U.S. patent application number 09/842923 was filed with the patent office on 2001-11-01 for solar generation system.
Invention is credited to Kimura, Fumiya, Kodama, Hirokazu, Nakata, Hirofumi, Nishida, Kiyoshi, Takebayashi, Tsukasa.
Application Number | 20010035180 09/842923 |
Document ID | / |
Family ID | 26591135 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035180 |
Kind Code |
A1 |
Kimura, Fumiya ; et
al. |
November 1, 2001 |
Solar generation system
Abstract
A solar generation system includes a standard solar cell string
and a substandard solar cell string. A DC voltage output from the
substandard solar cell string is boosted by a booster unit to the
level of the DC voltage output from the standard solar cell string,
and the DC voltage from the standard solar cell string and the
boosted DC voltage are applied to a DC/AC inverter, whereby an AC
power is obtained, which is supplied to a utility power supply.
Inventors: |
Kimura, Fumiya; (Uji-shi,
JP) ; Nakata, Hirofumi; (Tenri-shi, JP) ;
Takebayashi, Tsukasa; (Yamatotakada-shi, JP) ;
Kodama, Hirokazu; (Gojo-shi, JP) ; Nishida,
Kiyoshi; (Yamatotakada-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
26591135 |
Appl. No.: |
09/842923 |
Filed: |
April 27, 2001 |
Current U.S.
Class: |
126/572 |
Current CPC
Class: |
Y10S 136/293 20130101;
H02J 7/35 20130101; Y02B 10/12 20130101; Y02B 10/14 20130101; Y10S
136/291 20130101; Y02B 10/20 20130101; Y02B 10/10 20130101; Y10S
323/906 20130101 |
Class at
Publication: |
126/572 |
International
Class: |
F24J 002/40 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2000 |
JP |
2000-129865(P) |
Jul 31, 2000 |
JP |
2000-230790(P) |
Claims
What is claimed is:
1. A solar generation system boosting a DC voltage output from a
solar cell and supplying the boosted DC voltage to an inverter
apparatus converting the boosted DC voltage to an AC power,
comprising: a standard solar cell string having a standard number
of solar cell modules connected in series; a substandard solar cell
string having solar cell modules smaller in number than said
standard number connected in series; a boosting circuit for
boosting a DC voltage output from said substandard solar cell
string to a DC voltage output from said standard solar cell string;
and an input connecting circuit supplying the DC voltage boosted by
said boosting circuit and the DC voltage output from said standard
solar cell string to said inverter apparatus.
2. The solar generation system according to claim 1, wherein said
boosting circuit boosts the DC voltage output from said substandard
solar cell string by a boosting voltage ratio determined by the
ratio between said standard number and the number smaller than said
standard number.
3. The solar generation system according to claim 2, further
comprising a switch for manually switching the boosting voltage
ratio of said boosting circuit.
4. The solar generation system according to claim 2, further
comprising a control circuit controlling said boosting circuit by
setting said boosting voltage ratio by pulse width modulation.
5. The solar generation system according to claim 1, comprising a
plurality of said substandard solar cell strings; wherein said
boosting circuit is provided for each of said plurality of
substandard solar cell strings, and boosts the DC voltage output
from the corresponding substandard solar cell string.
6. The solar generation system according to claim 1, wherein said
boosting circuit is provided detachable between said substandard
solar cell string and said input connecting circuit.
7. The solar generation system according to claim 1, wherein a
power supply voltage is supplied from said standard solar cell
string to said boosting circuit.
8. The solar generation system according to claim 1, wherein said
input connecting circuit includes a backflow preventing circuit
preventing backflow of a current from said boosting circuit to said
substandard solar cell string, an input connecting and
disconnecting circuit for connecting or disconnecting said
substandard solar cell string to and from said boosting circuit,
and a lightning surge preventing circuit for preventing entrance of
lightning surge from said substandard solar cell string to said
boosting circuit.
9. The solar generation system according to claim 1, further
comprising a voltage control circuit for performing control to keep
constant the boosting ratio, when output voltage from said boosting
circuit is lower than an upper limit set voltage.
10. The solar generation system according to claim 9, wherein said
voltage control circuit performs control to keep constant an upper
limit voltage, when the output voltage from said boosting circuit
is higher than the upper limit set voltage.
11. The solar generation system according to claim 9, wherein said
voltage control circuit changes said boosting ratio.
12. The solar generation system according to claim 1, wherein said
input connecting circuit includes a trip signal generating circuit
for generating a trip signal in response to an output voltage being
an overvoltage, and an opening/closing circuit responsive to the
trip signal from said trip signal generating circuit for opening
connection between said substandard solar cell string and said
input connecting circuit.
13. The solar generation system according to claim 12, wherein said
trip signal generating circuit generates the trip signal when said
boosting circuit is short-circuited, so that connection between
said substandard solar cell string and said input connecting
circuit is opened by said opening/closing circuit.
14. The solar generation system according to claim 13, wherein said
trip signal generating circuit outputs the trip signal when it is
detected that a short-circuit current flows to said boosting
circuit and temperature is increased.
15. The solar generation system according to claim 13, wherein said
trip signal generating circuit generates the trip signal when
output voltage of said boosting circuit exceeds a predetermined
input voltage range.
16. The solar generation system according to claim 1, wherein said
boosting circuit includes a fuse for intercepting short-circuit
current from an output side.
17. The solar generation system according to claim 16, wherein said
fuse is connected in series with said boosting circuit, and opens a
flow path of said short-circuit current in accordance with
magnitude of said short-circuit current.
18. The solar generation system according to claim 1, further
comprising a box to be placed outdoors, accommodating at least said
input connecting circuit, said box including a drainage path
guiding rain water to a lower portion when the rain water
penetrates, and a discharge outlet discharging the rain water
guided to the lower portion to the outside.
19. The solar generation system according to claim 18, further
comprising a radiator placed outside said box, for externally
generation of heat from said boosting circuit and said backflow
preventing circuit.
