JPH11127542A - Method and device for detecting isolated operation of inverter and power conditioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an isolated operation of an inverter by means of an active system without lowering the efficiency of the output power of the inverter by superposing higher harmonics upon the output current or output voltage of the inverter by controlling the output current or voltage, and detecting the higher harmonics from the voltage or current appearing on a system side. SOLUTION: An isolated operation of an inverter 4 is detected based on the higher harmonics of a system voltage by periodically superposing a very small higher harmonic current upon the output current of the inverter 4, and detecting the higher harmonics at the timing corresponding to the superposing period of the current. Accordingly, a device for detecting isolated operation of inverter is provided with a higher harmonic superposing means 15 which superposes the small higher harmonic current upon the output current of the inverter 4, a higher harmonic detecting means 16 which detects the higher harmonics of the system voltage, a discriminating means 22 which discriminates the isolated operation based on the output of the detecting means 16, and a period control means 17 working as a timing control means for controlling the higher harmonic current superposing timing and the system voltage detecting timing corresponding to the superposing timing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter connected to a system power supply in a system interconnection system such as a photovoltaic power generation system, and more particularly, to an inverter when power supply from the system power supply is stopped. The present invention relates to a method and an apparatus for detecting an independent operation of an inverter, and a power conditioner.

[0002]

2. Description of the Related Art In recent years, when a distributed power supply such as a solar power generation and a system power supply (commercial power supply) are interconnected with an inverse power flow via an inverter, and the power supply cannot be provided only by the distributed power supply, A grid interconnection system in which power is supplied from the grid side has been developed.

In this type of system interconnection system, it is necessary to prevent reverse charging from the distributed power source to the system side in the event of an unexpected power outage or work power outage of the commercial power system. In addition, the isolated operation in which the supply of the electric power is stopped is detected and disconnected from the system side, and the driving of the inverter is stopped.

[0004] As a method of detecting such an isolated operation, a passive method of detecting an isolated operation by detecting a change in a voltage waveform or a phase when the operation is shifted from an interconnected operation to an isolated operation, and a method of detecting a change factor in an inverter. In addition, there is an active method in which the fluctuation factor does not appear in the output during the interconnected operation but appears during the independent operation and is detected.

[0005]

In general, the passive system can detect the islanding without affecting the system side, but has a disadvantage that the dead zone is wide.
The active method has a narrower dead band than the passive method.However, for example, in the reactive power fluctuation method in which the reactive power output from the inverter is changed, the active power output from the inverter is reduced in order to reduce the power factor. In any of the active power fluctuation systems in which the absolute value of the output current of the inverter is changed, there is a disadvantage that the efficiency of the output power is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to be able to detect an islanding operation by an active system without lowering the efficiency of output power.

[0007]

In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the islanding detection method of the present invention comprises:
A method for detecting an isolated operation of an inverter connected to a system power supply, the method comprising controlling an output current or an output voltage of the inverter, superimposing a harmonic on the output current or the output voltage, and generating a voltage appearing on a system side. Alternatively, the isolated operation is detected by detecting a harmonic of the current.

The present invention also provides an islanding operation detecting apparatus for detecting an islanding operation of an inverter connected to a system power supply, wherein the inverter controls an output current or an output voltage of the inverter to output the output current or the output voltage. A harmonic superimposing means for superimposing a harmonic on an output voltage; and a harmonic detecting means for detecting a harmonic of a voltage or a current appearing on a system side, and detecting an isolated operation based on an output of the harmonic detecting means. Is what you do.

Further, the islanding operation detecting apparatus of the present invention detects a harmonic of a system voltage by superimposing a harmonic current on an output current of an inverter. Correspondingly, there is provided a timing control means for controlling a timing of detecting a harmonic of the system voltage.

Further, it is preferable that the islanding detection device of the present invention is configured to separate harmonic components of the system voltage and to provide a positive feedback to the output current of the inverter.

Further, in the islanding detection device of the present invention, it is preferable that the level of the harmonic current to be superimposed is limited to a certain range.

[0013] The power conditioner of the present invention comprises:
It is provided with the islanding detection device of the present invention.

