JP7751192B2 - Microgrid Islanding Detection System - Google Patents

Description

The present invention relates to an islanding detection system that detects islanding among multiple distributed power generation systems in a microgrid.

In recent years, as shown in Non-Patent Document 1, the construction of "regional microgrids" has been considered as one form of distributed energy system, which can grasp the power flow of lower-level systems under normal circumstances and independently supply power in the event of a large-scale power outage due to a disaster or other event.

This regional microgrid connects multiple distributed power generation systems, including high-voltage distributed power generation systems (such as AC generators and battery systems) and low-voltage distributed power generation systems (such as solar power generation systems and micro-hydropower generation systems).

According to Non-Patent Document 2, as shown in Figure 5, an islanding detection device using an interharmonic injection method is connected to a distributed power generation system that is connected to a high-voltage grid. Furthermore, the power conditioner (PCS) of a solar power generation system in a distributed power generation system that is connected to a low-voltage grid is equipped with a new active islanding detection function, and the micro-hydropower generation system is connected to the grid via a PCS equipped with a new active islanding detection function.

However, as concerns raised in Non-Patent Document 3, when multiple photovoltaic power generation systems are present, a PCS equipped with a new active islanding detection function can cause flicker within the regional microgrid during steady-state operation. Furthermore, in distributed power generation systems with low-voltage interconnection, micro-hydropower generation systems cannot be directly connected to the grid and must be connected via an expensive PCS equipped with a new active islanding detection function.

"Guide to Building Regional Microgrids," Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, April 16, 2021 "Grid Interconnection Regulations JEAC9701-2016," Japan Electric Association, 2016 "6th Grid Code Review Meeting, Document 9: Preventing Voltage Flicker," Organization for Cross-regional Coordination of Transmission Operators, Japan, June 30, 2021

The present invention was developed to solve all of the above problems at once, and its main objective is to inexpensively detect islanding of each of multiple distributed power systems while suppressing flicker within the microgrid.

In other words, the islanding operation detection system of the present invention is an islanding operation detection system that detects islanding operation of multiple distributed power generation systems in a microgrid in which multiple distributed power generation systems are connected to a distribution line, and is characterized by comprising: a common active signal injection unit that injects an active signal for detecting islanding into the distribution line; an active signal detection unit that is provided in each of the multiple distributed power generation systems and detects the active signal injected by the common active signal injection unit; and an islanding operation detection unit that detects islanding operation of each of the multiple distributed power generation systems based on the detection signal obtained by the active signal detection unit.

With this type of islanding detection system, the active signal injected by a common active signal injection unit is detected by an active signal detection unit provided in each of the multiple distributed power systems, thereby detecting islanding in each of the multiple distributed power systems. This makes it possible to suppress flicker within the microgrid caused by PCSs equipped with a new active type islanding detection function. Furthermore, because it is only necessary to provide a common active signal injection unit for the multiple distributed power systems and an active signal detection unit in each distributed power system that detects the active signal, islanding detection in each of the multiple distributed power systems can be achieved inexpensively.

In a specific embodiment, the multiple distributed power systems preferably include a high-voltage-connected distributed power system and a low-voltage-connected distributed power system. Here, a high-voltage-connected distributed power system is a power system that includes distributed power sources such as AC generators and battery systems. A low-voltage-connected distributed power system is a power system that is connected to the grid via a transformer and includes distributed power sources such as solar power generation systems and micro-hydropower generation systems.

It is desirable that the distributed power generation system interconnected with a high voltage grid has the common active signal injection unit.
With this configuration, it is sufficient to provide a conventional islanding operation detection device in a distributed power generation system that is interconnected to a high voltage grid, and the configuration of the islanding operation detection system can be simplified.

If an islanding detection device is provided in one distributed power system as described above and the active signal injection unit included in the islanding detection device is used as a common active signal injection unit, it is expected that when that one distributed power system is disconnected, it will not be possible to detect the islanding operation of the other distributed power systems.
In order to suitably solve this problem, it is desirable that the common active signal injection unit be provided in a microgrid management facility that manages the microgrid.
With this configuration, it becomes possible to detect islanding of all of the distributed power systems, regardless of whether each of the distributed power systems is in parallel or disconnected.

In order to more precisely detect islanding in each of the multiple distributed power systems, it is desirable that the common active signal injection unit injects active signals of different orders into the distribution line. For example, it is conceivable to detect islanding in a high-voltage-connected distributed power system using a first-order active signal, and, when a high-voltage-connected distributed power system is disconnected, detect islanding in a low-voltage-connected distributed power system using a second-order active signal.

This invention, configured in this way, makes it possible to inexpensively detect islanding in each of multiple distributed power systems while suppressing flicker within the microgrid.

1 is a schematic diagram showing a configuration of an islanding operation detection system according to a first embodiment of the present invention; 10 is a time chart showing the operation from the occurrence of a ground fault to the parallel-off of each power supply system. FIG. 10 is a schematic diagram showing the configuration of an islanding operation detection system according to a second embodiment. FIG. 10 is a schematic diagram showing the configuration of an islanding operation detection system according to a third embodiment. FIG. 1 is a schematic diagram showing the configuration of a conventional islanding detection system in a microgrid.

First Embodiment
An islanding operation detection system 100 according to a first embodiment of the present invention will be described below with reference to the drawings.

<Configuration of islanding operation detection system 100>
As shown in Figure 1, the islanding operation detection system 100 of the first embodiment detects islanding operation of multiple distributed power systems 10, 20 in a microgrid MG in which multiple distributed power systems 10, 20 and loads 30, 40 are connected to a distribution line L1.

The microgrid MG of this embodiment is connected to the commercial power grid 200 via a distribution (microgrid interconnection) breaker S1, and the distribution line L1 of the microgrid MG is connected to a high-voltage interconnected distributed power system 10, a low-voltage interconnected distributed power system (distributed power source group) 20, a high-voltage load 30, and a low-voltage load 40. The low-voltage load 40 is connected to the distribution line L1 via a transformer 50.

Here, the high-voltage-connected distributed power supply system 10 (hereinafter also referred to as the "high-voltage side power supply system 10") is a power supply system that includes distributed power sources such as an AC generator 11 and a storage battery system 12. The high-voltage-connected distributed power supply system 10 is also connected to the distribution line L1 via a point-of-connection circuit breaker S2. The storage battery system 12 includes a power conditioner (PCS).

The low-voltage interconnected distributed power supply system 20 (hereinafter also referred to as the "low-voltage side power supply system 20") is connected to the distribution line L1 via a transformer 60, and is a power supply system that includes distributed power sources such as a photovoltaic power generation system (PV) 21 and a micro-hydroelectric power generation system 22. The photovoltaic power generation system 21 also includes a power conditioner (PCS).

Specifically, the islanding operation detection system 100 comprises a common active signal injection unit 1 that injects an active signal into the distribution line L1 to detect islanding operation, an active signal detection unit 2 that is provided in each of the multiple distributed power systems 10, 20 and detects the active signal injected by the common active signal injection unit 1, and an islanding operation detection unit 3 that detects islanding operation in each of the multiple distributed power systems 10, 20 based on the detection signal obtained by the active signal detection unit 2.

The common active signal injection unit 1 in this embodiment is provided in the high-voltage side power supply system 10. This active signal injection unit 1 injects an active signal of an interharmonic or integer harmonic. Specifically, it injects an injection current of an injection order that is a non-integer multiple (e.g., 2.25th to 2.75th) or an integer multiple (e.g., 2nd) of the fundamental wave of the power distribution system as an active signal into the power distribution line L1.

In addition, the active signal detection unit 2 provided in each of the distributed power systems 10 and 20 detects the active signal injected by the common active signal injection unit 1, and the active signal detection unit 2 in this embodiment measures the voltage of the injection order (active signal).

