Note: Descriptions are shown in the official language in which they were submitted.
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ENERGY GAUGE
FIELD OF THE INVENTION
This invention relates to an energy gauge for indicating the amount
of residual power available from a battery.
BACKGROUND ART
The battery industry has seen increased demand for battery
management technology, primarily due to the consumers' ever-increasing
requirements for the convenience of battery-powered portable equipment
such as cellular phones and laptop computers. Additionally, the battery
industry is seeing a movement toward an increased emphasis on electric
motor-driven tools and zero emission vehicles with the primary power
source for these new generation vehicles being batteries. This movement is
due to rapidly increasing government regulations and consumer concerns
about air and noise pollution. Another area which requires high efficiency
batteries is energy storage applications such as load-levelling,
emergency/standby power and power quality systems for sensitive
electronic components.
As a result of the increasing demand of battery-powered equipment,
the battery industry is under competitive pressure to produce an ideal cell.
An ideal cell is a cell that weighs almost nothing, takes up no space,
provides excellent cycle life and ~ gas ideal charge/discharge performance
and does not itself produce an environmental hazard at the end of its life.
The most popular technology utilised by the battery industry is the lead-acid
battery, which is being challenged to meet higher energy density, smaller
size, better performance levels, longer cycle life and guaranteed
recyclability.
Several manufacturers are researching exotic batteries, including
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nickel-metal-hydride, lithium-ion and the like but generally these types of
batteries are too expensive to make their use economically viable at this
stage, particularly for one of the fastest growing markets on earth,
two/three wheeled passenger vehicles. It is well recognised that battery
performance, even that of the existing lead-acid battery, can be improved
through proper management of the operating conditions of the battery.
There is a need for an accurate measuring device with appropriate
intelligence to monitor and determine the amount of power remaining in a
battery and providing instant information to an operator.
SUMMARY OF THE INVENTION
According to the invention there is provided an energy gauge for
indicating the amount of residual power available from a battery
comprising:-
(i) means for storing a predetermined value of a power
parameter indicative of full battery capacity,
(ii) means for determining the instantaneous power
consumption indicated by the parameter,
(iii) means for integrating the power consumption
indicative of the parameter since commencement
of use of the battery,
(iv) means for subtracting the integrated consumption
from the stored value of full capacity to provide a
value of power remaining, and
(v) readout means for providing a representation of the
power remaining.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a battery management system for
providing a predetermined power output from a battery
system,
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Fig. 2 is a block diagram of a generalised battery management
system according to a second embodiment,
Fig. 3 is a block diagram of the power control system shown in
Fig. 1 applied to a lead-acid battery system,
Fig. 4 is a graph of cycle numbers against battery capacity for a lead
acid battery with and without the power control system of
Fig. 2, and
Fig. 5 is a block diagram of the power control device shown in
Fig. 1. applied to a Redox-Gel battery system.
MODES OF PERFORMING THE INVENTION
The battery management system 10 shown in Fig. 1 is adapted to
provide a predetermined power output from a battery system 1 1 at the
terminals or output means 12 to which a load such as an electrical vehicle
is connected. Between the output terminals 12 and the terminals 13 of the
battery system 1 1 there is a control means 14 which senses predetermined
operating parameters of the battery system 1 1. The control means 14
supplies power from the battery system 1 1 to the output terminals 12
during a first mode of operation.
First capacitor means 15 connected between the battery system 1 1
and the control means 14 stores a predetermined quantity of power from
the battery system 1 1 during the first mode of operation of the control
means 14 and supplies its stored power to the battery system 1 1 in
response to a command signal from the control means 14 when the control
means is in a second mode of operation.
Second capacitor means 16 which is connected between the output
terminals 12 and the control means 14 stores a predetermined amount of
power from the battery system 1 1 when the control means 14 is in its first
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mode of operation and supplies its stored power to the output terminals 12
in response to a command signal from the control means 14 when the
control means 14 is in its second mode of operation.
Thus, the power control system incorporates two capacitor networks
and when the control means senses, for example, that the polarisation level
in the battery system 1 1 is too high or that a pre-set time interval has
elapsed since power was first supplied to the load, it initiates a back charge
to the battery system 1 1. In this discharge cycle, the control means 14
allows the energy stored in the first capacitor network 15 to charge the
battery system 1 1 and at the same time the second capacitor means 16
supplies uninterrupted power to the output terminals 12. The time interval
for this reverse cycle or discharge cycle is very small and as it is very
efficient it can be performed at regular intervals.
The reverse charge has the ability to disrupt and minimise the effects
and associated losses of polarisation within the battery system.
The power control system may also work in conjunction with a
charger to provide optimum performance and battery care at all times
during its operation. The power control system may be adapted to prevent
an unauthorised type of charger being connected to the battery system
thereby preventing a potential abuse and ensuring that the vehicle owner
does not attempt to charge the battery system with an incorrect charger at
home.
The power control system, the charger and the vehicle may
incorporate individual electronic signatures so that the entire system can be
tracked and monitored with a high degree of accuracy. Each time a battery
system is installed into a charger unit, the power control system will
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identify itself, the vehicle from which it has been removed as well as the
user.
The charger unit may monitor the energy level of the battery and
credit the users for this value, add the cost of the exchange, the electricity
5 and a monthly rental for the battery. Upon receipt of this payment either
by cash or credit card, a new battery is released and installed into the
vehicle. If the client has abused or tampered with the battery anyway this
will be identified by the charger.
The control system can be adapted to not only identify the energy
level of the battery, but it can also assess the driving range left based on
current energy usage levels. Thus, the vehicle driver will know how many
kilometres can be travelled on the remaining level of energy.
Each charger unit may be linked via a telemetry system to an
operation centre which enables constant monitoring of all stations in the
network of charging stations.
The power control system may include the functions and features of
speed control modules which means that the vehicle manager can eliminate
a speed control device from the vehicle and simply control the output via
the power control system. This reduces vehicle costs, reduces
manufacturer warranty exposure and can provide continuous performance
monitoring via the telemetry communication system.
The power control system may be applied to various battery systems
such as valve-regulated lead acid batteries, nickel metal hydride batteries
and redox-gel batteries with each system having its benefits and specific
target applications.
The power control system may also be used to improve the standby
performance of remote area power system, load levelling and emergency
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back-up battery systems. Stationary battery systems used in remote area
power systems and emergency back-up applications may be left fully
charged for extended periods. As cells self-discharge at different rates the
power control system can be programmed to scan the individual cell
conditions periodically and use cell-balancing techniques to balance the
cells internally. Alternatively, the charging system may be left on standby
and be controlled by the power control system as required.
A preferred embodiment of the power control system which is
shown in Fig. 2 in block form includes a microprocessor 40 and associated
software 57 that manages all of the following described functions. In this
instance the microprocessor is 8 bit running at 8MHz, however 4,16, 32 or
64 bit processors can be used. The processor speed could be 4MHz to
166MHz. Alternatively a Digital Signal Processing Chip could be used
depending on the individual battery requirements. The microprocessor has
EEPROM, ROM and RAM Memory. Alternatively an ASIC (Application
Specific Integrated Circuit) could be used.
The individual cell voltage measurement module 41 utilises a
separate wire connected to the junction of each cell. This wire is used
solely for the measurement of voltage. The voltage of each cell is
measured with reference to ground for batteries up to 24 Volts. This can
also be accomplished using direct measurement of each cell voltage as the
needs and accuracy requirements dictate.
Individual cell voltage measurement conditioning is achieved by
module 42 which includes a circuit in which the cell voltages are divided by
a resistor network and smoothed by a filter capacitor connected across the
ground resistor in the divider. Active filtering using operational amplifiers
or
other filtering means could be used. The voltages are scaled by the divider
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and filter to a voltage suitable for analog to digital conversion. In this
case
4.95 Volts represents the expected maximum voltage of each connection
to the battery. A 12 bit analog to digital converter is used for each cell
voltage to be measured. The analog to digital converter is controlled serially
by the microprocessor which converts each measured voltage to the cell
voltage by scaling each voltage and subtracting the voltage of the negative
side of each cell from the voltage of the positive side of the cell. This is
done for each cell and this method is applicable for cell voltages up to 24
or 30 Volts.
Above 24 or 30 Volts multiple stages of the above method can be
used by transmitting the serial digital data by means of optically coupled
serial communications thus isolating the cell voltages. Also applicable
would be the use of a Voltage to Frequency Converter connected across
each cell to directly measure the cell voltage and send this information as a
frequency to the microprocessor. These Voltage to Frequency converters
can be galvanically or optically coupled to the microprocessor which
measures the frequency and converts this to a voltage.
The current measurement module 43 measures the voltage across a
shunt resistor and scaling this value using a current sense amplifier with
active filtering. An alternative to this would be to use a Hall effect device
to measure the current with the appropriate signal conditioning.
Current measurement conditioning is achieved by circuit module 44
in which the voltage measured across the shunt is converted to a 0-5Volt
signal irrespective of the direction of the current which is then fed to an
input of the same 12 bit analog to digital converter used for the
measurement of voltage described above. The conditioning circuitry also
provides a digital input to the microprocessor indicating the direction of
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current flow. This is achieved via an integrated circuit with minimal external
components. Discrete component solutions would also be cost effective in
this area.
Temperature is measured by circuit module 45 using an integrated
circuit temperature sensor mounted on the circuit board. Any number of
these can be used and located in different areas for example the battery,
individual cells or outside for ambient temperature.
Temperature Measurement conditioning is achieved by circuit module
46 in which the temperature value is a voltage output and a low offset
voltage operational amplifier is used to scale this value to a 0-5Volt value
suitable for connection to an input of the same analog to digital converter
used for voltage and current measurement.
A Liquid Crystal Display 47 is used to display information such as
capacity remaining, kilometers remaining and any other information.
The display driver 48 is driven directly by the microprocessor 40 by
writing the appropriate value to a memory location based on a lookup table
stored inside the microprocessor 40. Depending on the microprocessor
requirements and LCD complexity a separate integrated circuit driver may
be used. A LED or gas plasma display could also be used. A Liquid Crystal
display module may also be used.
Audible indicator module 49 includes a piezo electric buzzer which
provides audible signal to the user. This is ideally driven directly from the
microprocessor or with a transistor driver if necessary.
A distance sensor 50 is mounted on the wheel should the battery be
used in a moving vehicle. This sensor 50 can take the form of either a
magnetic pickup where the magnet is located on the wheel and a hall effect
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pickup device is mounted on a stationary part of the vehicle or an optical
sensor.
Distance sensor conditioning is achieved by a circuit module 51 in
which the output of the distance sensor 50 is a frequency that is scaled
and measured by the microprocessor 40 which in turn converts this to a
speed or distance value.
Pressure sensor module 52 includes a pressure transducer with a low
voltage (in the order of 0-100mV) output is located in the battery.
Pressure sensor conditioning module 53 scales the output to
0-5Volts via a precision operational amplifier and fed to the analog to
digital
converter.
The communications module 54 ensures that all control and
communications signals from the battery charger are communicated via a
serial bus direct from the microprocessor 40. This serial bus can also
access a PC for calibration purposes.
To ensure long battery life all components of the optimiser are
chosen for low current consumption. The microprocessor, analog to digital
converter, and all other circuitry can be placed in a low current
consumption mode by a signal from the microprocessor to the low current
mode module 55.