According to the islanding detection method and the islanding detection device of the present invention, a harmonic is superimposed on the output current or the output voltage of the inverter, and the harmonic of the voltage or current appearing on the system side during the islanding operation is detected. Further, the isolated operation state can be detected by the active method without lowering the power efficiency as in the conventional power fluctuation method.

Further, according to the isolated operation detection device of the present invention, the timing of superimposing the harmonic current on the output current of the inverter and the timing of detecting the harmonic of the system voltage corresponding to the timing are controlled. Erroneous operation can be prevented.

Further, according to the islanding operation detecting apparatus of the present invention, since the harmonic component of the system voltage is separated and positively fed back to the output current of the inverter, the detection sensitivity of the islanding operation can be improved.

According to the isolated operation detecting device of the present invention, the level of the harmonic current to be superimposed is limited to a certain range. Can be.

According to the power conditioner of the present invention,
The isolated operation can be detected without lowering the power efficiency by the active method.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a configuration diagram of a solar power generation system according to one embodiment of the present invention.

The solar power generation system according to this embodiment
A solar cell 1 as a DC power supply, and a current control type power conditioner 2 including an islanding detection device according to the present invention.
The power conditioner 2 includes an inverter 4 that converts DC power from the solar cell 1 into AC power synchronized with the system power supply 3, and receives an output voltage and a command voltage value of the solar cell 1. Differential amplifier 5, a sine waveform generator 6 for detecting a system voltage and generating a 50 Hz or 60 Hz sine waveform, and a sine wave from the sine waveform generator 6 and an output of the differential amplifier 5. And an error amplifier 9 for amplifying the difference between the current command value and the output current of the inverter 4 detected by the current transformer (CT) 8, and the error amplifier 9. PWM control circuit 1 that performs a PWM control by outputting a switching signal to the switching element of inverter 4 so that the error signal of No. 9 becomes zero.
0, the switch 1
A protection circuit 13 is provided for performing a protection operation such as disconnecting the inverters 1 and 12 and stopping the driving of the inverter 4, and the above configuration is basically the same as the conventional example.
In addition, 14 is a load.

In this embodiment, a small harmonic current is superimposed on the output current of the inverter 4 at a constant period so that the isolated operation can be detected by the active method without lowering the efficiency of the output power. Then, a harmonic of the system voltage is detected at a timing corresponding to the superposition, and the islanding is detected based on the detected harmonic.

That is, the islanding operation detecting apparatus of this embodiment comprises a harmonic superimposing means 15 for superimposing a small harmonic current on the output current of the inverter 4, and a harmonic detecting means 16 for detecting a harmonic of the system voltage. And determining means 22 for determining whether or not the vehicle is in the isolated operation state based on the output of the harmonic detecting means 16, and controlling the timing of superimposing the harmonic current and the timing of detecting the system voltage corresponding to the timing. Control means 17 as timing control means
And

The harmonic superimposing means 15 includes a period control means 17
A harmonic output means 18 for outputting a harmonic at the timing of a harmonic superimposition command from the adder 19, and an adder 19 for adding the harmonic to the current command value from the multiplier 7. Is the fundamental harmonic, as shown in FIG.
For example, a fundamental harmonic generating means 20 for generating a third harmonic or a fifth harmonic, a multiplier 21 for adjusting a superimposed level of the fundamental harmonic based on a harmonic level command,
A switch circuit 23 for outputting the fundamental harmonic to the adder 19 at the timing of the harmonic superposition command from the cycle control means 17
The harmonic superimposing means 15 converts the harmonics at a constant cycle, for example, every other cycle, based on the harmonic superimposition command of the cycle control means 17, at a constant level corresponding to the harmonic level command. The constant level is controlled so as to be within 3%, which is the limit regulation of the system interconnection.

As shown in FIG. 3, the harmonic detecting means 16 includes an analog waveform detecting circuit 24 for detecting an analog waveform of the system voltage, and an A / D converting circuit 25 for A / D converting the detected analog waveform. And a discrete Fourier transform circuit (DFT) 2 to which the output of the A / D converter circuit 25 is given.
6 for detecting the harmonics of the system voltage at the timing of the detection command from the cycle control means 17.
The discrete Fourier transform circuit 26 computes only the level of a certain frequency band from the analog waveform in a discrete value system.
It calculates and outputs the level of the next harmonic.

