JP6031266B2 - Isolated operation detection method and isolated operation detection device - Google Patents

Description

  Embodiments described herein relate generally to an isolated operation detection method and an isolated operation detection device.

  Conventionally, a frequency shift method that shifts the frequency by applying positive feedback to frequency fluctuations during single operation is used as a single operation detection device that detects whether or not a distributed power source is disconnected from the power system and is operating alone. What to do has been proposed.

  Conventional isolated operation detection devices detect from 0.5 seconds to 1.0 seconds, but in recent years, a high-speed isolated operation detection method that detects from 0.1 seconds to 0.2 seconds has come to be desired. However, in order to detect at high speed, it is necessary to increase the gain of the positive feedback, and this may increase the occurrence frequency of flicker during the interconnection operation.

  On the other hand, conventionally, a method has been proposed for detecting a single operation at high speed by injecting reactive power by detecting that the harmonics of the AC voltage increase or the power supply voltage has risen when the single operation is performed. ing. When there are many capacitors connected to the AC power supply, or when the system is three-phase, when single operation is performed, harmonics that are multiples of three are canceled out in the case of three-phase, so the harmonics do not increase rapidly There is a case where it is difficult to detect high-speed operation independently.

  On the other hand, in the method of detecting the isolated operation by increasing the reactive power from the frequency by the positive feedback action, if the gain of the positive feedback is too large or the impedance of the distribution line is too high, the voltage fluctuates and flicker phenomenon occurs. Electric light flickering sometimes occurred.

One management indicators flicker is flicker coefficient [Delta] V _10. The flicker coefficient ΔV ₁₀ is a fluctuation value of 10 Hz in the flicker sensitivity curve. ΔV ₁₀ is compared with a predetermined allowable value, and if it is equal to or less than the allowable value, it is determined that the power quality is good.

Japanese Patent No. 4656131

  Embodiments of the present invention have been made in view of the above circumstances, and provide an isolated operation detection method and an isolated operation detection device that achieve high-speed detection of isolated operation and avoid a decrease in power quality. Objective.

According to the embodiment, the DC power is converted into AC power, the DC power is converted into AC power, and the inverter is operated alone in conjunction with the AC power system. And a voltage detection unit that detects an AC voltage output from the inverter, and an abnormality detection unit configured to detect an abnormality in voltage, frequency, and frequency change rate from the voltage detected by the voltage detection unit, A frequency detection unit that detects a frequency of an AC voltage output from the AC power system and the inverter, a frequency change rate detection unit that calculates a frequency change rate from the frequency detected by the frequency detection unit, and a frequency change rate When the frequency change rate is positive due to the first function of the reactive power or current phase angle, the reactive power flows when the frequency change rate is positive, and the frequency change rate is negative A first function unit for lagging reactive power by calculating the value of the reactive power or current phase angle to flow output by the second function of the reactive power or current phase angle with respect to frequency, when the frequency is greater than the reference frequency A second function unit that calculates and outputs a value of reactive power or current phase angle so that a lagging reactive power flows when a leading reactive power flows and a frequency is lower than the reference frequency, and an output of the first function unit And the output of the second function unit, an addition unit that outputs the result, a flicker coefficient calculation unit that calculates a flicker coefficient from the voltage detected by the voltage detection unit, and a value calculated by the flicker coefficient calculation unit There it is determined whether more than a predetermined threshold value, the so as to suppress the amount of variation of the reactive power or current phase angle with respect to the frequency change rate of the first function when exceeding a predetermined threshold value the A gain control unit that notifies the function unit, and a drive unit that controls the output power output from the inverter using the output of the addition unit, and stops the inverter when an abnormality is detected from the abnormality detection unit When the notification is received, the first function unit adjusts the gain of the first function to suppress the variation of the reactive power or the current phase angle with respect to the frequency change rate of the first function. An isolated operation detection device is provided.

FIG. 1 is a diagram schematically illustrating a configuration example of an isolated operation detection device according to the first embodiment. FIG. 2A is a diagram showing an example of the relationship between the frequency and the reactive power (or current phase angle) of the inverter bridge in the vicinity of the reference frequency. FIG. 2B is a diagram illustrating an example of the relationship between the frequency change rate and the reactive power (or current phase angle) of the inverter bridge in the vicinity of the reference frequency. FIG. 2C is a diagram illustrating another example of the relationship between the frequency change rate and the reactive power (or current phase angle) of the inverter bridge in the vicinity of the reference frequency. FIG. 3 is a diagram illustrating a flicker visibility curve. FIG. 4A is a diagram illustrating an example of a change in frequency when an isolated operation is detected. FIG. 4B is a diagram illustrating an example of a change in frequency when an isolated operation is detected. FIG. 5 is a diagram schematically illustrating another configuration example of the isolated operation detection device of the first embodiment. FIG. 6 is a diagram schematically illustrating a configuration example of the isolated operation detection device according to the second embodiment. FIG. 7 is a diagram illustrating an example of the relationship between the frequency deviation and the reactive power (or current phase angle) of the inverter bridge in the vicinity of the reference frequency. FIG. 8 is a diagram schematically illustrating another configuration example of the isolated operation detection device of the second embodiment.

  Hereinafter, an isolated operation detection method and an isolated operation detection device for an inverter according to an embodiment will be described with reference to the drawings.

  The inverter independent operation detection device according to the present embodiment synchronizes the voltage phase of the output power of the AC power system and the inverter, controls the output current to a predetermined current phase angle, and controls the reactive power of the output of the inverter. . Further, when the inverter is disconnected from the AC power system, the inverter is driven so that the reactive power of the inverter changes based on the frequency of the output voltage of the inverter. Furthermore, the characteristic curve of reactive power with respect to the frequency is moved so that the reactive power becomes almost zero following the normal frequency change (steady state) sufficiently, and the frequency is positively fed back to the fast frequency change (abnormal state). To control the direction to promote the change.

  The isolated operation detection device according to the present embodiment is an isolated operation detection protection device for an inverter that converts DC power output from a DC power source, such as a solar cell or a fuel cell, into AC power and operates in conjunction with an AC system. And detecting the voltage phase, frequency, and frequency change rate on the output side of the inverter, obtaining a reference phase from the detected voltage phase, and generating an AC current reference having a phase corresponding to the reference phase. In addition to controlling the output current, the reference phase θ is corrected according to the frequency and the value that changes according to the frequency change rate, thereby detecting that the inverter is disconnected from the AC system and performing the protection operation at high speed.

  That is, in the isolated operation detection device according to the present embodiment, when the AC side of the inverter is disconnected from the AC power system, the frequency of the AC power source and the frequency change rate slightly increase or decrease. An increase or decrease in the frequency and the frequency change rate is detected, and when the frequency is increased and the frequency change rate is positive, the current phase angle of the inverter is advanced and positive feedback is applied in the direction of further increasing the frequency. When an increase or decrease in the frequency and the frequency change rate is detected, and the frequency is decreased or the frequency change rate is negative, the current phase angle of the inverter is delayed and positive feedback is applied in the direction of further decreasing the frequency.

  As described above, the voltage, frequency, and frequency change rate of the AC power supply are detected by rapidly breaking the balance between the inverter output and the power consumption at the load, and stepped according to the frequency value and the frequency change rate. When the value that changes to exceeds a predetermined value, the isolated operation is detected at an early stage and the operation of the inverter is stopped.

Further, in the independent operation detecting apparatus of the present embodiment calculates the flicker coefficient [Delta] V ₁₀ from the system voltage, to adjust the amount of change in reactive power based on the frequency change rate when the flicker coefficient [Delta] V ₁₀ exceeds a predetermined threshold value, It suppresses flickering of electric lights.

FIG. 1 is a diagram schematically illustrating a configuration example of an isolated operation detection device according to the first embodiment.
The isolated operation detection device according to the present embodiment detects an isolated operation of the inverter bridge 2 that converts direct current power output from a direct current power source 1 including, for example, a solar cell or a fuel cell into alternating current power. The AC power output from the inverter bridge 2 is removed of high frequency components by PWM control by a filter including a reactor 3 and a capacitor 4, and supplied to a load 9 via a contactor 6.

  The isolated operation detection device according to the present embodiment includes a voltage detector 10 that detects an AC voltage that is output from the AC power system 8 and the inverter bridge 2 and supplied to the load 9, and an output voltage that is detected by the voltage detector 10. The reactive power Q or the current phase angle θ is controlled in a direction in which the frequency (f) is promoted by positive feedback, and the frequency (f) changes stepwise according to the frequency change rate (df / dt) of the frequency (f). The function means for controlling the reactive power Q or the current phase angle θ in the direction that promotes the change by positive feedback and the AC voltage supplied to the load 9 detects abnormalities in voltage, frequency, and frequency change rate. An abnormality detection means for outputting a signal for stopping the inverter bridge 2 in the case of the failure, a function means for synchronizing with the voltage phase of the outputs of the AC power system 8 and the inverter bridge 2 When the inverter bridge 2 is disconnected from the AC power system 8 by controlling the reactive power Q to the predetermined reactive power Q or the current phase angle θ by the output of the inverter and performing the reactive power control of the output of the inverter bridge 2, the frequency of the output voltage of the inverter bridge 2 Based on (f) and the frequency change rate (df / dt), the inverter bridge 2 is driven so that the reactive power Q changes, and the inverter bridge 2 is turned on when a signal for stopping the inverter bridge 2 is received from the abnormality detection means. Driving means for stopping.

  The AC voltage detected by the voltage detector 10 is supplied to the voltage relay 17, the frequency relay 18, and the frequency detection circuit 52 of the abnormality detection means.

  The drive means includes an amplifier 11, a current reference circuit 12, an amplifier 13, a PWM circuit 14, a drive unit 15, a PLL circuit 22, a phase shift circuit 23, and a sine wave circuit 26, and uses the output from the adder circuit 56. The output power of the inverter bridge 2 is controlled, and the inverter bridge 2 is stopped when an abnormality is notified from the abnormality detection circuit 19 of the abnormality detection means.

  The inverter bridge 2 is operated in conjunction with AC power supplied from the AC power system 8 via the circuit breaker 7. The AC voltage supplied to the load 9 is detected by the voltage detector 10 and supplied to the PLL circuit 22. The PLL circuit 22 inputs a signal V 22 synchronized with the AC voltage phase to the phase shift circuit 23, the phase is shifted based on the phase input from the addition circuit 56, and the sine wave is supplied to the current reference circuit 12 through the sine wave circuit 26. A signal Vs is input.

  The amplifier 11 detects the voltage of the DC power supply 1, compares it with the voltage reference V *, and inputs a signal V 11 obtained by amplifying the difference to the current reference circuit 12.

  Based on the shifted phase, the sine wave circuit 26 outputs a sine wave Vs, and the current reference circuit 12 corrects the current phase angle θ of the alternating current output from the inverter bridge 2 of the current reference I *. Thus, the current phase angle θ is corrected, and the reactive power Q of the inverter bridge 2 is controlled to have a predetermined phase characteristic.

  The current reference circuit 12 inputs the product of the signal V11 and the signal Vs to the amplifier 13 as an alternating current reference I *.

  The amplifier 13 controls the AC current reference I * and the output current of the inverter bridge 2 detected by the current detector 5 to coincide with each other, and the PWM circuit 14 performs PWM control of the inverter bridge 2 via the drive unit 15. .

On the other hand, the frequency f of the output voltage of the inverter bridge 2 is detected by the frequency detection circuit 28, and the phase of the output signal V _s of the sine wave circuit 26 is shifted by the phase shift circuit 23 via the function means to output the inverter reactive power. (I × Vsin θ) is controlled.

  The abnormality detection means includes a voltage relay 17 that detects an abnormality in the AC voltage supplied to the load 9, a frequency relay 18 that detects a frequency abnormality from the AC voltage supplied to the load 9, and an AC voltage supplied to the load 9. The frequency change rate relay 27 that detects an excessive frequency change rate (df / dt) and a signal that notifies the abnormality when an abnormality is detected by the voltage relay 17, the frequency relay 18, and the frequency change rate relay 27 is output. And an abnormality detection circuit 19 that performs the above-described operation.

  When an abnormality is detected by the abnormality detection means, the abnormality detection circuit 19 is supplied with a signal for notifying the drive unit 15 of the abnormality, and the drive unit 15 stops the inverter drive and opens the contactor 6 to complete the operation. The inverter bridge 2 is opened from the grid connection.

The function means includes a frequency detection circuit 52 that detects the frequency of the AC voltage output from the AC power system 8 and the inverter bridge 2, and a frequency change rate detection circuit that detects the frequency change rate of the frequency detected by the frequency detection circuit 52. 50, the reactive power Q with respect to the frequency or the characteristic function of the current phase angle θ causes the reactive power to flow when the frequency change is positive, so that the reactive power flows when the frequency change is negative, and the reactive power Q flows when the frequency change is negative. Alternatively, by the second function circuit 53 that calculates and outputs the value of the current phase angle θ and the reactive power Q with respect to the frequency change rate or the characteristic function of the current phase angle θ, the reactive power flows when the frequency change rate is positive. A first function circuit 51 for calculating and outputting the value of the reactive power Q or the current phase angle θ so that delayed reactive power flows when the frequency change rate is negative; Gain / limit control circuit 55 for adjusting the gain, or the upper and lower limit values of the function to be used in several circuit 51, an adding circuit 56 for adding the output of the second function circuit 53 and the output of the first function circuit 51, the flicker coefficient V ₁₀ arithmetic circuit 54.

  In FIG. 1, the frequency detection circuit 52 detects the frequency (f) of the power supplied to the load 9 from the AC voltage detected by the voltage detector 10 and transmits it to the second function circuit 53 and the frequency change rate detection circuit 50. To do.

  The frequency detection circuit 52 detects the zero cross signal of the AC power supply voltage, detects the frequency (f) with the next rise from the rise of the zero cross signal as one cycle, and takes one cycle from the fall of the zero cross signal to the next fall. For example, when the AC power supply is 50 Hz, the frequency (f) is detected every 10 ms. Thus, when the frequency (f) is detected by the frequency detection circuit 52, one cycle from the rise of the zero cross to the next rise is taken as one cycle, for example, when the AC power supply is 50 Hz, rather than detecting the frequency every 20 ms. Can be detected at high speed.

  The second function circuit 53 inputs an output V53 (reactive power or current phase angle θ) calculated from the received frequency (f) by a characteristic function to the adder circuit 56.

  FIG. 2A is a diagram illustrating an example of the relationship between the frequency (f) and the current phase angle (or reactive power) of the inverter bridge 2 in the vicinity of the reference frequency f0. As shown in FIG. 2A, in the vicinity of the reference (rated) frequency f0, the inverter bridge 2 has a characteristic that the current phase angle (or reactive power) increases in the advance direction as the inverter output frequency (f) increases.

  The frequency change rate detection circuit 50 detects the frequency change rate (df / dt) of the frequency (f) output from the frequency detection circuit 52 and transmits it to the first function circuit 51.

Flicker coefficient [Delta] V ₁₀ calculation circuit 54 calculates the flicker coefficient [Delta] V ₁₀ from the system voltage. The flicker coefficient ΔV ₁₀ represents flicker by the magnitude of flickering feeling, and is a fluctuation value of 10 Hz in the flickering visibility curve. The flicker coefficient ΔV ₁₀ calculation circuit 54 outputs the calculated flicker coefficient ΔV ₁₀ to the gain / limit control circuit 55.

FIG. 3 is a diagram illustrating a flicker visibility curve.
The flicker coefficient ΔV ₁₀ is calculated by the following equation (1).

In the above equation, a _N is a visibility coefficient, for example, visibility coefficient = 1 at 10 hertz and visibility coefficient = 0.563 at 3 hertz. ΔV _N is an effective value of the voltage fluctuation component of the fluctuation frequency fn obtained as a result of frequency analysis of voltage fluctuation, for example.

The gain / limit control circuit 55 determines whether or not the received flicker coefficient ΔV ₁₀ is equal to or greater than a predetermined threshold, and if the flicker coefficient ΔV ₁₀ is equal to or greater than the predetermined threshold, the current phase angle (or the frequency change rate based on the frequency change rate (or The first function circuit 51 is notified so as to adjust the amount of change in the reactive power), and flickering of the lamp is suppressed. When the flicker coefficient ΔV ₁₀ is less than the predetermined threshold, the gain / limit control circuit 55 does not adjust the change amount of the current phase angle (or reactive power) based on the frequency change rate. To notify.

  FIG. 2B is a diagram illustrating an example of the relationship between the frequency change rate (df / dt) and the current phase angle (or reactive power) of the inverter bridge 2 in the vicinity of the reference frequency f0.

When the flicker coefficient ΔV ₁₀ is less than the predetermined threshold value, the first function circuit 51 is notified by the flicker coefficient ΔV ₁₀ calculation circuit 54 not to adjust the gain, and the first function (not shown with a solid line) that does not adjust the gain. Function) to calculate the change amount of the current phase angle (or reactive power) based on the frequency change rate.

When the flicker coefficient ΔV ₁₀ is equal to or greater than a predetermined threshold value, the first function circuit 51 receives a notification from the gain / limit control circuit 55 to adjust the gain, and the first function with the gain adjusted (the function indicated by the broken line) ) To calculate the amount of change in the current phase angle (or reactive power) based on the frequency change rate. In this case, the adjustment amount of the gain has been made to suppress the variation of the current phase angle (or reactive power), frequency change using not magnitude function of the slope of the first function is the reference frequency f0 around when adjusting the gain Since the range of the rate is narrowed and the range of the frequency change rate using a function having a small slope is widened, the amount of gain adjustment suppresses the amount of change in the current phase angle (or reactive power).

Note that a plurality of gain adjustment amounts may be used according to the value of the flicker coefficient ΔV _{10. In} this case, the gain / limit control circuit 55 determines which adjustment amount is used, and the gain / limit control circuit. When the notification is made from 55 to the first function circuit 51, it may be notified together with which adjustment amount is used.

  FIG. 2C is a diagram illustrating another example of the relationship between the frequency change rate (df / dt) and the current phase angle (or reactive power) of the inverter bridge in the vicinity of the reference frequency f0.

When the flicker coefficient ΔV ₁₀ is less than the predetermined threshold value, the first function circuit 51 receives a notification from the flicker coefficient ΔV ₁₀ calculation circuit 54 not to adjust the upper limit value and the lower limit value, and does not adjust the upper limit value and the lower limit value. The amount of change in reactive power (or current phase angle) based on the frequency change rate is calculated using the first function (the function indicated by the solid line).

When the flicker coefficient ΔV ₁₀ is equal to or greater than a predetermined threshold, the first function circuit 51 receives a notification from the gain / limit control circuit 55 to adjust the upper limit value and the lower limit value, and adjusts the upper limit value and the lower limit value. The amount of change in the current phase angle (or reactive power) based on the frequency change rate is calculated by one function (one of the functions described with a broken line). At this time, the adjustment amount of the upper limit value and the lower limit value suppresses the change amount of the current phase angle (or reactive power), and when the upper limit value and the lower limit value are adjusted, the first function has the absolute value of the frequency change rate. When the value is larger than the predetermined value, the upper limit value or the lower limit value is set, and the amount of gain adjustment is suppressed from changing the current phase angle (or reactive power).

Note that a plurality of adjustment amounts for the upper limit value and the lower limit value may be used in accordance with the value of the flicker coefficient ΔV ₁₀ , and in that case, the gain / limit control circuit 55 determines which adjustment amount is used, and gain / When the notification is sent from the limit control circuit 55 to the first function circuit 51, which adjustment amount is used may be notified.

  When adjusting the upper and lower limit values of the function (first function) of the frequency change rate (df / dt), positive feedback is generated when the frequency change rate (df / dt) increases while the start time of the independent operation detection remains short. There is a merit that the isolated operation detection time does not become much longer as the time is reduced and the time is slightly extended.

When the overall gain of the function (first function) of the frequency change rate (df / dt) is lowered, the entire time is extended, so the isolated operation detection time tends to be longer than when the upper and lower limit values are adjusted. it is effective for lowering the voltage _{V 10.}

  Adjusting the gain or the upper and lower limit values of the first function as described above can suppress the occurrence of flicker phenomenon due to voltage fluctuation, and as a result, the occurrence of flickering of the lamp can be suppressed. .

4A and 4B are diagrams illustrating an example of a change in frequency when an isolated operation is detected.
The difference between the method of adjusting the gain and the method of adjusting the upper limit value and the lower limit value is that the simulation result of the isolated operation detection is between 40 ms and 60 ms from swoff (start of isolated operation) as shown in FIGS. 4A and 4B. A positive feedback of the frequency change rate is applied, and the frequency changes slowly at the beginning, and then rapidly rises. Therefore, rather than adjusting the gain as shown in FIG. 2A to lower the overall gain, the upper limit value and the lower limit value are adjusted as shown in FIG. 2B to reduce the frequency change rate (df / dt) (the range near f0). ), The method of keeping the gain high can be expected to shorten the time for detecting the isolated operation.

The first function circuit 51 outputs the output V ₅₁ obtained by using the first function with the gain or the upper / lower limit adjusted as described above to the adding circuit 56.

The adder circuit 56 outputs a value V ₅₆ obtained by adding the value received from the first function circuit 51 and the value received from the second function circuit 53 to the phase shift circuit 23. The phase shift circuit 23 shifts the phase of the output signal Vs of the sine wave circuit 26 by the reference phase obtained from the output V ₅₆ to control the output reactive power (I × Vsin θ) of the inverter bridge 2.

  As described above, the isolated operation detection device according to the present embodiment operates with the characteristics of the slip mode frequency shift, and as shown in FIGS. 2A to 2C, the frequency (f) and the frequency change rate are close to the rated frequency f0. The phase of the output signal Vs of the sine wave circuit 26 is shifted so that the current phase angle advances as the (df / dt) increases and the advance reactive power increases.

  That is, in the isolated operation detection device according to the present embodiment, when the AC side of the inverter is disconnected from the AC power system, the frequency (f) and the frequency change rate (df / dt) of the AC power source slightly increase or decrease. When an increase or decrease in the frequency (f) and the frequency change rate (df / dt) is detected and the frequency (f) is increased and the frequency change rate (df / dt) is positive, the current phase of the inverter bridge 2 is detected. The angle is advanced and positive feedback is applied in the direction in which the frequency (f) further increases. When an increase or decrease in the frequency (f) and the frequency change rate (df / dt) is detected, and the frequency (f) decreases or the frequency change rate (df / dt) is negative, the current phase angle of the inverter bridge 2 Is delayed and positive feedback is applied in the direction in which the frequency (f) further decreases.

  As described above, by rapidly breaking the balance between the output of the inverter and the load, the voltage relay 17, the frequency relay 18, and the frequency change rate relay 27 detect that the system has become an abnormal voltage or abnormal frequency. When the gate of the inverter is shut off due to a system abnormality, the contactor 6 is opened and the inverter is opened from the system.

Furthermore, in the present embodiment, by adjusting the gain or upper limit value of the first function on the basis of the value of the flicker coefficient V _10, it can be flicker voltage fluctuates to suppress the occurrence, the result, Generation | occurrence | production of the flicker of an electric light etc. can be suppressed.

FIG. 5 is a diagram schematically illustrating another configuration example of the isolated operation detection device of the first embodiment.
In the isolated operation detection device of this example, the inverter bridge 2 is a three-phase bridge. Reactors 3a, 3b, and 3c are connected to the AC side of inverter bridge 2, and reactors 3a, 3b, and 3c are delta-connected to filter capacitors 4a, 4b, and 4c. The current detectors 5a and 5b are connected in two phases and detect the output current of the inverter bridge 2.

  The PQ detection circuit 35 calculates active power P and reactive power Q from the output current of the inverter bridge 2 and the voltage of the load 9. The amplifier 11 detects the voltage of the DC power supply 1 and outputs an active power reference P * which is compared and amplified with the voltage reference V * to the amplifier 13a. The active power reference P * and the active power P output from the amplifier 11 are amplified by the amplifier 13a, and the signal V13a is input to the three-phase converter 34.

The output V ₅₆ of the adder circuit 56 is input to the reactive power reference circuit 33, and an error between the reactive power reference Q * output from the reactive power reference circuit 33 and the reactive power Q of the inverter bridge 2 detected by the PQ detection circuit 35. Is amplified by an amplifier 13b and output as a signal V13b. The signal V13b is input to the PWM circuit 14 via the three-phase converter 34, and the PWM circuit 14 controls the output current of the inverter bridge 2 via the drive unit 15 to control active power and reactive power. This is generally done for phase inverters.

  As described above, in the case of the single phase shown in FIG. 1, the reactive power was changed by changing the current phase angle to detect the single operation of the inverter bridge 2 at a high speed, but in the case of the three phase shown in FIG. By directly controlling the reactive power, the single operation of the inverter bridge 2 is detected at high speed. Therefore, in the present embodiment, the outputs of the first function circuit 51 and the second function circuit 53 are reactive power.

  As shown in FIG. 5, the configuration other than the above configuration is the same as that of the isolated operation detection device according to the first embodiment shown in FIG. 1.

That is, according to the isolated operation detection device and the isolated operation detection method of the inverter according to the present embodiment, the reactive power function (output V ₅₃ ) and the frequency change with respect to the frequency (f), as in the case of the first embodiment described above. The reactive power of the inverter bridge 2 is controlled by the sum of the reactive power function (output V ₅₁ ) with respect to the rate (df / dt), and as a result, when the inverter is operated independently, the gain of the positive feedback action is increased to increase the speed. To shift the frequency (f).

  Then, an abnormality is detected by the voltage relay 17 from the output of the voltage detector 10, a frequency abnormality is detected by the frequency relay 18, an excessive frequency change rate (df / dt) is detected by the frequency change rate relay 27, and an abnormality is detected. Inverter drive is stopped by the drive unit 15 via the circuit 19 (the gate of the drive element is cut off), and the interconnection breaker (contactor 6) is opened to completely disconnect the inverter bridge 2 from the grid interconnection. . As a result, according to the isolated operation detection device and the isolated operation detection method for an inverter according to this embodiment, the isolated operation detection protection can be speeded up.

  As described above, according to the isolated operation detection device and the isolated operation detection method for an inverter according to the above embodiment, when the frequency (f) increases, the reactive power changes in the forward direction and the frequency (f) decreases. When the reactive power changes in the delay direction and the output signal of the function circuit and the frequency change rate (df / dt) is positive, the reactive power changes in the forward direction, and when the frequency change rate (df / dt) is negative, the reactive power is Provided is an isolated operation detection device and an isolated operation detection method for an inverter capable of detecting at high speed in a frequency fluctuation range of a system power supply by configuring the reactive power to be controlled by the sum of an output signal of a function circuit changing in a delay direction. be able to.

  In addition, according to the isolated operation detection device and the isolated operation detection method of the inverter according to the above embodiment, it is possible to suppress the occurrence of flicker phenomenon due to voltage fluctuation, and as a result, the occurrence of flickering of a lamp or the like can be prevented. Can be suppressed.

  That is, according to the isolated operation detection device and the isolated operation detection method of the present embodiment, it is possible to provide an isolated operation detection device and an isolated operation detection method that achieve high-speed detection of isolated operation and avoid a decrease in power quality. it can.

  Next, an isolated operation detection method and an isolated operation detection device according to a second embodiment will be described with reference to the drawings. In the following description, the same components as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted.

An isolated operation detection method and an isolated operation detection device according to the present embodiment are an isolated operation detection method and an isolated operation detection device for an inverter that converts direct current power into alternating current power and that is linked to an alternating current power system. From the voltage of the AC power output from the system and the inverter, the output via the second function circuit is subjected to limit control or gain change from the frequency deviation Δf obtained from the difference between the past moving average frequency and the current moving average frequency By changing the reactive power of the inverter output from the addition result of both function circuit outputs through the circuit, the frequency is shifted by the positive feedback action when the inverter becomes an independent operation. calculates a count [Delta] V _10, when the flicker count [Delta] V ₁₀ reaches a set value abnormality, the gain of the first function To change the limit value.

  FIG. 6 is a diagram schematically illustrating a configuration example of the isolated operation detection device of the present embodiment. The isolated operation detection device of the present embodiment is different from the isolated operation detection device of the first embodiment described above only in the configuration of the function means.

The function means includes a frequency detection circuit 52, a frequency change rate detection circuit 50, a first function circuit 51, a first moving average circuit 58, a second moving average circuit 59, a second function circuit 53, and a flicker coefficient. A ΔV ₁₀ arithmetic circuit 54 and a gain / limit control circuit 55 are provided.

  For example, when the AC side of the inverter bridge 2 is disconnected from the AC power system, the frequency f on the AC power system 8 side slightly increases or decreases from the moving average fm of the frequency f. That is, the value obtained by subtracting the past moving average fm1 from the current moving average fm2 is the frequency deviation Δf (fm2−fm1 = Δf).

  In this case, the average time of the moving averages fm1 and fm2 is set longer than the isolated operation detection target time. In the present embodiment, the average time of the moving averages fm1 and fm2 is set to five times or more of the isolated operation detection target time. For example, when the isolated operation detection target time is 100 ms, the average time of the moving averages fm1 and fm2 is set to be five times or more of 100 ms, that is, 500 ms or more. The moving averages fm1 and fm2 are average values of the frequency f detected in the average time, and when the average time is t, the moving averages fm1 and fm2 are the sum of the frequencies f detected during the average time t. The value divided by the average time t.

  Note that the current moving average fm2 of the frequency is a value obtained by dividing the sum of the frequencies f detected from the present time until the average time t before by the average time t, and the past moving average fm1 of the frequency is It is a value obtained by dividing the sum of f detected between a predetermined time before the current time and before the average time t by the average time t. The average time t for calculating the current moving average fm2 and the average time t for calculating the past moving average fm1 may be non-overlapping time or overlapping time.

  1, the frequency detection circuit 52 detects the frequency f of the AC power system, the first moving average circuit 58 and the second moving average circuit 59 calculate the frequency moving averages fm1 and fm2, A frequency deviation Δf (Δf = fm2−fm1) is obtained by a subtracter. The frequency deviation Δf is output to the second function circuit 53.

  FIG. 7 is a diagram showing an example of the relationship between the frequency deviation and the reactive power (or current phase angle) of the inverter bridge in the vicinity of the reference frequency.

