JPH0884436A - Independent operation detection device for grid-connected inverter - Google Patents

Abstract

(57) [Summary] [Purpose] To provide an islanding operation detection device that detects when an inverter for grid interconnection of a distributed power source that is interconnected to an electricity system is disconnected from the electricity system and becomes an islanding operation. [Structure] The islanding detection device 10 includes a frequency detection circuit 1
1. A fluctuation signal generator 21, a frequency rise monitor circuit 22, a frequency fall monitor circuit 23, an inverting circuit 24, a frequency upper limit monitor circuit 25, a frequency lower limit monitor circuit 26, and an isolated operation signal generator circuit 27. Is monitored through the frequency detection circuit 11, and when the frequency rise monitor circuit 22 or the frequency fall monitor circuit 23 operates, the waveform of the output of the fluctuation signal generator 21 is inverted by 180 ° by the inversion circuit 24, By operating the frequency upper limit monitoring circuit 25 or the frequency lower limit monitoring circuit 26 in this state, the islanding operation signal generating circuit 27 outputs an islanding operation signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system in which a distributed power source is connected to a power system, and a distributed power source, for example, a grid interconnection inverter used in a fuel cell power generation system, a solar power generation system, or the like. The present invention relates to an isolated operation detection device for an inverter for grid interconnection, which detects that the system is disconnected from the power system during interconnection and the operation is independent.

[0002]

2. Description of the Related Art In a fuel cell power generation system, a solar power generation system or the like as a distributed power source, interconnection operation with a power system is performed for the purpose of supplying stable power to a load. In particular, in recent years, interconnection operation in the state of supplying power from a distributed power source to the commercial power system (hereinafter also referred to as reverse power flow) has been recognized, so isolated operation that occurs due to system loss such as interruption of the commercial power system (Islanding
ing)) phenomenon must be detected.

In the islanding phenomenon, when the system power is lost due to interruption of the commercial power system or the like, if the load and the power generation amount of the distributed power sources are balanced, the loss of the system power is detected on the distributed power source side. It is difficult to do so, and if this power system is recharged in this state from the commercial power system again, a short circuit condition may occur in the power system.Therefore, this islanding phenomenon can be reliably detected. There has been a demand for the above-mentioned methods of active landing detection (actively giving disturbance to the power system) as shown in the following.

.. A periodic minute fluctuation is generated in the reactive power of the distributed power source, and a fluctuation in the system frequency (50/60 Hz) is detected when the islanding phenomenon occurs. ． The active power of the distributed generator is periodically changed to detect the fluctuation of the system voltage and frequency when the islanding phenomenon occurs. ． An offset is applied to the internal oscillator that determines the output frequency of the grid-connected inverter of the distributed power supply, and the frequency change that appears in the power system when the islanding phenomenon occurs is detected.

.. Impedance is instantaneously and periodically inserted in parallel with the distributed power supply, and a sudden change in voltage or current at the impedance insertion end is detected. Among these methods, in the fuel cell power generation system, the solar power generation system, etc., without changing the active power,
Therefore, the above-mentioned method has been conventionally used in which there is no fluctuation in the DC output power of the battery (cell).

[0006]

The above-mentioned method of detecting the islanding phenomenon varies the reactive power from the distributed power source to the power system, and therefore the voltage variation of the power system may be affected depending on the variation value of the reactive power. This fluctuation value must be made as small as possible, so the frequency fluctuation when the islanding phenomenon occurs is also small, and the islanding detection device may malfunction due to the influence of noise such as simple system disturbance. I was afraid to do it.

In order to solve the above problem, conventionally, as shown in FIG. 7, the value of the fluctuation of the reactive power which is constantly injected into the power system is suppressed to several percent or less of the rated power of the distributed power source, and The detection level of the frequency monitoring circuit for detecting the islanding phenomenon is set to two levels, upper and lower, respectively, and the value of the reactive power fluctuation is increased for a minute time after the detection of the minute frequency displacement in the first step. A detection method has been proposed in which it is determined that the vehicle is in an isolated operation due to the operation of the frequency displacement detection, and the influence of noise or the like is avoided.

