Field of the Invention.
The present invention relates to a power supply system
provided with an electric cell.
Background of the Invention
As disclosed in, e.g., Patent document 1, there is
conventionally known a power supply system provided with a
rechargeable battery. The power supply system is designed
to supply an electric power discharged from the battery to
various kinds of devices serving as loads in the event that
an electric outage occurs in an electrical grid which
supplies an electric power from a commercial power source.
Patent document 1: Japanese Patent Application
Publication No. 2009-159730
Tn a power supply system provided in each home, the
upper limit of an electric current supplied from a
commercial power source is usually decided by a contract
with a power company. If an electric current equal to or
larger than a contracted current (i.e., a cutoff threshold)
is used by the loads of the power supply system provided in
the home, a limiter cuts off a power distribution path to
thereby stop the supply of the electric power to devices
through the electrical grid.

In the event that the power distribution path is cut
off by the limiter, the number of the devices of the power
supply system needs to be reduced so that the electric
current used by the devices serving as loads can be smaller
than a contracted electric current. In this state, the
limiter is powered and operated to resume the supply of
electric power from the commercial power source.
Summary of the Invention
In view of the above, the present invention provides a
power supply system capable of enabling a load to use an
electric current larger than a cutoff threshold triggering
the cutoff of a power distribution path, without having to
cut off the power distribution path through which an
electric power is supplied from a commercial power source to
the load.
In accordance with an embodiment of the present
invention, there is provided a power supply system
including: a current detection unit for detecting a current
used by a load; an electric cell; and a control unit for
controlling the electric power stored in the electric cell
to be supplied to the load if it is determined that the
current detected by the current detection unit exceeds a
cutoff threshold.
The power supply system may further include a breaker

provided in a power distribution path through which an
electric power is supplied from a commercial power source to
the load, the breaker being configured to cut off the power
distribution path if the electric current flowing through
the power distribution to the load larger than the cutoff
threshold and a discharging unit for distributing the
electric power stored in the electric cell to the load, the
electric cell being provided closer to the load than the
breaker. The control unit may be configured to drive the
discharging unit if it is determined that the current
detected by the current detection unit exceeds the cutoff
threshold.
With such configuration, the control unit drives the
discharging unit if it is determined that the current
detected by the current detection unit exceeds the cutoff
threshold. In response, the electric power stored in the
electric cell is distributed to the load. Accordingly, the
electric current supplied from the commercial power source
is reduced by the amount of the electric power supplied from
the electric cell. Since the electric cell is connected
closer to the load than the breaker, the electric power
discharged from the electric cell is distributed to the load
without passing through the breaker. Therefore, the power
distribution path through which the electric power is
supplied from the commercial AC power source to the DC
appliances 5 and the AC appliance 6 is not cut off, and it

becomes possible to enable the load to use an electric
current larger than the cutoff threshold triggering the
cutoff of the power distribution path.
The power supply system may further include a DC/AC
converter for converting inputted DC power to AC power. The
power supply system may be configured to distribute an
electric power through the DC/AC converter if the electric
power is supplied from the electric cell to an AC load
connected to the power distribution path at a secondary side
of the breaker.
With such configuration, the electric power can be
supplied to the AC load by converting the DC power
discharged from the electric cell to AC power through the
use of the DC/AC converter. Therefore, even if the electric
current used in the AC load exceeds the cutoff threshold, it
is possible to restrain the power distribution path from
being cut off.
Further, the electric cell may be a rechargeable
battery.
With such configuration, the time and effort required
in replacing the electric cell can be reduced by using the
rechargeable battery the electric cell.
The power supply system may further include a charging
unit for charging the electric cell. The control unit may
be configured to drive the charging unit if the breaker is
in a non-cutoff state.

