Islanding operation detection device, islanding operation detection method, and power conditioner equipped with islanding operation detection device

Abstract

To provide an islanding operation detection device that does not induce a voltage flicker phenomenon.SOLUTION: An islanding operation detection device 3 for detecting islanding operation of a power conditioner 1 comprises: a frequency detection unit 31 for detecting a frequency f of an output voltage of the power conditioner 1; a voltage detection unit 32 for detecting a size of an output voltage of the power conditioner 1; a first determination unit 331 for determining whether or not the frequency f detected by the frequency detection unit 31 meets with a first determination condition; a second determination unit 332 for determining whether or not a size of an output voltage detected by the voltage detection unit 32 meets with a second determination condition; and a logical AND unit 333 for determining that the power conditioner is in an islanding operation state when a state in which the first determination unit 331 has determined that the first determination condition is met and the second determination unit 332 has determined that the second determination condition is met, continues for a predetermined time or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an islanding operation detection device, an islanding operation detection method, and a power conditioner equipped with the islanding operation detection device. [Background technology]

[0002] 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.

[0003] 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.

[0004] As a measure to suppress the occurrence of voltage flicker, islanding detection devices capable of suppressing the amount of reactive power injection have been developed. For example, Patent Document 1 discloses an islanding detection device that suppresses the amount of reactive power injection when the possibility of islanding is low. Furthermore, Patent Document 2 discloses an islanding detection device that can prevent false detection of islanding operation and detection delays while reducing the amount of reactive power injection by alternately injecting lagging-phase reactive power and leading-phase reactive power and detecting islanding operation based on the integrated value obtained by integrating the absolute values ​​of the amount of change in the moving average value of the system frequency. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-93020 [Patent Document 2] Japanese Patent Application Publication No. 2019-92328 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the islanding detection devices disclosed in Patent Documents 1 and 2 suppress the amount of injection but still inject reactive power. Therefore, when a power conditioner equipped with such an islanding detection device is newly connected to a power distribution system, the reactive power injected into the power distribution system increases. Therefore, even when such a power conditioner is connected to a power distribution system already connected to a large number of power conditioners equipped with islanding detection devices, it will induce voltage flicker.

[0007] The present invention was devised under the circumstances described above, and its object is to provide an islanding operation detection device, an islanding operation detection method, and a power conditioner equipped with an islanding operation detection device that do not induce voltage flicker phenomenon. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides the following technical means.

[0009] The islanding operation detection device provided by a first 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 first detection unit that detects the frequency of the output voltage of the power conditioner; a second detection unit that detects the magnitude of the output voltage of the power conditioner; a first judgment unit that judges whether the frequency detected by the first detection unit matches a first judgment condition; a second judgment unit that judges whether the magnitude of the output voltage detected by the second detection unit matches a second judgment condition; and an islanding operation judgment unit that judges that the device is in an islanding operation state when the state in which the first judgment unit judges that the first judgment condition matches and the second judgment unit judges that the second judgment condition matches continues for a predetermined time or more.

[0010] In a preferred embodiment of the present invention, the first judgment condition is that the amount of change in the frequency is equal to or greater than a threshold value.

[0011] In a preferred embodiment of the present invention, the second judgment condition is that the magnitude of the output voltage is no longer within a predetermined range.

[0012] An islanding operation detection device provided by a 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 first detection unit that detects the frequency of the output voltage of the power conditioner; a second detection unit that detects the unbalance rate of the three-phase output voltage of the power conditioner; a first judgment unit that judges whether the frequency detected by the first detection unit matches a first judgment condition; a second judgment unit that judges whether the unbalance rate detected by the second detection unit matches a second judgment condition; and an islanding operation judgment unit that judges that an islanding operation state exists when the state in which the first judgment unit judges that the first judgment condition matches and the second judgment unit judges that the second judgment condition matches continues for a predetermined time or more.

[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 first and second aspects of the present invention.

[0014] An islanding operation detection method provided by a fourth aspect of the present invention is an islanding operation detection method for detecting the islanding operation of a power conditioner, and is characterized by comprising: a first detection step of detecting the frequency of the output voltage of the power conditioner; a second detection step of detecting the magnitude of the output voltage of the power conditioner; a first judgment step of judging whether the frequency detected in the first detection step matches a first judgment condition; a second judgment step of judging whether the magnitude of the output voltage detected in the second detection step matches a second judgment condition; and an islanding operation judgment step of judging that the first judgment condition is met in the first judgment step and that the state in which the second judgment step is met continues for a predetermined time or more. [Effects of the Invention]

[0015] According to the present invention, an islanding state is determined when the first determination unit determines that the frequency of the power conditioner's output voltage meets the first determination criterion and the second determination unit determines that the magnitude of the power conditioner's output voltage meets the second determination criterion.The islanding operation detection device of the present invention detects islanding in response to changes in the frequency and magnitude of the system voltage in the distribution system caused by another islanding operation detection device injecting an active signal such as reactive power into the distribution system, and therefore does not inject reactive power into the distribution system.Therefore, the islanding operation detection device of the present invention does not induce voltage flicker.

[0016] 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]

[0017] [Figure 1]1 is a block diagram for explaining a power conditioner equipped with an isolated operation detection device according to a first embodiment, showing the overall configuration of a power distribution system. [Figure 2] 10 is a flowchart for explaining an isolated-operation determination process performed by the isolated-operation detection device. [Figure 3] This is a time chart showing the change in frequency and effective voltage of the output voltage of a power conditioner, when a power outage occurs in a power distribution system to which a conventional power source and a new power source are connected. [Figure 4] 1 is a time chart showing the change in frequency and effective voltage of the output voltage of a power conditioner, in the case where a power distribution system connected only to conventional power sources experiences a power outage. [Figure 5] 1 is a time chart showing changes in the frequency and effective voltage of the output voltage of a power conditioner when a grid disturbance occurs. [Figure 6] FIG. 10 is a block diagram for explaining an islanding operation detection device according to a second embodiment, showing the overall configuration of a power distribution system. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] [First embodiment] FIG. 1 is a block diagram for explaining a power conditioner equipped with an islanding operation detection device according to a first embodiment, and shows the overall configuration of a power distribution system.

[0020] The power conditioner 1 converts DC power output by the DC power source A into AC power and outputs it to the connected power distribution system C. The combination of the power conditioner 1 and the DC power source A constitutes a distributed power source. The power distribution system C is a high-voltage power distribution system to which a load L, a conventional power source B1, and a new power source B2 are connected. The load L is a consumer that receives power supply. 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. Although multiple loads L, conventional power sources B1, and new power sources B2 are connected to distribution system C (and the low-voltage distribution system connected to distribution system C via a transformer), Fig. 1 shows only one of each as a representative. Distribution system C is connected to the power system via a circuit breaker. In the event of an accident in the power system, a protective device installed on the power system side opens the circuit breaker, and distribution system C is isolated from the power system (power outage state). As a result, power conditioner 1 connected to distribution system C, which has been isolated from the power system, enters an islanding operation state.

[0021] 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.

[0022] 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.

[0023] 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, which are 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, which will be 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. The configuration of the inverter device 2 is not limited.

[0024] 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.

[0025] 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.

[0026] 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 when 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 frequency detection unit 31, a voltage detection unit 32, a determination unit 33, and a stop processing unit 34.

[0027] The frequency detection unit 31 detects the frequency f of the output voltage of the power conditioner 1. The frequency detection unit 31 detects the frequency f based on a voltage signal input from the voltage sensor 5. The frequency detection unit 31 detects the frequency using, for example, a zero-crossing point counting method. The zero-crossing point counting method is a method of measuring the time between points (zero-crossing points) where the instantaneous value of the AC voltage crosses the zero level, and detecting the frequency from the reciprocal of the measured time. Note that the frequency detection method used by the frequency detection unit 31 is not limited. For example, the frequency detection unit 31 may detect the frequency using a multiplication type PLL (Phase Locked Loop). The frequency detection unit 31 outputs the detected frequency f to the determination unit 33.

[0028] The voltage detection unit 32 detects the effective voltage value v of the output voltage of the power conditioner 1. The voltage detection unit 32 detects the effective voltage value v based on the voltage signal input from the voltage sensor 5. The voltage detection unit 32 outputs the detected effective voltage value v to the determination unit 33. Note that the voltage detection unit 32 may also detect other indicators that represent the magnitude of the voltage, such as the maximum or average voltage value.

[0029] The determination unit 33 determines whether or not the inverter is in an islanding state based on the frequency f input from the frequency detection unit 31 and the effective voltage value v input from the voltage detection unit 32. The determination unit 33 includes a first determination unit 331, a second determination unit 332, a logical product unit 333, and a time determination unit 334.

[0030] The first determination unit 331 determines whether the frequency f matches a preset first determination condition. The first determination condition is set as a condition that can determine that islanding has occurred. When islanding has occurred, the islanding detection devices of the conventional power source B1 and the new power source B2 increase the reactive power injected to change the frequency of the voltage of the power distribution system C, and detect islanding when the frequency exceeds a threshold. The first determination condition is set based on the change in frequency at this time.

[0031] In this embodiment, the first determination condition is that the change Δf in frequency f is equal to or greater than a threshold Δf1. The first determination unit 331 calculates the change Δf in frequency f every predetermined cycle (for example, approximately 20 ms, but not limited thereto). The first determination unit 331 calculates the change Δf in frequency f as the absolute value of the difference between the frequency f input from the frequency detection unit 31 and the frequency f input one cycle before. The threshold Δf1 is set to a value that allows determination that islanding has occurred and that the frequency f has changed due to the injection of reactive power by the islanding detection devices of the conventional power source B1 and the new power source B2. For example, if the frequency f under normal conditions is 60 Hz, the threshold Δf1 is set to approximately 2.4 Hz. Note that the threshold Δf1 is not limited and can be set appropriately based on experiments, simulation results, on-site investigation results, or the like.

[0032] In this embodiment, the first determination unit 331 determines that the first determination condition is met when the calculated change amount Δf is equal to or greater than the threshold value Δf1. When the first determination unit 331 determines that the first determination condition is met, it outputs a first detection signal, which is a high-level signal, to the logical product unit 333. Note that the first determination condition is not limited as long as it is a condition that can determine that islanding has occurred. For example, when the change amount Δf fluctuates above and below the threshold value Δf1, in order to prevent the first determination unit 331 from repeatedly outputting and not outputting the first detection signal, the first determination condition may be that the state in which the change amount Δf is equal to or greater than the threshold value Δf1 continues for a determination time period.

[0033] The second determination unit 332 determines whether the effective voltage value v input from the voltage detection unit 32 matches the second determination condition. The second determination condition is also set with a condition that can determine that single operation has occurred. When single operation occurs, the single operation detection devices of the conventional power supply B1 and the new power supply B2 increase the reactive power to be injected. As a result, the output voltage of the power conditioner 1 changes significantly. The second determination condition is set based on the output voltage of the power conditioner 1 at this time.

[0034] In this embodiment, the second determination condition is that the effective voltage value v input from the voltage detection unit 32 does not fall within a predetermined range. The predetermined range is a range centered on the effective voltage value v0 of the rated voltage of the power conditioner 1, and is a range of v1 (<v0) or more and v2 (>v0) or less. Note that v1 and v2 are not limited. The predetermined range is set to be a range within which the effective voltage value v does not fall when single operation occurs. For example, a range of 80% or more and less than 120% of the rated voltage is set as the predetermined range. Note that the predetermined range is not limited to this range, and is appropriately set based on experiments, simulation results, or investigation results at the site.

[0035] In this embodiment, when the effective voltage value v becomes greater than v2 or when the effective voltage value v becomes less than v1, the second determination unit 332 determines that the second determination condition is met. When the second determination unit 332 determines that the second determination condition is met, it outputs a second detection signal, which is a high-level signal, to the logical product unit 333. Note that the second determination condition is not limited, and any condition that can determine that single operation has occurred may be used. For example, in order to prevent the second determination unit 332 from repeatedly outputting and not outputting the second detection signal when the effective voltage value v fluctuates above and below v1 (v2), the second determination condition may be that the state where the effective voltage value v does not fall within the predetermined range continues only for the determination time limit.

[0036] The logical product unit 333 generates a logical product signal of the signal input from the first determination unit 331 and the signal input from the second determination unit 332, and outputs the logical product signal to the time determination unit 334. Therefore, when the logical product unit 333 receives the first detection signal (high level signal) from the first determination unit 331 and the second detection signal (high level signal) from the second determination unit 332, it outputs a high level signal as the logical product signal to the time determination unit 334.

[0037] The time determination unit 334 measures the time from when the logical product signal input from the logical product unit 333 becomes a high level signal, and when the measured time has elapsed a predetermined time T0, it outputs an isolated operation detection signal to the stop processing unit 34.

[0038] Other grid disturbances, such as grid disturbances, may cause the frequency f to change, resulting in a change Δf exceeding the threshold value Δf1, or the effective voltage v to change beyond a predetermined range. The logical product unit 333 generates a logical product signal between the signal input from the first determination unit 331 and the signal input from the second determination unit 332. Therefore, even if one of the signals makes an erroneous determination, the other can be correctly determined to prevent such an erroneous determination. Even if both of the signals make an erroneous determination, the time for an erroneous determination due to grid disturbances or the like is short. The predetermined time T0 is set so that changes in the frequency f and the effective voltage v due to grid disturbances or the like are not determined to be an islanding operation. In this embodiment, the predetermined time T0 is set to, for example, 0.08 seconds. The predetermined time T0 is not limited.

[0039] When the stop processing unit 34 receives the islanding operation detection signal from the determination unit 33, it performs a process of stopping the power conditioner 1. Specifically, the stop processing unit 34 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 34 outputs an open command to the interconnection breaker 4 to disconnect the power conditioner 1 from the power distribution system C.

[0040] Grid interconnection regulations stipulate that power conditioners connected to a high-voltage distribution system must be disconnected within three seconds if they enter an islanding state. New power source B2 detects islanding within 0.2 seconds of a power outage and is disconnected from distribution system C, while conventional power source B1 detects islanding within one second of a power outage and is disconnected from distribution system C. Therefore, even if the islanding detection device 3 waits for the specified time T0 to elapse after detecting a change in system frequency (change in system voltage) caused by conventional power source B1 and new power source B2 increasing the amount of reactive power injected, the islanding detection device 3 can disconnect power conditioner 1 from distribution system C within three seconds.

[0041] 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.

[0042] 2 is a flowchart for explaining the islanding operation determination process performed by the determination unit 33 of the islanding operation detection device 3. The islanding operation determination process determines whether or not an islanding operation state is occurring based on a first determination condition, a second determination condition, and a time determination. The islanding operation determination process is executed when the inverter device 2 starts a power conversion operation while the power conditioner 1 is connected to the power distribution system C.

[0043] 2(a) shows the processing performed by the first determination unit 331. First, the amount of change Δf in frequency f is calculated based on the frequency f detected by the frequency detection unit 31 (S1). Next, it is determined whether the amount of change Δf is equal to or greater than a threshold value Δf1 (S2). If the amount of change Δf is less than the threshold value Δf1 (S2: NO), the processing returns to step S1, and the processing of steps S1 and S2 is repeated. On the other hand, if the amount of change Δf is equal to or greater than the threshold value Δf1 (S2: YES), it is determined that the first determination condition is met, a first detection signal is output (S3), and the processing ends.

[0044] 2(b) shows the processing performed by the second determination unit 332. First, it is determined whether the effective voltage value v detected by the voltage detection unit 32 falls within a predetermined range (v1≦v≦v2) (S11). If it falls within the predetermined range (S11: YES), the process returns to step S11 and the determination of step S11 is repeated. On the other hand, if it does not fall within the predetermined range (S11: NO), it is determined that the second determination condition is met, a second detection signal is output (S12), and the process ends.

[0045] 2(c) shows the processing performed by the logical product unit 333 and the time determination unit 334. First, it is determined whether or not a first detection signal has been input from the first determination unit 331 to the logical product unit 333 (S21). If the first detection signal has not been input (S21: NO), the process returns to step S21, and the determination of step S21 is repeated. On the other hand, if the first detection signal has been input (S21: YES), it is determined whether or not a second detection signal has been input from the second determination unit 332 to the logical product unit 333 (S22). If the second detection signal has not been input (S22: NO), the process returns to step S21, and the determination of steps S21 and S22 is repeated. On the other hand, if the second detection signal has been input (S22: YES), it is determined that both the first determination condition and the second determination condition are met, and time measurement is started (S23).

[0046] Next, it is determined whether the measured time has reached or exceeded a predetermined time TO (S24). If the measured time has not reached or exceeded the predetermined time TO (S24: NO), it is determined whether a first detection signal has been input from the first determination unit 331 to the AND unit 333 (S25). If the first detection signal has not been input (S25: NO), the process returns to step S21, and the determination in step S21 is repeated. In this case, the measurement is terminated, and the measured time is cleared to zero. On the other hand, if the first detection signal has been input (S25: YES), it is determined whether a second detection signal has been input from the second determination unit 332 to the AND unit 333 (S26). If the second detection signal has not been input (S26: NO), the process returns to step S21, and the determination in step S21 is repeated. In this case, the measurement is terminated, and the measured time is cleared to zero. On the other hand, if the second detection signal is input (S26: YES), the process returns to step S24, and the determinations in steps S24 to S26 are repeated.

[0047] In step S24, if the measured time reaches or exceeds the predetermined time T0 (S24: YES), an islanding operation detection signal is output (S27), and the process ends.

[0048] The stop processing unit 34 performs stop processing when an islanding operation detection signal is input from the determination unit 33. In the stop processing, a gate block signal is output to the inverter device 2, and an open command is output to the interconnection breaker 4. Note that the processing shown in each flowchart in FIG. 2 is an example, and the islanding operation determination processing performed by the determination unit 33 of the islanding operation detection device 3 is not limited to the above.

[0049] 3 and 4 are time charts showing the changes in the frequency f and effective voltage v of the output voltage when the power distribution system C shown in FIG. 1 experiences a power outage and the power conditioner 1 enters an islanding operation state. In each diagram, the horizontal axis indicates the time elapsed since the occurrence of the power outage, with 0 seconds representing the time. Note that the vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification have been appropriately enlarged or reduced for ease of understanding, and the waveforms shown have also been simplified, exaggerated, or emphasized for ease of understanding.

[0050] Figure 3 shows the case where a conventional power source B1 and a new power source B2 are connected to a power distribution system C (see Figure 1). The same applies when the conventional power source B1 is not connected to the power distribution system C, and only the new power source B2 is connected. Figure 3(a) shows the change in frequency f. Figure 3(b) shows the change in the amount of change Δf in frequency f. Figure 3(c) shows the change in the effective voltage v.

[0051] When a power outage occurs, the grid frequency of the power distribution system C changes slightly. The new power source B2 detects this frequency change and injects reactive power to raise or lower the grid frequency. Figure 3(a) shows the case where the grid frequency increases. Note that Figures 4(a) and 5(a), described later, also show the case where the grid frequency increases. The new power source B2 typically detects islanding and disconnects from the power distribution system C within 0.1 to 0.2 seconds of the power outage. Therefore, reactive power is injected after the power outage occurs, and the grid frequency increases. Since the frequency f of the output voltage of the power conditioner 1 matches the grid frequency, as shown in Figure 3(a), the frequency f increases for at least 0.1 seconds after the power outage. The subsequent change in frequency f depends on the number and capacity of the conventional power sources B1 and new power sources B2 connected to the power distribution system C, as well as the number and size of the loads L. As a result of the increase in frequency f, the change in frequency f, Δf, exceeds the threshold value Δf1 immediately after the power outage, as shown in Figure 3(b). When the amount of change Δf becomes equal to or greater than the threshold value Δf1, the first determination unit 331 determines that the first determination condition is met, and outputs a first detection signal.

[0052] Furthermore, when a power outage occurs and new power source B2 injects reactive power, the effective voltage v also changes. Figure 3(c) shows a case where the effective voltage v increases. Note that Figures 4(c) and 5(c), which will be described later, also show cases where the effective voltage v increases. As shown in Figure 3(c), the effective voltage v no longer falls within a predetermined range (becomes larger than v2). When the effective voltage v no longer falls within the predetermined range, the second determination unit 332 determines that the second determination condition is met and outputs a second detection signal. When the state in which the first determination unit 331 outputs the first detection signal and the second determination unit 332 outputs the second detection signal continues for a predetermined time T0 or longer, the islanding operation detection device 3 detects islanding operation and performs processing to stop the power conditioner 1.

[0053] Figure 4 shows the case where new power source B2 is not connected to distribution system C, and only conventional power source B1 is connected. Figure 4(a) shows the change in frequency f. Figure 4(b) shows the change in the amount of change Δf in frequency f. Figure 4(c) shows the change in effective voltage v.

[0054] In the example shown in Figure 4, since the new power source B2 is not connected, when a power outage occurs, the conventional power source B1 detects changes in the grid frequency and injects reactive power to raise the grid frequency. The conventional power source B1 detects islanding within 0.5 to 1 second of the power outage and is disconnected from the power distribution system C. Therefore, as shown in Figure 4(a), the frequency f rises for at least 0.5 seconds after the power outage. The subsequent change in frequency f depends on the number and capacity of the conventional power sources B1 connected to the power distribution system C, as well as the number and size of the loads L. Due to the increase in frequency f, the change Δf in frequency f exceeds the threshold Δf1 immediately after the power outage, as shown in Figure 4(b). When the change Δf exceeds the threshold Δf1, the first determination unit 331 determines that the first determination condition is met and outputs a first detection signal.

[0055] Furthermore, when a power outage occurs and conventional power supply B1 injects reactive power, the effective voltage v also changes. As shown in FIG. 4(c), the effective voltage v no longer falls within a predetermined range (becomes larger than v2). When the effective voltage v no longer falls within the predetermined range, the second determination unit 332 determines that the second determination condition is met and outputs a second detection signal. When the state in which the first determination unit 331 outputs the first detection signal and the second determination unit 332 outputs the second detection signal continues for a predetermined time T0 or more, the islanding operation detection device 3 detects islanding operation and performs processing to stop the power conditioner 1.

[0056] As shown in Figures 3 and 4, if a new power source B2 or a conventional power source B1 is connected to the power distribution system C, the islanding detection device 3 can detect islanding within 3 seconds and disconnect the power conditioner 1 from the power distribution system C.

[0057] Figure 5 is a time chart showing the changes in the frequency f and effective voltage v of the output voltage when a system disturbance occurs, even though the distribution system C is not experiencing a power outage. Figure 5 shows the case where a conventional power source B1 and a new power source B2 are connected to the distribution system C (see Figure 1). The same applies when only the conventional power source B1 or only the new power source B2 is connected to the distribution system C. The horizontal axis indicates the elapsed time since the occurrence of the system disturbance, with 0 seconds as the time. Figure 5(a) shows the change in frequency f. Figure 5(b) shows the change in the amount of change Δf in frequency f. Figure 5(c) shows the change in effective voltage v.

[0058] When a system disturbance occurs, the system frequency of the power distribution system C also changes slightly. Conventional power source B1 and new power source B2 detect the frequency change and inject reactive power, but because there is no power outage, frequency f does not increase. Therefore, as shown by the solid line in Figure 5(a), frequency f increases slightly but then immediately decreases. As a result, as shown by the solid line in Figure 5(b), the change Δf in frequency f does not exceed the threshold Δf1. Furthermore, if frequency f changes significantly instantaneously, as shown by the dashed line in Figure 5(a), the change Δf exceeds the threshold Δf1, as shown by the dashed line in Figure 5(b), and the first determination unit 331 determines that the first determination condition is met, but this state does not last long.

[0059] Furthermore, although conventional power source B1 and new power source B2 inject reactive power, the effective voltage v does not change significantly because there is no power outage. Therefore, as shown by the solid line in FIG. 5(c), the effective voltage v does not exceed the predetermined range (does not become larger than v2). Furthermore, as shown by the dashed line in FIG. 5(c), if the effective voltage v changes significantly instantaneously and no longer falls within the predetermined range (becomes larger than v2), the second judgment unit 332 judges that the second judgment condition is met, but this state does not continue for long. As described above, since the state in which the first judgment condition and the second judgment condition are met does not continue for more than the predetermined time T0, the islanding operation detection device 3 does not detect islanding.

[0060] Next, the effects of the isolated operation detection device 3 according to this embodiment will be described.

[0061] According to this embodiment, the islanding operation detection device 3 determines that an islanding operation has occurred when the first determination unit 331 determines that the frequency f meets the first determination condition, the second determination unit 332 determines that the effective voltage v meets the second determination condition, and this state continues for a predetermined time T0 or more. The first determination condition is set as a condition under which it can be determined that an islanding operation has occurred based on a change in the system frequency in the distribution system C caused by the islanding operation detection devices of the conventional power source B1 and the new power source B2 injecting reactive power into the distribution system C. The second determination condition is set as a condition under which it can be determined that an islanding operation has occurred based on a change in the system voltage in the distribution system C caused by the islanding operation detection devices of the conventional power source B1 and the new power source B2 injecting reactive power into the distribution system C. This allows the islanding operation detection device 3 to detect islanding without injecting reactive power into the distribution system. Therefore, the islanding operation detection device 3 does not induce voltage flicker. That is, in a power distribution system C where voltage flicker is not occurring, voltage flicker will not occur even if a large number of power conditioners 1 equipped with islanding operation detection devices 3 are added. Also, even if a large number of power conditioners 1 equipped with islanding operation detection devices 3 are added to a power distribution system C where voltage flicker is occurring, the voltage flicker will not be exacerbated.

[0062] Furthermore, according to this embodiment, the first determination unit 331 determines that the first determination condition is met when the calculated change Δf is equal to or greater than the threshold Δf1. The islanding operation detection devices of the conventional power source B1 and the new power source B2 further change the grid frequency by injecting reactive power according to the frequency deviation in order to detect islanding operation. Therefore, the grid frequency increases. The threshold Δf1 is set as a value that allows for determining that the frequency f has changed due to the injection of reactive power by the islanding operation detection devices of the conventional power source B1 and the new power source B2. Therefore, if the frequency f meets the first determination condition, it can be concluded that islanding has occurred. This allows the first determination unit 331 to appropriately determine whether islanding has occurred.

[0063] Furthermore, according to this embodiment, the second determination unit 332 determines that the second determination condition is met when the effective voltage value v no longer falls within a predetermined range. The islanding operation detection devices of the conventional power source B1 and the new power source B2 inject reactive power according to the frequency deviation to detect islanding operation. Therefore, the system voltage changes significantly. The predetermined range is set as a range that does not allow the effective voltage value v, which has changed due to the injection of reactive power by the islanding operation detection devices of the conventional power source B1 and the new power source B2, to fall within. Therefore, when the effective voltage value v meets the second determination condition, it can be concluded that islanding operation has occurred. This allows the second determination unit 332 to appropriately determine whether islanding operation has occurred.

[0064] Furthermore, according to this embodiment, the islanding operation detection device 3 determines that an islanding operation state exists only when a state in which both the determination by the first determination unit 331 and the determination by the second determination unit 332 are true continues for a predetermined time T0 or more. Therefore, even if either the first determination unit 331 or the second determination unit 332 makes an erroneous determination, the islanding operation detection device 3 can prevent an erroneous determination that an islanding operation state exists. Furthermore, the predetermined time T0 is set so that changes in the frequency f and the voltage effective value v due to grid disturbances or the like are not determined to be islanding operation. Therefore, even if both the first determination unit 331 and the second determination unit 332 make erroneous determinations due to grid disturbances or the like, an erroneous determination that an islanding operation state exists can be prevented. Furthermore, by adjusting each determination condition and the predetermined time T0, the islanding operation detection device 3 can reliably detect islanding operation while speeding up detection.

[0065] In the present embodiment, the first determination unit 331 calculates the amount of change Δf in frequency f for each predetermined cycle and determines whether the amount of change Δf satisfies the first determination condition, but this is not limiting. The first determination unit 331 may calculate an index indicating a change in frequency f and set the first determination condition for the index. A possible example of the index is the integral value of the rate of change of frequency f. In addition, in the present embodiment, the second determination unit 332 determines whether the effective voltage value v satisfies the second determination condition, but this is not limiting. The second determination unit 332 may receive an index indicating the magnitude of the voltage and set the second determination condition for the index. A possible example of the index is the maximum or average voltage.

[0066] In addition, in the present embodiment, the first determination condition is described as being that the amount of change Δf in frequency f is equal to or greater than a threshold value Δf1, but the present invention is not limited to this. The first determination condition may be any condition that can be determined based on frequency f to have occurred. In addition, in the present embodiment, the second determination condition is described as being that the effective voltage v has fallen out of a predetermined range and this state has continued for at least a second predetermined time T2, but the present invention is not limited to this. The second determination condition may be any condition that can be determined based on the effective voltage v (or another index representing the magnitude of the voltage) to have occurred.

[0067] In the present embodiment, the first determination unit 331 makes a determination based on the frequency f, and the second determination unit 332 makes a determination based on the effective voltage v. However, this is not limiting. The first determination unit 331 and the second determination unit 332 may make a 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 for the determination by the first determination unit 331 and the second determination unit 332 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 first determination condition set in the first determination unit 331 and the second determination condition set in the second determination unit 332 are set appropriately depending on the detected values ​​used.

[0068] Second Embodiment Fig. 6 is a block diagram for explaining an islanding operation detection device 3a according to the second 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 islanding operation detection device 3 according to the first embodiment (see Fig. 1) are given the same reference numerals, and duplicate explanations will be omitted. The islanding operation detection device 3a according to this embodiment differs from the islanding operation detection device 3 in that the second determination unit 332 makes a determination based on the unbalance rate of the three-phase AC voltage.

[0069] The islanding operation detection device 3a includes an unbalance rate detection unit 35 instead of the voltage detection unit 32. The unbalance rate detection unit 35 detects the three-phase unbalance rate based on the three-phase voltage signals input from the voltage sensor 5. The unbalance rate is the ratio of the negative-phase voltage to the positive-phase voltage. The method for detecting the unbalance rate by the unbalance rate detection unit 35 is not limited, and any conventionally known method can be used. The unbalance rate detection unit 35 outputs the detected unbalance rate to the determination unit 33.

[0070] The second determination unit 332 according to this embodiment determines whether the unbalance ratio input from the unbalance ratio detection unit 35 matches the second determination condition. The second determination condition is set as a condition that determines that islanding operation has occurred. When islanding operation occurs, the islanding operation detection devices of the conventional power source B1 and the new power source B2 increase the reactive power they inject. This increases the unbalance ratio of the three-phase output voltage of the power conditioner 1. The second determination condition is set based on the unbalance ratio at this time.

[0071] In this embodiment, the second judgment condition is that the unbalance rate is equal to or greater than a predetermined threshold. The threshold is set to a value that allows judgment that islanding has occurred and that the unbalance rate has changed due to the injection of reactive power by the islanding operation detection devices of the conventional power source B1 and the new power source B2. Note that the threshold is not limited and can be set appropriately based on the results of experiments, simulations, on-site investigations, etc.

[0072] In this embodiment, the islanding operation detection device 3a can detect islanding without injecting reactive power into the power distribution system, and therefore does not induce voltage flicker. Furthermore, the islanding operation detection device 3a has a common configuration with the islanding operation detection device 3, and therefore achieves the same effects as the islanding operation detection device 3.

[0073] The islanding operation detection device, the islanding operation detection method, and the power conditioner equipped with the islanding operation detection device according to the present invention are not limited to the above-described embodiments. The specific configurations of the individual parts of the islanding operation detection device, the islanding operation detection method, and the power conditioner equipped with 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, 3a: islanding operation detection device, 31: frequency detection unit, 32: voltage detection unit, 331: first determination unit, 332: second determination unit, 333: logical product unit, 35: unbalance rate detection unit

Claims

1. An islanding operation detection device that detects islanding operation of a power conditioner, a first detection unit that detects a frequency of an output voltage of the power conditioner; A second detection unit that detects the magnitude of the output voltage of the power conditioner; a first determination unit that determines whether or not the frequency detected by the first detection unit matches a first determination condition that does not include a duration condition; a second determination unit that determines whether or not the magnitude of the output voltage detected by the second detection unit matches a second determination condition that does not include a duration condition; an isolated operation determination unit that determines that the power plant is in an isolated operation state when a state in which the first determination unit determines that the first determination condition is met and the second determination unit determines that the second determination condition is met continues for a predetermined time or more; Equipped with An islanding operation detection device characterized by:

2. the first determination condition is that the amount of change in the frequency is equal to or greater than a threshold value; The islanding operation detection device according to claim 1 .

3. The second determination condition is that the magnitude of the output voltage is no longer within a predetermined range. The islanding operation detection device according to claim 1 or 2.

4. An islanding operation detection device that detects islanding operation of a power conditioner, a first detection unit that detects a frequency of an output voltage of the power conditioner; a second detection unit that detects an unbalance rate of an output voltage of three phases of the power conditioner; a first determination unit that determines whether or not the frequency detected by the first detection unit matches a first determination condition that does not include a duration condition; a second determination unit that determines whether the unbalance rate detected by the second detection unit matches a second determination condition that does not include a duration condition; an isolated operation determination unit that determines that the power plant is in an isolated operation state when a state in which the first determination unit determines that the first determination condition is met and the second determination unit determines that the second determination condition is met continues for a predetermined time or more; Equipped with An islanding operation detection device characterized by:

5. An isolated operation detection device according to any one of claims 1 to 4, A power conditioner characterized by the above.

6. An islanding operation detection method for detecting islanding operation of a power conditioner, comprising: a first detection step of detecting a frequency of an output voltage of the power conditioner; a second detection step of detecting the magnitude of the output voltage of the power conditioner; a first determination step of determining whether or not the frequency detected in the first detection step matches a first determination condition that does not include a duration condition; a second determination step of determining whether or not the magnitude of the output voltage detected in the second detection step matches a second determination condition that does not include a duration condition; an isolated operation determination step of determining that the power plant is in an isolated operation state when the state in which it is determined in the first determination step that the first determination condition is met and the state in which it is determined in the second determination step that the second determination condition is met continues for a predetermined time or more; Equipped with An islanding operation detection method.

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