However, in the case where the grid interconnection inverter is used as a distributed power source for grid interconnection operation in reverse power flow to the commercial power grid, if the reactive power fluctuation is suddenly increased when the islanding phenomenon occurs, the grid interconnection will occur. Since the system inverter does not have a large control delay due to the inertia of the rotating body unlike the distributed power source using the synchronous generator, for example, depending on the timing of the frequency displacement and the increase in the variation of the reactive power, the timing shown in FIG. As described above, the frequency fluctuation may be temporarily suppressed, and in such a case, there is a problem that the time for detecting the landing of land becomes long.

An object of the present invention is to provide an islanding operation detecting device for a grid interconnection inverter which solves the above problems.

[0010]

Means for Solving the Problems In an islanding operation detecting device for detecting that an inverter for grid interconnection of a distributed power source is disconnected during grid interconnection between a power system and a distributed power source to operate independently, A fluctuation signal generator that gives a periodic minute fluctuation to the reactive power setting device of the interconnection inverter, a frequency detection circuit that detects the frequency of the grid interconnection point or the output of the grid interconnection inverter, and the output of the frequency detection circuit In the first aspect of the present invention, the frequency rise monitor circuit and the frequency fall monitor circuit for monitoring minute fluctuations in the output of the fluctuation signal generator are operated when either the frequency rise monitor circuit or the frequency decrease monitor circuit operates. An inverting circuit that inverts the phase of the waveform for a predetermined minute time, and an inversion circuit and the fluctuation signal generator that constantly give a minute change to the reactive power at the receiving point, and the output of the frequency detecting circuit. A frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit that monitor the deviation from a fixed reference frequency, and an isolated operation signal generation that generates an isolated operation signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. In the second invention, the phase of the output waveform of the fluctuation signal generator is inverted and amplified for a predetermined minute time when either the frequency rise monitor circuit or the frequency fall monitor circuit operates. Frequency upper limit monitoring that constantly gives a minute change to the reactive power at the receiving point by the inverting amplification circuit that performs the above-mentioned inverting amplification circuit and the fluctuation signal generator, and monitors the deviation between the output of the frequency detection circuit and a predetermined reference frequency. A circuit and a frequency lower limit monitoring circuit, and a single operation signal that is generated when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. In the third invention, the phase of the output waveform of the fluctuation signal generator is set for a predetermined minute time when either the frequency rise monitor circuit or the frequency fall monitor circuit operates. An inverting holding circuit for holding the inverted peak value of the output waveform, and the inverting holding circuit and the fluctuation signal generator always give a minute change to the reactive power at the receiving point, and the output of the frequency detection circuit and a predetermined value are given. A frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit that monitor a deviation from a reference frequency, and an isolated operation signal generation circuit that generates an isolated operation signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. Further, in the fourth invention, when either the frequency rising monitor circuit or the frequency falling monitor circuit operates, the position of the output waveform of the fluctuation signal generator is increased. An inverting amplification holding circuit that holds the phase at the peak value of the output waveform obtained by inverting and amplifying the phase for a predetermined minute time, and the inverting amplification holding circuit and the fluctuation signal generator always give a minute change to the reactive power of the receiving point. An independent operation when the frequency upper limit monitoring circuit and the frequency lower limit monitoring circuit that monitor the deviation between the output of the frequency detection circuit and a predetermined reference frequency, and either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operate. An independent operation signal generation circuit for generating a signal.

[0011]

According to the isolated operation detecting device for the grid interconnection inverter of the present invention, the reactive power setter of the grid interconnection inverter during grid interconnection is subjected to periodic minute fluctuations to generate the reactive power at the grid interconnection point. Is periodically changed to actively break the balance state described above, the frequency of this grid connection point or the grid connection inverter is monitored, and if a minute change in this frequency is detected, the cycle The phase of the waveform of the minute fluctuation is set to 18
By performing 0 ° inversion, inversion amplification, inversion hold, or inversion amplification hold, more reliable and rapid detection of islanding can be performed.