20. The solar generation system according to claim 19, further
comprising a metal plate covering the radiator of said box and
supporting said box on a wall surface.
21. The solar generation system according to claim 20, wherein said
box has a lid portion that can be opened/closed, and said input
connecting circuit is operated by opening said lid.
22. The solar generation system according to claim 1, further
comprising an indicator turned on when said boosting circuit is
driven and turned off when operation of said boosting circuit is
stopped.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a solar generation system.
More specifically, the present invention relates to a solar
generation system in which a DC power generated by an independent
DC power source such as a solar cell is boosted by a booster unit
and converted to an AC voltage by an inverter apparatus to supply
power to general AC load for home and office use, or to feed power
to existing utility power supply.
[0003] 2. Description of the Background Art.
[0004] A solar cell as a DC power source outputs a DC power when
there is high solar insolation. The DC power can be output solely
by the solar cell without using other energy source such as a
storage battery, and no poisonous substance is discharged.
Therefore, the solar cell has been known as a simple and clean
energy source.
[0005] FIG. 15 is a block diagram showing an example of a
conventional solar generation system. For simplicity of the
drawing, only two solar cell strings 1a and 1b are shown in the
solar generation system. It is needless to say that normally, a
larger number of solar cell strings are provided. Generally, one
standard solar cell string includes eight or nine solar cell
modules (not shown) connected in series with each other.
[0006] In the solar generation system, when the DC output power
from solar cell strings 1a and 1b is converted to an AC power and
interconnected to a utility power supply 4, it is necessary to
interpose a power conditioner 3 between the solar cell strings 1a,
1b and the utility power supply 4. When a plurality of solar cell
strings 1 are to be interconnected to the utility power supply 4,
the plurality of solar cell strings 1 are connected in parallel
with the power conditioner 3. Power conditioner 3 includes backflow
preventing diodes 50a and 50b, so as to prevent backflow of the
current generated by the plurality of solar cell strings 1
connected in parallel. The DC power that has passed through
backflow preventing diodes 50a and 50b is converted to an AC power
by a DC/AC inverter 60, and supplied through a protection circuit
70 to the utility power supply 4.
[0007] Conventionally, it is a common practice for the solar
generation system in Japan that a plurality of solar cell strings
included therein are placed on a main portion of a roof facing
southward, and lines from the solar cell strings are connected to
power conditioner 3.
[0008] When the solar cell strings are to be placed on the roof of
a house, sometimes it is difficult to configure solar cell strings
by arranging solar cell modules only that surface of the roof which
faces southward and receiving the most of the sunshine. Solar cell
modules that are positioned not on the southward surface of the
roof may be arranged on the eastward or westward surface of the
roof to form the solar cell strings. Sometimes, the solar cell
strings are configured by placing small size solar cell modules
arranged in the remaining peripheral regions after the solar cell
modules are placed on the main portion of the southward surface of
the roof. More specifically, sometimes the number of
series-connected solar cell modules included in some solar cell
strings is different from other solar cell strings. In such a case,
different output voltages result from different solar cell
strings.
[0009] For example, when a standard solar cell string including the
standard number of series-connected solar cell modules and a
substandard solar cell string including series-connected modules of
smaller than the standard number are connected in parallel to the
power conditioner 3, only the power from the standard solar cell
having the standard output voltage is input to power conditioner 3,
and the power from the substandard solar cell string having the
substandard output voltage lower than the standard output voltage
cannot be fed to the power conditioner 3. Even when the power from
the substandard solar cell string is adapted to be fed to power
conditioner 3, it is impossible to obtain the maximum output power
that is the sum of the maximum power from the standard solar cell
string and the maximum power from the substandard solar cell
string, as can be seen from FIGS. 16A and 16B.
[0010] Unless the power from such a substandard solar cell string
can be fed efficiently to power conditioner 3, the area occupied by
the substandard solar cell string would be wasted.
[0011] In the graphs of FIGS. 16A and 16B, the abscissa represents
output voltage V and the ordinate represents output power P. In the
graph of FIG. 16A, the curve S represents an output power from the
standard solar cell string, while the curve N represents the output
power from the substandard solar cell string. More specifically,
the standard solar cell string has the maximum output power Ps,
while the substandard solar cell string has the maximum output
power Pn. The output power that is the sum of these two output
powers is as shown in FIG. 16B. The maximum output power Psn of the
output power curve (S+N) shown in FIG. 16B is considerably smaller
than the sum (Ps+Pn) of the maximum output powers Ps and Pn shown
in FIG. 16A. The reason for this is that the voltage position for
the maximum output power Ps of the standard solar cell string 1a is
different from the voltage position of the maximum output power Pn
from the substandard solar cell string 1b.
[0012] In view of the foregoing, a possible solution is to adjust
output voltages from the plurality of solar cell strings. For this
purpose, an impedance may be interposed between standard solar cell
string 1a and power conditioner 3. This method, however, is not
practical, as the power is lost by the impedance. Another
possibility is to use MG (Motor Generator) method to change the DC
voltage. This method, however, is not preferable as mechanical
vibration or noise is generated and the motor generator itself is
bulky.
[0013] In the solar cell generation system disclosed in Japanese
Patent Laying-Open No. 8-46231, boosted type DC-DC converters 80a
and 80b having maximum power point tracking function are
incorporated in each solar cell module or in each solar cell
string, as shown in FIG. 17. Such a solar generation system is
disadvantageous in that the circuit structure becomes complicated
and in that voltage adjustment for the solar generation system as a
whole must be performed in the initial design stage of each solar
cell string having different output voltages.
[0014] In Japanese Patent Laying-Open No. 8-46231, an isolation
transformer is connected. This increases the weight of the system
and lowers power conversion efficiency. In case of a malfunction of
the boosting circuit caused by a surge, it will trouble a repair
person to climb on the roof and to exchange the solar cell
module.
SUMMARY OF THE INVENTION
[0015] Therefore, a main object of the present invention is to
enable interconnection of a plurality of solar cell strings having
different output voltages to a utility power supply in a simple
manner, and to enable efficient use of the maximum output power of
the solar cell strings.
[0016] Briefly stated, the present invention relates to a solar
generation system in which a DC voltage output from a solar cell is
boosted, and the boosted DC voltage is supplied to an inverter
apparatus converting the DC voltage to an AC power, including a
standard solar cell string having a standard number of solar cell
modules connected in series, a substandard solar cell string having
solar cell modules smaller in number than the standard number
connected in series, a boosting circuit for boosting the DC voltage
output from the substandard solar cell string to a DC voltage
output from the standard solar cell string, and an input connecting
circuit for supplying the DC voltage boosted by the boosting
circuit and the DC voltage output from the standard solar cell
string to the inverter apparatus.
[0017] Therefore, according to the present invention, as the DC
voltage from the substandard solar cell string is increased to the
DC voltage of the standard solar cell string, interconnection to
the utility power supply is possible in a simple manner, and the
sum of the maximum outputs from respective solar cell strings can
be used as the final maximum output power.
[0018] More preferably, the boosting circuit boosts the DC voltage
output from the substandard solar cell string at a boosting voltage
ratio determined by the ratio between the standard number and the
number smaller than the standard number.
[0019] More preferably, the system includes a switch for manually
switching the boosting voltage ratio of the boosting circuit.
[0020] More preferably, the system includes a control circuit for
controlling the boosting circuit by setting the boosting voltage
ratio by pulse width modulation.
[0021] More preferably, a plurality of substandard solar cell
strings are provided, and boosting circuits are provided for
respective ones of the plurality of substandard solar cell strings,
for boosting the DC voltage output from the corresponding one of
the substandard solar cell strings.
[0022] More preferably, the boosting circuit is provided detachably
between the substandard solar cell strings and the input connecting
circuit.
[0023] More preferably, a power supply voltage is supplied to the
boosting circuit from the substandard solar cell string.
[0024] More preferably, the input connecting circuit includes a
backflow preventing circuit for preventing backflow of the current
from the side of the boosting circuit to the substandard solar cell
string, an input connecting/disconnecting circuit for connecting or
disconnecting the substandard solar cell string and the boosting
circuit, and a lightning surge preventing circuit for preventing
entrance of lightning surge from the substandard solar cell string
to the side of the boosting circuit.
[0025] More preferably, the system includes a voltage control
circuit performing control to keep constant the boosting ratio,
when the output voltage of the boosting circuit is lower than an
upper limit set voltage.
[0026] More preferably, when the output voltage of the boosting
circuit is higher than the upper limit set voltage, the voltage
control circuit performs control to keep constant the upper limit
voltage.
[0027] More preferably, the voltage control circuit changes the
boosting ratio.
[0028] More preferably, the input connecting circuit includes a
trip signal generating circuit generating a trip signal when the
output voltage attains to an over voltage, and a breaker opening
the connection between the substandard solar cell string and the
input connecting circuit in response to the trip signal from the
trip signal generating circuit.
[0029] More preferably, the trip signal generating circuit opens
connection between the substandard solar cell string and the input
connecting circuit by means of the breaker, by generating the trip
signal, when there is a short-circuit in the boosting circuit.
[0030] More preferably, the trip signal generating circuit outputs
a trip signal when it is detected that a short-circuit current
flows in the boosting circuit and the temperature is increased.
[0031] More preferably, the trip signal generating circuit
generates the trip signal when the output voltage of the boosting
circuit exceeds a predetermined input voltage range.
[0032] More preferably, the boosting circuit includes a fuse for
intercepting the short-circuit current from an output side.
[0033] More preferably, the fuse is connected in series with the
boosting circuit, and opens the path of the short-circuit current,
in accordance with the magnitude of the short-circuit current.
[0034] More preferably, the system includes a box placed outdoors,
housing at least the input connecting circuit, and the box includes
a drainage to guide rain water to a lower portion when rain water
enters, and an outlet opening for discharging the rain water guided
to the lower portion.
[0035] More preferably, a radiator is provided outside the box, for
generation of heat from the boosting circuit and the backflow
preventing circuit.
[0036] More preferably, the system includes a metal plate covering
the radiator of the box and supporting the box on a wall
surface.
[0037] More preferably, the box has a lid that can be
opened/closed, and the input connecting circuit is operated with
the lid opened.
[0038] More preferably, the system includes an indicator which is
turned on when the boosting circuit is driven, and which is turned
off in response to the stop of operation of the boosting
circuit.
[0039] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a schematic block diagram representing the solar
generation system in accordance with an embodiment of the present
invention.
[0041] FIGS. 2A and 2B are graphs representing output powers of a
standard solar cell string and a substandard solar cell string and
an output power provided when the output powers are connected in
parallel.
[0042] FIG. 3 is a block diagram showing a specific example of the
booster unit included in the solar generation system shown in FIG.
1.
[0043] FIG. 4 is a circuit diagram showing a specific example of
the boosting circuit included in the booster unit.
[0044] FIG. 5 shows a connection switch for manually determining
the boosting voltage ratio in the booster unit.
[0045] FIG. 6 is a block diagram representing a circuit for
controlling the switching device in the boosting circuit.
[0046] FIGS. 7A and 7B are graphs representing comparison between
the triangular wave and the setting signal, and the gate pulse
signal driving the switching device.
[0047] FIG. 8 is a block diagram of the booster unit in accordance
with one embodiment of the present invention.
[0048] FIG. 9 is a block diagram of a control circuit in the
booster unit shown in FIG. 1.
[0049] FIGS. 10A to 10C are waveform diagrams of various portions
of the control circuit.
[0050] FIGS. 11A to 11F are waveform diagrams of various portions
of the control circuit.
[0051] FIGS. 12A to 12C show the appearance of the box housing the
booster unit in accordance with one embodiment of the present
invention.
[0052] FIGS. 13A and 13B show internal structure of the box shown
in FIGS. 12A to 12C.
[0053] FIGS. 14A and 14B represent the structure of the lid of the
box shown in FIGS. 12A to 12C.
[0054] FIG. 15 is a block diagram representing a conventional solar
generation system.
[0055] FIGS. 16A and 16B are graphs representing the output powers
of the standard solar cell string and the substandard solar cell
string shown in FIG. 15 and the output power when the output powers
are connected in parallel.
[0056] FIG. 17 is a block diagram illustrating a method of
detecting an output voltage of a standard solar cell string and
generating a boosting voltage ratio corresponding thereto in the
booster unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] FIG. 1 is a block diagram of the solar generation system in
accordance with an embodiment of the present invention. In the
solar generation system, for simplicity of the drawing, only one
standard solar cell string 1a and one substandard solar cell string
1b are shown. It is needless to say that there may be larger number
of solar cell strings. Generally, standard solar cell string 1a
includes eight or nine solar cell modules (not shown). The
substandard solar cell string 1b includes solar cell module smaller
in number than the standard solar cell string 1a.
[0058] The output power of standard solar cell string 1a is
supplied to a DC/AC inverter 60 through a backflow preventing diode
50a included in power conditioner 3. The output power of
substandard solar cell string 1b is supplied to DC/AC inverter 60
through a booster unit 2 and a backflow preventing diode 50b. In
power conditioner 3, output powers from the plurality of backflow
preventing diodes 50a are put together and supplied to DC/AC
inverter 60. The AC output power from DC/AC inverter is supplied to
a utility power supply 4 through a protection circuit 70.
[0059] In the solar generation system such as shown in FIG. 1, the
output voltage of substandard solar cell string 1b is made equal to
the output voltage of standard solar cell string 1a by booster unit
2. Therefore, as can be seen from FIGS. 2A and 2B, the maximum
output power that is the sum of the maximum output power of
standard solar cell string 1a and the output power from substandard
solar cell string 1b is supplied to utility power supply 4.
[0060] Referring to FIGS. 2A and 2B, the abscissa represents an
output voltage V and the ordinate represents the output power P.
The curve S represents the output power from standard solar cell
string 1a, and the curve Nm represents the output power after the
output power of substandard solar cell string 1b is boosted by
booster unit 2. As can be seen from the graph of FIG. 2B, the
voltage position of the maximum output Pn of substandard solar cell
string 1a boosted by booster unit 2 is the same as that voltage
position of maximum output power Ps from the standard solar cell
string. Therefore, when the output powers S and Nm are added, the
output power curve will be S+Nm as shown in the graph of FIG. 2B,
and thus, maximum output power (Ps+Pn) can be obtained.
[0061] In this manner, by the solar generation system in accordance
with one embodiment of the present invention, by a simple method of
providing a booster unit 2 between the substandard solar cell
string 1b and power conditioner 3, the maximum output power (Ps+Pn)
that is the sum of the maximum output power Ps from the standard
solar cell string 1a and the maximum output power Pn from the
substandard solar cell string 1b can be supplied to the utility
power supply. Further, the booster unit 2 is easily detachable, and
therefore, when the substandard solar cell string 1b is changed to
a standard solar cell string 1a, the unit can be detached.
[0062] FIG. 3 is a schematic block diagram showing a specific
example of booster unit 2 shown in FIG. 1. Booster unit 2 includes,
in the order from an input terminal 21 at an input portion, an
input EMI (Electro Magnetic Interference) filter 22, a breaker 23,
a boosting circuit 24, an output EMI filter 25 and an output
terminal 26. Output terminal 26 is connected to an input terminal
of power conditioner 3.
[0063] The boosting ratio of boosting circuit 24 may be determined
by the ratio of series-connected solar cell modules in the standard
solar cell string 1a and the substandard solar cell string 1b.
Thus, the circuit configuration of boosting circuit 24 in booster
unit 2 is very simple. Further, a complicated control such as shown
in FIG. 17, in which a DC/DC converter 80b adjusts output voltage
of substandard solar cell string 1b using the output voltage of
standard solar cell string 1a as a reference voltage so that the
output voltage of substandard solar cell string 1b is made equal to
the output voltage of standard solar cell string 1a, is
unnecessary.
[0064] FIG. 4 is a circuit diagram showing a specific example of
boosting circuit 24 included in booster unit 2. In boosting circuit
24, a reactor 101 and a diode 102 are connected in series, a
capacitor 103 is connected between the cathode of diode 102 and the
ground, and a switching device 104 is connected between the anode
of diode 102 and the ground. As switching device 104, a BJT
(Bipolar Junction Transistor), an FET (Field Effect Transistor), an
IGBT (Insulated Gate Bipolar Transistor) or a GTO (Gate Turn Off
thyrister) may be used.
[0065] When switching device 104 is on, in the boosting circuit 24,
energy is stored in the reactor as current flows to reactor 101.
When the switching device 104 is turned off, the energy stored in
reactor 101 is changed to a current, which charges capacitor 103
through diode 102. When switching device 104 is again turned on,
energy is stored in reactor 101, and when switching device 104 is
turned off, the energy of reactor 101 is changed to a current, and
a voltage derived from the current is superposed on the voltage
charged to the capacitor 103, whereby the boosting is attained.
[0066] FIG. 5 schematically shows switches for determining the
boosting ratio. In this example, the boosting ration can be
determined by manually switching the switches. More specifically,
solar cell modules of the same type having the same characteristics
are generally used in the solar generation system. Therefore, the
voltage ratio between the standard solar cell string 1a and the
substandard solar cell string 1b, that is, the boosting ratio, can
be determined by a simple fixed integer ratio such as 8:4 to 8:7 or
9:4 to 9:7.
[0067] Therefore, when the boosting voltage ratio is to be set,
first, the number n.sub.1 (8 or 9) of the solar cell modules
included in standard solar cell string 1a is set by a switch 27a,
and then, the number n.sub.2 (4 to 7) of the solar cell modules
included in the substandard solar cell string 1b is set by a switch
27b. By manually operating these two switches 27a and 27b, the
output voltage of booster unit 2 is set to n.sub.1/n.sub.2 times
the output voltage of substandard solar cell string 1b connected
thereto, and hence the output voltage becomes equal to the output
voltage of standard serially connected solar cell string 1a.
[0068] FIG. 6 is a block diagram representing a control circuit
used when boosting circuit 24 is driven by PWM (Pulse Width
Modulation) control, and FIGS. 7A and 7B are waveform diagrams at
various portions of FIG. 6.
[0069] For the boosting voltage ratio set by the boosting ratio
setting unit 114 including switches 27a and 27b shown in FIG. 5, a
signal set value is calculated in accordance with the following
equation (1), by a signal setting operation unit 115.
(Signal Setting Value)=(set value of switch 27b)/(set value of
switch 27a) (1)
[0070] Referring to FIG. 7A, the signal set value M resulting from
the operation by signal setting operation unit 115 and a triangular
wave T having an amplitude value of 0 to 1 oscillated by a
triangular wave generating unit 116 are compared by a signal
comparing unit 117. When the signal set value M is smaller than the
triangular wave T, signal comparing unit 117 outputs a gate ON
level, and when the signal set value M is larger than the
triangular wave T, the comparing unit outputs a gate OFF level. As
a result, signal comparing unit 117 provides the pulse signal PS
shown in FIG. 7B. The ratio between the period of pulse signal PS
and the pulse width time (duty ratio) is represented by the
following equation (2).
(Duty Ratio)=1-(signal set value) (2)
[0071] The pulse signal PS is input to a gate drive unit 118 for
boosting circuit 24, and gate drive unit 118 drives switching
device 104 shown in FIG. 4. By utilizing such a method of boosting
under PWM control, the boosting circuit 24 can be realized in a
simple structure.
[0072] In order to drive booster unit 2, a power source therefor is
necessary. When a battery that can provide output constantly such
as a dry battery or a storage battery is used, booster unit will be
in operation night and day, if there is no power switch provided.
When the battery runs down, battery exchange is necessary. Further,
in order to obtain power for booster unit 2 from utility power
supply 4, a separate interconnection becomes necessary. When the
energy from the substandard solar cell string 1b connected to
booster unit 2 itself is used as the driving energy, booster unit
will operate only in the day time when substandard solar cell
string 1b is in operation, and the operation is automatically
stopped at night. Further, the solar cell never runs down, and
therefore, unlike a dry battery or a storage battery that is
drained, exchange is unnecessary. Further, interconnection from an
external power source is unnecessary.
[0073] As described above, according to the embodiment, in a solar
generation system including standard solar cell string 1a as well
as substandard solar cell string 1b, interconnection to the utility
power supply can be established in a simple manner, and a sum of
the maximum outputs from respective solar cell strings can
eventually be utilized as the maximum output power.
[0074] FIG. 8 shows a solar generation system including the booster
unit and the inverter apparatus in accordance with another
embodiment of the present invention.
[0075] Referring to FIG. 8, standard solar cell string 1a and
substandard solar cell string 1b are connected to booster unit, and
respective output powers are input to booster unit 2. Booster unit
2 is further connected to DC/AC inverter 60, and DC/AC inverter 60
converts the DC power output from booster unit 2 to an AC power
having the same phase and the frequency 50/60 Hz as the utility
power supply 4, and supplies it to the utility power supply 4.
[0076] Booster unit 2 includes a boosting apparatus 3, a control
circuit 15, a trip signal generating unit 28, backflow preventing
diodes 6a, 6b, lightning surge absorbers 7a, 7b and input breakers
8a and 8b.
[0077] Backflow preventing diodes 6a and 6b prevent backflow of the
DC current from booster unit 2 to solar cell strings 1a and 1b.
Lightning surge absorbers 7a and 7b prevent entrance of lightning
surge from solar cell strings 1a, 1b to booster unit 2. Input
breakers 8a and 8b connect and disconnect solar cell string 1a, 1b,
to and from booster unit 2.
[0078] Boosting apparatus 3 includes a reactor 9, a switching
device 10, a diode 11, a capacitor 13, a fuse 12 and a temperature
sensor 14. Reactor 9 stores and discharges energy of the DC power
input to booster unit 2. Switching device 10 switches on/off, in
accordance with a high frequency control output from control
circuit 15. Capacitor 13 stores the energy discharged from reactor
9 when switching device 10 turns off. Fuse 12 opens the circuit
when a current higher than a set value flows. Temperature sensor 14
monitors the temperature of switching device 10, and provides its
output to trip signal generating unit 28. An output voltage Vout of
booster unit 2 and a temperature signal Ts of temperature sensor 11
are applied to trip signal generating unit 28, and when the output
voltage Vout attains a voltage higher than a predetermined voltage,
trip signal generating unit 28 outputs a trip signal Tp for
tripping input breakers 8a and 8b.
[0079] FIG. 9 is a specific block diagram of control circuit 15
shown in FIG. 8. Referring to FIG. 9, control circuit 15 includes
an initial boosting ratio setting unit 16, an effective boosting
ratio setting unit 17, a boosting ratio comparing unit 18, a signal
setting operation unit 19, a triangular wave generating unit 20, a
signal comparing unit 21, a voltage comparing unit 22, a signal
setting operation unit 23, a triangular wave generating unit 24, a
signal comparing unit 25, an AND operating unit 26 and a gate drive
unit 27.
[0080] Initial boosting ratio setting unit 16 sets the ratio
between the number n1 of the solar cell modules included in
standard solar cell string 1a and the number n2 of the solar cell
modules included in substandard solar cell string 1b, that is,
boosting ratio .alpha.1 (=n1/n2). Effective boosting ratio setting
unit 17 sets for every sampling, the effective boosting ratio
.alpha.2 (=Vout1/Vin), from the input voltage Vin to the booster
unit 2 and the output voltage Vout1.
[0081] Initial boosting ratio .alpha.1 obtained from initial
boosting ratio setting unit 16 and the effective boosting ratio
.alpha.2 obtained from effective boosting ratio setting unit 17 are
compared by boosting ratio comparing unit 18, an error therebetween
is amplified and output to signal setting operation unit 19.
[0082] FIGS. 10A to 10C and 11A to 11F are waveform diagrams of the
control circuit in the booster unit shown in FIG. 9. Referring to
FIG. 10A, the signal set value Ma obtained by signal setting
operation unit 19 and the triangular wave Ta having the amplitude
value from 0 to 1 generated by triangular wave generating unit 20
are compared by the signal comparing unit 21, and when the signal
set value Ma is larger than the triangular wave Ta, signal
comparing unit 21 performs PWM control, providing gate OFF level.
As a result, signal comparing unit 21 provides a pulse signal
PSa.
[0083] Further, a preset voltage Vref1 and the output voltage Voutl
of booster unit 2 are input at every sampling and compared by
voltage comparing unit 22. The result is output to signal setting
operation unit 23. Further, referring to FIG. 10, a signal set
value Mb obtained at signal setting operation unit 23 and a
triangular wave Tb having an amplitude value from 0 to 1 generated
by triangular wave generating unit 24 are compared by signal
comparing unit 25, and when the signal set value Mb is larger than
the triangular wave Tb, signal comparing unit 25 performs PWM
control to output the gate OFF level.
[0084] As a result, signal comparing unit 5 provides a pulse signal
PSb. The pulse signals PSa and PSb are input to AND operating unit
26, and an AND operation is performed. As a result, a pulse signal
PSc is generated as shown in FIG. 10C. The pulse signal PSc is
input to gate drive unit 27 for switching device 10.
[0085] The operation of booster unit 2 structured as above is as
follow. As already described, booster unit 2 boosts the input
voltage based on the boosting ratio .alpha.(=n1/n2) determined from
the number n1 of the solar cell module in the standard solar cell
string 1a and the number n2 of solar cell modules in substandard
solar cell string 1b, and an output voltage therefrom is supplied
to DC/AC inverter 60. When the output voltage of booster unit 2 is
within the tolerable input voltage range of DC/AC inverter 60,
booster unit 2 performs such a control that makes constant the
boosting ratio. More specifically, control circuit 15 outputs the
pulse signal PSa (FIG. 10A) providing the gate OFF level, based on
the triangular wave Ta and the signal set value Ma obtained from
initial boosting ratio .alpha.1 and the effective boosting ratio
.alpha.2, to AND operating unit 26.
[0086] At this time, as the output voltage Voutl of booster unit 2
is within the input voltage range Vref1 of DC/AC inverter 60
(Vout1<Vref1), voltage comparing unit 22 has the signal set
value Mb having the amplitude value of 0 as an output of signal
setting operation unit 23 input to signal comparing unit 25. Then,
PWM control based on the triangular wave Tb and signal set value Mb
takes place in signal comparing unit 25, and a pulse signal PSb
having the pulse width of 1 such as shown in FIG. 11A is output to
AND operating unit 26. As the pulse signal PSb has the pulse width
1, a pulse signal PSc which is similar to pulse signal PSa is
output to gate drive unit 27 as a result of AND operation, as shown
in FIG. 11B. At this time, the target of control is to make
constant the boosting ratio.
[0087] When the DC/AC inverter 60 connected to the output side of
booster unit 2 is not in operation, there is no load on booster
unit 2, and therefore, when booster unit 2 performs the boosting
operation, the output voltage of booster unit 2 exceeds the
tolerable input voltage range of DC/AC inverter 60. Therefore, when
the output voltage of booster unit 2 is higher than the tolerable
input voltage range of DC/AC inverter 60, booster unit 2 performs
constant voltage control in which the boosting ratio .alpha. is
varied to be smaller so that the output voltage of booster unit 2
is within the tolerable input voltage range of DC/AC inverter
60.
[0088] More specifically, as the output voltage Voutl of booster
unit 2 is higher than the input voltage range Vref1 of DC/AC
inverter 60 (Vout 1>Vref1), in the control circuit 15, voltage
comparing unit 22 has the signal setting operation unit 23 provide
the signal set value Mb having the amplitude value not larger than
1 but larger than 0 (for example 0.1) to signal comparing unit 25.
Signal comparing unit 25 compares the triangular wave Tb with the
signal set value Mb, performs PWM control, and the pulse signal PSb
shown in FIG. 11D is output to AND operating unit 26.
[0089] At this time, if the pulse width of pulse signal PSb is
larger than the pulse signal PSa as shown in FIG. 11D, a pulse
signal PSc similar to pulse signal PSa is output to gate drive unit
27 as a result of the AND operation. In this state, the output
voltage Vout1 of booster unit 2 is higher than the input voltage
range Vref1 of DC/AC inverter 60 (Vout1>Vref1), voltage
comparing unit 22 has the signal setting operation unit 23 input
the signal set value Mb of the value larger than the last amplitude
value, to signal comparing unit 25. The triangular wave Tb and the
signal set value Mb are compared by signal comparing unit 25 and
PWM control is performed. In this manner, pulse signal PSb is input
from signal comparing unit 25 to AND operating unit 26.
[0090] As a result, a pulse signal PSb having such a pulse width as
shown in FIG. 11D is input to the AND operating unit 26, and when
the pulse width of pulse signal PSb is smaller than the pulse
signal PSa, AND operating unit 26 outputs a pulse signal PSc
similar to the pulse signal PSb to gate drive unit 27 as shown in
FIG. 11F. As a result, the control is switched from the control to
keep boosting ratio constant to the control in which the boosting
ratio .alpha. is made smaller, that is, to a constant voltage
control by which the output voltage of booster unit 2 is set within
the tolerable input voltage range of DC/AC inverter 60. At this
time, control target is to make constant the output voltage.
