JP3353549B2 - Islanding operation detection device of inverter for grid interconnection - Google Patents

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 supply is connected to an electric power system, wherein a distributed power supply, for example, a system interconnection inverter used in a fuel cell power generation system, a solar power generation system, or the like is provided. The present invention relates to an islanding operation detection device of a system interconnection inverter that detects disconnection from an electric power system during an interconnection and becomes an island operation.

[0002]

2. Description of the Related Art In recent years, interconnection operation in a state in which power is supplied from a distributed power supply to a commercial power system (hereinafter also referred to as reverse power flow) has been recognized, so that a system loss such as interruption of the commercial power system has been recognized. Islanding (Islanding (Is
landing)) phenomenon needs to be detected.

[0003] The islanding phenomenon is such that when system power is lost due to interruption of a commercial power system or the like and the load and the amount of power generated by the distributed power source are balanced, the loss of the system power is detected on the distributed power source side. It is difficult to detect this islanding phenomenon reliably, because if this power system is charged again from the commercial power system in this state, a short circuit may occur in the power system. Has been requested.

[0004] In a fuel cell power generation system, a photovoltaic power generation system, or the like as a distributed power source, there is no variation in the active power of the distributed power source, and therefore, there is no variation in the output power of the battery (cell). As shown in the figure, the value of the constant reactive power fluctuation injected into the power system is suppressed to several percent or less of the rated power of the distributed power supply, and the detection level of the frequency monitoring circuit for detecting the landing phenomenon is raised and lowered by two. As a step, there is a method in which the value of the reactive power fluctuation is increased by a minute time after the detection of the minute frequency displacement in the first stage, and the operation of the frequency displacement detection in the second stage at this time determines that the isolated operation has been performed. Proposed.

[0005]

However, in a case where a grid-connected inverter is used as a decentralized power source to perform a reverse power flow connection to a commercial power system, a sudden increase in reactive power fluctuations occurs when an islanding phenomenon occurs. When performed, the grid interconnection inverter does not have a large control delay due to the inertia of the rotating body as in a distributed power supply using, for example, a synchronous generator. However, as shown in FIG. 5, there is a case where the frequency fluctuation is once suppressed, and in such a case, there is a problem that the time required for the eye landing detection becomes long.

[0006] An object of the present invention is to provide an islanding operation detection device for a system interconnection inverter that solves the above-mentioned problems.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an islanding operation detection for detecting that a grid-connected inverter of a distributed power source is disconnected and becomes an isolated operation during interconnection between a power system and a distributed power source. In the device, a fluctuation signal generation circuit for generating a periodic minute fluctuation voltage, a frequency detection circuit for detecting a frequency of an output of a grid connection point or an inverter for grid connection, and monitoring for a small fluctuation of an output of the frequency detection circuit When the frequency rise monitoring circuit and the frequency rise monitoring circuit are operated, the amplitude is larger than the amplitude of the fluctuation signal generating circuit for a predetermined minute time, and when viewed from the grid interconnection inverter. When the phase advance signal generation circuit that generates the phase advance signal and the frequency drop monitoring circuit operate, the amplitude is larger than the amplitude of the fluctuation signal generation circuit for a predetermined minute time, and A lagging signal generating circuit for generating a lagging signal when viewed from the grid interconnection inverter, and switching and outputting one of the fluctuating signal generating circuit, the advancing signal generating circuit, and the lagging signal generating circuit A switching circuit that constantly provides a minute change to the reactive power setting device of the grid interconnection inverter; a frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit that monitor a deviation between an output of the frequency detection circuit and a predetermined reference frequency; 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.

[0008]

According to the isolated operation detection device for a grid interconnection inverter of the present invention, a periodic minute change is given to the set value of the reactive power setting device of the grid interconnection inverter during the system interconnection, and the system interconnection point is changed. Of the system interconnection point or the frequency of the system interconnection inverter is monitored, and if a slight increase in this frequency is detected, the reactive power is viewed from the system interconnection inverter. When a small signal of advanced phase is generated,
If in the eye landing state, the frequency further increases,
Also, if a small drop in the monitored frequency is detected, a small signal that is late when viewed from the grid interconnection inverter is generated. The effect is to reliably and quickly detect the landing phenomenon.

