Field of the Invention
The present invention relates to a power distribution
system which distributes an alternating current (AC) power
and a direct current (DC) power to load devices.
Background of the Invention
Conventionally, there is disclosed a power
distribution system which distributes an AC power and a DC
power in a building such as a house, a shop and an office
building in, e.g., Patent document 1. The power
distribution system of Patent document 1 includes a
distribution board and AC power outlets. Further, DC output
power terminals are provided in the AC power outlets, and a
transformer and a rectifier are disposed in the distribution
board.
In the distribution board, an AC voltage of 100 V or
200 V is converted into three types of AC voltages, e.g., 6
V, 3 V, and 1.5 V, through the transformer, and three types
of DC voltages, e.g., 6 V, 3 V and 1.5 V, are acquired by
rectifying the three types of AC voltages using a rectifier.
The three types of DC voltages produced in the distribution
board are distributed to the DC output power terminals.
From the viewpoint of the global environment
protection, there has been proposed a power distribution
system which performs grid-connected operation of a DC power
generation equipment such as a solar power generation
apparatus provided in the building and a commercial power
source (i.e., an AC power) supplied from a power company
(see, e.g., Patent document 2). In such a type of grid-
connected system, a DC power generated by the DC power
generation equipment is converted into an AC power by a
power converter (power conditioner) for converting a DC
power into an AC power, and is operated in conjunction with
an AC power of the commercial power source. Further, when
the power in excess of the power consumed by load in the
building is supplied from the DC power generation equipment,
a surplus power can be reversely supplied to the commercial
electric power source, which is so-called selling of power.
[Patent Documents]
[Patent document 1] Japanese Utility Model Application
Publication No. He„-i 4-128024
[Patent document 2] Japanese Patent Application
Publication No. 2003-284245
In a power distribution system described in Patent
document 2, when a DC power is supplied as in Patent
document 1, a DC power outputted from the DC power
generation equipment such as a solar power generation
apparatus is converted into an AC power in the power
conditioner and the AC power is converted into the DC power
again. For this reason, there occur the problems that the
power loss is increased and the power efficiency is reduced
due to the power conversion because two-stage power
conversion is performed.
Further, in order to efficiently distribute an AC
power and a DC power, the present applicant has proposed a
configuration in which there are provided a power
conditioner for converting a DC power outputted from the DC
power generation "equipment into an AC power and a DC-DC
converter for converting a voltage level of the DC power
outputted from the DC power generation equipment into a
desired voltage level; and the AC power and the DC power are
supplied from the power conditioner and the DC-DC converter,
respectively.
With such configuration in which the power conditioner
and the DC-DC converter are provided, the power conditioner
and the DC-DC converter may be operated at the same time.
In this case, the following problems arise. That is, when
the DC-DC converter is operated in the state in which an
amount of the power generated by the DC power generation
equipment is small, it does not operate stably. Accordingly,
the DC power is not stably supplied. Furthermore, if the
operation of the DC-DC converter becomes unstable, the
operation of the power conditioner may be disturbed.
Summary of the Invention
In view of the above, the present invention provides a
power distribution system for distributing an AC power and a
DC power, which is capable of stably operating a DC-DC
converter for outputting a DC power and supplying a stable
DC power.
In accordance with a first aspect of the present
invention, there is provided a power distribution system
including a DC-DC converter which converts a DC power
outputted from a DC power source into a DC power having a
desired voltage level and outputs the DC power, wherein the
DC-DC converter is controlled to operate only when an input
voltage thereof falls within a predetermined range.
Further, the power distribution system may include: a
power conditioner connected to the DC power source and an AC
power system, the power conditioner serving to convert the
DC power outputted from the DC power source into an AC power
synchronized with a phase of the AC power system, output the
AC power, and reversely supply the AC power to the AC power
system; and an operation control part which performs a
control so that the DC-DC converter operates only when the
input voltage of the DC-DC converter falls within the
predetermined range, wherein the power conditioner and the
DC-DC converter may be connected in parallel to the DC power
source, so that the power conditioner and the DC-DC
converter can be simultaneously operated.
By this configuration, the DC-DC converter for
outputting DC power can be stably operated, and stable DC
power can be supplied.
Preferably, the predetermined range is equal to or
narrower than an operating voltage range of the power
conditioner.
By this configuration, when the DC-DC converter is
operated while the power conditioner is being operated, the
DC-DC converter can be operated in the state in which the
input voltage is stabilized, thereby achieving stable
operation. Furthermore, the DC-DC converter can be
prevented from disturbing the operation of the power
conditioner.
in the power distribution system, the operation
control part may control the DC-DC converter to operate
after the lapse of a predetermined time period from when the
input voltage of the DC-DC converter enters the operating
voltage range.
With such configuration, the operation of the power
conditioner becomes stable, and then the DC-DC converter
starts to operate, which leads into further stable operation
of the DC-DC converter.
Further, the operation control part may control the
DC-DC converter to operate when an amount of variation in
the input voltage of the DC-DC converter per unit time is
equal to or lower than a predetermined value.
With this configuration, it is checked whether or not
the power conditioner operates stably, and then the DC-DC
converter starts to operate, thereby further stabilizing the
operation of the DC-DC converter.
The power distribution system may include a power
failure detection unit which detects a power failure of the
AC power system, wherein, when the power failure is detected
by the power failure detection unit, the operation control
part may widen the predetermined range to a larger range
than that in a non-power failure situation and operates the
DC-DC converter.
With such configuration, since the power conditioner
stops operating during a power failure, the DC-DC converter
can be operated within a wider range of the operating
voltage regardless of the operation of the power conditioner.
This makes it possible to more efficiently use the power
generated by a DC power source such as solar cells.
Further, the power distribution system may include a
power failure detection unit which detects a power failure
of the AC power system, wherein, when the power failure is
detected by the power failure detection unit, the operation
control part may stop operation of the DC-DC converter.
By doing so, in a case where the power conditioner
stops operating during the power failure and the DC-DC
converter becomes difficult to operate stably, the DC-DC
converter can be suppressed from operating unstably by
stopping the operation thereof.
Preferably, the DC power source includes solar cells,
and the operation control part changes a setting of the
operating voltage range based on the number of the solar
cells installed.
With such configuration, the DC-DC converter can be
operated within an appropriate operating voltage range based
on the peak voltage of the power generated by the solar
cells .
In accordance with a second aspect of the present
invention, there is provided a DC power distribution
apparatus including: a DC-DC converter which converts a DC
power outputted from a DC power source into a DC power
having a desired voltage level and outputs the DC power, the
DC-DC converter being connected to the DC power source in
parallel with a power conditioner which converts the DC
power outputted from the DC power source into an AC power
synchronized with a phase of an AC power system and outputs
the AC power, so that the DC-DC converter can be operated
simultaneously with the power conditioner; and an operation
control part which controls the DC-DC converter to operate
only when an input voltage of the DC-DC converter falls
within a predetermined range.
Brief Description of the Drawings
The objects and other features of the present
invention will become apparent from the following
description of embodiments, given in conjunction with the
accompanying drawings, in which:
FIG. 1 is a diagram illustrating the configuration of
a power distribution system in accordance with an embodiment
of the present invention;
FIGS. 2A and 2B are diagrams for explaining operation
of a power conditioner;
FIG. 3 is a diagram depicting a first configuration
example of an operation control part which controls
operation of the DC-DC converter in accordance with the
embodiment;
FIG. 4 is a graph illustrating a first example of an
operating range of the DC-DC converter controlled by the
operation control part in the first example of the
configuration;
FIG. 5 is a graph representing a second example of the
operating range of the DC-DC converter controlled by the
operation control part in the first example of the present
embodiment;
FIG. 6 is a diagram depicting a first example of an
input voltage waveform in controlling the operation of the
DC-DC converter;
FIG. 7 is a diagram illustrating a second example of
the input voltage waveform in controlling the operation of
the DC-DC converter;
FIG. 8 is a diagram representing a second
configuration example of the operation control part which
controls the operation of the DC-DC converter in accordance
with the embodiment; and
FIG. 9 is a diagram illustrating an application
example of the power distribution system in accordance with
the embodiment.
Detailed Description of the Embodiments
Hereinafter,.-embodiments of the present invention will
be described in more detail with reference to accompanying
drawings which form a part hereof. Throughout the drawings,
like reference numerals will be given to like parts.
An embodiment in which a power distribution system in
accordance with an embodiment of the present invention is
applied to a detached house will be described in detail with
reference to the accompanying drawings. However, the
building to which the power distribution system in
accordance with the present invention is applied is not
limited to the detached house, but the power distribution
system may be applied to each house of a multiple dwelling
house or an of f ice. building .
FIG. 1 illustrates a configuration of a power
distribution system in accordance with an embodiment of the
present invention. The power distribution system in
accordance with the embodiment includes solar cells 1, a
relay terminal box (hereinafter, also referred to as a
"connection box") 2, a power conditioner 3, an AC
distribution board 4, a DC-DC converter 5, and an AC-DC
converter 6.
The solar cells 1 include multiple (e.g., three in the
illustrated example) solar cell modules 1A, IB and 1C, and
serve as a DC power source. The relay terminal box 2
integrates a plurality of output cables 7 into a single
cable 8, the solar cell modules 1A, IB and 1C supplying DC
output through output cables 7. A solar power generation
apparatus including the solar cells 1 and the relay terminal
box 2 serves as an example of a DC power generation
equipment.
The power conditioner 3 converts the DC power
outputted from the solar cells 1 into an AC power in
synchronization with a phase of a commercial power source
(AC power system) AC, and reversely supplies the AC power to
the AC power system. The AC distribution board 4 branches
the AC power outputted from the AC power system or the power
conditioner 3, and distributes an electric power to houses
via a plurality of branch breakers (not shown).
The DC-DC converter 5 converts a voltage level of the
DC power outputted from the solar cells 1 into a desired
voltage level. The AC-DC converter 6 converts the AC power
supplied via the AC distribution board 4 into the DC power
with a desired voltage level. Furthermore, an AC load
device 13 is connected to an AC distribution line 11 which
distributes the AC power outputted from the AC distribution
board 4. A DC load device 14 is connected to a DC
distribution line 12 which distributes the DC power
outputted from the DC-DC converter 5 or the AC-DC converter
6.
The solar cell modules 1A ~ 1C have a conventional
well-known configuration in which multiple (e.g., eight in
the illustrated example} solar cells enclosed with an
envelope (not shown) are installed, e.g., on the roof of the
house. Further, the relay terminal box 2 is provided in a
closed box shape in which strings at an output side and a
load side are relayed through terminals and a reverse
current blocking device and a DC switch are provided if
necessary (e.g., see Japanese Industrial Standard C8960) .
The power conditioner 3 includes a step-up chopper
circuit (not shown) which steps up a DC output of the solar
cells 1, an inverter (not shown) which converts the DC
output stepped up by the step-up chopper circuit into an AC
sine-wave output in synchronization with the phase of the AC
power system, an inverter control circuit (not shown) which
adjusts the AC output by controlling the inverter, and a
grid connection protection device.
The AC distribution board 4 is provided as a box with
a door, like a so-called household distribution board (a
house board). In the box, a main breaker (not shown) which
primary side is connected to the AC power system, and a
plurality of branch breakers branched to conductive bars
(not shown} are accommodated, the conductive bars being
connected to a secondary side of the main breaker. Further,
an output line of the power conditioner 3 is taken into the
box of the AC di-stribution board 4, and is connected in
parallel with the AC power system AC in the box.
Furthermore, the AC distribution line 11 is connected to a
secondary side of the branch breaker, and the AC power is
supplied to a AC load device 13 provided in the house via
the AC distribution line 11. An outlet (not shown) to which
the AC load device 13 is connected is provided at the end of
the AC distribution line 11.
The DC-DC converter 5 includes, for example, a
switching regulator, and converts the voltage level of the
DC power outputted from the solar cells 1 into a desired
voltage level by performing the constant voltage regulation
which detects an output voltage and increases or decreases
the output voltage so that the detected output voltage
becomes equal to a target voltage (feedback control). The
AC-DC converter 6 includes, for example, a switching
regulator, an inverter, etc., and converts the AC power
outputted from the AC distribution board 4 to a DC power
having a desired voltage level by rectifying the AC voltage
into the DC voltage and performing the constant voltage
regulation on an output voltage.
The output terminals of the DC-DC converter 5 and the
AC-DC converter 6 are connected to the DC distribution line
12, and a protection circuit (not shown) is provided on the
DC distribution line 12. Further, one of the DC powers
converted to have the desired voltage level by the DC-DC
converter 5 and the AC-DC converter 6 is supplied to the DC
load device 14 via the DC distribution line 12. A DC power
distribution apparatus including, e.g., the DC-DC converter
5 and the AC-DC converter 6, may be provided to output a DC
power. An outlet (not shown) to which the DC load device 14
is connected is provided at the end of the DC distribution
line 12.
In the present embodiment, the power conditioner 3 is
connected in parallel with the DC-DC converter 5, so that
the power conditioner 3 and the DC-DC converter 5 can be
operated simultaneously. Further, the DC-DC converter 5 is
operated only when the input voltage falls within a
predetermined range.
Next, in the power distribution system in accordance
with the present embodiment, operation of the power
conditioner 3 will be described. FIGS. 2A and 2B are graphs
for explaining the operation of the power conditioner 3.
The inverter control circuit of the power conditioner
3 performs Maximum Power Point Tracking (MPPT) control in
which, when an output voltage or an output current of the
solar cells 1 is changed due to a change in the temperature
of the solar cells 1 or the intensity of solar radiation,
the operating point of the solar cells 1 moves to follow up
the maximum output point, thereby maximizing the DC output
of the solar cells 1. Since the MPPT control is well known,
a detailed description thereof will be omitted. Furthermore,
the grid connection protection device of the power
conditioner 3 monitors a voltage of the AC power system, and
reduces the output of the inverter by sending a command to
the inverter control circuit to stop MPPT control when the
voltage is higher than an appropriate value, thereby
suppressing an increase in a grid voltage.
The curve A shown in FIG. 2A illustrates an output
characteristic of the solar cells 1 under a specific solar
radiation condition. An output power PI is the power
(demanded DC power) supplied from the DC-DC converter 5 via
the DC distribution line 12 to the DC load device 14.
Initially, an operating point of the inverter control
circuit is determined as XI based on the demanded DC power
PI. When the inverter control circuit starts MPPT control
and adjusts an AC power supplied to the AC distribution line
11, the operating point moves to X2 coinciding with the peak
of the output characteristic curve A, and the solar cells 1
supplies the maximum output (e.g., the maximum power P2 in
FIG. 2A).
At this point, the difference (P2-P1) between the
maximum power P2 and the demanded DC power PI is supplied to
the AC load device 13 via the AC distribution line 11. Here,
when the supply power (P2-P1) of the power conditioner 3 is
lower than a consumed power of the AC load device 13, an AC
power from the AC power system AC is supplied to the AC load
device 13 via the AC distribution line 11. Meanwhile, when
the supply power (P2-P1) of the power conditioner 3 is
higher than the consumed power of the AC load device 13, the
excess of the AC power (P2-P1) is reversely supplied to the
AC power system from the power conditioner 3.
On the other hand, as shown in FIG. 2B, when the
output characteristic of the solar cells 1 decreases from
curve A to curve B because of the weakening of solar
radiation and, accordingly, the output power of the solar
cells 1 is lower than the demanded DC power PI, the inverter
control circuit stops the operation. In this case, the DC
load device 14 stops the operation, or the DC load device 14
is supplied with a power from an auxiliary power source
(battery or the like) separately provided.
Meanwhile, if the output power of the solar cells 1 is
higher than the demanded DC power PI even when the output
characteristic of the solar cells 1 decreases from the curve
A to the curve B, the inverter control circuit decreases the
output of the solar cells 1 by shifting the operating point
from XI to X3. Thereafter, the operating point reaches X4
which coincides with the peak of the output characteristic
curve B by second MPPT control and the maximum output
(maximum power P3) is supplied from the solar cells 1.
Further, even when the demanded DC power Pi changes, the
maximum output can be supplied from the solar cells 1 by
readjusting the MP.-PT control, as in the case when the solar
radiation changes which is described above.
The power distribution system in accordance with the
present embodiment distributes to the AC load device 13 the
AC power supplied from the AC power system via the AC
distribution board 4 or the AC power outputted from the
power conditioner 3. Further, the power distribution system
distributes to the DC load device 14 the DC power from the
solar cells 1 controlled at a constant voltage by the DC-DC
converter 5, or the DC power obtained by converting the AC
power supplied from the AC distribution board 4 using the
AC-DC converter 6. This makes it possible to more
efficiently distribute the DC power as compared to the case
where an AC power outputted from the power conditioner 3 is
converted into a DC power and then the DC power is
distributed.
Further, since the power conditioner 3 and the DC-DC
converter 5 are connected in parallel with respect to the
solar cells 1, the distribution of the output power of the
solar cells 1 to the DC load and the AC load is
automatically adjusted in response to a change in solar
radiation or DC load (i.e., a demanded DC power) . In this
case, the DC power is first supplied to the DC load device
14 via the DC-DC converter 5, and then is supplied to the AC
load device 13 as the AC power by the power conditioner 3,
and finally is supplied to the AC power system as the AC
power. As described above, even when the DC load or AC load
changes, the DC power outputted from the solar cells 1 is
automatically distributed to the DC load device 14, the AC
load device 13 and' the AC power system AC, thereby improving
power efficiency.
Next, the operation of the DC-DC converter 5 in the
power distribution system of the present embodiment will be
described.
FIG. 3 represents a first configuration example of a
operation control part which controls the operation of the
DC-DC converter 5 in accordance with the present embodiment.
The operation control part in accordance with the first
configuration example includes an input voltage monitoring
circuit 21 and an ON/OFF control circuit 22. The input
voltage monitoring circuit 21 monitors by detecting a
voltage inputted to the DC-DC converter 5 from the solar
cells 1, i.e., an output voltage of a DC power generated by
the solar cells 1.
The ON/OFF control circuit 22 turns on and off
operation of the DC-DC converter 5 by outputting a control
signal to the DC-DC converter 5 based on the results of the
detection of the input voltage monitoring circuit 21.
Specifically, the ON/OFF control circuit 22 performs an
operation control in such a way that the DC-DC converter 5
is turned on if the voltage inputted to the DC-DC converter
5 is within a predetermined range and is turned off if the
input voltage deviates from the predetermined range. The
input voltage monitoring circuit 21 and the ON/OFF control
circuit 22 may be configured to be provided inside or
outside the DC-DC converter 5.
FIG. 4 is a graph illustrating a first example of an
operating range of the DC-DC converter 5 which is controlled
by the operation control part of the first configuration
example shown in FIG. 3. FIG. 4 illustrates a relation
between voltage and current in the output power of the solar
cells 1 and a voltage range in which the DC-DC converter 5
operates. The output voltage and current of the solar cells
1 vary depending on a change in the intensity of solar
radiation. For example, a high voltage and current are
outputted when the intensity of solar radiation is high.
In the present embodiment, the predetermined range of
the high-voltage side within which the maximum output power
can be obtained from the solar cells 1 is set as the
operating voltage range of the DC-DC converter 5, and the
DC-DC converter 5 is operated by the ON/OFF control circuit
22 when the input voltage is within the operating voltage
range. When the intensity of solar radiation to the solar
cells is low, for example, at dawn or at dusk, an amount of
power generated is small and, accordingly, the output
voltage is low and unstable.
When the DC-DC converter 5 is operated in the state in
which the amount of power generated by the DC power
generation equipment is low, there may be cases where the
operation becomes unstable and the DC power is not supplied
stably. With the present embodiment, since the
predetermined range in which the input voltage is higher
than the predetermined voltage is set as the operating
voltage range, the DC-DC converter 5 can be stably operated
and the stable DC power can be supplied. Furthermore, the
DC-DC converter 5 does not disturb the operation of the
power conditioner 3.
FIG. 5 is a graph illustrating a second example of the
operating range of the DC-DC converter 5 which is controlled
by the operation control part of the first configuration
example shown in FIG. 3. As shown in FIG. 5, the operating
voltage range of the DC-DC converter 5 is set to a range
identical to or narrower than an operating voltage range of
the power conditioner 3, and the DC-DC converter 5 is
operated by the ON/OFF control circuit 22 when the input
voltage is within the set operating voltage range. When the
power conditioner 3 operates, the output voltage of the
solar cells 1, i.e., the input voltage of the DC-DC
converter 5, is stabilized by the above-described MPPT
control, and therefore the DC-DC converter 5 can be stably
operated.
The operation of the DC-DC converter 5 may be
controlled based on the time and/or the range of a variation
in voltage, in addition to the operating voltage range.
Such modified examples will be described below.
In a first modified example, the ON/OFF control
circuit 22 includes a timer for counting time, and starts to
operate the DC-DC converter 5 after a predetermined time
period has passed from the time when the input voltage
enters the predetermined operating voltage range of the DC-
DC converter 5. Accordingly, after the power conditioner 3
is operated, the DC-DC converter 5 can be operated.
Further, when the input voltage is lower than a
minimum operating voltage of the operating voltage range
after the DC-DC converter 5 has operated, the operation is
immediately stopped. After that, even when the input
voltage is returned to within a normal voltage range, the
operation is kept stopped, and the operation is resumed
after the lapse of a predetermined time period. Thus, since
the DC-DC converter 5 starts to operate after the power
conditioner 3 has stably operated, the operation of the DC-
DC converter 5 can be further stabilized. Furthermore,
there is no concern about the power conditioner 3 disturbing
the stable operation of the DC-DC converter 5.
In a second modified example, the ON/OFF control
circuit 22 monitors the input voltage of the DC-DC converter
5 using the detection result of the input voltage monitoring
circuit 21, and starts the operation when an amount of a
change in the input voltage per unit time (e.g., the range
of the change in the input voltage) becomes egual to or
lower than a predetermined value. Accordingly, it is
possible to check the power conditioner 3 for the operation
and then operate the DC-DC converter 5.
FIG. 6 is a diagram depicting a first example of an
input voltage waveform regarding the operation control of
the DC-DC converter 5. As shown in FIG. 6, the range of
variation in input voltage is large when the input voltage
of the DC-DC converter 5 increases, and then is reduced by
the operation of the power conditioner 3. In this case, the
input voltage of the DC-DC converter 5 is monitored, and the
operation thereof is turned on when it is determined that
the range of the input voltage per unit time is equal to or
lower than a predetermined value.
FIG. 7 is a diagram illustrating a second example of
an input voltage waveform regarding the operation control of
the DC-DC converter. The second example of FIG. 7 shows a
situation in which when the input voltage of the DC-DC
converter 5 increases, the input voltage is raised at first
and gradually reduced and stabilized by the operation of the
power conditioner 3. In this case, when it is determined
that the input voltage is raised and then gradually reduced,
the operation of the DC-DC converter 5 is turned on.
As described above, when the range of variation in the
input voltage of the DC-DC converter 5 is equal to or lower
than the predetermined value, the DC-DC converter 5 is
operated. It is possible to check the power conditioner 3
for stable operation using the input voltage and then
operate the DC-DC converter 5. Accordingly, the DC-DC
converter 5 can be operated more stably.
FIG. 8 represents an second configuration example of
the operation control part which controls the operation of
the DC-DC converter 5 in accordance with the present
embodiment. In the second configuration example, the
operation control part includes an input voltage monitoring
circuit 21, an ON/OFF control circuit 22 and a power failure
detection circuit 23 having a power failure detection
function. The power failure detection circuit 23 is
connected to a supply line through which the AC power is
supplied from the AC power system to the AC distribution
board 4 and the AC distribution line 11, and detects the
power failure of the AC power system.
The ON/OFF control circuit 22 controls the operation
of the DC-DC converter 5 based on the results of the
detection of the input voltage monitoring circuit 21 so that
the DC-DC converter 5 is turned on when the input voltage of
the DC-DC converter 5 falls within a predetermined range.
Furthermore, the ON/OFF control circuit 22 controls the
operation of the DC-DC converter 5 based on the results of
the detection of the power failure detection circuit 23.
