossless inductors and capacitors. In the case of a boost converter a transistor is turned on
by a high frequency duty cycle which shorts an inductor to ground. The inductor stores charge
until the transistor turns off. The charge then has a path through a diode to an output capacitor
where it is stored for some output load. The ideal relationship between input and output voltage
according to the control duty cycle is
This shows that output voltage is always larger than input voltage. In reality the output diode has
a voltage drop and parts exhibit losses, but the step-up function remains.
Figure 7: Boost Converter Schematic
Page | 17
For the scaled down demo version of 18 cells we require the output voltage to be between 28.8V
and 64.8V, which are the minimum and maximum voltages of the 18 series batteries. Thus we
will simulate the converter with a 27V input from a 3-phase power supply provided by Iowa
State University.
Given:
Input Voltage Vin
27V
Maximum Output Voltage Vout
70V
Frequency / Period Ts
100kHz/10us
Maximum Output Current Iout
3A
Minimum Output Current Imin
0.3A
Ripple Current, Vripple=Iripple*Rbat
0.05A
Rbat
8 mOhm/battery
Number of batteries
18
Find:
Max Duty Cycle Dmax= 1-Vin/Vout
61.4%
Inductor L=Vin*Ts/(2*Imin)*Dmax*(1-Dmax) 106 uH
Output capacitance Cap
>Iout/(Vripple*Rbat*#bat)
4166.67uF
Max Diode current @ Duty cycle=0
3A
Figure 8: Boost Converter Specification
Equations from http://focus.ti.com/download/trng/docs/seminar/Topic_3_Lynch.pdf
The inductor value is calculated at the boundary of discontinuous current mode and continuous
current mode operation. In continuous current mode the current through the inductor never falls
to zero which occurs if the output load is continuously high. If the output load becomes small
enough the boost converter enters discontinuous current mode and the transfer characteristics of
the circuit change. In order to avoid operating in discontinuous current mode the inductor is
chosen to be higher than this calculated inductor value. This circuit uses three 100uH toroidal
magnet-core inductors in series, although functionality is the same with at least one 106uH
inductor at appropriate peak currents.
Page | 18
The peak current in the inductor at maximum output load is the maximum input voltage divided
by the inductor value and the time that the transistor is open. Using 300uH the peak current is
1.45 A. Knowing that the system will output about 200W at 70V/3A, the input power will need
to be max output power multiplied by efficiency. Using a conservative efficiency of 70%
maximum input power is 267W. At 27V this means the input current is 267W/27V =9.88A.
Inductors rated at 17A Ipk were chosen to ensure they stay within the core saturation limit. If
they were to exceed this limit the part would function like an air core inductor, greatly affecting
the value of the inductance and the transfer function of the circuit.
The MOSFETs provided by the previous team were used as the switching device. It is a
TK20A60U, which has maximum ratings of 20A drain current and 600V drain source voltage.
In order to achieve maximum efficiency and drain current, a gate voltage of 12V is used. Since
the MSP430 microcontroller provides the PWM at 3.3V, a level shifting MOSFET driver is used.
The UCC27322 low side power MOSFET driver from Texas Instruments was chosen because it
can handle the large currents (up to 9A) that the transistor gate charge (27nC) will draw at 20ns
rise and fall times. It also has an enable input, which is useful for achieving low power draw
when the system is off. Other drivers were considered, but few had the capability to be driven
directly by a low voltage microcontroller without level shifting.
Boost Converter Control and the MSP430
Voltage and current feedback are used with an MSP430 microcontroller to control the charging
cycle. The voltage feedback is achieved using a voltage divider. The output voltage was
designed to be in the range of the MSP430 0V-3.3V ADC input.
The current feedback is achieved using a low side current sense resistor and an OPA335 op amp
from Texas Instruments. The op amp is operated in a non-inverting feedback loop and amplifies
the input signal to a wider range for the MSP430 0V-3.3V ADC input.
The MSP430G series microcontroller is used to isolate the boost converter and the MSP430F
series MCU used in the battery management system. The MSP430G turns on with an input
voltage, measures the battery voltage and current, avoids operation when the MSP430F detects a
fault in the batteries, and charges the batteries using the constant-current constant-voltage
method. The MSP430F can be used for cell balancing if a PC interface in undesired. The
communication with the Aardvark interface allows for active cell balancing. These two options
for cell balancing will need to be decided upon by the client and future senior design teams.
For complete implementation and testing code for the MSP430G please refer to the Appendix F,
G, and H.
Page | 19
Implementation and Testing: Boost Converter
The parts for the boost converter circuit were obtained and assembled piecewise on a 6 inch
breakout board. The parts list is provided below:
Part Name
Description
N-Channel
MOSFET
TK20A60U
INDUCTOR
TOROID PWR Inductor
100UH 17.6A
100uH
PROTOBOARD 8PIN
SOIC 8PIN
SIP
Protoboard
UCC27322
CAPACITOR
1500UF 100V
ELECT TSUP
DIODE
SCHOTTKY
100V 10A
TO220AC
LAUNCHPAD
DEV BRD
FOR
MSP430G2XX
C BOARD
FR4 1-SIDE
PPH 6.0X6.0
MOSFET
driver
Digikey
part
number
TK20A60
UQM-ND
Qua
ntity
Additional information
Non-stock at Digikey, not
1 recommended for future builds
513-1721ND
A single inductor can be used
3 instead (over 106uH)
9082CAND
29613673-5ND
Used to prototype the UCC2733
1 and the OPA335
1
Output
Capacitor
P6991-ND
Limits the converter output range
to under 100V, use a different
3 product for increased voltages
Diode
MBR1010
0GOS-ND
Low voltage drop, fast switching,
1 limited to 100V
Microcontrol
ler
29627570-ND
Very cheap microcontroller
1 development, limited code size
V2012-ND
Prototype board to hold the
1 components
Perf board
Figure 9: Boost Converter Bill of Materials
Wire used to connect high power components and to power sources is 12 gauge insulated copper
wire. Wire used to connect the low current data lines can be just about any gauge, although
insulated wire is preferred to avoid short circuits.
Page | 20
Testing of the Boost Converter
Testing is performed in stages:
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
Test 8
Low
Power
MOSFET
driver
Low
Power,
High
voltage
High
Power
MSP430G
inputs
MSP430G
outputs
High
Power
battery
output
High
power,
battery
output,
MCU
control
Testing just the boost converter circuit (transistor, diode, inductor, and
output capacitor) with a signal generator and a 30W 6V input supply.
Functionality of the MOSFET driver is confirmed separately from the
boost converter circuit.
Testing the boost converter and the MOSFET driver with a high power
supply at high input voltages (12-27V) and high loads to limit system
current. A function generator provides the PWM at 100kHz
Testing the boost converter and the MOSFET driver with a high power
supply at high voltage (27V) and low loads to simulate maximum output
current. A function generator provides the PWM at 100kHz
The voltage and current sensing circuits are verified and sampled with
the microcontroller.
Control of the PWM output is verified using a scope and the
microcontroller inputs.
Testing the boost converter at high power manually with a function
generator and a battery output.
The final demonstration of system functionality with constant current
and constant voltage charge control.
Figure 10: Boost Converter Test Stages
Figure 11 below shows the usage of the boost converter with a 27V input from a 3-phase power
supply.
Page | 21
Figure 11: 27 V Input for the Boost Converter
Boost Converter Test Results
The figures below shows the succesful testing of the
boost converter. Figure 12(left) shows the testing set
up of the boost converter with a high power supply at
27 V and low loads to simulate the maximum current
output. Then figure 13 (below) shows the output of the
boost converter at 61 % duty cycle and 27 V input
giving 65.636 V DC with a 25 ohms load.
Figure 12: Boost Converter Test Setup
Figure 13: Test 3 output at 61% duty cycle
The graphs in the next page shows the successful test results and efficiency of the boost
converter for Test 1 at low voltage, low current and Test 4 at high power, high voltage/current
with various loads. For Test 1 we received an output of 6-15 volts at 0.01 to 0.5 A at about 80 %
duty cycle depending on the load. And at the high power we successfully received an output
voltage of 65.5 V at 3.3 A which is also shown in figure 13. In figure 15, it demonstrates the
output voltages that we received using 23 ohms and 50 ohms at high power test simulation. Also
we received an efficiency of about 87% in our high power test.
Page | 22
Efficiency [%]
Boost Converter Efficiency
120.00%
100.00%
80.00%
60.00%
40.00%
20.00%
0.00%
Load (23 Ohms)
Load (55 Ohms)
1 5 10 15 20 25 30 35 40 45 50 55 60 65
PWM input [% duty cycle]
Figure 14: Average efficiency over the range of inputs is 87%
Boost Output at Varying Loads
Vo [V]
20
Vout [V]:21
Ohm
15
10
Vout [V]: 50
Ohm
5
0
0.05 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85
PWM [%/100]
Vout [V]: 85
Ohm
Figure 15: Test 1 output voltage with various loads
SMPS Output Voltage
Output Voltage [V]
80
60
40
Output V[23 Ohm]
20
Output V [50 Ohm]
0
1 5 10 15 20 25 30 35 40 45 50 55 60 65
PWM duty cycle [%]
Figure 16: Output voltage vs. PWM duty cycle for Test 4
Page | 23
Figure 18 below shows the successful output from a current sense resistor. We received an
output voltage raging from 0.1 V to 3.3 V when a varying current from 0.09 A to 3.44 A was
applied to the current sense circuit. The observed resistance was 0.1 ohms.
Figure 17: Schematic for current sense circuit
Constant Current Control
3.00
y = 0.0102x + 0.0039
Load Current [A]
2.50
2.00
Constant Current
Control
1.50
1.00
Linear (Constant
Current Control)
0.50
0.00
0.00
100.00
200.00
300.00
MSP 430 ADC value (10 bit 0-1023)
Figure 18: Output voltage from a Current Sense Circuit
Page | 24
The voltage sense circuit was a voltage divider made from a 100kOhm potentiometer. Its
transfer characteristics with the MSP430 can be seen in Figure 19.
Constant Voltage Control
80
y = 0.2853x + 0.0403
Load Voltage [V]
70
60
50
Constant Voltage
Control
40
30
Linear (Constant
Voltage Control)
20
10
0
0
100
200
300
MSP430 ADC value (10 bit 0-1023)
Figure 19: Output voltage from a voltage sense circuit
Boost converter Usage
The boost converter has various inputs and an output. One of the inputs is a 12V source which
powers the MOSFET driver directly and powers the MSP430 through a 3.3V linear regulator.
The other input is a 27V power source which enables the 3.3V linear regulator and the MOSFET
driver. Plugging in the 27V source starts the constant current constant voltage charging cycle
assuming a battery is detected and has no faults.
Page | 25
Battery Management System
The battery management system (BMS) will be required to measure current, voltage, and
temperature of the battery cells. This system will then report this information to the
microcontroller. With this communication between the BMS and the microcontroller, the
system will be able to perform a charging cycle, as well as active balancing of the cells.
The purpose of this design is to provide safety features in case of dangerous cell
conditions.
Cell monitoring and regulating
All of the duties of the battery management system are performed by a system of
integrated circuits designed and manufactured by Texas Instruments. The IC that we will
be using to monitor and regulate the Li-Ion batteries and send information to the
processor is the TI bq76PL536EVM-3, shown in figure 20. In the pictures below, the TI
evaluation module is connected to Aardvark USB-SPI adaptor. The adaptor is then
connected to the PC where the status of the batteries will be displayed in the main screen
software referred to as “Window Graphical User Interface”.
Figure 20: Connection between Bq76PL536EVM-3, computer, cells and adaptor
Technical Approach
.
Since the bq76PL536 EVM-3 is designed to balance 18 series battery cells we will have
to combine 5 of them to monitor and manage 90 series cells in large scale. Whereas, for
the small scale, we will charge (3*3) + (3*3) = 18 cells with two EVMs. As shown in the
figure above, we will daisy chain the host EVM with the slave EVM, and will monitor
three cells with each of the chips. This is to demonstrate that this design can be expanded
for large scale purposes. The detail process for implementing and testing this design
provided in the section below.
Page | 26
Implementation and Testing for the BMS: bq76PL536EVM-3
The battery management system relies on the Texas Instruments bq76PL536EVM-3
Evaluation Module and the Aardvark USB-SPI adaptor attached it a PC to display the
real-time system charging information. The bq76PL536EVM-3 is then attached multiple
MSP430s to complete the required system information loop that allows for adjustment to
the charging controls. This setup meets all requirements for under-voltage, over-voltage,
and over-temperature protection.
The bq76PL536EVM-3 integrates dedicated overcharge and under-voltage fault detection
for each cell and two over-temperature fault detection inputs for our device. The
protection circuits use a separate band-gap reference from the ADC system and operate
independently. The protector also uses separate I/O pins from the main communications
bus, and therefore is capable of signaling faults in hardware without intervention from the
host MSP430.
.
Figure 21: Main Window for the Evaluation software
Page | 27
VBRIC K
VCELLn
ADDR
LOG DEVICE
TSn
: The voltage measured by the bq76PL536 between the BATx and VSS pins
: The voltage measured between the pair of pins VCn – VCn-1 (i.e. VCELL2 = VC2 -VC1).
: Displays the address of the device being monitored in the measurement result area.
: Checking this box will add the contents of the device at this address to the log file.
: The voltage measured between the TSn+ and TSn- inputs, converted by the WinGUI to
temperature based on the characteristics of the thermistor used in the EVM design. The
EVM and WinGUI are configured to measure this voltage as a ratio of REG50, which
removes any offset or gain errors introduced by drift in the REG50 output.
Figure 22: Plot View of Cell Information within Evaluation software
Running of these integrated circuits include learning about the SMBus protocol, which is
a set of industry defined standards which allows a host controller to easily obtain large
amounts of data from the batteries over a single communication interface. In this case,
TI’s evaluation modules will be gathering information on the battery conditions and
communicating with two different MSP430s to making decisions. The MSP430G2231
will receive information from the EVM and will be used to control the voltage and
current part of the charging cycle. The MSP430F5529 will also receive information from
the EVM to be used to control the cell balancing aspect of the charging system. We will
be using the Aardvark adaptor, manufactured by TI, to gather the data and display it on a
PC, which uses the Evaluation software that is referred as the “WinGui” to display the
detailed status of each battery. This interface is the other option for balancing the during
charging cells. Balancing can be controlled by the computer if the MSP430F5529 is not
used . Figure 21 above and figure 22 on the previous page show images of the main
screens that will display system charging information.
An important aspect to this project is proving that multiple bq76PL536EVM-3 evaluation
module boards can be connected together to monitor a large number of cells. The
implementation and testing of the EVMs in the system will be focused on configuring the
EVMs for stacking and testing the communication of cell information to a PC.
Page | 28
Implementation of multiple EVM Stacking
When the bq76PL536EVM-3 arrives from TI it is ready to work as an independent board.
There are a few changes that will need to be made in order to create a configuration
where multiple EVM boards can be hooked together. To configure the system correctly,
first one board must be chosen as the main communication board. This board needs to be
configured to Host Mode. Next all other EVM boards must be changed to Slave mode. In
order to configure the Host and Slave EVMs, a number of resistors will need to be either
added or removed.
Host Mode:
1. Make sure there is a 0 ohm resistor
already at R36.
2. Insert 0 ohm resistors (RES0603) at
R213.
Slave Mode:
1. Remove the 0 ohm resistor at R36 and
add it to R33.
2. Insert a 100 K ohm resistor at R212.
Figure 23: (a & b) The Stacked EVMs
To Stack North:
1. Remove the 0 ohm resistors at R205,
R206, R207, R208, R209, R210, R211,
and R212.
2. Insert 0 ohm resistors (RES0603) at
R204, R213, R214, and R215.
To Stack South:
1. Remove the 0 ohm resistors at R8, R9,
R10, R11, R12, R13, R14, and R15.
2. Insert 0 ohm resistors at R5, R6, R7, and
R16.
Figure 24: (a & b) Resistor changes for EVM Stacking
To make an easy connection for stacking, part number FC10P connection cable can be
used. When the EVMs arrived from TI, one contained ten pin male connectors (Molex
90131-0765) on both ends and the other EVM required a ten pin male connection (Molex
90131-0765) to be soldered on. When running the BMS with multiple EVMs, the usb
cable will supply the needed 3.3VDC to turn on the EVM for SPI Communication. There
is no external power needed for the other EVMs in the stack. As long as cells are attached
to each device, communication will be established. In the case where the Aardvark usb
adapter is not used, either 3.3VDC or 5VDC will need to be applied to the Host EVM.
The EVM must be configured so its power jumper for either 3.3V or 5V. For a complete
schematic layout refer to Appendix E.
Page | 29
Testing of the bq76PL536EVM-3
DC Power Supply - EVM Test
Testing of the bq76PL536EVM-3 was conducted by first hooking up each EVM to three
DC power supplies. Each device on the boards would see the power supply voltage as if
battery cells were being monitored. This first test was done to each EVM that would be
used in the system to ensure the boards would be working correctly to monitor a group of
Lithium-Ion Batteries in the future. Each DC Power supply was set to 20 VDC while the
negative and positive connections were attached to the battery monitoring terminal of
each device on the board. The device would then see 6 cells at 3.33 VDC. The expected
results for this test would then be verified by getting the voltage information to display on
the computer screen.
(a)
(b)
Figure25(a): Bq76PL536EVM-3 DC Supply Testing setup with computer display
Figure26(b): A closer view of the DC Supply connections
DC Power Supply – EVM Test Results
The figure on the right shows the successful outcome of this test.
Figure 27 shows how device 1 thinks it is seeing six cells which
are all at 3.33 VDC, which is a combine voltage of 19.9VDC.
This test verifies that the communication is working correctly.
Figure 27: A close up view of voltage
information displayed for device 1
Page | 30
EVM Stack Testing
After configuring the two EVMs for stacking, it was important to test the system while
stacked together, along with being hooked up to the bank of 18 cells. Each device within
the EVM is designed to monitor three to six cells. With being limited to only having 18
cells, and wanting to keep the system voltage to a minimum, three cells were hooked up
to each device. Once all cells were hooked together in series and the voltage wires were
properly connected to the EVMs, the testing could begin. The expected results of this test
could also be verified by all six devices showing up in the device stack box in the display
interface on the PC. This test was successful when all battery information could be seen
from all six devices.
Figure 28: EVM Stacking Test setup while connected to Li-Ion cells
EVM Stacking Test Results
The results of this test were successful after a few minutes of plugging in the USB cable
and restarting the EVM PC software. Although the system did not always recognize all
six devices, eventually they were successfully found by communication interface. Figure
29 below shows that there are six devices found in the stack height and the v stack
voltage is around 59.1 VDC. With the total stack voltage being displayed, it can be seen
that the 18 cells all have about 3.3 VDC, which add up to the expected total. With the
successful implementation of this setup, proof that our complete system is working
properly will be easily displayed.
Figure 29 : EVM Stacking Test Results Display
Page | 31
Implementation and Testing of Complete System
Complete System Test – Charging Cycle
The input voltage is 27 VDC. Since the prototype system is scaled down to 18 series cells
from 90 series in 16 parallel branches, the output of our boost circuit simulation was
between 28.8 V to 64.8 V. Power will be provided for the BMS by a laboratory power
supply during testing. The EVM will then be connected to the SPI-USB Aardvark adaptor,
allowing a personal computer to control the boards. The evaluation software allows the
tester to evaluate the condition and state of the cells in the system and monitoring the
system in the evaluation module software.
All 18 batteries will be discharged to around 2 V apiece. The batteries will then be
connected to the EVM boards and a complete charging cycle will be implemented. The
cycle will include a constant current phase at 3A. When the charge reaches 80% the
cycle will switch from constant current to a constant voltage of 64.8V until fully charged.
The figure below shows the graphical representation of charging of 18 batteries over
time. All 18 were connected in series to one EVM board. The graph was generated by
the EVM software via the Aardvark interface from TI. Although the cycle was short, the
graph shows that voltage of batteries is increasing with time. The initial voltage of 18
cells was 54.2 V and after 25 seconds the voltage reading was 55 V. Combined with the
proper 3A output from the power supply, it shows this prototype can complete a proper
charging cycle.
Figure 30: Screen Print of a short full stack charge test
Page | 32
TI analog design contest
Being included in the TI analog design contest has helped immensely in the planning and
execution of this project. The superior support and quality of the TI products and personnel have
proved indispensible in creating a successful design. The specific TI products used are discussed
below. Full integration details including circuit diagrams and programming are provided in the
design section of Boost Circuit and Battery Management System and the Appendices.
MSP430G2231
The ADC on this microcontroller takes voltage and current measurements and outputs a
PWM waveform to control the boost converter. It will also detect the bq76PL536EVM-3
stack for fault information. By modulating the PWM signal, the microcontroller ensures
the system is in the correct phase of the constant current/constant voltage charging cycle.
TI support provided excellent skeleton code that considerably sped up development when
using the msp430 with the bq76PL536EVM-3 boards.
MSP430F5529
This microcontroller will monitor the system for faults due to undercharge, overcharging,
and overheating. When the full scale system is integrated, the fault protection can be
used to shut down the system or turn off power to a specific battery cluster. The
MSP430F5529 can also be used to manage the cell balancing of the finalized system.
bq76PL536EVM-3
The bq76PL536EVM-3 battery management boards combined with the aardvark adaptor
and the evaluation software are used to manage the cell balancing and fault detection of
the batteries. This system can also be used for cell balancing when communicating with a
PC. The management software also gives an excellent overall view of the system for
debugging and demonstration purposes. Two boards were used in series with 18 cells to
demonstrate the scaling capabilities necessary for the finalized product.
UCC27322 MOSFET driver
The UCC27322 MOSFET driver was used to boost the PWM output of the
MSP430G2231 to 12V to control the output of boost converter. It was the only driver
available with the required specifications that operated at the extremely low input on
threshold of 2V, making for a highly responsive driver with the MSP430 3.3V pwm.
OPA335
The OPA335 was used as a non-inverting amplifier to multiply the small voltage across
the sense resistor. It was useful in our circuit due to its low power consumption and
accurate results.
Page | 33
Security Consideration
There are few security concerns related to this project, however care should be given not
to give development information directly to the clients competitors.
Safety Consideration
When dealing with high voltages:
1. Keep one hand in a pocket to prevent conduction channel through the heart.
2. Set up a work area away from possible grounds.
3. If circuit boards need to be removed from its mountings use insulating material.
4. Discharge high voltage capacitors appropriately.
5. Remove metal objects such as jewelry.
6. Prove that exposed metal surfaces are grounded, as are outlet grounds.
7. Do not assume insulation integrity.
8. Do not leave an experiment unattended.
9. Do not work on an experiment while tired or not alert.
10. Ensure that someone is trained in CPR.
11. When working with high voltages, ensure two people are present in the high voltage
laboratory at all times.
Intellectual Property Consideration
The design for this project could potentially be patented, trademarked, and copyrighted.
Patent protection can be applied for with the U.S. Copyright Office, which handles
copyright registration in order to ensure a market claim to the product.
Commercialization considerations
This design is a prototype that could potentially become a commercial venture.
Page | 34
Possible risks and risk management
Risks have been identified throughout the project and tracked for resolution and
mitigation. A risk register is used to identify risk to the project:
Risk Register:
No
Risk
Risk Description
1
High power systems
Generate 324
VDC for
electrical car
motor
2
Electric shock
3
IC replacement
The risk of
electric shock is
possible when
working with a
charging system
In case any small
part of the system
malfunctions.
4
Over-temperature
Over-voltage
Under-voltage
5
Weight
6
Cost
Cells may suffer
thermal runaway
and cell rupture if
overheated or
overcharged
The mass of the
system.
Cost should be as
low as possible
Mitigation
Run simulations before physically
testing.
Start at a lower voltage level to test the
components before using it at the higher
voltage level.
Be careful when doing the circuit
testing, follow the rules listed in the
safety consideration.
Disconnect the problem section and
determine if further shut down is
necessary. Replace the faulty
component.
The bq76PL536 provided by TI is
available for protecting our system.
Ensure lightweight components are
utilized when possible
Only purchase necessary components.
Introduces risk with schedule if
replacement contingency parts are not
available.
Page | 35
Schedule
Page | 36
Hardware/Software Statement of work
Task 1 - Problem Definition:
Design a charger and battery management system operating from a 120 Vac source.
Subtask 1a – Define the problem
Subtask 1b – Identify the intended audience and End-Use
Subtask 1c – Define the requirements and constraints
Task 2 – Acquire a suitable power source
Find an inexpensive power source that can be used to demonstrate the prototype.
Subtask 2a – Compare alternatives.
Subtask 2b – Choose the best alternative based upon cost and ease of use
Task 3 – Boost Converter Design
Boost the output of the power source from 27V to between 28.8V and 64.8V.
Subtask 3a – Select component values
Subtask 3b – Simulate
Subtask 3c – Code an MSP430 to control the PWM
Task 4 – bq76PL536EVM-3BMS system design
Implement a scalable battery management system using two bq76PL536EVM-3
boards to monitor nine series cells each.
Subtask 4a – Acquire the boards from TI.
Subtask 4b – Modify the boards so they work in master/slave configuration.
Subtask 4c – Code an MSP430 to control the fault response.
Subtask 4d – Code an MSP430 to control the cell balancing.
Task 5 – Building and Testing
Build and test the systems designed in Tasks 2 through 4
Subtask 5a – Gather materials and components
Subtask 5b – Solder the components onto perf board
Subtask 5c – Code the various MSP430s
Subtask 5d – Test each system individually and together for complete
functionality.
Task 6 – Documentation and Demonstration
Provide End-Project Documentation and Project Reporting, as well as demonstrate the
project to faculty.
Subtask 5a – Write End-Project Documentation
Subtask 5b – Write Project Report
Subtask 5c – Develop a project poster
Subtask 5d – Weekly reporting
Subtask 5e – Demonstrate the project to the client and IRP panel
Page | 37
Resources
Items
Cost
Parts and Materials:
a. Bq76PL536EVM-3
$400
b. MSP430
$75
c. Various Discrete components
$50
d. TK20A60U N-Channel Mosfet
$5.78
$10.40
e. INDUCTOR TOROID PWR 100UH 17.6A
f.
PROTO-BOARD 8PIN SOIC 8PIN SIP
$4.11
g. UCC27322 mosfet driver
$3.64
h. CAPACITOR 1500UF 100V ELECT TSUP
$3.04
i.
DIODE SCHOTTKY 100V 10A TO220AC
$2.38
j.
LAUNCHPAD DEV BRD FOR MSP430G2XX
$4.30
k. C BOARD FR4 1-SIDE PPH 6.0X6.0
Subtotal:
$10.59
$569.24
a. Test and Build equipment
b. oscilloscope, function generator, digital multimeter
$0
c. soldering equipment
$0
Subtotal:
$0
Labor at $20.00/hour:
$20,000
a. Pramit Tamrakar
$4,000
b. Matt Schulte
$4,000
c. Jimmy Skadal
$4,000
d. Hao Wang
$4,000
e. William Zimmerman
$4000
Subtotal:
$20,000
Total:
$40,569.24
Page | 38
Future Work
We have a proof of concept and control system for a battery charging system. Our
prototype system charges 18 series cells in two EVMs. The next step is to develop a full
sized system that charges 90 cells and 16 parallel packs. The parts we have chosen are
scalable and appropriate for this task. After the large scale 90 cell and 16 parallel pack
configuration is successful, an appropriate transformer must be chosen to convert from a
standard wall outlet to the DC power needed to run that system. This working system
must then be made rugged enough to withstand conditions in the field. After these steps
are completed a commercially viable product should result.
Closing Summary
With global demand for oil increasing and supplies more difficult to obtain, the price of
oil based fuels for transportation is expected to rise. The need to find a viable alternative
to oil necessitates researching in electric alternatives. The long wait time to charge
Electric Vehicle batteries makes transitioning from internal combustion engines to battery
electric vehicles inconvenient for a society dependent on traveling large distances.
Electric vehicles have to be convenient, safe, and affordable to meet the needs of
consumers without major sacrifices in perceived quality of life. Lithium ion batteries
support a high energy density and are the preferred source of mobile electric power. This
project implements a solution for a battery management system for a large number of
lithium ion cells.
There are still many problems to solve when charging an electric vehicle and the goals
for this project are to find the best solutions for those problems. The use of 120VAC
outlet would be ideal for home charging, but means that we must work with the
restrictions of home outlets. Home charging is a very important problem to solve for this
project.
Scaling down problems and focusing on solving each step was very essential to
successfully building this charger. Scaling down allowed the team to focus on
developing a working solution without dealing with dangerous voltage levels during
conception. Our project goal to successfully implement a lithium-ion battery charger
prototype for the electric vehicle owned by Adan Cervantes and Element 1 Systems is
completed.
Page | 39
Project Team Information
Client’s Information
Adan R. Cervantes
Principle system Engineer
Email Address: [email protected]
3286 North Center Point Road, Marion, IA 52302
Phone: (319) 929-8928
www.element1systems.com
Faculty advisor Information
Ayman A. Fayed
Assistant Professor
Email Address: [email protected]
Dept. of Electrical & Computer Engineering
Iowa State University
2117 Coover Hall Ames, IA 50011
Phone: (515) 294-6112 Fax: (515) 294-8432
http://home.eng.iastate.edu/~aafayed/
Student Team Information
Pramit Tamrakar
Major: Electrical Engineering
Email Address: [email protected]
918 NE Crestmoor Place Apt 306, Ankeny, IA 50021
Phone: 515-203-5291
Jimmy Skadal
Major: Electrical Engineering
Email Address: [email protected]
3819 Tripp St Unit 7, Ames, IA 50014
Phone: 563-320-6878
Matthew Schulte
Major: Electrical Engineering
Email Address: [email protected]
3223 Frederiksen Ct, Ames, IA 50010
Phone: 319-396-9959
Hao Wang
Major: Electrical Engineering
Email Address: [email protected]
230 Raphael Ave Unit 9, Ames, IA 50014
Phone: 515-520-9372
William Zimmerman
Major: Electrical Engineering
Email: [email protected]
1310 Garfield Ave, Ames, IA 50014
Page | 40
References
"A123Systems :: Products." A123Systems. 2009. Web. 10 Oct. 2010.
<http://www.a123systems.com/a123/products>.
"Battery Management - Battery Fuel Gauge - BQ76PL102 - TI.com." TI.com. Texas
Instruments, Oct.-Nov. 2009. Web. 10 Oct. 2010.
<http://focus.ti.com/docs/prod/folders/print/bq76pl102.html>.
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Instrument, July-Aug. 2010. Web. 10 Oct. 2010.
<http://focus.ti.com/docs/prod/folders/print/bq76pl536.html>.
Baxter, Tyler, Brian Chee, Liam Keams, Philip Leo, and Philip Schmitz. Lithium Ion
Battery Charging: Portable Renewable Power Module. May 10-15 Senior Design
Project, Fall 2009. Sept.-Oct. 2010. <http://seniord.ece.iastate.edu/may1015/>.
"Block Diagram (SBD) - Battery Management: High Cell Count for HEV - TI.com."
TI.com. Texas Instruments. Web. 11 Oct. 2010.
<http://focus.ti.com/docs/solution/folders/print/599.html>.
"BQ78PL114 BQ76PL102 Evaluation Kit - BQ78PL114EVM-001 - TI Tool Folder."
TI.com. Texas Instruments, 14 Jan. 2010. Web. 10 Oct. 2010.
<http://focus.ti.com/docs/toolsw/folders/print/bq78pl114evm-001.html>.
“Brusa.” Brusa. 2010. Web. 10 Oct. 2010.
< http://www.brusa.biz/e_welcome.html>.
"Li-Ion Battery Charger Solution Using the MSP430 Microcontrollers Slaa287 - TI.com."
TI.com. Texas Instruments, Dec.-Jan. 2005. Web. 10 Oct. 2010.
<http://focus.ti.com/lit/an/slaa287/slaa287.pdf>.
"Linear Technology - LTC6802-1 - Multicell Battery Stack Monitor." Linear Technology
- Linear Home Page. Linear.com, 2009. Web. 10 Oct. 2010.
<http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1037,C1786,
P86662#descriptionSection>.
"NOTES ON HIGH VOLTAGE SAFETY." Nanoscience at UNM. Web. 14 Oct. 2010.
<http://nnin.unm.edu/safety/Hi_Voltage_Safety.html>.
“Supply and Demand, Prius Style.” Wired Magazine. 2008. Web. 10 Oct. 2010.
<http://www.wired.com/autopia/2008/07/supply-and-dema/>.
“UCC28019 Evaluation Module.” TI.com. Texas Instruments, 01 Mar 2007. Web 10 Oct
2010. < http://focus.ti.com/docs/toolsw/folders/print/ucc28019evm.html>.
Page | 41
"USB Interface Adapter EVM - USB-TO-GPIO - TI Tool Folder." TI.com. Texas
Instruments, Aug.-Sept. 2006. Web. 10 Oct. 2010.
<http://focus.ti.com/docs/toolsw/folders/print/usb-to-gpio.html>.
"Electric Car." Wikipedia, the Free Encyclopedia. Web. 14 Oct. 2010.
<http://en.wikipedia.org/wiki/Level_1,_2,_and_3_charging#Level_1.2C_2.2C_and_3_ch
arging>.
Page | 42
Appendix A
Below is information about charging a lithium-ion battery from the TI data sheet SLAA287
Page | 43
Appendix B
Below is the part of the information to connect the bq76pl536 evaluation modules to an MSP430F5529.
This is necessary if the output laptop is not desired, and performs the fault and cell balancing control.
Provided code and further information can be found at
http://focus.ti.com/analog/docs/litabsmultiplefilelist.tsp?literatureNumber=slaa478&docCategoryId=1&
familyId=413
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Appendix C
Battery definitions for the MSP430F
//******************************************************************************
//THIS PROGRAM IS PROVIDED "AS IS". TI MAKES NO WARRANTIES OR
//REPRESENTATIONS, EITHER EXPRESS, IMPLIED OR STATUTORY,
//INCLUDING ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS
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//(U.S.$500).
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//Program without any charge or restriction. You may
//distribute to third parties, provided that you transfer a
//copy of this license to the third party and the third party
//agrees to these terms by its first use of the Program. You
//must reproduce the copyright notice and any other legend of
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Page | 57
//rights not specifically granted under this license. Except
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//*****************************************************************************
/**
* @file data_flash.h
*
* @brief this file contains all the definitions of the battery pack
*
* @author Daniel Torres - Texas Instruments, Inc
* @date November 2010
* @version 1.0 Initial version
* @note Built with IAR for MSP430 Version: 5.10
*/
#ifndef DATA_FLASH_H
#define DATA_FLASH_H
//Battery pack definition
#define NUMBER_OF_BQ_DEVICES 3 //3 BQ76PL536 devices are connected
#define NUMBER_OF_CELLS
18 //MAX number of cells in the system
#define MAX_CELLS_NUMBER_IN_BQ 6 //MAX number of cells per BQ76PL536 device
#define CELL_BALANCING_EN
1 //set to 1 to enable cell balancing
#define ONE_MINUTE
60
//Battery pack information and threshold values
#define dCOV_THRESHOLD
3700 //COV_THRESHOLD
[mV]
#define dCOV_RECOVERY_THRESHOLD
3600 //COV_RECOVERY_THRESHOLD [mV]
#define dCOV_TIME
5 //20 //COV_TIME (max value 32) [100ms]
#define dCUV_THRESHOLD
2000 //CUV_THRESHOLD
[mV]
#define dCUV_RECOVERY_THRESHOLD
2200 //CUV_RECOVERY_THRESHOLD [mV]
#define dCUV_TIME
5 //20 //CUV_TIME (max value 32) [100ms]
#define dPACK_OVER_TEMP1
#define dPACK_OT_TIME1
#define dPACK_OVER_TEMP2
#define dPACK_OT_TIME2
50
2000
50
2000
//3 PACK_OVER_TEMP1 [st C]
//PACK_OT_TIME1
[ms]
//3 PACK_OVER_TEMP2 [st C]
//PACK_OT_TIME2
[ms]
//PACK_END_OF_CHARGE_VOLTAGE [mV]
#define dPACK_END_OF_CHARGE_VOLTAGE (DWORD)dCOV_THRESHOLD*NUMBER_OF_CELLS
#define dCC_CV_QUAL_TIME
20 //CC_CV_QUAL_TIME
[s]
Page | 58
//PACK_END_OF_DISCHARGE_VOLTAGE[mV]
#define dPACK_END_OF_DISCHARGE_VOLTAGE (DWORD)dCUV_THRESHOLD*NUMBER_OF_CELLS
#define dEND_OF_DISCHARGE_QUAL_TIME 20 //END_OF_DISCHARGE_QUAL_TIME [s]
#define dCHARGE_CURRENT
1100 //CHARGE_CURRENT
[mA]
#define dCHARGE_TAPER_CURRENT
300 //CHARGE_TAPER_CURRENT
#define dCHARGE_TAPER_TIME
(DWORD)240*ONE_MINUTE//CHARGE_TAPER_TIME[s]
#define dMAX_CHARGE_TIME
(DWORD)200*ONE_MINUTE//MAX_CHARGE_TIME [s]
[mA]
//FULL_DISCHARGE_CLEAR_VOLTS [mV]
#define dFULL_DISCHARGE_CLEAR_VOLTS dPACK_END_OF_DISCHARGE_VOLTAGE
//FULL_CHARGE_CLEAR_VOLTS [mV]
#define dFULL_CHARGE_CLEAR_VOLTS
dPACK_END_OF_CHARGE_VOLTAGE
#define dDELTA_CHARGE_V
300 //DELTA_CHARGE_V
[mv]
#define dCHARGE_DISCHARGE_TIME
(DWORD)5*ONE_MINUTE//CHARGE_DISCHARGE_TIME [s]
#define dDELTA_DISCHARGE_V
200 //DELTA_DISCHARGE_V
[mV]
#define dSOV_THRESHOLD
4200 //SOV_THRESHOLD
[mV]
#define dSOV_RECOVERY_THRESHOLD
3800 //SOV_RECOVERY_THRESHOLD
#define dSOV_TIME
3000 //SOV_TIME
[ms]
[mV]
#define dCELL_IMBALANCE_FAIL_THRESHOLD 500 //CELL_IMBALANCE_FAIL_THRESHOLD[mV]
#define dCELL_IMBALANCE_FAIL_TIME
(DWORD)120*ONE_MINUTE//CELL_IMBALANCE_FAIL_TIME[s]
#define dBALANCE_TIME
(DWORD)1*ONE_MINUTE
//BALANCE_TIME A.K.A CB_TIME[s]
#define dBALANCE_VOLTS_THRESHOLD
50 //BALANCE_VOLTS_THRESHOLD [mV]
#define dMIN_BALANCE_VOLTS
dCUV_RECOVERY_THRESHOLD
//MIN_BALANCE_VOLTS[mV]
#define dMAX_BALANCE_TIME
(DWORD)120*ONE_MINUTE//MAX_BALANCE_TIME[s]
/**
* @brief Global defines
*/
.
//definition of the Parameters structure
typedef enum PARAM_ID
{
/*Voltage*/
COV_THRESHOLD, //COV_THRESHOLD = 0,
COV_RECOVERY_THRESHOLD,
COV_TIME,
CUV_THRESHOLD,
CUV_RECOVERY_THRESHOLD,
Page | 59
CUV_TIME,
/*Temperature*/
PACK_OVER_TEMP1,
PACK_OT_TIME1,
PACK_OVER_TEMP2,
PACK_OT_TIME2,
/*Charge and Discharge*/
PACK_END_OF_CHARGE_VOLTAGE,
CC_CV_QUAL_TIME,
PACK_END_OF_DISCHARGE_VOLTAGE,
END_OF_DISCHARGE_QUAL_TIME,
CHARGE_CURRENT,
CHARGE_TAPER_CURRENT,
CHARGE_TAPER_TIME,
MAX_CHARGE_TIME,
FULL_DISCHARGE_CLEAR_VOLTS,
FULL_CHARGE_CLEAR_VOLTS,
DELTA_CHARGE_V,
CHARGE_DISCHARGE_TIME,
DELTA_DISCHARGE_V,
/*Safety*/
SOV_THRESHOLD,
SOV_RECOVERY_THRESHOLD,
SOV_TIME,
/*Balancing*/
CELL_IMBALANCE_FAIL_THRESHOLD,
CELL_IMBALANCE_FAIL_TIME,
BALANCE_TIME,
BALANCE_VOLTS_THRESHOLD,
MIN_BALANCE_VOLTS,
MAX_BALANCE_TIME
} param_id_t;
/**
* @brief Global functions declaration
*/
.
extern unsigned short get_u16_value(param_id_t param_id);
extern unsigned long get_u32_value(param_id_t param_id);
#endif
/*EOF*/
Page | 60
Appendix D
Below is the Quick User Guide for the EVM
TI bq76PL536EVM-3 Quick User Guide
Aadrvark-JP1 selects power from the USB connection through the Aardvark when installed in the
“USB” position.
AC power- The JP1 should be configured to use power from the 5VDC adapter by installing the jumper
in the “EXT 5VDC” position. To use 5VDC adapter, 2.5mm DC jack needs to be installed on the EVM.
5VDC adopter needs to 5V 100mA power supply and DC plug is 2.5mm. Center pin is positive. If USB
doesn’t supply sufficient power then use power from the 5VDC adapter.
1.1 Configure The EVM
With cells
1. Remove jumpers JP1-18 (18) located near the black battery connectors P1-P3 to reduce the
current draw of the board.
2. Connect cells to the supplied mating connectors with screw terminals BEFORE plugging the
connector into the EVM at P1, the large black connector on the left edge of the board.
3. The bottom-most pin of the battery connector is the most negative connection to the board from
the battery stack. This is the negative end of cell 1. The next pin up the connector is the positive
end of cell (and the negative end of cell 2).
4. Pin 7 of P1 (P1.7) is connected to P2.1 on the board, and the banana jack located between P1 and
P2.
5. The battery connections should be made secure, a loose connection may result in device
destruction.
1.2 With 12-26 VDC power supply
1. Install jumpers JP1-18 (18) located near the black battery connectors P1-P3 before connecting
power supplies.
2. Connect an appropriate power supply capable of supplying 12-26VDC to connector P1, then plug
P1 into the EVM connector.
3. Plug additional supplies into P2 and P3. Plug additional supplies into P2 and P3. The supplies
must be isolated from each other and from earth ground to avoid unintentional short circuits.
4. A separate supply is required for each IC.
5. The supply negative connection is made to pin 1 of the mating connector, the pin that will
connect to the bottom-most pin of the mating connector.
6. The positive connection is made to pin 7, the top-most on the connector.
7. Alternately use the banana plug connections in lieu of using the black P1-3 connectors.
1.3 Connecting the EVM
Connection order
1. Configure the EVM jumpers per 1.1
2. Connect the EVM to the Power Supplies or cells, turn on the supplies at ~12 to 24V is
recommended. The Absolute Maximum voltage per IC is 36V and should not be exceeded, 30V
is the recommended maximum continuous voltage.
Page | 61
3. Connect the USB cable to the Aardvark and your PC.
4. “A” version is designed to use USB power from Aardvark. 5V DC adapter is not required. For
None “A” version, plug the supplied wall adapter into an AC outlet. Connect the DIN plug to the
EVM board
5. Connect the Aardvark ribbon cable to the 10 pin header on the EVM board The Aardvark adapter
should be connected last during power-up, and disconnected first when powering down. If not
using the wall adapter to supply power, it must be after starting the Windows application to avoid
a turn-on issue with the Aardvark adapter. Many laptop computers power off their USB ports
when they go into sleep, standby, or hibernate modes. If the device the Aardvark is connected to
remains powered when this happens, the Aardvark may suffer permanent damage.
6. Start the WinGUI User Interface software supplied with the EVM and installed earlier.
Page | 62
Appendix E
Below are the binder drawings for the bq76PL536EVM-3 to illustrate the use of the EVM in
large scale (daisy chain).
Page | 63
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Page | 65
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Page | 67
Appendix F
Below is the user guide to set up the MSP430
Setting up the MSP430 Launchpad
 Go to http://processors.wiki.ti.com/index.php/Download_CCS and download the code
limited version, which requires a my.TI account:




Run the installation
Connect the launchpad hardware by USB.
Start Code Composer Studio v4
Start a new CCS Project and select the following options:
Page | 68



To add program files to the project, shown with the example project pre loaded on the
MSP430:
Project->Add Files to Active Project
C:\Program Files\Texas Instruments\ccsv4\msp430\examples\msp430x2xx\Csource\msp430x2xx_fet_1.c
To debug (compile and load the program onto the launchpad) click Target->Debug
Active Project
The program is now loaded on the microcontroller, and can be run directly from debug by
pressing F8 or Run from the Target menu.
Page | 69
Appendix G
Operational Manual by 491 Team
Authors: Deogratius Mpinge, Michael Healy, Abdelmagid Yousif, Spenser Mussmann
What is the high level objective of the project?
The objective is to create an efficient system to monitor and charge lithium ion batteries for use in electric
vehicles. This project will create the base case to eventually be capable of monitoring sixteen parallel
packs of ninety cells in series. This project will also address AC to DC converters for charging from
either wall outlets or other power sources.
What are the key functional requirements of the system?
Functional Requirements
○ Achieve 100 Mile Range Per Full Battary Charge
○ Monitor Temperature of Cells
○ Prevent Overcharging
○ Monitor Battery Charge
○ Develop Constant Current Constant Voltage Charging Procedure
What has been actually implemented?
The system relies on several hardware components to monitor and regulate the charging of the batteries.
The battery management hardware is bq76PL536EVM developed by Texas Instruments. This project will
have two of these battery management systems in series, each connected to nine lithium ion batteries. The
management hardware will be connected to a PC to actively monitor the current conditions of the
charging. The PC will be able to control a MSP430 microprocessor, which controls the output of a boost
converter. The Boost converter is powered by a wall AC power supply and will control the voltage and
current entering the battery management hardware.
How to setup the system?
1. Gather all items needed, that include:
a. Computer or laptop
b. Boost Converter
c. 120 VAC wall outlet
d. Texas Instruments UCC28019, PFC boost converter control integrated circuit
e. TI bq76PL536EVM-3 Microprocessor for cell monitoring
f. Aardvark USB-SPI , a USB connection adaptor
g. Monitoring system software
h. 18 series connected lithium ion battery cells
i. USB Cable
j. Power cable for the battery banks
2. Turn ON the computer
3. Connect the cell monitoring microprocessor to the USB connection adapter
4. Connect the USB cable to the computer and the USB adapter
5. Connect the boost converter to the battery bank using the power cable
6. Connect the boost converter to the wall outlet
7. Open the user interface software in the computer to monitor the cells
8. Turn ON the boost converter
The setup should be completed now and the system is ready.
Page | 70
Test results observed?
The monitoring system user interface provides the user with valuable data about the battery cells.
The most important data presented is the voltage level and graphical plot for the voltage and the
temperature in each cell.
Critique of the project:
○ The monitoring system can be scaled up to be used in electric vehicles by using different power supply
○ The team analyzed several different models before deciding which would produce the most efficient
charging.
○ A minimized design should be considered since the final product is intended for a vehicle.
Does the implementation meet the specification?
The implementation meets the specification by:
-Coding for the MSP430 PWM output and ADC has been completed
-Components for the buck converter have been sourced
-Basic resistor divider input has been implemented to changed the PWM duty cycle
Page | 71
Appendix F
Constant current test code
//Constant Current test code
//The output pwm is low by defualt and will only increase with a voltage input
//The delay each cycle was found to be necessary in practice due to a lack
//in time for the boost converter to respond to very fast increases in pwm.
//Otherwise the power fet quickly becomes continuously on and the inductor shorts.
//As an added precaution, the maximum duty cycle is set to 110/150.
#include <msp430g2231.h>
void delay(unsigned int ms);
double voltage_calc(int adc_value);
void main(void)
{
//The LED on pin P1.0 is used for visual feedback of the pwm switching feedback
P1DIR |= 0x01;
//High Frequency Clock Configuration
WDTCTL = WDTPW + WDTHOLD;
// Stop WDT
BCSCTL1 |= 0xF;
// High frequency mode, Highest Range Select
DCOCTL |= 0x70;
// Range 7
//Pulse Width Modulation
P1DIR |= 0x0C;
P1SEL |= 0x0C;
CCR0 = 150;
CCTL1 = OUTMOD_6;
CCR1 = 0;
TACTL = TASSEL_2 + MC_1;
// P1.2 and P1.3 output
// P1.2 and P1.3 TA1/2 options
// PWM Period
// CCR1 toggle/set
// CCR1 PWM duty cycle
// SMCLK, up to CCR0
//Analog to Digital Converter Initialization
ADC10CTL1 = INCH_3;
Output Unit 0, single conversion
ADC10CTL0 = ADC10ON + ADC10SHT_3 + ADC10IE;
Interrupt Enabled
for (;;) {
//Constant Current
ADC10CTL0 |= ENC + ADC10SC;
__bis_SR_register(CPUOFF + GIE);
// Clock Divider, Input Channel 3 (P1.3), Timer A
// Sample reference Vcc and Vss, enable core,
// Sampling and conversion start
// LPM0, ADC10_ISR will force exit
//Change "3" to desired output current in amps
if (current_calc(ADC10MEM) > 3 && CCR1 != 0)
{
Page | 72
P1OUT |= 0x01;
CCR1--;
}
if (current_calc(ADC10MEM) < 3 && CCR1 != 110)
{
P1OUT &= 0x00;
CCR1++;
}
delay(100);
}
}
//Input: value of output current adc
//Output: calculated output current obtained in practice in amps
double current_calc(int adc_value)
{
return((adc_value*0.0102+0.0039);
}
// Millisecond delay
void delay(unsigned int ms)
{
while (ms--)
{
__delay_cycles(16000); // set for 16Mhz change it to 1000 for 1 Mhz
}
}
// ADC10 interrupt service routine breaks from LPM
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR (void)
{
__bic_SR_register_on_exit(CPUOFF);
// Clear CPUOFF bit from 0(SR)
}
Page | 73
Appendix G
Constant voltage test code
//Constant Voltage test code
//The output pwm is low by defualt and will only increase with a voltage input
//The delay each cycle was found to be necessary in practice due to a lack
//in time for the boost converter to respond to very fast increases in pwm.
//Otherwise the power fet quickly becomes continuously on and the inductor shorts.
//As an added precaution, the maximum duty cycle is set to 110/150.
#include <msp430g2231.h>
void delay(unsigned int ms);
double voltage_calc(int adc_value);
void main(void)
{
//The LED on pin P1.0 is used for visual feedback of the pwm switching feedback
P1DIR |= 0x01;
//High Frequency Clock Configuration
WDTCTL = WDTPW + WDTHOLD;
// Stop WDT
BCSCTL1 |= 0xF;
// High frequency mode, Highest Range Select
DCOCTL |= 0x70;
// Range 7
//Pulse Width Modulation
P1DIR |= 0x0C;
P1SEL |= 0x0C;
CCR0 = 150;
CCTL1 = OUTMOD_6;
CCR1 = 0;
TACTL = TASSEL_2 + MC_1;
// P1.2 and P1.3 output
// P1.2 and P1.3 TA1/2 options
// PWM Period
// CCR1 toggle/set
// CCR1 PWM duty cycle
// SMCLK, up to CCR0
//Analog to Digital Converter Initialization
ADC10CTL1 = INCH_1;
Output Unit 0, single conversion
ADC10CTL0 = ADC10ON + ADC10SHT_3 + ADC10IE;
Interrupt Enabled
for (;;) {
//Constant Voltage
ADC10CTL0 |= ENC + ADC10SC;
__bis_SR_register(CPUOFF + GIE);
// Clock Divider, Input Channel 1 (P1.1), Timer A
// Sample reference Vcc and Vss, enable core,
// Sampling and conversion start
// LPM0, ADC10_ISR will force exit
//Change "65" to desired output voltage in volts
if (voltage_calc(ADC10MEM) > 65 && CCR1 != 0)
{
Page | 74
P1OUT |= 0x01;
CCR1--;
}
if (voltage_calc(ADC10MEM) < 65 && CCR1 != 110)
{
P1OUT &= 0x00;
CCR1++;
}
delay(100);
}
}
//Input: value of output voltage adc
//Output: calculated output voltage obtained in practice in volts
double voltage_calc(int adc_value)
{
return((adc_value*0.2853+0.0403);
}
// Millisecond delay
void delay(unsigned int ms)
{
while (ms--)
{
__delay_cycles(16000); // set for 16Mhz change it to 1000 for 1 Mhz
}
}
// ADC10 interrupt service routine breaks from LPM
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR (void)
{
__bic_SR_register_on_exit(CPUOFF);
// Clear CPUOFF bit from 0(SR)
}
Page | 75
Appendix H
Full system code
//******************************************************************************
// MSP430G2xx - Boost Converter Control
//
// Description: This program generates one PWM output on P1.2 using
// Timer_A configured for up/down mode. The value in CCR0, 128, defines the PWM
// period and the value in CCR1 the PWM duty cycle.