With such configuration, the control unit drives the
charging unit during the non-cutoff state of the breaker in
which the electric power can be supplied from the commercial
power source to the load. This makes it possible to charge
the electric power supplied from the commercial power source
to the electric cell.
The power supply system may further include a power
generation unit for converting natural energy to an electric
power.
In -he photovoltaic power generation and the wind
power generation using natural energy such as the sunlight
and the wind, the power generation amount depends on the
weather or other conditions. Accordingly, even if the power
supply system is provided with the power generation unit,
the cutoff threshold is set greater in preparation for a
situation that no electric power is generated by the power
generation unit. It is however typical that the cost
involved in using the commercial power source becomes higher
as the cutoff threshold grows larger. With the
configuration noted above, it is possible to enable the load
to use an electric current larger than the cutoff threshold.
This makes it possible to set the cutoff threshold in
conformity with the power generation time during which an
electric power is generated by the power generation unit.
In other words, the cutoff threshold value is set, e.g., at
such a value as to supplement the electric current generated

by rhe power generation unit. This makes it possible to
reduce costs as compared with a case where the cutoff
threshold value is set at such a value that the electric
power can be supplied from the commercial power source to
the load during the non-power-generation time.
Brief Description of the Drawings
The objects and features of the present invention will
become apparent from the following description of preferred
embodiments given in conjunction with the accompanying
drawings, in which:
Fig. 1 is a block diagram showing a power supply
system in accordance with an embodiment of the present
invention;
Fig. 2 is a block diagram for explaining an AC
distribution board and a control unit; and
Fig. 3 is a flowchart illustrating an operation of the
power supply system.
Detailed Description of the Preferred Embodiments
Hereinafter, embodiments of the present invention will
be described with reference to the accompanying drawings,
which form a part hereof. Throughout the drawings, like
reference numerals will be given to like parts, and

redundant description thereof will be omitted.
A power supply system in accordance with an embodiment
of the present invention will be described with reference to
Figs. 1 to 3.
As shown in Fig. 1, a house is provided with a power
supply system 1 for supplying an electric power to a variety
of home appliances (such as an illuminating device, an air
conditioner, an electric device and an audiovisual device)
installed in a home. The power supply system 1 supplies an
electric power of a commercial AC power source 2 as a home-
use commercial power source to operate various kinds of
appliances. In addition, the power supply system 1 also
supplies an electric power of a solar cell generating the
electric power with a natural energy such as sunlight to
operate the various kinds of appliances. The power supply
system 1 supplies the electric power not only to DC
appliances 5 operating with the DC power inputted from a DC
power source but also to an AC appliance 6 operating with
the AC power inputted from an AC power source 2. In the
following description, a house will be taken as an example
of the place in which the power supply system is installed.
However, the present invention is not limited thereto but
may be applied a multi-dwelling unit, an apartment, an
office and a factory.
The power supply system 1 is provided with a
controller 7 as a system power distribution board and a DC

distribution board in which a DC breaker is arranged) 8.
The power supply system 1 is further provided with a control
unit 9 ana a relay unit 10 for controlling operations of the
DC appliances 5 installed in the house.
An AC distribution board 11 for dividing the AC power
is connected to the controller 7 via an AC power line 12.
The controller 7 is connected to the commercial AC power
source 2 via the AC distribution board 11 and is connected
to the solar cell 3 via a DC power line 13. The controller
7 receives AC power from the AC distribution board 11 and
receives DC power from the solar cell 3. The controller 7
converts the AC power and the DC power to specified DC power
to be used as the source power of the appliances. The
controller 7 outputs the converted DC power to the DC
distribution board 8 via a DC power line 14 or to a battery
16 as an electric cell via a DC power line 15 to thereby
store the DC power in the battery 16. Not only does the
controller 7 receive the AC power from the AC distribution
board 11 but also the controller 7 can convert the electric
power from the solar cell 3 or the battery 16 to an AC power
and supply the AC power to the AC distribution board 11.
The controller 7 exchanges data with the DC distribution
board 8 via a signal line 17.
The DC di stri bution board 8 is a kind of breaker
corresponding to the DC power. The DC distribution board 8
divides the DC power inputted from the controller 7 and

outputs the divided DC power to the control unit 9 via a DC
power line 18 or to the relay unit 10 via a DC power line
19. The DC distribution board 8 exchanges data with the
control unit 9 via a signal line 20 or with the relay unit
10 via a signal line 21.
A plurality of DC appliances 5 is connected to the
control unit 9. The DC appliances 5 are connected to the
control unit 9 via DC supply lines 22 each of which has a
pair of lines capable of transmitting both the DC power and
data therethrough. The electric power and the data are
transmitted to the DC appliances 5 Lhrough the respective DC
supply lines 22 by virtue of so-called power line
communications in which communications signals for
transmitting data with a high-frequency carrier wave are
overlapped with the DC power to be supplied to the DC
appliances 5 by using a pair of lines. For example, both
the electric power and the data are transmitted to each of
the DC appliances 5 by using a pair of lines. The control
unit 9 receives the DC power for the DC appliances 5 via a
DC power line 18. Based on an operation instruction
obtained from the DC distribution board 8 via a signal line
20, the control unit 9 determines which of the DC appliances
5 is to be controlled in what manner. Then, the control
unit 9 outputs the DC power and the operation instruction to
the designated DC appliances 5 via the DC supply lines 22,
thereby controlling the operations of the corresponding DC

appliances 5.
Switches 23 operated to switch over the operations of
the DC appliances 5 are connected to the control unit 9 via
a DC supply line 22. In addition, a sensor 24 for detecting
electric waves transmitted from, e.g., an infrared remote
controller is connected to the control unit 9 via the DC
supply line 22. Accordingly, the DC appliances 5 are
controlled by transmitting communications signals via the DC
supply lines 22 in response to not only the operation
instruction from the DC distribution board 8 but also the
operation of the switches 23 and the detection in the sensor
24.
A plurality of DC appliances 5 is connected to the
relay unit 10 via individual DC power lines 25. The relay
unit 10 receives the DC power for the DC appliances 5 via a
DC power line 19 and determines which of the DC appliances 5
is to be operated based on an operation instruction obtained
from the DC distribution board 8 via the signal line 21.
The relay unit 10 controls the operations of the DC
appliances 5 determined to be operated by turning on and off
the supply of power to the corresponding DC appliances 5 via
the DC power lines 25 using relays built therein. A
plurality of switches 26 for manually operating the DC
appliances 5 is connected to the relay unit 10. The DC
appliances 5 are controlled by manually operating the
switches 26 and causing the relays to turn on and off the

supply of the power tc the DC power lines 25.
DC sockets 27 installed in the house in the form of,
e.g., a wall socket and a floor socket, are connected to the
DC distribution board 8 via a DC power line 28. If the
plugs (not shown) of the DC appliances 5 are inserted into
-he DC sockets 27, it is possible to directly supply the DC
power to the DC appliances 5.
A power meter 29 capable of remotely measuring the
amount of the power used in the commercial AC power source 2
is connected between the commercial AC power source 2 and
the AC distribution board 11. The power meter 29 is
equipped with not only the function of remotely measuring
the amount of the power used in the commercial AC power
source 2 but also, e.g., a power line communications
function and a wireless communications function. The power
meter 2 9 transmits the measurement results to a power
company or the like through power line communications or
wireless communications.
The power supply system 1 is provided with a network
system 30 that makes it possible to control various kinds of
home appliances through network communications. The network
system 30 includes a home server 31 as a control unit
thereof. The home server 31 is connected to an outdoor
management server 32 via a network N such as the Internet
and is also connected to home appliances 34 via a signal
line 33. The home server 31 is operated by the DC power

supplied from the DC distribution board 8 via a DC power
line 35.
A control box 3 6 for managing the operations of
various kinds of home appliances controlled through network
communications is connected to the home server 31 via a
signal line 37. The control box 36 is connected to the
controller 7 and the DC distribution board 8 via a signal
line 17. The control box 36 is capable of directly
controlling the DC appliances 5 via a DC supply line 38. A
gas/tap water meter 39 capable of remotely measuring, e.g.,
the amount of gas and tap water used, is connected to the
control box 36. The control box 36 is connected to an
operation panel 40 of the network system 30. A monitoring
device 41 formed of, e.g., a door phone extension unit, a
sensor or a camera, is connected to the operation panel 40.
If an operation instruction for the various kinds of
home appliances is inputted via the network N, the home
server 31 notifies the control box 36 of the operation
instruction and operates the control box 36 so that the home
appliances can be operated based on the operation
instruction. Moreover, the home server 31 can provide
various kinds of information obtained from the gas/tap water
meter 39 to the management server 32 via the network N. If
an abnormality detected by the monitoring device 41 is
notified to the home server 31 through the operation panel
40, the home server 31 provides the information on the

detected abnormality to the management server 32 via the
network N.
Next, the AC distribution board 11 and the controller
7 will be described with reference to Fig. 2.
The power supply system 1 of the present embodiment
includes a power distribution path 45 through which the
electric power is supplied from the commercial AC power
source 2 to the AC distribution board 11. In the power
distribution path 45, a first line L1 and a second line L2
are applied with an AC voltage of 100 V supplied from the
commercial AC power source 2. In contrast, a third line L3
is kept at 0 V.
As shown in Fig. 2, a limiter 4 6 serving as a breaker,
a main breaker 47 and a branch breaker 48 are arranged
within the AC distribution board 11 in the named order from
the side of the commercial AC power source 2 as the primary
side. The limiter 46, the main breaker 47 and the branch
breaker 48 are connected to the power distribution path 45.
An AC detector (hereinafter often referred to as "CT") 49 as
a current detection unit for acquiring electric currents
flowing through the first line L1 and the second line L2 is
provided in the power distribution path 45 between the
limiter 4 6 and the main breaker 47.
The limiter 46 cuts off the power distribution path 45
in the event that the electric current supplied to the power
distribution path 45 exceeds a contracted current threshold

K1 (e.g., 20 A at 100 V and one half current at 200 V) which
is a cutoff threshold set based on a contact with a power
company providing the commercial AC power source 2. In
other words, when the electric power is used at the
secondary side to which the DC appliances 5 and the AC
appliance 6 are connected, an electric current corresponding
to the capacity of the loads flows through the limiter 46.
in case where an electric current larger than the contracted
current threshold Kl is supplied from the commercial AC
power source 2, a bimetal (not shown) provided within the
limiter 4 6 is heated and bent by large amount of the
electric current, thereby separating contact points and
stopping the supply of electric power from the commercial AC
power source 2. The limiter 45 cuts off the power
distribution path 45 if the total current A flowing the
first line L1 and the second line L2 exceeds the contracted
current threshold value K1.
The main breaker 47 connected to the power
distribution path 45 at the secondary side of the limiter 46
cuts off the power distribution path 45 if an abnormal
current flows due to the occurrence of electric leakage or
short circuit at the secondary side. The branch breaker 48
is provided to individually correspond to branch paths 51
branched in a corresponding relationship with the AC
appliance 6 or each of the rooms in a house. The branch
breaker 48 individually cuts off each of the branch paths 51

if the electric current supplied through the respective
branch paths 51 exceeds a branch current threshold K2 set
smaller than the contracted current threshold value K1.
On the other hand, the controller 7 includes an AC/DC
converter 52, a DC/AC inverter 53 as a DC/AC converter, a
DC/DC converter 54, a discharging circuit 55 as a
discharging means, a charging circuit 56 as a charging means
and a control unit 57. The control unit 57 serves as a
control means that distributes an electric current to the DC
appliances 5 and the AC appliance 6 by controlling the
branch breaker 48, the AC/DC converter 52, the DC/AC
inverter 53, the DC/DC converter 54, the discharging circuit
55 and the charging circuit 56. In other words, the control
unit 57 is configured to, based on the detection result from
the CT 49, control the electric current A supplied from the
commercial AC power source 2.
More specifically, the AC/DC converter 52 receives AC
power from the commercial AC power source 2 through the AC
distribution board 11, converts the AC power to DC power and
then outputs the DC power to the DC distribution board 8.
The DC/DC converter 54 converts the voltage of the DC power
generated by the solar cell 3 to a voltage usable in the DC
appliances 5 and then outputs the converted voltage to the
DC distribution board 8.
The charging circuit 56 outputs DC power to the
battery 16 and charges the battery 16 with the DC power. In

other words, the DC power supplied from the commercial AC
power source 2 and converted by the AC/DC converter 52, and
the DC power generated by the solar cell 3 and voltage-
converted by the DC/DC converter 54 are outputted by the
charging circuit 56 to the battery 16 and are changed in the
battery 16. The discharging circuit 55 discharges the
charged battery 16, thereby causing the battery 16 to output
DC power.
The DC/AC inverter 53 converts the DC power outputted
from the battery 16 and the DC power generated by the solar
cell 3 to AC power. The AC power thus converted is applied
to the AC appliance 6 through the branch path 51 to which
the branch breaker 48 is connected.
Next, the operation of the power supply system 1
configured as above, particularly the operation of the power
supply system 1 in a non-power-generation state in which the
solar cell 3 does not generate an electric power, will be
described with reference to the flowchart shown in Fig. 3.
In step S110, the control unit 57 sums up the electric
currents of the first line L1 and the second line L2
detected by the CT 49 and consequently acquires the electric
current A supplied from the commercial AC power source 2.
In step S120, the control unit 57 determines whether the
electric current A thus acquired exceeds the contracted
current threshold K1 at which the limiter 46 cuts off the
power distribution path 45. In general, the limiter 46 is