[0012]

1 is a circuit diagram showing a first embodiment of an islanding operation detecting device for an inverter for grid interconnection according to the present invention. In FIG. 1, a fuel cell power generation system 1 is composed of a fuel cell main body 2, a grid interconnection inverter 3, and a distribution transformer 4, 5 is a load, and 6 is an electric power system.

Reference numeral 7 is a load distribution circuit breaker, 8 is a distributed power source side circuit breaker of the fuel cell power generation system 1 as a distributed power source, and 9 is a power receiving point circuit breaker for receiving power from the power system 6. . Further, the islanding operation detection device 10 is composed of a frequency detection circuit 11 including a frequency / voltage converter and the like, and an islanding operation detection unit 20.
Is, for example, a fluctuation signal generator 21 that generates a periodic minute sinusoidal minute signal, a comparator that monitors minute fluctuations in the output value of the frequency detection circuit 11, and a frequency rise monitoring circuit 22 and a frequency fall monitoring that include a setter. When the circuit 23 and either the frequency rise monitoring circuit 22 or the frequency fall monitoring circuit 23 are operated, the phase of the output waveform of the fluctuation signal generator 21 is connected to the output of the fluctuation signal generator 21 for a predetermined minute time. An inversion circuit 24 including an inversion OR gate, a NOR gate, a three-state buffer, and a three-state inverter
, The inverting circuit 24 and the fluctuation signal generator 21 give a periodic minute fluctuation to the setting value of the reactive power setting device (not shown) of the grid interconnection inverter 3, and the reactive power at the power receiving point A (see FIG. 1) is always small. The frequency upper limit monitoring circuit 25 and the frequency lower limit monitoring circuit 26, which are composed of a comparator and a setter that monitor the deviation between the output of the frequency detection circuit 11 and a predetermined reference frequency. It is composed of an isolated operation signal generation circuit 27 including an OR gate that generates an isolated operation signal when any one of the monitoring circuits 26 operates.

The operation of the islanding operation detecting apparatus 10 shown in FIG. 1 will be described below with reference to the operation waveform diagram shown in FIG. In FIG. 2, at a time t ₀ shown in FIG. 2B, in a state where the amount of power generation supplied from the grid interconnection inverter 3 of the fuel cell power generation system 1 and the amount of power consumed by the load 5 are balanced. When the electric power system 6 is disconnected by the receiving point breaker 9 due to an accident on the electric power system 6 side, an islanding phenomenon occurs between the fuel cell power generation system 1 and the load 5. In such a state, the fluctuation signal generator 21 and the inverting circuit 2
4 and to have a presence reactive power fluctuations by, shown in FIG. 2 (B), the frequency variation such as between time t ₀ ~t ₁ is generated, the frequency falling monitoring circuit 23 operates at time t _1, The phase of the reactive power fluctuation at the power receiving point A is inverted by 180 ° by the inverting circuit 24 (see FIG. 2A). Frequency variation at this time is shown in FIG. 2 (B), to expand as time t ₁ ~t _2, shown in FIG. 2 (B), lower frequency limit monitoring circuit 26 operates at time t _2, the islanding The signal generation circuit 27 detects the islanding phenomenon (see FIG. 2).
(See (C)).

FIG. 3 is a circuit configuration diagram showing a second embodiment of an isolated operation apparatus for a grid interconnection inverter according to the present invention, and a description of members having the same configuration as in FIG. 1 will be omitted. That is, in FIG. 3, the islanding operation detection device 30 is
It is composed of a frequency detection circuit 11 and an isolated operation detection unit 31, and this isolated operation detection unit 31 is a fluctuation signal generator 21.
And a frequency rise monitor circuit 22 and a frequency fall monitor circuit 23 that monitor minute fluctuations in the output value of the frequency detection circuit 11.
And when either the frequency rise monitor circuit 22 or the frequency fall monitor circuit 23 operates, the fluctuation signal generator 21
Gate connected to the output of the variable signal generator 21 for inverting and amplifying the phase of the output waveform of the fluctuation signal generator 21 for a predetermined minute time, NOR
Gate, 3-state buffer, 3-state inverter,
An inverting amplifier circuit 32 including an amplifier, and an inverting amplifier circuit 32
And the fluctuation signal generator 21 constantly give a minute change to the reactive power at the power receiving point A (see FIG. 3) via the grid interconnection inverter 3, and the deviation between the output of the frequency detection circuit 11 and a predetermined reference frequency. Frequency upper limit monitoring circuit 25 and frequency lower limit monitoring circuit 26 for monitoring, and an isolated operation signal generation circuit 27 that generates an isolated operation signal when either the frequency upper limit monitoring circuit 25 or the frequency lower limit monitoring circuit 26 operates.
It consists of and.

The operation of the islanding operation detecting device 30 shown in FIG. 3 will be described below with reference to the operation waveform chart shown in FIG. In FIG. 4, at a time t ₀ shown in FIG. 4B, in a state where the amount of power generation supplied from the grid interconnection inverter 3 of the fuel cell power generation system 1 and the amount of power consumed by the load 5 are balanced. Then, when the power system 6 is disconnected by the power receiving point breaker 9, an islanding phenomenon occurs between the fuel cell power generation system 1 and the load 5. In such a state, if the fluctuation of the reactive power is given by the fluctuation signal generator 21 and the inverting amplifier circuit 32, the frequency fluctuation such as between time t _{0 and} t ₁ shown in FIG. 4B occurs. Then, at time t ₁ , the frequency drop monitoring circuit 23 operates, and the phase of the reactive power fluctuation at the power receiving point A is inverted and amplified by 180 ° by the inverting amplifier circuit 32 (see FIG. 4A). At this time, the frequency fluctuation is
Since the time is expanded from time t _{1 to} t ₂ shown in (B),
The frequency lower limit monitoring circuit 26 operates at time t ₂ shown in FIG. 4B, and the islanding phenomenon is promptly detected by the islanding signal generation circuit 27 (see FIG. 4C).

FIG. 5 is a circuit configuration diagram showing a third embodiment of an independent operation apparatus for a grid interconnection inverter according to the present invention, and a description of members having the same configuration as in FIG. 1 will be omitted. That is, in FIG. 5, the islanding operation detection device 40 is
It is composed of a frequency detection circuit 11 and an isolated operation detection unit 41. The isolated operation detection unit 41 is a fluctuation signal generator 21.
And a frequency rise monitor circuit 22 and a frequency fall monitor circuit 23 that monitor minute fluctuations in the output value of the frequency detection circuit 11.
And when either the frequency rise monitor circuit 22 or the frequency fall monitor circuit 23 operates, the fluctuation signal generator 21
, NOR connected to the output of the variable signal generator 21 for inverting and holding the phase of the output waveform of the fluctuation signal generator 21 for a predetermined minute time.
Gate, 3-state buffer, 3-state inverter,
The inverting and holding circuit 42 composed of a peak hold circuit, and the inverting and holding circuit 42 and the fluctuation signal generator 21 always give a minute change to the reactive power at the power receiving point A (see FIG. 5) via the grid interconnection inverter 3. , When the frequency upper limit monitoring circuit 25 and the frequency lower limit monitoring circuit 26 for monitoring the deviation between the output of the frequency detection circuit 11 and a predetermined reference frequency, and the frequency upper limit monitoring circuit 25 or the frequency lower limit monitoring circuit 26 operate. , An isolated operation signal generating circuit 27 for generating an isolated operation signal.

The operation of the islanding operation detecting device 40 of FIG. 5 will be described below with reference to the operation waveform diagram shown in FIG. In FIG. 6, at a time t ₀ shown in FIG. 6B, in a state where the amount of power generation supplied from the grid interconnection inverter 3 of the fuel cell power generation system 1 and the amount of power consumed by the load 5 are balanced. Then, when the power system 6 is disconnected by the power receiving point breaker 9, an islanding phenomenon occurs between the fuel cell power generation system 1 and the load 5. In such a state, if the fluctuation of the reactive power is given by the fluctuation signal generator 21 and the inverting holding circuit 42, the frequency fluctuation such as the time t _{0 to} t ₁ shown in FIG. 6B occurs. Then, at time t ₁ , the frequency drop monitoring circuit 23 operates, and the inverting holding circuit 42 inverts and holds the phase of the reactive power fluctuation at the power receiving point A by 180 ° (see FIG. 6A). At this time, the frequency fluctuation is as shown in FIG.
Since the time is expanded from time t _{1 to} t ₂ shown in (B),
The frequency lower limit monitoring circuit 26 operates at time t ₂ shown in FIG. 6B, and the islanding phenomenon is promptly detected by the islanding signal generation circuit 27 (see FIG. 6C).

In the description of the embodiment of the present invention shown in FIGS. 1 to 6, the case where the frequency drop monitor circuit 23 and the frequency lower limit monitor circuit 26 operate has been described, but the frequency rise monitor circuit 22 and the frequency drop monitor are described. One of the circuits 23 operates to operate the frequency upper limit monitoring circuit 25 and the frequency lower limit monitoring circuit 26.
If any of the above is activated, the islanding operation signal generation circuit 27 can detect the islanding operation.

[0020]

According to the isolated operation detecting apparatus of the present invention,
The reactive power at the grid interconnection point is periodically changed to actively break the balance state, and the frequency of this grid interconnection point or the grid interconnection inverter is monitored, and a minute change in this frequency is detected. If so, the phase of the waveform of the fluctuation signal is 180 °
By performing the inversion, the inversion amplification, the inversion holding, or the inversion amplification holding, the isolated operation can be detected more reliably and quickly.

Moreover, the present invention can be realized by adding a simple circuit as described in the embodiment, and the reliability and the economical effect can be brought about to the distributed power source.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of an islanding operation detection device according to a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram for explaining the operation of FIG.

FIG. 3 is a circuit configuration diagram of an islanding operation detecting device according to a second embodiment of the present invention.

FIG. 4 is an operation waveform diagram illustrating the operation of FIG.

FIG. 5 is a circuit configuration diagram of an islanding operation detecting device according to a third embodiment of the present invention.

6 is an operation waveform diagram for explaining the operation of FIG.

FIG. 7 is an operation waveform diagram for explaining the operation of the conventional islanding operation detection device.

FIG. 8 is an operation waveform diagram for explaining the operation of the conventional islanding operation detection device.

[Explanation of symbols]

1 ... Fuel cell power generation system, 2 ... Fuel cell main body, 3 ... System interconnection inverter, 4 ... Distribution transformer, 5 ... Load, 6
... power system, 7 ... load distribution circuit breaker, 8 ... distributed power source side circuit breaker, 9 ... power receiving point circuit breaker, 10, 30, 40 ... islanding operation detection device, 11 ... frequency detection circuit, 20, 31, 41
... individual operation detection unit, 21 ... fluctuation signal generator, 22 ... frequency rise monitor circuit, 23 ... frequency fall monitor circuit, 24 ... inversion circuit, 25 ... frequency upper limit monitor circuit, 26 ... frequency lower limit monitor circuit, 27 ... independent operation Signal generation circuit, 32 ... Inversion amplification circuit, 42 ... Inversion holding circuit, A ... Power receiving point.

