1
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
PHOTOVOLTAIC POWER GENERATION DRIVE SYSTEM AND METHOD FOR
CONTROLLING PHOTOVOLTAIC POWER GENERATION DRIVE SYSTEM
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
PHOTOVOLTAIC POWER GENERATION DRIVE SYSTEM AND METHOD FOR
CONTROLLING PHOTOVOLTAIC POWER GENERATION DRIVE SYSTEM
5
Field
[0001] The present invention relates to a photovoltaic
power generation drive system that drives a load by using
electric energy derived from power generated by a solar
10 panel, and a method for controlling the photovoltaic power
generation drive system.
Background
[0002] A photovoltaic power generation drive system that
15 drives a motor as a load controls the output power of a
solar panel so as to stably continue to drive the motor, by
adjusting the rotation speed of the motor so that the
output power of the solar panel is equal to or greater than
a maximum power point of the solar panel. The maximum
20 power point changes due to an environmental change such as
a change in the amount of sunlight or a change in
temperature at a location where the solar panel is
installed. When solar output power falls below the maximum
power point, the motor will malfunction. The solar output
25 power refers to the output power of the solar panel.
[0003] Patent Literature 1 discloses adjusting the
output voltage of a solar panel so that the output voltage
of the solar panel exceeds a voltage of a maximum power
point by estimating a margin of solar output power with
30 respect to the maximum power point based on changes in the
output voltage of the solar panel in the case of repeatedly
changing the rotation speed of a motor. According to the
technique of Patent Literature 1, a photovoltaic power
3
generation drive system can reduce malfunctions of the
motor even when the solar output power continuously changes
due to environmental changes, by maintaining a state in
which the output voltage of the solar panel exceeds the
voltage of the maximum power point and 5 a deviation of the
output voltage from the voltage of the maximum power point
is within a tolerable range.
Citation List
10 Patent Literature
[0004] Patent Literature 1: Japanese Patent No. 6105733
Summary
Technical Problem
15 [0005] According to the technique of Patent Literature 1,
the photovoltaic power generation drive system performs
adjustments in such a way as to detect the output voltage
of the solar panel by repeatedly changing the rotation
speed of the motor until the output voltage of the solar
20 panel exceeds the voltage of the maximum power point and
the deviation of the output voltage from the voltage of the
maximum power point falls within the tolerable range.
Therefore, the photovoltaic power generation drive system
has a problem in that it takes time for the output voltage
25 of the solar panel to be maintained at an appropriate value.
[0006] Furthermore, according to the technique of Patent
Literature 1, the photovoltaic power generation drive
system needs to repeatedly change the rotation speed of the
motor at a preset timing so as to detect a change of the
30 maximum power point. Therefore, even when there is no
change in solar output power and it is not necessary to
perform adjustment for controlling the solar output power,
the photovoltaic power generation drive system needs to
4
perform adjustment by repeatedly changing the rotation
speed at the timing. Thus, there has been a problem that
the motor cannot be driven stably.
[0007] The present invention has been made in view of
the above, and an object of the present 5 invention is to
obtain a photovoltaic power generation drive system capable
of reducing time required for adjustment for controlling
the output power of a solar panel and stably driving a load.
10 Solution to Problem
[0008] In order to solve the above-described problems
and achieve the object, a photovoltaic power generation
drive system according to the present invention is a
photovoltaic power generation drive system that drives a
15 load by using electric power output by a solar panel. The
photovoltaic power generation drive system according to the
present invention includes: an inverter circuit unit that
converts a DC voltage into an AC voltage according to a
pulse signal and outputs the AC voltage, the DC voltage
20 being output by the solar panel; a frequency limit value
calculation unit that calculates a limit value of an output
frequency based on frequency-voltage characteristics of the
AC voltage set in advance and a value of the DC voltage
output by the solar panel, the output frequency being a
25 frequency of the AC voltage; and an output frequency
calculation unit that calculates a command value of the
output frequency and outputs, to the inverter circuit unit,
a pulse signal based on the command value or the limit
value.
30
Advantageous Effects of Invention
[0009] The photovoltaic power generation drive system
according to the present invention has the effect of
5
enabling a reduction in time required for adjustment for
controlling the output power of the solar panel and
enabling the load to be stably driven.
Brief Description 5 of Drawings
[0010] FIG. 1 is a diagram illustrating a schematic
configuration of a photovoltaic power generation drive
system according to a first embodiment of the present
invention.
10 FIG. 2 is a diagram illustrating a solar panel, a
drive device, and a motor included in the photovoltaic
power generation drive system illustrated in FIG. 1.
FIG. 3 is a diagram describing the relationship
between DC voltage output by the solar panel illustrated in
15 FIG. 2 and the output frequency of an inverter circuit unit.
FIG. 4 is a diagram illustrating an example of the
relationship between a frequency limit value and AC voltage,
the frequency limit value being calculated by a frequency
limit value calculation unit included in the drive device
20 illustrated in FIG. 2.
FIG. 5 is a diagram illustrating another example of
the relationship between the frequency limit value and the
AC voltage, the frequency limit value being calculated by
the frequency limit value calculation unit included in the
25 drive device illustrated in FIG. 2.
FIG. 6 is a flowchart illustrating a procedure for
operation to be performed by a control unit included in the
drive device illustrated in FIG. 2.
FIG. 7 is a diagram illustrating a hardware
30 configuration for implementing the functions of the control
unit included in the drive device illustrated in FIG. 2 by
using dedicated hardware.
FIG. 8 is a diagram illustrating a hardware
6
configuration for implementing the functions of the control
unit included in the drive device illustrated in FIG. 2 by
using of a processor.
Description 5 of Embodiments
[0011] Hereinafter, a photovoltaic power generation
drive system and a method for controlling the photovoltaic
power generation drive system, according to an embodiment
of the present invention will be described in detail with
10 reference to the drawings. Note that the present invention
is not limited to the embodiment.
[0012] First Embodiment.
FIG. 1 is a diagram illustrating a schematic
configuration of a photovoltaic power generation drive
15 system 1 according to a first embodiment of the present
invention. FIG. 2 is a diagram illustrating a solar panel
2, a drive device 5, and a motor 6 included in the
photovoltaic power generation drive system 1 illustrated in
FIG. 1. The photovoltaic power generation drive system 1
20 drives the motor 6 as a load by using electric power output
by the solar panel 2. The motor 6 is, for example, an
induction motor. The photovoltaic power generation drive
system 1 includes the drive device 5 that converts a DC
voltage supplied by the solar panel 2 into an AC voltage,
25 and outputs the AC voltage to the motor 6.
[0013] The drive device 5 includes a capacitor 3 and an
inverter circuit unit 4. The capacitor 3 stores the DC
voltage supplied by the solar panel 2. The inverter
circuit unit 4 converts the DC voltage stored in the
30 capacitor 3 into an AC voltage, and outputs the AC voltage.
Furthermore, the drive device 5 includes a voltage
detection unit 10, a current detection unit 11, and a
control unit 20. The voltage detection unit 10 detects the
7
DC voltage stored in the capacitor 3. The current
detection unit 11 detects current on the output side of the
inverter circuit unit 4. The control unit 20 controls the
drive device 5. Note that FIG. 2 illustrates the
functional configuration of the 5 control unit 20.
[0014] The inverter circuit unit 4 converts the DC
voltage supplied by the solar panel 2 into an AC voltage
with a frequency suitable for the motor 6 according to a
pulse signal output by the control unit 20. The inverter
10 circuit unit 4 applies the converted AC voltage to the
motor 6. Specifically, the inverter circuit unit 4
controls the frequency and voltage level of the AC voltage
by variable voltage variable frequency (VVVF) control.