designed to cut off the power distribution path 45 when an
electric current equal to or larger than the contracted
current threshold K1 is supplied for a specified time period
or more.
If the electric current A is equal to or smaller than
the contracted current threshold Kl (if YES in step S120),
the control unit 57 determines that the power distribution
path 45 is less likely to be cut off. Then, the control
unit 57 determines whether the battery 16 is charged to a
target charging amount (step S130) . When repeatedly charged
to a full charging capacity, the battery 16 suffers from
accelerated degradation, as a result of which the chargeable
capacity of the battery 16 grows smaller. In the present
embodiment, therefore, a charging amount smaller than the
full charging capacity (e.g., 80% of the full charging
capacity) is set as the target charging amount.
If the battery 16 is charged with the target charging
amount (if YES in step S130;, the control unit 57 determines
that there is no need to further charge the battery 16. The
control unit 57 repeatedly performs the steps of the
flowchart shown in Fig. 3 while the electric power is
supplied from the commercial AC power source 2 to the DC
appliances 5 or the AC appliance 6 connected to the
secondary side. For that reason, if it is determined in
step S130 that there is no need to further charge the
battery 16 (if YES in step S130), the control unit 57

returns back to step S110 and acquires the electric current
A by performing the processing of step S110 again.
Or. the other hand, if the charged amount of the
battery 16 is less than the target charging amount (if NO in
step S130), the control unit 57 determines that there is a
need to charge the battery 16. Then, the control unit 57
charges the battery 16 by controlling the branch breaker 48,
the AC/DC converter 52 and the charging circuit 56 (step
S140). In other words, the electric power supplied from the
commercial AC power source 2 is divided into the electric
power which is to be supplied to the AC appliance 6 through
the branch breaker 48 and the electric power which is to be
converted to DC power by the AC/DC converter 52. The DC
power converted by the AC/DC converter 52 is supplied to the
respective DC appliances 5 through the DC distribution board
8 and is outputted and charged to the battery 16 through the
charging circuit 56. In order to repeatedly perform the
processing steps of the flowchart, the control unit 57
returns back to step S110 and acquires the electric current
A again (step S110).
On the other hand, if it is determined in step S120
that the electric current A is larger than the contracted
current threshold K1 (if NO in step S120), the control unit
57 determines that the electric current A exceeds the
contracted current threshold Kl. Then, the control unit 57
discharges the battery 16 by controlling the discharging

circuit 55 (step S150). In such case, thee electric power
discharged from the battery 16 is supplied to the DC
appliances 5 through the DC distribution board 8, so that
the AC power coming from the commercial AC power source 2 is
supplied to the AC appliance 6. Therefore, as compared with
a case where both of the DC appliances 5 and the AC
appliance 6 are powered by the electric power coming from
the commercial AC power source 2, it is possible to reduce
the electric power supplied from the commercial AC power
source 2, and the electric current A becomes smaller, so
that the power distribution path 45 is prevented from being
cut off by the limiter 46, whereby the power distribution
path 45 is kept in a normal (non-cutoff) state. If the load
of the AC appliance 6 is heavy, the DC power discharged from
the battery 16 is converted to AC power by the DC/AC
inverter 53 and is supplied to the AC appliance 6. Further,
in order to repeatedly perform the processing steps of the
flowchart, the control unit 57 returns back to step S110 and
acquires the electric current A again (step S110) .
Next, description will be made on the operation of the
power supply system 1 during the power generation time in
which the solar cell 3 generates an electric power and
supplies the electric power thus generated.
First, the control unit 57 controls the DC/DC
converter 54 to convert the voltage of the DC power
generated by the solar cell 3 and to output the voltage-

converted DC power to the DC distribution board 8. At the
same time, the control unit 57 controls the DC/AC inverter
53 and the branch breaker 48 to convert the DC power
generated by the solar cell 3 to AC power and to supply the
AC power to the AC appliance 6.
Further, if the amount of the electric power generated
by the solar cell 3 is greater than the amount of the
electric power used by the DC appliances 5 and the AC
appliance 6 connected to the power supply system 1, the
control unit 57 controls the charging circuit 56 so that the
DC power outputted from the DC/DC converter 54 can be
changed in the battery 16.
In the event that the electric current A detected by
the CT 4 9 grows larger than the contracted current threshold
Kl, the control unit 57 controls the discharging circuit 55
to discharge the electric power stored in the battery 16.
In other words, if the DC appliances 5 and the AC appliance
6 use an electric current exceeding the sum of the electric
current generated by the solar cell 3 and the contracted
current threshold Kl. , the electric power is supplied from
the battery 16 to the DC appliances 5 and the AC appliance.
Thus, the electric current A detected by the CT 49 becomes
smaller.
The power supply system 1 of the embodiment described
above can provide the following effects.
(1) The control unit 57 drives the discharging circuit

55 if it is determined that the electric current A detected
by the CT 49 exceeds the contracted current threshold Kl.
In response, the electric power stored in the battery 16 is
distributed to the DC appliances 5 and the AC appliance 6.
Accordingly, the electric current A supplied from the
commercial AC power source 2 is reduced by the amount of the
electric power supplied from the battery 16. Since the
battery 16 is connected closer to the DC appliances 5 and
the AC appliance 6 than the limiter 46, the electric power
discharged from the battery 16 is distributed to the DC
appliances 5 and the AC appliance 6 without passing through
the limiter 46. Therefore, the power distribution path 45
through which the electric power is supplied from the
commercial AC power source to the DC appliances 5 and the AC
appliance 6 is not cut off, and it becomes possible to
enable the DC appliances 5 and the AC appliance 6 to use an
electric current larger than the contracted current
threshold Kl triggering the cutoff of the power distribution
path 45.
(2) The electric power can be supplied from the
battery 16 to the AC appliance 6 by converting the DC power
discharged from the battery 16 to AC power through the use
of the DC/AC inverter 53. Therefore, even if the electric
current used in the AC appliance 6 exceeds the contracted
current threshold Kl, the cutoff of the power distribution
path 45 can be prevented by supplying the electric power

from the battery 16 to the AC appliance 6.
(3) The time and effort required in replacing an
electric cell can be reduced by using the rechargeable
battery 16 as an electric cell that serves as a backup power
source.
(4) The control unit 57 drives the charging circuit 56
during the non-cutoff state of the limiter 4 6 in which the
electric power can be supplied from the commercial AC power
source 2 to the DC appliances 5 and the AC appliance 6.
This makes it possible to charge the electric power supplied
from the commercial AC power source 2 to the battery 16.
(5) In the photovoltaic power generation using the
sunlight, the power generation amount depends on the weather
or other conditions. Accordingly, even if the conventional
power supply system is provided with the solar cell 3, the
contracted current threshold Kl is set greater in
preparation for a situation that no electric power is
generated by the solar cell 3. It is however typical that
the cost involved in using the commercial AC power source 2
becomes higher as the contracted current threshold Kl grows
larger.
In the present embodiment, it is possible to enable
the DC appliances 5 and the AC appliance 6 to use the
electric current A larger than the contracted current
threshold Kl. This makes it possible to set the contracted
current threshold Kl in conformity with the power generation

time during which electric power is generated by the solar
cell 3. In other words, the contracted current threshold Kl
is set, e.g., at such a value as to supplement the electric
current generated by the solar cell 3. This makes it
possible to reduce costs as compared with the conventional
case where the contracted current threshold Kl is set at
such a value that the electric power can be supplied from
the commercial AC power source 2 to the DC appliances 5 and
the AC appliance 6 during the non-power-generation time.
The power supply system 1 of the embodiment described
above may be modified as follows.
The power supply system 1 may include a power
generation unit using natural energy, such as a wind power
generation unit for generating an electric power by rotating
a propeller with a wind, a geothermal power generation unit
using terrestrial heat or a hydro power generation unit
using energy from water. Alternatively, the power supply
system 1 may not include the above described power
generation unit noted and the solar cell 3.
Since an electric cell has an upper limit in its
charging capacity, a large cell having an increased charging
capacity needs to be used if discharging is performed over
an extended period of time. Accordingly, the power supply
system 1 may include a generator capable of arbitrarily
generating an electric power, e.g., a fuel cell that
generates an electric power by reacting hydrogen contained

