Note: Descriptions are shown in the official language in which they were submitted.
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DUTY CYCLE CONTROLLER FOR HIGH POWER FACTOR BATTERY
CHARGER
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to battery chargers and more particularly to generation
of a duty cycle signal for use in controlling switches in a battery charger to
control current flow to a battery being charged by the battery charger while
maintaining a high power factor at an AC input of the battery charger.
2. Description of Related Art
In conventional battery chargers, AC line voltage is stepped down by a
transformer to produce a low voltage AC source which is connected to a
switching array including Metal Oxide Semiconductor Field Effect Transistors
(MOSFETs) for example, to provide a desired amount of current to a battery
to be charged. MOSFETs have some "on" resistance which causes heat to
be generated in the MOSFETs due to current flow through semiconductor
junctions thereof. This heat can build up, if not properly dissipated, to a
point
where the MOSFETs can become damaged. Heat however, can be
controlled by reducing the amount of current supplied to a battery connected
to the charger.
Battery chargers are connected to an AC line circuit through a breaker, such
as a 15 Amp breaker, for example and thus it is important not to attempt to
draw more current than allowed by the breaker from the AC line circuit.
Typically, users of battery chargers have no way of limiting AC line current
supplied to a battery charger as most chargers provide few controls and many
simply have only a line plug for controlling the operation of the charger. Use
of the line plug provides only on/off functions and involves no regard for
other
circuits that may be supplied by or through the same breaker.
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In all battery chargers battery voltage and current must be controlled to
avoid
damaging the battery being charged. Typically conventional chargers employ
circuitry that implements a slow control loop that adjusts the current
supplied
to the battery to achieve the desired battery voltage. The use of the slow
control loop involves producing a current command signal that is shaped to
mimic the incoming voltage waveform to produce a high bandwidth AC current
command signal to control the current drawn from the AC power source.
Since the high bandwidth current command signal mimics the input AC
voltage waveform, high power factor is achieved.
However, the above-described methodology only works if the circuit topology
permits control of the current. In particular, as long as the instantaneous AC
input voltage, divided by the transformer turns ratio, is kept less than the
battery voltage, the above methodology can be used to control the current
supplied to the battery and maintain a high power factor. Under these
conditions, the charger can be operated as a boost converter using either the
leakage inductance of the transformer, or a discrete inductor as a boost
inductor and the current may be properly controlled.
However, low frequency or hybrid low/high frequency battery chargers (and
inverter/chargers) must operate over a wide range of input and output voltage.
The turns ratio of the transformer places a limit on the range of input and
output voltage over which boost mode (and current control) is possible. When
the instantaneous AC input voltage divided by the transformer turns ratio
exceeds the battery voltage the battery current is essentially uncontrolled
and
limited only by parasitic impedances in the AC source, the charger, the
battery, and the associated wiring. To avoid this situation, some charger
manufacturers employ circuits that adjust the phase angle at which a triac on
the AC input is fired, to keep the AC input voltage in an allowable range.
However, in this situation only very coarse control of battery current is
possible and such control may be unpredictable due to battery and AC source
characteristics.
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SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a duty cycle
controller apparatus for producing a duty cycle signal for controlling
switching
of switches of a battery charger having an AC input for receiving power and
an output for supplying power to charge a battery in response to switching of
the switches, while maintaining a high power factor at the AC input. The duty
cycle controller apparatus includes a current command signal generator
having a plurality of signal inputs for receiving a plurality of signals
representing a plurality of operating conditions of the charger, a plurality
of
current command outputs and a processor operably configured to generate a
plurality of current command signals at the current command outputs in
response to respective sets of operating conditions. The duty cycle controller
apparatus further includes a selector operably configured to select a current
command signal having a lowest value and produce a lowest current
command signal in response thereto. The duty cycle signal controller
apparatus further includes a duty cycle signal generator having a battery
current signal input, a battery voltage signal input, an AC voltage waveform
input, an AC current waveform input and a duty cycle signal output. The duty
cycle signal generator is operably configured to produce a duty cycle signal
at
the duty cycle signal output in response to the lowest current command
signal, a battery voltage signal (VBA-rr), a battery current signal (IBATT),
an AC
voltage waveform signal (VAC) and an AC current waveform signal OW.
The current command signal generator may comprise a first current command
signal generator for generating a first current command signal (CCS1).
The first current command signal generator may comprise battery type and
charger mode signal inputs for receiving a battery type signal and a charger
mode signal respectively and a battery voltage signal input for receiving the
battery voltage signal (VBA-rr).
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The first current command signal generator further comprises a battery
voltage command signal generator operably configured to produce a battery
voltage command signal in response to the battery type signal and the
charger mode signal and includes a difference signal generator operably
configured to produce the first current command signal in response to a
difference between the battery voltage command signal and the battery
voltage signal.
The first current command signal generator further comprises a first current
command signal output for providing the first current command signal to the
selector.
The current command signal generator may comprise a user interface for
producing the battery type signal in response to user input identifying the
type
of battery being charged.
The current command signal generator may comprise a second current
command signal generator operably configured to produce a second current
command signal (CCS2).
The second current command signal generator may comprise a temperature
signal input for receiving a temperature signal (TH) representing temperature
of the charger, a maximum temperature signal input for receiving a maximum
temperature signal (TmAx) representing maximum temperature of the charger,
a derating range signal input for receiving a derating temperature range
signal (TDERATERANGE) specifying a range of temperature over which charging
current must be reduced to avoid overheating the charger and a maximum
charger current signal input for receiving a maximum charger current signal
(ICHARGEMAX) representing maximum battery current to be applied to the
battery.
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The second current command signal generator further comprises a
temperature ratio generator for generating a temperature ratio of a difference
between the maximum temperature signal and the temperature signal to the
temperature derate range signal and a multiplier for multiplying the maximum
charger current signal by the temperature ratio to produce the second current
command signal and further comprises a second current command signal
output for providing the second current command signal (CCS2) to the
selector.
The second current command signal generator may further comprise a clamp
for clamping the temperature ratio to an upper bound.
The second current command signal generator may further comprise a low
pass filter for filtering the temperature signal prior to supplying the
temperature signal to the temperature ratio generator.
The current command signal generator may comprise a third current
command signal generator for generating a third current command signal
(CCS3).
The third current command signal generator may comprise an efficiency
signal input for receiving an efficiency signal (E) representing efficiency of
the
charger, an AC rms voltage signal input for receiving an AC rms signal
(VACRMS) representing input AC rms voltage, a breaker derating signal input
for receiving a breaker derating signal (B) representing a derating factor for
derating a rated current of a breaker through which AC current is supplied to
the charger, a breaker rating current signal input for receiving a breaker
rating
current signal II
V BREAKERRATING) representing a rated current of the breaker
through which current is supplied to the charger, a load current signal input
for
receiving a load current signal i t
vLOAD) representing load current supplied to a
load connected to the same breaker through which current is supplied to the
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charger, and a battery voltage signal input for receiving the battery voltage
signal (VBATT).
The third current command signal generator further includes a computation
device in communication with the efficiency signal input, the ACrms voltage
signal input, the breaker derating signal input, the breaker rating current
signal
input, the load current signal input and the battery voltage signal input, for
producing the third current command signal (CCS3) according to the relation:
CCS3= (E)(VACRMS)((B)(IBREAKER) ¨ (ILOAD))
VBATT
The third current command signal input further includes a third current
command output for providing the third current command signal to the
selector.
The third current command signal generator may comprise a user interface for
producing the breaker rating current signal in response to user input.
The duty cycle controller apparatus may further comprise a user interface for
producing the breaker derating signal in response to user input.
The current command signal generator may comprise a fourth current
command signal generator for generating a fourth current command signal
(CCS4).
The fourth current command generator may comprise a phase control mode
signal input for receiving a phase control mode signal indicating whether or
not the charger is operating in a phase control mode, a battery voltage signal
input for receiving the battery voltage signal (VBATT), a high side turns
signal
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input for receiving a signal (NH) representing the number of high side turns
of
wire on a high voltage side of a transformer of the charger, a low side turns
signal input for receiving a signal (NO representing the number of low side
turns of wire on a low voltage side of the transformer, an AC rms voltage
signal input for receiving an AC rms signal (VAcRms) representing input AC
rms voltage to the charger, a maximum charger current signal input for
receiving a maximum charger current signal (ICHARGERMAX) representing
maximum charger current.
The fourth current command generator may further comprise a computation
unit operable to compute the fourth current command signal (CCS4)
according to the relation below when the phase mode signal indicates the
charger is operating in a phase control mode:
CCS4 = (VBATT)(NH)* (ICHARGERMAX)
(NL)(VACRMS) * 242
The computation unit is operable to cause the fourth current command signal
to be equal to the maximum battery current signal when the charger is not
operating in the phase control mode.
The fourth current command generator may further comprise a fourth current
command signal output for providing the fourth current command signal to the
selector.
The current command signal generator may comprise a fifth current command
signal generator for generating a fifth current command signal (CCS5).
The fifth current command signal generator may comprise a low AC voltage
derating signal input for receiving a low AC voltage derating signal
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(VLoWACDERATE), an AC rms voltage signal input for receiving an AC rms
voltage signal (VAcRms) representing input AC rms voltage, a maximum
charger current signal input for receiving a maximum charger current signal
(IcHARGERMAX) representing maximum charger current and a low AC voltage
derating range signal input for receiving a low AC voltage derating range
signal (VLOWACDERATERANGE).
The fifth current command signal generator further comprises a computation
device connected to the low AC voltage derating signal input, the AC rms
voltage signal input, the maximum charger current signal input and the low AC
voltage derating range signal input, for producing the fifth current command
signal (CCS5) according to the relation:
CCS5 = PLOWACDERATE) - (VACRMS))(ICHARGERMAX)
VLOWACDERATERANGE
The fifth current command signal generator further comprises a fifth current
command signal output for providing the fifth current command signal (CCS5)
to the selector.
The selector may comprise a store for storing at least one of the plurality of
current command signals.
The selector may comprise a comparator for performing a plurality of
comparisons, for successively comparing the contents of the store with a
compared signal. The compared signal is one of the current command signals
other than the one of the plurality of current command signals stored in the
store. After each comparison, where the compared signal is less than the
contents of the store, the contents of the store are replaced with a value
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representing the compared signal. Where the compared signal is not less than
the contents of the store, the contents of the store are left as they were
before
the comparison.
The selector may comprise a signal generator for producing the lowest current
command signal in response to the contents of the store after performing the
plurality of comparisons.
The duty cycle signal generator comprise a power command generator for
generating a power command in response to the lowest current command
signal and the battery current signal received at the battery current signal
input.
The duty cycle signal generator may further comprise an AC current
command signal generator for producing an AC current command signal in
response to the power command signal and the AC voltage waveform signal
received at the AC voltage waveform input.
The duty cycle signal generator may comprise a duty cycle error signal
generator for generating a duty cycle error signal in response to the AC
current command signal and the AC current waveform signal received at the
AC current waveform input.
The duty cycle signal generator may comprise a reference duty cycle
generator for producing a reference duty cycle signal. The reference duty
cycle generator may comprise an AC voltage signal input for receiving an AC
input voltage signal representing AC input voltage (VAC) to the charger, a
battery voltage signal input for receiving the battery voltage signal
representing battery voltage (VBATT), and a turns ratio input for receiving a
signal representing a turns ratio (N) of a transformer of the charger.
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The duty cycle generator further includes a computing function for producing
the reference duty cycle signal according to the relation:
Ref Duty Cycle = VAC
N VBATT
The duty cycle signal generator may comprise an adder for adding the
reference duty cycle signal and the duty cycle error signal to produce the
duty
cycle signal.
The duty cycle signal generator may comprise a clamp for bounding the duty
cycle signal.
The signal inputs to the duty cycle controller apparatus may include a
plurality
of inputs for receiving signals representing measured quantities, a plurality
of
inputs for receiving user-supplied variables and a plurality of inputs for
receiving a plurality of fixed values.
The plurality of inputs for receiving measured variables may include inputs
for
receiving signals representing input AC voltage, input AC current, temperature
of charger, charger mode, phase control mode, and load current.
The plurality of inputs for receiving user supplied variables may include a
plurality of inputs for receiving signals representing battery type, battery
size
and breaker rating of a breaker through which AC current is supplied to the
battery charger.
The plurality of inputs for receiving fixed values includes inputs for
receiving
signals representing maximum allowable temperature of the charger, a
derating range over which current output of the charger is derated due to
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temperature, a temperature ratio clamping value specifying a temperature
ratio that cannot be exceeded, a breaker derating value representing a factor
for derating a breaker through which AC current for the charger is supplied,
an
efficiency value representing the efficiency of the charger, a number
representing the number of turns on a high voltage side of a transformer of
the charger, a number representing the number of turns on a low voltage side
of the transformer of the charger, a voltage value representing a low AC
voltage value below which output current of the charger is to be derated, a
voltage range value representing a range of AC input voltages for which the
output current of the charger should be derated and a maximum charger
current.
In accordance with another aspect of the invention, there is provided a
battery
charger comprising the duty cycle controller above and further comprising a
gate drive controller operable to receive the duty cycle signal and operable
to
produce at least one gate drive signal in response to the duty cycle signal
and
a switching circuit for switching current to a battery being charged by the
battery charger, the switching circuit being controlled by the at least one
gate
drive signal.
In accordance with another aspect of the invention, there is provided an
apparatus for producing a duty cycle signal for controlling switching of
switches of a battery charger having an AC input for receiving power and an
output for supplying power to charge a battery in response to switching of the
switches, while maintaining a high power factor at the AC input. The
apparatus includes provisions for receiving a plurality of signals
representing
a plurality of operating conditions of the charger, the signals including a
battery voltage signal (VBArr), a battery current signal BA1-0, an AC voltage
waveform signal (VAC) and an AC current waveform signal (IAc). The
apparatus further includes provisions for generating a plurality of current
command signals in response to respective sets of operating conditions,
provisions for selecting a current command signal having the lowest value to
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produce a lowest current command signal and provisions for producing the
duty cycle signal in response to the lowest current command signal, the
battery voltage signal, the battery current signal, the AC voltage waveform
signal and an AC current waveform signal.
The provisions for generating a plurality of current command signals may
comprise provisions for generating a first current command signal.
The provisions for generating the first current command signal may comprise
provisions for receiving a battery type signal and a charger mode signal
respectively, provisions for receiving the battery voltage signal (VBArr),
provisions for generating a battery voltage command signal in response to the
battery type signal and the charger mode signal and provisions for producing
the first current command signal in response to a difference between the
battery voltage command signal and the battery voltage signal.
The provisions for generating the first current command signal may comprise
provisions for producing the battery type signal in response to user input
identifying battery type.
The provisions for generating a plurality of current command signals may
comprise provisions for generating a second current command signal.
The provisions for generating the second current command signal may
comprise provisions for receiving a temperature signal representing
temperature of the charger, provisions for receiving a maximum temperature
signal representing maximum temperature of the charger, provisions for
receiving a derating temperature range signal specifying a range of
temperature over which charging current must be reduced to avoid
overheating the charger, provisions for receiving a maximum battery current
signal representing maximum battery current to be applied to the battery and
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provisions for receiving a battery type signal and a charger mode signal
respectively.
The provisions for generating the second current command signal may further
include provisions for generating a temperature ratio of a difference between
the maximum temperature signal and the temperature signal, to the
temperature derating range signal and provisions for multiplying the maximum
battery charge current signal by the temperature ratio to produce the second
current command signal.
The provisions for generating the second current signal further may comprise
provisions for clamping the temperature ratio to an upper bound.
The provisions for generating the second current command signal further may
comprise provisions for low pass filtering the temperature signal prior to
supplying the temperature signal to the provisions for generating the
temperature ratio.
The provisions for generating the plurality of current command signals may
comprise provisions for generating a third current command signal.
The provisions for generating the third current command signal generator may
comprise provisions for receiving an efficiency signal (E) representing
efficiency of the charger, provisions for receiving an AC rms signal (VAcRms)
representing input AC rms voltage to the charger, provisions for receiving a
breaker derating signal (B) representing a derating factor for derating a
rated
current of a breaker through which current is supplied to the charger,
provisions for receiving a breaker rating current signal (IBREAKERRATING)
representing a rated current of the breaker through which current is supplied
to the charger, provisions for receiving a load current signal ( "LOAD)
representing load current supplied to a load connected to the same breaker
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through which current is supplied to the charger and provisions for receiving
the battery voltage signal (VBArr).
The provisions for generating the third current command signal may further
include provisions for producing the third current command signal (CCS3)
according to the relation:
CCS3= (E)(VACRMS)((B)(IBREAKER) ¨ (I LOAD))
VBATT
The provisions for generating the third current command signal may comprise
provisions for producing the breaker rating current signal in response to user
input.
The provisions for generating the third current command signal may comprise
provisions for producing the breaker derating signal in response to user
input.
The provisions for generating the plurality of current command signals may
comprise provisions for generating a fourth current command signal.
The provisions for generating the fourth current command signal may
comprise provisions for receiving a phase control mode signal indicating
whether or not the charger is operating in a phase control mode, provisions
for receiving the battery voltage signal (VBATT), provisions for receiving a
signal representing the number of high side turns of wire on a high voltage
side of a transformer of the charger, provisions for receiving a signal
representing the number of low side turns of wire on a low voltage side of the
transformer, provisions for receiving an AC rms signal (VAcRms)
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representing input AC rms voltage to the charger and provisions for receiving
a maximum charger current signal representing maximum charger current.
The provisions for generating the fourth current command signal may include
provisions for producing the fourth current command signal (CCS4) according
to the relation below when the phase mode signal indicates the charger is
operating in a phase control mode:
CCS4 = (VBATT)(NH)* (ICHARGERMAX)
(NL)(VAcRMs) * 2-\12
The provisions for generating the fourth current command signal may further
include provisions for causing the fourth current command signal (CCS4) to
be equal to the maximum battery current signal when the charger is not
operating in the phase control mode.
The provisions for generating the plurality of current command signals may
comprise provisions for generating a fifth current command signal.
The provisions for generating the fifth current command signal may comprise
provisions for receiving a low AC voltage derating signal (VLOWACDERATE),
provisions for receiving an AC rms signal (VAcRms) representing input AC
rms voltage to the charger, provisions for receiving a maximum charger
current signal (ICHARGERMAX) representing maximum charger current to be
applied to the battery and provisions for receiving a low AC voltage derating
range signal (VLOWACDERATERANGE)-
The provisions for producing the fifth current command signal may include
provisions for producing the fifth current command signal (CCS5) according to
the relation:
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CCS5 = PLOWACDERATE) - (VACRMS))(ICHARGERMAX)
VLOWACDERATERANGE
The apparatus may further comprise provisions for storing at least one of the
plurality of current command signals.
The provisions for selecting may comprise provisions for performing a
plurality
of comparisons, for successively comparing the contents of the store with a
compared signal. The compared signal may be one of the current command
signals other than the one stored in the store. After each comparison, where
the compared signal is less than the contents of the store, the contents of
the
store are replaced with a value representing the compared signal and where
the compared signal is not less than the contents of the store, the contents
of
the store are left as they were before the comparison.
The provisions for selecting may comprise provisions for producing the lowest
current command signal in response to the contents of the store after
performing the plurality of comparisons.
The provisions for producing the duty cycle signal may comprise provisions
for generating a power command in response to the lowest current command
signal and the battery current signal.
The provisions for producing the duty cycle signal further may comprise
provisions for producing an AC current command signal in response to the
power command signal and the AC voltage waveform signal.
The provisions for producing the duty cycle signal may comprise provisions
for generating a duty cycle error signal in response to the AC current
command signal and the AC current waveform signal.
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The provisions for producing the duty cycle signal may comprise provisions
for receiving a signal representing a turns ratio (N) of a transformer of the
charger and provisions for producing a reference duty cycle signal according
to the relation:
Ref Duty Cycle = VAC
N VBATT
The provisions for producing the duty cycle signal may comprise generating
the duty cycle signal in response to the reference duty cycle signal and the
duty cycle error signal.
The provisions for producing the duty cycle signal may comprise bounding the
duty cycle signal.
In accordance with another aspect of the invention, there is provided a
method of producing a duty cycle signal for controlling switching of switches
of
a battery charger having an AC input for receiving power and a charge output
for supplying power to charge a battery in response to switching of the
switches, while maintaining a high power factor at the AC input. The method
involves receiving a plurality of signals representing a plurality of
operating
conditions of the charger, the signals including a battery voltage signal
(VBA-rr), a battery current signal (IBArr), an AC voltage waveform signal
(VAC)
and an AC current waveform signal (lAc). The method further involves
generating a plurality of current command signals in response to respective
sets of operating conditions.
The method further involves selecting a current command signal having the
lowest value to produce a lowest current command signal and producing the
duty cycle signal in response to the lowest current command signal, the
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battery voltage signal, the battery charge current signal, the AC voltage
signal
and the AC current waveform signal.
Generating a plurality of current command signals may involve generating a
first current command signal.
Generating the first current command signal may involve receiving a battery
type signal and a charger mode signal respectively, generating a battery
voltage command signal in response to the battery type signal and the
charger mode signal and producing the first current command signal in
response to a difference between the battery voltage command signal and the
battery voltage signal.
Generating the first current command signal may involve producing the
battery type signal in response to user input identifying battery type.
Generating the plurality of current command signals may further involve
generating a second current command signal.
Generating the second current command signal may further involve receiving
a temperature signal representing temperature of the charger, receiving a
maximum temperature signal representing maximum temperature of the
charger, receiving a derating temperature range signal specifying a range of
temperature over which charging current must be reduced to avoid
overheating the charger and receiving a maximum charger current signal
representing maximum charger current.
The method may further involve generating a temperature ratio of a difference
between the maximum temperature signal and the temperature signal, to the
temperature derate range signal, and multiplying the maximum battery charge
current signal by the temperature ratio to produce the second current
command signal.
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The method may further involve clamping the temperature ratio to an upper
bound.
The method may further involve low pass filtering the temperature signal prior
to supplying the temperature signal to the temperature ratio generator.
Generating the plurality of current command signals may involve generating a
third current command signal.
Generating the third current command signal generator may involve receiving
an efficiency signal (E) representing efficiency of the charger, receiving an
AC
rms signal (VAcRms) representing input AC rms voltage to the charger and
receiving a breaker derating signal (B) representing a derating factor for
derating a rated current of a breaker through which current is supplied to the
charger.
The method may further involve receiving a breaker rating current signal
(IBREAKERRATING) representing a rated current of the breaker through
which current is supplied to the charger and receiving a load current signal
(ILoAD) representing load current supplied to a load connected to the same
breaker through which current is supplied to the charger.
The method may further involve producing the third current command signal
(CCS3) according to the relation:
CCS3= (E)(VACRMS)((B)OBREAKER) ¨ (ILOAD))
VBATT
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Generating the third current command signal may involve producing the
breaker rating current signal in response to user input.
Generating the third current command signal generator may involve producing
the breaker derating signal in response to user input.
Generating the plurality of current command signals may comprise generating
a fourth current command signal.
Generating the fourth current command may involve receiving a phase control
mode signal indicating whether or not the charger is operating in a phase
control mode, receiving a signal representing the number of high side turns of
wire on a high voltage side of a transformer of the charger and receiving a
signal representing the number of low side turns of wire on a low voltage side
of the transformer.
The method may involve receiving an AC rms signal (VAcRms) representing
input AC rms voltage to the charger and receiving a maximum charger current
signal (ICHARGERMAX) representing maximum charger current to be applied to
the battery.
The method may further involve producing the fourth current command signal
(CCS4) according to the relation below when the phase mode signal indicates
the charger is operating in a phase control mode:
CCS4 = (VBATT)(Nl-I)* (ICHARGERMAX)
(NL)(VAcRMS) * 242
The method may further involve causing the fourth current command signal
(CCS4) to be equal to the maximum battery current signal when the charger is
not operating in the phase control mode.
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Generating the plurality of current command signals may involve generating a
fifth current command signal.
Generating the fifth current command signal may involve receiving a low AC
voltage derating signal (VLOWACDERATE), receiving an AC rms signal
(VACRMS) representing input AC rms voltage to the charger, receiving a
maximum charger current signal (ICHARGERMAX) representing maximum charger
current to be applied to the battery and receiving a low AC voltage derating
range signal (VLOWACDERATERANGE);
The method may further involve producing the fifth current command signal
(CCS5) according to the relation:
CCS5 = ((VLOWACDERATE) - (VACRMS))(ICHARGERMAX)
VLoWACDERATERANG E
The method may further involve storing at least one of the plurality of
current
command signals.
Selecting may involve performing a plurality of comparisons, for successively
comparing the contents of the store with a compared signal, the compared
signal being the current command signals other than one of the plurality of
current command signals that is stored in the store. After each comparison,
where the compared signal is less than the contents of the store. The method
may involve replacing the contents of the store with a value representing the
compared signal and where the compared signal is not less than the contents
of the store, leaving the contents of the store as they were before the
comparison.
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Selecting may involve producing the lowest current command signal in
response to the contents of the store, after performing the plurality of
comparisons.
Producing the duty cycle signal may involve generating a power command in
response to the lowest current command signal and the battery current signal.
Producing the duty cycle signal may further involve producing an AC current
command signal in response to the power command signal and the AC
voltage waveform signal.
Producing the duty cycle signal may involve generating a duty cycle error
signal in response to the AC current command signal and the AC current
waveform signal.
Producing the duty cycle signal may involve producing a reference duty cycle
signal by receiving a signal representing a turns ratio (N) of a transformer
of
the charger and producing the reference duty cycle signal according to the
relation:
Ref Duty Cycle = VAC
N VBATT
Producing the duty cycle may involve generating the duty cycle signal in
response to the reference duty cycle signal and the duty cycle error signal.
Producing the duty cycle may comprise bounding the duty cycle signal.
_
__
CA 02489701 2013-06-03
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In accordance with another aspect of the invention, there is provided a
computer readable medium encoded with codes for directing a processor
circuit to carry out the method and any of its variations above.
In general the invention permits various sets of operating conditions of the
charger to be used to establish a plurality of current command signals, the
lowest of which is used to finally control the duty cycle of switches in the
charger to prevent inappropriate conditions being experienced or caused by
the charger.
Other aspects and features of the present invention will become apparent to
those ordinarily skilled in the art upon review of the following description
of
specific embodiments of the invention in conjunction with the accompanying
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
In drawings which illustrate embodiments of the invention,
Figure 1 is a block diagram of a battery charger according to a first
embodiment of the invention;
Figure 2 is a block diagram of a duty cycle controller apparatus
of the
battery charger shown in Figure 1;
Figure 3 is a functional representation of a first current command
signal
generator of the duty cycle controller apparatus shown in Figure 2;
CA 02489701 2004-12-10
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Figure 4 is a schematic representation of a plurality of battery
tables
relating charger mode to a battery voltage command signal and a
maximum battery current signal for respective types of batteries
that may be charged by the charger shown in Figure 1;
Figure 5 is a functional representation of a second current
command signal
of the duty cycle controller apparatus shown in Figure 2;
Figure 6 is a functional representation of a third current command
signal of
the duty cycle controller apparatus shown in Figure 2;
Figure 7 is a functional representation of a fourth current
command signal
of the duty cycle controller apparatus shown in Figure 2;
Figure 8 is a functional representation of a fifth current command signal
of
the duty cycle controller apparatus shown in Figure 2;
Figure 9 is a flowchart illustrating the operation of a selector
of the duty
cycle controller apparatus shown in Figure 2;
Figure 10 is a schematic representation of a plurality of inputs to
the duty
cycle controller apparatus shown in Figure 2.
Figure 11 is a schematic representation of a gate drive controller
of the
charger shown in Figure 1.
Figure 12 is a schematic representation of waveforms of signals
produced
by or used by the gate drive controller shown in Figure 11.
DETAILED DESCRIPTION
Referring to Figure 1, a battery charger according to a first embodiment of
the
invention is shown generally at 10. The battery charger 10 includes a high
CA 02489701 2004-12-10
-25-
voltage circuit shown generally at 12, a low voltage circuit shown generally
at
14, a supervisory controller 16, a duty cycle controller 18, a user interface
94
and a gate drive controller 98.
The high voltage circuit 12 includes an AC plug 20 for receiving power from a
receptacle 22 connected to an AC power source 24 through a breaker 26. The
breaker 26 may be rated for 15 Amps, for example. The high voltage circuit 12
further includes an on/off switch 28 and line and neutral input terminals 30
and 32, respectively. The line and neutral input terminals 30 and 32 are
connected to a high voltage winding 34 of a transformer 36 coupling the high
and low voltage circuits 12 and 14 together. The input line terminal 30 is
connected to the high voltage winding 34 of the transformer through a current
sensor 38 or a plurality of current sensors operable to produce an AC input
current waveform signal (IAc). In this embodiment, the neutral terminal 32 is
connected to the high voltage winding 34 of the transformer 36 through a triac
40 controlled by the supervisory controller 16. An input voltage sensor shown
generally at 42 is connected between the line and neutral terminals 30 and 32
and is operable to produce an input AC voltage waveform signal (VAC) and an
input AC rms voltage waveform signal (VAcRms). Also connected to the input
line and neutral terminals 30 and 32 is a second receptacle 44 and a load
current sensor 46 for sensing load current drawn through the receptacle 44
from the high voltage circuit 12 to power any AC device that may be
connected to the receptacle. The load current sensor 46 is operable to
produce a load current signal (ILoADRms) indicating load current supplied to
the
AC device.
The low voltage circuit 14 includes a low voltage winding 48 of the
transformer
36 connected to a switching network 50 of transistors 52, 54, 56 and 58
connected in a full wave bridge topology to provide a positive DC voltage
terminal 60 and a negative DC voltage terminal 62. The positive terminal 60
includes a battery current sensor 64 for producing a battery current signal
(IBArr) representing current supplied to a battery 66 connected between the
CA 02489701 2004-12-10
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positive and negative terminals 60 and 62. A battery voltage sensor 68 is
connected across first and second battery connections 70 and 72 to which the
battery 66 is connected, to measure battery voltage. The battery voltage
sensor 68 thus produces a battery voltage signal (VBAT-r) representing battery
voltage.
The transistors 52, 54, 56 and 58 are connected to a heat sink (not shown) to
which is connected a temperature sensor 74 in thermal communication
therewith for producing a charger temperature signal representing
temperature of the heat sink and more generally, temperature of the charger.
The supervisory controller 16 is operable to receive signals from any of the
sensors 38, 42, 46, 64, 68 and 74, and possibly other sensors measuring
operating parameters of the charger. The supervisory controller 16 is
conventional and generally ensures that common operating conditions of the
charger are kept within limits, as is common in the art. Of importance,
however, in this embodiment, the supervisory controller 16 has an output 80
for producing a charger mode signal indicating the charger mode in which the
charger is operating. The charger mode may include bulk, absorption,
equalize and float modes, for example. Alternatively, a state of charge signal
representing state of charge of the battery 66 may be employed.
The supervisory controller 16 further has a phase control signal output 82 for
producing a signal indicating whether or not the charger is operating in a
phase control mode. The supervisory controller 16 also has an output 84 for
providing a triac control signal for controlling firing of the triac 40 to
keep the
peak AC voltage across the high voltage winding 34 of the transformer 36
within limits. This avoids a reflected voltage in the low voltage winding 48
of
the transformer, of a magnitude that would cause the transistors 52, 54, 56
and 58 to be short circuited as a result of the net voltage applied thereto as
a
result of the combination of the voltage across the low voltage winding 48 and
the voltage provided by the battery 66.
CA 02489701 2004-12-10
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The duty cycle controller 18 as a plurality of inputs shown generally at 90
for
receiving signals representing measured quantities including those produced
by the current sensor 38, voltage sensor 42, load current sensor 46, battery
current sensor 64, battery voltage sensor 68 and temperature sensor 74.
In particular, referring to Figure 10, inputs 90 include a battery voltage
signal
input 91 for receiving the battery voltage signal (VBA-rr), a battery current
signal input 93 for receiving the battery current signal (IBarr), an AC
voltage
waveform signal input 95 for receiving the AC voltage waveform signal (VAC),
an AC current waveform signal input 97 for receiving the AC current waveform
signal (lAc), an AC rms voltage signal input 99 for receiving the AC rms
voltage signal (VAcRms) representing input AC rms voltage, a load current
signal input 105 for receiving the load current signal (ILOADRMS)
representing load current supplied to a load connected to the same breaker
(26) through which current is supplied to the charger, a temperature signal
input 103 for receiving a temperature signal (TN) representing temperature of
the charger, a charger mode signal input 107 for receiving a charger mode
signal representing the charger mode of the charger, a phase control mode
signal input 109 for receiving the phase control mode signal indicating
whether or not said charger is operating in a phase control mode and may
include a battery temperature signal input 101 for receiving a battery
temperature signal TBATT representing the temperature of the battery (66).
The duty cycle controller 18 further includes a plurality of user inputs 92
for
receiving user-supplied signals including a battery type signal input 111 for
receiving a battery type signal indicative of the type of battery being
charged.
Alternatively, the battery type signal may be fixed so that the charger is
only
useable with a specified type of battery. This signal may indicate the battery
is a wet lead acid type, or a gel cell, for example.
_
CA 02489701 2004-12-10
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The plurality of user inputs 92 further includes a breaker current signal
input
113 for receiving a breaker rating current signal (IBREAKER RATING)
representing a rated current of the breaker rating through which current is
supplied to the charger.
The plurality of user inputs 92 further includes a battery size input 89 for
receiving a battery size signal indicative of the size of the battery being
charged, in Amp-hours, for example. Alternatively, the battery size signal may
be provided by a pre-stored or hard-coded value, where the charger is only
intended for use with batteries of a particular size.
The plurality of inputs 92 may further include a plurality of inputs for
receiving
from the user interface 94 signals representing fixed parameters, representing
various other operating parameters of the charger and conditions under which
it operates. Generally these parameters may be entered using the user
interface 94 and corresponding signals are produced and stored in a stored
parameters memory shown generally at 96. The user interface 94 may
present prompts to the user to prompt for entry of these parameters. The user
interface 94 may act to produce signals in response to user input for receipt
at
the following inputs of the duty cycle controller: a maximum temperature
signal input 115 for receiving a maximum temperature signal (TmAx)
representing maximum temperature of the charger, a derating range signal
input 117 for receiving a derating temperature range signal (TDERATERANGE)
specifying a range of temperature over which charging current must be
reduced to avoid overheating the charger, an efficiency signal input 121 for
receiving an efficiency signal (E) representing efficiency of the charger, a
breaker derating signal input 123 for receiving a breaker derating signal (B)
representing a derating factor for derating a rated current of a breaker
through
which AC current is supplied to said charger, a high side turns signal input
125 for receiving a signal (NH) representing the number of high side turns of
wire on a high voltage side of a transformer of the charger, a low side turns
signal input 127 for receiving a signal (NO representing the number of low
CA 02489701 2004-12-10
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side turns of wire on a low voltage side of the transformer, a low AC voltage
derating signal input 129 for receiving a low AC voltage derating signal
(VLOWACDERATE), and a low AC voltage derating range signal input 131 for
receiving a low AC voltage derating range signal (VLOWACDERATERANGE),
and a maximum charger current signal input 133 for receiving a maximum
charger current signal (ICHARGERMAX) representing the maximum charger
current available from the charger. Some of these signals may be factory set
rather than input by a user.
Referring back to Figure 1, in response to signals received at the measured
value inputs 90, the user inputs 92 and in response to the stored parameters
96, the duty cycle controller produces a duty cycle signal for receipt by the
gate drive controller 98 which, in response to the duty cycle signal, produces
gate drive signals G1, G2, G3 and G4 for controlling respective transistors
52,
54, 56, and 58 of the switching network 50 to ultimately control the amount of
current supplied to the battery 66 to control the voltage across the battery
while, at the same time, maintaining a high power factor in power drawn at the
line and neutral terminals 30 and 32 of the high voltage circuit 12 of the
charger.
It will be appreciated that the supervisory controller 16, the duty cycle
controller 18, the user interface 94 and the gate drive controller 98 may be
embodied in a microprocessor or digital signal processor, for example, or a
combination of a microprocessor and/or digital signal processor and/or
discrete hardware elements. For example, the gate drive controller 98 may be
conveniently implemented by logic gates, the supervisory controller 16 and
user interface 94 may be implemented by a common microprocessor and the
duty cycle controller may be implemented in a digital signal processor. It
will
be appreciated that in any microprocessor implementation, the
microprocessor may include a processor in communication with a computer-
_
CA 02489701 2004-12-10
-30-
readable medium encoded with codes for directing the processor to carry out
the methods described herein and/or variations thereof.
Referring to Figure 2, the duty cycle controller apparatus is shown in greater
detail at 100. In general, the duty cycle controller apparatus 100 includes a
current command signal generator shown generally at 102, a selector shown
generally at 104, and a duty cycle signal generator shown in broken outline at
106. The current command signal generator 102 has a plurality of signal
inputs 108 for receiving a plurality of signals representing a plurality of
operating conditions of the charger, this plurality of inputs 108 being in
communication with inputs 90 and 92 shown in Figure 10. It also has a
plurality of current command outputs shown generally at 110 and includes a
processor 112 operably configured to generate a plurality of current command
signals at the current command outputs 110 in response to respective sets of
operating conditions represented by the signals received at the plurality of
signal inputs 108.
The selector 104 is configured to receive the plurality of current command
signals and to select a current command signal having a lowest value and to
produce a lowest current command signal in response thereto.
The duty cycle signal generator 106 has a battery current signal input 114, a
battery voltage signal input 116, an AC voltage waveform input 118, an AC
current waveform input 120 in communication with the general inputs to the
duty cycle controller, by the same names (93, 91, 95, 97 in Figure 10) and
further includes, a lowest current command input 122 and a duty cycle signal
output 124. The duty cycle signal generator 106 is configured to produce the
duty cycle signal at the duty cycle signal output 124 in response to the
lowest
current command signal, the battery current signal, the battery voltage
signal,
the AC voltage waveform signal and the AC current waveform signal received
at inputs by the same names 122, 114, 116, 118, and 120, respectively.
CA 02489701 2004-12-10
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In the embodiment shown, the current command signal generator includes
first, second, third, fourth and fifth current command signal generators 130,
132, 134, 136 and 138, operable to produce first, second, third, fourth and
fifth
current command signals at first, second, third, fourth and fifth current
command signal outputs 140, 142, 144, 146 and 148, respectively. The
current command signal outputs 140, 142, 144, 146 and 148 are connected to
respective current command signal inputs 150, 152, 154, 156 and 158,
respectively, of the selector 104.
It will be appreciated that the duty cycle controller shown in Figure 2 may
desirably be implemented in a digital signal processor capable of
implementing a plurality of functions including the first, second, third,
fourth
and fifth current command signal generators 130 to 138. Consequently, the
functionality of each of these generators will be described in functional
terms,
it being understood that the functions described may be used to specify a
design structure for designing or configuring a suitable digital signal
processor
or programming a programmable digital signal processor for performing the
functions described herein. Throughout this description references to
"signals"
or a "signal", may be construed as any digital or analog electrical, optical,
or
electromagnetic entity operable to represent information. Hence, a number
stored in memory, for example, is deemed to be a "signal" or "signals", as
will
be appreciated by one of ordinary skill in the art.
Referring to Figures 3 and 10, a functional description of the first current
command signal generator is shown generally at 160 and includes a battery
voltage command signal generator 162 and a difference signal generator
shown generally at 164. The battery voltage command signal generator 162
has battery type and charger mode signal inputs 166 and 168 (in
communication with inputs 111 and 107, respectively) for receiving the battery
type signal and charger mode signal, respectively.
CA 02489701 2004-12-10
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Referring to Figure 4, in the embodiment shown, the memory (170) of the duty
cycle controller is configured to represent a plurality of battery type
tables, as
shown at 172. Each battery type table associates a charger mode 174 for a
given battery type with a battery voltage command value 176 and a maximum
battery current value (IBArrmAx) 178. The battery voltage command value 176
and battery current value IBArrmAx 178 are set by the manufacturer of the
battery and generally indicate the maximum value voltage and current that
may be applied to the battery in a given charger mode. Thus, referring to
Figures 3 and 4, for a given battery type signal received at the battery type
signal input 166, and for a given charger mode signal received at the charger
mode signal input 168, the battery voltage command signal generator
addresses the memory 170 shown in Figure 1 to find a battery type table
indicated by the battery type signal and then, within the identified table,
uses
the charger mode signal to find a battery voltage command value 176
associated with the charger mode represented by the charger mode signal.
Optionally, the battery voltage command signal generator 162 may have a
further battery temperature signal input 177 in communication with the battery
temperature signal input 101. The battery voltage command signal generator
162 may be configured to modify the battery voltage command signal
produced in response to the battery type signal and the charger mode signal,
in response to the battery temperature signal.
The battery voltage command value 176 is produced at a battery voltage
command signal output 180 of the battery voltage command signal generator
162. The output 180 is connected to a corresponding input of the difference
signal generator 164. The difference signal generator 164 further has a
battery voltage signal input 181 in communication with the battery voltage
input 91 for receiving the battery voltage signal. The difference signal
generator is operably configured to produce the first current command signal
in response to a difference between the battery voltage command signal and
the battery voltage signal. The difference signal generator 164 has an output
CA 02489701 2004-12-10
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182 which acts as a first command signal output of the first current command
signal generator 160, for providing the first current command signal to the
selector 104 shown in Figure 2.
Referring to Figures 5 and 10, the functionality of the second current
command signal generator is shown generally at 132. The second current
command signal generator 132 includes a temperature signal input 200 in
communication with the temperature signal input 103, for receiving the
temperature signal (TH) representing temperature of the charger, a maximum
temperature signal input 202 in communication with the maximum
temperature signal input 115 of the duty cycle controller for receiving the
maximum temperature signal (TmAx) representing maximum temperature of
the charger, a derating range signal input 204 in communication with the
derating range signal input 131 of the duty cycle controller for receiving the
derating temperature range signal (TDERATERANGE) specifying a range of
temperature over which charging current must be reduced to avoid
overheating the charger and a maximum charger current signal input 206 in
communication with the maximum charger current signal input 133 for
receiving the maximum charger current signal (ICHARGERMAX) representing
maximum charger current available.
The functionality of the second current command signal generator 132
includes a temperature ratio generator 212 for generating a temperature ratio
of a difference between the maximum temperature signal received at the
maximum temperature signal input 202 and the temperature signal received
at the temperature signal input 200 to the temperature derate range indicated
by the temperature derate range signal received at the temperature derating
range signal input 204. In addition, the second command signal generator 132
includes a multiplier 214 for multiplying the maximum charger current signal
(IcHARGERMAX) by the temperature ratio to produce the second current
command signal at an output 216 thereof. The output 216 acts as the second
current command signal output of the second current command signal
CA 02489701 2004-12-10
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generator 132 for providing the second current command signal to the
selector 104 shown in Figure 2. Optionally and desirably, the second current
command signal generator 132 includes a lowpass filter function 218 for
lowpass filtering the temperature signal representing the temperature of the
charger prior to supplying the temperature signal to the temperature ratio
generator 212. The lowpass filter may have a cutoff frequency of about 1 Hz,
for example. In addition, desirably, the second current command signal
generator 132 includes a clamping function 220 for clamping the temperature
ratio to an upper bound prior to use of the temperature ratio by the
multiplier
214. In addition, a test function (not shown) may be included in the second
command generator to test whether the temperature TH is greater than the
derating temperature TmAx and to only perform the reduction from maximum
charger current provided by the multiplier 214 when TH is greater than TMAX=
Otherwise, the second current command is set to the maximum charger
current (IcHARGERMAX)=
Referring to Figures 6 and 10, the third current command signal generator is
shown generally at 134. The third current command signal generator 134
includes an efficiency signal input 230 in communication with the efficiency
signal input 121, for receiving the efficiency signal representing efficiency
of
the charger. It also includes an AC rms voltage signal input 232 in
communication with the AC rms voltage signal input 99 for receiving the AC
rms voltage signal (VACRms) representing input AC rms voltage. The third
current command signal generator 134 shown in Figure 6 further includes a
breaker derating signal input 234 in communication with the breaker derating
input 123 for receiving the breaker derating signal (B). The third current
command signal generator 134 further includes a breaker rating current signal
input 236 in communication with the breaker rating current signal input 113
for
receiving the breaker rating current signal (IBREAKERRATING) representing a
rated
current of the breaker 26 through which current is supplied to the charger.
The
third current command signal generator 134 further includes a load current
signal input 238 in communication with the load current signal input 101, for
CA 02489701 2004-12-10
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receiving the load current signal (1L0AD) representing load current supplied
to a
load connected to the same breaker through which current is supplied to the
charger. The third current command signal generator 134 further includes a
battery voltage signal input 240 in communication with the battery voltage
signal input 91, for receiving the battery voltage signal produced by the
battery voltage sensor 68 shown in Figure 1.
The third current command signal generator further includes a computation
function for producing the third current command signal CCS3 according to
the relation:
CCS3= (E)(VACRMS)((B)(IBREAKER) ¨ (ILOAD))
VBATT
Alternatively, the use of the VBArr signal may be replaced with a constant
value, especially where the third current command signal generator is
implemented in a digital signal processor in which divide functions use a
significant amount of processor resources.
The value (CCS3) produced by the above relation is used to provide a signal
at an output 242 of the third current command signal generator 134 to provide
the third current command signal to the selector 104 shown in Figure 2.
Referring to Figures 7 and 10, the functionality of the fourth current command
signal generator is shown generally at 136. The fourth current command
signal generator 136 includes a phase control mode signal input 250 in
communication with the phase control mode signal input 109 for receiving the
phase control mode signal indicating whether or not the charger is operating
in a phase control mode. The fourth current control signal generator 136
further includes a battery voltage signal input 252 in communication with the
battery voltage signal input 91 for receiving the battery voltage signal. The
___
CA 02489701 2004-12-10
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fourth current control signal generator 136 further includes high and low side
turns signal inputs 254 and 256 in communication with high and low side turns
signal inputs 125 and 127, respectively, for receiving the high turns signal
(NH)
and for receiving the low turns signal (NO. The fourth current command signal
generator 136 further includes an AC rms voltage signal input 258 in
communication with the AC rms voltage signal input 99 for receiving the AC
rms signal (VAcRms) representing input AC rms voltage to the charger. The
fourth current command signal generator 136 further includes a maximum
charger current signal input 260 for receiving the maximum charger current
signal ICHARGERMAX from the maximum charger current input 133.
The fourth current control signal generator 136 includes a test function 262
for
testing whether or not the phase control mode signal received at the phase
control mode signal input 250 indicates that the charger is in the phase
control
mode. If the charger is not in the phase control mode, a current command
signal assignment function 264 causes the fourth current command signal to
be equal to the maximum charger current signal ICHARGERMAX. When the phase
control mode signal indicates the charger is in the phase control mode, a
computation function 266 computes the value of the fourth current command
signal according to the relation:
CCS4 = (VBATT)(NH)* (ICHARGERMAX)
(NO(VAcRms) * 2-12
The fourth current command signal, whether produced by the assignment
function 264 or the computation function 266, is provided at an output 268 of
the fourth current command signal generator for providing the fourth current
command signal to the selector 104 shown in Figure 2.
Referring to Figures 8 and 10, the fifth current command signal generator is
shown generally at 138 and includes a low AC voltage derating signal input
CA 02489701 2004-12-10
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270 in communication with the low AC voltage derating signal input 129 for
receiving the low AC voltage derating signal (VLOWACDERATE), and an AC rms
voltage signal input 272 in communication with the AC rms voltage signal
input 99 for receiving the AC rms voltage signal (VAcRms) representing input
AC rms voltage. The fifth current command signal generator 138 further
includes a maximum charger current signal input 274 in communication with
the maximum charger current signal input 133, for receiving the maximum
battery current signal (IcHARGERMAX).
The fifth current command signal generator 138 further includes a low AC
voltage derating signal input 276 in communication with the low AC derating
signal input 129 for receiving the low AC voltage derating range signal
(VLOWACDERATERANGE).
The fifth current command signal generator 138 further includes a test
function 277 for determining whether the AC rms voltage signal represents a
voltage less than a low AC derating voltage as represented by the low AC
derating voltage signal (VLOWACDERATE). If the test function 277 determines
that
the AC rms voltage is less than the low AC derating voltage, a computation
device 279 produces the fifth current command signal according to the
relation:
CCS5 = ((VLOWACDERATE) - (VACRMS))(ICHARGERMAX)
VLOWACDERATERANGE
If the test function 277 determines that the AC rms voltage is not less than
the
low AC derating voltage, an assignment function 281 sets the fifth current
command signal equal to the maximum charger current signal (IcHARGERmAx).
The fifth current command signal is provided at an output 278 of the fifth
current command signal generator to provide the fifth current command signal
to the selector 104.
CA 02489701 2004-12-10
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Referring to Figure 2, the selector includes a store 280, such as a register
or
memory location for storing at least one of the plurality of current commands
received at the current command signal inputs 150 through 158. Only one of
the current command signals, for example, need be stored. In this
embodiment, the first current command signal is initially stored in the store
280.
The selector 104 further includes a comparator 282 for performing a plurality
of comparisons for successively comparing the contents of the store 280 with
successive compared signals. A compared signal is one of the current
command signals other than the one stored in the store 280. After each
comparison, where the compared signal is less than the contents of the store
280, the contents of the store are replaced with a value representing the
compared signal. Where the compared signal is not less than the contents of
the store, the contents of the store are left the way they were before the
comparison.
Referring to Figure 9, a process executed by the selector 104 is shown
generally at 350. The process is illustrated by representing blocks of code
that may be stored in computer readable media and readable by a processor
to direct the processor to carry out the process. In this regard, the process
begins with a first block of codes 352 that directs the processor to store the
first current command signal in the store 280. The block 354 directs the
processor to select a compared signal, i.e. one of the second through fifth
current command signals, and determine whether the compared signal is less
than the signal stored in the store 280. If not, block 356 directs the
processor
to determine whether all current command signals have been compared to the
contents of the store 280 and if not, to select the next current command
signal
and compare it to the contents of the store. If the currently compared current
command signal is less than the contents of the store 280, block 355 directs
the processor to replace the contents of the store with the currently compared
signal. A block of codes 356 directs the processor to determine whether all
CA 02489701 2004-12-10
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current command signals have been subjected to this process. When all
current command signals have been subjected to this process, block 358
directs the processor to provide the contents of the store 280 at the output
119 of the selector 104. When the process is finished, the contents of the
store 280 thus represent the current command signal with the lowest value.
Thus, for example, the first current command signal is received in the store
280. Next, the second current command signal is used as a comparison
signal and if the second current command signal is less than the contents of
the store 280, i.e., currently the first current command signal, the store is
replaced with the contents of the second current command signal. Then, the
third current command signal is used as the compared signal and is
compared by the comparator 282 to the contents of the store 280 which are
currently the second current command signal. If the third current command
signal is less than the current contents of the store 280, i.e., the second
current command signal, the store is replaced with the third current command
signal. Next, the fourth current command signal acts as the compared signal
and the comparator compares the fourth current command signal with the
contents of the store 280, i.e., the third current command signal. If the
fourth
current command signal is not less than the contents of the store 280, for
example, the store is left undisturbed and remains holding the third current
command signal. Then, the fifth current command signal acts as the
compared signal and the comparator 282 compares the fifth current command
signal to the contents of the store 280 which are currently set at the third
current command signal. If the fifth current command signal is less than the
contents of the store 280, the contents of the store are replaced with the
fifth
current command signal and the fifth current command signal is provided at
the output 119 of the selector as the lowest current command signal.
As described earlier, the selector 104 may be implemented in the same digital
signal processor that implements the current command signal generator, a
CA 02489701 2004-12-10
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separate digital signal processor or may be implemented as discrete
hardware elements.
Referring back to Figure 2, the duty cycle signal generator 106 comprises a
power command generator 300 for generating a power command signal in
response to the lowest current command signal and the battery current
command signal received at the battery current signal input 114. In the
embodiment shown, the power command generator includes a lowpass filter
302 for lowpass filtering the battery current signal and for providing it to a
difference amplifier 304 that may provide gain and filter functions and
ultimately compute a difference between the lowest current command signal
and the battery current signal, to produce the power command signal at an
output 306 thereof.
Up to and including the power command generator 300, the components may
be configured to implement a "slow" control loop with a bandwidth of 10 ¨ 20
Hz, for example. Sampling for digital signal processor implementations may
be at 60 Hz, for example. The remainder of the components in the duty cycle
controller 100 are desirably configured to implement a "fast' control loop
having a bandwidth of perhaps more than 500 Hz and sampling rates of 12
kHz, for example may be used in DSP implementations of these components.
The duty cycle signal generator 106 further comprises an AC current
command signal generator 308 for producing an AC current command signal
in response to the power command signal produced by the power command
generator 300 and the AC voltage waveform signal received at the AC voltage
waveform input 118. In this embodiment, the AC current command signal
generator 308 includes a multiplier 310 which multiplies the power command
signal produced at the output 306 of the power command generator 300 with
the AC voltage waveform signal received at the AC voltage waveform input
118. The multiplier has an output 312 at which the AC current command
signal is produced.
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The duty cycle signal generator 106 further comprises a duty cycle error
signal generator shown generally at 314 for generating a duty cycle error
signal in response to the AC current command signal from the output 312 of
the AC current command signal generator 308, and the AC current waveform
signal received at the AC current waveform input 120. In this embodiment the
duty cycle error signal generator includes a difference amplifier 316 that may
provide gain and filtering functions to the duty cycle error signal ultimately
produced. The duty cycle error signal is produced at an output 318 of the duty
cycle error signal generator 314.
The duty cycle signal generator 106 further includes a reference duty cycle
generator 320 for producing a reference duty cycle signal at an output 322
thereof. The reference duty cycle generator 320 has an AC voltage signal
input 324 for receiving the AC input voltage signal representing AC input
voltage (VAC) to the charger, as received at the AC voltage waveform input
118. In addition, the reference duty cycle signal generator 320 further
includes
a battery voltage signal input 326 for receiving the battery voltage signal
received at the battery voltage signal input 116. The reference duty cycle
signal generator further includes a turns ratio input 328 for receiving a
signal
representing the turns ratio of the transformer 36 shown in Figure 1. The
turns
ratio may be computed from the NH and NL signals received at the inputs 254
and 256 of the fourth current command signal generator shown in Figure 7,
for example. The reference duty cycle signal generator further includes a
computing function 330 for producing the reference duty cycle signal at the
output 322 according to the relation:
Ref Duty Cycle = VAC
N VBATT
Still referring to Figure 2, the duty cycle signal generator 106 further
includes
an adder 332 for adding the reference duty cycle signal produced at the
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output 322 to the duty cycle error signal produced at the output 318 to
produce a duty cycle signal at an output 334 thereof. The duty cycle signal
produced at the output 334 may be provided directly to the gate drive
controller 98 shown in Figure 1, but preferably is provided through a clamping
function 335 which clamps the duty cycle signal to limits between minus one (-
1) and one (1). Alternatively, other limits may be employed.
Desirably, the clamped duty cycle signal is provided at the output 124 of the
duty cycle signal generator and is provided to the gate drive controller 98.
The
gate drive controller uses the duty cycle signal to produce gate drive signals
G1, G2, G3 and G4 to control the transistors 52, 54, 56 and 58 to regulate
current flow to the battery 66.
Referring to Figure 11, in this embodiment, the gate drive controller 98
includes a triangle wave generator 360 having an output 362 for generating a
triangle wave signal having voltage excursions symmetrically above and
below zero as shown at 364 in Figure 12. The triangle wave signal is applied
to inverting inputs 366 and 368 of first and second comparators 370 and 372.
The duty cycle signal output 124 shown in Figure 2 is in communication with
the non-inverting input 374 of the first comparator 370 and is further in
communication with an input 376 of a polarity reverser 378, which reverses
the polarity of the signal received at the input 376. As shown in Figure 12,
the
duty cycle signal (D) is depicted at 377 and the same signal with reversed
polarity (-D) is depicted at 379. Increasing the duty cycle signal causes the
signals shown at 377 and 379 to spread apart symmetrically from a zero
voltage reference 381 and decreasing the duty cycle signal causes them to
move closer together symmetrically toward the zero voltage reference.
The polarity reverser 378 has an output 380 in communication with a non-
inverting input 382 of the second comparator 372. The first comparator 370
has an output 384 that produces the first gate drive signal G1 and this output
is connected to an inverter 386 having an output 388 for providing the second
_
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gate drive signal G2. The second comparator 372 has an output 390 that
produces the third gate drive signal G3 and this output is connected to an
inverter 392 having an output 394 for providing the fourth gate drive signal
G4.
The effect of the gate drive signal circuit shown in Figure 11 is shown in
Figure 12 in which gate drive signals G1-G4 are shown at 400, 402, 404 and
406 respectively. The gate drive signals G1-G4 are active only while the
triangle waveform signal is above or below the duty cycle signals 377 and
379. Thus as the duty cycle signal increases, the time during which the
transistors controlled by the gate drive signals are on is reduced and when
the
duty cycle signal decreases, the time during which the transistors controlled
by the gate drive signals are on is increased. From the waveforms shown in
Figure 12, it will be appreciated that the clamp 335 shown in Figure 2 is
desirably set to clamp the duty cycle signal to a value corresponding to a
peak
of the triangle waveform produced by the triangle waveform generator 360.
Referring to Figure 2, effectively, the first current command signal generator
130 produces a first current command signal on the basis of the battery
voltage, battery type and charger mode. This would be a desirable current
command signal if the charger were not subject to temperature increases due
to current draw, sharing breaker capacity with other loads, phase control due
to excessive AC input voltages relative to reflected battery voltages and AC
input voltage fluctuations below nominal levels. The second, third, fourth and
fifth current command signal generators 132, 134, 136, 138 provide current
command signals that address each of these conditions and, in effect, the
selector 104 shown in Figure 2 acts to select the lowest current command
signal value from among the five current command signals to operate the
charger in a safe and reliable manner.
For example, when the second current control signal is lowest, the charger
may be operating under conditions in which it could overheat, but this
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condition is prevented by the second current command signal. Alternatively, if
the charger is operating in a mode in which current drawn from the second
receptacle 44 shown in Figure 1 in addition to the current drawn by the
charger may exceed the current available from the breaker 26, the third
current command signal may be lowest and will cause the duty cycle to be
suitably adjusted to prevent overloading the breaker 26.
Alternatively, where the AC input voltage exceeds the reflected battery
voltage through the turns ratio of the transformer such that the charger is
placed in the phase control mode by the supervisory controller, the fourth
current command signal may be the lowest current command signal, and
thereby limit the duty cycle to prevent short circuit conditions from
occurring in
the low voltage circuit 14.
Alternatively, in the event that the AC input voltage is lower than a nominal
AC
voltage, the fifth current control signal generator 138 will generate a
current
control signal attempting to adjust the duty cycle to prevent excessive
current
from being drawn from the AC input.
Thus, various sets of operating conditions of the charger are used to
establish
a plurality of current command signals, the lowest of which is used to finally
control the duty cycle to prevent inappropriate conditions being experienced
or caused by the charger.
In some embodiments, fewer or more than the five current command signals
described above may be used. For example, different combinations of current
command signals may be used. In general, however, the first current
command signal is important as this represents the theoretical best current
command based strictly on battery parameters. The remaining current
command signals are dependent upon other factors besides battery
parameters. Thus, depending upon which set of parameters and conditions it
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is sought to guard against, the appropriate signal generators may be selected
for inclusion.
