JP7068619B2 - Independent operation detection device, grid interconnection inverter and independent operation detection method - Google Patents

Description

The present invention relates to a solitary operation detection device, a grid interconnection inverter using the solitary operation detection device, and a solitary operation detection method.

Distributed power sources such as photovoltaic power generation devices, fuel cells, and storage batteries are connected to the power system via a grid-connected inverter. This grid interconnection inverter converts the DC power of the distributed power source into AC power, and performs an operation for reverse power flow of the AC power to the power system.

Here, if the grid interconnection inverter continues to operate in a state where a power failure occurs due to an accident in the power system or the like, power is locally supplied to the power system. Then, an accident such as an electric shock may occur during the recovery work of the power system accident. Therefore, the grid interconnection inverter is provided with an independent operation detection device for detecting the independent operation and disconnecting the grid interconnection inverter from the power system.

Then, as the independent operation detection device, the system interconnection inverter constantly injects reactive power whose lagging phase and leading phase change periodically into the power system, and detects the change in frequency that occurs when the power system fails. There is something to detect driving.

Since this isolated operation detection device injects reactive power into the power system, it can be a cause of flicker failure. Specifically, the system voltage changes depending on the fluctuation period of the lagging phase and the leading phase of the reactive power.

In order to avoid this flicker failure, it is conceivable to reduce the injection amount of the reactive power, but then the change in frequency that occurs when the isolated operation occurs is also small. Since the frequency accuracy of the CPU used in the grid interconnection inverter is limited by the CPU clock, if the injection amount of reactive power is reduced, it becomes difficult to accurately detect that the frequency is out of the predetermined frequency range, and the operation is independent. False detection or detection delay may occur.

As a solution to this problem, as shown in Patent Document 1, a change in the frequency integrated value when an invalid power whose lagging phase and leading phase change periodically is injected is detected, and the frequency integrated value is predetermined. It is considered that the reactive power is increased when the frequency is out of the frequency range to reliably detect that the operation is independent.

However, in this isolated operation detection device, when the injection amount of the reactive power is small, the change in frequency is also small, and it becomes difficult to detect whether or not the frequency is out of the frequency range. If the injection amount of reactive power is increased to facilitate this detection, not only will flicker failure be a factor, but also the instantaneous voltage drop that occurs in the power system and the vibration component that occurs when the feeder of the distribution network is switched will cause an error in independent operation. There is a possibility that detection will be performed and the grid interconnection inverter will be stopped unnecessarily.

Japanese Unexamined Patent Publication No. 2006-246650

Therefore, the present invention has been made to solve the above-mentioned problems, and its main object is to prevent erroneous detection and detection delay of isolated operation while reducing the injection amount of reactive power.

That is, the independent operation detection device according to the present invention detects the independent operation of the inverter circuit that converts the DC power of the distributed power supply into AC power and outputs it to the power system, and the output power of the inverter circuit is predetermined. It is an independent operation detection device that superimposes an invalid power whose lag phase and lead phase change alternately in the set cycle of the above and detects the independent operation of the inverter circuit based on the fluctuation of the frequency of the electric power system. The first moving average value obtained by the moving average of the first moving average section and the second moving average value obtained by the moving average of the second moving average section which is a section before the first moving average section at the frequency of The average difference calculation unit that sequentially calculates the difference between the two, the integration unit that integrates the absolute value of the difference obtained by the average difference calculation unit at predetermined time intervals, and the integration value obtained by the integration unit and the predetermined integration. It is provided with a comparison unit for comparing with a threshold value, and is characterized in that the independent operation of the inverter is detected by using the comparison result obtained by the comparison unit.

In such a solitary operation detection device, it is obtained by the first moving average value obtained by the moving average of the first moving average section and the moving average of the second moving average section which is a section before the first moving average section. The difference from the second moving average value to be calculated is sequentially calculated, the absolute value of the difference is integrated at predetermined time intervals, and the integrated value is compared with the predetermined integrated threshold value. While reducing the amount, it is possible to prevent erroneous detection and detection delay in independent operation. Details will be described later.

In particular, in order to make the effect of the present invention remarkable, the first moving average section is a half cycle of the set cycle, and the second moving average section has the set cycle more than the first moving average section. It is desirable that it is the half cycle of the set cycle before the half cycle of.

As a specific calculation mode of the integration circuit, it is desirable that the integration circuit integrates the absolute value of the difference every half time of the set cycle.