  The second function circuit 53 outputs a current phase angle (or reactive power) with respect to the frequency deviation Δf input using, for example, a current phase angle (or reactive power) characteristic function as shown in FIG. The output V53 of the second function circuit 53 is input to the adder circuit 56.

  The configuration other than the above is the same as in the first embodiment.

  That is, the reactive power of the output power of the inverter bridge 2 or the current phase angle angle of the inverter bridge 2 follows the characteristic function of the first function and the second function, and the reactive power flows when the frequency deviation Δf is positive (+). When the frequency deviation Δf is negative (−), the delay reactive power is controlled to flow. Similarly, when the frequency change rate df / dt is positive (+), the reactive power flows forward and the frequency change rate df / When dt is negative (-), control is performed so that delayed reactive power flows.

  As described above, when the frequency deviation Δf increases (+), the reactive power is advanced and positive feedback is applied to further increase the frequency f. When the frequency deviation Δf decreases (−), a delayed reactive power is supplied, and the frequency f is rapidly shifted by applying positive feedback so as to further decrease the frequency f.

  Further, in this embodiment, since the input of the second function circuit 53 is the frequency deviation Δf, the power factor does not fluctuate in a steady state even if the frequency f is a gentle change.

According to this embodiment, as in the first embodiment described above, if the flicker coefficient [Delta] V ₁₀ is increased, the flicker by adjusting the positive feedback amount of gain or upper limit value of the frequency change ratio df / dt In addition, it is possible to realize an isolated operation detection method and an isolated operation detection device that can detect an isolated operation at high speed.

  That is, according to the isolated operation detection device and the isolated operation detection method of the present embodiment, it is possible to provide an isolated operation detection device and an isolated operation detection method that achieve high-speed detection of isolated operation and avoid a decrease in power quality. it can.

FIG. 8 is a diagram schematically illustrating another configuration example of the isolated operation detection device of the second embodiment.
In the isolated operation detection device of this example, the inverter bridge 2 is a three-phase bridge. Reactors 3a, 3b, and 3c are connected to the AC side of inverter bridge 2, and reactors 3a, 3b, and 3c are delta-connected to filter capacitors 4a, 4b, and 4c. The current detectors 5a and 5b are connected in two phases and detect the output current of the inverter bridge 2.

The PQ detection circuit 35 calculates active power P and reactive power Q from the output current of the inverter bridge 2 and the voltage of the load 9. The amplifier 11 detects the voltage of the DC power supply 1 and outputs an active power reference P * which is compared and amplified with the voltage reference V * to the amplifier 13a. The active power reference P * and the active power P output from the amplifier 11 are amplified by the amplifier 13 a and the signal V _{13 a} is input to the three-phase converter 34.

The output V ₅₆ of the adder circuit 56 is input to the reactive power reference circuit 33, and an error between the reactive power reference Q * output from the reactive power reference circuit 33 and the reactive power Q of the inverter bridge 2 detected by the PQ detection circuit 35. Is amplified by an amplifier 13b and output as a signal _V13a . The signal V13b is input to the PWM circuit 14 via the three-phase converter 34, and the PWM circuit 14 controls the output current of the inverter bridge 2 via the drive unit 15 to control active power and reactive power. This is generally done for phase inverters.

  As described above, in the case of the single phase shown in FIG. 6, the reactive power was changed by changing the current phase angle to detect the single operation of the inverter bridge 2 at a high speed, but in the case of the three phase shown in FIG. By directly controlling the reactive power, the single operation of the inverter bridge 2 is detected at high speed. Therefore, in the present embodiment, the outputs of the first function circuit 51 and the second function circuit 53 are reactive power.

  Except for the above configuration, the configuration is the same as that of the isolated operation detection device according to the second embodiment shown in FIG.

That is, according to the isolated operation detection device and the isolated operation detection method of the inverter according to the present embodiment, the reactive power function (output V ₅₃ ) and the frequency change rate with respect to the frequency deviation Δf, as in the case of the first embodiment described above. The reactive power of the inverter bridge 2 is controlled by the sum of the reactive power function (output V ₅₁ ) with respect to (df / dt). As a result, when the inverter is in an independent operation, the gain of the positive feedback action is increased to increase the speed. Shift the frequency (f).

  Then, an abnormality is detected by the voltage relay 17 from the output of the voltage detector 10, a frequency abnormality is detected by the frequency relay 18, an excessive frequency change rate (df / dt) is detected by the frequency change rate relay 27, and an abnormality is detected. Inverter drive is stopped by the drive unit 15 via the circuit 19 (the gate of the drive element is cut off), and the interconnection breaker (contactor 6) is opened to completely disconnect the inverter bridge 2 from the grid interconnection. . As a result, according to the isolated operation detection device and the isolated operation detection method for an inverter according to this embodiment, the isolated operation detection protection can be speeded up.

  As described above, according to the isolated operation detection device and the isolated operation detection method of the inverter according to the above-described embodiment, when the frequency deviation Δf increases, the reactive power changes in the advance direction, and when the frequency deviation Δf decreases, the reactive power When the frequency change rate (df / dt) is positive, the reactive power changes in the forward direction, and when the frequency change rate (df / dt) is negative, the reactive power is delayed. It is possible to provide an isolated operation detection device and an isolated operation detection method for an inverter which can detect at high speed in the frequency fluctuation range of the system power supply by controlling the reactive power by the sum of the output signal of the function circuit which changes to it can.

  In addition, according to the isolated operation detection device and the isolated operation detection method of the inverter according to the above embodiment, it is possible to suppress the occurrence of flicker phenomenon due to voltage fluctuation, and as a result, the occurrence of flickering of a lamp or the like can be prevented. Can be suppressed.

  That is, according to the isolated operation detection device and the isolated operation detection method of the present embodiment, it is possible to provide an isolated operation detection device and an isolated operation detection method that achieve high-speed detection of isolated operation and avoid a decrease in power quality. it can.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

2 ... inverter, 8 ... AC power system, [Delta] V _{10 ...} flicker coefficient, 10 ... voltage detector (voltage detection unit), 50 ... frequency change rate detection circuit, 51 ... first function circuit (first function portion) 52 ... Frequency Detection circuit (frequency detection unit), 53 ... second function circuit (second function unit) 54 ... flicker coefficient V ₁₀ calculation circuit (flicker coefficient calculation unit), 55 ... gain / limit control circuit (gain control unit, limit control unit) ), 56... Addition circuit (addition unit), 58... First moving average circuit (first moving average unit), 59... Second moving average circuit (second moving average unit).

Claims (10)

An independent operation detection device for an inverter that converts DC power to AC power and operates in conjunction with an AC power system,
A voltage detector for detecting an AC voltage output from the AC power system and the inverter;
From the voltage detected by the voltage detection unit, an abnormality detection unit configured to detect abnormality of voltage, frequency and frequency change rate,
A frequency detector for detecting the frequency of the AC voltage output from the AC power system and the inverter;
A frequency change rate detector that calculates a frequency change rate from the frequency detected by the frequency detector;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. A first function part for calculating and outputting the value of the angle;
Reactive power or current by the second function of reactive power or current phase angle with respect to frequency so that when the frequency is higher than the reference frequency , the reactive power flows forward, and when the frequency is lower than the reference frequency , the reactive reactive current flows. A second function part for calculating and outputting the value of the phase angle;
An adder for adding and outputting the output of the first function part and the output of the second function part;
A flicker coefficient calculator that calculates a flicker coefficient from the voltage detected by the voltage detector;
It is determined whether or not the value calculated by the flicker coefficient calculation unit exceeds a predetermined threshold value, and when it exceeds the predetermined threshold value, the amount of change in reactive power or current phase angle with respect to the frequency change rate of the first function is suppressed. a gain control unit for notifying the first function unit as,
A drive unit that controls output power output from the inverter using the output of the addition unit, and stops the inverter when an abnormality is detected from the abnormality detection unit ;
When the first function unit receives the notification, the first function unit adjusts the gain of the first function to suppress the variation of the reactive power or the current phase angle with respect to the frequency change rate of the first function. . An independent operation detection device for an inverter that converts DC power to AC power and operates in conjunction with an AC power system,
A voltage detector for detecting an AC voltage output from the AC power system and the inverter;
From the voltage detected by the voltage detection unit, an abnormality detection unit configured to detect abnormality of voltage, frequency and frequency change rate,
A frequency detector for detecting the frequency of the AC voltage output from the AC power system and the inverter;
A frequency change rate detector that calculates a frequency change rate from the frequency detected by the frequency detector;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. A first function part for calculating and outputting the value of the angle;
Reactive power or current by the second function of reactive power or current phase angle with respect to frequency so that when the frequency is higher than the reference frequency , the reactive power flows forward, and when the frequency is lower than the reference frequency , the reactive reactive current flows. A second function part for calculating and outputting the value of the phase angle;
An adder for adding and outputting the output of the first function part and the output of the second function part;
A flicker coefficient calculator that calculates a flicker coefficient from the voltage detected by the voltage detector;
It is determined whether or not the value calculated by the flicker coefficient calculation unit exceeds a predetermined threshold value, and when it exceeds the predetermined threshold value, the amount of change in reactive power or current phase angle with respect to the frequency change rate of the first function is suppressed. and limit control unit for notifying the first function unit as,
A drive unit that controls output power output from the inverter using the output of the addition unit, and stops the inverter when an abnormality is detected from the abnormality detection unit ;
When the first function unit receives the notification, the first function unit adjusts an upper limit value and a lower limit value of the first function to suppress a variation in reactive power or current phase angle with respect to a frequency change rate of the first function. An independent operation detection device. The inverter includes a three-phase bridge,
The drive unit is configured to control the active power and reactive power of the output power of the inverter using the output from the addition unit, and to stop the inverter when an abnormality is notified from the abnormality detection unit The isolated operation detection device according to claim 1 or claim 2. An independent operation detection device for an inverter that converts DC power to AC power and operates in conjunction with an AC power system,
A voltage detector for detecting an AC voltage output from the AC power system and the inverter;
From the voltage detected by the voltage detection unit, an abnormality detection unit configured to detect abnormality of voltage, frequency and frequency change rate,
A frequency detector for detecting the frequency of the AC voltage output from the AC power system and the inverter;
A frequency change rate detector that calculates a frequency change rate from the frequency detected by the frequency detector;
A first moving average unit that calculates a first moving average of frequencies detected by the frequency detection unit between a past time and a predetermined time before;
A second moving average unit that calculates a second moving average of the frequencies detected by the frequency detection unit from the present to a predetermined time before;
A subtractor that calculates a frequency deviation obtained by subtracting the first moving average from the second moving average;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. A first function part for calculating and outputting the value of the angle;
The value of the reactive power or current phase angle so that when the frequency deviation is positive, the advanced reactive power flows when the frequency deviation is positive, and when the frequency deviation is negative, the delayed reactive power flows when the frequency deviation is negative. A second function part for calculating and outputting
An adder for adding and outputting the output of the first function part and the output of the second function part;
A flicker coefficient calculator that calculates a flicker coefficient from the voltage detected by the voltage detector;
It is determined whether or not the value calculated by the flicker coefficient calculation unit exceeds a predetermined threshold value, and when it exceeds the predetermined threshold value, the amount of change in reactive power or current phase angle with respect to the frequency change rate of the first function is suppressed. a gain control unit configured to notify the first function unit as,
A drive unit that controls output power output from the inverter using the output of the addition unit, and stops the inverter when an abnormality is detected from the abnormality detection unit ;
When the first function unit receives the notification, the first function unit adjusts the gain of the first function to suppress the variation of the reactive power or the current phase angle with respect to the frequency change rate of the first function. . An independent operation detection device for an inverter that converts DC power to AC power and operates in conjunction with an AC power system,
A voltage detector for detecting an AC voltage output from the AC power system and the inverter;
From the voltage detected by the voltage detection unit, an abnormality detection unit configured to detect abnormality of voltage, frequency and frequency change rate,
A frequency detector for detecting the frequency of the AC voltage output from the AC power system and the inverter;
A frequency change rate detector that calculates a frequency change rate from the frequency detected by the frequency detector;
A first moving average unit that calculates a first moving average of frequencies detected by the frequency detection unit between a past time and a predetermined time before;
A second moving average unit that calculates a second moving average of the frequencies detected by the frequency detection unit from the present to a predetermined time before;
