JP7545844B2 - Islanding operation detection device, islanding operation detection method, and power conditioner equipped with islanding operation detection device - Google Patents

Description

The present invention relates to an islanding operation detection device, an islanding operation detection method, and a power conditioner equipped with an islanding operation detection device.

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 load of the distribution system when the distribution system to which the distributed power source is connected is disconnected from the power grid. If the islanding detection device detects islanding, it will disconnect the distributed power source from the distribution system and stop 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.

In the Grid Interconnection Regulations (JEAC 9701-2016), the following active methods are permitted for detecting islanding: frequency shift, slip mode frequency shift, reactive power fluctuation, and QC mode frequency shift. These methods are called conventional active methods. In the Grid Interconnection Regulations, it is stipulated that the conventional active method of islanding detection device should disconnect the power conditioner from the distribution system within 0.5 to 1 second (when connected to a low-voltage distribution line) when a power outage occurs and the system enters an islanding state. In addition, the Grid Interconnection Regulations recognize the frequency feedback method with step injection as a method that detects the power conditioner faster than the conventional active method. This method is called the new active method. In the Grid Interconnection Regulations, it is stipulated that the new active method of islanding detection device should instantly disconnect the power conditioner from the distribution system when a power outage occurs and the system enters an islanding state, and is generally set to disconnect within 0.1 to 0.2 seconds. Each of these methods actively injects an active signal, which represents reactive power, into the power distribution system and detects islanding according to changes in the detected frequency. Therefore, when many distributed power sources are connected to a power distribution system, a large amount of reactive power is injected into the power distribution system. Furthermore, the amount of reactive power injected is increased according to the frequency deviation. Therefore, when a system disturbance occurs, each distributed power source increases the amount of reactive power injected, which can cause the system voltage to oscillate and voltage flicker to occur.

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. In addition, Patent Document 2 discloses an islanding detection device that can prevent false detection and detection delay of islanding while reducing the amount of reactive power injection by alternately injecting lagging phase reactive power and leading phase reactive power and detecting islanding based on the integrated value obtained by integrating the absolute value of the amount of change in the moving average value of the system frequency.

JP 2017-93020 A JP 2019-92328 A

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 amount of reactive power injected into the power distribution system increases. Therefore, even if such a power conditioner is connected to a power distribution system to which a large number of power conditioners equipped with islanding detection devices are already connected, it will induce the voltage flicker phenomenon.

The present invention was conceived in light of the above circumstances, and aims to provide an islanding detection device, an islanding detection method, and a power conditioner equipped with an islanding detection device that do not induce voltage flicker.

To solve the above problems, the present invention provides the following technical solutions:

The isolated operation detection device provided by the first aspect of the present invention is an isolated operation detection device that detects the isolated operation of a power conditioner, and includes a detection unit that detects electrical characteristics related to the output of the power conditioner, and a judgment unit that judges whether the detection value detected by the detection unit matches a judgment condition and judges that the power conditioner is in an isolated operation state when the detection value matches a judgment condition, and is characterized in that the judgment condition is a condition for judging a change in the electrical characteristics caused by another isolated operation detection device arranged in a power distribution system to which the power conditioner is connected injecting an active signal into the power distribution system.

The "electrical characteristics" include voltage, current, power (active power, reactive power), and frequency. They also include the voltage, current, power, and frequency of a specified harmonic component. The "detected value detected by the detection unit" includes not only the magnitude of the voltage, current, power, and frequency, but also deviation (amount of change from a reference) and rate of change. The "active signal" is a signal that the islanding detection device injects into the power distribution system when it detects islanding using an active method, and includes, for example, reactive power and active power.

In a preferred embodiment of the present invention, the determination condition is that the detection value does not fall within a predetermined range for a predetermined period of time or more.

In a preferred embodiment of the present invention, the detection unit detects the frequency of the output voltage of the power conditioner as the detection value.

In a preferred embodiment of the present invention, the detection unit further detects a second detection value different from the detection value, and the determination unit determines that the system is in an isolated operation state only when the detection value matches the determination condition and the second detection value matches the second determination condition.

The power conditioner provided by the second aspect of the present invention is equipped with the islanding detection device provided by the first aspect of the present invention.

The islanding detection method provided by the third aspect of the present invention is an islanding detection method for detecting the islanding operation of a power conditioner, and includes a detection step for detecting electrical characteristics related to the output of the power conditioner, and a determination step for determining whether the detection value detected in the detection step matches a determination condition and, if so, determining that the power conditioner is in an islanding operation state, wherein the determination condition is a condition for determining a change in the electrical characteristics caused by another islanding detection device disposed in the power distribution system to which the power conditioner is connected injecting an active signal into the power distribution system.

According to the present invention, the judgment unit judges that an islanding state exists when the detection value matches the judgment condition. The islanding detection device of the present invention detects islanding in response to changes in electrical characteristics in the distribution system caused by another islanding detection device injecting active signals such as reactive power into the distribution system, and therefore does not inject reactive power into the distribution system. Therefore, the islanding detection device of the present invention does not induce the voltage flicker phenomenon.

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

1 is a block diagram for explaining a power conditioner equipped with an isolated operation detection device according to a first embodiment, and shows the overall configuration of a power distribution system. 4 is a flowchart for explaining an islanding operation detection process performed by the islanding operation detection device. 1 is a time chart showing the change in frequency of the output voltage of a power conditioner, where (a) shows the case where a power distribution system to which a conventional power source and a new power source are connected experiences a power outage, and (b) shows the case where a power distribution system to which only a conventional power source is connected experiences a power outage. 1 is a time chart showing a change in frequency of the output voltage of a power conditioner when a grid disturbance occurs. FIG. 11 is a block diagram showing an internal configuration of an isolated operation detection device according to a second embodiment.

The following describes in detail the embodiment of the present invention with reference to the drawings.

[First embodiment]

Figure 1 is a block diagram for explaining a power conditioner equipped with an isolated operation detection device according to the first embodiment, and shows the overall configuration of a power distribution system.

The power conditioner 1 converts the 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 is 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 detection device. In this embodiment, the case where the islanding detection device of the conventional power source B1 detects islanding operation using a frequency shift method is described as an example. The detection method of the islanding 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 detection device. A load L, a conventional power source B1, and a new power source B2 are each 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 as a representative. The power 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 the power distribution system C is separated from the power system (power outage state). As a result, the power conditioner 1 connected to the power distribution system C that has been separated from the power system goes into an isolated operation state.

The DC power source 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 source A outputs the generated DC power to the power conditioner 1. Note that the DC power source A is not limited to generating DC power using a solar cell. For example, the DC power source 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 it.

The power conditioner 1 includes an inverter device 2, an islanding detection device 3, a grid-connection circuit breaker 4, and a voltage sensor 5. The power conditioner 1 is connected to the power distribution system C via the grid-connection circuit breaker 4.

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 isolated 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 the power conversion operation. The configuration of the inverter device 2 is not limited.

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 isolated 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 isolated operation state.

The voltage sensor 5 detects the output voltage of the power conditioner 1 and inputs the detected voltage signal to the isolated 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.

The islanding operation detection device 3 detects the islanding operation of the power conditioner 1. The islanding operation detection device 3 detects the islanding operation based on the voltage signal input from the voltage sensor 5, and when the islanding operation is detected, the islanding operation detection device 3 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 determination unit 32, and a stop processing unit 38.

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 the voltage signal input from the voltage sensor 5. The frequency detection unit 31 detects the frequency, for example, by 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. The frequency detection method of the frequency detection unit 31 is not limited. For example, the frequency detection unit 31 may detect the frequency using a multiplication PLL (Phase Locked Loop). The frequency detection unit 31 outputs the detected frequency f to the determination unit 32. The frequency detection unit 31 corresponds to the "detection unit" of the present invention, and the frequency f corresponds to the "detection value" of the present invention.

The judgment unit 32 makes a judgment based on the frequency f input from the frequency detection unit 31. The judgment unit 32 judges whether or not the frequency f matches a preset judgment condition. The judgment condition is set as a condition that can determine that an islanding operation has occurred. When an islanding operation occurs, the islanding detection devices of the conventional power source B1 and the new power source B2 increase the injected reactive power to change the frequency of the voltage of the power distribution system C, and detect the islanding operation when the frequency exceeds a threshold value. The judgment condition is set based on the change in frequency at this time.

In this embodiment, the judgment condition is that the state in which the frequency f does not fall within the predetermined range continues for a predetermined time T ₁ or more. The predetermined range is a range centered on the normal frequency f ₀ of the output voltage of the power conditioner 1, and is a range of f ₁ (>f ₀ ) or less and f ₁ '(<f ₀ ) or more. For example, when the frequency f ₀ is 60 Hz, f ₁ = 61 Hz and f ₁ ' = 59 Hz. Note that f ₁ and f ₁ ' are not limited. The predetermined range is set to a range in which the frequency changed due to the injection of reactive power by the islanding detection device of the conventional power source B1 and the new power source B2 does not fall within when islanding occurs. The predetermined range is appropriately set based on the results of experiments, simulations, or on-site investigations. However, the frequency f may rise and exceed the predetermined range due to system disturbances other than islanding. However, in this case, the time during which the frequency f exceeds the predetermined range is short. The predetermined time _T1 is set so that an increase in frequency f due to system disturbance or the like is not determined as islanding. In this embodiment, the predetermined time _T1 is set to, for example, 0.3 seconds in accordance with the requirement for continued operation during an accident (FRT requirement). Note that the predetermined time _T1 is not limited.

In this embodiment, the judgment unit 32 judges that the judgment condition is met when a state in which the frequency f is greater than _f1 or a state in which the frequency f is smaller than _f1 ' continues for a predetermined time _T1 or more. When the judgment unit 32 judges that the frequency f meets the judgment condition, it judges that an islanding operation state is occurring, and outputs an islanding operation detection signal, which is, for example, a high-level signal, to the stop processing unit 38. Note that the judgment condition is not limited, and may be any condition that can determine that an islanding operation has occurred.

When an isolated operation detection signal is input from the determination unit 32, the stop processing unit 38 performs a process of stopping the power conditioner 1. Specifically, the stop processing unit 38 outputs a gate block signal to the inverter device 2 to stop the power conversion operation of the inverter device 2. The stop processing unit 38 also outputs an opening command to the interconnection circuit breaker 4 to disconnect the power conditioner 1 from the power distribution system C.

The grid interconnection regulations stipulate that a power conditioner connected to a high-voltage distribution system must be disconnected within 3 seconds if it goes into an islanding state. The new power source B2 detects islanding within 0.2 seconds of a power outage and is disconnected from the distribution system C, and the conventional power source B1 detects islanding within 1 second of a power outage and is disconnected from the distribution system C. Therefore, even if the predetermined time _T1 is waited for after the conventional power source B1 and the new power source B2 capture the change in the system frequency caused by increasing the amount of reactive power injected, the islanding detection device 3 can disconnect the power conditioner 1 from the distribution system C within 3 seconds.

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

Figure 2 is a flowchart for explaining the islanding operation detection process performed by the islanding operation detection device 3. The islanding operation detection process is a process for detecting an islanding operation based on a judgment condition. The islanding operation detection 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.

First, it is determined whether the frequency f detected by the frequency detection unit 31 is within a predetermined range ( _f1 ' ≤ f ≤ _f1 ) (S1). If it is within the predetermined range (S1: YES), the process returns to step S1 and the determination in step S1 is repeated. On the other hand, if it is not within the predetermined range (S1: NO), timing is started (S2).

Next, it is determined whether the measured time is equal to or greater than a predetermined time _T1 (S3). If the measured time is not equal to or greater than the predetermined time _T1 (S3: NO), it is determined whether the frequency f is within a predetermined range ( _f1 ' ≤ f ≤ _f1 ) (S4). If the frequency f is not within the predetermined range (S4: NO), the process returns to step S3, and the determinations of steps S3 and S4 are repeated.

In step S4, if the frequency f falls within the predetermined range (S4: YES), the process returns to step S1, and the determination in step S1 is repeated. In this case, the clocking is terminated and the clocked time is cleared to zero. In addition, in step S3, if the predetermined time _T1 or more is reached (S3: YES), it is determined that the state in which the frequency f does not fall within the predetermined range has continued for the predetermined time _T1 or more, and the determination condition is met. In this case, it is determined that the system is in an isolated operation state, a stop process is performed (S5), and the first detection process is terminated. In the stop process, 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 process shown in the flowchart of FIG. 2 is just an example, and the isolated operation detection process performed by the isolated operation detection device 3 is not limited to the one described above.

Figure 3 is a time chart showing the change in frequency f of the output voltage when the power distribution system C shown in Figure 1 goes into a power outage and the power conditioner 1 goes into an isolated operation state. The horizontal axis shows the time elapsed since the power outage occurred, with 0 seconds as the time. The vertical axis shows frequency f. 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 each waveform shown has been simplified, exaggerated, or emphasized for ease of understanding.

Figure 3 (a) shows the case where a conventional power source B1 and a new power source B2 are connected to the power distribution system C (see Figure 1). Note that 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.

When a power outage occurs, the system frequency of the power distribution system C changes slightly. The new power source B2 detects the frequency change and injects reactive power to raise or lower the system frequency. FIG. 3(a) shows a case where the system frequency rises. Note that FIG. 3(b) and FIG. 4 also show a case where the system frequency rises. The new power source B2 generally detects isolated operation within 0.1 to 0.2 seconds after a power outage and is disconnected from the power distribution system C. Therefore, reactive power is injected after the power outage occurs, and the system frequency rises. Since the frequency f of the output voltage of the power conditioner 1 coincides with the system frequency, as shown in FIG. 3(a), the frequency f rises and exceeds _f1 , which is the upper limit frequency of the predetermined range, 0.1 seconds before the power outage occurs. The subsequent change in frequency f varies depending on the number and capacity of the conventional power sources B1 and the new power sources B2 connected to the power distribution system C, and the number and size of the loads L.

As shown by the solid line in Fig. 3(a) , even when the frequency f changes from increasing to decreasing, if the state in which the frequency f exceeds _f1 (a state not falling within a predetermined range) continues for a predetermined time _T1 or more, the isolated operation detection device 3 determines that the frequency f meets the judgment condition, detects an isolated operation, and disconnects the power conditioner 1 from the power distribution system C. Also, as shown by the dashed line in Fig. 3(a) , even if the frequency f further increases or is maintained without decreasing, if the state in which the frequency f exceeds _f1 continues for a predetermined time _T1 or more, the isolated operation detection device 3 determines that the frequency f meets the judgment condition, detects an isolated operation, and disconnects the power conditioner 1 from the power distribution system C.

Figure 3 (b) shows a case where new power source B2 is not connected to the power distribution system C, and only conventional power source B1 is connected.

In the case of Fig. 3(b), since the new power source B2 is not connected, when a power outage occurs, the conventional power source B1 detects the change in the system frequency and injects reactive power to raise the system 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 Fig. 3(b), during the period from the occurrence of the power outage to 1 second, the frequency f rises and exceeds _f1 , which is the upper limit frequency of the specified range. 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, and the number and size of the loads L, etc.

As shown by the solid line in Fig. 3(b) , even when the frequency f changes from increasing to decreasing, if the state in which the frequency f exceeds _f1 continues for a predetermined time _T1 or more, the isolated operation detection device 3 determines that the frequency f meets the judgment condition, detects an isolated operation, and disconnects the power conditioner 1 from the power distribution system C. Also, as shown by the dashed line in Fig. 3(b) , even if the frequency f further increases or is maintained without decreasing, if the state in which the frequency f exceeds _f1 continues for a predetermined time _T1 or more, the isolated operation detection device 3 determines that the frequency f meets the judgment condition, detects an isolated operation, and disconnects the power conditioner 1 from the power distribution system C.

As shown in Figures 3(a) and (b), if a new type 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.

Figure 4 is a time chart showing the change in frequency f of the output voltage when power distribution system C is not in a power outage state but a system disturbance occurs. The horizontal axis shows the time that has elapsed since the occurrence of the system disturbance, taken as 0 seconds. The vertical axis shows frequency f. Figure 4 shows the case where a conventional power source B1 and a new power source B2 are connected to power distribution system C (see Figure 1). The same applies when only conventional power source B1 and only new power source B2 are connected to power distribution system C.

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 since there is no power outage, the frequency f does not increase. Therefore, as shown by the solid line in Figure 4, the frequency f does not exceed _f1 . Also, as shown by the dashed line in Figure 4, even if the frequency f exceeds _f1 instantaneously, the state in which the frequency f exceeds _f1 does not continue for the predetermined time _T1 or more. Therefore, in these cases, the islanding detection device 3 does not detect an islanding operation since the judgment condition is not met.

Next, we will explain the effects of the isolated operation detection device 3 according to this embodiment.

According to this embodiment, the isolated operation detection device 3 determines that an isolated operation state exists when the determination unit 32 determines that the frequency f matches the determination condition for determining that an isolated operation has occurred. The isolated operation detection device 3 detects an isolated operation according to the change in the system frequency in the distribution system C caused by the isolated operation detection devices of the conventional power source B1 and the new power source B2 injecting reactive power into the distribution system C, and therefore does not inject reactive power into the distribution system C. Therefore, the isolated operation detection device 3 does not induce the voltage flicker phenomenon. In other words, if the distribution system C does not have a voltage flicker phenomenon, the voltage flicker phenomenon does not occur even if many power conditioners 1 equipped with the isolated operation detection device 3 are added. Furthermore, even if many power conditioners 1 equipped with the isolated operation detection device 3 are added to the distribution system C in which the voltage flicker phenomenon occurs, the voltage flicker phenomenon is not promoted.

In addition, according to this embodiment, the islanding operation detection device 3 detects islanding operation based on the frequency f of the output voltage of the power conditioner 1. In order to detect islanding operation, the islanding operation detection devices of the conventional power source B1 and the new power source B2 further change the system frequency by injecting reactive power according to the frequency deviation. Therefore, the islanding operation detection device 3 can appropriately detect islanding operation.

Furthermore, according to this embodiment, the judgment condition is that the state in which the frequency f does not fall within a predetermined range continues for a predetermined time _T1 or more. The predetermined range is set as a range in which the frequency f does not fall within the range that has been 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 when islanding occurs. Furthermore, the predetermined time _T1 is set so that an increase in frequency f due to system disturbance or the like is not judged as islanding operation. Therefore, when the frequency f matches the judgment condition, it can be concluded that islanding has occurred. This allows the judgment unit 32 of the islanding operation detection device 3 to appropriately detect islanding operation.

In the present embodiment, the isolated operation detection device 3 detects an isolated operation based on the frequency f of the output voltage of the power conditioner 1 detected by the frequency detection unit 31, but the present invention is not limited to this. The isolated operation detection device 3 may use the frequency of the output current or output power of the power conditioner 1. The isolated operation detection device 3 may detect an isolated operation based on electrical characteristics such as the voltage, current, and power (active power, reactive power) output by the power conditioner 1. The isolated operation may be detected based on the voltage, current, power, and frequency of a predetermined harmonic component such as the third, fifth, and seventh order. The detection value used by the determination unit 32 is not limited to the detection value that detects the magnitude of the voltage, current, power, and frequency, but may be a deviation (amount of change from a reference) and a rate of change. The determination condition set in the determination unit 32 is appropriately set according to the detection value used. For example, the judgment unit 32 may determine that the system is in isolated operation without waiting for the specified time _T1 to continue, based on the judgment condition that the detected value exceeds the upper or lower limit of a specified range (does not fall within the specified range).

Second Embodiment
Fig. 5 is a block diagram showing the internal configuration of the isolated operation detection device according to the second embodiment. In the figure, elements that are the same as or similar to those in the isolated operation detection device 3 according to the first embodiment (see Fig. 1) are given the same reference numerals and redundant explanations will be omitted.

The isolated operation detection device 3a according to this embodiment differs from the isolated operation detection device 3 in that the judgment unit 32 makes judgments using two types of detection values.

The isolated operation detection device 3a further includes a voltage detection unit 39. The voltage detection unit 39 detects the effective voltage value v of the output voltage of the power conditioner 1. The voltage detection unit 39 detects the effective voltage value v based on a voltage signal input from the voltage sensor 5. The voltage detection unit 39 outputs the detected effective voltage value v to the determination unit 32. In this embodiment, the voltage detection unit 39 also corresponds to the "detection unit" of the present invention, and the effective voltage value v corresponds to the "second detection value" of the present invention. The voltage detection unit 39 may detect the maximum or average voltage value, etc.

The judgment unit 32 according to the second embodiment makes a judgment based on the frequency f input from the frequency detection unit 31 and the effective voltage value v input from the voltage detection unit 39. The judgment unit 32 includes a first judgment unit 321, a second judgment unit 322, and an AND unit 323. The first judgment unit 321 is a functional block similar to the judgment unit 32 according to the first embodiment, and judges whether the frequency f input from the frequency detection unit 31 matches the judgment condition. If the first judgment unit 321 judges that the frequency f matches the judgment condition, it outputs a first detection signal, which is a high-level signal, to the AND unit 323.

The second determination unit 322 determines whether the voltage effective value v input from the voltage detection unit 39 matches the second determination condition. In this embodiment, the second determination condition is set as a condition that can determine that an islanding operation has occurred based on the voltage effective value v, and is, for example, that the state in which the voltage effective value v does not fall within the second predetermined range has continued for more than _a second predetermined time T2. The second predetermined range is a range centered on the voltage effective value _v0 of the output voltage of the power conditioner 1 during normal operation, and is a range of _v1 (> _v0 ) or less and _v1 '(< _v0 ) or more. Note that _v1 and _v1 ' are not limited. The second predetermined range is set as a range in which the voltage effective value v that 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 does not fall within when an islanding operation occurs. The second predetermined range is appropriately set based on an experiment, a simulation result, or an on-site investigation result. However, the voltage effective value v may rise and exceed the second predetermined range due to system disturbances other than the isolated operation. In this case, however, the time during which the voltage effective value v exceeds the second predetermined range is short. The second predetermined time _T2 is set so that an increase in the voltage effective value v due to system disturbances or the like is not determined as an isolated operation. In this embodiment, the second predetermined time _T2 is set to, for example, 0.3 seconds according to the operation continuation requirement during an accident (FRT requirement). Note that the second predetermined time _T2 is not limited. In this embodiment, the second determination unit 322 determines that the second determination condition is met when the state in which the voltage effective value v is greater than _v1 or the state in which the voltage effective value v is smaller than _v1 ' continues for the second predetermined time _T2 or more. When the second determination unit 322 determines that the voltage effective value v meets the second determination condition, it outputs a second detection signal, which is a high-level signal, to the AND unit 323. The second determination condition is not limited as long as it is a condition that can determine that an islanding operation has occurred.