The islanding detection unit 3 then uses the voltage of the injection order (active signal) measured by the active signal detection unit 2 to detect when each of the distributed power systems 10, 20 is in islanding operation. For example, the islanding detection unit 3 compares the voltage of the injection order (active signal) with a predetermined judgment value, and detects islanding operation of the distributed power systems 10, 20 if the voltage is equal to or greater than the predetermined judgment value.

In this embodiment, the islanding detection unit 3 is provided in each distributed power system. The high-voltage side power system 10 is provided with an interharmonic injection type islanding detection device 70, which constitutes the active signal injection unit 1, active signal detection unit 2, and islanding detection unit 3. In the low-voltage side power system 20, the active signal detection unit 2 and islanding detection unit 3 are provided in each of the photovoltaic power generation system 21 and the micro-hydropower generation system 22. The photovoltaic power generation system 21 incorporates the functions of the active signal detection unit 2 and the islanding detection unit 3 in its PCS. When islanding is detected by each islanding detection unit 3, the interconnection point breaker S2, etc., of the corresponding distributed power generation system 10, 20 is opened, thereby disconnecting the distributed power generation system 10, 20 individually. In the low-voltage side power system 20, each distributed power source (photovoltaic power generation system, micro-hydropower generation system) is disconnected separately.

<Operation of the islanding detection system>
Next, the operation of the islanding operation detection system 100 of the first embodiment from the occurrence of a ground fault to the parallel-off of each of the distributed power systems 10 and 20 will be described with reference to FIG.

When the grid is operating normally, the high-voltage power supply system 10 is also in operation while the low-voltage power supply system 20 is in operation. Furthermore, if the high-voltage power supply system 10 is used as the grid power supply for the microgrid MG during autonomous operation of the microgrid MG, then when the grid power supply is operating normally, the high-voltage power supply system 10 is also in operation while the low-voltage power supply system 20 is in operation.

When the microgrid MG is connected to the upper system (commercial power system) 200 and a ground fault occurs within the microgrid MG (time T1), the substation 300 on the upper system 200 side detects this and opens the distribution circuit breaker S1 within, for example, one second (time T2). As a result, the entire microgrid MG enters islanding operation.

At this time, the interharmonic (active signal) injected by the active signal injection unit 1 of the islanding detection device 70 is detected quickly (0.2 seconds or less) by voltage monitoring by the active signal detection unit 2 of the low-voltage side power supply system 20. This indirectly detects a ground fault and disconnects the low-voltage side power supply system 20 (time T3).

Meanwhile, in the high-voltage side power supply system 10, the islanding operation detection device 70 directly detects a ground fault (islanding operation), independently of the detection of a ground fault by the substation 300. As a result, the high-voltage side power supply system 10 is paralleled off (time T2'). Note that the timing for paralleling off the high-voltage side power supply system 10 is after paralleling off the low-voltage side power supply system 20.

<Effects of First Embodiment>
According to the islanding detection system 100 of the first embodiment configured as described above, the active signal injected by the common active signal injection unit 1 is detected by the active signal detection unit 2 provided in each of the plurality of distributed power systems 10, 20, thereby detecting islanding operation in each of the plurality of distributed power systems 10, 20, thereby suppressing flicker in the microgrid caused by a PCS equipped with an islanding operation detection function of the new active method. Furthermore, because a common active signal injection unit 1 is provided for the plurality of distributed power systems 10, 20 and only the active signal detection unit 2 is provided in each of the plurality of distributed power systems 10, 20 without providing active signal injection means in each of the plurality of distributed power systems 10, 20, detection of islanding operation in each of the plurality of distributed power systems 10, 20 can be achieved inexpensively.

Specifically, in the first embodiment, islanding operation of the high-voltage side power supply system 10 is detected by the islanding operation detection device 70, and islanding operation of the low-voltage side power supply system 20 is detected using an active signal injected by the islanding operation detection device 70. Therefore, there is no need to use a PCS equipped with a new active islanding operation detection function in the low-voltage side power supply system 20. As a result, it is possible to inexpensively detect islanding operation of each of the multiple distributed power supply systems 10, 20 while suppressing the occurrence of flicker within the microgrid.

Second Embodiment
Next, an islanding operation detection system 100 according to a second embodiment of the present invention will be described with reference to the drawings. Note that the following description focuses on configurations that are different from those of the first embodiment.

<Configuration of islanding operation detection system 100>
3 , in the islanding operation detection system 100 of the second embodiment, a common active signal injection unit 1 is provided in a microgrid management facility 400 that manages the microgrid MG. In addition, the microgrid management facility 400 is provided with an active signal injection command unit 4 that inputs an active signal injection command to the active signal injection unit 1.

<Operation of islanding detection system 100>
In the islanding operation detection system 100 of the second embodiment, the active signal injection unit 1 is provided separately from the distributed generation system 20 that is connected to the high voltage grid, and therefore the following control is possible.

(1) Control 1
Distributed power supply operation control that enables operation of the low-voltage side power supply system 20 even when the high-voltage side power supply system 10 is disconnected or stops operating when the system is healthy.

(2) Control 2
Parallel/isolation control of low-voltage side power supply system 20 during stand-alone operation of microgrid MG by high-voltage side power supply system 10

As an example of the use of the above control 2, in a microgrid MG that experiences a short-term power outage when transitioning from grid-connected operation to isolated operation, when the microgrid MG is started up, the active signal injection command unit 4 can stop the active signal injection unit 1, and instead of starting up the low-voltage side power supply system 20, "only start up the high-voltage side power supply system 10 to share the loads 30, 40 within the microgrid MG," as shown in steps 1 to 3 below.

Step 1
The battery system 12 of the high-voltage side power supply system 10 is started up, the interconnection point breaker S2 is turned on, and the battery system 12 shares the loads 30, 40 in the microgrid MG.

Step 2
The loads 30 and 40 in the microgrid MG are transferred from the storage battery system 12 of the high-voltage side power supply system 10 to the AC generator 11 .

Step 3
After the load sharing to the AC generator 11 of the high-voltage side power supply system 10 is completed, the active signal injection command unit 4 starts up the active signal injection unit 1 and starts up the low-voltage side power supply system 20 .

The reason why the low-voltage power supply system 20 is not started up at the same time as step 1 is that a sudden change in solar radiation, etc., could cause a sudden change in the output of the low-voltage power supply system 20, which could adversely affect the operation of step 2. The reason why the start-up of the high-voltage power supply system 10 is divided into steps 1 and 2 is to allow the storage battery system 12, which starts up quickly, to quickly supply power to the load.

<Effects of the Second Embodiment>
In addition to the effects of the first embodiment, the islanding operation detection system 100 of the second embodiment configured as described above enables distributed power source operation control that enables operation of the low-voltage side power supply system 20 even when the high-voltage side power supply system 10 is paralleled off or stops operating when the grid is healthy. Furthermore, the islanding operation detection system 100 of the second embodiment enables parallel/parallel-off control of the low-voltage side power supply system 20 when the high-voltage side power supply system 10 is operating the microgrid MG in an isolated manner.

Third Embodiment
Next, an islanding operation detection system 100 according to a third embodiment of the present invention will be described with reference to the drawings. Note that the following description will focus on configurations that are different from those of the second embodiment.

<Configuration of islanding operation detection system 100>
4 , in the islanding detection system 100 of the third embodiment, a common active signal injection unit 1 injects active signals of different orders into a distribution line L1. As in the second embodiment, this active signal injection unit 1 is provided in a microgrid management facility 400 that manages a microgrid MG. The microgrid management facility 400 also includes an active signal injection command unit 4 that inputs an active signal injection command to the active signal injection unit 1.

Specifically, the active signal injection unit 1 is configured to be able to output a first active signal (interharmonic of injection order 1) and a second active signal (interharmonic of injection order 2) of a different order from the first active signal separately to the power distribution line L1. Here, the active signal injection unit 1 has a first active signal injection unit 1a that injects the first active signal, and a second active signal injection unit 1b that injects the second active signal.

<Operation of islanding detection system 100>
The islanding operation detection system 100 of this embodiment enables more precise parallel/disconnection control of the multiple distributed power systems 10 and 20.

An example of parallel/disconnection control of the distributed power supply systems 10 and 20 is described below. Here, an example is shown in which a second active signal (interharmonic of injection order 2) is used to detect islanding of the low-voltage side power supply system 20 during isolated operation of the microgrid MG.

Depending on the microgrid MG, it may be necessary for the low-voltage side power supply system 20 to detect islanding even during autonomous operation of the microgrid MG (in this case, the high-voltage side power supply system 10 corresponds to the grid power supply). In such cases, the islanding judgment value for the low-voltage side power supply system 20 will be different between detecting islanding operation while connected to the commercial power grid 200 and detecting islanding operation during autonomous operation of the microgrid MG. If both were to be judged using the same injection order, the latter would have a higher impedance both when healthy and in islanding operation, and the voltage judgment value for the injection order component would be higher. However, if both were to be judged using the same injection order, some means would be needed to notify the low-voltage side power supply system 20 of the operating state of the microgrid MG.

Therefore, it is decided in advance that two injection orders will be used, with a first active signal of injection order 1 being used when connected to the commercial grid, and a second active signal of injection order 2 being used when the microgrid is in isolated operation. In this case, the active signal detection unit 2 of the high-voltage side power supply system 10 detects the first active signal, and the active signal detection unit 2 of the low-voltage side power supply system 20 detects the second active signal. Then, if the active signal injection command unit 4 of the microgrid management equipment 400 changes the active signal (injection order) in each case, the low-voltage side power supply system 20 can easily recognize which interconnection state it is in (compared to when one injection order is used commonly for both).

<Effects of the Third Embodiment>
According to the islanding operation detection system 100 of the third embodiment configured in this manner, in addition to the effects of the first and third embodiments, it is possible to detect islanding operation of each of the multiple distributed power systems 10, 20 in more detail.

<Other Modified Embodiments>
The present invention is not limited to the above-described embodiment.

For example, in the above embodiment, an islanding operation detection unit 3 was provided in each distributed power generation system, but a common islanding operation detection unit 3 may be provided in an external computer such as the microgrid management facility 400 to detect islanding operation of multiple distributed power generation systems 10, 20.

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the invention.

100... Islanding operation detection system MG... Microgrid L1... Distribution line 10... High-voltage interconnected distributed power system (high-voltage side power supply system)
20... Low-voltage interconnected distributed power supply system (low-voltage power supply system)
1...active signal injection unit 2...active signal detection unit 3...islanding operation detection unit 400...microgrid management equipment

Claims (2)

1. An islanding operation detection system for detecting islanding operations of a plurality of distributed power generation systems in a microgrid in which the plurality of distributed power generation systems are connected to a distribution line, the system comprising:
the plurality of distributed power supply systems include a high-voltage interconnected distributed power supply system and a low-voltage interconnected distributed power supply system,
a common active signal injection unit that injects an active signal for detecting islanding into the distribution line;
an active signal detection unit provided in each of the high-voltage-interconnected distributed power system and the low-voltage-interconnected distributed power system , the active signal detection unit detecting the active signal injected by the common active signal injection unit;
an islanding operation detection unit that is provided in each of the high-voltage-interconnected distributed power system and the low-voltage-interconnected distributed power system, and that detects islanding operation of each of the high-voltage-interconnected distributed power system and the low-voltage-interconnected distributed power system based on the detection signal obtained by the active signal detection unit ;
the high-voltage interconnected distributed power system includes the common active signal injection unit,
an islanding operation detection unit provided in the low-voltage-interconnected distributed power system detects islanding operation of the low-voltage-interconnected distributed power system using the active signal injected by the common active signal injection unit of the high-voltage-interconnected distributed power system;
The common active signal injection unit
a first active signal injection unit that injects a first active signal used when interconnected to a commercial grid;
and a second active signal injection unit that is used during islanded operation of the microgrid and that injects a second active signal that is of a different order from the first active signal . The islanding detection system according to claim 1 , wherein the common active signal injection unit is provided in a microgrid management facility that manages the microgrid.