A subtractor that calculates a frequency deviation obtained by subtracting the first moving average from the second moving average;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. A first function part for calculating and outputting the value of the angle;
The value of the reactive power or current phase angle so that when the frequency deviation is positive, the advanced reactive power flows when the frequency deviation is positive, and when the frequency deviation is negative, the delayed reactive power flows when the frequency deviation is negative. A second function part for calculating and outputting
An adder for adding and outputting the output of the first function part and the output of the second function part;
A flicker coefficient calculator that calculates a flicker coefficient from the voltage detected by the voltage detector;
It is determined whether or not the value calculated by the flicker coefficient calculation unit exceeds a predetermined threshold value, and when it exceeds the predetermined threshold value, the amount of change in reactive power or current phase angle with respect to the frequency change rate of the first function is suppressed. and limit control unit for notifying the first function unit as,
A drive unit that controls output power output from the inverter using the output of the addition unit, and stops the inverter when an abnormality is detected from the abnormality detection unit ;
When the first function unit receives the notification, the first function unit adjusts an upper limit value and a lower limit value of the first function to suppress a variation in reactive power or current phase angle with respect to a frequency change rate of the first function. An independent operation detection device. The inverter includes a three-phase bridge,
The drive unit is configured to control the active power and reactive power of the output power of the inverter using the output from the addition unit, and to stop the inverter when an abnormality is notified from the abnormality detection unit The isolated operation detection device according to claim 4 or 5. Detect AC voltage output from AC power system and inverter,
Detect the frequency of the detected AC voltage,
Calculate the frequency change rate from the detected frequency,
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. Calculate the corner value,
Reactive power or current by the second function of reactive power or current phase angle with respect to frequency so that when the frequency is higher than the reference frequency , the reactive power flows forward, and when the frequency is lower than the reference frequency , the reactive reactive current flows. Calculate the phase angle value,
The output power output from the inverter is controlled using a value obtained by adding the output of the first function and the output of the second function , and abnormalities in voltage, frequency, and frequency change rate are detected from the detected AC voltage. Is an isolated operation detection method that stops the inverter when an abnormality is detected.
Calculate the flicker coefficient from the detected AC voltage,
Determining whether the calculated flicker coefficient value exceeds a predetermined threshold;
An isolated operation detection method, wherein when the predetermined threshold value is exceeded, a gain of the first function is adjusted to suppress a variation in reactive power or current phase angle with respect to a frequency change rate of the first function. Detect AC voltage output from AC power system and inverter,
Detect the frequency of the detected AC voltage,
Calculate the frequency change rate from the detected frequency,
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. Calculate the corner value,
Reactive power or current by the second function of reactive power or current phase angle with respect to frequency so that when the frequency is higher than the reference frequency , the reactive power flows forward, and when the frequency is lower than the reference frequency , the reactive reactive current flows. Calculate the phase angle value,
The output power output from the inverter is controlled using a value obtained by adding the output of the first function and the output of the second function , and abnormalities in voltage, frequency, and frequency change rate are detected from the detected AC voltage. Is an isolated operation detection method that stops the inverter when an abnormality is detected.
Calculate the flicker coefficient from the detected AC voltage,
Determining whether the calculated flicker coefficient value exceeds a predetermined threshold;
An isolated operation detection method, wherein when the predetermined threshold value is exceeded, an upper limit value and a lower limit value of the first function are adjusted to suppress a variation amount of reactive power or current phase angle with respect to a frequency change rate of the first function. Detect AC voltage output from AC power system and inverter,
Detect the frequency of the detected AC voltage,
Calculate the frequency change rate from the detected frequency,
Calculating a first moving average of the frequencies detected by the frequency detector from a past time point to a predetermined time ago,
Calculating a second moving average of the frequencies detected by the frequency detection unit from the present to a predetermined time before,
Calculating a frequency deviation obtained by subtracting the first moving average from the second moving average;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. Calculate the corner value,
The value of the reactive power or current phase angle so that when the frequency deviation is positive, the advanced reactive power flows when the frequency deviation is positive, and when the frequency deviation is negative, the delayed reactive power flows when the frequency deviation is negative. And
The output power output from the inverter is controlled using a value obtained by adding the output of the first function and the output of the second function , and abnormalities in voltage, frequency, and frequency change rate are detected from the detected AC voltage. Is an isolated operation detection method that stops the inverter when an abnormality is detected.
Calculate the flicker coefficient from the detected AC voltage,
Determining whether the calculated flicker coefficient value exceeds a predetermined threshold;
An isolated operation detection method, wherein when the predetermined threshold value is exceeded, a gain of the first function is adjusted to suppress a variation in reactive power or current phase angle with respect to a frequency change rate of the first function. Detect AC voltage output from AC power system and inverter,
Detect the frequency of the detected AC voltage,
Calculate the frequency change rate from the detected frequency,
Calculating a first moving average of the frequencies detected by the frequency detector from a past time point to a predetermined time ago,
Calculating a second moving average of the frequencies detected by the frequency detection unit from the present to a predetermined time before,
Calculating a frequency deviation obtained by subtracting the first moving average from the second moving average;
The reactive power or current phase is such that when the frequency change rate is positive, the advance reactive power flows when the frequency change rate is positive, and when the frequency change rate is negative, the delayed reactive power flows when the frequency change rate is negative. Calculate the corner value,
The value of the reactive power or current phase angle so that when the frequency deviation is positive, the advanced reactive power flows when the frequency deviation is positive, and when the frequency deviation is negative, the delayed reactive power flows when the frequency deviation is negative. And
The output power output from the inverter is controlled using a value obtained by adding the output of the first function and the output of the second function , and abnormalities in voltage, frequency, and frequency change rate are detected from the detected AC voltage. Is an isolated operation detection method that stops the inverter when an abnormality is detected.
Calculate the flicker coefficient from the detected AC voltage,
Determining whether the calculated flicker coefficient value exceeds a predetermined threshold;
An isolated operation detection method, wherein when the predetermined threshold value is exceeded, an upper limit value and a lower limit value of the first function are adjusted to suppress a variation amount of reactive power or current phase angle with respect to a frequency change rate of the first function.

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