The term ‘‘Battery Monitoring’’ is used in a wide range of
meanings, from occasional manual readings of voltages, of electrolyte gravity
SG and level, and visual cell inspection, through periodical tests of capacity
or manual measurement of battery resistance, to fully automated on-line
supervision in critical applications with means for real-time estimation of
residue bridging time, or of battery wear and tear.
Here the term Battery Monitoring is used for supervision
without manual engagement, which is state-of- the-art with many cycling
batteries in automobiles like automatically guided vehicles (AGVs), forklift
trucks, submarines, electrically driven cars and trucks, as well as with
standby batteries in telecom and UPS applications. With consumer applications,
any mobile phone, laptop or pocket computer, or even a wristwatch is equipped
with a device providing some information with respect to energy being left.
The specific situation of the automotive battery becomes
obvious, technically impeding Battery Monitoring in the automotive fields:
- They are scarcely ever been completely charged, i.e. ‘opportunity charge’ is standard.
- Recharge is performed with a wide range of different current rates.
- Discharge virtually never starts from a full SOC.
- Discharge is performed with a wide range of different current rates. Sometimes full discharge or (unfortunately) even over-discharge occurs.
- Operational temperature may even exceed the window from 30 to 70 degrees
While the term
‘‘Battery Monitoring’’ comprises
- Taking and/or receiving data from and/or about the battery
- Processing of this information, including predictions of performance, and
- Being or a unit, i.e. only passive surveillance and evaluation
The term ‘‘Battery Management’’ means active feedback to the
battery. This may comprise control of current or voltage levels, control of
recharge conditions, limiting of the operational windows with respect to SOC
and/or temperature, battery temperature management, etc.
An appropriate Battery Management may enhance and improve,
but is not a precondition for, a successful Energy Management. It is Energy
Management, preferably including Battery Management, which, based on the information
from Battery Monitoring, allows for a self-standing operation of a system
without manual input—the comfort and the technical necessity requested for a
vehicle at the beginning of the 21st century.
Battery Monitoring allows for best use of the capability of
a battery of given size, to guarantee power supply for high reliability
devices, and for replacement strategies. Further-more, monitoring of the actual
state-of-charge allows for an electrical power management which may include
both reducing consumption of electrical power by limiting of operable luxury
applications as well as increase of power generation by appropriate control of
alternator or even idle speed and automatic gearbox control.
Battery Monitoring may be needed if
1. Energy has to be provided for a component which is
essential for operation, e.g. an Electromechanical Power Steering (EPS) or an
Electro-hydraulic Power Braking (EHB) system, an electrically powered
suspension stabilization system, or an automatic gear shift;
2. An Electrical Energy Management (EEM) has to
guarantee, e.g. for future cranking capability;
3. The cranking capability has to be supervised to
operate a stop/start-system;
4. An indication of battery fatigue is needed for
garage service to replace the battery.
Battery Monitoring consists of data acquisition, data
processing, and some prediction of the future. For different technical goals,
different information with respect to the future is needed. Any approach for
Battery Monitoring may be classified according to the following criteria, which
may be combined, too, e.g. data acquisition from both long-term and the nearest
past, and prediction of both battery status and behavior.
A. Data
Acquisition
1. Type of data: Battery status/battery
behavior/operational conditions
2. Time scale of data acquisition: From long-term
history/near past
3. Source of data: External battery parameters
/internal battery parameters (e.g. electrolyte properties)/vehicle data (e.g.
engine rpm, speed, and environmental temperature).
4. Data achieved from: Undisturbed battery behavior/
after electrical stimulation.
B. Data
analysis
1. Analysis of operational history (i.e. conditions the
battery had to suffer so far).
2. Analysis of previous performance (i.e. behavior the
battery has shown so far).
3. Analysis of actual performance (i.e. recent and
actual battery behavior and status).
C. Prediction
of battery performance under a hypothetical future electrical load
1. Point in time for prediction: Near future (just now,
with the present battery status)/medium future (in several hours or days, when
the battery charge and temperature may have been changed).
2. Type of predicted battery data: Status (temperature,
state-of-charge)/load behavior.
D. Determination
of available electrical energy
This is a special case of C, with the standard capacity test
scheme as the hypothetical (future) electrical load.
E. Determination
of battery degradation (state-of-health (SOH) figure of merit).
While Battery Monitoring may provide information about the
status of the battery, this knowledge is not a goal by itself. The final
technical benefit has to be made clear, and a strategy and means to achieve
this goal have to be worked out, to find out the relevant properties of the
battery which have to be considered and evaluated.
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