Voltage flicker detection device, islanding operation detection device equipped with said voltage flicker detection device, and power conditioner equipped with said islanding operation detection device

Abstract

To provide a voltage flicker detection device capable of detecting voltage flicker caused by injecting an active signal by an islanding operation detection device.SOLUTION: A voltage flicker detection device 31 comprises: a frequency detection unit 41 for detecting an instantaneous value frequency f of a voltage on the basis of a voltage signal input from a voltage sensor 5; a frequency determination unit 45 for determining generation of voltage flicker on the basis of fluctuation of the instantaneous value frequency f; an effective value detection unit 51 for detecting a voltage effective value on the basis of the voltage signal; a voltage determination unit 55 for determining generation of the voltage flicker on the basis of fluctuation of the voltage effective value v; and a logical AND unit 46 for detecting the voltage flicker on the basis of a first determination result of the frequency determination unit 45 and a second determination result of the voltage determination unit 55.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a voltage flicker detection device that detects voltage flicker, an islanding operation detection device that includes the voltage flicker detection device, and a power conditioner that includes the islanding operation detection device. [Background technology]

[0002] In a power distribution system, voltage flicker occurs due to sudden load fluctuations and the like. Voltage flicker causes lighting to flicker, so it is mandatory to suppress it. For example, Patent Document 1 discloses a reactive power compensator that suppresses voltage flicker. As described in Patent Document 1, voltage flicker is generally expressed as "ΔV 10 " and is detected by comparing this index value with a threshold. There are various causes of voltage flicker, such as load fluctuations and reactive power injection. ΔV 10 The detection method using the method detects voltage flicker based on voltage fluctuations, and can detect all voltage flicker regardless of the cause of its occurrence. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-131081 Summary of the Invention [Problem to be solved by the invention]

[0004] However, there is a demand for detecting voltage flicker based on a specific cause, rather than detecting all voltage flicker. For example, there is a demand for detecting only voltage flicker caused by an islanding detection device injecting an active signal (e.g., reactive power).

[0005] The present invention has been devised in light of the above circumstances, and has as its object to provide a voltage flicker detection device that can detect voltage flicker caused by an islanding operation detection device injecting an active signal. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides the following technical means.

[0007] A voltage flicker detection device provided by a first aspect of the present invention is characterized by comprising a first frequency detection unit that detects the instantaneous value frequency of a voltage based on a voltage signal input from a voltage sensor, a frequency judgment unit that determines the occurrence of voltage flicker based on fluctuations in the instantaneous value frequency, a voltage detection unit that detects the magnitude of the voltage based on the voltage signal, a voltage judgment unit that determines the occurrence of voltage flicker based on fluctuations in the magnitude of the voltage, and a detection unit that detects voltage flicker based on the first judgment result of the frequency judgment unit and the second judgment result of the voltage judgment unit.

[0008] In a preferred embodiment of the present invention, the voltage flicker detection device further includes a change amount detection unit that detects the change amount of the instantaneous value frequency, a low-pass filter that extracts only frequency components below an upper limit frequency from the change amount, and a first PP value detection unit that detects a first PP value, which is the peak-to-peak value per unit time of the change amount extracted by the low-pass filter, and the frequency determination unit makes a determination by comparing the first PP value with a frequency threshold value.

[0009] In a preferred embodiment of the present invention, the voltage flicker detection device further includes a second PP value detection unit that detects a second PP value, which is the peak-to-peak value of the voltage magnitude per unit time, a second frequency detection unit that detects a voltage frequency, which is the frequency of fluctuations in the voltage magnitude, and an index value calculation unit that calculates an index value from the second PP value and the voltage frequency, and the voltage judgment unit makes a judgment by comparing the index value with an index threshold value.

[0010] In a preferred embodiment of the present invention, the voltage flicker detection device further includes a threshold adjustment unit that adjusts the frequency threshold or the index threshold based on how the first PP value or the index value changes from when the detection unit changes from a state in which it does not detect voltage flicker to a state in which it does detect voltage flicker.

[0011] The islanding operation detection device provided by the second aspect of the present invention is an islanding operation detection device that detects the islanding operation of a power conditioner, and is characterized by comprising: a voltage flicker detection device provided by the first aspect of the present invention that detects the occurrence of voltage flicker in a distribution system to which the power conditioner is connected; an active detection unit that actively detects islanding operation by injecting a first active signal into the distribution system; a passive detection unit that detects islanding operation based on a change in electrical characteristics caused by another islanding operation detection device arranged in the distribution system injecting a second active signal into the distribution system; and a switching unit that switches the active detection unit between a state in which it is activated and a state in which it is deactivated depending on the detection result of the voltage flicker detection device.

[0012] The "first active signal" and "second active signal" are signals that the islanding detection device injects into the power distribution system when it actively detects islanding, and include, for example, reactive power and active power. The "electrical characteristics" include voltage, current, power (active power, reactive power), and frequency. They also include the voltage, current, power, and frequency of predetermined harmonic components.

[0013] A power conditioner provided by a third aspect of the present invention is characterized by including the islanding operation detection device provided by the second aspect of the present invention. [Effects of the Invention]

[0014] According to the present invention, the frequency determination unit determines the occurrence of voltage flicker based on fluctuations in the instantaneous voltage frequency, and the voltage determination unit determines the occurrence of voltage flicker based on fluctuations in the voltage magnitude. The detection unit then detects voltage flicker based on the first determination result of the frequency determination unit and the second determination result of the voltage determination unit. Voltage flicker caused by an islanding operation detection device injecting an active signal varies not only in voltage but also in voltage phase (instantaneous voltage frequency). The voltage flicker detection device according to the present invention makes a determination based on fluctuations in the instantaneous voltage frequency in addition to a determination based on fluctuations in voltage magnitude, and detects voltage flicker based on both determination results. Therefore, the voltage flicker detection device according to the present invention can detect voltage flicker caused by an islanding operation detection device injecting an active signal.

[0015] Other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram for explaining an islanding operation detection device including a voltage flicker detection device according to a first embodiment, showing the overall configuration of a power distribution system. [Figure 2] FIG. 2 is a block diagram showing details of the internal configuration of the voltage flicker detection device. [Figure 3] FIG. 10 is a waveform diagram showing the simulation results of the first determination unit of the voltage flicker detection device. [Figure 4] FIG. 10 is a diagram illustrating flicker visibility. [Figure 5] FIG. 10 is a waveform diagram showing the simulation results of the second determination unit of the voltage flicker detection device. [Figure 6] FIG. 10 is a block diagram showing details of the internal configuration of a voltage flicker detection device according to a second embodiment. [Figure 7] FIG. 10 is a block diagram for explaining a voltage flicker detection device according to a third embodiment, showing the overall configuration of a power distribution system. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] [First embodiment] FIG. 1 is a block diagram for explaining an islanding operation detection device including a voltage flicker detection device according to a first embodiment, and shows the overall configuration of a power distribution system.

[0019] Power conditioner 1 converts DC power output by DC power source A into AC power and outputs it to the connected power distribution system C. The combination of power conditioner 1 and DC power source A is a distributed power source. Power distribution system C is a high-voltage power distribution system, and a load L is connected to it. Load L is a consumer that receives power supply.

[0020] When connecting a distributed power source to a power grid, the power conditioner must be equipped with an islanding detection device to prevent islanding. Islanding occurs when a distributed power source continues to supply power to the loads of the power distribution grid even if the distribution grid to which the distributed power source is connected is disconnected from the power grid. When an islanding detection device detects islanding, it disconnects the distributed power source from the distribution grid and stops the supply of power from the distributed power source to the load. There are passive and active methods for detecting islanding, and various detection methods have been developed.

[0021] The Grid Interconnection Regulations (JEAC 9701-2016) recognize active islanding detection methods, including frequency shift, slip mode frequency shift, reactive power variation, and QC mode frequency shift. These methods are referred to as conventional active methods. The Grid Interconnection Regulations stipulate that conventional active islanding detection devices must disconnect the power conditioner from the distribution grid within 0.5 to 1 second (when connected to a low-voltage distribution line) when a power outage occurs and the power conditioner enters islanding mode. The Grid Interconnection Regulations also recognize the step injection frequency feedback method, which offers faster detection speeds than conventional active methods. This method is referred to as the new active method. The Grid Interconnection Regulations stipulate that new active islanding detection devices must instantly disconnect the power conditioner from the distribution grid when a power outage occurs and the power conditioner enters islanding mode; typically, they are configured to disconnect within 0.1 to 0.2 seconds. Each of these methods actively injects an active signal, representing reactive power, into the distribution system and detects islanding based on changes in the detected frequency. Therefore, when a large number of distributed power sources are connected to a distribution system, a large amount of reactive power is injected into the system. The amount of reactive power injected also increases according to frequency deviation. Therefore, when a system disturbance occurs, each distributed power source increases the amount of reactive power injected, which can cause system voltage oscillations and voltage flicker. The power conditioner 1 is equipped with an islanding detection device 3 (described below) that does not induce voltage flicker.

[0022] A conventional power source B1 and a new power source B2 can be connected to the power distribution system C. In this embodiment, the conventional power source B1 and the new power source B2 may be connected, disconnected, or connected but stopped, and are therefore indicated by dashed lines in FIG. 1 . The conventional power source B1 is a distributed power source equipped with a power conditioner having a conventional active-type islanding operation detection device. In this embodiment, an example is described in which the islanding operation detection device of the conventional power source B1 detects islanding operation using a frequency shift method. The detection method of the islanding operation detection device of the conventional power source B1 is not limited. The new power source B2 is a distributed power source equipped with a power conditioner having a new active-type islanding operation detection device. A plurality of loads L, conventional power sources B1, and new power sources B2 can be connected to the power distribution system C (and the low-voltage power distribution system connected to the power distribution system C via a transformer), but FIG. 1 shows only one of each. The power distribution system C is connected to the power system via a circuit breaker. In the event of an accident in the power grid, a protective device installed on the power grid side opens the circuit breaker, and power distribution grid C is isolated from the power grid (power outage state). As a result, power conditioner 1 connected to power distribution grid C, which has been isolated from the power grid, enters an islanding state.

[0023] The DC power supply A outputs DC power and includes, for example, a solar cell. The solar cell generates DC power by converting solar energy into electrical energy. The DC power supply A outputs the generated DC power to the power conditioner 1. Note that the DC power supply A is not limited to one that generates DC power using a solar cell. For example, the DC power supply A may be a fuel cell or a storage battery, or may be a device that converts AC power generated by a diesel engine generator or a wind turbine generator into DC power and outputs the DC power.

[0024] The power conditioner 1 includes an inverter device 2, an islanding operation detection device 3, an interconnection breaker 4, and a voltage sensor 5. The power conditioner 1 is connected to a power distribution system C via the interconnection breaker 4.

[0025] The inverter device 2 converts DC power input from the DC power source A into AC power and outputs it. The inverter device 2 includes, for example, an inverter circuit, a filter circuit, and a control circuit (not shown). The inverter circuit converts DC power into AC power by switching a switching element (not shown) on and off based on a PWM signal input from the control circuit. The filter circuit removes high-frequency components caused by switching. The control circuit controls the inverter circuit. The control circuit generates a PWM signal that controls the output current of the inverter device 2 and outputs it to the inverter circuit. When a gate block signal (described later) is input from the islanding operation detection device 3, the control circuit stops generating the PWM signal. In this case, the inverter circuit stops switching, and the inverter device 2 stops its power conversion operation. Furthermore, when the islanding operation detection device 3 instructs the control circuit to inject an active signal (e.g., reactive power), the control circuit injects the active signal into the inverter circuit. The configuration of the inverter device 2 is not limited.

[0026] The interconnection circuit breaker 4 cuts off the connection between the power conditioner 1 and the power distribution system C. The interconnection circuit breaker 4 is normally closed, and the power conditioner 1 is connected to the power distribution system C. However, when an open command, which will be described later, is input from the islanding operation detection device 3, the interconnection circuit breaker 4 is opened, and the power conditioner 1 is disconnected from the power distribution system C. This prevents the power conditioner 1 from entering an islanding operation state.

[0027] The voltage sensor 5 detects the output voltage of the power conditioner 1 and inputs the detected voltage signal to the islanding operation detection device 3. The voltage sensor 5 may also be used to control the inverter device 2. In this case, the voltage sensor 5 also inputs the detected voltage signal to the control circuit of the inverter device 2.

[0028] The islanding operation detection device 3 detects islanding operation of the power conditioner 1. The islanding operation detection device 3 detects islanding operation based on a voltage signal input from the voltage sensor 5, and if islanding operation is detected, stops the power conditioner 1 and disconnects it from the power distribution system C. The islanding operation detection device 3 includes a voltage flicker detection device 31, a switching unit 36, an active detection unit 32, a passive detection unit 33, a logical OR unit 34, and a stop processing unit 35.

[0029] The voltage flicker detection device 31 is configured to detect whether or not a conventional power source B1 or a new power source B2 (hereinafter, when not distinguishing between them, will be referred to collectively as "operating power source B") that is operating at or above a specified level is connected to the power distribution system C. In this embodiment, the voltage flicker detection device 31 detects whether or not an operating power source B that is operating at or above a specified level is connected (hereinafter, referred to as "connection state") by detecting whether or not voltage flicker is occurring in the power distribution system C due to reactive power injection by an islanding operation detection device. The voltage flicker detection device 31 detects the connection state based on a voltage signal input from the voltage sensor 5, and outputs a detection signal to the switching unit 36 ​​when it is determined that an operating power source B that is operating at or above a specified level is connected.

[0030] 2 to 5 are diagrams illustrating the voltage flicker detection device 31. The voltage flicker detection device 31 detects both frequency fluctuations and voltage fluctuations to detect the occurrence of voltage flicker in terms of both frequency and voltage. FIG. 2 is a block diagram showing the details of the internal configuration of the voltage flicker detection device 31. The voltage flicker detection device 31 includes a frequency detection unit 41, a change amount detection unit 42, a low-pass filter 43, a PP value detection unit 44, a frequency determination unit 45, an RMS value detection unit 51, a PP value detection unit 52, a frequency detection unit 53, an index value calculation unit 54, a voltage determination unit 55, and a logical product unit 46. The frequency detection unit 41, the change amount detection unit 42, the low-pass filter 43, the PP value detection unit 44, and the frequency determination unit 45 are components for detecting voltage flicker from frequency fluctuations, and when referred to collectively, are referred to as a "first determination unit 49." The effective value detection unit 51, the PP value detection unit 52, the frequency detection unit 53, the index value calculation unit 54, and the voltage judgment unit 55 are components for detecting voltage flicker from voltage fluctuations, and when referred to collectively, are referred to as the "second judgment unit 59."

[0031] The frequency detection unit 41 detects the frequency f of the system voltage of the power distribution system C. The frequency detection unit 41 detects the frequency f of the instantaneous value of the voltage based on the voltage signal input from the voltage sensor 5. The frequency detection unit 41 detects the frequency, for example, using a zero-crossing point counting method. The zero-crossing point counting method measures the time between points where the instantaneous value of the AC voltage crosses the zero level (zero-crossing points) and detects the frequency from the reciprocal of the measured time. The frequency detection method used by the frequency detection unit 41 is not limited. For example, the frequency detection unit 41 may detect the frequency using a multiplication phase-locked loop (PLL). The power distribution system C is a three-phase AC distribution system, and the voltage sensor 5 detects the voltage signal of each phase. The frequency detection unit 41 detects the frequency of the voltage signal of each phase and outputs the average value of the three frequencies as the frequency f. The frequency detection unit 41 may also output the frequency of the voltage signal of one representative phase (e.g., the U phase) as the frequency f. The frequency detection unit 41 outputs the detected frequency f to the change amount detection unit .

[0032] The change amount detection unit 42 receives the frequency f from the frequency detection unit 41 and detects the amount of change Δf in the frequency f. The change amount detection unit 42 receives the frequency f every predetermined cycle (for example, about 20 ms, although this is not limited thereto) and calculates the difference between the input frequency f and the frequency f input one cycle before as the amount of change Δf. Hereinafter, this predetermined cycle will be referred to as a "frequency detection cycle." The change amount detection unit 42 outputs the detected amount of change Δf to the low-pass filter 43.

[0033] The low-pass filter 43 extracts only frequency components of 30 Hz or less from the amount of change Δf continuously input from the change amount detection unit 42, and outputs them to the PP value detection unit 44. Since humans perceive lighting flicker at frequencies between 2 and 30 Hz, in this embodiment, the low-pass filter 43 removes frequency components greater than 30 Hz.

[0034] The PP value detection unit 44 detects the peak-to-peak value (hereinafter referred to as "PP value") of the change Δf (frequency components of 30 Hz or less) input from the low-pass filter 43. In this embodiment, to capture frequency changes of 2 Hz or more, the PP value is detected over a period of 500 ms, which is a 2 Hz cycle. The PP value detection unit 44 detects the PP value while shifting the detection range for each frequency detection cycle (for example, approximately 20 ms). The PP value detection unit 44 outputs the detected PP value to the frequency determination unit 45.

[0035] The frequency determination unit 45 determines the occurrence of voltage flicker by comparing the PP value input from the PP value detection unit 44 with a predetermined threshold Δf0. The threshold Δf0 is set to a value at which it can be determined that voltage flicker is occurring, for example, approximately 0.05 Hz. Note that the threshold Δf0 is not limited and can be appropriately set based on experimental, simulation, on-site investigation results, etc. If the PP value input from the PP value detection unit 44 remains equal to or greater than the threshold Δf0 for a first determination time T1 or longer, the frequency determination unit 45 determines that voltage flicker is occurring and outputs a first determination signal, which is a high-level signal, to the AND unit 46. The first determination time T1 is set to exclude cases where the PP value exceeds the threshold Δf0 for only a very short time. In this embodiment, the first determination time T1 is set to, for example, 10 seconds. Note that the first determination time T1 is not limited and can be appropriately set based on experimental, simulation, on-site investigation results, etc.

[0036] FIG. 3 is a waveform diagram showing the simulation results of the first determination unit 49 of the voltage flicker detection device 31. FIG. 3(a) shows the time change of the frequency f detected by the frequency detection unit 41. FIG. 3(b) shows the time change of the change amount Δf detected by the change amount detection unit 42. FIG. 3(c) shows the time change of the PP value of the change amount Δf detected by the PP value detection unit 44. At time "0," a voltage fluctuation is generated, and as shown in FIG. 3(a), the frequency f fluctuates significantly thereafter. As a result, as shown in FIG. 3(b), the change amount Δf also fluctuates significantly. Then, as shown in FIG. 3(c), the PP value continues to exceed the threshold value Δf0. If this state continues for the first determination time T1, the frequency determination unit 45 determines that voltage flicker is occurring and outputs a first determination signal.

[0037] The effective value detection unit 51 detects the effective voltage value v of the system voltage of the power distribution system C. The effective value detection unit 51 detects the effective voltage value v based on the voltage signal input from the voltage sensor 5. The power distribution system C is a three-phase AC power distribution system, and the voltage sensor 5 detects the voltage signal of each phase. The effective value detection unit 51 detects the effective voltage value from the voltage signal of each phase and outputs the average of the three effective voltage values ​​as the effective voltage value v. Note that the effective value detection unit 51 may also output the effective voltage value of the voltage signal of one representative phase (e.g., the U phase) as the effective voltage value v. The effective value detection unit 51 outputs the detected effective voltage value v to the P-P value detection unit 52 and the frequency detection unit 53. Note that the effective value detection unit 51 may detect another index representing the magnitude of the voltage, such as the maximum or average voltage value, instead of the effective voltage value.

[0038] The PP value detection unit 52 detects the peak-to-peak value (hereinafter referred to as the "PP value") of the voltage effective value v input from the effective value detection unit 51. Like the PP value detection unit 44, the PP value detection unit 52 detects the PP value over a 500 ms period, which is a 2 Hz cycle, in order to capture voltage fluctuations of 2 Hz or more. Like the PP value detection unit 44, the PP value detection unit 52 also detects the PP value while shifting the detection range for each frequency detection cycle (for example, approximately 20 ms). The PP value detection unit 52 outputs the detected PP value to the index value calculation unit 54.

[0039] The frequency detector 53 detects the frequency f of the fluctuation of the effective voltage v. V The frequency detector 53 detects the frequency f based on the voltage effective value v input from the effective value detector 51. V In this embodiment, the time from when the PP value detection unit 52 detects the upper peak value to when it detects the lower peak value is defined as a half cycle, and the frequency f V The frequency detection method of the frequency detection unit 53 is not limited, and the detection may be performed in the same manner as the frequency detection unit 41, or in another manner. The frequency detection unit 53 detects the detected frequency f V to the index value calculation unit 54.

[0040] The index value calculation unit 54 calculates an index value for determining voltage flicker. Generally, voltage flicker is determined by the following formula: 10 " and this index value is managed so that it is equal to or less than a regulated value (for example, "0.45"). 10 The index value ΔV is similar to X Figure 4 shows the flicker visibility curve a, which shows the visibility of flicker for each frequency of voltage fluctuation as a coefficient. ΔV 10 The index value ΔV is calculated as the square root of the integrated value of the square of the product of the change in the frequency component and the flicker visibility coefficient at that frequency for each frequency component contained in the one-minute voltage fluctuation. X is ΔV 10 Specifically, the index value calculation unit 54 multiplies the PP value of the voltage effective value v detected by the PP value detection unit 52 by the frequency f detected by the frequency detection unit 53. V By multiplying the coefficient according to X The coefficients used here are a simplified version of the visibility curve a, and are calculated based on the frequency f V When the frequency is 3 Hz or more, it is set to "1", and when it is less than 3 Hz, it is set to "0.6" (shown by the solid line b in Figure 4). X The coefficient used to calculate the index value ΔV 10 Since the value is greater than the coefficient used to calculate (see visibility curve a), the index value ΔV X is the index value ΔV 10 The index value ΔV calculated by the index value calculation unit 54 is a larger value. X The method for calculating the index value ΔV is not limited to this. X For example, the general index value ΔV 10 The index value calculation unit 54 may calculate the calculated index value ΔV X is output to the voltage determination unit 55.

[0041] The voltage determination unit 55 determines the index value ΔV X a predetermined threshold ΔV X0 The occurrence of voltage flicker is determined by comparing with the threshold value ΔV X0 is set to a value that can be used to determine whether voltage flicker is occurring. For example, the index value ΔV 10 The threshold value ΔV is set to "0.45", which is the same as the regulation value of X0 is not limited, and is set appropriately based on the results of experiments, simulations, or on-site investigations. X is the threshold ΔV X0 If the above state continues for a second determination time T2 or longer, it is determined that voltage flicker is occurring, and a second determination signal, which is a high-level signal, is output to the AND unit 46. The second determination time T2 is the time when the index value ΔV X For a very short time, the threshold ΔV X0 In this embodiment, the second determination time T2 is set to, for example, 3 seconds. Note that the second determination time T2 is not limited to a specific value and may be set appropriately based on experiments, simulation results, on-site investigation results, or the like.

[0042] 5A and 5B are waveform diagrams showing the simulation results of the second determination unit 59 of the voltage flicker detection device 31. FIG. 5A shows the time variation of the voltage effective value v detected by the effective value detection unit 51 (see the solid line v in the figure, the vertical axis on the left), and the time variation of the PP value of the voltage effective value v detected by the PP value detection unit 52 (see the dashed line PP in the figure, the vertical axis on the right). FIG. 5B shows the time variation of the frequency f detected by the frequency detection unit 53. V 5(c) shows the time change of the index value ΔV detected by the index value calculation unit 54. X At time "0", the voltage fluctuation causes the voltage effective value v to fluctuate greatly. This causes the PP value to rise and the frequency f V is decreasing. ΔV X was almost "0" until time "0", but after time "0" it rose to ΔV X0If this state continues for the second determination time T2, the voltage determination unit 55 determines that voltage flicker is occurring and outputs a second determination signal.

[0043] The logical product unit 46 generates a logical product signal of the signal input from the frequency determination unit 45 and the signal input from the voltage determination unit 55, and outputs the result to the switching unit 36. Therefore, when the logical product unit 46 receives a first determination signal (high level signal) from the frequency determination unit 45 and a second determination signal (high level signal) from the voltage determination unit 55, the logical product unit 46 outputs a detection signal that is a high level signal. On the other hand, when the logical product unit 46 does not receive the first determination signal (high level signal) from the frequency determination unit 45 or does not receive the second determination signal (high level signal) from the voltage determination unit 55, the logical product unit 46 outputs a low level signal. In other words, the logical product unit 46 outputs a detection signal only when the first determination unit 49 detects voltage flicker from frequency fluctuations and the second determination unit 59 detects voltage flicker from voltage fluctuations. As described above, when the voltage flicker detection device 31 determines that voltage flicker is occurring in the power distribution system C, it determines that an operating power source B greater than the specified level is connected to the power distribution system C, and outputs a detection signal to the switching unit 36.

[0044] The switching unit 36 ​​switches between a state in which the active detection unit 32 is enabled and a state in which it is disabled. The switching unit 36 ​​outputs an ON signal, which is, for example, a high-level signal, when the active detection unit 32 is enabled, and outputs an OFF signal, which is, for example, a low-level signal, when the active detection unit 32 is disabled. The switching unit 36 ​​outputs an OFF signal while a detection signal is being input from the voltage flicker detection device 31. Furthermore, the switching unit 36 ​​switches the OFF signal to an ON signal when a state in which no detection signal is being input from the voltage flicker detection device 31 continues for a third determination time T3.

[0045] Even if the voltage flicker converges and the voltage flicker detection device 31 no longer outputs a detection signal, voltage fluctuations still remain in the power distribution system C to a degree that is not deemed to be voltage flicker. Operating the active detection unit 32 in this state may increase the voltage fluctuations, causing the voltage flicker to recur and the voltage flicker detection device 31 to output a detection signal. In this case, the switching unit 36 ​​switches from an ON signal to an OFF signal, resulting in a state in which the ON and OFF signals are alternately switched over in a short period of time. The third determination time T3 is set to prevent this state from occurring by delaying the timing at which the switching unit 36 ​​switches the OFF signal to an ON signal. The third determination time T3 is set to the time from when the voltage flicker converges and the voltage flicker detection device 31 no longer outputs a detection signal until the voltage fluctuations converge to a certain degree (to a degree that will not cause the voltage flicker to recur even when the active detection unit 32 is operating).

[0046] Furthermore, the grid interconnection regulations stipulate that a power conditioner connected to a high-voltage distribution system must be disconnected within three seconds if it experiences an islanding operation. In this embodiment, the third judgment time T3 is set to two seconds or less, taking into consideration that the active detection unit 32 detects islanding operation within one second so that islanding operation can be detected within three seconds. The specific value of the third judgment time T3 is set appropriately based on experimentation, simulation results, on-site investigation results, or the like. Note that the switching unit 36 ​​may switch the OFF signal to the ON signal when the third judgment time T3 is not set and the detection signal is no longer input from the voltage flicker detection device 31.

[0047] The active detection unit 32 has the same function as a conventional active islanding detection device and detects islanding by injecting an active signal. In this embodiment, the active signal is reactive power. Specifically, the active detection unit 32 sets a target value for reactive power in the control circuit of the inverter device 2, thereby injecting reactive power into the inverter device 2. The active detection unit 32 then detects islanding based on a voltage signal input from the voltage sensor 5. In this embodiment, the active detection unit 32 detects islanding using, for example, a slip mode frequency shift method. Note that the method for detecting islanding by the active detection unit 32 is not limited. The active detection unit 32 is in a functional state while receiving an ON signal from the switching unit 36, and injects reactive power to detect islanding. On the other hand, the active detection unit 32 is in a non-functional state while receiving an OFF signal from the switching unit 36, and does not inject reactive power. When the active detection unit 32 detects islanding, it outputs an active detection signal, for example, a high-level signal, to the logical OR unit 34.

[0048] The passive detection unit 33 detects islanding based on the voltage signal input from the voltage sensor 5 without injecting reactive power. The passive detection unit 33 detects islanding based on changes in the electrical characteristics of the power distribution system C caused by increasing the reactive power injected by the islanding detection devices of the conventional power source B1 and the new power source B2 when islanding occurs. In this embodiment, the passive detection unit 33 detects islanding based on the voltage signal input from the voltage sensor 5. Specifically, the passive detection unit 33 detects frequency f based on the voltage signal input from the voltage sensor 5. Note that the frequency detection process of frequency f may also be performed by the frequency detection unit 41 of the voltage flicker detection device 31. The passive detection unit 33 then determines whether frequency f matches a preset judgment condition. The judgment condition is set as a condition that can determine that islanding has occurred. When islanding occurs, the islanding detection devices of the conventional power source B1 and the new power source B2 increase the reactive power they inject to change the voltage frequency of the power distribution system C, and detect islanding when the frequency exceeds a threshold. The judgment condition is set based on the change in frequency at this time.

[0049] In this embodiment, the determination condition is that the change Δf in frequency f is equal to or greater than the threshold value Δf1 for a predetermined time period T0 or longer. The passive detection unit 33 calculates the change Δf in frequency f for each frequency detection cycle. The calculation method for the change Δf is the same as that used by the change detection unit 42 of the voltage flicker detection device 31. The change detection unit 42 of the voltage flicker detection device 31 may also be used to detect the change Δf. The threshold value Δf1 is set to a value that determines whether islanding has occurred and whether the frequency f has changed due to reactive power injection by the islanding detection devices of the conventional power source B1 and the new power source B2. The threshold value Δf1 is not limited and can be set appropriately based on experimental results, simulation results, on-site investigation results, or the like. However, system disturbances other than islanding may also cause the frequency f to change and the change Δf to be equal to or greater than the threshold value Δf1. In such cases, the change Δf remains equal to or greater than the threshold value Δf1 for a short period of time. The predetermined time T0 is set so that a change in frequency f due to a system disturbance or the like is not determined to be islanding operation. Note that the predetermined time T0 is not limited.

[0050] In this embodiment, the passive detection unit 33 determines that the determination condition is met when the calculated change amount Δf remains equal to or greater than the threshold value Δf1 for a predetermined time period T0 or longer. When the passive detection unit 33 determines that the determination condition is met, it outputs a passive detection signal, which is a high-level signal, to the logical sum unit 34.

[0051] The logical sum unit 34 generates a logical sum signal of the signal input from the active detection unit 32 and the signal input from the passive detection unit 33, and outputs the logical sum signal to the stop processing unit 35. Therefore, when an active detection signal (high level signal) is input from the active detection unit 32, or when a passive detection signal (high level signal) is input from the passive detection unit 33, the logical sum unit 34 outputs an islanding operation detection signal, which is a high level signal, to the stop processing unit 35. In other words, when at least one of the active detection unit 32 or the passive detection unit 33 detects islanding operation, the logical sum unit 34 determines that an islanding operation state is occurring, and outputs the islanding operation detection signal, which is a high level signal, to the stop processing unit 35.

[0052] When the stop processing unit 35 receives an islanding operation detection signal from the logical sum unit 34, it performs a process of stopping the power conditioner 1. Specifically, the stop processing unit 35 outputs a gate block signal to the inverter device 2 to stop the power conversion operation of the inverter device 2. In addition, the stop processing unit 35 outputs an open command to the interconnection breaker 4 to disconnect the power conditioner 1 from the power distribution system C.

[0053] The islanding operation detection device 3 may be realized as an analog circuit or a digital circuit. The processing performed by each unit may be designed as a program, and a computer may function as the islanding operation detection device 3 by executing the program. The program may also be recorded on a recording medium and read by a computer.

[0054] When voltage flicker is detected, the active detection unit 32 does not function, but the passive detection unit 33 does. In this case, because an operating power source B greater than the specified amount is connected to the power distribution system C, the passive detection unit 33 can detect islanding operation when islanding occurs. On the other hand, when voltage flicker is not detected, the active detection unit 32 functions. Like a conventional active islanding operation detection device, the active detection unit 32 detects islanding operation by injecting reactive power. Therefore, in this case, when islanding operation occurs, the active detection unit 32 can detect islanding operation. As described above, the islanding operation detection device 3 can detect islanding operation whether or not voltage flicker is detected.

[0055] As described above, the switching unit 36 ​​delays the timing of switching the OFF signal to the ON signal. However, because the third determination time T3 is set to within two seconds, even if the timing at which voltage flicker is no longer detected and the timing at which a power outage occurs are simultaneous, the active detection unit 32 starts functioning after the voltage flicker has converged and the third determination time T3 has elapsed (within two seconds). The active detection unit 32 detects islanding within one second, so it can detect islanding within three seconds of the occurrence of a power outage. Furthermore, because the switching unit 36 ​​delays the timing at which it switches the OFF signal to the ON signal, the active detection unit 32 injects reactive power after the voltage fluctuations have almost converged. Therefore, the recurrence of voltage flicker is suppressed.

[0056] Next, the effects of the voltage flicker detection device 31 and the isolated operation detection device 3 according to this embodiment will be described.

[0057] In this embodiment, the frequency determination unit 45 determines the occurrence of voltage flicker based on fluctuations in the frequency f of the instantaneous voltage value, and the voltage determination unit 55 determines the occurrence of voltage flicker based on fluctuations in the effective voltage value v. The logical product unit 46 outputs a detection signal only when both the frequency determination unit 45 and the voltage determination unit 55 detect voltage flicker. Voltage flicker caused by the islanding detection device injecting an active signal varies not only in voltage but also in voltage phase (instantaneous value frequency). The voltage flicker detection device 31 makes a determination based on fluctuations in the instantaneous value frequency of the voltage in addition to a determination based on fluctuations in the voltage magnitude, and detects voltage flicker based on both determination results. Therefore, the voltage flicker detection device 31 can detect voltage flicker caused by the islanding detection device injecting an active signal.

[0058] Furthermore, in this embodiment, change amount detection unit 42 detects change amount Δf in frequency f, low-pass filter 43 extracts only frequency components of 30 Hz or less from change amount Δf, and PP value detection unit 44 detects the PP value of change amount Δf for 500 ms input from low-pass filter 43. Then, frequency determination unit 45 compares the PP value with threshold value Δf0 to determine the occurrence of voltage flicker. Therefore, frequency determination unit 45 can appropriately determine the occurrence of voltage flicker according to the fluctuation width of the 2 to 30 Hz component of the fluctuation in frequency f.

[0059] Furthermore, according to this embodiment, the PP value detector 52 detects the PP value of the effective voltage v for 500 ms, and the frequency detector 53 detects the frequency f of the effective voltage v. V The index value calculation unit 54 calculates the PP value of the effective voltage v and the frequency f V The index value ΔV is calculated by multiplying it by a coefficient according to X Then, the voltage determination unit 55 calculates the index value ΔV X threshold ΔV X0 Therefore, the voltage determining unit 55 can appropriately determine the occurrence of voltage flicker according to the fluctuation width of the component of 2 Hz or more of the fluctuation of the effective voltage value v.

[0060] Furthermore, according to this embodiment, the index value calculation unit 54 calculates the PP value of the effective voltage v and the frequency f V The index value ΔV is calculated by multiplying it by a coefficient according to X Calculate the coefficient ΔV 10 Therefore, the index value calculation unit 54 calculates ΔV 10 In addition, the calculation load is significantly reduced compared to when the index value ΔV X The coefficient used to calculate the index value ΔV 10 Since this value is greater than the visibility coefficient used to calculate the index value ΔV X is the index value ΔV 10 Therefore, the voltage determining unit 55 can prevent voltage flicker from being missed when it is detected.

[0061] Furthermore, according to this embodiment, the switching unit 36 ​​switches the active detection unit 32 to a disabled state when the voltage flicker detection device 31 detects the occurrence of voltage flicker in the power distribution system C. As a result, when voltage flicker is occurring, the islanding operation detection device 3 disables the active detection unit 32 and enables only the passive detection unit 33 to function, thereby detecting islanding. In this case, the islanding operation detection device 3 does not inject reactive power, and therefore does not induce voltage flicker. On the other hand, the switching unit 36 ​​switches the active detection unit 32 to a enabled state when the voltage flicker detection device 31 does not detect the occurrence of voltage flicker. As a result, the islanding operation detection device 3 enables the active detection unit 32 to function and injects reactive power when no voltage flicker is occurring. In this case, because the operating power source B is not connected in excess of the specified level, injecting reactive power does not induce voltage flicker. In other words, the islanding operation detection device 3 can detect islanding without inducing voltage flicker.

[0062] The method of determining voltage flicker based on fluctuations in frequency f in voltage flicker detection device 31 is not limited. For example, voltage flicker detection device 31 does not need to include low-pass filter 43, and the detection range for PP value detection in PP value detection unit 44 is not limited to 500 ms. When the PP value becomes equal to or greater than threshold value Δf0, frequency determination unit 45 may determine the occurrence of voltage flicker without waiting for the first determination time T1 to elapse. Furthermore, the method of determining voltage flicker based on fluctuations in effective voltage value v in voltage flicker detection device 31 is not limited. For example, the detection range for PP value detection in PP value detection unit 52 in voltage flicker detection device 31 is not limited to 500 ms, and the index calculated by index value calculation unit 54 is not limited to ΔV X The voltage determination unit 55 determines the index value ΔV X is the threshold ΔV X0 If the voltage flicker detection device 31 detects the voltage fluctuation, it may determine whether or not a voltage flicker has occurred without waiting for the second determination time T2 to elapse. 10 and if the calculated value is equal to or greater than the regulation value, it may be determined that voltage flicker is occurring.

[0063] In the present embodiment, the passive detection unit 33 performs the determination based on the frequency f. However, the present invention is not limited to this. The passive detection unit 33 may perform the determination based on electrical characteristics such as the voltage, current, power (active power, reactive power), and frequency output by the power conditioner 1, as well as the voltage, current, power, and frequency of predetermined harmonic components such as the third, fifth, and seventh harmonic components. The detected values ​​used by the passive detection unit 33 for the determination may be the magnitude, deviation (amount of change from a reference), amount of change, and rate of change of the electrical characteristics. The unbalance rate may be detected from the three-phase AC voltage, and the detected value used for the determination may be the unbalance rate. The determination conditions set in the passive detection unit 33 are appropriately set depending on the detection values ​​used. For example, the passive detection unit 33 may determine that the determination conditions are met when the detection value is equal to or greater than a threshold value, without waiting for the predetermined time T0 to elapse. The determination conditions are not limited, and may be any conditions that can determine that islanding has occurred.

[0064] The passive detection unit 33 may also use two or more types of detection values ​​to detect islanding operation separately. For example, the passive detection unit 33 may detect islanding operation based on the amount of change Δf in frequency f as described above, and separately detect islanding operation based on the effective voltage value v of the grid voltage, and detect islanding operation when both detect islanding operation. The passive detection unit 33 may also detect islanding operation when at least one of the two detects islanding operation.

[0065] Second Embodiment 6 is a block diagram showing the details of the internal configuration of a voltage flicker detection device 31a according to the second embodiment. In the figure, elements that are the same as or similar to those in the voltage flicker detection device 31 according to the first embodiment (see FIG. 2) are given the same reference numerals, and redundant explanations will be omitted. Note that the configuration other than the voltage flicker detection device 31a is the same as in the first embodiment, so illustrations and explanations thereof will be omitted. The voltage flicker detection device 31a according to this embodiment differs from the voltage flicker detection device 31 in that it has an automatic threshold adjustment function.

[0066] The voltage flicker detection device 31a according to the second embodiment further includes a threshold value changing unit 47. The threshold value changing unit 47 is configured to change the threshold value and the determination time set in the frequency determining unit 45 and the voltage determining unit 55. The threshold value changing unit 47 receives the PP value of the change amount Δf from the PP value detecting unit 44, and calculates the index value ΔV X The threshold value changing unit 47 receives the signal (ON signal and OFF signal) output from the switching unit 36. When the ON signal input from the switching unit 36 ​​is switched to the OFF signal, or when the AND unit 46 starts to output the detection signal, the threshold value changing unit 47 changes the PP value of the amount of change Δf and the index value ΔV X The change in Δf is recorded. The PP value and index value ΔV X The threshold value Δf0 and the first determination time T1 of the frequency determination unit 45, and the threshold value ΔV X0 and the value of the second judgment time T2. When a voltage flicker is detected and the active detection unit 32 stops functioning, the voltage flicker converges, but the manner of convergence differs depending on the connection state of the operating power source B and the state of the power distribution system C. The threshold change unit 47 changes the PP value of the variation Δf and the index value ΔV X The threshold value and determination time for determining whether a voltage flicker has been detected are adjusted to optimal values ​​according to how the voltage flicker changes.

[0067] For example, the PP value and the index value ΔV of the change Δf from when the active detection unit 32 stopped functioning are X If the change in is relatively slow, it is considered that the total capacity of the operating power source B is relatively large compared to the capacity of the power distribution system C. In this case, the threshold value is made smaller and the determination time is shortened. This makes it possible to speed up the detection of voltage flicker. Also, it is possible to return the active detection unit 32 to normal operation after the voltage flicker has converged (not to determine that the voltage flicker has converged until it has become considerably smaller). Note that the logic for adjusting the threshold value and determination time by the threshold change unit 47 is not limited. Also, the threshold change unit 47 adjusts the PP value of the amount of change Δf or the index value ΔV XAlternatively, the threshold value changing unit 47 may adjust only the threshold value or only the determination time. Alternatively, the adjustment may be made to only either the frequency determining unit 45 or the voltage determining unit 55.

[0068] In this embodiment, the voltage flicker detection device 31a also makes a determination based on fluctuations in the instantaneous value frequency of the voltage in addition to a determination based on fluctuations in the magnitude of the voltage, and detects voltage flicker based on both determination results. Therefore, the voltage flicker detection device 31a can detect voltage flicker caused by the islanding operation detection device injecting an active signal. Furthermore, the voltage flicker detection device 31a has a common configuration with the voltage flicker detection device 31, and therefore achieves the same effects as the voltage flicker detection device 31. Furthermore, according to this embodiment, the threshold value changing unit 47 determines the PP value of the amount of change Δf and the index value ΔV X Therefore, the active power source detector 31 can automatically adjust the threshold value and the determination time for determining whether a voltage flicker has been detected to optimal values. For example, the active power detector 32 automatically adjusts the threshold value and the determination time for determining whether a voltage flicker has been detected to optimal values ​​based on the change in the voltage flicker. X If the change in voltage is relatively slow, and the threshold value changing unit 47 is set to reduce the threshold value and shorten the determination time, the voltage flicker detection can be accelerated, making it possible to detect signs of voltage flicker occurrence. Also, since the active detection unit 32 can be prevented from being restored until the voltage flicker has reliably converged, the recurrence of voltage flicker can be suppressed when the active detection unit 32 is restored.

[0069] Third Embodiment 7 is a block diagram for explaining a voltage flicker detection device 31b according to the third embodiment, showing the overall configuration of a power distribution system. In the figure, elements that are the same as or similar to those in the power conditioner 1 (see FIG. 1) according to the first embodiment are given the same reference numerals, and duplicated explanations will be omitted. The voltage flicker detection device 31b according to this embodiment differs from the voltage flicker detection device 31 in that it is not built into the islanding operation detection device 3b.

[0070] The voltage flicker detection device 31b according to the third embodiment is not built into the islanding operation detection device 3b, but is a separate, independent device. The islanding operation detection device 3b according to the third embodiment does not include a voltage flicker detection device, and receives a voltage flicker detection signal from the voltage flicker detection device 31b, which is an independent device. The voltage flicker detection device 31b has the same functions as the voltage flicker detection device 31 according to the first embodiment. In other words, the internal configuration of the voltage flicker detection device 31b is the same as the block diagram shown in FIG. 2.

[0071] In this embodiment, the voltage flicker detection device 31b also makes a determination based on fluctuations in the instantaneous value frequency of the voltage in addition to a determination based on fluctuations in the voltage magnitude, and detects voltage flicker based on both determination results. Therefore, the voltage flicker detection device 31b can detect voltage flicker caused by the islanding operation detection device injecting an active signal. Furthermore, the voltage flicker detection device 31b has a common configuration with the voltage flicker detection device 31, and therefore achieves the same effects as the voltage flicker detection device 31.

[0072] Furthermore, the voltage flicker detection device 31b can be used for purposes other than inputting a detection signal to an islanding operation detection device. For example, the voltage flicker detection device 31b may input a voltage flicker detection signal to a reactive power compensator that suppresses voltage flicker. Furthermore, the voltage flicker detection device 31b may be built into the reactive power compensator. In other words, the uses and arrangement of the voltage flicker detection device according to the present invention are not limited.

[0073] The voltage flicker detection device, the islanding operation detection device including the voltage flicker detection device, and the power conditioner including the islanding operation detection device according to the present invention are not limited to the above-described embodiments. The specific configurations of the respective parts of the voltage flicker detection device, the islanding operation detection device including the voltage flicker detection device, and the power conditioner including the islanding operation detection device according to the present invention can be freely designed and modified in various ways. [Explanation of symbols]

[0074] 1: power conditioner, 3, 3b: islanding operation detection device, 31, 31a, 31b: voltage flicker detection device, 32: active detection unit, 33: active detection unit, 36: switching unit, 41: frequency detection unit, 42: change amount detection unit, 43: low pass filter, 44: PP value detection unit, 45: frequency determination unit, 51: effective value detection unit, 52: PP value detection unit, 53: frequency detection unit, 54: index value calculation unit, 55: voltage determination unit, 46: logical product unit, 47: threshold value change unit, 5: voltage sensor, C: power distribution system

Claims

1. a first frequency detection unit that detects an instantaneous value frequency of a voltage based on a voltage signal input from a voltage sensor; a frequency determination unit that determines whether a voltage flicker occurs based on a fluctuation in the instantaneous value frequency; a voltage detection unit that detects the magnitude of a voltage based on the voltage signal; a voltage determination unit that determines whether or not a voltage flicker has occurred based on a fluctuation in the magnitude of the voltage; a detection unit that detects voltage flicker only when the frequency determination unit determines that voltage flicker is occurring and the voltage determination unit determines that voltage flicker is occurring; A voltage flicker detection device comprising:

2. a change amount detection unit that detects a change amount of the instantaneous value frequency; a low-pass filter that extracts only frequency components equal to or lower than an upper limit frequency from the amount of change; a first PP value detection unit that detects a first PP value, which is a peak-to-peak value per unit time of the amount of change after extraction by the low-pass filter; Furthermore, the unit time is a period of a lower limit frequency of a frequency component to be extracted from the amount of change, The frequency determination unit performs the determination by comparing the first PP value with a frequency threshold value.

2. The voltage flicker detection device according to claim 1.

3. a second PP value detection unit that detects a second PP value that is a peak-to-peak value of the magnitude of the voltage per unit time; a second frequency detection unit that detects a voltage frequency that is a frequency of fluctuations in the magnitude of the voltage; an index value calculation unit that calculates an index value from the second PP value and the voltage frequency; Furthermore, the voltage determination unit performs the determination by comparing the index value with an index threshold value.

3. The voltage flicker detection device according to claim 2.

4. The detector further includes a threshold adjusting unit that adjusts the frequency threshold or the index threshold based on how the first PP value or the index value changes when the detector changes from a state where it does not detect a voltage flicker to a state where it detects a voltage flicker.

4. The voltage flicker detection device according to claim 3.

5. An islanding operation detection device that detects islanding operation of a power conditioner, The voltage flicker detection device according to any one of claims 1 to 4, which detects occurrence of voltage flicker in a power distribution system to which the power conditioner is connected; an active detection unit that actively detects islanding by injecting a first active signal into the power distribution system; a passive detection unit that detects an islanding operation based on a change in electrical characteristics caused by another islanding operation detection device disposed in the power distribution system injecting a second active signal into the power distribution system; and a switching unit that switches the active detection unit between a functioning state and a non-functioning state according to the detection result of the voltage flicker detection device; Equipped with An islanding operation detection device characterized by:

6. An isolated operation detection device according to claim 5, A power conditioner characterized by the above.

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