The AND unit 323 generates a logical AND signal between the signal input from the first judgment unit 321 and the signal input from the second judgment unit 322, and outputs the logical AND signal to the stop processing unit 38. Therefore, when the AND unit 323 receives the first detection signal (high level signal) from the first judgment unit 321 and the second detection signal (high level signal) from the second judgment unit 322, it outputs the isolated operation detection signal, which is a high level signal, to the stop processing unit 38. In other words, when the judgment unit 32 according to the second embodiment judges that the frequency f matches the judgment condition and that the effective voltage value v matches the second judgment condition, it judges that the inverter is in an isolated operation state and outputs the isolated operation detection signal to the stop processing unit 38.

In this embodiment, the same effects as in the first embodiment can be achieved. Furthermore, according to this embodiment, the judgment unit 32 judges that an isolated operation state is occurring when it is determined that the frequency f matches the judgment condition and the effective voltage value v matches the second judgment condition. Therefore, the isolated operation detection device 3a can reliably detect isolated operation while speeding up detection by adjusting each judgment condition.

In addition, instead of the AND unit 323, the judgment unit 32 may be provided with an OR circuit that generates a logical sum signal of the signal input from the first judgment unit 321 and the signal input from the second judgment unit 322. In other words, the judgment unit 32 may determine that the inverter is in an isolated operation state when it is determined that the frequency f matches the judgment condition or the effective voltage value v matches the second judgment condition.

The detection values used by the determination unit 32 for the determination are not limited to a combination of frequency f and effective voltage v. The determination unit 32 may also make a determination based on three or more types of detection values. In other words, the determination unit 32 may use any number of detection values to make a determination.

The isolated operation detection device, the isolated operation detection method, and the power conditioner equipped with the isolated operation detection device according to the present invention are not limited to the above-mentioned embodiments. The specific configurations of each part of the isolated operation detection device, the isolated operation detection method, and the power conditioner equipped with the isolated operation detection device according to the present invention can be freely designed in various ways.

1: Power conditioner, 3, 3a: Isolated operation detection device, 31: Frequency detection unit, 32: Judgment unit, 39: Voltage detection unit

Claims (7)

An isolated operation detection device for detecting an isolated operation of a power conditioner,
A detection unit that detects electrical characteristics related to an output of the power conditioner;
a determination unit that determines whether or not the detection value detected by the detection unit matches a determination condition, and when the detection value matches, determines that the power conditioner is in an isolated operation state and stops the power conditioner ;
Equipped with
the determination condition is a condition for determining a change in the electrical characteristic caused by an active signal being injected into the power distribution system by another islanding operation detection device disposed in the power distribution system to which the power conditioner is connected,
An islanding detection device characterized by: does not have the capability of injecting an active signal into the distribution system;
The islanding detection device according to claim 1 . The determination condition is that the detected value is out of a predetermined range for a predetermined period of time or more.
3. The isolated operation detection device according to claim 1 or 2 . The detection unit detects a frequency of an output voltage of the power conditioner as the detection value.
4. An isolated operation detection device according to claim 1. The detection unit further detects a second detection value different from the detection value,
the determination unit determines that the power generating device is in an isolated operation state only when the detection value matches the determination condition and the second detection value matches a second determination condition.
5. An isolated operation detection device according to claim 1 . The isolated operation detection device according to any one of claims 1 to 5 is provided.
The power conditioner is characterized by the above. An islanding operation detection method for detecting an islanding operation of a power conditioner, comprising:
A detection step of detecting an electrical characteristic related to an output of the power conditioner;
a determination step of determining whether the detection value detected in the detection step matches a determination condition, and if the detection value matches, determining that the power conditioner is in an isolated operation state and stopping the power conditioner ;
Equipped with
the determination condition is a condition for determining a change in the electrical characteristic caused by an active signal being injected into the power distribution system by another islanding operation detection device disposed in the power distribution system to which the power conditioner is connected,
2. An islanding operation detection method comprising:

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