[0015] The current detection unit 11 detects U-phase, V15
phase, and W-phase currents output by the inverter circuit
unit 4. Note that these phase currents are collectively
referred to as output current. The control unit 20
calculates a command value of an output frequency based on
the value of the DC voltage detected by the voltage
20 detection unit 10 and the value of the output current
detected by the current detection unit 11. The output
frequency refers to the frequency of the AC voltage output
by the inverter circuit unit 4. The control unit 20
outputs, to the inverter circuit unit 4, a pulse signal
25 based on the calculated command value or a frequency limit
value to be described below. The pulse signal refers to a
pulse-width modulated (PWM) signal.
[0016] The control unit 20 feedback-controls the
inverter circuit unit 4. The control unit 20 includes an
30 anomalous voltage drop determination unit 12. The
anomalous voltage drop determination unit 12 monitors the
result of DC voltage detection performed by the voltage
detection unit 10, and determines whether a drop in DC
8
voltage is an anomalous voltage drop when the drop in DC
voltage occurs. Furthermore, the control unit 20 includes
a frequency limit value calculation unit 13, an
acceleration/deceleration interruption determination unit
14, and an output frequency calculation 5 unit 15. The
frequency limit value calculation unit 13 calculates a
frequency limit value that is a limit value of output
frequency. The acceleration/deceleration interruption
determination unit 14 determines interruption and
10 resumption of acceleration or deceleration of the rotation
of the motor 6. The output frequency calculation unit 15
calculates a command value of the output frequency. Each
functional unit included in the control unit 20 is
implemented by execution of a control program by means of
15 hardware. The control program is a program for
implementing a method for controlling the photovoltaic
power generation drive system 1 of the first embodiment.
[0017] The anomalous voltage drop determination unit 12
detects an anomaly in a voltage drop based on a change in
20 the value of the DC voltage detected by the voltage
detection unit 10. Specifically, the anomalous voltage
drop determination unit 12 determines that an anomalous
voltage drop has occurred in the case where a DC voltage
value decrease reaching or exceeding a threshold value has
25 occurred within a set time set in advance from the start of
the voltage drop. Furthermore, the anomalous voltage drop
determination unit 12 determines that the DC voltage is
normal in the case where a DC voltage value decrease
reaching or exceeding the threshold value has not occurred
30 within the set time.
[0018] The anomalous voltage drop determination unit 12
outputs 1-bit information indicating whether an anomalous
voltage drop has occurred. A signal “1” is output when it
9
is determined that an anomalous voltage drop has occurred,
and a signal “0” is output when it is determined that the
DC voltage is normal. Note that the signal to be output by
the anomalous voltage drop determination unit 12 is not
limited to “0” and “1”, but may be any signal 5 as long as it
is possible to recognize whether an anomalous voltage drop
has occurred.
[0019] The frequency limit value calculation unit 13
calculates a frequency limit value based on the value of
10 the DC voltage detected by the voltage detection unit 10
and V/F characteristics that are frequency-voltage
characteristics of AC voltage set in advance. It can be
said that the V/F characteristics are characteristics of a
change in output voltage with respect to a change in output
15 frequency. Furthermore, when “1” is output from the
anomalous voltage drop determination unit 12 to the
frequency limit value calculation unit 13, the frequency
limit value calculation unit 13 performs subtraction
correction of the calculated frequency limit value. When
20 “0” is output from the anomalous voltage drop determination
unit 12 to the frequency limit value calculation unit 13,
the frequency limit value calculation unit 13 does not
perform subtraction correction of the calculated frequency
limit value.
25 [0020] FIG. 3 is a diagram describing the relationship
between the DC voltage output by the solar panel 2
illustrated in FIG. 2 and the output frequency of the
inverter circuit unit 4. The vertical axis of a graph
illustrated in the upper part of FIG. 3 represents the DC
30 voltage “VD”. The vertical axis of a graph illustrated in
the lower part of FIG. 3 represents the frequency limit
value “f”. The horizontal axes of these two graphs
represent time.
10
[0021] As described above, the frequency limit value
calculation unit 13 calculates the frequency limit value
based on the value of the DC voltage. In the case where
the DC voltage starts to drop at time t1 and a decrease in
the value of the DC voltage has reached 5 or exceeded a
threshold value ΔVTH at time t2 before a set time Δt
elapses from time t1, the anomalous voltage drop
determination unit 12 determines that the voltage drop
started at time t1 is an anomalous voltage drop, and
10 outputs “1” indicating the determination result to the
frequency limit value calculation unit 13. Since “1” is
output from the anomalous voltage drop determination unit
12 to the frequency limit value calculation unit 13, the
frequency limit value calculation unit 13 performs
15 subtraction correction in which the frequency limit value
calculated based on the value of the DC voltage is
subtracted by Δf. Until the set time Δt elapses from time
t2, the frequency limit value calculation unit 13 uses, as
the frequency limit value, a value obtained as a result of
20 the subtraction correction.
[0022] In the case where a DC voltage value decrease
reaching or exceeding the threshold value ΔVTH has not
occurred before the set time Δt elapses from time t2, the
anomalous voltage drop determination unit 12 determines
25 that the DC voltage at time t3 is normal, and outputs “0”
to the frequency limit value calculation unit 13. Since “0”
is output from the anomalous voltage drop determination
unit 12 to the frequency limit value calculation unit 13,
the frequency limit value calculation unit 13 does not
30 perform subtraction correction of the frequency limit value
calculated based on the value of the DC voltage. The
photovoltaic power generation drive system 1 can prevent
malfunction of the motor 6 due to an anomalous voltage drop
11
by performing subtraction correction of the frequency limit
value when the anomalous voltage drop occurs.
[0023] Here, a description will be given of a specific
method for calculating the frequency limit value to be
performed by the frequency limit value calculation 5 unit 13.
The frequency limit value calculation unit 13 calculates
the frequency limit value based on the V/F characteristics
suitable for the intended use or load characteristics of
the motor 6. The photovoltaic power generation drive
10 system 1 limits the output frequency by means of the
frequency limit value based on the V/F characteristics so
that the output voltage of the inverter circuit unit 4 does
not reach or exceed the DC voltage stored in the capacitor
3. As a result, the photovoltaic power generation drive
15 system 1 can prevent inverter output power, which is the
output power of the inverter circuit unit 4, from reaching
or exceeding solar output power, which is the output power
of the solar panel 2.
[0024] Two examples of the frequency limit value
20 calculation method will be described below. A calculation
method according to a first example is a frequency limit
value calculation method to be adopted when the motor 6 is
used as a constant torque load. The frequency limit value
calculation unit 13 calculates fL1 that is a frequency
25 limit value intended for a constant torque load, based on
the V/F characteristics represented by formula (1) below.
In formula (1) and each formula to be described below, VD
denotes a DC voltage that is a result of detection
performed by the voltage detection unit 10, f0 denotes a
30 base frequency of the inverter circuit unit 4, Vf0 denotes
a base frequency voltage of the inverter circuit unit 4, VS
denotes an output start voltage of the inverter circuit
unit 4, and fS denotes the output start frequency of the
12
inverter circuit unit 4. The output start voltage refers
to the output voltage of the inverter circuit unit 4 at the
start of driving the motor 6, and is the lower limit of
voltage at which the inverter circuit unit 4 can normally
operate in driving the motor 6. The output 5 start frequency
refers to the frequency of the output voltage of the
inverter circuit unit 4 at the start of driving the motor 6,
and is an output frequency corresponding to the lower limit
voltage. The frequency limit value calculation unit 13
10 calculates the frequency limit value by substituting each
value of the DC voltage, the base frequency, the base
frequency voltage, the output start voltage, and the output
start frequency into formula (1).
[0025]
15 [Formula 1]
... (1)
[0026] FIG. 4 is a diagram illustrating an example of
the relationship between the frequency limit value and AC
voltage, the frequency limit value being calculated by the
20 frequency limit value calculation unit 13 included in the
drive device 5 illustrated in FIG. 2. The vertical axis of
a graph illustrated in FIG. 4 represents the frequency
limit value “fL1” intended for a constant torque load. The
horizontal axis of the graph represents the AC voltage “VA”.
25 In FIG. 4, the relationship between the frequency limit
value and the AC voltage is represented by a straight-line
graph. The graph illustrated in FIG. 4 shows V/F
characteristics to be applied when the motor 6 is used as a
constant torque load.
30 [0027] A calculation method according to a second
example is a frequency limit value calculation method to be
  D S S
f 0 S
S
L1 V V f
V V
f 0 f
f   



13
adopted when the motor 6 is used as a reduced torque load.
The frequency limit value calculation unit 13 calculates
fL2 that is a frequency limit value intended for a reduced
torque load, based on the V/F characteristics represented
by formula (2) below. The frequency 5 limit value
calculation unit 13 calculates the frequency limit value by
substituting each value of the DC voltage, the base
frequency, the base frequency voltage, the output start
voltage, and the output start frequency into formula (2).
10 [0028]
[Formula 2]
... (2)
[0029] FIG. 5 is a diagram illustrating another example
of the relationship between the frequency limit value and
15 AC voltage, the frequency limit value being calculated by
the frequency limit value calculation unit 13 included in
the drive device 5 illustrated in FIG. 2. The vertical
axis of a graph illustrated in FIG. 5 represents the
frequency limit value “fL2” intended for a reduced torque
20 load. The horizontal axis of the graph represents the AC
voltage “VA”. In FIG. 5, the relationship between the
frequency limit value and the AC voltage is represented by
a curve graph. The graph illustrated in FIG. 5 shows V/F
characteristics to be applied when the motor 6 is used as a
25 reduced torque load. As described above, the frequency
limit value calculation unit 13 can change the frequency
limit value calculation methods according to the intended
use or load characteristics of the motor 6.
[0030] The acceleration/deceleration interruption
30 determination unit 14 determines interruption and
resumption of acceleration or deceleration of the rotation
   
V V 2
f 0 V f V 2
V
V 2 V
f 0 f
f
S f 0
S S f 0
D
f 0 S
S
L2  
   
 
 


14
of the motor 6 based on the solar output power and the
inverter output power. The drive device 5 interrupts and
resumes acceleration/deceleration according to
determination by the acceleration/deceleration interruption
determination unit 14. As a result, 5 the drive device 5
prevents an increase in inverter output power due to the
effect of a temporary load increase that occurs during
acceleration/deceleration of the motor 6. The drive device
5 prevents the occurrence of a drop in DC voltage due to
10 the inverter output power reaching or exceeding the solar
output power, by preventing the increase in the inverter
output power. As a result, the drive device 5 can prevent
malfunction of the motor 6 during acceleration/deceleration
of the motor 6.
15 [0031] Specifically, the acceleration/deceleration
interruption determination unit 14 can obtain the solar
output power by formula (3) below. The
acceleration/deceleration interruption determination unit
14 can obtain the inverter output power by formula (4)
20 below. In formula (3), PS denotes the solar output power,
and PS0 denotes a solar reference output power. The solar
reference output power refers to a solar output voltage to
be output when the output voltage of the inverter circuit
unit 4 is equal to the base frequency voltage. In formula
25 (4), PI denotes the inverter output power, and I denotes
the output current that is the result of detection
performed by the current detection unit 11.
[0032]
[Formula 3]
30 ... (3)
[0033]
S0
f 0
D
S P
V
V
P  
15
[Formula 4]
... (4)
[0034] When the calculated inverter output power is
equal to or greater than the calculated solar output power,
the acceleration/deceleration interruption 5 determination
unit 14 makes a determination to the effect that
acceleration should be interrupted. Furthermore, when the
calculated inverter output power is less than the
calculated solar output power, the
10 acceleration/deceleration interruption determination unit
14 makes a determination to the effect that acceleration
should be resumed. The acceleration/deceleration
interruption determination unit 14 outputs 1-bit
information indicating the result of determination on
15 interruption and resumption of acceleration. A signal “0”
is output when it is determined that acceleration should be
interrupted, and a signal “1” is output when it is
determined that acceleration should be resumed. Note that
the signal to be output by the acceleration/deceleration
20 interruption determination unit 14 is not limited to “0”
and “1”, but may be any signal as long as it is possible to
distinguish between determination results of interruption
and resumption of acceleration.
[0035] The output frequency calculation unit 15
25 calculates a command value of the output frequency based on
the result of determination by the
acceleration/deceleration interruption determination unit
14 and the result of frequency limit value calculation
performed by the frequency limit value calculation unit 13.
30 The output frequency calculation unit 15 outputs, to the
inverter circuit unit 4, a pulse signal based on the
command value calculated by the output frequency
P V I I D  
16
calculation unit 15 or the frequency limit value calculated
by the frequency limit value calculation unit 13.
[0036] Next, specific operation of the control unit 20
will be described. FIG. 6 is a flowchart illustrating a
procedure for operation to be performed by 5 the control unit
20 included in the drive device 5 illustrated in FIG. 2.
In step S1, the anomalous voltage drop determination unit
12 monitors an anomalous drop in DC voltage. The anomalous
voltage drop determination unit 12 determines that an
10 anomalous voltage drop has occurred in the case where a DC
voltage value decrease reaching or exceeding the threshold
value has occurred within the set time. The anomalous
voltage drop determination unit 12 determines that the DC
voltage is normal in the case where a DC voltage value
15 decrease reaching or exceeding the threshold value has not
occurred within the set time.
[0037] In step S2, the acceleration/deceleration
interruption determination unit 14 calculates the inverter
output power and the solar output power. In step S3, the
20 frequency limit value calculation unit 13 calculates the
frequency limit value based on the value of the DC voltage
that is a result of detection performed by the voltage
detection unit 10.
[0038] In step S4, the frequency limit value calculation
25 unit 13 determines whether an anomalous voltage drop has
occurred based on the output from the anomalous voltage
drop determination unit 12 to the frequency limit value
calculation unit 13. In the case where an anomalous
voltage drop has occurred (step S4, Yes), the control unit
30 20 causes the process to proceed to step S5. Meanwhile, in
the case where an anomalous voltage drop has not occurred
(step S4, No), the control unit 20 causes the process to
proceed to step S6.
17
[0039] In step S5, the frequency limit value calculation
unit 13 performs subtraction correction of the frequency
limit value calculated in step S3. In step S6, the output
frequency calculation unit 15 determines whether the
inverter output power is less than the 5 solar output power
based on the output from the acceleration/deceleration
interruption determination unit 14 to the output frequency
calculation unit 15. When the inverter output power is
less than the solar output power (step S6, Yes), the
10 control unit 20 causes the process to proceed to step S8.
Meanwhile, when the inverter output power is equal to or
greater than the solar output power (step S6, No), the
control unit 20 causes the process to proceed to step S7.
[0040] In step S7, the output frequency calculation unit
15 15 outputs, to the inverter circuit unit 4, a pulse signal
based on a command value relevant to the previous frequency
command. In step S8, the output frequency calculation unit
15 determines whether the frequency limit value calculated
in step S3 or step S5 is less than a command value of the
20 output frequency calculated this time. When the frequency
limit value is less than the command value (step S8, Yes),
the control unit 20 causes the process to proceed to step
S10. Meanwhile, when the frequency limit value is equal to
or greater than the command value (step S8, No), the
25 control unit 20 causes the process to proceed to step S9.
[0041] In step S9, the output frequency calculation unit
15 outputs, to the inverter circuit unit 4, a pulse signal
based on the command value of the output frequency
calculated this time. In step S10, the output frequency
30 calculation unit 15 outputs, to the inverter circuit unit 4,
a pulse signal based on the frequency limit value
calculated in step S3 or step S5. Thus, the control unit
20 ends the operation according to the procedure
18
illustrated in FIG. 6.
[0042] The functions of the control unit 20 included in
the drive device 5 are implemented by use of processing
circuitry. The processing circuitry is dedicated hardware
to be installed in the drive device 5 5. The processing
circuitry may be a processor that executes a program stored
in a memory.
[0043] FIG. 7 is a diagram illustrating a hardware
configuration for implementing the functions of the control
10 unit 20 included in the drive device 5 illustrated in FIG.
2 by using dedicated hardware. Processing circuitry 41
that is the dedicated hardware is a single circuit, a
composite circuit, a programmed processor, a parallelprogrammed
processor, an application specific integrated
15 circuit (ASIC), a field-programmable gate array (FPGA), or
a combination thereof.
[0044] FIG. 8 is a diagram illustrating a hardware
configuration for implementing the functions of the control
unit 20 included in the drive device 5 illustrated in FIG.
20 2 by using a processor 42. The processor 42 and a memory
43 are connected such that the processor 42 and the memory
43 can communicate with each other. The processor 42
executes a program stored in the memory 43.
[0045] The processor 42 is a central processing unit
25 (CPU), a processing device, an arithmetic device, a
microprocessor, a microcomputer, or a digital signal
processor (DSP). The functions of the control unit 20 are
implemented by the processor 42, and software, firmware, or
a combination of software and firmware. The software or
30 firmware is described as a program, and stored in the
memory 43. The memory 43 is a built-in memory such as a
nonvolatile or volatile semiconductor memory. Examples of
such a nonvolatile or volatile semiconductor memory include
19
a random access memory (RAM), a read only memory (ROM), a
flash memory, an erasable programmable read only memory
(EPROM), and an electrically erasable programmable read
only memory (EEPROM) (registered trademark).
[0046] Some of the functions of the control 5 unit 20 may
be implemented by dedicated hardware, and the other
functions of the control unit 20 may be implemented by
software or firmware. Thus, the functions of the control
unit 20 can be implemented by hardware, software, firmware,
10 or a combination thereof.
[0047] According to the first embodiment, the
photovoltaic power generation drive system 1 calculates a
limit value of output frequency based on V/F
characteristics and the value of DC voltage output by the
15 solar panel 2. When the inverter output power is equal to
or greater than the solar output power and the limit value
is less than a command value, the photovoltaic power
generation drive system 1 outputs, to the inverter circuit
unit 4, a pulse signal with a frequency based on the limit
20 value. The photovoltaic power generation drive system 1
enables the inverter output power to be adjusted such that
the inverter output power is less than the solar output
power, and also enables reduction of malfunctions of the
motor 6 by limiting the output frequency by means of the
25 limit value based on the V/F characteristics. The
photovoltaic power generation drive system 1 does not
require adjustment that is performed in such a way as to
detect the output voltage of the solar panel 2 by
repeatedly changing the rotation speed of the motor 6.
30 Thus, it is possible to reduce time required for adjustment
for controlling the solar output power. The photovoltaic
power generation drive system 1 does not need to repeatedly
change the rotation speed of the motor 6 at a preset timing.
20
Therefore, the motor 6 can be stably driven when the solar
output power does not change. As a result, the
photovoltaic power generation drive system 1 has the effect
of enabling a reduction in time required for adjustment for
controlling the output power of the 5 solar panel 2 and
enabling a load to be stably driven.
[0048] The configurations set forth in the above
embodiment show examples of the subject matter of the
present invention, and it is possible to combine the
10 configurations with another technique that is publicly
known, and is also possible to make omissions and changes
to part of the configurations without departing from the
gist of the present invention.
15 Reference Signs List
[0049] 1 photovoltaic power generation drive system; 2
solar panel; 3 capacitor; 4 inverter circuit unit; 5
drive device; 6 motor; 10 voltage detection unit; 11
current detection unit; 12 anomalous voltage drop
20 determination unit; 13 frequency limit value calculation
unit; 14 acceleration/deceleration interruption
determination unit; 15 output frequency calculation unit;
20 control unit; 41 processing circuitry; 42 processor;
43 memory.
25
21
We Claim :
1. A photovoltaic power generation drive system for
driving a load by using electric power output by a solar
panel, the system comprising:
an inverter circuit unit to convert 5 a DC voltage into
an AC voltage according to a pulse signal and output the AC
voltage, the DC voltage being output by the solar panel;
a frequency limit value calculation unit to calculate
a limit value of an output frequency based on frequency10
voltage characteristics of the AC voltage set in advance
and a value of the DC voltage output by the solar panel,
the output frequency being a frequency of the AC voltage;
and
an output frequency calculation unit to calculate a
15 command value of the output frequency and output, to the
inverter circuit unit, a pulse signal based on the command
value or the limit value.
2. The photovoltaic power generation drive system
20 according to claim 1, wherein when an output power of the
inverter circuit unit is equal to or greater than an output
power of the solar panel and the limit value is less than
the command value, the output frequency calculation unit
outputs a pulse signal based on the limit value.
25
3. The photovoltaic power generation drive system
according to claim 1 or 2, wherein when an output power of
the inverter circuit unit is equal to or greater than an
output power of the solar panel and the limit value is
30 equal to or greater than the command value, the output
frequency calculation unit outputs a pulse signal based on
the command value.
22
4. The photovoltaic power generation drive system
according to any one of claims 1 to 3, further comprising:
an anomalous voltage drop determination unit to
determine whether a drop in the DC voltage is an anomalous
voltage drop, based on a change in the 5 value of the DC
voltage output by the solar panel, wherein
when it is determined that the drop in the DC voltage
is an anomalous voltage drop, the frequency limit value
calculation unit performs subtraction correction of the
10 calculated limit value.
5. The photovoltaic power generation drive system
according to any one of claims 1 to 4, wherein the
frequency limit value calculation unit calculates the limit
15 value fL1 based on formula (1) below:
[Formula 1]
... (1),
where VD is the DC voltage, f0 is a base frequency of
the inverter circuit unit, Vf0 is a base frequency voltage
20 of the inverter circuit unit, VS is an output start
pressure of the inverter circuit unit, and fS is an output
start frequency of the inverter circuit unit.
6. The photovoltaic power generation drive system
25 according to any one of claims 1 to 4, wherein the
frequency limit value calculation unit calculates the limit
value fL2 based on formula (2) below:
[Formula 2]
... (2),
  D S S
f 0 S
S
L1 V V f
V V
f 0 f
f   



   
V V 2
f 0 V f V 2
V
V 2 V
f 0 f
f
S f 0
S S f 0
D
f 0 S
S
L2  
   
 
 


23
where VD is the DC voltage, f0 is a base frequency of
the inverter circuit unit, Vf0 is a base frequency voltage
of the inverter circuit unit, VS is an output start
pressure of the inverter circuit unit, and fS is an output
start frequency of the inverter 5 circuit unit.
7. A method for controlling a photovoltaic power
generation drive system that drives a load by using
electric power output by a solar panel, the photovoltaic
10 power generation drive system including an inverter circuit
unit to convert a DC voltage into an AC voltage according
to a pulse signal and output the AC voltage, the DC voltage
being output by the solar panel, the method comprising:
a step of calculating a limit value of an output
15 frequency based on frequency-voltage characteristics of the
AC voltage set in advance and a value of the DC voltage
output by the solar panel, the output frequency being a
frequency of the AC voltage; and
a step of calculating a command value of the output
20 frequency and outputting, to the inverter circuit unit, a
pulse signal based on the command value or the limit value.