The fundamental wave and, for example, the third harmonic are:
These are shown by the following equations 1 and 2, respectively. In each equation, N is the number of samplings per cycle.

[0027]

(Equation 1)

[0028]

(Equation 2)

The determination means 22 to which the output of the discrete Fourier transform circuit 26 is given determines whether or not the level of the detected harmonic has exceeded a predetermined level. An operation command is output to the protection circuit 13 assuming that the vehicle is in the islanding operation state.

In a normal interconnection operation, the system voltage is not affected by the output current of the inverter 4, so that the harmonics superimposed on the output current do not appear. Since the system voltage is determined by the load and the state of the load 14, a harmonic of the output current appears in the system voltage, and the harmonic operation is detected by the harmonic detecting means 16 to detect the isolated operation. The protection command is output to the protection circuit 13.

As shown in FIG. 4, the cycle control means 17 outputs a harmonic superposition command to the harmonic superposition means 15 every other cycle, for example, based on the system frequency clock obtained from the system voltage. A superimposition command output circuit 27;
A timing adjusting circuit 28 that shifts the timing of the harmonic superposition command and outputs the same to the harmonic detection means 16 as a detection command to adjust the timing of the harmonic superposition and the timing of the harmonic detection, To prevent malfunction due to harmonics of the system voltage due to disturbances unrelated to the superposition of

FIG. 5 shows the system voltage and output during normal interconnection operation when the third harmonic is superimposed by 10% by the power conditioner 2 of the present invention having the above configuration in order to make it easier to understand. It is a waveform diagram showing a current,
FIG. 6 is a waveform diagram showing the system voltage and the output current during the single operation.

During normal interconnection operation, the system voltage is not affected by the output current of the inverter 4, so that the third harmonic superimposed on the output current does not appear in the system voltage as shown in FIG. However, in the isolated operation state, since the system voltage is determined by the output current of the inverter 4 and the state of the load 14, a third harmonic of the output current appears in the system voltage as shown in FIG. , Harmonic detection means 1
By detecting at step 6, the islanding operation is detected.

As described above, the harmonics are superimposed on the output current, and the occurrence of the harmonics in the system voltage during the islanding operation is detected to detect the islanding operation. Therefore, the passive system is used similarly to the conventional active system. In addition to being able to more accurately detect the islanding operation, the power efficiency is not reduced unlike the conventional power fluctuation method.

(Embodiment 2) FIG. 7 is a configuration diagram of a photovoltaic power generation system according to another embodiment of the present invention, and portions corresponding to the above-described embodiment are denoted by the same reference numerals. .

In this embodiment, the harmonic components of the system voltage are separated and positively fed back to the output current of the inverter 4. For this reason, the system voltage is superimposed by the harmonic superimposing means 15. Separation means 2 for separating harmonic components
9 and a gain adjusting circuit 3 which adjusts the gain of the harmonic component from the separating means 29 and outputs it to the harmonic superimposing means 15.
0.

The separating means 29, as shown in FIG.
An analog waveform detection circuit 31 for detecting an analog waveform of a system voltage, and an A / D converter for A / D converting the detected analog waveform
A / D conversion circuit 32 and a band-pass filter 35 composed of a combination of a low-pass filter 33 and a high-pass filter 34 to which an output of the A / D conversion circuit 32 is applied, and gain adjustment by separating only harmonic components It is configured to output to the circuit 30. Note that this separating means may be configured in a hardware manner by providing a filter circuit in front of the A / D conversion circuit.

In the isolated operation state, harmonics appear in the system voltage, so that the output of the analog waveform detection circuit 31 has a waveform shown by a broken line in FIG. 9, from which the harmonic components are separated and the gain is adjusted. As a result, a harmonic indicated by a solid line in FIG. 9 is output from the gain adjustment circuit 30 and supplied to the harmonic superimposing means 15.

Other configurations are the same as those of the above-described embodiment, and the description thereof will be omitted.

According to this embodiment, since the harmonic component of the system voltage is positively fed back, if the harmonic of the system voltage increases during the islanding operation, the harmonic component further increases. The sensitivity will be improved.