[0091] When the output voltage exceeds the input voltage range of
DC/AC inverter 60 while the booster unit 2 performs the constant
voltage control, that is, even when the boosting ratio a is made
smaller and an overvoltage state occurs as it is impossible to
further reduce the boosting ratio .alpha., the input breaker 8b is
tripped, so that a line to the solar cell string 1b is opened. More
specifically, trip signal generating unit 28 monitors the output
voltage Vout2 as shown in FIG. 8. When the output voltage Vout2
becomes larger than a preset tolerable input voltage range Vref2 of
DC/AC inverter 60 (Vref1<Vref2) (Vout2>Vref2), a trip signal
Tp is sent from trip signal generating unit 28 to input breaker 8b,
and input breaker 8b is tripped, opening the path to the solar cell
string 1b.
[0092] When switching device 10 is short-circuited, short-circuit
current flows between solar cell string 1b and switching device 10.
When the short-circuit current flows, the temperature of switching
device 10 increases. If the short-circuit current flows
continuously, the temperature of switching device 10 will be much
increased, possible resulting in malfunction of booster unit 2.
Therefore, trip signal generating unit 28 monitors the temperature
Ts of switching device 10 through a temperature sensor 29 attached
to switching device 10. When a set temperature is reached, trip
signal generating unit 28 transmits an input breaker trip signal Tp
to trip input breaker 8b, so that the path to the solar cell string
1b is opened. In this manner, continuous flow of the short-circuit
can be intercepted.
[0093] When a short-circuit current flows on the output side of
booster unit 2, that is, to the side of DC/AC inverter 60,
malfunction of switching device 10 or the like is possible.
Therefore, fuse 12 provided in the preceding stage of capacitor 13
in boosting apparatus 3 is blown off, preventing continuous flow of
the short-circuit current.
[0094] As switching device 10 of booster unit 2 shown in FIG. 8, an
FET (Field Effect Transistor), an IGBT (Insulated-Gate Bipolar
Transistor) or the like may be used. Control circuit 15 may be
implemented by an analog circuit or a digital circuit.
[0095] FIGS. 12A to 12C show appearance of the box containing the
booster unit in accordance with one embodiment of the present
invention. FIG. 12A is a front view, 12B is a side view and 12C is
a bottom view. FIGS. 13A and 13b show internal structure of the box
shown in FIGS. 12A to 12C. FIG. 13A is a front view with the cover
of FIG. 12B removed, and FIG. 13B is a bottom view. FIGS. 14A and
14B show the structure of the lid member shown in FIG. 12A. FIG.
14A is a front view of the lid, and FIG. 14B is a cross section
showing how the lid is attached.
[0096] Box 30 shown in FIGS. 12A to 12C accommodates booster unit 2
shown in FIG. 8 and, as shown in FIG. 12B, the box is placed
vertically along a wall surface 40 outdoors. Box 30 includes a body
portion 31 and a cover 32 covering the same. As shown in FIG. 13A,
a barrier portion 33 serving as a drainage path is formed along the
top and side surfaces in the body portion 31. Barrier portion 33
guides rain water penetrating between body portion 31 and cover 32
to a lower portion of body portion 31, and discharges the water to
the outside through a rain outlet 34 as a discharge outlet, formed
at the lower portion of body portion 31. Thus, conductive portions
of boosting apparatus 3 and control circuit 15 accommodated in the
body 30 placed outdoors are protected from rain water.
[0097] On the lower portion (right side of FIG. 12B) of body
portion 31 of box 30, a heat sink 35 is attached. On heat sink 35,
switching device 10 in boosting apparatus 3 and backflow preventing
diodes 6a and 6b shown in FIG. 8 are attached, so that heat
generated by the loss of switching device 10 in boosting apparatus
3 and by backflow preventing diodes 6a and 6b can be radiated to
the outside, and thus radiation effect is improved.
[0098] Further, a metal plate 41 having a rectangular shape with
one side opened is provided surrounding the heat sink 35. Inside
the metal plate 41, a hook 42 is formed to hold the body portion
31. As metal plate 41 is attached to wall surface 40 and body
portion 31 is held by hook 42, box 30 can be attached in the
vertical direction along the wall surface 40. Metal plate 41 is
formed to cover heat sink 35, so as to prevent burning by
accidentally touching the heat sink 35 which is heated by the heat
generated by the loss from backflow preventing diodes 6a and 6b as
well as switching device 10 when boosting apparatus 3 is in
operation.
[0099] There is an indicator unit 36 at the central portion of
cover 32 of box 30. When boosting apparatus 3 is activated,
indicator unit 36 is turned on, and when the operation of the
apparatus stops, it turns off. Thus, whether booster unit 2 is in
operation in the day time with much sunlight or not can be
confirmed without the necessity to open the body of booster unit 2.
For example, if the indicator unit is off in the day time, it can
be noticed that boosting apparatus 3 is not in operation.
Therefore, whether booster unit 2 operates normally or not can be
confirmed by the indicator unit 36.
[0100] Further, a lid portion 37 is provided at a lower portion of
cover 32 to cover an opening portion. When removed from body 31,
the lid portion 37 allows operation of input breakers 8a and 8b
mounted on the body 31, as shown in FIG. 13A. An attachment rail
portion 38 is formed on one side of lid portion 37 as shown in FIG.
14A, and a fitting 39 is attached on the other side. A water proof
member 45 such as rubber is adhered at the contact portion between
lid portion 37 and body 31.
[0101] Fitting 39 has a fixing plate 391 and knob 392. When knob
392 is rotated, fixing plate 391 rotates and by this operation, it
is possible to attach and detach the lid portion 37 to and from the
body of booster unit 2. When lid portion 37 is opened, it is
possible to operate input breakers 8a and 8b. Therefore, without
the necessity to open the body of booster unit 2, input breakers 8a
and 8b can be operated from the outside simply by opening lid
portion 37. Further, no screw is used at the lid portion 37.