The isolated operation detection device of the present invention increases the reactive power superimposed on the output power of the inverter circuit when the integrated value is larger than the integrated threshold value in the comparison result obtained by the comparison circuit. It is further desirable to include a generation unit and a solitary operation detection unit that detects the solitary operation of the inverter circuit when the frequency of the power system after increasing the reactive power is equal to or higher than a predetermined frequency threshold value. With this configuration, it is possible to more reliably detect the independent operation of the grid interconnection inverter.

It is desirable that the reactive power generation unit increases the reactive power when the integrated value is larger than the integrated threshold value for a predetermined time. With this configuration, it is possible to more reliably detect the independent operation of the grid interconnection inverter.

It is desirable that the independent operation detection unit detects the independent operation of the inverter when the frequency of the power system continues to be equal to or higher than the frequency threshold value for a predetermined time. With this configuration, it is possible to more reliably detect the independent operation of the grid interconnection inverter.

Further, the inverter system according to the present invention is characterized by including an inverter that converts DC power of a distributed power source into AC power and outputs it to a power system, and the above-mentioned independent operation detection device.

Further, the isolated operation detection method according to the present invention is a method for detecting the isolated operation of an inverter that converts DC power of a distributed power source into AC power and outputs it to a power system, and the output power of the inverter is predetermined. It is an independent operation detection method that detects the independent operation of the inverter based on the fluctuation of the frequency of the power system by superimposing the invalid power whose lag phase and lead phase change alternately in the set cycle, and is the frequency of the power system. The difference between the first moving average value obtained by the moving average of the first moving average section and the second moving average value obtained by the moving average of the second moving average section which is a section before the first moving average section. The average difference calculation step for sequentially calculating the above, the integration step for integrating the absolute value of the difference obtained by the average difference calculation step at predetermined time intervals, and the integration value and the predetermined integration threshold value obtained by the integration step. It is characterized by comprising a comparison step for comparing with and, and detecting the independent operation of the inverter by using the comparison result obtained by the comparison step.

According to the present invention configured as described above, it is possible to prevent erroneous detection and detection delay in isolated operation while reducing the injection amount of reactive power.

It is a figure which shows typically the circuit structure of the grid interconnection inverter of 1st Embodiment. It is a functional block diagram about the determination function of the independent operation of 1st Embodiment. It is a block diagram of the arithmetic processing of the average difference calculation unit and the integration unit. It is a schematic diagram which shows the fluctuation of each value after the occurrence of a solitary operation. It is a schematic diagram which shows the fluctuation of each value after the step change of a frequency in the non-occurrence of a solitary operation. It is a figure which shows the determination method of the comparison part of 2nd Embodiment. It is a figure which shows the determination method of the isolated operation detection part of the 2nd Embodiment. It is a figure which shows the simulation result of the signal processing at the time of a step change of a frequency in the absence of a solitary operation. It is a figure which shows the simulation result of the signal processing at the time of a lamp change of a frequency in the absence of a solitary operation.

Hereinafter, an embodiment of a grid-connected inverter system having an isolated operation detection device according to the present invention will be described with reference to the drawings.

<First Embodiment>
As shown in FIG. 1, the grid interconnection inverter 100 of the first embodiment is provided between a distributed power source 200 which is a DC power source such as a photovoltaic power generation device and a power system 300 such as a commercial power system. The DC power of the distributed power source 200 is converted into AC power and back-fed to the power system 300.

Specifically, the grid interconnection inverter 100 is independently connected to the distributed power source 200, the inverter circuit 2 that converts DC power into AC power, the inverter circuit control device 3 that controls the inverter circuit 2, and the inverter circuit 2. It is provided with an independent operation detection device 4 for detecting operation.

A filter 5 including a reactor 51 and a capacitor 52 is provided on the output side of the inverter circuit 2 in order to remove high frequency components. Further, on the output side of the inverter circuit 2, a current detection unit 6 for detecting the output current of the inverter circuit 2 and a voltage detection unit 7 for detecting the system voltage of the power system 300 are provided. Further, on the output side of the inverter circuit 2, a switch 8 such as an electromagnetic switch for interconnecting and disconnecting the grid interconnection inverter 100 and the power system 300 is provided.

The inverter circuit 2 is a three-phase inverter equipped with three sets of six switching elements (not shown), and direct current is obtained by switching on and off of each switching element based on the PWM signal input from the inverter circuit control device 3. Converts power to AC power.

The inverter circuit control device 3 PWM-controls the inverter circuit 2 by using the output current of the inverter circuit 2 obtained by the current detection unit 6 and the system voltage obtained by the voltage detection unit 7. Specifically, the inverter circuit controller 3 includes a PLL (Phase-Locked Loop) circuit 31, a positive coordinate converter (UVW / dq conversion) 32, a generated power calculator 33, a current controller 34, and an inverse coordinate converter (dq /). It is equipped with a UVW conversion) 35, a PWM modulator 36, and the like.

The independent operation detection device 4 superimposes the output power of the grid interconnection inverter 2 with the reactive power in which the delayed phase and the leading phase change alternately in a predetermined set cycle, and the frequency of the power system 300 (hereinafter, also referred to as a grid frequency). The independent operation of the inverter circuit 2 is detected based on the fluctuation of.).

Specifically, as shown in FIG. 2, the isolated operation detection device 4 includes an ineffective power generation unit 41 that generates ineffective power superimposed on the output power of the grid interconnection inverter 100, and a frequency calculation unit 42 that calculates the grid frequency. An average difference calculation unit 43 that calculates a predetermined average difference from the system frequency obtained by the frequency calculation unit 42, and an integration unit that integrates the absolute values of the differences obtained by the average difference calculation unit 43 at predetermined time intervals. It includes a comparison unit 45 for comparing the integrated value obtained by the integration unit 44 with a predetermined integration threshold value, and an independent operation detection unit 46 for detecting the independent operation of the inverter circuit 2.

As shown in FIG. 3, the reactive power generation unit 41 generates reactive power (hereinafter, also referred to as a periodic active signal) in which the lagging phase and the leading phase change alternately in a predetermined set cycle. The reactive power generation unit 41 of the present embodiment generates a periodic active signal whose phase changes alternately at a period of 2.4 Hz and a phase of ± 0.5 degrees.

When the inverter circuit 2 is operated independently, this periodic active signal causes a frequency fluctuation of ± 0.14 Hz when the system frequency is 50 Hz, and a frequency fluctuation of ± 0.17 Hz when the system frequency is 60 Hz. Then, the reactive power generation unit 41 inputs a command value for outputting this periodic active signal to the current controller 34 of the inverter circuit control device 3.

The frequency calculation unit 42 calculates the system frequency from the output signal output from the PLL circuit 31 of the inverter circuit control device 3. The frequency calculation unit 42 may calculate the system frequency from the system voltage detected by the voltage detection unit 7 without going through the PLL circuit 31. The system frequency calculated by the frequency calculation unit 42 is input to the average difference calculation unit 43 and the comparison unit 45.

As shown in FIGS. 3 and 4, the average difference calculation unit 43 sequentially calculates the first moving average value obtained by the moving average of the first moving average section at the system frequency calculated by the frequency calculation unit 42. Further, the average difference calculation unit 43 sequentially calculates the second moving average value obtained by the moving average of the second moving average section, which is a section before the first moving average section, at the system frequency. Then, the average difference calculation unit 43 sequentially calculates the difference between the first moving average value and the second moving average value.

In the average difference calculation unit 43 of the present embodiment, both the first moving average section and the second moving average section are set to half the cycle of the setting cycle of the periodic active signal. Further, the average difference calculation unit 43 sets the second moving average section as half a cycle before the set cycle of the first moving average section. The number of frequency samples in the half cycle of the setting cycle of the periodic active signal is, for example, 10 when the system frequency is 50 Hz and 12 when the system frequency is 60 Hz.

The integration unit 44 calculates the absolute value of the difference calculated by the average difference calculation unit 43, and integrates the absolute value at predetermined time intervals. The integration unit 44 of the present embodiment integrates the absolute values for half of the set cycle.

As shown in FIG. 3, this integrated value stabilizes after a predetermined time has elapsed from the occurrence of the isolated operation (1.5 cycles after the periodic active signal in the present embodiment). The stable value of the integrated value is obtained by "frequency change value due to periodic active signal" x "number of integrated samples (number of frequency samples)", and when the system frequency is 50 Hz, 1.40 (= 0.14 Hz x 10). (Sample), and when the system frequency is 60 Hz, it is 2.04 (= 0.17 Hz × 12 samples).

The comparison unit 45 compares the integrated value sequentially calculated by the integrating unit 44 with a predetermined integration threshold value. Here, the predetermined integration threshold value can be a value of a predetermined ratio (for example, 70%) to the stable value of the integrated value. Then, the signal indicating the comparison result of the comparison unit 45 is input to the independent operation detection unit 46.

The independent operation detection unit 46 acquires a signal indicating the comparison result of the comparison unit 45, and determines that the inverter circuit 2 is in the independent operation state when the integrated value is equal to or higher than a predetermined integrated threshold value. Then, when the inverter circuit 2 determines that the inverter circuit 2 is in the independent operation state, the independent operation detection unit 46 outputs an open signal to the switch 8 to open the switch 8. As a result, the grid interconnection inverter 100 is disconnected from the power grid 300.

Note that FIG. 5 shows each value when the system frequency changes stepwise (in a state other than independent operation). By performing the same arithmetic processing as above, the integrated value calculated by the integrating unit 44 does not exceed a predetermined integration threshold value, so that it is not determined to be an independent operation.

Here, in order to further prevent erroneous detection when the system frequency changes stepwise or when the lamp changes, the independent operation detection unit 46 continues for a predetermined time for a period in which the integrated value is equal to or greater than a predetermined integrated threshold value. If this is the case, it may be determined that the inverter circuit 2 is in an independent operation state.

<Effect of the first embodiment>
According to the grid interconnection inverter 100 of the first embodiment, the first moving average value obtained by the moving average of the first moving average section and the second moving average section which is a section half a cycle before the first moving average section. Since the difference from the second moving average value obtained by the moving average of is sequentially calculated, the absolute value of the difference is integrated at predetermined time intervals, and the integrated value is compared with the predetermined integrated threshold value. It is possible to prevent erroneous detection and detection delay of independent operation while reducing the injection amount of ineffective power.

<Second Embodiment>
Next, the grid interconnection inverter 100 according to the second embodiment will be described. The same or corresponding configurations as those in the first embodiment are designated by the same reference numerals.

The grid interconnection inverter 100 of the second embodiment has a different function of the independent operation detection device 4 from the first embodiment.

That is, the isolated operation detection device 4 of the second embodiment increases the injection amount of the reactive power when the integrated value obtained by the integrating unit 44 becomes equal to or more than a predetermined integration threshold value. The independent operation of the inverter circuit 2 is detected by the frequency change caused by the reactive power.

The functions of each part will be described below.
The comparison unit 45 of the second embodiment determines whether or not the integrated value after the continuation of the 1.5 cycles after the state in which the frequency is changed by the periodic active signal continues for 1.5 cycles is equal to or higher than the predetermined integration threshold value. Is determined.

Specifically, as shown in FIG. 6, the comparison unit 45 acquires the system frequency calculated by the frequency calculation unit 42 and determines whether or not there is a change in the system frequency. Here, the presence or absence of a frequency change is determined by whether or not a predetermined change determination threshold value has been reached. Where a delay occurs from the occurrence of the isolated operation to the arrival of the change determination threshold value, if the delay time is within 100 ms, it is considered that the disconnection can be performed within 1 second from the occurrence of the isolated operation. Therefore, the predetermined change determination threshold value is set to a value at which the delay time is 100 ms at the maximum.

Then, when it is determined that the frequency change of the system frequency continues for 1.5 cycles, the comparison unit 45 determines whether or not the integrated value after the lapse of the 1.5 cycles is equal to or higher than the predetermined integration threshold value. do. Here, the predetermined integration threshold value is a value of a predetermined ratio (for example, 70%) to the stable value of the integrated value.

Then, the reactive power generation unit 41 increases the reactive power superimposed on the output power of the inverter circuit 2 when the integrated value is larger than the integrated threshold value in the comparison result obtained by the comparison unit 45. Here, the phase of the increasing reactive power (hereinafter, also referred to as an increasing active signal) is on the side where the frequency increases (as viewed from the grid interconnection inverter 100) so that the reactive powers do not cancel each other out when a plurality of units are in operation. Fix it on the leading side). The reactive power generation unit 41 continuously superimposes the above-mentioned periodic active signal even after the reactive power is increased. Then, the reactive power generation unit 41 inputs the command value for outputting the periodic active signal and the increasing active signal to the current controller 34 of the inverter circuit control device 3.

As shown in FIG. 7, the isolated operation detection unit 46 is used when the system frequency after the reactive power is increased by the reactive power generation unit 41 (after the injection of the increased active signal) becomes equal to or higher than a predetermined frequency threshold value. , Detects the independent operation of the inverter circuit 2.

Here, the predetermined frequency threshold value is a value obtained by adding a predetermined set value to the system frequency immediately before increasing the injection amount of the reactive power.
It is conceivable that the system frequency immediately before is the average value of, for example, 3 cycles before increasing the injection amount in consideration of the variation in the system frequency.
The predetermined set value added to the immediately preceding system frequency is determined based on the amount of change in frequency that occurs in the maximum injection amount of reactive power, and in the present embodiment, the frequency that occurs in the maximum injection amount of reactive power. It is half of the amount of change.
It should be noted that the maximum injection amount of the reactive power avoids an excessive increase in the injection amount of the reactive power, and the overfrequency (for example, 103% of the system frequency, +1.50 Hz in the case of 50 Hz, and +1 in the case of 60 Hz. 80Hz). Specifically, the maximum injection amount is set so that the amount of change in frequency is +2.50 Hz in the case of 50 Hz, and the amount of change in frequency is set to +3.00 Hz in the case of 60 Hz. ing. In this case, the predetermined set value is +1.25 Hz in the case of 50 Hz and +1.50 Hz in the case of 60 Hz.

Further, as shown in FIG. 7, the isolated operation detecting unit 46 detects the isolated operation of the inverter circuit 2 when the state where the system frequency is equal to or higher than the frequency threshold value continues for a predetermined time.

Here, the margin time from the increase in the injection of the reactive power to the determination of the independent operation detection is from the following equations 1 to 175 ms.
(Equation 1: Margin time from increase of injection of reactive power to judgment of independent operation)
Margin time = "Within 1 second of disconnection"-"Invalid power increase judgment time"-"Switch operation time"
= "Within 1 second of disconnection"-"1.5 cycle + measurement delay"-"Switch operation time"
= 1000ms- (625ms + 100ms) -100ms
= 175ms

On the other hand, the processing time until the independent operation detection determination is the injection increase time of the reactive power + the duration (detection time limit).
Here, in order to prevent erroneous detection, the frequency threshold value or higher is set to independent operation for 3 consecutive cycles (maximum 60 ms). Further, the injection increase time of the reactive power is set to half a cycle (about 100 ms) of the periodic signal so that the sequence is disconnected in 1 second from the independent operation.
Then, the processing time until the isolated operation detection determination is 165 ms from the following equation 2.
(Equation 2: Time required to detect independent operation due to increased injection of reactive power)
Processing time = Reactive power injection increase time + Detection time limit
= Half cycle of the periodic component of reactive power + Detection time limit
≒ 100ms + 60ms
= 160ms
As described above, the grid interconnection inverter 100 can be disconnected from the power grid 300 within 1 second from the occurrence of the independent operation.

Next, the simulation results of the determination operation of the independent operation detection device 4 when the system frequency changes stepwise and when the lamp changes will be described.

FIG. 8 is a simulation result when the system frequency changes stepwise. The step change is 50 Hz → 50.8 Hz 3 cycles → 50.8 Hz.
As can be seen from the integrated value in FIG. 8, the frequency change has not continued for 1.5 cycles since the start of the frequency change (condition 1: ×), and the integrated value after 1.5 cycles from the start of the frequency change is zero. (Condition 2: ×), and it can be seen that the independent operation is not erroneously detected due to the step change.

FIG. 9 is a simulation result when the system frequency changes with a lamp. As for the lamp change, the frequency change rate was set to 2 Hz / sec from 50 Hz to 51.5 Hz.
Looking at the integrated value in FIG. 9, the frequency change continues for 1.5 cycles from the start of the frequency change (condition 1: 〇), and the integrated value 1.5 cycles after the start of the frequency change is equal to or higher than the integrated threshold value. (Condition 2: ○). However, it differs from the case of independent operation in the following points.

That is, the stable value of the integrated value (value corresponding to 2 Hz / sec) during the lamp change is different. Further, the integrated value becomes zero in 1.5 cycles of the periodic active signal from the end of the lamp change.
Therefore, it is desirable that the comparison unit 45 further determines the lamp fluctuation. That is, the comparison unit 45 determines whether or not the lamp fluctuates 1.5 cycles after the start of the frequency change. Specifically, the comparison unit 45 determines whether or not the integrated value is within the lamp fluctuation determination range. Here, the lamp fluctuation range is from a stable value (3.60) when the lamp change is 1.8 Hz / sec to a stable value (4.40) when the lamp change is 2.2 Hz / sec. According to the comparison result of the comparison unit 45, the independent operation detection unit 46 does not increase the injection amount of the reactive power because it is not the independent operation when the integrated value is within the lamp fluctuation range.

<Effect of the second embodiment>
According to the grid interconnection inverter 100 of the second embodiment, it is possible to more reliably detect the isolated operation as compared with the first embodiment.

<Other modified embodiments>
The present invention is not limited to the above embodiment.

In the first embodiment, the first moving average section and the second moving average section are both half cycles of the set cycle of the reactive power, but may be other periods. Further, the first moving average section and the second moving average section may be in different periods from each other.

Further, although the second moving average section is set to be half a cycle before the set cycle than the first moving average section, it may be other than that.

In addition, the integration unit 44 integrates the absolute value of the difference obtained by the difference average calculation unit every half cycle of the periodic component, but it may integrate every other time. good.

In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

100 ... Grid interconnection Inverter 200 ... Distributed power supply 300 ... Power system 2 ... Inverter circuit 3 ... Inverter circuit control device 4 ... Independent operation detection device 41 ... Invalid power generation Unit 42 ・ ・ ・ Frequency calculation unit 43 ・ ・ ・ Average difference calculation unit 44 ・ ・ ・ Integration unit 45 ・ ・ ・ Comparison unit 46 ・ ・ ・ Independent operation detection unit

Claims (8)

It detects the independent operation of the inverter circuit that converts the DC power of the distributed power supply into AC power and outputs it to the power system, and the output power of the inverter circuit alternates between the delayed phase and the leading phase in a predetermined set cycle. It is a solitary operation detection device that continuously superimposes the ineffective power that changes to the above regardless of the fluctuation of the system frequency and detects the solitary operation of the inverter circuit based on the fluctuation of the frequency of the power system.
The first moving average value obtained by the moving average of the first moving average section at the frequency of the power system and the second moving obtained by the moving average of the second moving average section which is a section before the first moving average section. An average difference calculation unit that sequentially calculates the difference from the average value,
An integration unit that integrates the absolute value of the difference obtained by the average difference calculation unit at predetermined time intervals, and an integration unit.
A comparison unit for comparing the integrated value obtained by the integration unit with a predetermined integration threshold value is provided.
An independent operation detection device that detects the independent operation of the inverter circuit by using the comparison result obtained by the comparison unit. The first moving average section is a half cycle of the set cycle, and is
The isolated operation detection device according to claim 1, wherein the second moving average section is a half cycle of the set cycle before the set cycle of the first moving average section. The independent operation detection device according to claim 1 or 2, wherein the integration unit integrates the absolute value of the difference every half time of the set cycle. In the comparison result obtained by the comparison unit, when the integrated value is larger than the integrated threshold value, the reactive power generation unit that increases the reactive power superimposed on the output power of the inverter circuit, and the reactive power generation unit.
Any of claims 1 to 3, further comprising a solitary operation detection unit that detects the solitary operation of the inverter circuit when the frequency of the power system after increasing the reactive power is equal to or higher than a predetermined frequency threshold value. The stand-alone operation detection device according to item 1. The independent operation detection device according to claim 4, wherein the reactive power generation unit increases the reactive power when a state in which the integrated value is larger than the integrated threshold value continues for a predetermined time. The isolated operation detecting device according to claim 4 or 5, wherein the isolated operation detecting unit detects the isolated operation of the inverter circuit when the frequency of the power system is equal to or higher than the frequency threshold value for a predetermined time. .. An inverter circuit that converts the DC power of a distributed power source into AC power and outputs it to the power system.
A grid interconnection inverter including the independent operation detection device according to any one of claims 1 to 6. This is a method of detecting the independent operation of an inverter circuit that converts the DC power of a distributed power supply into AC power and outputs it to the power system. The output power of the inverter circuit is alternately delayed and advanced in a predetermined set cycle. It is a solitary operation detection method that continuously superimposes the ineffective power that changes to the above regardless of the fluctuation of the system frequency and detects the solitary operation of the inverter circuit based on the fluctuation of the frequency of the power system.
The first moving average value obtained by the moving average of the first moving average section at the frequency of the power system and the second moving obtained by the moving average of the second moving average section which is a section before the first moving average section. An average difference calculation step that sequentially calculates the difference from the average value,
An integration step that integrates the absolute value of the difference obtained by the average difference calculation step at predetermined time intervals, and
A comparison step for comparing the integrated value obtained by the integrated step with a predetermined integrated threshold value is provided.
An isolated operation detection method for detecting the isolated operation of the inverter circuit by using the comparison result obtained by the comparison step.

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