As presented to July 2009. Battery Management Systems for Electric Vehicles.
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Transcript of As presented to July 2009. Battery Management Systems for Electric Vehicles.
As presented to
July 2009
Battery Management Systems for Electric Vehicles
Comparison:Lead vs. Lithium in EVs Charging
Lead-acid batteries charges well in a long string Over voltage in a cell is not good, but generally passes the current to the
next cell in an equalization cycle with little damage. Cell balancing can be done with a sophisticated charger (IUIa cycle)
Lithium batteries OK in a string, but over voltage on a individual cell can do serious cell damage.
Individual cell charging is solution, or Balancing cells and charge in a string.
Discharging Lead can tolerate discharging to 0% State of charge (SOC) with some
cycle life damage. Lithium will have serious damage when discharging below 2.0V, can be
completely ruined.
Lead-Acid Discharge Curve
http://www.trojanbattery.com/BatteryMaintenance/Testing.aspx
5.7
5.8
5.9
6
6.1
6.2
6.3
6.4
6.5
0102030405060708090100110
6V Lead Acid Battery Discharge Curve
BatteryVoltage
State of Charge
Lithium Discharge Curves
Lithium Batteries have a fairly flat discharge curve with sharp shoulders
http://enerdel.com/content/view/105/88/
Lithium BMS Challenges
1. Must not Over-Charge an individual cell
2. Must not Over-Discharge an individual cell
3. Must not let cells get too hot during charge or discharge
ENTER THE LITHIUM BMS Many thoughts and discussions on what constitutes a Battery
Management System (BMS): Monitor and Detect Cell Over-Charge, and cut off charger Monitor and Detect Cell Over-discharge and alert operator, or cut off
system power. Cell Balance for string charging Temperature Monitoring Remaining State of Charge determination
This is done in your cell phone & laptop, why not in your car? High voltages and high currents make it difficult
Sparse BMS technology availability has held up Lithium conversion projects.
BMS Topology: Distributed Put voltage monitor and
discharge balancer on each cell, with digital communications for charger cutoff and status.
Advantages: Simpler design and construction and its potential for higher reliability in an automotive environment. Disadvantages: Large number of mini-slave printed circuit boards which are needed and the difficulty of mounting them on some cell types.
BMS Topology: Modular
Advantages: Does not need printed circuit boards connected to individual cells. Disadvantages: Master-Slave isolated communications can be challenging in an EV.
Several Slave controllers consolidate data to a master
BMS Topology: Centralized
Centralized Master Control Unit
Advantages: Single installation point. No complex inter-vehicle communications Disadvantages: Typical EV batteries are distributed in the vehicle, requiring wiring to a central location. Single source for balancer heat generation.
Central Master
Control Unit
1
Li-Ion BMS Market options Investigate BMS solution for highway capable
EV conversion Needs to support typical DC system:
160 AH prismatic LiFeP04 (3.2V), 250A + systems40-48 cells (128 to 153 volts)Must monitorShould manage, report and balance
Li-Ion BMS optionsC
om
pan
y
(1)
Top
olo
gy
(3)
No o
f cells
(4)
Bala
n.
(5
)
Tem
per.
(6
)
Dis
pla
y
Fu
el
gau
ge (
8)
Over
Volt
P
rote
cti
on
Com
m.
(9)
Case
(10
)
Pri
ce,
48
-cell
(11
)
Agni motors Stybrook Ltd
Distrib.
1~200 ✓ - - - - Wire - ~$1000
Black Sheep Technology
Modular
4~any ✓ ✓ - ✓ ✓ Serial
Plastic / metal
~$2200
Elithion Distrib.
1~255 ✓ ✓ ✓ ✓ ✓ Wire CAN RS23
2
-
~$2000 - $4000
EV power Distrib.
1~any ✓ - - - ✓ Wire Metal
~$1800*
Li-Ion BMS options (continued)C
om
pan
y
(1)
Top
olo
gy
(3)
No o
f cells
(4)
Bala
n.
(5
)
Tem
per.
(6
)
Dis
pla
y
Fu
el
gau
ge (
8)
O
ver
Volt
P
rote
cti
on
Com
m.
(9)
Case
(10
)
Pri
ce,
48
-cell
(11
)
High Tech Systems (SSI?)
Distrib.
1~any ✓ ✓ ? - ? Wire
-
??
Ningbo Yangming Elite Power (BMS 50)
Modular
Up to 50,
higher available
✓ ✓ ✓ ✓ - ? Metal $1789
PackTrakr from KJ Hall Motor Co
Modular
6~40 - ✓ ✓ - - RS232
Plastic $710 (40 cells only)
REAP systems
Modular
4~168
✓ ✓ ✓ ✓ ✓ Bus -
697 x 4 = $2788*
Volt Blocher
Distrib.
1~any ✓ - - - opt Opt wire
- $864-1008
assembled
BMS Honorable Mention Lithium Balance – No published specs or pricing Gary Goodrum – DIY BMS Ckt, 24 cell on Endless
Sphere, Low current device for bikes Metric Mind – Custom BMS, no pricing for BMS products Boundless – creates custom battery packs. Hot Juice Electric BEQ – Balance only Manzanita Micro – Partial solution, 4 cells for $250 Open Source BMS projects – no resolutions
Small Print:1. Company: A few other companies are getting ready to offer Li-Ion BMSs, but are not yet ready to be listed here. 2. Class:
• Simple: analog technology, just able to detect that some cell's voltage is too low or too high• Fancy: sophisticated digital technology, able to measure and report every cell voltage, and to calculate SOC
3. Topology: See previous slides4. Number of cells: this is the acceptable range in the number of cells in series. The number of cells in parallel does
not matter.5. Balance: The BMS is able to remove energy just from the most charged cells, to allow the other cells to reach the
same level of charge. 6. Temperature: The BMS is able to measure and report individual cells' temperature. 7. Current sense: The BMS includes a current sensor or at least an input for a current sensor, to measure battery
current. This enables the BMS to react to excessive current, and to calculate the SOS or DOD.8. "Fuel gauge": a.k.a.: "Gas Gauge". The BMS calculates the SOC (State Of Charge) or DOD (Depth Of
Discharge), by integrating the battery current.9. Communications:
• Wire: separate wires are used, each with a single, specific function, such as to turn on the charger relay.• CAN: CAN bus, common in vehicles and European industrial equipment.• RS232: serial point-to-point communication, usually used only for initial set-up and testing, but some time also available for communication during operation.
10. Case: Whether the BMS controller is enclosed (metal or plastic case), or it is an open PCB assembly. Unless otherwise noted, any cell-mounted boards are assumed to be open PCB assemblies.
11. Price: from manufacturers' websites or discussion with their clients.
Hardy EV Flex BMS Centralized BMS Architecture Miniature In car display and operator alerts Battery monitoring for over-voltage, under voltage 3 versions in production
Up to 36 cells - For NEVs and small EVs Up to 48 cells – For DC systems Up to 84 cells – Prius plug-in conversions and AC systems
Temperature monitoring Adjustable voltage and temperature thresholds Cell balancing with built-in thermal management Full diagnostic self test identifies faulty wiring Internal Log allows identification of problem batteries USB Log Option for detailed cell monitoring logs Current monitor option for state of charge determination Works with charger up to AC: 25A 240V Priced for EV conversions: $891 for 48 cell system
Data logger option $50 Current Monitor option $60
www.ConvertTheFuture.com