For example, the ON/OFF control circuit 22 performs one of
first and second control examples to control the operation
of the DC-DC converter 5 in the event of a power failure,
which will be described below.
In the first control example, when a power failure is
detected, the operating voltage range of the DC-DC converter
5 is widened compared to that in a non-power-failure
situation, and then the DC-DC converter 5 is operated in the
wide voltage range. Since the operation of the power
conditioner 3 stops during the power failure, the power
generated by the solar cells 1 can be effectively utilized
by operating the DC-DC converter 5 in the wider range
regardless of the operation of the power conditioner 3. In
this case, i.e., in the event of a power failure, the power
can be supplied by distributing the DC power from the solar
cells 1.
Meanwhile, in the second control example, when a power
failure is detected, the operation of the DC-DC converter 5
is stopped. Since the operation of the power conditioner 3
stops during the power failure, the DC-DC converter 5 may be
difficult to stably operate. Therefore, the unstable
operation of the DC-DC converter 5 can be suppressed by
stopping the opera-tion thereof.
Furthermore, in each above-described example of the
configuration and operation of the present embodiment, the
setting of the operating voltage range of the DC-DC
converter 5 may be changed, and the operating voltage range
may be changed according to the number of solar cells 1
installed (a peak voltage of the amount of power generated).
In this case, the operating voltage range of the DC-DC
converter 5 on which the ON/OFF control circuit 22 performs
an ON/OFF control is previously set according to the number
of solar cells 1 installed (e.g., the number of solar cells
installed in series) when the power distribution system is
installed. Thus, it is possible to operate the DC-DC
converter 5 in an appropriate operating voltage range
according to the peak voltage of the amount of power
generated by the solar cells 1.
Next, an application example will be described in
which the power distribution system of the present
embodiment is applied to a hybrid power distribution system
which includes solar cells and a battery and distributes an
AC power and a DC power. FIG. 9 illustrates an application
example of the power distribution system in accordance with
the present embodiment.
The power distribution system of the application
example includes an AC distribution board 104 for
distributing an AC power to an AC load device via an AC
distribution line 106, and a DC distribution board 110 as a
DC distribution device which distributes a DC power to a DC
load device via a DC distribution line 107. A commercial
power source (AC power system) 105 as an AC power source and
a power conditioner 103 are connected to the input terminals
of the AC distribution board 104, and the AC distribution
line 106 and the DC distribution board 110 are connected to
the output terminals of the AC distribution board 104. The
AC distribution board 104 branches the AC power supplied
from the commercial power source 105 or the power
conditioner 103, and outputs to the AC distribution line 106
and the DC distribution board 110.
Further, there are provided solar cells 101 which
receive solar light, generate a DC power by performing
photoelectric conversion on the solar light, and output the
DC power, and a battery 102 formed of a secondary battery
capable of storing a DC power and outputting the stored DC
power, as the DC power sources of the power distribution
system. The solar cells 101, the battery 102 and the AC
distribution board 104 are connected to the input terminals
of the DC distribution board 110, and the DC distribution
line 107 is connected to the output terminal of the DC
distribution board 110. The DC distribution board 110
includes a solar cell converter 111, a battery converter 112,
an AC-DC converter 113, a control unit 114, and a display
unit 115.
The output line of the solar cells 101 is branched,
and is then connected to the power conditioner 103 and the
solar cell converter 111 of the DC distribution board 110.
The power conditioner 103 converts the DC power outputted
from the solar cells 101 into the AC power synchronized with
the phase of the commercial power source 105, and reversely
supplies the AC power to the commercial power source 105.
The solar cell converter 111 includes a DC-DC converter; and
converts the DC power outputted from the solar cells 101
into a DC power having a desired voltage level and outputs
the resulting DC power. The battery converter 112 includes
a DC-DC converter; and converts the DC power outputted from
the battery 102 into a DC power having a desired voltage
level and outputs the resulting DC power. The AC-DC
converter 113 converts the AC power supplied from the AC
distribution board 104 into a DC power having a desired
voltage level, and outputs the DC power.