Further, since the detection sensitivity is improved, the ratio of the harmonic current superimposed on the output current of the inverter 4 can be reduced as compared with the above embodiment.

(Other Embodiments) In the above-described embodiment, although the output current of the inverter is controlled to superimpose the harmonic current, and the harmonic of the system voltage is detected, the isolated operation is detected. As another embodiment, the output voltage of the inverter may be controlled to superimpose the harmonic voltage, and the harmonic appearing in the system current may be detected to detect the isolated operation.

In the above embodiment, for example, only the third harmonic or only the fifth harmonic is superimposed, but a plurality of harmonics may be superimposed. In this case, in order to satisfy the system interconnection standard, the superimposed harmonics need to be within 5% in total.

Although the above embodiment has been described by applying to a photovoltaic power generation system using a solar cell as a power source, another embodiment of the present invention uses another power source such as a fuel cell. Of course, the present invention may be applied to a distributed power supply system.

The present invention is not limited to a software configuration, but may be a hardware configuration.

[0046]

As described above, according to the present invention, harmonics are superimposed on the output current or output voltage of the inverter, and the harmonics of the voltage or current on the system side that appear when the isolated operation mode is established are detected. As a result, the isolated operation can be detected by the active method without lowering the power efficiency as in the conventional power fluctuation method.

Since the timing for superimposing the harmonic current and the timing for detecting the harmonic of the system voltage are controlled, malfunction due to disturbance can be prevented.

Furthermore, since the harmonic component of the system voltage is separated and positively fed back to the output current of the inverter, the detection sensitivity of the isolated operation can be improved.

Further, since the level of the harmonic current to be superimposed is limited to a certain range, it is possible to satisfy the restriction of the harmonic, which is the standard for the interconnection operation with the system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a photovoltaic power generation system according to one embodiment of the present invention.

FIG. 2 is a configuration diagram of harmonic output means of FIG. 1;

FIG. 3 is a configuration diagram of harmonic detection means of FIG. 1;

FIG. 4 is a configuration diagram of a cycle control unit of FIG. 1;

FIG. 5 is a waveform diagram of a system voltage and an output current during a normal interconnection operation.

FIG. 6 is a waveform diagram of a system voltage and an output current during an isolated operation.

FIG. 7 is a configuration diagram of a solar power generation system according to another embodiment of the present invention.

FIG. 8 is a configuration diagram of a separating unit of FIG. 7;

FIG. 9 is a waveform diagram of a system voltage for explaining the operation.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Solar cell 3 System power supply 2, 2 ₁ Power conditioner 4 Inverter 15 Harmonic superimposing means 16 Harmonic detecting means 17 Period control means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinichi Murashige 10 Omron Co., Ltd.

Claims (6)

[Claims] 1. A method for detecting an isolated operation of an inverter connected to a system power supply, comprising: controlling an output current or an output voltage of the inverter to superimpose a harmonic on the output current or the output voltage; A method for detecting an isolated operation of an inverter, wherein the isolated operation is detected by detecting a harmonic of a voltage or a current appearing on a system side. 2. An apparatus for detecting an isolated operation of an inverter connected to a system power supply, wherein the harmonics superimpose a harmonic on the output current or the output voltage by controlling an output current or an output voltage of the inverter. A single wave inverter comprising: a wave superimposing means; and a harmonic detecting means for detecting a harmonic of a voltage or a current appearing on a system side, and detecting an islanding operation based on an output of the harmonic detecting means. Operation detection device. 3. The harmonic superimposing means superimposes a harmonic current on an output current of an inverter, and the harmonic detecting means detects a harmonic of a system voltage. The isolated operation detection device for an inverter according to claim 2, further comprising timing control means for controlling a timing of superimposing and a timing of detecting a harmonic of the system voltage in accordance with the timing. 4. The apparatus for detecting the isolated operation of an inverter according to claim 3, wherein a harmonic component of the system voltage is separated and positively fed back to an output current of the inverter. 5. The isolated operation detection device for an inverter according to claim 3, wherein a level of the harmonic current to be superimposed is limited to a certain range. 6. A power conditioner comprising the inverter independent operation detection device according to claim 2. Description: