U.S. patent application number 11/581463 was filed with the patent office on 2007-02-08 for voltage converter control apparatus and method.
This patent application is currently assigned to Toyota Jidosha Kubushiki Kaisha. Invention is credited to Masaki Okamura, Eiji Sato.
Application Number | 20070029954 11/581463 |
Document ID | / |
Family ID | 19191371 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070029954 |
Kind Code |
A1 |
Okamura; Masaki ; et
al. |
February 8, 2007 |
Voltage converter control apparatus and method
Abstract
By using a target voltage Vc* of a capacitor connected to the
output side of a DC/DC converter and a voltage Vb of a battery
connected to the input side of the DC/DC converter, a duty ratio D
as a drive instruction of the DC/DC converter is calculated. By
using the voltage Vb, the electromotive force Vbo of the battery,
and the charge/discharge current Ib of the battery, an internal
resistance Rb is calculated. According to the internal resistance
Rb and the electromotive force Vbo, the current value when the
battery output becomes maximum is set as the upper limit value of
the optimal current range IR, the DC/DC converter is
driven/controlled by limiting the duty ratio D so that the current
Ib is within the range of the optimal current range IR. Thus, it is
possible to appropriately convert the battery input voltage.
Inventors: |
Okamura; Masaki;
(Toyota-shi, JP) ; Sato; Eiji; (Aichi-ken,
JP) |
Correspondence
Address: |
KENYON & KENYON LLP
1500 K STREET N.W.
SUITE 700
WASHINGTON
DC
20005
US
|
Assignee: |
Toyota Jidosha Kubushiki
Kaisha
Toyota-shi
JP
|
Family ID: |
19191371 |
Appl. No.: |
11/581463 |
Filed: |
October 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10500041 |
Jun 23, 2004 |
|
|
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PCT/JP03/00192 |
Jan 14, 2003 |
|
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11581463 |
Oct 17, 2006 |
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Current U.S.
Class: |
318/139 |
Current CPC
Class: |
Y02T 10/72 20130101;
B60L 50/51 20190201; B60L 2240/549 20130101; Y02T 90/12 20130101;
Y02T 10/7072 20130101; B60L 15/007 20130101; H02M 1/0022 20210501;
Y02T 10/70 20130101; H02M 3/157 20130101; B60L 7/14 20130101; Y02T
90/14 20130101; H02M 7/529 20130101; Y02T 10/64 20130101; Y02T
10/92 20130101; B60L 53/22 20190201; B60L 2240/547 20130101; H02J
2207/20 20200101; H02M 7/53873 20130101; B60L 15/2045 20130101;
B60L 2210/10 20130101 |
Class at
Publication: |
318/139 |
International
Class: |
H02P 5/00 20060101
H02P005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2002 |
JP |
2002-007960 |
Claims
1. A voltage conversion device having a reactor for temporarily
storing energy based on a current from a power source, for
converting a voltage of the power source, which is input while
utilizing the reactor, into a desired voltage through switching of
a switching element to output, comprising: a voltage detection
circuit for detecting a voltage of the power source; and a control
circuit for applying switching control to the switching element
such that the detected voltage remains within a predetermined range
which is determined based on the electromotive voltage of the power
source, and further, such that an output voltage of the voltage
conversion device becomes equal to a target voltage which is
determined based on a target output amount of a load which is
driven based on the output of the voltage conversion device,
wherein the power source is chargeable and dischargeable, and, an
output obtained through conversion into the desired voltage is
supplied to a load.
2. A voltage conversion method for converting a voltage of a power
source, which is input while utilizing a reactor for temporarily
storing energy based on a current from the power source, into a
desired voltage through switching of a switching element to output,
comprising: detecting a voltage of the power source; and applying
switching control to the switching element such that the detected
voltage remains within a predetermined range which is determined
based on the electromotive voltage of the power source, and
further, such that an output voltage of the voltage conversion
device becomes equal to a target voltage which is determined based
on a target output amount of a load which is driven based on the
output of the voltage conversion device, wherein the power source
is chargeable and dischargeable, and, an output obtained through
conversion into the desired voltage is supplied to a load.
3. A computer readable recording medium storing a control program
for controlling a voltage conversion device having a reactor for
temporarily storing energy based on a current from a power source
which is chargeable and dischargeable, for converting a voltage of
the power source, which is input while utilizing the reactor, into
a desired voltage through switching of a switching element to
output to a load, the program having a computer to execute
switching control of the switching element such that the voltage of
the power source remains within a predetermined range which is
determined based on the electromotive voltage of the power source,
and further, such that an output voltage of the voltage conversion
device becomes equal to a target voltage which is determined based
on a target output amount of a load which is driven based on the
output of the voltage conversion device.
4. A control program for controlling a voltage conversion device
having a reactor for temporarily storing energy based on a current
from a power source which is chargeable and dischargeable, for
converting a voltage of the power source, which is input while
utilizing the reactor, into a desired voltage through switching of
a switching element to output to a load, the program having a
computer to execute: switching control of the switch element such
that the voltage of the power source remains within a predetermined
range which is determined based on the electromotive voltage of the
power source, and further, such that an output voltage of the
voltage conversion device becomes equal to a target voltage which
is determined based on a target output amount of a load which is
driven based on the output of the voltage conversion device.
Description
TECHNICAL FIELD
[0001] The present invention relates to a control device and a
voltage conversion method for a voltage conversion device, a
recording medium, a program, a driving system, and a vehicle
carrying the driving system. In particular, the present invention
relates to a device having a reactor for temporary storage of
energy based on a current from a power source, for converting a
voltage of the power source, which is input using the reactor, into
a desired voltage through switching of a switching element to
output.
BACKGROUND ART
[0002] As a conventional driving system of the above-described
kind, there is proposed a system comprising, for example, a battery
serving as a power source of the driving system, a DC/DC converter
for applying DC/DC conversion to an input voltage from the battery,
a load having an inverter for converting an output from the DC/DC
converter into a multi-phase AC current and a motor for rotation
driving while receiving the multi-phase AC current from the
converter, and a capacitor arranged between the DC/DC converter and
the load and connected to the positive and negative bussbars
(lines) of the inverter circuit. In such a system, the DC/DC
converter applies DC/DC conversion to an input voltage from the
battery and the converted voltage is then stored in the capacitor
so that the load is driven using the power-stored capacitor then
considered as a DC power source.
[0003] In this system, while driving control of a DC/DC converter
is performed such that the amount of power corresponding to an
output required by a load, or "a load requiring output", can be
obtained from the battery, the voltage stored in the capacitor can
remain in a stable condition while the driving system can achieve
stable driving. General batteries are designed to be capable of
supplying an amount of power corresponding to a load requiring
output. However, there may be situations in which, depending on the
condition of the battery, a battery cannot supply an amount of
power corresponding to a load requiring output when, for example,
the battery inner resistance has increased due to low battery
temperature. Were the DC/DC converter be, in such a case, given
driving control simply such that an amount of power corresponding
to a load requiring output is fed to the load, power consumption
due to inner resistance of the battery may increase, resulting in a
drop in power supplied to the load.
DISCLOSURE OF INVENTION
[0004] Control by a voltage conversion device of the present
invention enables more appropriate conversion of an input voltage
from a power source depending on the condition of the power
source.
[0005] Specifically, with control by a voltage conversion device
according to one aspect of the present invention, a current range
setting means sets a range of current from a power source based on
output characteristics of the power source corresponding to the
condition of the power source, which is determined by a condition
detection means, and a control means controls switching of a
switching element such that the current from the power source
remains in the current range set by the current range setting
means. This arrangement enables more appropriate extraction of an
output from the power source based on the output characteristics of
the power source corresponding to the condition of the power
source. Here, "output characteristic of a power source" refers to
correlation between an output and a current from the power
source.
[0006] With control by a voltage conversion device according to
another aspect of the present invention, a ratio range setting
means sets a range of ratios each between a period with an upper
switching element remaining in an ON state and a period with a
lower switching element remaining in an ON state, or a ratio range,
based on output characteristics of the power source corresponding
to the condition of the power source, which is determined by the
condition detection means, and a control means controls the ratio
between the periods with the respective switching elements
remaining in an ON state so as to remain within the ratio range set
by the ratio range setting means. This arrangement enables more
appropriate extraction of an output from the power source based on
the output characteristics of the power source depending on the
condition of the power source. Here, "output characteristics of a
power source" refers to correlation between an output of the power
source and a ratio between periods with the respective switching
elements remaining in an ON state.
[0007] With control by a voltage conversion device according to
another aspect of the present invention, the control means controls
switching of a switching element such that the voltage of the power
source, which is detected by the voltage detection means, remains
in a predetermined range. Monitoring the condition of the power
source by monitoring its voltage enables more appropriate
extraction of an output from the power source.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIG. 1 is a block diagram schematically showing a structure
of a driving system 20 according to one embodiment of the present
invention;
[0009] FIG. 2 is a diagram showing an example of the driving system
20;
[0010] FIG. 3 is a flowchart of an exemplary DC/DC converter
driving control routine to be executed by an electronic control
unit 40 of the driving system 20 in the embodiment;
[0011] FIG. 4 is a map illustrating relationship between inner
resistance Rb and temperature of a battery 22;
[0012] FIG. 5 is a diagram showing one example of output
characteristic of the battery 22;
[0013] FIG. 6 is a diagram showing output characteristics of the
battery 22 with the inner resistance Rb of the battery 22 being a
value R0 and those of the battery 22 with the inner resistance Rb
being a value 1 (R1>R0);
[0014] FIG. 7 is a diagram showing an exemplary load driving
control routine to be executed by the electronic control unit 40 of
the driving system 20;
[0015] FIG. 8 is a diagram schematically showing a structure of a
driving system 120 of a second embodiment of the present
invention;
[0016] FIG. 9 is a diagram showing an exemplary DC/DC converter
driving control routine to be executed by an electronic control
unit 140 of the driving system 120 in the second embodiment;
[0017] FIG. 10 is a diagram showing an example of output
characteristics of the battery 122;
[0018] FIG. 11 is a diagram showing setting of an optimum duty
ratio DR;
[0019] FIG. 12 is a flowchart of an exemplary DC/DC converter
driving control routine to be executed by an electric control unit
of a driving system in a modified example;
[0020] FIG. 13 is a flowchart of an exemplary DC/DC converter
driving control routine to be executed by an electronic control
unit 40 of the driving system in the embodiment; and
[0021] FIG. 14 is a flowchart of an exemplary DC/DC converter
driving control routine to be executed by the electronic control
unit 40 of the drive system in the embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] In the following, embodiments of the present invention will
be described.
[0023] FIG. 1 is a schematic diagram showing a structure of a
driving system 20 in an embodiment of the present invention of the
present invention. The driving system 20 in the embodiment
comprises, as shown, a battery 22, a DC/DC converter 24 serving as
a voltage conversion device for applying DC/DC conversion to an
input voltage from the battery 22 to output, a capacitor 26 adapted
to storing an output current from the DC/DC converter 24, a load 28
adapted to being driven using a stored current in the capacitor 26,
and an electronic control unit 40 for controlling the entire
device.
[0024] The battery 22 may be prepared, for example, as a secondary
battery of nickel hydrogen or lithium ion.
[0025] The DC/DC converter 24 comprises two serially connected
transistors T1, T2, two diodes D1, D2, and a reactor L, in which
the two transistors T1, T2 are respectively connected to the
positive and negative lines and on the source and sink sides of the
load 28; the two diodes D1, D2 are reverse parallel connected to
the transistors T1, T2, respectively; and the reactor L is
connected to a point at which connecting the transistors T1,
T2.
[0026] In the DC/DC converter 24, when the transistor T2 is turned
on, a short circuit is formed connecting the battery 22, the
reactor L, and the transistor T2, so that energy according to a DC
current flowing from the battery 22 is stored in the reactor L.
When the transistor T2 is then turned off, the energy stored in the
reactor L is then stored in the capacitor 26 via the diode D1. In
the above, the voltage of the capacitor 26 can become higher than a
voltage fed by the battery 22. In this DC/DC converter 24, it is
also possible to charge the battery 22 using stored charge in the
capacitor 26. In this sense, the DC/DC converter 24 constitutes an
elevating/descending voltage chopper circuit which can charge the
capacitor 26 through turning on/off of the transistors T1, T2 and
also charge the battery using stored charge in the capacitor 26. It
should be noted that the reactor of the DC/DC converter 24 may
employ a coil.
[0027] The load 28 may have a structure, as shown in FIG. 2, for
example, comprising an inverter and a generator or a motor as
mounted in an electric and/or hybrid vehicle (see FIG. 2(a)) or a
structure comprising two parallel connected inverters respectively
connected to a motor and a generator (see FIG. 2(b)), though the
motor or generator as mounted to an electric or hybrid vehicle is
not an exclusive example and any electric device which can be
driven using power from the battery 22 is also applicable.
[0028] The electronic control unit 40 is constructed as a micro
processor having a CPU 42 as a main component, as shown in FIG. 1,
and comprising a ROM 44 for storing a process program, a RAM 46 for
temporal data storage, and input/output ports (not shown). The
electronic control unit 40 receives via an input port a battery
voltage Vb from a voltage sensor 30 mounted to the battery 22, a
battery current Ib from a current sensor 32 mounted to a power line
connecting the battery 22 and the DC/DC converter 24, a capacitor
voltage Vc from a voltage sensor 34 mounted to the capacitor 26,
and a command value concerning driving of the load 28. Meanwhile,
the electronic control unit 40 outputs, via an output port, a
switching control signal to the transistors T1, T2 of the DC/DC
converter 24 and a driving control signal to the load 28.
[0029] Operation of the thus structured driving system 20 of the
embodiment, in particular, driving control of the DC/DC converter
24, will be described.
[0030] FIG. 3 is a flowchart of an example of a DC/DC converter
driving control routine to be executed by the electronic control
unit 40 of the driving system 20 in the embodiment. This routine is
repetitively performed at predetermined intervals of time (for
example, 0.2 msec).
[0031] Specifically, upon start of the DC/DC converter driving
control routine, the CPU 42 of the electronic control unit 40 reads
information concerning condition of the battery 22, including a
capacitor target voltage Vc*, a battery voltage Vb from the voltage
sensor 30, a battery current Ib from the current sensor 32, and a
battery electromotive voltage Vbo (S100). Here, a capacitor target
voltage Vc* is determined based on a required output P which serves
as a command value concerning driving of the load 28, in other
words, determined as a voltage of the capacitor 26 necessary in
driving the load 28 using an amount of output equal to a required
output P. A battery electromotive voltage Vbo exhibits a
substantially constant voltage value even though the temperature or
current of the battery 22 should change and is preset as a constant
in the embodiment. It should be noted that, as a battery
electromotive voltage Vbo, a battery voltage Vb with the battery
current Ib being 0 may be measured using a voltage sensor and
stored in the RAM 46 or the like.
[0032] After the reading of the information concerning condition of
the battery 22, a ratio between a period with the upper transistor
T1 remaining in an ON state (T1on) and that with the lower
transistor T2 remaining in an ON state (T2on), or a duty ratio D,
is calculated as "T1on/(T1on+T2on)" based on the read capacitor
target voltage Vc* and battery voltage Vb and using the expression
(1) be low wherein .alpha. corresponds to correction of the duty
ratio D. D=Vb/Vc*+.alpha. (1)
[0033] Subsequently, internal resistance Rb of the battery is
calculated based on the read battery voltage Vb, battery
electromotive voltage Vbo, and battery current Ib (step S104).
Rb=(Vbo-Vb)/Ib (2)
[0034] Although the inner resistance Rb of the battery 22 is
obtained using the above expression (2) in this embodiment, the
inner resistance may be obtained based on the temperature of the
battery 22. For example, correlation between the inner resistance
Rb and temperature of the battery 22 may be obtained in advance in
an experiment and stored in the form of a map in the ROM 44, so
that, given the temperature T of the battery 22, the inner
resistance Rb corresponding to the given temperature T can be
introduced from the map. An example of a map showing correlation
between the inner resistance Rb and temperature of the battery 22
is shown in FIG. 4.
[0035] With the inner resistance Rb obtained, the optimum current
range IR is determined based on the inner resistance Rb and the
battery electromotive voltage Vbo read at step S100 (step S106).
Here, the optimum current range IR is a range of battery current Ib
corresponding to outputs which can be extracted from the battery 22
by driving the DC/DC converter 24. Specifically, the optimum
current range IR is a range the upper limit of which is defined by
a current corresponding to the maximum output BPmax which can be
extracted from the battery 22. The optimum current range IR will be
described below.
[0036] An output BP which can be extracted from the battery 22 is
expressed as the expression (3) using a battery voltage Vb and a
battery current Ib. BP=Vb.times.Ib (3)
[0037] The battery voltage Vb is expressed as the expression (4)
using the inner resistance Rb and electromotive voltage Vbo of the
battery 22. Vb=Vbo-Ib.times.Rb (4) Substitution of the expression
(4) into the expression (3) results in the expression (5).
BP=(Vbo-Ib.times.Rb).times.Ib=-Rb(Ib-Vbo/2Rb).sup.2+Vbo.sup.2/4Rb
(5)
[0038] The expression (5) exhibits output characteristics of the
battery 22, as shown in FIG. 5, concerning correlation between a
battery output BP and a battery current Ib. As shown in FIG. 5, in
order to extract the maximum output Vbo.sup.2/4Rb from the battery
22, the DC/DC converter 24 may be given driving control such that
the battery current Ib becomes equal to a value Vb/2Rb. As such,
should driving control of the DC/DC converter 24 be conducted such
that the battery current Ib exceeds a value Vb/2Rb, power
consumption by the inner resistance Rb of the battery 22 will
increase, resulting in drop of output BP extracted from the battery
22.
[0039] FIG. 6 shows output characteristics of the battery 22 with
its inner resistance Rb equal to a value R0 and those with its
inner resistance Rb equal to a value R1 (R1>R0). As shown in
FIG. 6, with the inner resistance Rb equal to a value R0, the
amount of output corresponding to a required output P of the load
can be provided using an output BP extracted from the battery 22.
With the inner resistance Rb equal to a value R1, on the other
hand, it cannot be fully provided using an output BP from the
battery 22. When such an amount of power cannot be fully provided
using an output BP from the battery 22, and should the DC/DC
converter 24 then be given driving control so as to increase the
battery current Ib over a value Vb/2Rb (that is, to increase a
boosting rate), only a reduced amount of output BP can be extracted
from the battery 22. With a drop of output BP extracted from the
battery 22, the shortage is compensated for using the power stored
in the capacitor 26 and, therefore, the voltage of the capacitor 26
is remarkably reduced.
[0040] Therefore, in such a case, when driving control of the DC/DC
converter 24 is conducted such that the battery current Ib remains
in a current range having an upper limit of a value Vb/2Rb, the
maximum output BPmax from the battery 22 can be reliably obtained
while a voltage drop with the capacitor 26 can be minimized even
when the amount of power corresponding to the required output P of
the load 28 cannot be fully provided using an output BP of the
battery 22.
[0041] Here, it should be noted that the optimum current range IR
is not necessarily a range having an upper limit defined by a
current value Vb/2Rb corresponding to the maximum output BPmax of
the battery 22. Alternatively, the optimum current range IR may
have an upper limit defined by a value slightly smaller than a
current value Vb/2Rb or even by a value little larger than a value
Vb/2Rb as long as it is within a tolerable range.
[0042] After setting the optimum current range IR as described
above, whether or not the battery current Ib remains in the optimum
current range IR is determined (step S108). When it is determined
that the battery current Ib remains in the optimum current range
IR, it is concluded that the duty ratio D calculated at step S102
requires no limitation. Thus, the DC/DC converter 24 is given
driving control using the duty ratio D (step S110) and a limitation
flag F is turned off (step S112) before the present routine is
completed.
[0043] Meanwhile, when it is determined that the battery current Ib
does not remain in the optimum current range IR, the duty ratio D
calculated at step S102 is limited such that the battery current Ib
remains in the optimum current range IR. Thereafter, the DC/DC
converter 24 is given driving control using the thus limited duty
ratio D (step S114) and the limitation flag F is turned on (step
S116) before the present routine is completed. It should be noted
that the limitation flag F indicates whether or not a current duty
ratio D is limited and is used in driving control of the load 28 to
be described later.
[0044] In the following, driving control of the load 28 will be
described.
[0045] FIG. 7 is a flowchart of an example of a load driving
control routine to be executed by an electronic control unit 40 of
the driving system 20 in this embodiment. This routine is
repetitively performed at predetermined intervals of time (e.g.,
every 0.2 msec).
[0046] Upon start of the load driving control routine, the CPU 42
of the electronic control unit 40 reads a load requiring output P
which is to be used as a command value concerning driving of the
load 28 (step S150). Then, whether or not the limitation flag F,
as, manipulated at steps S112 and S116, remains in an ON state is
determined (step S152). When it is determined that the limitation
flag F remains in an OFF state, in other words, when the duty ratio
D of the DC/DC converter 24 is not limited at the step S110 of the
routine of FIG. 3, the load 28 is given driving control so as to be
driven using an output corresponding to the load requiring output P
(step S154) before the present routine is completed.
[0047] Meanwhile, when it is determined that the limitation flag F
remains in an ON state, in other words, when the duty ratio D of
the DC/DC converter 24 is limited at step S114 of the routine of
FIG. 3, the load 28 is given driving control while limiting the
load requiring output (or using a limited output LP). This
limitation is employed to reduce an output of the load 28 while
considering that an output BP corresponding to a load requiring
output P cannot be fully extracted from the battery 22 when the
duty ratio D of the DC/DC converter 24 is limited. This arrangement
makes it possible to bring the voltage Vc of the capacitor 26 into
a stable condition (condition near a target voltage Vc*) by
bringing the output from the battery 22 and that from the load 28
closer to each other.
[0048] It should be noted that limitation of a load requiring
output P (a limited output LP) can be applied, for example, through
subtraction of a deviation energy from a load requiring output P,
the deviation energy being a deviation between the amount of energy
of the capacitor 26 corresponding to the capacitor voltage Vc which
is determined by the voltage sensor 34 in the current routine and
that in the last routine. That is, the limitation of a load
requiring output P can be achieved using the expression (6), in
which C represents a capacitance of the capacitor 26. LP=P-Cx
(present Vc.sup.2-last Vc.sup.2)/2 (6)
[0049] Alternatively, the limitation of a load requiring output P
can be achieved using, as a load requiring output P, a limited
output LB which is obtained through subtraction beforehand by a
predetermined value, or using, as a limited output LP, a load
requiring output P which is read in the last routine.
[0050] After driving the load 28 at step S156, a capacitor target
voltage Vc* and a capacitor voltage Vc, which is detected using the
voltage sensor 34, are read (step S158), and whether or not a
deviation between the capacitor target voltage Vc* and capacitor
voltage Vc exceeds a threshold .DELTA.Vref is determined (step
S160). When it is determined that the deviation exceeds the
threshold .DELTA.Vref, the driving system 20 is terminated (step
S162) before the present routine is completed.
[0051] Specifically, a deviation in excess of the threshold
.DELTA.vref indicates that the voltage Vc is significantly deviate
from the target voltage Vc* of the capacitor 26 even though an
output of the load 28 is limited, which is considered as an
abnormal operation of the driving system 20 and the operation of
the driving system 20 is thus terminated. The driving system 20 can
be terminated by halting switching operation of the transistors T1,
T2 of the DC/DC converter 24 or driving of the load 28.
[0052] Meanwhile, when it is determined that the deviation between
the capacitor target voltage Vc* and the capacitor voltage Vc is
less than or equal to the threshold value .DELTA.Vref, it is
considered that the driving system 20 is in a normal operation and
the present routine is completed.
[0053] In the driving system 20 according to this embodiment as
described above, a duty ratio D is adjusted such that a battery
current Ib remains in the optimum current range IR having an upper
limit defined by a current value corresponding to the maximum
output BPmax of the battery 22 and driving control of the DC/DC
converter 24 is applied using the thus adjusted duty ratio D. This
arrangement ensures the optimum power PBmax which can be output
from the battery 22, so that a voltage drop of the capacitor 26 can
be suppressed, while driving the load 28 in a stable condition,
even when a power corresponding to an output P required by the load
28 cannot be extracted from the battery 22.
[0054] Moreover, because the output of the load 28 is limited when
the duty ratio D is limited, the voltage Vc of the capacitor 26 can
be maintained at a more stable condition using the target voltage
Vc*. This allows use of any capacitor 26 having a smaller capacity.
Further, as operation of the system is terminated should, despite
limitation imposed on an output of the load 28, the voltage Vc of
the capacitor 26 not be in a stable condition, system safety can be
ensured.
[0055] In the following, a driving system 120 according to a second
embodiment of the present invention will be described.
[0056] FIG. 8 is a schematic diagram showing a structure of a
driving system 120 according to a second embodiment of the present
invention. The hardware structure of the driving system 120
according to the second embodiment is identical to that of the
driving system 20 in the first embodiment, with the notable
exception that the driving system 120 does not have a current
sensor 32, which is included in the driving system 20. Therefore,
structural elements of the driving system 120 in the second
embodiment, identical to those of the driving system 20 in the
first embodiment are identified using similar reference numbers
added by 100, and not explained again.
[0057] FIG. 9 is a flowchart of an example of a DC/DC converter
driving control routine to be executed by the electronic control
unit 140 of the driving system 120 in the second embodiment. That
is, the driving system 120 in the second embodiment performs the
routine of FIG. 9, rather than that of FIG. 3. This routine of FIG.
9 is repetitively performed at predetermined intervals of time (for
example, 0.2 msec).
[0058] Specifically, upon start of the DC/DC converter driving
control routine, the CPU 142 of the electronic control unit 140
reads a capacitor target voltage Vc*, a capacitor voltage Vc, a
battery voltage Vb, and a battery electromotive voltage Vbo (step
S200). Then, the CPU 142 calculates a duty ratio D based on the
read capacitor target votlate Vc* and battery voltage Vb and using
the expression (1) described above (step S202), and then determines
the optimum duty range DR based on the read out capacitor voltage
Vc and battery electromotive voltage Vbo (step S204). Here, the
optimum duty range DR is a range of duty ratios D corresponding to
outputs which can be extracted from the battery 22 by driving the
DC/DC converter. Specifically, the lower limit of the optimum duty
range DR is defined by a duty ratio D corresponding to the maximum
output BPmax which can be extracted from the battery 122.
[0059] In the following, the optimum duty range DR will be
described in detail.
[0060] An output BP when the driving system 120 is viewed from the
load 128 is expressed using the expression (7) below, based on the
duty ratio D, the capacitor voltage Vc, and the battery current ib.
BP=Vc.times.Ib.times.D (7)
[0061] The battery current Ib is expressed using the expression (8)
below. Ib=(Vbo-D.times.Vc)/Rb (8)
[0062] Substitution of the expression (8) into the expression (7)
results in the expression (9).
BP=-Vc.sup.2/Rb(D-Vbo/2Vc).sup.2+Vbo.sup.2/4Rb (9)
[0063] The expression (9) exhibits output characteristics of the
battery 122, as shown in FIG. 10, concerning correlation between an
output BP and a duty ratio D. As shown in FIG. 10, in order to
extract the maximum output Vbo.sup.2/4Rb from the battery 122, the
DC/DC converter 124 is to be given driving control such that the
duty ratio D becomes equal to a value Vbo/2Vc. As such, should
driving control of the DC/DC converter 124 be conducted such that
the duty ratio D becomes smaller than a value Vb/2Vc (that is, to
increase a boosting rate), an output BP extracted from the battery
122 will decrease.
[0064] Therefore, when driving control of the DC/DC converter 124
is conducted such that the duty ratio D remains in a range having a
lower limit of a value Vbo/2Vc, the maximum output Bpmax from the
battery 122 can be ensured while the load 128 can be driven in a
stable condition.
[0065] Here, it should be noted that the optimum duty range DR is
not necessarily the range having a lower limit defined by a current
value Vbo/2Vc corresponding to the maximum output BPmax of the
battery 122. Alternatively, an output values lightly smaller than
the maximum output of the battery 122 may be set as an output upper
limit while a regenerative upper limit is also set, so that a range
defined by the lower duty ratio Dlow corresponding to the output
upper limit and by the upper duty ratio Dhi corresponding to the
regenerative upper limit may be used as the optimum duty range DR.
Still alternatively, a value slightly larger or smaller than a duty
ratio Vbo/2Vc may be used as the upper limit, as long as it is
within a tolerable range.
[0066] After setting the optimum duty range DR as described above,
whether or not the duty ratio D calculated at step S202 remains in
the optimum duty range DR is determined (step S206). When it is
determined that the duty ratio D remains in the optimum duty range
DR, the DC/DC converter 124 is given driving control using the duty
ratio D (step S208) and a limitation flag F is turned off (step
S210) before the present routine is completed.
[0067] Meanwhile, when it is determined that the duty ratio D
calculated at step S202 does not remain in the optimum duty range
DR, the duty ratio D is limited so as to remain within the optimum
duty range DR and the DC/DC converter 124 is given driving control
using the thus limited duty ratio D (step S212). Further, the
limitation flag F is turned on (step S214) before the present
routine is completed.
[0068] As described above, as driving control of the DC/DC
converter 124 is conducted such that the duty ratio D remains in
the optimum duty range DR, the driving system 120 in the second
embodiment can ensure the maximum output BPmax from the battery 122
and thus produce the same advantage as that of the driving system
20 in the first embodiment. In particular, because inner resistance
of the driving system 122, which cannot easily be calculated with
accuracy, is not used as a control parameter for the DC/DC
converter 124, controllability of the DC/DC converter 124 can be
enhanced. However, through the load driving routine of FIG. 7, the
same advantage as that of the driving system 20 in the first
embodiment can be obtained also with respect to driving of the load
128.
[0069] In the following, a driving system according to a third
embodiment of the present invention will be described. The hardware
structure of the driving system according to the third embodiment
is identical to that of the driving system 120 in the second
embodiment. Therefore, structural elements of the modified driving
system identical to those of the driving system 120 in the second
embodiment are not explained again.
[0070] The third driving system performs a DC/DC converter driving
control routine as shown in FIG. 12, rather than that of FIG. 3 or
FIG. 9. Specifically, upon start of the routine, the CPU of the
electronic control unit reads a capacitor target voltage Vc*, a
battery voltage Vb, and a battery electromotive voltage Vbo (step
S300). Then, the CPU calculates a duty ratio D based on the read
capacitor target votlate Vc* and battery voltage Vc and using the
above-described expression (1) (step S302) and determines whether
the battery voltage Vb read at step S300 is greater than or equal
to a value Vbo/2 (step S304). When it is determined that the
battery voltage Vb is greater to or equal to a value Vbo/2, the
DC/DC converter is given driving control using the duty ratio D
calculated at step S302 (step S306) and the limitation flag F is
turned off (step S308) before the present routine is completed.
[0071] Meanwhile, when it is determined that the battery voltage Bv
is smaller than a value Vbo/2, the duty ratio D is limited such
that the battery voltage Vb becomes greater than or equal to a
value Vbo/2 (that is, to increase a boosting rate). Then, the DC/DC
converter 124 is driven using the thus limited duty ratio D (step
S310) and the limitation flag F is turned on (step S314) before the
present routine is completed.
[0072] Here, the significance of the determination made at S304 as
to whether or not the battery voltage Vb is greater than or equal
to a value Vbo/2 will be described.
[0073] A battery voltage Vb can be calculated based on a battery
electromotive voltage Vbo, a battery current Ib, and inner
resistance Rb and using the expression (10) below.
Vb=Vbo-Ib.times.Rb (10)
[0074] Meanwhile, as a battery current Ib when the maximum output
Bpmax is extracted from a battery is equal to a value Vbo/2Rb, as
described above with reference to the driving system 20 in the
first embodiment, a battery voltage Vb at this time can be
expressed using the expression (11) below. Vb=Vbo/2 (11)
[0075] From the fact that driving control of the DC/DC converter 24
is conducted such that a battery current Ib becomes less than or
equal to a value Vbo/2Rb in the driving system 10 of the first
embodiment, it can be understood that driving control of the DC/DC
converter must be conducted such that the battery voltage Vb
becomes equal to Vbo/2 or larger, in other words, a voltage drop
due to the inner resistance of the battery becomes equal to a value
Vbo/2 or smaller in the driving system of the third embodiment.
This is the significance of the determination as to whether or not
the battery voltage Vb is greater than or equal to a value Vbo/2.
Therefore, the driving system in the third embodiment also can
produce the same advantage as that which can be produced by the
driving systems 20, 120 in the first and second embodiments.
Through the load driving routine of FIG. 7, the same advantage as
that which can be obtained by the driving system 20 in the first
embodiment can be obtained also with respect to driving of the load
128.
[0076] It should be noted that, although driving control of the
DC/DC converter is conducted using a limited duty ratio D when the
battery voltage Vb is smaller than a value Vbo/2, a limited duty
ratio D may be used in driving control of the DC/DC converter when
the battery voltage Vb is smaller than a value slightly larger than
a value Vbo/2. Alternatively, a limited duty ratio D may be used in
driving control of the DC/DC converter also when the battery
voltage Vb is smaller than a value slightly smaller than a value
Vbo/2 as long as it is within a tolerable range.
[0077] In the following, a fourth embodiment of the present
invention will be described. The hardware structure of the fourth
embodiment is identical to that of the first embodiment of FIG.
1.
[0078] In the fourth embodiment, a battery voltage Vb, a battery
current Ib, and a battery electromotive voltage Vbo of the battery
22 are determined, similar to the above embodiments, and an inner
resistance Rb of the battery 22 is always detected using the
above-described expression (2). Further, the maximum permissible
current Ibmax is determined based on at least one of the capacity
of a current which can be supplied to the transistors T1, T2, which
serve as switching elements of the DC/DC converter 24, or that
which can be supplied to the battery 22, and stored in the ROM 44
or the like in the electronic control unit 40, for example. That
is, the maximum permissible current Ibmax is determined by
selecting either one, or a larger one, of the capacities of a
current which can be supplied to the transistors T1, T2 or which
can be supplied to the battery 22. It should be noted that any
non-volatile memory may be employed for the ROM 44, with are
writable EEPROM or a flash memory being preferable.
[0079] The upper and lower limits of a duty ratio D in switching of
the transistors T1, T2 are determined based on the maximum
permissible current Ibmax, an inner resistance Rb of the battery
22, an electromotive voltage Vbo of the battery 22, and a voltage
Vdc of the capacitor 26, and the switching in the DC/DC converter
24 is limited such that the duty ratio D remains in that range.
[0080] That is, as indicated by the above expression (8), the
current Ib of the battery 22 is expressed as
Ib=(Vbo-D.times.Vc)/Rb, the duty ratio D is expressed as
D=(Vbo-Rb.times.Ib)/Vc. Then, the duty ratio D is controlled so as
to remain in a range
(Vbo-Rb.times.Ibmax)/Vc.ltoreq.D.ltoreq.(Vbo-Rb.times.(-Ibmax)/Vc,
wherein the positive sign attached to Ibmax corresponds to a
direction of discharging from the battery 22, while the negative
sign corresponds to the direction of charging.
[0081] Operation according the fourth embodiment will be described
referring to FIG. 13.
[0082] Initially, a command concerning a target voltage Vc* of the
capacitor 26 and the maximum permissible current Imax are received
(S400). It should be noted that a battery voltage Vb, a battery
current Ib, a battery electromotive voltage Vbo, and inner
resistance Rb are also received.
[0083] Based on the received target voltage Vc*, a duty ratio
command D is calculated (S402). This calculation is performed as
D=(Vbo-Vb)/Ib, similar to the above.
[0084] Subsequently, the lower limit Dmin=(Vbo-Rb.times.Ibmax)Vc
and Dmax=(Vbo-Rb.times.(-Ibmax))/Vc of the duty ratio D are
calculated (S404).
[0085] Then, whether or not the duty ratio D calculated at S402
remains in a range defined by the lower limit Dmin and the upper
limit Dmax is determined (S406). When it is determined as YES at
S406, the DC/DC converter 24 is driven using the calculated duty
ratio D (S408). Meanwhile, when it is determined as NO at S406, the
DC/DC converter 24 is driven using the duty ratio Dmin in the case
where the duty ratio D is smaller than the value Dmin or the duty
ratio Dmax in the case where the duty ratio D is larger than the
value Dmax, so that the duty ratio D remains in a range
Dmin.ltoreq.D.ltoreq.Dmax (S410).
[0086] As described above, by controlling the duty ratio of the
transistors T1, T2 so as to remain in a predetermined range, it is
possible to limit the current Ib so as not to exceed the maximum
permissible current of the transistors T1, T2, which serve as
switching elements of the DC/DC converter 24, or the maximum
permissible current of the battery 22.
[0087] In the following, a fifth embodiment of the present
invention will be described. Although whether or not the duty ratio
D remains in a predetermined range is determined and the duty ratio
is controlled such that the battery current Ib remains in a
predetermined range in the fourth embodiment, in the fifth
embodiment whether or not the battery current Ib remains in a
predetermined range is determined and, when it does not, the duty
ratio is adjusted such that the battery current Ib remains in the
predetermined range.
[0088] Initially, a command concerning a target voltage Vc* of the
capacitor 26 and the maximum permissible current Imax are received
(S500). In addition, a battery voltage Vb, a battery current Ib, a
battery electromotive voltage Vbo, and inner resistance Rb are also
received. Based on the received target voltage Vc*, a duty ratio
command D is calculated (S502). This calculation is performed as
D=(Vbo-Vb)/Ib, similar as in the above. The processing at S500 and
S502 is identical to that at S400, S402.
[0089] Subsequently, a battery current Ib is received (S504) and
whether or not the received battery current Ib is greater than or
equal to 0 is determined (S506).
[0090] Determination of YES at S506 indicates that the current Ib
is in a discharging direction. Then, whether or not the current Ib
exceeds the maximum permissible current Ibmax is determined (S508).
In such a case, when the determination at S508 is YES, the current
Ib remains out of a predetermined range and variable X=.alpha. is
set (S510). Meanwhile, a determination of NO at S508 indicates that
the current Ib remains in a predetermined range and variable X=0 is
set (S512).
[0091] Determination NO at S506 indicates the current Ib in a
discharging direction and, then, whether or not the current Tb is
smaller than the maximum permissible current -imbax is determined
(S514). Determination YES at S514 indicates that the current Ib
remains out of a predetermined range and a variable X=-.alpha. is
set (S516). Meanwhile, determination NO at S514 indicates that the
current Ib remains in a predetermined range and the variable X=0 is
set (S518).
[0092] Then, the variable X is added to the duty ratio D calculated
at S502 to thereby limit the duty ratio and driving control of the
DC/DC converter 24 is conducted based on the limited duty ratio D
(S520). That is, when the current Ib is in a discharging direction
and in excess of Ibmax, a is added to the calculated duty ratio D
to thereby expand a period with the upper transistor T1 remaining
in an ON state and reduce the current Ib. When the current Ib is in
a charging direction and smaller than Ibmax, on the other hand,
-.alpha. is added to the calculated duty ratio D to thereby expand
a period with the lower transistor T2 remaining in an ON state and
reduce the charge current Ib.
[0093] In the fifth embodiment, by controlling the duty ratio of
the transistors T1, T2, similar to the fourth embodiment, it is
possible to limit the current Ib so as not to exceed the maximum
permissible current of the transistors T1, T2, which serve as
switching elements of the DC/DC converter 24, or the maximum
permissible current of the battery 22.
[0094] It should be noted that the driving systems of the fourth
and fifth embodiments can be used in combination with any
combination of those of the first, second, and third embodiments as
described above.
[0095] It should also be noted that, although the electric control
units 40, 140 conduct driving control of both the DC/DC converters
24, 124 and the loads 28, 128 in the driving systems 20, 120 of the
first through fifth embodiments, driving control of the DC/DC
converters 24, 124 and the loads 28, 128 may be conducted using
separate electronic control units which exchange information
through communication.
[0096] It should also be noted that, although capacitors 26, 126
are provided between the DC/DC converters 24, 124 and the loads 28,
128 in the driving systems 20, 120 in the first through fifth
embodiments, may also be configured such that the capacitors 26,
126 are not be provided.
[0097] According to one aspect, there is preferably provided a
program for having a computer to operate as a control system for
applying driving control to a DC/DC converter and/or a load.
According to another aspect, there is preferably provided a
computer readable recording medium which stores the program. This
medium may include any of a variety of recording media, such as a
CD-ROM, DVD-ROM, a flexible disk, or the like. By installing such a
program into a computer and executing the computer, an advantage of
the present invention can be similarly produced.
[0098] In the above, embodiments of the present invention are
described while referring to examples. However, the present
invention is not limited to these examples and can be implemented
in a variety of manners without departing from the scope of the
present invention.
* * * * *