JPH0716552U - Distributed power source isolated operation prevention device - Google Patents

Abstract

(57) [Summary] [Purpose] When the power system is cut off, the inverter output of the distributed power supply and the load are forcibly unbalanced without causing power loss due to active power. [Structure] The distributed power supply (3) of the lower system, which includes the inverter (2) that converts the direct-current power generated by the solar cell unit (1), which is a small-capacity power supply, to alternating current and controls the reactive power to a constant level is the power system of the upper system. (4), which supplies power to the load (5) selectively from the distributed power source (3) or the power system (4), the reactor (11) is connected to the inverter output circuit of the distributed power source (3). ) And its reactor (11) are interval-controlled to turn on at a predetermined timing.
-It consists of switching elements (12) to turn off, and when the power system (4) is cut off, the imbalance of the inverter output of the distributed power supply (3) and the consumption of the load (5) do not remain balanced. A series circuit (13) forcibly generating a state is connected in parallel.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an isolated operation prevention device for a distributed power supply, and more specifically, a distributed power supply of a lower system including an inverter that converts direct-current power generated by a small-capacity power supply such as photovoltaic power generation into alternating current and constantly controls its reactive power The present invention relates to an isolated operation prevention device for a distributed power source that reliably disconnects the distributed power source from the system when the power system is shut off in a system that is connected to the power system.

[0002]

[Prior art]

 In recent years, solar power generation systems have been used as clean new energy sources, and there are various forms of usage. One of them is an interconnection system in which a solar power generation system and a power system from a power company are electrically connected, and the solar power generation system receives backup power from the power system.

A specific example of this interconnection system will be described below with reference to FIG.

In the interconnected system, as shown in the figure, the lower distributed power supply (3) including the inverter (2) connected to the solar cell unit (1) which is a kind of small capacity power supply This is a system that is connected to the grid (4) and selectively supplies power from the distributed power supply (3) or the power grid (4) to the load (5) such as electrical equipment. The inverter (2) normally controls the reactive power in a constant manner, that is, Q = 0, so that all of the reactive power is supplied from the power system (4), which is the upper system, to the load (5). , For example, by a voltage type voltage control system. In such an interconnected system, the power from the power system (4) is supplied to the load (5) according to the amount that cannot be covered by the distributed power source (3). The power supply (3) shares a certain ratio with the power consumption of the load (5) at the same time.

Here, when the power system (4) is cut off for some reason and a power failure occurs, and the power system (4) that is the upper system is disconnected, the inverter (2) of the distributed power supply (3) will be described later. Reverse charge detection is performed by inverter control.

For example, when the amount of solar radiation in the solar cell unit (1) is large, the output from the solar cell unit (1) is larger than the consumption in the load (5). The phase is controlled so as to be increased. However, because the power system (4) is disconnected as described above, the phase lead of the inverter output is not absorbed, and as a result, the frequency of the inverter output rises, and reverse charging can be detected as a frequency abnormality. On the other hand, conversely to the above, when the amount of solar radiation in the solar cell unit (1) is small, the output from the solar cell unit (1) is smaller than the consumption in the load (5), so the inverter (2) Then, control is performed to delay the phase in order to reduce the inverter output. However, as in the case of the above, since the power system (4) is disconnected, the delay in the phase of the inverter output is not absorbed, and as a result, the frequency of the inverter output decreases, and reverse charging can be detected as a frequency abnormality.

The active power in the inverter control has been described above, but the reactive power is as follows. That is, as described above, the inverter (2) controls Q = 0, but nevertheless, when the power system (4) is disconnected, ineffective power flows to the load (5) and the load (5) When reactive power> 0 in), the output voltage drops due to the control in the inverter (2), and conversely, when reactive power <0 in the load (5), output voltage rises. However, reverse charging can be detected as an abnormal voltage.

As described above, due to the frequency abnormality and the voltage abnormality, the inverter output of the distributed power source (3) and the consumption amount of the load (5) are unbalanced based on the output of the solar cell unit (1). For example, it is possible to detect reverse charge, and there is no problem because the distributed power supply (3) can be disconnected from the system by turning off the disconnection switch (6) based on the detection output. However, depending on the amount of solar radiation in the solar cell unit (1), the inverter output of the distributed power source (3) and the amount of consumption by the load (5) may be in a balanced state and reverse charge detection may not be possible. In this balanced state, no current flows to the system and there is no change in state, so even if the power system (4) is disconnected during a power outage of the power system (4), the presence or absence of the disconnection cannot be determined, and the distributed power supply ( There is a high possibility that the distributed generator (3) will operate independently without being able to disconnect 3).

Therefore, in order to prevent the independent operation of the distributed power source (3), the inverter output of the distributed power source (3) and the consumption amount of the load (5) are balanced in the event of a power failure of the power system (4). It is necessary to have a device that forcibly breaks this state and imbalances it so that it does not remain. Conventionally, as an isolated operation prevention device for the distributed power source (3) that imbalances the inverter output of the distributed power source (3) and the consumption of the load (5), the output of the inverter (2) is It is known that a series circuit (9) of a resistor (7) and a switching element (8) is connected in parallel.

In this device, even if an attempt is made to balance the output of the inverter of the distributed power source (3) and the consumption of the load (5), the resistance (7) is controlled by the ON / OFF control by the switching element (8). An unbalanced state can be forcibly generated by causing a potential difference between the distributed power source (3) and the load (5) by the amount of voltage drop due to. If an imbalance occurs in this way, reverse charging can be detected by inverter control, as described above, and the presence or absence of disconnection in the power system (4) can be determined, and the solution can be determined based on the detected output. It is possible to turn off the column switch (6) and quickly disconnect the distributed power supply (3).

[0011]

[Problems to be solved by the device]

 By the way, in the past, in the event of a power failure in the power system (4), the balance output is forcibly broken so that the inverter output of the distributed power source (3) and the consumption of the load (5) do not remain in balance. The resistance (7) is used as an isolated operation prevention device for the distributed power supply (3) to be unbalanced, but in that case, there were the following problems.

That is, when the inverter output of the distributed power source (3) and the consumed amount of the load (5) are unbalanced, active power flows through the resistor (7), and the power loss is accordingly reduced. Occurs. The power loss consumed by the load (5) such as an electric device is a burden on the user of the load (5) as it is, the effective power is wasted, and the use of the resistor (7) is a preferable means for the user. Was not.

Therefore, the present invention was proposed in view of the above problems, and an object thereof is to provide an inverter output of a distributed power supply without causing power loss due to active power when the power system is cut off. It is an object of the present invention to provide an isolated operation prevention device for a distributed power source that can forcibly unbalance the load and the load.

[0014]

[Means for Solving the Problems]

 As a technical means for achieving the above-mentioned object, the present invention is an electric power system in which a subordinate distributed power source including an inverter for converting direct-current electric power generated by a small-capacity electric power source into alternating current and controlling the reactive power thereof to a higher electric power system. In this system, the reactor and its reactor are interval-controlled in the inverter output circuit of the distributed power source to turn on / off at a predetermined timing. It is characterized by connecting in parallel a series circuit that consists of switching elements that forcibly generate an unbalanced state so that the inverter output of the distributed power supply and the load do not remain balanced when the power system is cut off.

Further, it is desirable that the switching element perform interval control at a timing based on a duty ratio in which the ON time of the reactor is shorter than the OFF time.

Further, a reactive power monitoring circuit for detecting that reactive power of a predetermined level or more is generated from the inverter for a certain period of time is additionally provided between the inverter output circuit of the distributed power source and the series circuit of the reactor and the switching element. Is also possible.

[0017]

[Action]

 The distributed power supply islanding prevention device according to the present invention switches the reactor connected in parallel to the distributed power supply inverter output circuit so that the inverter output of the distributed power supply and the load do not remain balanced when the power system is cut off. By controlling the interval with an element and turning it on and off constantly at a specified timing, this state is forcibly collapsed and unbalanced so that the inverter output of the distributed power supply and the load do not remain balanced. By generating this unbalanced state, reverse charging can be detected by the inverter control, and it is possible to determine whether or not the power system is disconnected. In this case, in the reactor, only reactive power flows, so that power loss due to active power does not occur.

Further, if the reactor interval control by the switching element is performed by the timing based on the duty ratio in which the reactor ON time is shortened with respect to the OFF time, a plurality of dispersions can be performed for a single power system. Even when a power supply is installed, the probability that the ON / OFF timing of the reactor in each distributed power supply will be in the opposite phase and the inverter output of the distributed power supply and the load will eventually be balanced can be minimized. Even in this case, it is possible to ensure the forced generation of the unbalanced state.

Further, by providing a reactive power monitoring circuit between the inverter output circuit and the series circuit of the reactor and the switching element, the reactive power monitoring circuit detects the reactive power generated from the inverter when the power system is cut off. As a result, it becomes possible to detect reverse charge in a short time based on the reactor interval control by the switching element, prior to reverse charge detection based on frequency abnormality or voltage abnormality by the inverter control.

[0020]

【Example】

 An embodiment in which the islanding prevention device for a distributed power source according to the present invention is applied to an interconnection system for electrically connecting a solar power generation system and a power system from a power company will be described with reference to FIGS. 1 to 5. . It should be noted that the same or corresponding parts as those in FIG.