The control unit 114 includes an information
processing device such as a microcomputer or the like, and
is responsible for the control of the operations of the
respective components of the DC distribution board 110. The
control unit 114 performs the ON/OFF control of the
operations of the solar cell converter 111, the battery
converter 112 and the AC-DC converter 113. Further, the
control unit 114 performs the control of the output voltage,
and the control of display of the display unit 115. The
display unit 115 includes an liquid crystal display device,
and displays various types of information, such as the
operating status of the DC distribution board 110, using a
character(s), a numeral(s), and/or an image(s) based on the
instructions of the control unit 114.
In such power distribution system, the DC-DC converter
can be stably operated and the DC power can be stably
supplied, by applying the configuration of the above-
described present embodiment to the DC-DC converter of the
solar cell converter 111.
In the above-described embodiment, although the
configuration in which the solar power generation apparatus
includes solar cells as a DC power source is illustrated,
the present invention is not limited thereto, but the
present invention may be applied to other DC power
generation equipment such as a fuel cell power generation
apparatus including fuel cells. It is apparent that the
above embodiments and modified examples can be combined with
each other.
While the invention has been shown and described with
respect to the embodiments, the present invention is not
limited thereto. It will be understood by those skilled in
the art that various changes and modifications may be made
without departing from the scope of the invention as defined
in following claims.
WE CLAIM:
1. A power distribution system comprising:
a DC-DC converter which converts a DC power outputted
from a DC power source into a DC power having a desired
voltage level and outputs the DC power;
wherein the DC-DC converter is controlled to operate
only when an input voltage thereof falls within a
predetermined range.
2. The power distribution system of claim 1, further
comprising:
a power conditioner connected to the DC power source
and an AC power system, the power conditioner serving to
convert the DC power outputted from the DC power source into
an AC power synchronized with a phase of the AC power system,
output the AC power, and reversely supply the AC power to
the AC power system; and
an operation control part which performs a control so
that the DC-DC converter operates only when the input
voltage of the DC-DC converter falls within the
predetermined range;
wherein the power conditioner and the DC-DC converter
are connected in parallel to the DC power source, so that
the power conditioner and the DC-DC converter can be
simultaneously operated.
3. The power distribution system of claim 2, wherein the
predetermined range is equal to or narrower than an
operating voltage range of the power conditioner.
4. The power distribution system of claim 3, wherein the
operation control part controls the DC-DC converter to
operate after the lapse of a predetermined time period from
the time when the input voltage of the DC-DC converter
enters the operating voltage range.
5. The power distribution system of claim 2, wherein the
operation control part controls the DC-DC converter to
operate when an amount of variation in the input voltage of
the DC-DC converter per unit time is equal to or lower than
a predetermined value.
6. The power distribution system of claim 3, further
comprising:
a power failure detection unit which detects a power
failure of the AC power system;
wherein, when the power failure is detected by the
power failure detection unit, the operation control part
widens the predetermined range to a larger range than that
in a non-power failure situation and operates the DC-DC
converter.
7. The power distribution system of claim 2, further
comprising:
a power failure detection unit which detects a power
failure of the AC power system;
wherein, when the power failure is detected by the
power failure detection unit, the operation control part
stops operation of the DC-DC converter.
8 . The power distribution system of claim 3, wherein the
DC power source includes solar cells; and the operation
control part changes a setting of the operating voltage
range based on the number of the solar cells installed.
9. A DC power distribution apparatus comprising:
a DC-DC converter which converts a DC power outputted
from a DC power source into a DC power having a desired
voltage level and outputs the DC power, the DC-DC converter
being connected to the DC power source in parallel with a
power conditioner which converts the DC power outputted from
the DC power source into an AC power synchronized with a
phase of an AC power system and outputs the AC power, so
that the DC-DC converter can be operated simultaneously with
the power conditioner; and
an operation control part which controls the DC-DC
converter to operate only when an input voltage of the DC-DC
converter falls within a predetermined range.

ABSTRACT

A power distribution system includes a DC-DC converter
which outputs a DC power after converting the DC power
outputted from a DC power source to a desired voltage level.
In the power distribution system, the DC-DC converter is
controlled so as to operate only when the input voltage
falls in a predetermined range.