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

Claims (4)

[Claims] Claim: What is claimed is: 1. An isolated operation detection device for detecting when a distributed power source grid interconnection inverter is disconnected during grid interconnection between an electric power system and a distributed power source to detect isolated operation. A fluctuation signal generator that gives a periodic minute fluctuation to the reactive power setting device, a frequency detection circuit that detects the frequency of the output of the grid interconnection point or the inverter for grid interconnection, and a small fluctuation of the output of the frequency detection circuit When the frequency rise monitor circuit and the frequency fall monitor circuit to be monitored, and either the frequency rise monitor circuit or the frequency fall monitor circuit operate, the phase of the output waveform of the fluctuation signal generator is inverted for a predetermined minute time. The inverting circuit, the inverting circuit and the fluctuation signal generator constantly give a minute change to the reactive power at the receiving point, and monitors the deviation between the output of the frequency detecting circuit and a predetermined reference frequency. A frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit, and an islanding operation signal generating circuit that generates an islanding operation signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. An independent operation detection device for a grid-connected inverter. 2. A grid interconnection inverter in a grid operation detecting device for detecting that the grid interconnection inverter of a distributed power supply is disconnected during grid interconnection between a power system and a distributed power source to detect an islanding operation. A fluctuation signal generator that gives a periodic minute fluctuation to the reactive power setting device, a frequency detection circuit that detects the frequency of the output of the grid interconnection point or the inverter for grid interconnection, and a small fluctuation of the output of the frequency detection circuit When the frequency rise monitor circuit and the frequency fall monitor circuit to be monitored, and either the frequency rise monitor circuit or the frequency fall monitor circuit operate, the phase of the output waveform of the fluctuation signal generator is inverted for a predetermined minute time. An inverting amplifier circuit that amplifies the output voltage, and the inverting amplifier circuit and the fluctuation signal generator always give a minute change to the reactive power at the receiving point, and the output of the frequency detection circuit and a predetermined reference frequency A frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit for monitoring a deviation from the frequency deviation, and an islanding operation signal generating circuit for generating an islanding operation signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. An isolated operation detection device for a grid interconnection inverter, which is characterized in that 3. A grid interconnection inverter in a grid operation detecting device for detecting when the grid interconnection inverter of a distributed power source is disconnected during grid interconnection between a power system and a distributed power source to detect an islanding operation. A fluctuation signal generator that gives a periodic minute fluctuation to the reactive power setting device, a frequency detection circuit that detects the frequency of the output of the grid interconnection point or the inverter for grid interconnection, and a small fluctuation of the output of the frequency detection circuit The phase of the output waveform of the fluctuation signal generator is inverted for a predetermined minute time when either the frequency rise monitor circuit or the frequency fall monitor circuit to be monitored and the frequency rise monitor circuit or the frequency fall monitor circuit operate. An inverting holding circuit for holding the peak value of the output waveform, and a constant change in the reactive power of the receiving point are always given by the inverting holding circuit and the fluctuation signal generator, A frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit that monitor a deviation between a force and a predetermined reference frequency, and an islanding operation that generates an islanding operation signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. An isolated operation detection device for a grid interconnection inverter, comprising a signal generation circuit. 4. An independent operation detection device for detecting that the inverter for grid interconnection of a distributed power source is disconnected during grid interconnection between the power system and the distributed power source to be in independent operation, the inverter for grid interconnection. A fluctuation signal generator that gives a periodic minute fluctuation to the reactive power setting device, a frequency detection circuit that detects the frequency of the output of the grid interconnection point or the inverter for grid interconnection, and a small fluctuation of the output of the frequency detection circuit The frequency rising monitor circuit and the frequency falling monitor circuit to be monitored, and when either the frequency rising monitor circuit or the frequency falling monitor circuit operates, the phase of the output waveform of the fluctuation signal generator is inverted and amplified for a predetermined minute time. The inverting amplification holding circuit that holds the peak value of the output waveform, and the inverting amplification holding circuit and the fluctuation signal generator always give a minute change to the reactive power at the receiving point, Generates an islanding signal when either the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit that monitors the deviation between the output of the detection circuit and a predetermined reference frequency or the frequency upper limit monitoring circuit or the frequency lower limit monitoring circuit operates. An independent operation detection device for a grid interconnection inverter, comprising: