JP4926146B2 - Isolated operation detection method and isolated operation detection device - Google Patents

Description

  The present invention relates to an isolated operation detection method and an isolated operation detection device for detecting that a distributed power supply has shifted to an isolated operation state in a grid interconnection system in which a distributed power supply is connected to a commercial power system.

  Various grid interconnection systems have been proposed in order to link private power generation facilities such as demand cogeneration facilities to the power grid. In this type of grid-connected system, if the power system's substation breaker is opened due to an accident in the power system, etc., and the power supply from the commercial power system is stopped (shut off), the distributed power equipment is connected to the system. If the system is operated while the system is operating, a reverse power flow from the distributed power source will normally flow into the power system that is in a power failure state, which may cause an electric shock accident or the like due to a single operation and threaten safety. For this reason, the function of reliably detecting the isolated operation state of the distributed power supply facility and disconnecting (disconnecting) the distributed power supply facility from the commercial power system, that is, the function of preventing the isolated operation of the distributed power supply is indispensable.

  Therefore, various isolated operation detection methods for detecting that the distributed power supply has been in an isolated operation state due to a system power failure or the like have been proposed. As such a detection method, an active islanding detection method and a passive islanding detection method are known.

  The passive detection method has no influence on the system, and even if a plurality of islanding detection devices exist in the commercial power system, it is possible to avoid a decrease in sensitivity of islanding detection due to mutual interference. However, in the conventional passive detection method, there is a possibility that erroneous detection may occur when a state change similar to that at the time of shifting to the single operation occurs due to a load change or the like during the parallel operation. In addition, in the method of detecting isolated operation from changes in the voltage, phase, and frequency of the fundamental wave component, if the load and power generation amount match at the location where the distributed power source is installed, those changes are small when shifting to isolated operation It is difficult to detect islanding with high accuracy.

Therefore, Patent Document 1 discloses an isolated operation detection method that can clearly detect the transition to isolated operation and that reduces the possibility of erroneous detection due to an event other than the transition to isolated operation. In the method disclosed in Patent Document 1, voltage and current at a connection point between a commercial power system and a distributed power source are continuously measured, and a predetermined odd-order harmonic admittance value is calculated based on measured values of voltage and current. calculate. The isolated operation state is detected when the calculated change in the harmonic admittance value exceeds a predetermined threshold. The change of the harmonic admittance value due to the shift to the single operation can be clearly detected, and the occurrence of the false detection due to the event other than the shift to the single operation is unlikely to occur.
JP 2006-240669 A

  In the case of the isolated operation detection method disclosed in Patent Document 1, when a large-capacity transformer that has been cut off is connected by turning on the breaker, an inrush current is generated due to charging of the transformer. As a result, the harmonic admittance value may change even though it is not in the isolated operation state, and may be erroneously detected as the isolated operation state.

  Therefore, the present invention solves the above-mentioned problems and avoids erroneous detection of isolated operation caused by the introduction of a large-capacity transformer without affecting the detection of isolated operation when the isolated operation is actually formed. An object of the present invention is to provide a method for detecting an isolated operation.

  Another object of the present invention is to provide an isolated operation detection device for carrying out such an isolated operation detection method.

  In order to solve the above problems, the isolated operation detection method of the present invention continuously measures the voltage and current at the connection point between the commercial power system and the distributed power source, and determines a predetermined value based on the measured value of the voltage and current. A method of calculating an odd-order harmonic admittance value, and detecting an isolated operation state based on a change in the calculated harmonic admittance value exceeding a predetermined threshold Yt, comprising: When the voltage level V2 of the second harmonic component is determined and the voltage level V2 exceeds a predetermined threshold value Vt, the detection of the isolated operation state is stopped for a certain period from the time when the voltage level V2 exceeds the predetermined threshold value Vt. It is characterized by preventing.

  The isolated operation detection device of the present invention is applied to a grid interconnection system that can supply power from a distributed power source by a private power generator to a consumer load connected to a commercial power system. From the measurement output of each of the voltage measurement unit that continuously measures the voltage at the system point, the current measurement unit that continuously measures the current at the connection point of the distributed power source, and each of the voltage measurement unit and the current measurement unit A harmonic analysis unit that calculates at least one harmonic component of a predetermined order, and a voltage value and a current value of the harmonic for each order calculated by the harmonic analysis unit, An admittance value calculation unit that calculates an admittance value for each of the admittance value, and a change in the admittance value for the harmonics of at least one order calculated by the admittance value calculation unit, When the state that exceeds the constant threshold value Yt persisted predetermined time, and a index determination section for outputting a determination result indicating that the dispersed power supply shifts to the islanding state. And a second harmonic determining unit that determines whether or not the voltage level V2 of the second harmonic component at the interconnection point exceeds a predetermined threshold value Vt. When it is detected that the voltage level V2 exceeds the threshold value Vt, erroneous detection is prevented by stopping detection of the isolated operation state for a certain period from the time point when the voltage level V2 exceeds the threshold value Vt. .

  According to the present invention, the detection of isolated operation is stopped by using the voltage level of the second harmonic component as an index, so that erroneous detection of isolated operation due to the introduction of a large-capacity transformer is actually detected. This can be avoided without affecting the detection of islanding when formed.

  The present invention can take the following forms based on the above-described configuration.

  That is, in the isolated operation detection method or isolated operation detection device of the present invention, it is preferable to set the threshold value Vt to 2 to 10 times the voltage level V2 in a steady state.

  The voltage level V2 is repeatedly detected at predetermined time intervals, and the voltage level V2 detected at a detection time after the detection time of the voltage level V2 is detected based on the detected voltage level V2. A threshold value Vt can be generated.

  Further, it is preferable that the detection of the voltage level V2 is sequentially performed every basic wave one cycle period.

  Further, an admittance value is calculated for the harmonic component of at least one of the third, fifth, seventh, ninth, eleventh, and thirteenth orders, and the calculated higher order harmonics. Based on the change in the admittance value for each of the components, the isolated operation state can be detected.

  Further, when an admittance value is calculated for each of a plurality of harmonic components of a plurality of orders, and a state in which the change in the admittance value exceeds the threshold value Yt for a predetermined time for at least one of the calculated harmonic components of each order, It is preferable to determine that it is an isolated operation. In that case, it is preferable to use only the admittance value for each of the fifth and seventh harmonic components.

(Embodiment)
Hereinafter, an isolated operation detection method and an apparatus for carrying out the method according to an embodiment of the present invention will be specifically described with reference to the drawings. FIG. 1 is a block diagram showing a grid interconnection system in which the method of the present embodiment is implemented.

  A commercial power grid 1 in FIG. 1 is connected to a load 2 of a customer, and power from the distributed power source 3 can be supplied to the load 2 via the interconnection section 4. The system is configured. When the private power generation device is a direct current power supply device such as a solar cell or a fuel cell, the output of the power generation device is controlled and supplied to the same voltage and the same frequency as the commercial power system 1 by an inverter. An isolated operation detection device 5 is connected to the interconnection point between the commercial power system 1 and the distributed power supply 3 to detect that the distributed power supply 3 has shifted to the isolated operation state. The isolated operation detection device 5 has a configuration for carrying out the isolated operation detection method in the present embodiment.

  The isolated operation detection device 5 calculates a predetermined odd-order harmonic admittance value at the connection point between the commercial power system and the distributed power source, and the calculated change in the harmonic admittance value exceeds a predetermined threshold Yt. Based on the above, the single operation state is detected. As the order of the harmonic used for detection of the isolated operation state, at least one of the third order, the fifth order, the seventh order, the ninth order, the eleventh order, and the thirteenth order can be used. In particular, when a fifth or seventh harmonic component is used, it is most effective for detecting an isolated operation (see Japanese Patent Application No. 2007-97732). In addition, it is desirable that at least one of the calculated harmonic components of each order is determined as an isolated operation when a state in which the change in the admittance value exceeds the threshold value Yt continues for a predetermined time.

  For more reliable detection, an admittance value is calculated for each of the harmonic components of a plurality of orders, and the change in the admittance value exceeds a predetermined threshold Yt for at least one of the calculated harmonic components of each order. It is desirable to determine that it is an isolated operation based on whether or not it has been. If the admittance values for the fifth and seventh harmonic components are used, the most accurate determination can be made.

  Therefore, by performing isolated operation detection using only the admittance values for each of the fifth and seventh harmonic components, the harmonic analysis logic is simplified while enabling highly accurate detection. It is possible to reduce the CPU capacity for analysis and shorten the analysis time. Therefore, in the present embodiment, a case where admittance values for the fifth and seventh harmonic components are used will be described as an example.

  The isolated operation detection device 5 includes a voltage measurement unit 6 that continuously measures the voltage at the connection point of the distributed power source 3 and a current measurement unit 7 that continuously measures the current at the connection point of the distributed power source 3. The measurement outputs of the voltage measurement unit 6 and the current measurement unit 7 are supplied to the harmonic analysis units 9a and 9b via the fundamental wave component removal units 8a and 8b, respectively. Each of the harmonic analysis units 9a and 9b calculates fifth-order and seventh-order harmonic components and supplies them to the admittance value calculation unit 10. For the analysis of the harmonic component in the harmonic analysis units 9a and 9b, for example, a method of calculating the harmonic component by wavelet transforming the measured values of voltage and current can be applied. The admittance value calculation unit 10 calculates admittance values for the fifth and seventh harmonics from the voltage values and current values of the fifth and seventh harmonics.

  The admittance values for the fifth and seventh harmonics calculated by the admittance value calculation unit 10 are supplied to the admittance index determination unit 11. The admittance index determination unit 11 compares the change in the admittance values of the fifth and seventh harmonics with the threshold value Yt, and when the distributed power source 3 exceeds the threshold value Yt for at least one harmonic, The determination result indicating that the process has shifted to is output.

  The measurement output of the voltage measurement unit 6 is also supplied to the second harmonic determination unit 12. The second harmonic determination unit 12 calculates the voltage level V2 of the second harmonic component from the voltage measurement value supplied from the voltage measurement unit 6, and determines whether the level has exceeded a predetermined threshold value Vt. judge.

  The determination results of the admittance index determination unit 11 and the second harmonic determination unit 12 are supplied to the comprehensive determination unit 13. The comprehensive determination unit 13 outputs the detection result of the isolated operation based on the determination result of the admittance index determination unit 11, but changes its operation according to the determination result of the second harmonic determination unit 12.

  That is, when the determination result in the second harmonic determination unit 12 indicates that the voltage level of the second harmonic exceeds the predetermined threshold value Vt, the comprehensive determination unit 13 detects the isolated operation. Stop. The stop of the isolated operation is continued for a certain period from the time point when the determination result in the second harmonic determination unit 12 indicates that the voltage level of the second harmonic exceeds the threshold value Vt. As a result, erroneous detection of isolated operation can be prevented.

  A detection signal indicating the determination result of the isolated operation state by the comprehensive determination unit 13 is supplied to the interconnection unit 4. When the detection signal from the comprehensive determination unit 13 indicates the single operation state of the distributed power source 3, the interconnection unit 4 disconnects the distributed power source 3 from the commercial power system 1. The comprehensive determination unit 13 stops supplying detection results to the interconnection unit 4 in place of the operation of stopping the isolated operation detection as described above, according to the determination result in the second harmonic determination unit 12. The signal may be locked to a state indicating that the operation is to be performed, that is, that the operation is not an isolated operation.

  The state in which the voltage level of the second harmonic exceeds the threshold value Vt greatly occurs when a large-capacity transformer is connected by turning on the circuit breaker due to an excitation inrush current accompanying charging of the transformer. However, during the single operation, the state where the voltage level of the second harmonic exceeds the threshold value Vt occurs only for a very short period, so that the stop of the single operation detection due to the state hardly occurs. The voltage level of the second harmonic is effective as an index for preventing erroneous detection of isolated operation.

  The threshold value Vt for determining the voltage level of the second harmonic in the second harmonic determining unit 12 is set to a value larger than the change at the time of shifting to the independent operation and the normal change, and smaller than the change at the time of disturbance such as an accident. There is a need.

  In addition, when the harmonic admittance value changes greatly with the charging of the transformer even though no isolated operation is formed, the fluctuation of the harmonic admittance value continues for a certain period. It is desirable to stop detection.

  The change (D) in the admittance value calculated and determined by the admittance value calculation unit 10 and the admittance index determination unit 11 is defined as follows. That is, the admittance value at a certain time point t1 is (Y1), and the admittance value at a time point t0 a certain time before the time point t1 is (Y0).

D = (Y1-Y0) / Y0 (1)
Further, when actually measuring the change (D) in the admittance value, the average value of the admittance values in the respective predetermined time ranges corresponding to the time points t0 and t1 can be measured to calculate the change. desirable. For example, average values of admittance values from time t0 to 0.01 seconds and from time t1 to 0.01 seconds are measured. That is, the average time corresponds to 0.5 cycle in the 50 Hz system. A change in the admittance value is calculated using the average value. At this time, it is desirable that the change in the admittance value is calculated at predetermined time intervals, and when the threshold value Yt is exceeded for a predetermined time, it is determined that the state is in an isolated operation state.

  In accordance with this definition, the change (D) in the admittance value is calculated from the obtained admittance values for the fifth and seventh harmonic components of the current and voltage measured values at the interconnection point. If any of the fifth and seventh admittance changes exceeds the set threshold value Yt over a predetermined period, it is determined that the vehicle is operating independently.

  Since it is desirable to be able to determine the isolated operation as quickly as possible, it is better that the predetermined time required for determining that the threshold value Yt has been exceeded is shorter. However, if the threshold value Yt is exceeded as in the case of an instantaneous beard, it is determined as the isolated operation. If this happens, there is a high possibility of false detection. Therefore, the determination is performed over a certain period of time. For example, as an example of the present embodiment, a favorable result can be obtained by setting a predetermined period for detecting a state exceeding the threshold Yt to 0.08 seconds (corresponding to 4 cycles in a 50 Hz system). However, in order to analyze harmonics with high accuracy, for example, the measurement data of 2000 points (0.0005 second sampling) is captured per second.

  The fact that it is preferable to limit the target harmonic admittance to only the fifth and seventh orders is based on the results of demonstration tests in actual systems. In other words, it has been proved by the verification test that the fifth-order or seventh-order harmonic admittance value always decreases if an isolated operation occurs in the power system. The threshold value Yt of the change in admittance value (D) for determining the islanding operation is set within a limited range of -0.1 to -0.9 from the results of the demonstration test in the actual system. As a result, it was found that a practically appropriate determination result can be obtained. That is, since the fifth or seventh admittance value changes in a decreasing direction due to the occurrence of an isolated operation, according to the equation (1) that defines the change (D) of the admittance value, from −0.1 A sufficient range of variation is included in the range of -0.9.

  Next, the second harmonic determination unit 12 determines the voltage level of the second harmonic, which is a feature of the present invention, and stops detection of an isolated operation when a predetermined threshold value Vt is exceeded. The operation will be described. FIG. 2 shows a configuration example for detecting that the voltage level of the second harmonic exceeds a predetermined threshold value Vt in the second harmonic determination unit 12.

  Three-phase line voltages VAB, VBC, and VCA are output from the line voltage measuring units 20a to 20c in FIG. The line voltages VAB, VBC, and VCA are converted into phase voltages input to the subtractors 21a to 21c, amplified by the amplifiers 22a to 22c, and then input to the discrete Fourier transform units 23a to 23c.

  The discrete Fourier transform units 23a to 23c perform a discrete Fourier transform using the clock signal supplied from the clock generator 24. The sampling interval is, for example, 50 Hz × 48 sampling. The discrete Fourier transform of the phase voltage data is sequentially executed for one cycle period of the fundamental wave. From the discrete Fourier transform units 23a to 23c, a Fourier transform of the second harmonic of the fundamental wave 1 cycle period is output.

  The outputs of the discrete Fourier transform units 23a to 23c are input to the symmetric component calculating unit 25, and the level of the symmetric component (normal phase, reverse phase) of the second harmonic is calculated. In addition, it is good also as a structure calculated about each phase. The output of the symmetrical component extraction unit 25 is input to the absolute value calculation units 26a and 26b, and the absolute value level of the second harmonic component is calculated for each of the positive phase side and the negative phase side.

  On the other hand, the outputs of the absolute value calculation units 26a and 26b are supplied as one input of the comparators 30a and 30b after passing through the smoothers 27a and 27b, the delay units 28a and 28b, and the amplifiers 29a and 29b, respectively. The outputs of the absolute value calculators 26a and 26b are directly supplied as the other input of the comparators 30a and 30b, respectively. The outputs of the comparators 30a and 30b are input to the OR determiner 31. In this way, by performing the same processing for each of the positive phase side and the reverse phase side and making the detection result OR determination, it is possible to prevent erroneous detection of the isolated operation more reliably.

  With the above configuration, the signals smoothed by the smoothers 27a and 27b are amplified by a factor of three by the amplifiers 29a and 29b after a predetermined time delay, and used as a threshold value Vt for determining the voltage level of the second harmonic. Supplied. That is, if the voltage at the interconnection point is in a steady state, signals indicating the average level of the steady value signal are output from the smoothers 27a and 27b. By delaying this signal for a predetermined time and amplifying it by a factor of 3, a level three times the steady value is supplied as the threshold value Vt.