To achieve the required levels of accuracy the analog inputs to the
microprocessor are calibrated by the calibration module 56 and the
calibration factors and offsets are store in EEPROM memory.
The software 57 is preferably polling orientated as well as being
interrupt driven for time critical events such as current time, distance and
wheel sensor monitoring for energy use integration.
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The software samples current at regular time intervals and integrates
current with respect to time to provide amperehours used and remaining
data. The amperehours used and remaining is corrected depending on
loads during the current cycle. The software is adapted to:-
5 (i) calculate power and Ampere-Hours consumption,
(ii) calculate average power and average Ampere-Hours
consumption,
(iii) calculate power and Ampere-Hour capacity available,
(iv) calculate time available at current Ampere-Hour
10 consumption,
(v) calculate distance available at current Ampere-Hour
consumption,
(vi) calculate time available and distance to go at a
specified Ampere-our consumption,
(vii) initiates low battery power and/or Ampere-Hour
alarm when available capacity approaches critical level,
and
(viii) display status of all the above features.
The microprocessor 40 can also drive FETS or IGBT's to control the
current to a motor 58. This can provide a single pulse width modulated
control for a brushed type motor, or a quasi sinusoid control with multiple
outputs for brushless multiple type motors such as reluctance motors or
brushless DC motors.
A FET or IGBT switch 59 is used for security and protection of the
battery. FETS with a low on resistance are used.
The switch 59 is controlled by switch control module 60 which is
driven by the microprocessor 40 and the drive of the FETS or IGBT's
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utilises a switched power supply to boost the voltage to enable high side
driving.
In the resistance control module 61, the microprocessor controls a
FET the function of which is to periodically charge a capacitor to a voltage
above the battery voltage and discharge this capacitor into the battery
whilst at the same time switch another capacitor whose charge can hold
the load current.
The output of an energy gauge 62 is displayed on the LCD display as
capacity remaining. This value is calculated by integrating the current over
time. Current is sampled at regular intervals and this value is subtracted
from an accumulator and then scaled to 100% to give a capacity remaining
output.
The internal resistance/impedance module 63 calculated the internal
resistance and impedance by means of measuring the change in voltage
before and after a step change in current. This can occur both during
charge and discharge. AC current or voltage may be injected into the
battery and the resultant voltage or current is measured to calculate internal
resistance and impedance.
The cell balancing module 64 operates so that when one cell is
considered to be self discharged more than others in the group, power is
taken from the entire group, converted to an appropriate voltage using a
switched mode power converter and distributed to the weakest cell thus
balancing the cells.
Conventional lead-acid batteries suffer from limited capacity
utilisation, low depth of discharge, short cycle life, low energy density,
thermal management problems and the need for constant boost charging to
maintain cell equalisation. The lead-acid batteries also require long charge
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times and high charge currents can only be used for a few minutes at very
low states-of-charge. If high currents are used they normally result in
higher than allowable voltages being reached leading to electrolyte loss and
a reduction in the battery's capacity. The time to recharge a lead-acid
battery with boost charging can be up to 4 hours at best if a proper charge
profile is followed.
The cycle life of a lead-acid battery varies greatly depending on the
depth-of-discharge reached during cycling. For electric vehicle applications
a 90-100% DOD (Depth of Discharge) may not by uncommon and at these
DOD levels, the cycle life of conventional deep cycle lead-acid batteries
would be approximately 300 cycles.
Fig. 3 shows the power control system 20 applied to a lead-acid
battery of proven lead-acid format, however, it utilises advanced spiral
wound technology for its cell structures. The twelve individual cells 21 are
formed from electrodes with surface large areas, which are spiral would to
form individual cells with very low resistance. Advanced electrolytes have
been developed to assist in allowing very high currents to be extracted
from the battery system. The battery system involves the integration of
the power control system 20 with the spiral wound cell technology and
improved electrolytes. The cells 21 are connected in series by the bus 22
which is also connected to the first capacitor means 23, the control means
24, second capacitor means 25 and output terminals 26. The dotted line
27 represents the command signal from the control means 24 to the first
capacitor means 23. The use of a Valve-Regulated lead-acid format offers,
a proven technology at a relatively low cost as a starting point for a "rental
energy" system.
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By utilising the power control system 20 and reconfiguring the
battery design to optimise the benefits of these features, there is provided
a battery that offers significant improvements in the form of increased
current flow, capacity, increased cycle life and reduced recharge times at
only a marginally higher manufactured cost.
This is demonstrated in Fig. 4 which is a graph of cycle numbers
against battery capacity for a lead acid battery with and without the power
control system of the invention. A cycle is from charging to discharging
and back to charging.
The increased current flow capability means that power and capacity
utilisation is improved resulting in a higher obtainable amp-hour rating and
the extension of vehicle range. The increased cycle life means that the
battery can be recharged more times before replaced, thereby, lowering the
annual operating costs. The reduced charging times mean that the battery
can be turned around faster, thereby, reducing the number of spare
batteries required in the rental energy system.
The power control system may also be applied to conventional NiMH
batteries which employ advanced processed and high purity materials that
normally lead to a very high cost for the battery systems. Expanded nickel
foams with high purity nickel hydroxide compounds and processed metal
alloy materials all need a very high degree of quality control in order to
obtain a high performance battery.
NiMH hydride batteries can also suffer from self-discharge problems
and can also be affected by temperature. On certain systems the
extraction of high current can cause damage the battery cells and care
must be taken not to over charge the batteries. In this respect, advanced
battery chargers are needed to ensure proper charging.
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The NiMH battery system of this embodiment utilises advanced
NiMH technology that has been designed to take full advantage of the
benefits provided by the battery power control system. The cell structure
utilises spiral would cell technology allowing the production of cells which
have a much higher power output capability. The power control system is
integrated into the battery pack cells. The power control system has the
ability to significantly reduce polarisation effects allowing the battery
system to provide higher current without jeopardising cycle life.
The integrated unit is effectively a stand-alone intelligent energy
storage system as the power control system monitors all the unit's
functions. The power control system can take active steps to maintain
optimal battery performance, at the same time resulting in improved cycle
life.
This Ni-MH system is ideally suited for a "rental Energy" system as
its benefits include high energy density, high power, long cycle life and
quick recharge time. The system will allow greater travelling distances for
electric vehicles in comparison to the valve regulated battery system but at
a slightly higher cost. The production cost, however, of the system of this
embodiment is significantly lower than existing products with estimates at
current costs indicating a total price for the NiMH system almost 1 /10 the
price of current available small production units.
The NiMH system is particularly suitable for electric bicycles where a
small battery systems offering long range travel is desirable.
The power control system may also be applied to Redox batteries
which have been under investigation for many years. These batteries have
mainly been in the form of Redox flow batteries which store energy in liquid
electrolytes which are stored separately to the battery stack. During
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operation, the electrolytes are recirculated through the system and energy
is transferred to and from the electrolytes. The redox flow batteries usually
suffer from a low energy density and pumping losses associated with
recirculating the electrolyte through the system. In certain cases, high self-
5 discharge rates are possible depending on the membranes or if internal
shunt currents exist.
The redox gel battery differs from the redox flow principle in that the
electrolytes do not need to be re-circulated since the electrolytes are super
concentrated gels.
10 Conventional battery systems employ some form of solid metal
electrodes that involve phase transfer reactions. This usually leads to
increased weight and loss in efficiencies. The redox gel battery employs
super concentrated gels, which contain a high concentration of positive and
negative reactive ions in the respective gels. All reactive species are
15 contained in the gels and no phase transfer reactions are involved which
leads to high efficiencies due to minimal losses.
The power control system of the invention can be integrated in the
Redox gel battery pack to reduce the effects of polarisation. As the gels
are super concentrated, polarisation tends to be higher when high loads are
applied to the battery system. A power control system specifically
designed for the redox gel battery can alleviate many of the constraints in
the design of the redox gel cell system.
The power control system 30 shown in Fig. 5 includes a bus system
31 which inter connects the cells 32, the control means 33, the first
capacitor means 34, the second capacitor means 35 and the output
terminals 36. Line 37 represents the command signal.
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The control means 33 specifically designed for the redox gel cell also
performs a number of monitoring functions, such as monitoring the
individual cell voltages and temperatures. It can also monitor the internal
pressure of the sealed battery pack and ascertain the allowable load limits
of the system at any given condition. The control means 33 has the added
and important ability to be able to take active steps in maintaining optimal
battery performance at any state-of-charge. With this high degree of
system control the system can utilise its total capacity repeatedly and over
a very long cycle life.
This system is extremely cost competitive and offers superior
performance to current available energy storage system. The electrodes
employed the redox gel cells simply function to allow the transfer of energy
into and out of the gel electrolytes. The electrodes are inert and can be
produced from specially developed conducting plastic ,materials.
This system incorporates the redox gel cells and the power control
system to produce an energy storage system that has almost double the
energy density of the NiMH system. The system also has very long cycle
life due to the stability of the gel electrolytes. The system has a whole is
very cost effective. With its lightweight and robustness it is well suited to
the battery exchange process for the "rental energy" vehicles.
Another embodiment of the invention relates to a battery charging
and conditioning module that integrates with a battery performable power
control system, which is integrated into a battery system.
Battery systems suffer a number of problems with one of the main
limitations being incorrect charging or gang charging where the overall
battery condition is recorded and an applicable charge applied. This
concept however does not allow for the condition of individual cells and
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therefore the highest charged cell us usually overcharged and the lowest
charged cell is usually undercharged. The result is that the overall battery
life is significantly reduced.
Another problem is that batteries cannot accept high charge currents
because of the internal effects if internal resistance on the various
components. Fast charging usually has the effect of gassing where
hydrogen gas is given off which are not only dangerous but also limits the
life of the battery due to electrolyte degradation. This charger works in
conjunction with the power control system and limits the internal resistance
thereby permitting faster recharge rates without affecting the battery cycle
life.
The present invention provides a unique battery charging and
conditioning module that integrates with a power control system which is
integrated into a battery system. The main function of this power control
system is to reduce the polarisation effects due to the internal resistance of
the batteries. Importantly, it has allowed control of multiple on-board
functions such as monitoring individual cells, providing power output
control functions, operating in conjunction with special battery charges
providing protection and a conditioning function.
Special battery chargers can identify the power control system and
therefore the battery module serial number, which are relayed to the
operations centre via a telemetry communications systems. Once the
battery has been recorded and the clients account verified, the battery
charger is permitted, by the power control system, to commence charging.
The actual charging function is carried out in conjunction with the
power control system to ensure that each cell is monitored and treated or
conditioned to its specific requirements. This capability prevents damage
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to cells through undercharging or overcharging and therefore significantly
improves the overall battery cycle life.
The battery charger is capable of identifying the type of battery and
automatically selects the correct charging format. If an unauthorised
battery is installed into the charger it will not permit connection. The
charger is also capable, through feedback from the power control system of
detecting whether the battery has been charged by any other means or
whether the optimisation module or battery have been tampered with in
any way and pass this information on to the operations centre.
Each charger unit is linked via a telemetry system to the operations
centre, which enables constant monitoring of all stations in the network,
plus the location of each battery and status of each account.
INDUSTRIAL APPLICABILITY
The battery management system can be used in a Rental Energy
Concept where it is installed into a range of service applications in the form
of vending machines, manually installed recharge modules, automatic
battery removal and replacement carousels, robotic battery replacement
facilities and parking/charging stations.