in a gas with oxygen. The combined use of the generator and
the electric cell makes it possible to restrain the electric
cell from becoming larger in size. In other words, the
electric cell is discharged until the generator starts power
generation, so that the electric power can be rapidly
supplied when the power consumption gets increased, thereby
restraining the limiter 46 from cutting off the power
distribution path 45. Further, even when an electric cell
having a small charging capacity is used, the time period
for supplying an electric current equal to or greater than
the contracted current threshold Kl can be extended by
supplying the electric power from the generator.
In the event that a fuel cell or a power generation
unit such as a wind power generation unit generates the
electric power equal to or greater than the amount of
electric power consumed by the DC appliances 5 and the AC
appliance 6, the excess power may be stored in the battery
16. In other words, if the power supply system 1 is
provided with a power generation unit, the electric power
may be charged in the battery 16 regardless of the cutoff
state and the non-cutoff state of the power distribution
path 45.
A primary battery capable of performing only a
discharging operation may be provided as an electric cell,
in which case a completely discharged primary battery may be
replaced with a new one.

The DC/AC inverter 53 may be omitted and the DC power
discharged from the battery 16 may be supplied to only the
DC appliances 5.
A discharging startup threshold (e.g., 18A at 100 V)
equal to or smaller than the contracted current threshold Kl
may be set in advance and an electric power may be
discharged from the battery 16 when the electric current A
becomes equal to or larger than the discharging startup
threshold. Alternatively, an electric power may be
discharged from the battery 16 when the electric current A
becomes equal to or greater than the contracted current
threshold Kl.
A current detection unit for detecting the electric
current used in the DC appliances 5 and the electric current
used in the AC appliance 6 may be provided independently of
each other. In this case, the AC power outputted from the
commercial AC power source 2 may be supplied to the AC
appliance 6 and the DC power outputted from the battery 16
may be supplied to the DC appliances 5, and the DC power may
be converted to AC power and may be supplied to the AC
appliance 6 when the electric current used in the AC
appliance 6 is larger than the contracted current threshold
Kl. Power loss is generated when converting the DC power to
the AC power and vice versa. Therefore, if the conversion
between the DC power and the AC power is reduced, it becomes
possible to reduce the power loss and to increase the

efficiency.
While the invention has been shown and described with
respect to the embodiments, it will be understood by those
skilled in the art that various changes and modification may
be made without departing from the scope of the invention as
defined in the following claims.

WE CLAIM:
1. A power supply system, comprising:
a current detection unit for detecting a current used
by a load;
an electric cell; and
a control unit for controlling the electric power
stored in the electric cell to be supplied to the load if it
is determined that the current detected by the current
detection unit exceeds a cutoff threshold.
2. The power supply system of claim 1, further comprising:
a breaker provided in a power distribution path through
which an electric power is supplied from a commercial power
source to the load, the breaker being configured to cut off
the power distribution path if the electric current flowing
through the power distribution to the load larger than the
cutoff threshold; and
a discharging unit for distributing the electric power
stored in the electric cell to the load, the electric cell
being provided closer to the load than the breaker,
wherein the control unit is configured to drive the
discharging unit if it is determined that the current
detected by the current detection unit exceeds the cutoff
threshold.

3. The power supply system of claim 2, further comprising:
a DC/AC converter for converting inputted DC power to
AC power,
wherein the power supply system is configured to
distribute an electric power through the DC/AC converter if
the electric power is supplied from the electric cell to an
AC load connected tO the power distribution path at a
secondary side of the breaker.
4. The power supply system of claim 2 or 3, wherein the
electric cell is a rechargeable battery.
5. The power supply system of claim 4, further comprising:
a charging unit for charging the electric cell,
wherein the control unit is configured to drive the
charging unit if the breaker is in a non-cutoff state.
6. The power supply system of any one of claims 2 to 5,
further comprising:
a power generation unit for converting natural energy
to an electric power.

ABSTRACT

A power supply system includes a current detection
unit for detecting a current used by a load and an electric
cell. The power supply system further includes a control
unit fcr controlling the electric power stored in the
electric cell to be supplied to the load if it is determined
that the current detected by the current detection unit
exceeds a cutoff threshold.