1. A flicker prevention device for a power system to which a power conditioner performing system interconnection of a distributed power supply is connected, the flicker prevention device comprising: a power converter to inject delay reactive power 5 or lead reactive power into the power system; a frequency detector to detect a system frequency of an AC voltage on the power system; a frequency change amount calculation unit to calculate a change amount of 10 the detected system frequency; and a controller configured to control, when a first control characteristic is selected, the power converter to output the lead reactive power in response to an increase in the system frequency and to output the delay reactive power in response to an decrease in the system frequency, and, when a second control characteristic is 15 selected, to control the power converter to output the delay reactive power in response to the increase in the system frequency and to output the lead reactive power in response to the decrease in the system frequency, wherein the controller, when increase of the change amount of the system frequency is detected while controlling the power converter according to selected one of the 20 first control characteristic and the second control characteristic, switches the selected one of the first control characteristic and the second control characteristic to the other control characteristic.

2. The flicker prevention device according to claim 1, further comprising: 25 a voltage detector to detect a system voltage effective value of an AC voltage on the power system; and a voltage change amount calculation unit to calculate a change amount of the system voltage effective value, wherein the controller selects one of the first control characteristic and the 30 second control characteristic according to a phase relationship between a temporal change according to a flicker period in the change amount of the system voltage effective value and a temporal change according to the flicker period in the change amount of the system frequency. 44

3. The flicker prevention device according to claim 1 or claim 2, further comprising: a voltage detector to detect a system voltage effective value of an AC voltage on the power system; and a voltage change amount calculation 5 unit to calculate a change amount of the system voltage effective value, wherein the controller selects one control characteristic from the first control characteristic and the second control characteristic according to a phase relationship between a temporal change according to a flicker period in the change 10 amount of the system voltage effective value and a temporal change according to the flicker period in the change amount of the system frequency in a non-output period of the reactive power by the power converter, and controls the reactive power output from the power converter according to the one control characteristic when the output of the reactive power is started from the power converter. 15

4. The flicker prevention device according to claim 2 or claim 3, wherein the controller selects the first control characteristic when a phase difference between a temporal change in the change amount of the system voltage effective value and a temporal change in the change amount of the system frequency with 20 the flicker period set to 360 degrees is closer to 180 degrees than 0 degrees, and selects the second control characteristic when the phase difference is closer to 0 degrees than 180 degrees.

5. The flicker prevention device according to any one of claims 1 to 4, 25 wherein the controller reduces a ratio of magnitude of the reactive power to the change amount of the system frequency during a given period set when switching between the first control characteristic and the second control characteristic so as to avoid sudden change of the reactive power output from the power converter. 30 6. The flicker prevention device according to any one of claims 1 to 5, wherein the controller includes: a control arithmetic unit that calculates a reactive power instruction value according to a predetermined control operation with the change amount calculated 35 by the frequency change amount calculation unit as input; and 45 a power converter control unit that generates a control instruction for the power converter to output the reactive power according to the reactive power instruction value, the control operation is performed such that the reactive power instruction value is set such that magnitude of the reactive 5 power and an absolute value of the change amount are proportional to each other according to a product of a proportional gain and the change amount, and a polarity of the proportional gain is different between the first control characteristic and the second control characteristic. 10

7. The flicker prevention device according to claim 6, wherein an absolute value of the proportional gain is set to a smaller value in a region where an absolute value of the change amount is smaller than a determination value as compared with a region where an absolute value of the change amount is larger than the 15 determination value.

8. The flicker prevention device according to claim 7, wherein the proportional gain is set to zero in a region where an absolute value of the change amount is smaller than the determination value. 20

9. The flicker prevention device according to any one of claims 1 to 6, wherein the frequency change amount calculation unit calculates the change amount according to a difference between a moving average value of the system frequency in a first period before a current point of time and a moving average value 25 of the system frequency in a second period before the first period.

10. The flicker prevention device according to any one of claims 1 to 6, wherein the frequency change amount calculation unit calculates the change amount according to a difference between a reference value of the system frequency 30 and a moving average value of the system frequency in a first period before a current point of time.

11. A flicker prevention control method for a power system to which a power conditioner performing system interconnection of a distributed power supply 35 is connected, the flicker prevention control method comprising: 46 detecting a system frequency that is a frequency of an AC voltage on the power system; calculating a change amount of the detected system frequency; and controlling, when a first control characteristic is selected, the power converter to output a lead reactive power in 5 response to an increase in the system frequency and to output a delay reactive power in response to an decrease in the system frequency, and controlling, when a second control characteristic is selected, the power converter to output the delay reactive power in response to the increase in the system frequency and to output the lead reactive power in response to the 10 decrease in the system frequency, wherein when increase of the change amount of the system frequency is detected while controlling the power converter according to selected one of the first control characteristic and the second control characteristic, the selected one of the first control characteristic and the second control characteristic is switched to the 15 other control characteristic.

12. The flicker prevention control method according to claim 11, wherein the controlling includes: generating a reactive power instruction value by a control operation 20 according to a selected one control characteristic of the first and second control characteristics with the calculated change amount as input; and generating a control instruction for the power converter to output reactive power according to the reactive power instruction value, and the reactive power instruction value is generated such that 25 while the first control characteristic is selected, the power converter outputs the lead reactive power to compensate for the change amount when the change amount has a polarity indicating an increase in the system frequency, and the power converter outputs the delay reactive power to compensate for the change amount when the change amount has a polarity indicating a decrease in the system 30 frequency, and while the second control characteristic is selected, the power converter outputs the delay reactive power to compensate for the change amount when the change amount has the polarity indicating the increase in the system frequency, and the power converter outputs the lead reactive power to compensate for the change 35 amount when the change amount has the polarity indicating the decrease in the 47 system frequency.

Description:AS ATTACHED , Claims:I/We Claim:
1. A flicker prevention device for a power system to which a power
conditioner performing system interconnection of a distributed power supply is
connected, the flicker prevention device comprising:
a power converter to inject delay reactive power 5 or lead reactive power into
the power system;
a frequency detector to detect a system frequency of an AC voltage on the
power system;
a frequency change amount calculation unit to calculate a change amount of
10 the detected system frequency; and
a controller configured to control, when a first control characteristic is
selected, the power converter to output the lead reactive power in response to an
increase in the system frequency and to output the delay reactive power in response
to an decrease in the system frequency, and, when a second control characteristic is
15 selected, to control the power converter to output the delay reactive power in
response to the increase in the system frequency and to output the lead reactive
power in response to the decrease in the system frequency, wherein
the controller, when increase of the change amount of the system frequency
is detected while controlling the power converter according to selected one of the
20 first control characteristic and the second control characteristic, switches the
selected one of the first control characteristic and the second control characteristic
to the other control characteristic.
2. The flicker prevention device according to claim 1, further comprising:
25 a voltage detector to detect a system voltage effective value of an AC
voltage on the power system; and
a voltage change amount calculation unit to calculate a change amount of
the system voltage effective value,
wherein the controller selects one of the first control characteristic and the
30 second control characteristic according to a phase relationship between a temporal
change according to a flicker period in the change amount of the system voltage
effective value and a temporal change according to the flicker period in the change
amount of the system frequency.
44
3. The flicker prevention device according to claim 1 or claim 2, further
comprising:
a voltage detector to detect a system voltage effective value of an AC
voltage on the power system; and
a voltage change amount calculation 5 unit to calculate a change amount of
the system voltage effective value,
wherein the controller selects one control characteristic from the first
control characteristic and the second control characteristic according to a phase
relationship between a temporal change according to a flicker period in the change
10 amount of the system voltage effective value and a temporal change according to
the flicker period in the change amount of the system frequency in a non-output
period of the reactive power by the power converter, and controls the reactive power
output from the power converter according to the one control characteristic when
the output of the reactive power is started from the power converter.
15
4. The flicker prevention device according to claim 2 or claim 3, wherein
the controller selects the first control characteristic when a phase difference
between a temporal change in the change amount of the system voltage effective
value and a temporal change in the change amount of the system frequency with
20 the flicker period set to 360 degrees is closer to 180 degrees than 0 degrees, and
selects the second control characteristic when the phase difference is closer to 0
degrees than 180 degrees.
5. The flicker prevention device according to any one of claims 1 to 4,
25 wherein the controller reduces a ratio of magnitude of the reactive power to the
change amount of the system frequency during a given period set when switching
between the first control characteristic and the second control characteristic so as to
avoid sudden change of the reactive power output from the power converter.
30 6. The flicker prevention device according to any one of claims 1 to 5,
wherein
the controller includes:
a control arithmetic unit that calculates a reactive power instruction value
according to a predetermined control operation with the change amount calculated
35 by the frequency change amount calculation unit as input; and
45
a power converter control unit that generates a control instruction for the
power converter to output the reactive power according to the reactive power
instruction value,
the control operation is performed such that the reactive power instruction
value is set such that magnitude of the reactive 5 power and an absolute value of the
change amount are proportional to each other according to a product of a
proportional gain and the change amount, and
a polarity of the proportional gain is different between the first control
characteristic and the second control characteristic.
10
7. The flicker prevention device according to claim 6, wherein an absolute
value of the proportional gain is set to a smaller value in a region where an absolute
value of the change amount is smaller than a determination value as compared with
a region where an absolute value of the change amount is larger than the
15 determination value.
8. The flicker prevention device according to claim 7, wherein the
proportional gain is set to zero in a region where an absolute value of the change
amount is smaller than the determination value.
20
9. The flicker prevention device according to any one of claims 1 to 6,
wherein the frequency change amount calculation unit calculates the change
amount according to a difference between a moving average value of the system
frequency in a first period before a current point of time and a moving average value
25 of the system frequency in a second period before the first period.
10. The flicker prevention device according to any one of claims 1 to 6,
wherein the frequency change amount calculation unit calculates the change
amount according to a difference between a reference value of the system frequency
30 and a moving average value of the system frequency in a first period before a
current point of time.
11. A flicker prevention control method for a power system to which a
power conditioner performing system interconnection of a distributed power supply
35 is connected, the flicker prevention control method comprising:
46
detecting a system frequency that is a frequency of an AC voltage on the
power system;
calculating a change amount of the detected system frequency; and
controlling, when a first control characteristic is selected, the power
converter to output a lead reactive power in 5 response to an increase in the system
frequency and to output a delay reactive power in response to an decrease in the
system frequency, and controlling, when a second control characteristic is selected,
the power converter to output the delay reactive power in response to the increase
in the system frequency and to output the lead reactive power in response to the
10 decrease in the system frequency,
wherein when increase of the change amount of the system frequency is
detected while controlling the power converter according to selected one of the first
control characteristic and the second control characteristic, the selected one of the
first control characteristic and the second control characteristic is switched to the
15 other control characteristic.
12. The flicker prevention control method according to claim 11, wherein
the controlling includes:
generating a reactive power instruction value by a control operation
20 according to a selected one control characteristic of the first and second control
characteristics with the calculated change amount as input; and
generating a control instruction for the power converter to output reactive
power according to the reactive power instruction value, and
the reactive power instruction value is generated such that
25 while the first control characteristic is selected, the power converter outputs
the lead reactive power to compensate for the change amount when the change
amount has a polarity indicating an increase in the system frequency, and the power
converter outputs the delay reactive power to compensate for the change amount
when the change amount has a polarity indicating a decrease in the system
30 frequency, and
while the second control characteristic is selected, the power converter
outputs the delay reactive power to compensate for the change amount when the
change amount has the polarity indicating the increase in the system frequency, and
the power converter outputs the lead reactive power to compensate for the change
35 amount when the change amount has the polarity indicating the decrease in the
47
system frequency.