[0009]

FIG. 1 is a circuit diagram showing an embodiment of an apparatus for detecting an isolated operation of an inverter for system interconnection according to the present invention. In FIG. 1, a fuel cell power generation system 1 includes a fuel cell main body 2, a system interconnection inverter 3, and a power distribution transformer 4, reference numeral 5 denotes a load, and reference numeral 6 denotes a power system.

Reference numeral 7 denotes a circuit breaker for load distribution, 8 denotes a circuit breaker on the distributed power supply side of the fuel cell power generation system 1 as a distributed power supply, and 9 denotes a power receiving point circuit breaker for receiving power from the power system 6. . Further, the islanding operation detecting device 10 includes a frequency detecting circuit 11 including a frequency / voltage converter and the like, and an islanding operation detecting section 20.
Is, for example, a fluctuation signal generation circuit 21 for generating a periodic sinusoidal minute signal, a comparator for monitoring a minute change in the output value of the frequency detection circuit 11, a frequency rise monitor circuit 22 including a setting device, and a frequency fall monitor. A circuit 23, an OR circuit 24 for detecting that either the frequency rise monitor circuit 22 or the frequency fall monitor circuit 23 has been operated, a Schmitt circuit 25 for converting the output of the fluctuation signal generation circuit 21 into a pulse waveform, Counter circuit 2 for measuring waveform
6, a negative peak hold circuit 27 serving as a leading signal generation circuit for holding a negative peak value of the output of the fluctuation signal generation circuit 21, and a positive peak value of the output of the fluctuation signal generator 21 A positive-polarity peak hold circuit 28 serving as a late-phase signal generating circuit, and switching signals of the fluctuating signal generating circuit 21, negative-polarity peak hold circuit 27, and positive-polarity peak hold circuit 28 are switched to connect the grid-connected inverter 3
A small variation in the set value of the reactive power setting device (not shown), the frequency rise monitoring circuit 22 and the frequency drop monitoring circuit 2
3, a switching circuit 29 composed of an AND / OR gate circuit, a three-state buffer, and the like for calculating the signal to be selected based on the output of each counter circuit 26; And a frequency upper limit monitor circuit 30 and a frequency lower limit monitor circuit 31 each including a comparator and a setter for monitoring a deviation between the output of the frequency detection circuit 11 and a predetermined reference frequency.
Alternatively, when any one of the frequency lower limit monitoring circuits 31 operates, it includes an isolated operation signal generation circuit 32 including an OR gate that generates an isolated operation signal.

The operation of the islanding detection apparatus 10 shown in FIG. 1 will be described below with reference to the operation waveform diagrams shown in FIGS. In FIG. 2, 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, time t ₀ shown in FIG. When the power system 6 is disconnected by the power receiving point circuit breaker 9 due to an accident on the 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 generation circuit 21 and the switching circuit 29 cause a fluctuation in the reactive power, and the fluctuation has a (+) polarity and the fuel cell power generation system with respect to the power system 6 as shown in FIG. 1 gives a slower phase reactive power fluctuation,
(-) when the fuel cell power generation system 1 to the power grid 6 in polarity and is configured to provide a more reactive power fluctuation of the phase advance is shown in FIG. 2 (B), the time t ₀ ~t ₁ between The frequency rise monitoring circuit 22 operates at time t ₁ , and the waveform of the reactive power fluctuation at the receiving point A is changed by the switching circuit 29 to the negative peak hold circuit 2.
7 is output. (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), the upper frequency limit monitoring circuit 30 operates at time t _2, the islanding Signal generation circuit 3
2 detects the landing phenomenon (see FIG. 2).
(C)).

In FIG. 3, a power generation amount and a load 5 supplied from the grid interconnection inverter 3 of the fuel cell power generation system 1 are shown.
In the state where the amount of power consumed in
When the power system 6 is disconnected by the power receiving point circuit breaker 9 due to an accident on the power system 6 side at time t ₀ shown in (B), an islanding phenomenon occurs between the fuel cell power generation system 1 and the load 5. In such a state, if the reactive power variation is given by the variation signal generating circuit 21 and the switching circuit 29 and the polarity of the reactive power variation is the same as that of FIG. 2, the times t _{0 to} t shown in FIG. A frequency fluctuation such as ₁ occurs, and the frequency drop monitoring circuit 23 operates at time t ₁ , and the waveform of the reactive power fluctuation at the power receiving point A is output from the positive peak hold circuit 28 by the switching circuit 29. (FIG. 3
(A)). Frequency variation at this time, to expand the show, as the time t ₁ ~t ₂ FIG. 3 (B), the FIG. 3 (B)
Shown in upper frequency limit monitoring circuit 31 is operated at time t _2, the eye landing phenomenon is detected by the single operation signal generation circuit 32 (see FIG. 3 (C)).

[0013]

According to the islanding detection device of the present invention,
Periodically changes the reactive power at the grid connection point, monitors the frequency of this grid connection point or the grid connection inverter, and if a small change in this frequency is detected, changes in the direction of further expansion , The islanding can be detected more reliably and quickly.

Moreover, by adding a simple circuit as described in the embodiment, the present invention can be realized, and it is possible to improve the reliability and economic effect of the distributed power supply.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an islanding operation detection apparatus showing an embodiment of the present invention.

FIG. 2 is an operation waveform diagram illustrating the operation of FIG. 1;

FIG. 3 is an operation waveform diagram illustrating the operation of FIG. 1;

FIG. 4 is an operation waveform diagram for explaining the operation of the conventional islanding detection device.

FIG. 5 is an operation waveform diagram for explaining the operation of the conventional islanding detection device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel cell power generation system, 2 ... Fuel cell main body, 3 ... Grid connection inverter, 4 ... Distribution transformer, 5 ... Load, 6
... power system, 7 ... circuit breaker for load distribution, 8 ... circuit breaker on the distributed power supply side, 9 ... circuit breaker at receiving point, 10 ... islanding detection device,
11: frequency detection circuit, 20: islanding operation detection unit, 21:
Fluctuation signal generating circuit, 22 ... frequency rise monitoring circuit, 23 ...
Frequency drop monitor circuit, 24 ... OR circuit, 25 ... Schmitt circuit, 26 ... Counter circuit, 27 ... Negative peak hold circuit, 28 ... Positive peak hold circuit, 29 ... Switching circuit, 30 ... Frequency upper limit monitor circuit, 31 ... Frequency lower limit monitoring circuit, 32: isolated operation signal generation circuit, A: power receiving point.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02J 3/00-5/00 H02H 3/46

Claims (1)

(57) [Claims] 1. An isolated operation detecting device for detecting that an inverter for system interconnection of a distributed power supply is disconnected during a connection between a power system and a distributed power supply to perform an isolated operation, comprising: , A frequency detection circuit that detects a frequency of an output of a grid connection point or a grid connection inverter, a frequency rise monitoring circuit that monitors a minute variation in an output of the frequency detection circuit, and a frequency fall A monitoring circuit for generating a signal having an amplitude larger than the amplitude of the fluctuation signal generating circuit for a predetermined short period of time when the frequency rise monitoring circuit is operated, and of generating a leading signal when viewed from the grid interconnection inverter; A phase signal generation circuit, when the frequency drop monitoring circuit operates, the amplitude of the fluctuation signal generation circuit is larger than the amplitude of the fluctuation signal generation circuit for a predetermined short time, and A delay signal generating circuit that generates a signal that is delayed when viewed, and switching and outputting any one of the fluctuation signal generating circuit, the leading signal generating circuit, and the retarding signal generating circuit. A switching circuit that constantly provides a minute change to the reactive power setting device of the inverter; a frequency upper limit monitoring circuit and a frequency lower limit monitoring circuit that monitors a deviation between an output of the frequency detection circuit and a predetermined reference frequency; An islanding operation detection device for a grid interconnection inverter, comprising: an islanding operation signal generation circuit that generates an islanding operation signal when any of the frequency lower limit monitoring circuits operates.