  Thus, if a level three times the steady value is used as the threshold value Vt for the determination for detecting an increase in the voltage level of the second harmonic, an appropriate determination result can be stably obtained. The delay devices 28a and 28b are interposed so that the threshold value Vt output from the amplifiers 29a and 29b immediately increases during a transient when the voltage level of the second harmonic increases by delaying for a predetermined time. This is to avoid the problem.

  The signals directly input to the comparators 30a and 30b from the absolute value calculators 26a and 26b are signals (second harmonic level signals) to be determined for determining the voltage level of the second harmonic. In the comparators 30a and 30b, the second harmonic level signal is compared with the threshold value Vt output from the amplifiers 29a and 29b, and when the second harmonic level signal exceeds the threshold value Vt, the level excess is exceeded. The signal shown is output. The output signal of the OR determination unit 31 that receives the outputs of the comparators 30a and 30b is supplied to the comprehensive determination unit 13 in FIG. 1, and the detection of the isolated operation is temporarily stopped.

  Note that the threshold Vt is three times the average level of the steady value signal, and can be set as appropriate according to the specification. Considering the stability of the operation, it is desirable to set the level to 2 to 10 times the steady value.

  FIGS. 3 and 4 show a case where a single operation is formed with respect to the state of fluctuation of the voltage level (V2) of the second harmonic and the change of the admittance value (Y5) with respect to the fifth harmonic, and a transformer. The difference when charging occurs will be described. 3 and 4, (a) shows the fluctuation of the voltage level of the second harmonic, and (b) shows the fluctuation of the change rate of the admittance value with respect to the fifth harmonic.

  FIG. 3 shows a state where an isolated operation is formed. The part where the value of Y5 in (b) rapidly decreases indicates the formation of an isolated operation. When the single operation occurs in this way, V2 exceeds the threshold value Vt at the same time as shown in FIG. Therefore, even if the detection of the isolated operation is stopped based on the increase in V2, the stop period hardly occurs and there is substantially no influence on the detected independent operation. The reason why V2 gradually increases on the right side of the figure is based on a problem in signal processing and is not related to the original operation.

  On the other hand, FIG. 4 shows a state when charging of the transformer occurs. In this case, as shown in (a), as the charging of the transformer occurs, V2 rises rapidly, and the state exceeding the threshold value Vt continues for a length of time close to the transient phenomenon occurrence period. . In addition, the value of Y5 in (b) also decreases, and the state is the same as in the case of isolated operation. In this case, since the time indicated by the arrow for V2 exceeding the threshold value Vt is sufficiently long, the time during which the isolated operation is erroneously detected due to a decrease in the value of Y5 is stopped during that period. Decrease enough.

  As described above, even when the same admittance value change as when switching to isolated operation occurs due to the charging of the transformer when the circuit breaker is turned on, detection of isolated operation is appropriately stopped to avoid occurrence of erroneous detection. be able to.

  ADVANTAGE OF THE INVENTION According to this invention, the erroneous detection of the independent operation state accompanying injection | throwing-in of a large capacity | capacitance transformer can be avoided, and it is useful for control of the grid connection system which connected the distributed power source to the commercial power system.

The block diagram which shows the grid connection system in which the isolated operation detection apparatus in embodiment of this invention was installed The block diagram which shows the structural example for determining the voltage level of the 2nd harmonic in the same independent operation detection apparatus (A) is a figure which shows the fluctuation | variation of the voltage level of a 2nd harmonic, and (b) is a figure which shows the fluctuation | variation of the change rate of the admittance value with respect to a 5th harmonic in the case of isolated operation formed. (A) is a figure which shows the fluctuation | variation of the voltage level of a 2nd harmonic in case charging of a transformer generate | occur | produced, (b) is a figure which shows the fluctuation | variation of the change rate of the admittance value with respect to a 5th harmonic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Commercial power system 2 Load 3 Distributed power supply 4 Interconnection part 5 Independent operation detection device 6 Voltage measurement part 7 Current measurement part 8a, 8b Fundamental wave component removal part 9a, 9b Harmonic wave analysis part 10 Admittance value calculation part 11 Admittance index determination Unit 12 second harmonic determination unit 13 comprehensive determination unit 20a to 20c line voltage measurement unit 21a to 21c subtractor 22a to 22c amplifier 23a to 23c discrete Fourier transform unit 24 clock generator 25 symmetry calculation unit 26a, 26b absolute Value calculation units 27a and 27b Smoothers 28a and 28b Delay devices 29a and 29b Amplifiers 30a and 30b Comparator 31 OR decision unit

Claims (14)

Continuously measure the voltage and current at the connection point between the commercial power system and the distributed power source,
Calculate harmonic odd admittance values of a predetermined odd order based on the measured values of voltage and current,
In the isolated operation detection method for detecting the isolated operation state based on the calculated change in the harmonic admittance value exceeding a predetermined threshold Yt,
The voltage level V2 of the second harmonic component at the interconnection point is determined, and when the voltage level V2 exceeds a predetermined threshold value Vt, the detection of the isolated operation state is stopped for a certain period from that point. An isolated operation detection method characterized by preventing erroneous detection.   The islanding operation detection method according to claim 1, wherein the threshold value Vt is set to 2 to 10 times the voltage level V2 in a steady state.   The voltage level V2 is repeatedly detected at predetermined time intervals, and based on the detected voltage level V2, the threshold value Vt for the voltage level V2 detected at a detection time after the detection time of the voltage level V2 The isolated operation detection method according to claim 2, wherein:   The islanding operation detection method according to claim 3, wherein the detection of the voltage level V <b> 2 is sequentially performed every fundamental wave cycle period.   An admittance value is calculated for the harmonic component of at least one of the third, fifth, seventh, ninth, eleventh, and thirteenth orders, and the calculated harmonic component of the order The isolated operation detection method according to any one of claims 1 to 4, wherein an isolated operation state is detected based on a change in admittance value for each.   An admittance value is calculated for each of a plurality of harmonic components of a plurality of orders, and at least one of the calculated harmonic components of each order is operated independently when a change in admittance value exceeds the threshold Yt for a predetermined time The islanding operation detection method according to claim 5, wherein   The islanding operation detection method according to claim 6, wherein only the admittance values for each of the fifth and seventh harmonic components are used. It is applied to a grid interconnection system that can supply power from a distributed power source by a private power generator to a consumer load connected to a commercial power system.
A voltage measuring unit for continuously measuring the voltage at the interconnection point of the distributed power source;
A current measurement unit that continuously measures the current at the interconnection point of the distributed power source;
A harmonic analysis unit that calculates at least one harmonic component of a predetermined order from the measurement outputs of the voltage measurement unit and the current measurement unit;
An admittance value calculation unit for calculating an admittance value for each of the harmonic components of each of the harmonics from a voltage value and a current value of the harmonics of the respective orders calculated by the harmonic analysis unit;
Regarding the change in the admittance value for the harmonics of at least one order calculated by the admittance value calculation unit, when the state exceeding a predetermined threshold Yt has continued for a predetermined time, the distributed power source has shifted to the single operation state. In the isolated operation detection device comprising an index determination unit that outputs a determination result indicating
A second harmonic determination unit that determines whether or not the voltage level V2 of the second harmonic component at the interconnection point exceeds a predetermined threshold Vt;
When the second harmonic determination unit detects that the voltage level V2 exceeds the threshold value Vt, the detection of the isolated operation state is stopped for a certain period from the time when the voltage level V2 exceeds the threshold value Vt. An isolated operation detection device characterized by preventing detection.   The isolated operation detection device according to claim 8, wherein the threshold value Vt is set to 2 to 10 times the voltage level V2 in a steady state.   The second harmonic determination unit repeatedly detects the voltage level V2 at predetermined time intervals, and detects at a detection time after the detection time of the voltage level V2 based on the detected voltage level V2. The isolated operation detection device according to claim 9, wherein the threshold value Vt for the voltage level V2 to be generated is generated.   The isolated operation detection device according to claim 10, wherein the second harmonic determination unit sequentially detects the voltage level V2 for each fundamental wave cycle period.   An admittance value is calculated for the harmonic component of at least one of the third, fifth, seventh, ninth, eleventh, and thirteenth orders, and the calculated harmonic component of the order The isolated operation detection device according to any one of claims 8 to 11, wherein an isolated operation state is detected based on a change in admittance value for each.   An admittance value is calculated for each of a plurality of harmonic components of a plurality of orders, and at least one of the calculated harmonic components of each order is operated independently when a change in admittance value exceeds the threshold Yt for a predetermined time The isolated operation detection device according to claim 12, which is determined as follows.   The isolated operation detection device according to claim 13, wherein only the admittance values for the fifth and seventh harmonic components are used.

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