JPH10257678A - Isolation prevention device for inverter for grid connection - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To detect the isolated operation state of a grid interconnection inverter in a short time and prevent voltage fluctuation and power factor fluctuation at a customer service entrance. SOLUTION: The present invention relates to a system in which DC power is converted into AC power by a grid connection inverter in a power generation device and connected to a power system. A PT1 for detecting a frequency signal c of the system, a voltage / frequency converter 11, PT2, a CT for detecting a power point power value from the system, a power point power calculator 12, and an inverter 3 to the system 14 A reactive power fluctuation command b for causing periodic reactive power fluctuation is output, and a trip command a to the disconnecting breaker 6 when the isolated operation state of the inverter 3 is detected by the frequency signal c. And a reactive power fluctuation command generator 10 that outputs the reactive power fluctuation command b from the power receiving point power signal d to zero when the power generation device 1 is on the power receiving side of the system 14. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power generator which converts DC power into AC power by an inverter and connects the power system to an electric power system. More specifically, the present invention relates to an islanding prevention device for an inverter for system interconnection, which actively gives disturbance to the output of a power generator.

[0002]

2. Description of the Related Art In a power generator using an inverter that uses a fuel cell, a storage battery, or the like as a DC power supply, an interconnection operation with AC power of a power system is performed for the purpose of stable power supply. In particular, in recent years, interconnection operation in a mode of supplying generated power to the commercial power system (hereinafter referred to as reverse power flow) has been recognized, so that the islanding phenomenon that occurs due to system loss such as interruption of the commercial power system is prevented. Are determined by guidelines.

[0003] Usually, when the system voltage is lost due to a system interruption or the like, and a certain customer or load and the output of the power generator are balanced and the system does not enter a power outage state, a short circuit is generated when the power system is restored. Because of the danger of
The prevention of the above-mentioned islanding phenomenon is required, and the following active (active disturbance is given to the generated power)
An anti-landing system has already been provided.

(1) A periodic fluctuation of reactive power is generated from a power generator, and a fluctuation of a system frequency (50 or 60 Hz) is detected when an islanding occurs. (2) The power generated by the power generator is periodically changed to detect a change in system voltage or frequency at the occurrence of the landing. (3) A frequency bias is applied to an internal oscillator or the like of the inverter of the power generation device, and a frequency change appearing in the system when an islanding occurs is detected. (4) Impedance is instantaneously and periodically inserted in parallel with the power generator, and a sudden change in voltage or current fluctuation at the insertion end of the impedance is detected.

[0005] Among these methods, the method (4) requires an impedance facility in addition to the power generator, and when the power system has a high voltage or a special high voltage, the eye landing prevention device itself becomes large. The method (1) is usually used because there is a problem that the cost is high, and a method that does not involve fluctuation of the active power is convenient in a system using a fuel cell or a storage battery as a DC power supply. I have.

[0006]

The above-mentioned system (1) is based on the principle of supplying fluctuating reactive power from a power generator to a power system. For this reason, in order to increase the detection accuracy of the islanding phenomenon, it is necessary to increase the amount of change in the reactive power, and when the value of the transmission power to the power system during the reverse power flow decreases, the reactive power fluctuation from the power generator causes There is a case where a problem in power factor management arises because the voltage at the customer entrance tends to fluctuate, and the power factor at the receiving point greatly fluctuates in accordance with the reactive power fluctuation.

To avoid such a problem, FIG.
As shown in (1), the amount of constant reactive power fluctuation supplied to the power system is suppressed to a very small value, and the frequency fluctuation detection level for detecting the islanding phenomenon is set to two levels. Later, a method of rapidly increasing the reactive power fluctuation amount (reactive power command value) has been proposed. In addition,
In FIG. 4, e shows the waveform of the reactive power command value.

However, the method of FIG. 4 has a new problem that the detection time tends to be long since the detection of the frequency fluctuation is performed in two stages. Therefore, the present invention provides an islanding prevention device for a grid-connected inverter capable of detecting an islanding phenomenon with high accuracy in a relatively short time and suppressing voltage fluctuation and power factor fluctuation at a customer service entrance. What you want to do.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a power generator which operates by linking DC power to an electric power system via an inverter, wherein an islanding phenomenon is caused by an operation of a circuit breaker or a switch of the electric power system. It was made by paying attention to. That is, in the case of a power generator that is connected to the grid by an inverter, in the event of an accident such as a line short circuit in the customer premises, the inverter's semiconductor element has a small resistance to overcurrent or overvoltage, and the inverter's protection circuit operates to generate power. The circuit breaker of the device is opened, and at this time, even if a power failure occurs in the power system, the islanding phenomenon does not occur.

As described above, the present invention relates to a system for converting DC power into AC power and interconnecting the power system with a power system using a grid-connecting inverter in a power generator. In addition to the frequency signal, the receiving point power signal from the receiving point power detection means is also input to the reactive power fluctuation command generating means to be supplied, so that when the receiving point power value is on the receiving side of the power system, it is invalid. The power fluctuation command is set to zero, or more preferably, the reactive power fluctuation command is gradually reduced to a predetermined small value when the power receiving point power value falls below a predetermined value on the power transmission side with respect to the power system. It is intended to be.

According to the present invention configured as described above,
By setting the reactive power fluctuation command to zero when the power receiving point power value is on the power receiving side with respect to the power system, a large reactive power fluctuation is given during normal reverse power flow and the detection sensitivity of the landing phenomenon is secured, In addition, when there is no reverse power flow, it is possible to suppress the voltage fluctuation and the power factor fluctuation at the customer entrance which are caused by the fluctuation of the reactive power. More preferably, when the power receiving point power value falls below a predetermined value on the power transmission side with respect to the power system, the reactive power fluctuation command is narrowed down to a predetermined minute value in a stepwise manner so that there is no reverse power flow. Not only that, even when the reverse power flow is small, it is possible to suppress the voltage fluctuation and the power factor fluctuation at the customer entrance while maintaining the detection sensitivity of the islanding phenomenon.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, FIG. 1 is a single-line diagram showing the islanding prevention device of the present embodiment together with a power generator and a load connected to an electric power system. In FIG. 1, reference numeral 1 denotes a DC power from a DC power supply 2 such as a fuel cell or the like;
This is a power generator that converts the power into AC power and outputs it. Reference numeral 4 denotes an insulating transformer connected to the AC side of the inverter 3.

On the other hand, reference numeral 14 denotes a power system of an interconnection destination. Circuit breakers 6, 7, and 8, a power receiving transformer 9, and a circuit breaker are provided between the insulating transformer 4 and the high-voltage distribution line of the power system 14. The vessel 13 is connected. Here, a circuit breaker 6 is a circuit breaker for disconnecting the power generator 1, a circuit breaker 7 is a load circuit breaker such as a distribution breaker for distributing a load circuit composed of a general in-house load 5, and a circuit breaker 8
Is a secondary circuit breaker of the power receiving transformer 9, and a circuit breaker 13 is a power receiving point circuit breaker that is used for receiving power from a high-voltage distribution line, for example, when a premises accident occurs.

Next, reference numeral 20 denotes an islanding prevention device according to the present embodiment. In this islanding prevention device 20, reference numeral 11 denotes a voltage / frequency converter for converting a voltage between the circuit breakers 6 and 8 detected by the instrument transformer PT1 into a frequency, and 12 denotes an instrument transformer PT2 and a current transformer CT. This is a power receiving point power calculator that calculates a power receiving point power value from the detected voltage and current at the power receiving point. Reference numeral 10 denotes the input of the frequency signal c from the voltage / frequency converter 11 and the power receiving point power signal d from the power receiving point power calculator 12, and the disconnection circuit breaker trip command a and the reactive power fluctuation command b. It is a reactive power fluctuation command generator to output. The trip command a is applied to the disconnecting circuit breaker 6, and the reactive power fluctuation command b is applied to the inverter 3.

In the above configuration, the instrumentation transformer PT1 and the voltage / frequency converter 11 provide frequency detection means, and the instrumentation transformer PT2, the current transformer CT and the power receiving point power calculator 12 provide power receiving point power detecting means. The reactive power fluctuation command generator 10 and the inverter 3 constitute a reactive power fluctuation generating means.

FIG. 2 shows an example of a reactive power fluctuation command generator 10A corresponding to the first and second aspects of the present invention. In FIG. 2, reference numeral 21 denotes a fluctuation signal oscillator that outputs a fluctuation signal g serving as a source of the fluctuation command, and 22 denotes an amplifier that amplifies the fluctuation signal g and outputs a fluctuation command h. Reference numeral 23 denotes a decision unit that outputs a predetermined trigger signal i only when the power point power signal d is input and when the signal d has a positive polarity, and the power point power signal d is When it is positive. Reference numeral 24 denotes a three-terminal voltage follower that makes the input fluctuation command h valid only when the trigger signal i is input, and outputs it as a reactive power fluctuation command b.

Further, the OFC is a comparator that generates an output signal j when the frequency signal c exceeds a value set by the setter VR1 when the frequency signal c is input. The UFC is a comparator that outputs the frequency signal c by the setter VR2. Output signal k
Is a comparator that generates An OR gate 25 energizes the relay 26 when any of the output signals j and k is input, and outputs a trip command a for tripping the disconnecting circuit breaker 6 in FIG.

Next, the operation of FIG. 2 will be described with reference to FIG. First, in FIG. 1, the DC power of the DC power supply 2 is converted into AC power according to the frequency and voltage of the system by the inverter 3 and supplied to the load 5 via the circuit breakers 6 and 7. At the normal time when the islanding does not occur, the frequency signal c output from the voltage / frequency converter 11 is in a rated state, the comparators OFC and UFC in FIG. 2 are off, and the output signals j and k are Has been reset. At this time, since the OR gate 25 is also off, the trip signal a is reset.

Now, when the capacity of the load 5 is smaller than the output of the power generator 1, a part of the output power of the power generator 1 is transmitted to the power system 14 via the power receiving circuit breaker 13.
Power receiving point power signal d output from power receiving point power calculator 12
Is the positive polarity on the power transmission side. Therefore, since the decision unit 23 in FIG. 2 sets the trigger signal i, a fluctuation command h obtained by amplifying the fluctuation signal g by the amplifier 22 is output as the reactive power fluctuation command b via the voltage follower 24. Will be.

In this state, when a switch (not shown) on the power system 14 side is opened and an islanding phenomenon occurs, the frequency fluctuates due to the fluctuation of the reactive power of the inverter 3 and the frequency signal of the voltage / frequency converter 11 Since c fluctuates from the rated value, the comparator OFC or UFC shown in FIG. 2 operates to turn on the OR gate 25, energize the relay 26, and set the trip signal a. At this time, the comparator OF
Since each of the frequency detection levels by C and UFC is one stage, the detection time does not become longer as in the prior art shown in FIG. As described above, since the disconnecting circuit breaker 6 of FIG. 1 is opened and the power generation device 1 is disconnected, the islanding state is immediately canceled.

When the capacity of the load 5 is larger than the output of the power generator 1, the power receiving circuit breaker 1
Insufficient power is received via 3. In this case,
The output of the power receiving point power calculator 12 has a negative polarity on the power receiving side with respect to the power system. Accordingly, since the decision unit 23 in FIG. 2 resets the trigger signal i, the voltage follower 24 is also reset, and the reactive power fluctuation command b is also reset.

In this state, if the switch on the side of the power system 14 is opened and an islanding phenomenon occurs, the output power of the inverter 3 cannot cover the capacity of the load 5, so that the inverter 3 stops due to an overcurrent. Therefore, the frequency naturally drops. Therefore, the comparator UFC in FIG. 2 operates to turn on the OR gate 25, the relay 26 is excited, and the trip signal a is set. As a result, the disconnecting circuit breaker 6 is opened and the power generation device 1 is disconnected, so that the islanding state is immediately canceled.

In the configuration shown in FIG. 2, the load 5 shown in FIG.
When the capacity of the power generation device 1 is approximately equal to the output of the power generation device 1 and the load 5 fluctuates, as described in claim 2, after the power receiving point power signal d becomes negative (power receiving side), If hysteresis is provided so that the trigger signal i of the decision unit 23 is not set until an appropriate value of the positive polarity (power transmission side) is reached, the reactive power fluctuation output of the inverter 3 rapidly turns on and off.
Voltage fluctuations and power factor fluctuations at the power receiving point caused by repeated turning off can be prevented.

Next, FIG. 3 shows an example of a reactive power fluctuation command generator 10B according to the third aspect of the present invention. In the following, the same components as those in FIG. 2 are denoted by the same reference numerals, description thereof will be omitted, and different portions will be mainly described. In the reactive power fluctuation command generator 10B of FIG. 3, the fluctuation command h, which is the output of the amplifier 22, is input to the amplifier 27, and the output is the reactive power fluctuation command b. The receiving point power signal d is directly input to the amplifier 27. In the amplifier 27, when the value of the receiving point power signal d becomes equal to or less than a predetermined value of the positive polarity on the power transmission side with respect to the power system, the amplification factor is increased stepwise. It is configured to decrease (narrow down) from 1 to a minute value.

Next, the operation of FIG. 3 will be described with reference to FIG. In FIG. 1, when the capacity of the load 5 is sufficiently smaller than the output of the power generation device 1, most of the output power of the power generation device 1 is transmitted to the power system 14 via the power receiving circuit breaker 13. The signal d has a positive polarity on the power transmission side with respect to the power system. Therefore, since the amplification factor of the amplifier 27 in FIG. 3 is 1, the fluctuation command h obtained by amplifying the fluctuation signal g by the amplifier 22 is output via the amplifier 27 as the reactive power fluctuation command b.

In this state, if the switch on the power system 14 side is opened and the islanding phenomenon occurs, the frequency signal c of the voltage / frequency converter 11 fluctuates from the rated value in the same manner as described above. The OFC or UFC operates to turn on the OR gate 25, energize the relay 26, and set the trip signal a. Thereby, the disconnecting circuit breaker 6 of FIG. 1 is opened and the power generator 1 is disconnected,
The islanding condition is immediately resolved.

When the capacity of the load 5 is slightly smaller than the output of the power generator 1, a small part of the output power of the power generator 1 is transmitted to the power system 14 via the power receiving circuit breaker 13, so that the power receiving point The power signal d has a small positive value on the power transmission side with respect to the power system. Accordingly, the amplification factor of the amplifier 27 is a value narrowed down from 1, and the fluctuation signal g is
The fluctuation command h obtained by amplification by 2 is converted into a small reactive power fluctuation command b by the amplifier 27 and output.

In this state, when the switch on the power system 14 side is similarly opened and an islanding phenomenon occurs, the reactive power fluctuation output of the inverter 3 is a very small value, but the power transmitted to the system side itself is small. , The frequency signal c of the voltage / frequency converter 11 fluctuates from the rated value. Therefore, the comparator O in FIG.
When the FC or UFC operates to turn on the OR gate 25,
The relay 26 is excited and the trip signal a is set. Therefore, since the disconnecting circuit breaker 6 is opened and the power generator 1 is disconnected, the islanding state is immediately resolved.

When the capacity of the load 5 is larger than the output of the power generator 1, power is supplied from the power system 14 to the power receiving side via the power receiving point circuit breaker 13, and the basic operation is the same as that of FIG. become.

Further, when the capacity of the load 5 is equal to the output of the power generator 1, the variation of the reactive power is stopped in the configuration of FIG. 2, so that the islanding phenomenon may continue. In the configuration shown in FIG. 3, however, reactive power is output from the inverter 3 based on the reactive power fluctuation command b, albeit minute, so that the detection and prevention of the eye landing can be sufficiently performed.

[0031]

As described above, according to the present invention, when the DC power is converted into AC power by the grid connection inverter and the grid is connected to the grid, the power is switched by operating the switch of the power grid. When the islanding phenomenon occurs, it can be immediately detected to prevent the isolated operation of the grid interconnection inverter. In addition, when there is no transmission power from the customer, the reactive power fluctuation due to the operation of the inverter is not generated, so that the voltage fluctuation at the customer service entrance can be prevented and the power factor management of the customer can be easily performed.

[Brief description of the drawings]

FIG. 1 is a single-line diagram showing an islanding prevention device according to an embodiment of the present invention, together with a power generator and a load connected to an electric power system.

FIG. 2 is a block diagram showing an example of a reactive power fluctuation command generator in FIG.

FIG. 3 is a block diagram showing another example of the reactive power fluctuation command generator in FIG. 1;

FIG. 4 is a diagram showing an example of a reactive power command value and a frequency fluctuation waveform in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Power generator 2 DC power supply 3 Inverter for system interconnection 4 Insulation transformer 5 Load 6 Breaker for disconnection 7 Load circuit breaker 8 Secondary circuit breaker for power receiving transformer 9 Transformer for power receiving 10, 10A, 10B Invalid Power fluctuation command generator 11 voltage / frequency converter 12 power receiving point power calculator 13 power receiving point circuit breaker 14 power system 20 islanding prevention device 21 fluctuation signal oscillator 22 amplifier 23 determiner 24 voltage follower 25 OR gate 26 for trip command output Relay PT1, PT2 Instrument transformer CT Current transformer OFC, UFC Comparator VR1, VR2 Setter a Disconnect circuit breaker trip command b Reactive power fluctuation command c Frequency signal d Power receiving point power signal g Fluctuation signal h Fluctuation command i Trigger signal j, k Comparator output signal

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Nagasawa 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A system for converting a DC power into an AC power by an inverter for system interconnection in a power generating apparatus and interconnecting the AC power with a power system, comprising: frequency detection means for detecting a system frequency and outputting a frequency signal thereof; A receiving point power detecting means for detecting a receiving point power value from the power system, and a reactive power fluctuation command for causing a periodic reactive power fluctuation in the power system by the inverter, and
Reactive power fluctuation command generating means for outputting an open signal to the disconnecting circuit breaker of the power generator when the isolated operation state of the grid interconnection inverter is detected based on the frequency signal output from the frequency detecting means. Wherein the reactive power fluctuation command generating means sets the reactive power fluctuation command to zero when the power receiving point power value is on the power receiving side with respect to a power system, Single-operation prevention device. 2. The system according to claim 1, wherein the reactive power fluctuation command is set to zero when the power value of the power receiving point is on the power receiving side with respect to the power system. An isolated operation prevention device for a grid interconnection inverter, wherein when a power value reaches a predetermined value on a power transmission side with respect to a power system, the power setting is restored to an original set value. 3. A system for converting a DC power into an AC power by an inverter for system interconnection in a power generating apparatus and interconnecting the AC power with a power system, comprising: frequency detection means for detecting a system frequency and outputting a frequency signal thereof; A receiving point power detecting means for detecting a receiving point power value from the power system, and a reactive power fluctuation command for causing a periodic reactive power fluctuation in the power system by the inverter, and
Reactive power fluctuation command generating means for outputting an open signal to the disconnecting circuit breaker of the power generator when the isolated operation state of the grid interconnection inverter is detected based on the frequency signal output from the frequency detecting means. The reactive power fluctuation command generating means, when the power point power value is less than or equal to a predetermined set value on the power transmission side with respect to the power system, the reactive power fluctuation command stepwise the predetermined minute value An isolated operation prevention device for a grid-connected inverter, characterized in that the power consumption of the system is reduced.