The feature of the present invention is that the lower distributed power source (3) including the voltage type voltage control type inverter (2) connected to the solar cell unit (1) as shown in FIG. In the interconnected system that is connected to the grid (4) and selectively supplies power from the distributed power supply (3) or the power grid (4) to the load (5) such as electrical equipment, the distributed power supply (3) The inverter output circuit consists of a reactor (11) and a switching element (12) that controls the reactor (11) by turning it on and off constantly at a specified timing. When the power system (4) is cut off, a distributed power supply is provided. This is because the inverter output of (3) and the load (5) are connected in parallel so that the unbalanced state is forcibly generated so that the load (5) does not remain balanced. In the figure, (14) is a disconnect switch that is turned off by detection output based on reverse charge detection by the inverter (2) or reactive power detection by a reactive power monitoring device described later.

The embodiment shown in FIG. 1 is a case where one distributed power source (3) is connected to a single power system (4), and as shown in FIG. 2, the reactor (11) is interval-controlled. The duty ratio is set so that the ON time and OFF time of the switching element (12) are the same.

In this embodiment, the switching element (12) is so arranged that the inverter output of the distributed power source (3) and the consumption of the load (5) do not remain in balance during a power failure of the power system (4). By controlling the reactor (11) at intervals by turning it on and off, a voltage difference is generated between the inverter (2) of the distributed power supply (3) and the load (5). That is, if the switching element (12) is in a balanced state when it is turned on, it is in an unbalanced state when it is turned off, and conversely, if it is in a balanced state when it is turned off, it is unbalanced when it is turned on. By generating this unbalanced state, it is possible to detect the reverse charge by controlling the inverter, and it is possible to determine whether or not the power system (4) is disconnected, and based on the detection output from the inverter (2) for detecting the reverse charge. Then, by turning off the disconnection switch (14), the distributed power supply (3) is quickly disconnected from the system. In this case, in the reactor (11), only reactive power flows, so that power loss due to active power does not occur.

Here, when one distributed power source (3) is connected to a single power system (4) as in the embodiment of FIG. 1, the ON time of the switching element (12) is increased. An unbalanced state can be generated with certainty by using a duty ratio in which the OFF time and the OFF time are the same. However, as shown in FIG. 3, a plurality of distributed power sources (3) [see (a ₁ ) (a ₂ ) ... (a _n )] are connected to a single power system (4). In this case, the ON / OFF timing of the switching element (12) may be 180 ° out of phase in the interval control of the reactor (11) in each distributed power supply (3), and in that case, the distributed power supply ( There is a possibility that the inverter output of 3) and the consumption of the load (5) will eventually be balanced, and the distributed power supply (3) may operate independently.

Therefore, as a means for solving this problem, in the embodiment shown in FIG. 3, the duty ratio of the switching element (12) of each reactor (11) is made different from that in the embodiment shown in FIG. . That is, as shown in FIG. 4, the ON time of the switching element (12) is set shorter than the OFF time. This allows multiple distributed power sources (3) to have the probability that the ON / OFF timing of the switching element (12) will be 180 ° different and opposite phase in the interval control of the reactor (11) in each distributed power source (3). It can be made as small as possible [see (a ₁ ) (a ₂ ) ... (a _n ) in the figure], and the inverter output of the distributed power supply (3) and the consumption of the load (5) eventually balance. To prevent this from happening and to ensure the forced generation of that unbalanced state.

The shorter the ON time of the switching element (12) with respect to the OFF time, the smaller the probability that the ON / OFF timing of the switching element (12) will be in the opposite phase. It is preferable to generate an imbalanced state between the inverter output of 1) and the consumption of the load (5) because it can be more sufficiently ensured.

Further, in the above-described two embodiments, the reverse charge detection is performed by the function of the inverter (2) itself, that is, the voltage abnormality based on the inverter control, and the presence or absence of the disconnection of the power system (4) is determined. However, since reactive power flows through the reactor (11) in an unbalanced state generated by the reactor (11) and the switching element (12), by detecting this reactive power, the power system (4) is disconnected. It is also possible to determine the presence or absence of.

Therefore, in the embodiment shown in FIG. 5, between the inverter output circuit of each distributed power source (3) shown in FIG. 3 and the series circuit (13) of the reactor (11) and the switching element (12), Attach a reactive power monitoring circuit (15) that detects when reactive power of a predetermined level or higher is generated from the inverter (2) for a certain period of time. The reactive power monitoring circuit (15) is detected by, for example, a series connected current transformer (16) and a parallel connected transformer (17), and the current transformer (16) and the transformer (17). It consists of a detection circuit (18) that detects the phase difference between current and voltage. The reactive power monitoring circuit (15) may have a circuit configuration that detects a potential difference in addition to the phase difference.

In this embodiment, as described above, at the time of power failure of the power system (4), the inverter output of the distributed power source (3) and the load () are controlled by the interval control of the reactor (11) by the switching element (12). 5) is forcibly unbalanced with the consumption amount, but here, before the reverse charge detection is performed by the voltage abnormality based on the inverter control by the generation of this unbalanced state, the reactive power monitoring circuit (15) Operate. That is, normally, since the inverter (2) controls Q = 0, there is no phase difference between current and voltage, but when reactive power flows through the reactor (11) due to the generation of the unbalanced state, the phase difference is generated. Occurs. Therefore, in the reactive power monitoring circuit (15), the phase difference is detected by the detection circuit (18) via the current transformer (16) and the transformer (17), so that the reactive power of a predetermined level or more is generated. The occurrence of a certain period of time is detected, the presence or absence of disconnection of the power system (4) is determined, the disconnection switch (14) is turned off based on the detection output, and the distributed power supply (3) is promptly removed from the grid. Disconnect.

With this configuration, it is possible to determine whether or not the power system (4) is disconnected in a short time before the reverse charge detection is performed due to the voltage abnormality based on the inverter control, and the reactor (11) It is preferable because the reactive power flowing through the can be minimized.

In the above embodiment, the case where the reverse charge detection is performed by the voltage abnormality based on the inverter control by the voltage type voltage control method has been described, but the present invention is not limited to this, and the voltage type current control is performed. It is also possible to detect reverse charge by frequency abnormality based on inverter control by the method.

[0032]

[Effect of device]

 According to the present invention, even when the inverter output of the distributed power source and the load are balanced when the power system is cut off, the balance state is forcibly broken and unbalanced by the reactor and the switching element. This makes it possible to detect reverse charging by controlling the inverter, determine whether or not the power system is disconnected, and quickly and reliably prevent the isolated operation of the distributed power sources. Only electric power flows, and there is no power loss due to active power.

Further, in the reactor interval control by the switching element, if the ON time is shorter than the OFF time and the timing is based on the duty ratio, when a plurality of distributed power supplies are installed in a single power system. However, the probability that the distributed power output and the load will eventually be balanced can be minimized, and the generation of the unbalanced state can be ensured. It can be prevented quickly and reliably.

Further, if a reactive power monitoring circuit is additionally provided, reverse charge detection can be performed in a short time and quick response can be made, and reactive power can be reduced as much as possible, as compared with the case of frequency abnormality or voltage abnormality by inverter control. It is possible to prevent the isolated operation of the distributed power generation, which can be performed more quickly.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an isolated operation prevention device for a distributed power source according to the present invention.

FIG. 2 is a timing chart showing ON / OFF states of the switching element of FIG.

FIG. 3 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 4 is a timing chart showing ON / OFF states of the switching element of FIG.

5 is a schematic configuration diagram showing a modified example of FIG.

FIG. 6 is a schematic configuration diagram showing a conventional example of an isolated operation prevention device for a distributed power source.

[Explanation of symbols]

 1 Small-capacity power supply (solar cell unit) 2 Inverter 3 Distributed power supply 4 Power system 5 Load 11 Reactor 12 Switching element 13 Series circuit 15 Reactive power monitoring circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H02M 7/48 M 9181-5H

Claims (3)

[Scope of utility model registration request] 1. A distributed power supply of a lower system including an inverter for converting generated DC power of a small-capacity power supply to AC and controlling the reactive power thereof at a constant level is connected to a power system of an upper system, and from the distributed power supply or the power system. In the one that selectively supplies power to the load, the inverter output circuit of the distributed power supply includes a reactor and a switching element that performs interval control of the reactor to turn ON / OFF at a predetermined timing, and when the power system is cut off, An isolated operation prevention device for a distributed power supply, comprising a parallel connection of a series circuit for forcibly generating an unbalanced state so that the inverter output of the distributed power supply and the load do not remain balanced. 2. The isolated operation prevention apparatus for a distributed power source according to claim 1, wherein the switching element performs interval control at a timing based on a duty ratio in which the ON time of the reactor is shorter than the OFF time. 3. A reactive power monitoring circuit is provided between the inverter output circuit of the distributed power source and the series circuit of the reactor and the switching element to detect that reactive power of a predetermined level or higher is generated from the inverter for a certain period of time. The isolated operation preventing device for a distributed power source according to claim 2.