LiFePO4 Formula Hybrid Charger
Design Team #9
Kevin Friedman, So/ware Manger, EE Jiaming Zhou, Hardware Manager/Archivist, EE Michael Shepard, Project Manager, EE Faculty Advisors: Dr. Elbuluk Dr. Madanayake December 2, 2011 Need/Goals
2012 SAE Formula Hybrid competition
•  1st Year All Electric
•  Batteries Need A Charger
Charger For LiFePO4 Batteries
-
An Ideal Battery Charger :
• 
Charges Battery Quickly And Safely
• 
Prevents Overcharging
• 
Automatically Adjusts Output
• 
Monitors Battery Cells’ Temperature & Voltage
• 
Detects Battery Faults
• 
Displays Important Battery Data to User
2 Design Requirements
Engineering Requirements
Justification
Must charge 75% of the battery in less than 4 During the competition, quick battery
hours.
charge times are needed.
The user display must be in decimal number A user should not have to decode CAN
format using proper engineering units for voltage, data to be able to read and use the
current and temperature levels.
charger.
The charger must reduce the output current to 1A If the current is more than 1A when the
once a single battery cell reaches 3.9V and is Cell reaches 3.9V, the battery risks
shunted by the battery controller.
overcharging.
The charger must accept a 120V AC, 15A power This is a standard rating for residential
input.
outlets.
3 Design Requirements
Engineering Requirements
Justification
The entire charger must be movable by a single The charger will need to be moved with
person and have simple connections to the car/ the vehicle in order to charge its
power source.
batteries.
The charger must remove all power to the battery One second should be enough time for
within 1 second during a fault or over-current even a very slow relay to trip and
situation.
disconnect power.
The charger must contain a 20A fuse and a GFI be These safety features greatly reduce the
able to detect a leakage current of at least 15mA.
risk of electric shock.
The charger must display specific errors including Specific errors allow the user some
loss of CAN signal, over-current, over- insight into why the charger is not
temperature, and GFI fault.
operating.
4 Charger Hardware
5 Charger Hardware-AC/DC Converter
6 Charger Hardware-GFI
•  Current Transformer Output
–  𝑉
​ ↓𝑜𝑢𝑡,𝐶𝑇 =(​​𝐼↓𝐿 /𝑡𝑢𝑟𝑛𝑠 )​𝑅↓𝐵𝑢𝑟𝑑𝑒𝑛 =(​​𝐼↓𝐿 /1011 )200Ω=​𝐼↓𝐿 ×0.1978Ω.
•  Filter
–  𝑓
​ ↓𝑐𝑢𝑡𝑜𝑓𝑓 =100𝐻𝑧=​1/2∗𝜋∗𝑅∗𝐶 , 𝐿𝑒𝑡 𝐶=1𝜇𝐹,𝑅=​
1/2∗𝜋∗1𝜇𝐹∗100𝐻𝑧 =1.592𝑘𝛺
7 Charger Hardware-GFI
•  Schmitt Trigger
–  𝑉
​ ↓𝑟𝑒𝑓𝑟𝑒𝑛𝑐𝑒 =​𝑅↓7 /​𝑅↓7 +​𝑅↓8 ×5𝑉=​51𝐾Ω/51𝑘Ω+1𝑀Ω ×5𝑉=𝟎.𝟐𝟒𝟐𝟔𝑽,
–  ​𝑉↓𝑇𝐿 =​𝑉↓𝑟𝑒𝑓𝑟𝑒𝑛𝑐𝑒 ×(1+​𝑅↓5 /​𝑅↓6 )−​𝑅↓5 /​𝑅↓6 ×​𝐿↓+ =0.2426×(1+​300Ω/10𝑘Ω )−​300Ω/10𝑘Ω ×5𝑉=𝟎.𝟏𝟎𝑽,
–  ​𝑉↓𝑇𝐻 =​𝑉↓𝑟𝑒𝑓𝑟𝑒𝑛𝑐𝑒 ×(1+​𝑅↓5 /​𝑅↓6 )−​𝑅↓5 /​𝑅↓6 ×​𝐿↓− =0.2426×(1+​300Ω/10𝑘Ω )−​300Ω/10𝑘Ω ×0𝑉=𝟎.𝟐𝟓𝟎𝑽.
Top Graph: Current Input, BoVom Graph: GFI Output 8 Charger Hardware-AC/DC Rectifier/Filter
•  𝑉
​ ↓𝑜 =​𝑉↓𝑟𝑚𝑠 ×√⁠2 =120×√⁠2 =169.705​𝑉↓𝐷𝐶 ≅170​𝑉↓𝐷𝐶 •  𝐹
​ ↓𝑓𝑖𝑙𝑡𝑒𝑟,𝑐𝑢𝑡𝑜𝑓𝑓 =​1/𝜋×√⁠𝐿𝐶 =​1/𝜋×√⁠15µμH×2.2mF =1752𝐻𝑧
9 Charger Hardware-Relay/Fuse
•  Sends a cut-off signal for a GFI or over current
fault to remove power to the charger.
•  The power is not restored until the reset button
is pushed by the user.
10 Charger Hardware-Relay/Fuse
•  The relay opens and cuts power on a GFI Fault or
Over current fault
•  LEDS illuminate to indicate specific fault
•  Relay opens and stays open until the fault clears and
user hits the rest button
11 Charger Hardware-Charger
12 Charger Hardware-Battery
11V
9.73V
7A
0.0393
11.5V
10.4V
7A
0.0332
12V
10.9V
7A
0.0332
12.5V
11.4V
7A
0.0332
13V
11.95V
7A
0.0314
13.5V
12.23V
7A
0.0393
14V
12.63V
7A
0.0429
•  BaVery Model and Measurement of internal Resistance •  Note: 13 Charger Hardware-Variable DC/DC Converter
•  Varied output from 0-20A, 0-130V
•  Frequency of Switching: 100kHz
•  Vs is approximately 150V
14 Charger Hardware-Variable DC/DC Converter
•  Buck Converter
•  ​𝑉↓𝑜 /​𝑉↓𝑖𝑛𝑝𝑢𝑡 =𝐷
•  ​𝑉↓𝑜,𝑚𝑎𝑥 =​𝑉↓𝑏𝑎𝑡𝑡𝑒𝑟𝑦 +​𝐼↓𝑜 Σ𝑅=3.9×24+20×1.96=132.8𝑉
–  𝐷=​𝑉↓𝑜 /​𝑉↓𝑠 =​132.8/169 =0.786
•  𝐿
​ ↓2,𝑚𝑖𝑛 =​(1−𝐷)∗𝑅/2𝑓 =​(1−0)×2/100×​10↑3 =10µμ𝐻
•  𝐶
​ ↓3,𝑚𝑖𝑛 =​1−𝐷/8𝐿(​∆​𝑉↓𝑜 /​𝑉↓𝑜 )​𝑓↑2 =​1−0.786/8(0.9×​
10↑−3 )(2%)​(25×​10↑3 )↑2 =8.73𝜇𝐹
•  Filter
–  ​𝐹↓𝑐𝑢𝑡𝑜𝑓𝑓 =​1/𝜋×√⁠𝐿𝐶 =​1/𝜋×√⁠15µμH×2.2mF =1752𝐻𝑧
15 Charger Hardware-Variable DC/DC Converter
•  Buck Converter Output at 20A and 133V
•  20% Voltage Ripple
•  20% Current Ripple
16 Charger Hardware-Hall Effect Current Sensor
Output Voltage (V) Output Voltage versus Sensed Current 5 4 3 2 1 0 1 3 5 7 9 11 13 15 17 19 21 23 25 Sensed Current (A) •  Overcorrect Signal goes high when the current
reaches 25A
–  Over current Value adjusting R13 and R14
•  LABVIEW connects directly from the output of
the sensor
17 Charger Hardware-Controller
18 Charger Hardware-Controller
•  The charger will contain a type B USB
connection which connects to a Computer
Containg t
19 Hardware- Mechanical Drawing
20 Software Design
•  The user display must be in decimal number
format using proper engineering units for
voltage, current, and temperature levels.
•  The charger must reduce the output current to
1A once a single battery cell reaches 3.9V and
is shunted by the battery controller.
•  The charger must display specific errors
including loss of CAN signal, over-current, overtemperature, and GFI fault.
21 Software- Interfacing
Voltage to Control Current
CAN message
Car
NI USB-8473
Computer with
LabVIEW
NI-USB-6009
Charger
Shutdown Signal
Analog Current
•  NI USB-8473 to collect CAN message
•  NI USB-6009 for analog/digital I/O
•  Computer with LabVIEW as main controller
22 Charge Characteristics
I
23 Software- Overview
• 
• 
• 
• 
Read ADC
Store Current
Sensor Reading
Read CAN
Store decoded
CAN message
values
Compare Values
Output Voltage to
Control Current
Trigger Shutdown
Count
Current sensor reading stored as digital value
CAN message contains volt/temp information for each cell
Compare values with stored warning values
Output voltage controls PWM circuit
24 Software- Current Control
,
Con]nues Model of DC/DC Buck Converter: Discrete Model of DC/DC Buck Converter: Note: n is the ra]o of the sampling freq and switching freq 25 Software- Current Control
26 Software- Current Control Pseudo Code
Data PWM_PERIOD DUTY_ON DUTY_RATIO DESIRED_CURRENT SENSOR_VOLTAGE MEASURED_CURRENT CURRENT_ERROR NOMINAL_ DUTY_RATIO NOMINAL_ DUTY_ON DUTY_ON_DIFFERENCE PWM_VOLTAGE CUT_OFF CODE REPEAT { READ DESIRED_CURRENT READ SENSOR_VOLTAGE COMPUTE MEASURED_CURRENT = k * SENSOR_VOLTAGE COMPUTE CURRENT_ERROR = DESIRED_CURRENT – MEASURED_CURRENT DUTY_ON_DIFFERENCE = CURRENT_ERROR * Kp READ NOMINAL_ DUTY_RATIO COMPUTE NOMINAL_DUTY_ON = NOMINAL_ DUTY_RATIO * PWM_PERIOD COMPUTE DUTY_ON = NOMINAL_DUTY_ON + DUTY_ON_DIFFERENCE COMPUTE DUTY_RATIO = DUTY_ON / PWM_PERIOD WHILE DUTY_ON > 0.8 DUTY_ON = 0.8 ENDWHILE COMPUTE PWM_VOLTAGE PRINT PIN AO0 = PWM_VOLTAGE } UNTIL CUT_OFF = 1 27 Software-PWM Pseudo Code
Data
DUTY_ON
PWM_PERIOD
DUTY_OFF
PWM_voltage
PR2
DUTY_RATIO
Code
Configure PM0 for output
WHILE (1)
{
PWM_Voltage=ADC_PIN6
DUTY_RATIO= PWM_Voltage/5
PWM_PERIOD=(PR2+1)*4*Tosc
DUTY_ON= PWM_PERIOD*DUTY_RATIO
DUTY_OFF = PWM_PERIOD - DUTY_ON
turn on PIN 5
delay for DUTY_ON
turn off PIN 5
delay for DUTY_OFF
}
Input Output PWM Duty Ra]o (%) Voltage(V) (at 100kHz) 0 0 0.5 10 1 20 1.5 30 2 40 2.5 50 3 60 3.5 70 4 80 4.5 90 5 100 28 Software-Flow Chart
Analog Current
A/D
Conversion
Digital Current
Compare to
Warning
Presets
No
Out of Bounds?
Yes
Shutdown
signal
Cut Power
Yes
Yes
Any Temp
Over Limit?
No
CAN data
Decode
Temp/Voltage
Compare to
Warning
Presets
No
Any Cells
Over 3.7V?
Timer
Overflow?
Yes
Reduce
Charging
Current to
4Amps
No
Count
Yes
Any Cells
Over 3.9V?
Reduce
Charging
Current to
1Amp
29 Thank You
30