//
// A single Analog to Digital conversion is performed on Pin 1.1 and
//
the low power mode is entered while the conversion is taking place.
//
The conversion value is used as feedback for increasing or decreasing
//
the PWM signal duty cycle.
//
//
MSP430x2xx
//
-----------------------//
/|\|
XIN|//
||
|
//
--|RST
XOUT|//
|
|
// Vout>---|A1/P.1 P1.2/TA1|--> CCR1 - PWM
//
|
|
// Iout>---|A3/P1.3
|
//
|
|
// VIN >---|A5/P1.5
|
//
//
// sdmay11-04
// Iowa State University
// November 2010
// Built with CCE Version: 4.2
//******************************************************************************
#include <msp430g2231.h>
#define C_CURRENT = 3; //Amps
#define C_CURRENT_MIN = 0.3 //Amps, stop charging constant voltage at this current
#define NUMBER_OF_BATTERIES = 18;
#define BAT_VOLTAGE_MIN = 1.6; //Volts
#define BAT_VOLTAGE_MAX = 3.6; //Volts
#define PACK_VOLTAGE_MIN = NUMBER_OF_BATTERIES*BAT_VOLTAGE_MIN; //Volts
#define PACK_VOLTAGE_MAX = NUMBER_OF_BATTERIES*BAT_VOLTAGE_MAX; //Volts
#define PWM_UPPER_LIMIT = 100; // 100 over 150 is a duty cycle of 0.66
#define PWM_LOWER_LIMIT = 0; // duty cycle of 0
char state = 0; //0=MSP430 startup/discharge/wait for charge 1=Constant Current 2=Constant Voltage
Page | 76
double current_calc(int adc_value);
double voltage_calc(int adc_value);
void delay(unsigned int ms);
void main(void)
{
P1DIR |= 0x01;
//High Frequency Clock Configuration
WDTCTL = WDTPW + WDTHOLD;
// Stop WDT
BCSCTL1 |= 0xF;
// High frequency mode, Highest Range Select
DCOCTL |= 0x70;
// Range 7
//Pulse Width Modulation
P1DIR |= 0x0C;
P1SEL |= 0x0C;
CCR0 = 150;
CCTL1 = OUTMOD_6;
CCR1 = 0;
TACTL = TASSEL_2 + MC_1;
// P1.2 and P1.3 output
// P1.2 and P1.3 TA1/2 options
// PWM Period
// CCR1 toggle/set
// CCR1 PWM duty cycle
// SMCLK, up to CCR0
//Analog to Digital Converter Initialization
ADC10CTL1 = INCH_1;
Channel 1, Timer A Output Unit 0, single conversion
ADC10CTL0 = ADC10ON + ADC10SHT_3 + ADC10IE;
Interrupt Enabled
// Clock Divider, Input
// Sample reference Vcc and Vss, enable core,
for (;;) {
switch(state)
{
//MSP430 power on, beginning state
case 0:
//Start by getting the input voltage
ADC10CTL1 = INCH_5;
// Input channel 5 for input voltage sense
ADC10CTL0 |= ENC + ADC10SC;
// Sampling and
conversion start
__bis_SR_register(CPUOFF + GIE);
// LPM0, ADC10_ISR will force exit
if (ADC10MEM < 200)
{
state=0;
//Wait a minute before checking to recharge
delay(60000);
}
else
{
//Start by getting the output voltage (battery voltage)
ADC10CTL1 = INCH_1;
// Input channel 1 for input voltage sense
Page | 77
ADC10CTL0 |= ENC + ADC10SC;
// Sampling and
conversion start
__bis_SR_register(CPUOFF + GIE);
// LPM0, ADC10_ISR will
force exit
//Set to charge if the voltage is between the constant current
boundary
if((voltage_calc(ADC10MEM) < PACK_VOLTAGE_MAX) &&
(voltage_calc(ADC10MEM) > PACK_VOLTAGE_MIN))
{
state=1;
}
}
break;
//Constant Current
case 1:
//Input plugged in, ready to charge constant current
//Start by getting the output voltage (battery voltage)
ADC10CTL1 = INCH_1;
// Input channel 1 for input voltage sense
ADC10CTL0 |= ENC + ADC10SC;
// Sampling and
conversion start
__bis_SR_register(CPUOFF + GIE);
// LPM0, ADC10_ISR will force exit
//Set to constant voltage if the voltage is greater than the pack max
voltage
if(voltage_calc(ADC10MEM) > PACK_VOLTAGE_MAX)
state=2;
//otherwise, perform constant current changes to the power supply
//Constant Current
ADC10CTL1 = INCH_3;
// Input channel 3 for current
ADC10CTL0 |= ENC + ADC10SC;
__bis_SR_register(CPUOFF + GIE);
// Sampling and conversion start
// LPM0, ADC10_ISR will force exit
if (current_calc(ADC10MEM) > C_CURRENT && CCR1 != 0)
{
P1OUT |= 0x01;
CCR1--;
}
if (current_calc(ADC10MEM) < C_CURRENT && CCR1 != 110)
{
P1OUT &= 0x00;
CCR1++;
}
break;
//Constant voltage
case 2:
Page | 78
//Check the output current to determine if charge is finished
ADC10CTL1 = INCH_3;
//
Input channel 3 for current
ADC10CTL0 |= ENC + ADC10SC;
// Sampling and conversion start
__bis_SR_register(CPUOFF + GIE);
// LPM0, ADC10_ISR will force exit
if (voltage_calc(ADC10MEM) < C_CURRENT_MIN);
state=0;
//Constant Voltage
ADC10CTL1 = INCH_1;
// Input channel 3 for current
ADC10CTL0 |= ENC + ADC10SC;
// Sampling and conversion start
__bis_SR_register(CPUOFF + GIE);
// LPM0, ADC10_ISR will force exit
if (voltage_calc(ADC10MEM) > PACK_VOLTAGE_MAX && CCR1 != 0)
{
P1OUT |= 0x01;
CCR1--;
}
if (voltage_calc(ADC10MEM) < PACK_VOLTAGE_MAX && CCR1 != 110)
{
P1OUT &= 0x00;
CCR1++;
}
}
delay(100);
}
}
//Input: value of output current adc
//Output: calculated output current obtained in practice in amps
double current_calc(int adc_value)
{
return((adc_value*0.0102+0.0039);
}
//Input: value of output voltage adc
//Output: calculated output voltage obtained in practice in volts
double voltage_calc(int adc_value)
{
return((adc_value*0.2853+0.0403);
}
// Delays by the specified Milliseconds
void delay(unsigned int ms)
{
while (ms--)
{
__delay_cycles(16000); // set for 16Mhz change it to 1000 for 1 Mhz
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}
}
// ADC10 interrupt service routine breaks from LPM
#pragma vector=ADC10_VECTOR
__interrupt void ADC10_ISR (void)
{
__bic_SR_register_on_exit(CPUOFF);
// Clear CPUOFF bit from 0(SR)
}
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Appendix I
3.3V Regulated source from 12V
Figure 31: Various components require a 3.3V source, and the LM317 voltage regulator is used from the input
12V source
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