-62- SOC 100% Over-charge risk Over-discharge risk Estimation error Estimation error Working range Over-charge risk Over-discharge risk Estimation error enlarge Estimation error Working range 0% charge upper limit discharge lower limit Estimation accuracy LOW Estimation accuracy HIGH Shingo TSUCHIYA *1 automobiles, the cost of the battery, available occupant space, and the driving range have become issues, and thus making further evolution of the BMS is required. This paper introduces new technical contents in BMS development that are available to achieve cost reduction, downsizing, high precision cell voltage detection and high efficiency for increasing driving range, combined with improvements in safety protection reliability of the lithium-ion battery with which there are inherent smoke and fire risks. 2. Integration of System with High Voltage A conventional BMS consists of multiple components: a battery control unit (Batt-ECU); cell voltage sensors (CVSs); and a leakage sensor. Since the number of battery cells is large, an example would be a CVS arranged for each battery module of 12 cells in series connection, where the cell information measured by the CVS is sent to the Batt-ECU via communication bus, and each cell is controlled by the Batt-ECU, such system being called a distributed BMS. However, the use of a distributed BMS causes substantial increases in vehicle cost with the increased unit cost due to the use of multiple CVSs and electric harness for inter-unit communication. In consideration of this situation, an integrated BMS has been developed, greatly reducing costs by combining the Batt-ECU, CVSs and a leakage sensor into one unit (Fig. 2). *1 BMS Development Department, R&D Operations ※ Received 28 August 2017 1. Introduction The issues of global warming and the tightening of legal restrictions have caused the market environment to move towards widespread use and expansion of electrically driven vehicles. Hybrid electric vehicles (HEVs) and zero emission vehicles (ZEVs) are equipped with rechargeable lithium-ion batteries (LiBs) to drive the traction motor and accessories. In order to expand the energy density of the high voltage battery and maximize battery performance, a battery management system (BMS) using technologies of high precision cell voltage detection and highly efficient energy loss reduction, is indispensable (Fig. 1). Today, various HEVs and ZEV’s are released by vehicle manufacturers, and it can be said that electrically driven vehicles have entered into a period of expansion. However, as a consequence of the electrification of Technical Digest Integrated Battery Management System Combining Cell Voltage Sensor and Leakage Sensor ※ Fig. 1 Maximize effective use of battery performance
6
Embed
Technical Digest Integrated Battery Management System ... · Integrated Battery Management System Combining Cell Voltage Sensor and Leakage Sensor: hindrance factor for accuracy harness
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
-62-
Integrated Battery Management System Combining Cell Voltage Sensor and Leakage Sensor
SOC100%
Over-charge risk
Over-discharge risk
Estimation error
Estimation error
Working range
Over-charge risk
Over-discharge risk
Estimation error
enlarge
Estimation error
Working range
0%
chargeupper limit
dischargelower limit
Estimation accuracyLOW
Estimation accuracyHIGH
Shingo TSUCHIYA*1
automobiles, the cost of the battery, available occupant
space, and the driving range have become issues, and
thus making further evolution of the BMS is required.
This paper introduces new technical contents in
BMS development that are available to achieve cost
reduction, downsizing, high precision cell voltage
detection and high efficiency for increasing driving
range, combined with improvements in safety
protection reliability of the lithium-ion battery with
which there are inherent smoke and fire risks.
2. Integration of System with High Voltage
A convent ional BMS consis ts of mul t ip le
components: a battery control unit (Batt-ECU); cell
voltage sensors (CVSs); and a leakage sensor.
Since the number of battery cells is large, an
example would be a CVS arranged for each battery
module of 12 cells in series connection, where the
cell information measured by the CVS is sent to
the Batt-ECU via communication bus, and each cell
is controlled by the Batt-ECU, such system being
called a distributed BMS.
However, the use of a distributed BMS causes
substantial increases in vehicle cost with the
increased unit cost due to the use of multiple CVSs
and electric harness for inter-unit communication.
In consideration of this situation, an integrated
BMS has been developed, greatly reducing costs
by combining the Batt-ECU, CVSs and a leakage
sensor into one unit (Fig. 2).
*1 BMS Development Department, R&D Operations
※ Received 28 August 2017
1. Introduction
The issues of global warming and the tightening
of legal res t r ic t ions have caused the market
environment to move towards widespread use and
expansion of electrically driven vehicles.
Hybrid e lect r ic vehic les (HEVs) and zero
emiss ion vehic les (ZEVs) are equipped wi th
rechargeable lithium-ion batteries (LiBs) to drive the
traction motor and accessories. In order to expand
the energy density of the high voltage battery and
maximize battery performance, a battery management
system (BMS) using technologies of high precision
cell voltage detection and highly efficient energy
loss reduction, is indispensable (Fig. 1).
Today, various HEVs and ZEV’s are released
by vehicle manufacturers, and it can be said that
electrically driven vehicles have entered into a
period of expansion.
However, as a consequence of the electrification of
Technical Digest
Integrated Battery Management System Combining
Cell Voltage Sensor and Leakage Sensor ※
Fig. 1 Maximize effective use of battery performance
TechnicalDigests
-63-
Keihin Technical Review Vol.6 (2017)
Li-ion leakage detection
leakage sensorcell voltage sensor
battery ECU
leakhigh voltageconnection
control
battery residualquantity info.
PCU
MG ECU
BMS
battery cooling control
systemintegration
Cellvoltage
temperature
current
mask processing according to the voltage fluctuation
state of the battery, have been introduced in order to
distinguish battery transient voltage fluctuation from
leakage resistance fluctuation, and thus detection
accuracy has been greatly improved (Fig. 4).
Expanding these techniques to various cell
numbers and into the platform, a BMS that can deal
with various battery cell number variations has been
developed (Fig. 5).
Fig. 2 Integrated BMS with system diagram
leakageresistance
FG
FG(Frame GND)
levelconversion
battery voltagedetection
Large peak value = large leakage resistanceLow peak value = low leakage resistance
BPF
MPU
Signalamplifier
referencesignal
generator
FFT processingresistancecalculation
mask processingexternal BMS
LiB
Fig. 3 Leakage detection block diagram
BMS passing voltagebattery transient voltage fluctuation
starting voltageovercurrent cut-off
induction noise
inverter SW noise
1st, 2nd ordercommon mode noise
sudden acceleration
strong regenerative
Fig. 4 Effectiveness of FFT & mask in image
PCB for BMS
Lower case
Upper cover
Fig. 5 BMS for 48 cells (left) and 96 cells (right)
Furthermore, with regard to the cell voltage
monitoring part of the CVS, a new circuit has been
developed in which a level shift type flying capacitor
circuit configuration based on conventional discrete
components has been modified, and the new circuit
has been designed whereby the input protection
which was necessary for each cell can be conducted
for multiple cells. With this technique, the protection
components are minimized while also reducing leakage
current, and functional integration of the cell voltage
monitoring part into a one chip IC was also achieved.
In comparison with the conventional unit, the CVS part
was downsized by 84% and cost was also reduced.
This IC is normally called LiB-IC, it has the multiple
functions, such as cell voltage detection, cell balancing,