Title: Connection-switched capacitor storage system
Abstract: A connection-switched capacitor storage system comprises plural capacitors, parallel monitors connected with the capacitors, respectively, switches for switching the connections of the capacitors from a series combination to a parallel combination or vice versa, and a control portion. The parallel monitors bypass the charging current for the capacitors when the terminal voltages of the capacitors exceed a given voltage, thus limiting increases of the terminal voltages of initializing the terminal voltages of the capacitors to their original level. The control portion controls initialization and switching of the connections of the capacitors. The control portion causes the parallel monitors to initialize the capacitors near the voltage at which the connections of the capacitors are switched by the switches.
Patent Number: 6,885,170 Issued on 04/26/2005 to Okamura, et al.
| Inventors:
|
Okamura; Michio (Kanagawa, JP);
Yamagishi; Masaaki (Kanagawa, JP)
|
| Assignee:
|
Advanced Capacitor Technologies, Inc. (Tokyo, JP);
Okamura Laboratory, Inc. (Kanagawa, JP);
Kabushiki Kaisha Powersystems (Kanagawa, JP)
|
| Appl. No.:
|
263474 |
| Filed:
|
October 2, 2002 |
Foreign Application Priority Data
| Oct 02, 2001[JP] | 2001-305944 |
| Current U.S. Class: |
320/166; 320/117 |
| Intern'l Class: |
H02J 007//00 |
| Field of Search: |
320/166,117,116,118,120,121,126,167,122
307/110
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Sherry; Michael
Assistant Examiner: Luk; Lawrence
Attorney, Agent or Firm: Webb Ziesenheim Logsdon Orkin & Hanson, P.C.
Claims
1. A connection-switched capacitor storage system comprising:
a plurality of capacitors;
parallel monitors connected in parallel with said capacitors, respectively, each
of said parallel monitors acting to limit increases of a terminal voltage of a
respective one of the capacitors by bypassing a charging current for the capacitor
when the terminal voltage exceeds a given set voltage, the parallel monitors having
a function of initializing terminal voltages of the capacitors to their initial
state;
switching means for switching connections of said capacitors from a series combination
to a parallel combination or vice versa; and
control means for controlling the initializing operation of each parallel monitor
to initialize the terminal voltage of a respective one of the capacitors to its
initial level based on an overall voltage of the capacitors or on the terminal
voltage of a certain capacitor typical of said plurality of capacitors, said control
means also acting to control operation of said switching means to switch the connections
of the capacitors,
wherein said voltage at which the connections of the capacitors are switched
by said switching means is within a ±10% range about the voltage at which
the connections of the capacitors are switched, and
wherein said control means causes said parallel monitor to initialize the capacitor
voltages to their initial level near a voltage at which the connections of the
capacitors are switched by said switching means.
2. A connection-switched capacitor storage system comprising:
a plurality of capacitors;
parallel monitors connected in parallel with said capacitors, respectively, each
of said parallel monitors acting to limit increases of a terminal voltage of a
respective one of the capacitors by bypassing a charging current for the capacitor
when the terminal voltage exceeds a given set voltage, the parallel monitors having
a function of initializing terminal voltages of the capacitors to their initial
state;
switching means for switching connections of said capacitors from a series combination
to a parallel combination or vice versa; and
control means for controlling the initializing operation of each parallel monitor
to initialize the terminal voltage of a respective one of the capacitors to its
initial level based on an overall voltage of the capacitors or on the terminal
voltage of a certain capacitor typical of said plurality of capacitors, said control
means also acting to control operation of said switching means to switch the connections
of the capacitors,
wherein said voltage assumed immediately before the connections of the capacitors
are switched by said switching means is within a minus 10% range from the voltage
at which the connections are switched, and
wherein said control means causes said parallel monitors to initialize the capacitor
voltages to their initial level near a voltage at which the connections of the
capacitors are switched by said switching means.
3. A connection-switched capacitor storage system comprising:
a plurality of capacitors;
parallel monitors connected in parallel with said capacitors, respectively, each
of said parallel monitors acting to limit increases of a terminal voltage of a
respective one of the capacitors by bypassing a charging current for the capacitor
when the terminal voltage exceeds a given set voltage, the parallel monitors having
a function of initializing terminal voltages of the capacitors to their initial
state;
switching means for switching connections of said capacitors from a series combination
to a parallel combination or vice versa; end
control means for controlling the initializing operation of each parallel monitor
to initialize the terminal voltage of s respective one of the capacitors to its
initial level based on an overall voltage of the capacitors or on the terminal
voltage of a certain capacitor typical of said plurality of capacitors, and control
means also acting to control operation of said switching means to switch the connections
of the capacitors,
wherein said voltage assumed immediately after the connections of the capacitors
are switched by said switching means is within a plus 10% range from the voltage
at which the connections of the capacitors are switched, and
wherein said control means causes said parallel monitors to initialize the capacitor
voltages to their initial level near a voltage at which the connections of the
capacitors are switched by said switching means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a connection-switched capacitor storage system
comprising a plurality of capacitors, monitors connected in parallel with the capacitors,
respectively, switches for switching the connections of the capacitors from a series
combination to a parallel combination or vice versa, and control means. Each parallel
monitor acts to bypass the charging current when the terminal voltage of the corresponding
capacitor exceeds a given voltage value. Thus, the parallel monitors limit the
terminal voltages of the capacitors to a voltage set for initializing. That is,
the parallel monitors have a function of initializing the capacitors to their original
state (hereinafter often referred to simply as initialization or initializing state).
The control device controls the initializing operation of the parallel monitors
according to the terminal voltages of the capacitors. The control device also controls
the switching operation of the switches for switching the connections of the capacitors.
2. Description of Related Art
A capacitor storage system consisting of a combination of capacitors and an electronic
circuit is known as an ECS (energy capacitor system). Those energy capacitor systems
which are equipped with parallel monitors having a function of initializing capacitor
voltages to their initial level and which have a function of switching the connections
of the capacitors have been studied and verified in terms of their performance
in a Japanese national project NEDO (New Energy and Industrial Technology Development
Organization): Final Report of on-the-spot Research on new Procedure for Load Leveling,
March 2000. Its performance has been valued highly and put into practical use.
Electric storage systems equipped with parallel monitors having a function
of initializing capacitor voltages to their initial level have been proposed by
the present Applicants and others, for example, in Japanese Patents Laid-Open Nos.
2000-152508, 2000-217250, and 2001-186681 (U.S. Pat. No. 6,404,170).
Electric storage systems having a function of switching the connections
of capacitors have been also proposed by the present Applicants and others, for
example, in Japanese Patents Laid-Open Nos. 2000-152495 (U.S. Pat. No. 6,133,710),
2000-209775, and 2000-253572 (U.S. Pat. No. 6,317,343).
An example of the structure of an electric storage system fitted with parallel
monitors having a function of initializing capacitor voltages to their initial
level is now given. FIG. 5 shows one example of the configuration of a capacitor
storage portion having comparators acting as parallel monitors which are used,
respectively, for initializing and for detection of a full charge condition. Shown
in this figure are a charger
11, comparators
12,
13, OR-gates
14,
15, capacitors C, diodes D, resistors Rs, transistors Tr, and
initializing switches S
1. Vful and Vini indicate set voltages, respectively.
In FIG. 5, each capacitor C is an electric double-layer capacitor, for example,
for storing electrical energy. The comparator
12 for initializing to initial
state is used as a means for operating the transistor Tr connected in parallel
with the capacitor C in such a way that the charging current is bypassed at the
first set voltage Vini. The comparator
13 for detection of a full charge
is used as a means for detecting the second set voltage Vful to judge that a full
charge voltage higher than the first set voltage has been reached. When the capacitor
C is initialized to its original state, if the terminal voltage of the capacitor
C is about to exceed the set voltage Vini, the transistor Tr and resistor Rs together
form a bypass circuit for the charging current, thus limiting the charging current.
That is, a part of the charging current is bypassed. The current is set by the
resistor Rs. The initializing switch S
1 activates or deactivates the operation
for initializing the capacitor C. When the initializing mode is selected, an initialization
execution signal S issued by the charger
11 activates the operation.
The charger
11 charges plural capacitors C connected in series. The charger
11 stops the charging operation if a full charge voltage is detected from
any capacitor C. For example, the outputs F from the comparators
13 for
detection of a fully charged state are logically ORed. Thus, the charger judges
which of the plural capacitors has reached full charge. Then, the charging is ended.
Furthermore, when charging for initialization is started, the charger
11
turns on (closes) the initializing switch S
1 by the initialization execution
signal S, thus starting charging. The outputs I from the comparators
12
for initializing the capacitors are logically ORed. Thus, the charger judges which
of the capacitors has started to undergo an operation for bypassing the charging
current. The bypass operation signals I from the comparators
12 are ORed
by each OR gate
14. Output signals F from the comparators
13 indicating
a full charge are ORed by each OR gate
15, and a signal for stopping constant-current
charging is supplied to the charger
11.
Accordingly, the set voltage Vful is set to the full charge voltage
of each capacitor. The set voltage Vini is set to an initializing voltage lower
than the set voltage Vful. When the initializing switch S
1 is closed (turned
ON) and charging is done, the capacitor charged to the set voltage Vini first is
first started to be charged at a decreased charging rate by the bypass circuit
consisting of the transistor Tr and resistor Rs by bypassing a part of the charging
current. In this way, the capacitors are successively charged at a decreased charging
rate. When any capacitor reaches full charge, the charger
11 stops the constant-current
charging. If necessary, trickle charging is done.
An example of the configuration of an electric storage system having a function
of switching the connections of capacitors is next described. FIGS. 6
a to
6c show one example of the configuration of a capacitor storage system
in which the connections of capacitors are switched. Shown in these figures are
capacitors CA
1-CA
3, CB
1-CB
3 and switches SS, SA
1-SA
3, SB
1-SB
3.
Referring to FIGS. 6
a to
6c, the capacitors CA
1-CA
3
and CB
1-CB
3 form two sets of capacitors A and B. Each set of capacitors
is made up of the same number of capacitors connected in series. Each of the capacitors
CA
1-CA
3 and CB
1-CB
3 may be a capacitor bank consisting
of plural capacitors connected in series or parallel-series. If necessary, a parallel
monitor is appropriately connected with each capacitor. The switch SS is a series-connection
switch for connecting the two sets of capacitors A and B in series. One set of
capacitors A and the switch SS are connected at a series connection point. The
switches SA
1-SA
3 are one set of switching means for connecting this
series connection point with one series connection point of the other set of capacitors
B and with the series connection points between the capacitors CB
1-CB
3.
The switches SB
1-SB
3 are the other set of switching means for connecting
the series connection point between the set of capacitors B and the switch SS with
the other series connection end of the set of capacitors A and with the series
connection points between the capacitors A.
Then, the capacitors CA
1-CA
3 and CB
1-CB
3 are connected
in series as shown in FIG. 6
d by closing only the switch SS as shown in
FIG. 6
a. The center capacitor CA
3 of one set of capacitors A and
the center capacitor CB
3 of the other set of capacitors B are connected
in parallel as shown in FIG. 6
e by opening the switch SS and closing the
switch SA
3 of one set of switching means and the corresponding switch SB
3
of the other set of switching means as shown in FIG. 6
b.
Similarly, the series combination of the center capacitors CA
3
and CA
2 of one set of capacitors A and the series combination of the center
capacitors CB
3 and CB
2 of the other set of capacitors B are connected
in parallel as shown in FIG. 6
f by closing the switch SA
2 of one
set of switching means and the corresponding switch SB
2 of the other set
of switching means and opening all the other switches as shown in FIG. 6
c.
Then, the series combination of the capacitors CA
1-CA
3 of one
set of capacitors A and the series combination of the capacitors CB
1-CB
3
of the other set of capacitors B are connected in parallel as shown in FIG. 6
g
by closing the switch SA
1 of one set of switching means and the corresponding
switch SB
1 of the other set of switching means and opening all the other switches.
As described above, the connections of the plural capacitors CA
1-CA
3
and CB
1-CB
3 are switched and controlled as shown in FIGS. 6
d to
6g, by selectively connecting one of the switches SA
1-SA
3
of one set of switching means and one of the switches SB
1-SB
3 of
the other set of switches or the switch SS. In this way, the voltages are adjusted.
Variations in the voltages accompanying charging and discharging can be suppressed.
For example, the capacitors CA
1-CA
3 and CB
1-CB
3 are
all connected in series and charging is started as shown in FIG. 6
d. When
the terminal voltage on the charging side rises to a given value, the voltage is
lowered by an amount corresponding to the capacitors CA
3 and CB
3
by switching the combination to the combination shown in FIG. 6
e. Furthermore,
if the terminal voltage on the charging side again increases to the given value
due to charging, the terminal voltage on the charging side can be prevented from
exceeding the given value by switching the combination successively to the combinations
respectively shown in FIGS. 6
f and
6g.
Where discharging is started in the connection combination shown in FIG. 6
g
and the load is fed, if the output voltage drops to the given value, the decrease
in the output voltage is compensated by switching the connection combination to
the combination shown in FIG. 6
f. If the output voltage further drops to
a certain value, the connection combination is successively switched to the connection
combinations respectively shown in FIGS. 6
e and
6d. Consequently,
the output voltage can be prevented from decreasing below the certain value. Furthermore,
the overall current flowing during charging and discharging is allocated to only
the switch SS that connects all the capacitors CA
1-CA
3, CB
1-CB
3
in series. The other switches SA
1-SA
3 and SB
1-SB
3 only
need to have a current capacity that is half of the overall current. In addition,
only one switch is connected in series with each capacitor at any stage. Therefore,
loss caused by turn-on voltage of switches, which would present a problem where
the switches were made of semiconductors, can be reduced to a minimum.
In the system used thus far, however, parallel monitors having a function of
initializing
capacitors to their initial state and a function of switching the connections of
the capacitors between series and parallel combinations are combined in a simple
manner as mentioned previously. Therefore, there arises the case where both functions
perform conflicting operations. It has been confirmed that the energy efficiency
of the capacitor storage system can drop.
The observed decreases of the efficiency are only 1% to 2%. However, the actual
value of the overall charge/discharge efficiency of the whole capacitor storage
system using switching of the connections of capacitors is as high as 94%. Therefore,
where the decreases of the efficiency are only 1% to 2% as mentioned previously,
increasing the efficiency further will greatly contribute to expansion of the application
of the capacitor storage system.
SUMMARY OF THE INVENTION
The present invention is intended to solve the foregoing problem. It is an object
of the present invention to provide a capacitor storage system which has a function
of switching the connections of capacitors and provides improved energy efficiency
by reducing power loss caused when the capacitors having parallel monitors are
initialized to their initial state.
This object is achieved by a connection-switched capacitor storage system comprising:
a plurality of capacitors; parallel monitors connected in parallel with the capacitors,
respectively, each of the parallel monitors acting to limit increases of the terminal
voltage of a respective one of the capacitors by bypassing a charging current for
the capacitor when the terminal voltage exceeds a given set voltage, the parallel
monitors having a function of initializing their respective capacitors to their
initial state; switching means for switching the connections of the capacitors
from a series combination to a parallel combination or vice versa; and control
means for controlling initializing operation of each parallel monitor to initialize
the terminal voltage of a respective one of the capacitors to its initial level
based on the overall voltage of the capacitors or on the terminal voltage of a
given capacitor typical of the plurality of capacitors, the control means also
acting to control operation of the switching means to switch the connections of
the capacitors. The control means causes the parallel monitors to initialize the
terminal voltages of the capacitors near a voltage at which the connections of
the capacitors are switched by the switching means.
The control means is characterized in that it causes the parallel monitors to
perform an initializing operation to initial state at a voltage immediately preceding
the voltage at which the connections of the capacitors are switched by the switching
means. The control means causes only those of the parallel monitors whose connections
should be switched by the switching means to perform the initializing operation.
Alternatively, when all of the capacitors are connected in series, the control
means causes the parallel monitors to perform the initializing operation. The control
means causes the parallel monitors to perform the initializing operation at a voltage
assumed immediately after the connections of the capacitors are switched by the
switching means.
Other objects and features of the invention will appear in the course of the
description thereof, which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a connection-switched capacitor storage system
according to the present invention;
FIG. 2 is a flowchart schematically illustrating processing performed by the
capacitor storage system shown in FIG. 1 in charging mode, the processing including
execution of an initializing operation;
FIGS. 3
a-3
d are diagrams showing a method of switching
the connections of shift-type, two stages of capacitors;
FIG. 4 is a diagram illustrating the variations in the overall current flowing
through an electrical storage portion 1 of a capacitor storage system according
to the present invention when the connections of the capacitors are switched, variations
in the terminal voltages of the capacitors, and an example of a method of setting
a voltage Vini used for initializing to initial state;
FIG. 5 is a diagram showing one example of a capacitor storage portion having
parallel monitors acting as comparators which are used respectively for initializing
to initial state and for detection of a full charge; and
FIGS. 6
a-6
g are diagrams showing one example of the configuration
of a connection-switched capacitor storage system according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention are hereinafter described with reference
to the accompanying drawings. Referring to FIG. 1, there is shown a connection-switched
capacitor storage system according to the present invention, the capacitor storage
system being fitted with parallel monitors. This system has an electrical storage
portion
1, a charging circuit
2, and a charge/discharge control portion
3. The electrical storage portion
1 includes capacitors C. A set
voltage used for initializing to initial state is indicated by
4. Another
set voltage used for switching or full charge is indicated by
5.
In FIG. 1, the electrical storage portion
1 includes the capacitors C
having
parallel monitors as shown in FIG.
5 and FIGS. 6
a to
6g
as well as switches for switching the connections of the capacitors from a
series combination to a parallel combination or vice versa as shown in FIGS. 6
a
to
6g. The electrical storage portion has a function of switching
the connections of the parallel monitors and the capacitors C. The parallel monitors
have a function of initializing the capacitors to their initial state. The charging
circuit
2 controls the charging current and charges the capacitors C of
the electrical storage portion
1 in plural charging modes including constant-current
charging mode and trickle charging mode. The charge/discharge control portion
3
monitors voltages in the electrical storage portion
1, controls initializing
to initial state, and switches the connections of the capacitors, thus controlling
the charging circuit
2.
When the charge/discharge control portion
3 is monitoring the voltages
in the electrical storage portion
1, the control portion detects the terminal
voltage of each capacitor C or the terminal voltage of a typical one of the capacitors
C, thus monitoring the charge state. For example, in the circuit shown in FIG.
5, the control portion
3 monitors a bypass operation signal I for initializing
to initial state and a bypass operation signal F on full charge. When an initializing
operation to initial state is performed and the charge/discharge control portion
3 controls the initializing operation of the electrical storage portion
1, the initializing circuit is activated. In the circuit of FIG. 5, for
example, switches S
1 are closed by an initialization execution signal S.
When the charge/discharge control portion
3 switches the connections of
the capacitors in the electrical storage portion
1, the control portion
monitors the voltages in the electrical storage portion
1, judges a switching
voltage, and controls the switches, thus switching the connections of the capacitors.
For instance, in the circuit shown in FIG. 6
a, the control portion controls
the states of switches SS, SA
1-SA
3, and SB
1-SB
3, i.e.,
selectively opens and closes them. When the charge/discharge control portion
3
controls the charging circuit
2, the control portion monitors the charge
state of the electrical storage portion
1 to thereby judge whether a full
charge has been reached. Then, the charging is stopped or the charging mode is
switched to trickle charging mode. For example, in the circuit shown in FIG. 5,
the bypass operation signal F on full charge is detected, and the full charge state
is determined.
The set voltage
4 for initializing to initial state is stored, for example,
in a memory that holds the set voltage Vini for setting each capacitor of the electrical
storage portion
1 to its initial state. Where all the capacitors are connected
in series and initialized to their initial state, for example, according to an
initialization execution mode (described later), the voltage Vini is set for each
individual capacitor, if the connections of some capacitors have been switched
to parallel combinations and initialization should be done. The set voltage
5
for switching or full charge is stored, for example, in a memory that holds the
full charge voltage Vful at which the connections of the capacitors of the electrical
storage portion
1 are switched, charging is stopped, or charging mode is
switched to trickle charging. The voltage at which the connections of the capacitors
are switched may be the overall voltage of the electrical storage portion
1
or the terminal voltage of a capacitor that forms a reference. For example, in
the circuit shown in FIGS. 6
a to
6g, whenever the overall
voltage of the electrical storage portion
1 reaches a given voltage, the
connections are switched from combination D to combination E, from combination
E to combination F, and from combination F to combination G. The charging is stopped
when a full charge condition is reached. At this time, the determination may be
made based on the terminal voltage of the capacitor CA
1 while regarding
it as a typical capacitor.
FIG. 2 is a flowchart schematically illustrating processing performed in charging
mode, the processing including execution of initializing to initial state. FIG.
3 is a diagram showing a method of switching the connections of shift-type, two
stages of capacitors. FIG. 4 shows variations of the overall voltage of the electrical
storage portion
1 when the connections of the two stages of capacitors of
shift type are switched, variations in the terminal voltages of the capacitors,
and an example of a method of setting a voltage Vini used for initializing to initial state.
Referring to the flowchart of FIG. 2, the processing in the charging mode
including execution of initialization begins with making a decision as to whether
the voltage has reached a voltage range in which initializing to initial state
can be executed (step S
11). When the voltage has reached the range, the
initialization execution signal S for the capacitors to be initialized is kept
ON for a given time (step S
12). A decision is made as to whether the voltage
has reached a voltage at which the connections should be switched (step S
13).
If the voltage has reached the latter voltage, only those switches which correspond
to the capacitors whose connections should be switched are switched (step S
14).
After that, if a full charge voltage is detected (step S
15), trickle charging
is done, or charger stops (step S
16).
Some methods are available to switch the connections of the capacitor depending
on the type of arrangement of the capacitors and on the number of stages of the
capacitors. A shift-type, two-stage-switched capacitor arrangement consisting of
four capacitors is shown in FIGS. 3
a to
3d. Variations of
the overall voltage of the electrical storage portion
1 when the connections
of the capacitors are switched are shown in FIG.
4. Variations of the voltages
of the capacitors are also shown in FIG.
4. An example of a method of setting
the voltage Vini used for initializing to initial state is also shown in FIG.
4.
The connections of the capacitors are switched from a combination shown in FIG.
3
d to a combination shown in FIG. 3
c at point A of FIG.
4.
The connections of the capacitors are switched from the combination shown in FIG.
3
c to a combination shown in FIG. 3
b at point B of FIG.
4.
At point A of FIG. 4, capacitors C
2 and C
3 are switched from a series
combination to a parallel combination. Therefore, if there is a difference between
the charging voltage of the capacitor C
2 and the charging voltage of the
capacitor C
3 at this point, the higher one is discharged, while the lower
one is charged. A relatively large current is supplied. The two capacitors are
forced to have the same voltage in a short time.
If the capacitor bank is made up of a single capacitor, essentially the same
operation
is performed, though the method is different from the initializing of parallel
monitors. In this circuit, if the set voltage Vini set for initializing the parallel
monitors to their initial state is selected to lie at point C of FIG. 4 that is
close to the full charge set voltage Vful where the capacitor bank is not affected
by switching of the connections of the capacitors, each capacitor will experience
two operations in one charging cycle, i.e., initializing operation and equalizing
operation under different conditions. In actual operation, the initializing operation
is performed relatively slowly. The connections of the capacitors are switched
almost instantly. Therefore, priority is given to the latter voltage allotment.
If the initializing operation using the parallel monitor is performed more completely,
then more electric power will be consumed. The result is that the charge/discharge
efficiency of the electrical storage system drops.
The present invention is characterized in that the voltage Vini for the parallel
monitors is essentially set in such a way that the initializing operation using
the parallel monitors is completed before an operation for switching the connections
of the capacitors is started. In this case, all the capacitors C
1-C
4
may be initialized to their original state immediately before the connections of
the capacitors are switched from the combination of FIG. 3
d to the combination
of FIG. 3
c. Alternatively, only the capacitors C
2 and C
3 whose
connections should be switched may be initialized (point A of FIG.
4), and
only capacitors C
1 and C
4 whose connections should be switched may
be initialized (point B of FIG. 4) immediately before the connections of the capacitors
are switched from the combination of FIG. 3
c to the combination of FIG.
3
b.
It is to be understood that the present invention is not limited to the embodiment
above but various changes and modifications are possible. For example, in the embodiment
above, initialization is done immediately before the connections of some capacitors
are switched. The initialization may also be done immediately after the connections
of such capacitors are switched. Energy loss due to two operations, i.e., initializing
and equalization, increases in going away from the points A and B at which the
connections of the capacitors are switched, such as the point C of FIG.
4.
Therefore, the loss can be reduced greatly simply by bringing the initializing
point close to the points A and B where the connections of the capacitors are switched
instead of close to the point C of FIG. 4 (e.g., a voltage point lying in an approximately
±10% range about the voltage point at which the connections of the capacitors
are switched). This corresponds to voltages within a minus 10% range from the voltage
at which the connections are switched where initialization is done immediately
before the connections are switched. It corresponds to voltages within a plus 10%
range from the voltage at which the connections are switched where initialization
is done immediately after the connections are switched. Furthermore, the voltage
Vini set for initialization and the full charge set voltage Vful may be held by
the voltage-setting memory
4 and the switching-and-full charge-setting memory
5, respectively. The parallel monitors for the capacitors of the electrical
storage portion
1 may be set by the charge/discharge control portion
3.
In addition, parallel monitors having fixed settings may also be used.
As can be understood from the description made thus far, the present invention
provides a connection-switched capacitor storage system comprising: a plurality
of capacitors; parallel monitors connected in parallel with the capacitors, respectively,
each of the parallel monitors acting to limit increases of the terminal voltage
of a respective one of the capacitors by bypassing a charging current for the capacitor
when the terminal voltage exceeds a given set voltage, the parallel monitors having
a function of initializing their respective capacitors to their initial state;
switching means for switching the connections of the capacitors from a series combination
to a parallel combination or vice versa; and control means for controlling initializing
operation of each parallel monitor to initialize the terminal voltage of a respective
one of the capacitors to its initial level based on the overall voltage of the
capacitors or on the terminal voltage of a given capacitor typical of the plurality
of capacitors. The control means also acts to control the operation of the switching
means to switch the connections of the capacitors. The control means causes the
parallel monitors to initialize the terminal voltages of the capacitors near a
voltage at which the connections of the capacitors are switched by the switching
means. Therefore, the initialization is done at a low voltage. This reduces power
loss. Decrease of the efficiency due to switching of the connections of the capacitors
can be alleviated.
Initialization using the parallel monitors is done by the control
means at a voltage assumed immediately before the connections of the capacitors
are switched by the switching means. The control means causes the parallel monitors
to initialize only capacitors whose connections should be switched by the switching
means. Alternatively, when all the capacitors are connected in series, initialization
using the parallel monitors is done. In addition, the control means causes the
parallel monitors to initialize their respective capacitors at a voltage assumed
immediately after the connections of the capacitors are switched by the switching
means. Only capacitors whose connections have not been switched by the switching
means are initialized by the parallel monitors. Therefore, power loss due to initialization
is reduced to a minimum. The power loss of the capacitors having the parallel monitors
due to initialization is decreased. The energy efficiency of the electrical storage
system having a function of switching the connections of the capacitors can be improved.
Having thus described our invention with the detail and particularity required
by the Patent Laws, what is desired protected by Letters Patent is set forth in
the following claims.
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