Therefore, it is unnecessary to use a special tool to remove lid
portion 37 from box 30. Therefore, it is possible to easily
disconnect booster unit 2 and solar cell 1b or DC/AC inverter 60 in
case of emergency, for example, and therefore safety of the overall
system can be improved.
[0102] As described above, according to the present embodiment, a
space for installation dedicated for interconnection inside and
outside of a building is saved as regards the connection between
the DC power source such as solar cell strings 1a and 1b with the
booster unit 2 and the DC/AC inverter 60, the dedicated box 30 is
integrated to reduce the cost of the overall apparatus, appearance
inside and outside of the building is not spoiled as lines and
wires for interconnection are reduced. Further, when booster unit 2
is in operation, overvoltage to DC/AC inverter 60 is prevented and
generation of a short-circuit current in case of malfunction or
short circuit of switching device 10 can be intercepted, thus a
safe apparatus is realized.
[0103] Further, a boosting circuit boosting the DC power voltage, a
backflow preventing circuit preventing backflow of current from the
boosting means to the DC power source, an input
connecting/disconnecting unit for connecting or disconnecting the
DC power source to and from the boosting circuit, and a lightning
surge preventing circuit preventing entrance of lightning surge
from the DC power source to the boosting circuit are provided, so
that backflow of current from the boosting apparatus and the
inverter apparatus to the solar cell can be prevented and it is
possible to safely connect or disconnect the solar cell and the
boosting circuit and the boosting circuit and the inverter
apparatus, at the time of engineering work, for example.
[0104] Further, entrance of lightning surge from the solar cell
side to the boosting circuit and the inverter apparatus in case of
thunderbolt can be prevented, and therefore safety of the inverter
apparatus is ensured. Further, a DC power having the same DC
voltage as that of standard solar cell string can be supplied even
from a substandard solar cell string to the inverter apparatus, and
therefore limited space of a building roof, for example, can be
efficiently used.
[0105] Further, when the output voltage of the booster unit is
lower than the upper limit set voltage, boosting circuit performs
the control to make constant the boosting ratio, so that a DC power
comparable to that of a standard solar cell string can be supplied
from a substandard solar cell string to the inverter apparatus.
Therefore, a limited space of a building roof, for example, can be
efficiently utilized.
[0106] Further, when the output voltage of the booster unit is
higher than the upper limit set voltage, the boosting circuit
performs control to make constant the upper limit voltage, and
therefore overvoltage to the inverter apparatus possibly causing a
malfunction can be prevented.
[0107] When the boosting circuit is in operation in the day time
with high amount of sunshine, control is performed to make constant
the boosting ratio, and when the output voltage increases to be
higher than the upper limit set voltage, the control to keep
constant the boosting ratio is stopped and control is performed to
keep constant the upper limit voltage by changing the boosting
ratio, so that the output voltage does not exceed the upper limit.
In this manner, overvoltage to the inverter apparatus possibly
causing a malfunction can be prevented.
[0108] Further, trip signal generating circuit generates a trip
signal when the output voltage becomes excessive, so that
connection to the substandard solar cell string is opened by the
opening circuit. While the booster unit is in operation in the day
time with high amount of sunshine and control is performed to keep
constant the boosting ratio or keep constant the voltage, the trip
signal generating circuit trips and opens the circuit when an
overvoltage is detected by the boosting circuit. Therefore, over
voltage to the inverter apparatus possibly causing a malfunction
can be prevented.
[0109] As to the trip function in the breaker, when the booster
unit is in operation in the day time with high amount of sunshine,
boosting circuit is short-circuited, a short-circuit current flows
between the solar cell and the boosting circuit and the temperature
of the boosting circuit increases, then the trip signal generating
circuit generates a trip signal to open the circuit when the
temperature increase is larger than the set value. Consequently,
continuous flow of the short-circuit current is prevented, and
hence malfunction of the booster unit caused by the short-circuit
current can be prevented.
[0110] The boosting circuit includes a fuse for intercepting the
short-circuit current from the output side. Therefore, when the
inverter apparatus is short-circuited, the short-circuit current
flows from the inverter apparatus to the booster unit and the
short-circuit current flows in the circuit, the fuse operates to
open the circuit and prevents continuous flow of the short-circuit
current. Therefore, malfunction of the booster unit caused by the
short-circuit current can be prevented.
[0111] The fuse is connected in series with the boosting circuit,
and the path through which the short-circuit current flows is
opened in accordance with the magnitude of the short-circuit
current. Therefore, when the inverter apparatus is short-circuited
and the short-circuit current flows from the inverter apparatus to
the booster unit and the short-circuit current flows in the
circuit, the fuse provided in the boosting circuit is blown off,
opening the circuit. Thus, continuous flow of the short-circuit
current can be prevented, and malfunction caused by the
short-circuit current can be prevented.
[0112] Further, at least the input/output terminal is accommodated
in a box placed outdoors, and the box includes a drainage path
guiding the rain water to the lower portion when the rain water
penetrates and a discharge outlet for discharging the rain water
guided to the lower portion to the outside. Therefore, entrance of
the rain water to the conductive portions of the inverter apparatus
and the control circuit can be prevented. Further, as a dedicated
box is formed integrally, the cost of the overall apparatus can be
reduced.
[0113] Further, a radiator for generation of heat from the boosting
circuit and the backflow preventing circuit to the outside is
provided on the outside of the box. Thus, the effect of radiation
can be enhanced.
[0114] Further, as a metal plate covering the radiator of the box
and supporting the box on the wall surface is provided, possibility
of burning by accidentally touching the radiator can be prevented
and the box can be attached on a wall surface.
[0115] Further, a lid portion that can be opened is provided on the
box, and by operating the input connecting/disconnecting unit with
the lid opened, it is possible to separate the booster unit from
the DC power source in case of emergency.
[0116] Further, an indicator means that turns off when the boosting
circuit is driven and turns off when the operation of the boosting
circuit stops is provided on the box. Therefore, it can be readily
confirmed whether the boosting circuit is normally operating or
not.
[0117] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *